Tonight’s sky of new research

TNGC-SIDM I: Evolution of massive cluster mergers under the self-interacting dark matter paradigm

Wonki Lee, Dylan Nelson, Myungkook J. Jee+8 more

• Astrophysics of Galaxies

AstronomerThis pilot study uses magnetohydrodynamical cosmological zoom-in simulations of two TNG-Cluster mergers, with M200c approximately 9 × 10^14 and 2 × 10^14 solar masses, to compare collisionless CDM with SIDM. The SIDM models assume isotropic, velocity-independent scattering with cross-section per unit mass of 1 cm²/g, plus a 0.5 cm²/g run for the lower-mass system; mass resolution and the galaxy formation model remain unchanged. In the simulations, self-interactions produce an isothermal dark matter core, distinctive intracluster-light substructures, and changes in multi-wavelength plasma observables. Shock-to-shock separation evolves similarly across the tested self-interaction models, offering a reference for identifying approximately 100–200 kpc differences in halo separation induced by self-interactions. In the massive merger, the main halo centroid is displaced from the brightest cluster galaxy by up to approximately 20 kpc, exceeding the subcluster offset and persisting beyond 4 Gyr after first pericenter. These are simulated signatures, not observational detections of SIDM. The limited pilot study highlights sample selection and proposes double-radio-relic mergers and massive clusters with evidence of ancient major mergers as promising testbeds.

PublicCould dark matter interact with itself? This study explores that possibility through computer simulations of two merging galaxy clusters, rather than through new observations. The researchers compared dark matter that does not collide with itself against specific models in which it does. In the simulations, self-interactions changed the dark matter’s central structure, patterns of light from stars between galaxies, and signals from the hot gas. The separation between two shock fronts evolved similarly in the tested self-interacting models, potentially providing a reference for comparing the dark matter halos’ positions. In the more massive merger, the main dark matter halo’s center remained displaced from the brightest galaxy for more than four billion years after the clusters’ first close passage. These results do not establish that real dark matter self-interacts. They suggest promising types of clusters to examine and emphasize that choosing suitable mergers matters.

Young explorerDark matter is something in space that we cannot see directly. Scientists made computer versions of two crashes between huge groups of galaxies. They tried dark matter that could bump into itself and dark matter that could not. The bumps changed where the dark matter gathered and some patterns of light. This does not prove real dark matter bumps into itself. It gives scientists clues about which galaxy groups to look at next.

Audible curvaton: modulated phase transition as the origin of large-scale curvature perturbations and gravitational wave anisotropies

Wen-Yuan Ai, Gabriele Franciolini, Xin Wang+1 more

• High Energy Physics - Phenomenology

AstronomerThe authors propose a post-inflationary first-order phase transition whose bubble nucleation history is modulated by fluctuations in a light spectator field acquired during inflation. The mechanism generates large-scale curvature perturbations and correlated intrinsic gravitational-wave anisotropies. Their theoretical analysis shows that it can reproduce the observed curvature-perturbation amplitude while producing a strong stochastic gravitational-wave background in the frequency bands of LISA, Taiji, and TianQin. A specific benchmark predicts strongly enhanced intrinsic gravitational-wave anisotropies and local primordial non-Gaussianity potentially accessible to future large-scale-structure surveys. These are model predictions, not reported detections.

PublicThe paper proposes a way to produce the early cosmic variations that helped shape the universe. After inflation, an early period of rapid expansion, a change of state could have occurred through the formation of bubbles. Fluctuations in a light field could have changed when those bubbles formed, creating both variations in cosmic curvature and gravitational waves whose strength varies across the sky in a related pattern. The authors show that the idea can match the observed size of the curvature variations and predict a strong gravitational-wave background at frequencies targeted by planned space detectors. One example also predicts a departure from a simple statistical pattern in the primordial variations that future surveys might detect. The abstract reports a theoretical proposal, not observations of these predicted signals.

Young explorerScientists have an idea about how the very young universe got its big patterns. They think bubbles might have formed as the universe changed, and a field could have made the bubbles start at different times. That could make patterns in space and tiny waves in space itself. Their idea can fit the size of patterns astronomers have already found. Future tools might look for the waves and other clues, but scientists have not found those clues in this study.

Forecasting a Cosmological 21 cm Stacking Detection with Early HIRAX Data

Pascal Hitz, Devin Crichton, Alexandre Refregier

• Instrumentation and Methods for Astrophysics

AstronomerThis simulation-based forecast assesses statistical detection of post-reionization cosmological 21 cm emission with an early-stage 36-dish HIRAX configuration through cross-correlation with an external source catalogue. The pipeline propagates a halo-model signal, Galactic and extragalactic foregrounds, and instrumental noise into simulated visibilities, applies delay-domain foreground filtering, and produces ringmaps for 120 days at a single zenith pointing over 700–800 MHz and approximately 3547 square degrees. Stacking at known three-dimensional source positions tests sensitivity to filtering, source count, catalogue completeness, and redshift uncertainty. Redshift precision is the strongest requirement: spectroscopic uncertainties of σ_z/(1+z) ∼ 0.001 preserve a significant simulated signal despite realistic filtering and substantial catalogue incompleteness, whereas photometric uncertainties of ∼ 0.01 strongly suppress it for realistic delay cutoffs. A Euclid-like spectroscopic sample yields a forecast minimum signal-to-noise ratio of 11 at the most conservative tested delay cutoff, 100 ns. These are simulated detection prospects, not an observational detection.

PublicResearchers used computer simulations to test whether an early 36-dish version of the HIRAX radio telescope could detect the collective radio signal from hydrogen across large regions of the Universe. Their method combines simulated radio maps at galaxy positions supplied by another survey, allowing a faint shared signal to build up. The simulations include interfering radio emission and instrument noise and represent 120 days of observing. Accurate galaxy distances, inferred from redshifts, prove especially important: the precision typical of spectroscopic measurements preserves a strong signal, even when many catalogue sources are missing, while the larger uncertainties associated with photometric measurements greatly weaken it. For a spectroscopic galaxy sample resembling one from Euclid, the simulated signal-to-noise ratio is at least 11 under the most conservative foreground-filtering setting tested. This is a forecast of what the method could achieve, not a detection in real observations.

Young explorerHydrogen gas far away makes a very faint radio signal. Scientists used a computer to pretend that a group of radio dishes was listening for it, with lots of other radio sounds getting in the way. They tried adding up the pretend maps at places where galaxies were listed. This worked much better when they knew the galaxies’ distances very well. If the distances were too fuzzy, the signal was much harder to find. The computer test looks promising, but it is not a discovery made by listening to the real sky.

Scalar-Assisted Growth of Supermassive Black Holes: Boson-Mass Windows and Observational Constraints

Jorge Castelo Mourelle, Darío Núñez Zúñiga, Saeed Fakhry+1 more

• General Relativity and Quantum Cosmology

AstronomerThis phenomenological model evolves black-hole growth in redshift within flat ΛCDM, combining a finite baryonic reservoir accreting through an Eddington-like channel with a bosonic scalar cloud transferring mass through an effective quasibound-state decay rate. Scans over boson mass and initial black-hole, cloud, and baryonic masses assess accelerated growth to 10^9 solar masses. For the black-hole mass scales explored, boson masses of approximately 10^-19–10^-16 eV yield efficient scalar transfer, rapid cloud depletion, and substantially earlier growth; outside this interval, growth remains mainly baryonic. The efficient window corresponds to a preferred dimensionless coupling α = μ M_BH and shifts approximately as μ ∝ M_BH^-1. Comparison with observed quasar masses and luminosities instead favors roughly 10^-21–10^-20 eV. The authors interpret these ranges as not necessarily conflicting because growth efficiency depends on black-hole mass and evolutionary stage. These are model-dependent findings, not an observational detection of scalar-assisted growth, and complementary roles for different boson masses in black-hole growth and dark-matter phenomenology remain open.

PublicCould a cloud of hypothetical particles help a black hole grow faster? This study models black holes fed simultaneously by a limited supply of ordinary matter and a cloud of bosonic particles, asking whether they could reach a billion times the Sun’s mass sooner. In the calculations, only certain particle masses substantially speed up growth; otherwise, ordinary matter does most of the feeding. Comparisons with observed quasar masses and brightness favor lighter particles than those that most efficiently accelerate growth in the explored models. That difference need not be a contradiction: the most effective particle mass changes with the black hole’s mass and stage of growth. The study explores a possible mechanism rather than demonstrating that real black holes grow this way.

Young explorerBlack holes can grow by taking in matter. Scientists used a model to ask whether a cloud of tiny, not-yet-confirmed particles could help them grow faster. In the model, some kinds of particles helped much more than others. Looking at real, bright objects powered by black holes pointed toward lighter particles instead, but the best helpers may change as a black hole grows. We do not yet know whether this idea happens in space.

Kinetic Theory of the EFTofLSS : A Halo-Based Approach

Om Kishor Hebbar, Caio B. de S. Nascimento, Arka Banerjee

AstronomerThis simulation-based study develops a framework linking EFTofLSS counterterms to the dynamics of individual dark matter halos. In cosmological N-body simulations, halo accretion contributes to the trace of the halo-based effective stress tensor, and hence to background pressure and effective sound speed; anisotropic accretion generates its traceless component, contributing to shear viscosity. Halos with virial masses above 10^12 solar masses/h account for approximately 95%, 85%, and 70% of the full simulation-box background pressure, effective sound speed, and shear viscosity, respectively, with the fractions depending on the EFT cutoff scale. Counterterm contributions are dominated by cluster-scale halos of roughly 10^14–10^15 solar masses/h and halos with larger inflow rates. These findings support an accretion-driven, out-of-equilibrium kinetic interpretation of the counterterms. The framework offers a connection between short-scale structure dynamics and physics-informed priors for large-scale cosmological observables; the abstract does not report observational validation.

PublicTo describe how dark matter gathers into structures across the universe, physicists use a theory that summarizes small-scale activity through effective pressure and other terms. This study investigates what produces those terms using computer simulations, rather than observations. The researchers find that dark matter flowing into halos contributes to effective pressure and sound speed, while uneven inflow contributes to a shear-viscosity term. Halos above the study's mass threshold supply most, but not all, of these contributions, with the exact shares depending on the scale used to separate small and large structures. Cluster-scale halos and halos with faster inflow dominate. The findings support an explanation based on ongoing growth rather than equilibrium and provide a framework for connecting halo dynamics to large-scale cosmological modeling.

Young explorerScientists used computers to study how dark matter gathers into big clumps. Their computer worlds showed that matter flowing into these clumps helps explain some parts of a rulebook for how dark matter moves. Matter coming in unevenly matters too. Very big clumps and clumps gathering matter faster were especially important. This is a clue from computer models, not something the scientists directly saw in the sky.

The Atacama Cosmology Telescope: DR6 Constraints on Isotropic Time-Dependent Cosmic Birefringence from Axion-like Particles

Zachary B. Huber, Huajian Yang, Steve K. Choi+7 more

AstronomerUsing ACT CMB polarization measurements from 2017–2022 and an EB power spectrum estimator, the authors search for oscillatory polarization rotation induced by axion-like particle (ALP) coupling to photons. They probe periods from days to years, corresponding to ALP masses of 2.5 × 10^-23 to 4.8 × 10^-20 eV, and find no evidence for a signal. They set a 95% upper bound of g_phi_gamma < 1.1 × 10^-11 (m_phi / 10^-21 eV) GeV^-1. This bound assumes ALPs constitute all dark matter and that the field amplitude is stochastically distributed; it is more conservative than bounds obtained with the deterministic-field assumption used in some previous CMB analyses. The authors report the strongest CMB-polarization bounds to date under the stochastic-field assumption. Their methodology handles more than 10,000 time-sliced ACT depth-1 polarization maps. Such maps are expected to be a standard Simons Observatory data product, enabling future searches with greater sensitivity and longer observing spans.

PublicAxion-like particles are hypothetical particles that might account for much or all of dark matter. If they interact with light, they could make its polarization—the orientation of its oscillations—rotate back and forth over time. Researchers searched for this effect in measurements of the universe’s oldest light taken by the Atacama Cosmology Telescope between 2017 and 2022. They found no evidence of the predicted signal and placed limits on how strongly these particles could interact with light over the tested mass range. The limits assume that axion-like particles make up all dark matter and allow for statistical variation in the particle field’s amplitude. Under that assumption, the authors report the strongest limits from this type of cosmic microwave background search so far. Their analysis method could support more sensitive, longer-running searches with the Simons Observatory; those improvements are future prospects, not results of this study.

Young explorerScientists wonder whether tiny, unseen particles could be the dark matter in space. These particles might make a special pattern in very old light turn back and forth. Scientists checked telescope measurements but did not find that turning. This does not mean the particles cannot exist. It helps scientists say how strongly the particles could affect light, if they make up all the dark matter and behave the way the study assumes.

Cosmology with strong gravitational lenses

Tommaso Treu

AstronomerThis review presents strong gravitational lensing as an independent, complementary probe of cosmic expansion and matter distribution. Time-delay and multiplane lenses can constrain H₀ and the dark energy equation of state, while lensed-image distortions probe dark matter subhalo abundance and internal structure without requiring dark matter to interact with light. It surveys recent advances enabled by JWST, lens modeling, and stellar dynamics, highlighting an H₀ measurement with 3% precision under the assumption of flat Λ cold dark matter cosmology and a tentative detection of dark matter self-interaction. Neither example resolves the broader open questions. Looking ahead, Euclid, Rubin, Roman, and Square Kilometer Array surveys are expected to increase known strong-lens samples by orders of magnitude; their anticipated cosmological impact is a prospect, not an achieved result.

PublicGravity can bend light, and the resulting distorted images offer a way to study the universe’s expansion and dark matter. This review explains how strong gravitational lensing complements other methods for investigating dark energy, dark matter, and disagreements over the cosmic expansion rate. Recent progress draws on JWST observations and improved modeling. One highlighted measurement reached 3% precision for the expansion rate, but within a particular cosmological model. Another finding suggests dark matter may interact with itself, although that evidence remains tentative. Future surveys are expected to discover vastly more gravitational lenses, potentially making this approach much more powerful over the next decade.

Young explorerGravity can bend light and change the pictures we see in space. Scientists study those pictures to learn how the universe grows and where hidden matter is. This review describes some progress, but the big puzzles are not solved. One clue about how hidden matter behaves is still uncertain. Future sky searches are expected to find many more bent-light pictures to study.

specwizard: A Public Python Framework for Creating Synthetic Absorption Spectra from Hydrodynamical Simulations

Andrés Arámburo-García, Tom Theuns, Joop Schaye+1 more

• Astrophysics of Galaxies
• Instrumentation and Methods for Astrophysics

AstronomerThe authors present specwizard, a publicly available modular Python package for synthesising absorption spectra from hydrodynamical simulations. It combines NIST atomic data with CLOUDY ionisation fractions for multiple ionising backgrounds to model bound–bound and bound–free absorption. Features include column-density-conserving projection, natural broadening of Lyman-series lines, and optional instrumental resolution and noise. Applications to EAGLE include a synthetic quasar spectrum at z = 3.2 with H I Lyman-series absorption, damping wings and Lyman-limit absorption, as well as circumgalactic metal lines and an investigation of correlated H I and Si III absorption. The authors report that the synthetic Lyman-alpha forest reproduces key observational diagnostics: the redshift evolution of mean transmission, the transmission probability distribution and the transmission power spectrum. Using EAGLE’s agreement with the measured evolution of the temperature–density relation, they infer the evolution of the ionising-background amplitude and report excellent agreement with recent theoretical models and measurements. This background estimate is an inference based on the simulation, not a direct measurement.

PublicThe researchers introduce specwizard, freely available software that predicts how gas in computer simulations absorbs light. It can produce simulated quasar spectra, including absorption by hydrogen and metals, and optionally account for instrument resolution and noise. Using the EAGLE simulation, they demonstrate hydrogen absorption features and explore gas around simulated galaxies. They report that the simulated absorption matches several important statistical properties measured in the Lyman-alpha forest, a pattern of hydrogen absorption in quasar light. Because EAGLE also matches measurements of how gas temperature varies with density over time, the researchers use it to estimate how the strength of the radiation that ionises gas changes over time. Their inferred radiation strength agrees well with recent models and measurements, but depends on the simulation rather than being measured directly.

Young explorerGas in space can take little bits out of light passing through it. The scientists made a computer tool that shows what this might look like in pretend universes made by computers. Some patterns it made matched patterns seen in real space. They also used a pretend universe to work out how strong some radiation in space might have been. That was an estimate, not a direct measurement.

Low-cost neural summaries for cosmological inference: an ensemble of convolutional neural networks trained on approximate simulations

Iñigo Sáez-Casares, Davide Bianchi, Matteo Calabrese+1 more

AstronomerThis simulation study tests whether neural compression trained on inexpensive, low-resolution particle-mesh matter overdensity fields transfers to higher-fidelity simulations. Selected outputs from an ensemble of convolutional networks are concatenated to constrain Omega_m and sigma_8 in high-resolution particle-mesh simulations, which cost about 1,000 times more per simulation; a Gaussian-process emulator built from high-resolution simulations supplies theoretical predictions. The ensemble extracts information beyond the reference binned power spectrum, whereas a single network can be less informative. Of three subset-selection strategies, a greedy search based on posterior volume gives the tightest constraints with the fewest networks. The summary also outperforms the power spectrum for halo catalogues from independent high-resolution N-body simulations across different number densities and redshifts, despite training on matter fields at z=0. These results demonstrate transfer within simulated data, not validation on observations.

PublicThe researchers tested a way to reduce the expense of teaching machine learning to extract information about the Universe’s matter distribution. They trained several neural networks on fast, simplified simulations, then combined selected networks to analyze much more detailed simulations. The combined summary constrained the amount of matter and the strength of its clustering more tightly than a standard analysis of the power spectrum. It also worked better for simulated dark matter halo catalogues, even though those differed from the training data. Combining networks mattered: one network alone could perform worse than the standard method. The results suggest that cheaper training simulations can still produce useful analysis tools, but the tests used simulated universes rather than actual observations, and high-resolution simulations were still needed to predict the summary’s behavior.

Young explorerScientists made pretend maps of where matter is spread through space. They taught a team of computer helpers using simple maps that were quicker to make. Then they tried the team on more detailed pretend maps. Together, the helpers found more clues about how much matter there was and how clumpy it was than another method did. One helper alone was not always better. This worked on computer-made maps; they have not shown here that it works on the real sky.

Testing Departures from the ΛCDM model in f(T) Gravity with DESI DR2

Jie Zheng, Mingzhi Wang, Ming Zhang

AstronomerThe authors constrain power-law, exponential, and hyperbolic-tangent f(T) gravity models using combinations of DESI DR2 BAO, CMB information, and Pantheon+ Type Ia supernova data. They distinguish shifts in marginalized parameter constraints from relative model performance under information criteria. The power-law model’s mild departure from ΛCDM with BAO+CMB disappears when supernovae are added. The exponential model retains a preference for a nonzero deformation parameter in the full analysis, but this does not translate into a clear statistical preference over ΛCDM. Including CMB distance priors substantially changes the allowed hyperbolic-tangent parameter space, and that model performs worse statistically for the combined data. The inferred transition redshift z_T remains relatively stable across models and data combinations. These results indicate that departures from ΛCDM are parameterization- and dataset-dependent rather than a generic feature of f(T) gravity.

PublicSome recent analyses of cosmological observations have hinted that the standard model of the universe, ΛCDM, might need modification. This study tests whether those hints also appear in three versions of an alternative theory of gravity called f(T), using DESI measurements, cosmic microwave background information, and observations of Type Ia supernovae. The outcome depends on both the version of the theory and the observations included. A mild departure in the power-law version disappears when supernova data are added. The exponential version retains a parameter-level hint of a departure, but statistical criteria do not clearly favor it over the standard model. The hyperbolic-tangent version’s allowed parameters change substantially when microwave background distance information is included, and it performs worse statistically with the combined data. Meanwhile, the inferred time of the universe’s transition from slowing expansion to accelerating expansion remains relatively consistent. The study does not establish a replacement for the standard model; it shows that the reported departures are not shared by all three alternatives.

Young explorerScientists use big ideas to explain how the universe grows. They checked three different gravity ideas against clues from space. One idea seemed a little different from the usual explanation, but that difference went away when they added more clues. Another still looked a little different, but it was not clearly better than the usual explanation. The third did worse when the clues were put together. So these clues do not show that the usual explanation needs to be replaced.

Galaxy-to-galaxy stochasticity has a limited impact on reionization and the 21-cm signal at fixed mean emissivity

Shihai Zhu, Yuxiang Qin

AstronomerUsing the Meraxes semi-analytic model, the authors separate the effects of galaxy-to-galaxy scatter from accompanying changes in mean radiative emissivity. They vary escape-fraction and SFR–halo mass scatter across three ionising-source prescriptions, and test X-ray luminosity scatter and removal of SFR scatter for heating sources. Without recalibration, changes in mean emissivity shift reionization and IGM heating histories and substantially alter the 21-cm signal. Restoring the relevant mean emissivities makes the global ionisation and thermal histories converge, with residual power-spectrum differences below the forecast sensitivity of a deep SKA-Low observation. Weak changes in ionisation morphology remain, depending on the dominant ionising galaxies and their response to photoheating. Within the models and scales tested, these results favour prioritising mean-emissivity calibration over resolving galaxy-to-galaxy scatter; they are modelling results, not observational detections.

PublicGalaxies differ in how much radiation they release, but this modelling study suggests that their average output may matter more than those differences for understanding how early galaxies ionised and heated the gas between them. Using a galaxy model called Meraxes, the researchers changed the variation between galaxies. When those changes also altered the population’s average radiation output, they substantially changed the predicted timing of ionisation and heating and the hydrogen 21-centimetre radio signal. When the average output was restored, the predicted overall histories became similar, and remaining differences in the signal’s power spectrum fell below what a deep SKA-Low observation is forecast to detect. Some small differences in the spatial pattern of ionised gas remained. The conclusion applies to the models and scales studied, rather than establishing that galaxy-to-galaxy differences never matter.

Young explorerLong ago, galaxies gave off light that helped change and warm the gas between them. Scientists used a computer model to try making some galaxies give off more light and others less. Changing how much light all the galaxies gave off on average made a big difference. But when the scientists kept that average the same, the gas changed and warmed in almost the same way, even though the galaxies were different from one another. Some small differences in the gas patterns remained. This is what their computer model suggests, not something they have directly seen in the sky.

Exact map-space beam convolution via spin-mapmaking

Camille Demay, Magdy Morshed, Martina Gerbino+1 more

AstronomerThe authors present a spin-mapmaking-based method for propagating beam-convolution systematics directly to CMB maps, particularly suited to main-beam studies. It combines scanning information compressed into precomputed h-maps with beam and sky harmonic coefficients, enabling efficient simulations across an experiment’s full focal plane. Validation against pixel-centered time-ordered-data-level full-sky convolution yields agreement to numerical precision for circular, elliptical, and Planck HFI scanning beams. As an application, simulated beam-convolved Planck maps show excellent power-spectrum agreement with QuickPol. These are simulation and method-validation results, not new cosmological measurements; the approach is intended to support systematic-error control for upcoming high-sensitivity CMB experiments. The authors release Smarties4Planck to generate these simulated Planck maps.

PublicFuture experiments studying the cosmic microwave background aim to investigate the Universe’s particle content and search for a faint signal from primordial gravitational waves. Their increased sensitivity will require careful modeling of distortions introduced by the instruments. This work presents a faster way to simulate how a telescope’s beam shapes a sky map, using compressed information about its scanning pattern. Tests with several beam shapes agreed to numerical precision with a reference calculation. Simulated Planck maps also showed excellent agreement with an existing analysis pipeline when comparing their power spectra. The work validates a simulation tool, rather than reporting a detection of gravitational waves or new particle physics. The authors make their Planck-map simulation code, Smarties4Planck, publicly available.

Young explorerScientists want to study very old light from space, but a telescope can blur the picture. This team made a computer tool to copy that blurring directly onto pretend sky pictures. They checked it against another calculation, and the answers matched very closely. The tool could help scientists understand what their telescopes do to the pictures. It did not find a new signal in space.

Thermalization of the Primordial Stochastic Gravitational-Wave Background

Hongguang Zhang, Zhengyang Qiu, Sirui Wang+1 more

• High Energy Physics - Theory

AstronomerThis theoretical analysis challenges the interpretation of the inflationary stochastic gravitational-wave background as a preserved record of the earliest universe. The authors argue that the high graviton occupation numbers implied by the inflationary spectrum enhance graviton self-interactions and drive rapid thermalization. They calculate that approximately 80% of primordial gravitons form a Bose–Einstein distribution, erasing their primordial information. For typical inflation parameters, they predict a present-day thermal peak at about 1.4 × 10^8 Hz with a peak amplitude Ω of about 3.5 × 10^-13. The predicted spectrum falls sharply away from this peak, placing it beyond the reach of PTAs, LISA, and LIGO. The authors identify microwave cavity resonators and dielectric haloscopes as potential high-frequency probes; the abstract reports no detection.

PublicGravitational waves produced during inflation are often treated as a record of the universe’s earliest moments. This theoretical study argues that much of that record could be erased. According to the authors’ calculations, the large number of gravitons—the particles associated with gravitational waves—would strengthen their interactions, causing about 80% to settle into a thermal distribution. Using typical inflation parameters, they predict that this altered background would peak today near 140 million hertz. Its strength would drop sharply at other frequencies, putting it beyond the reach of PTAs, LISA, and LIGO. The authors point instead to high-frequency detector approaches, including microwave cavity resonators and dielectric haloscopes, as possible ways to probe it. These are theoretical predictions, not an observed signal.

Young explorerTiny ripples from the very young universe might carry clues about what happened long ago. Scientists used calculations to suggest that most of these ripples could mix together and lose their old clues, a little like mixing paint until you cannot see the first colors. They predict that the changed ripples would wiggle extremely fast, so different kinds of detectors would be needed to look for them. They have not seen this happen; it is an idea worked out with math.

Bouncing Bianchi Type I Universes with Interacting Vacuum

Marco Bruni, Rodrigo Maier, Thomas Waters

AstronomerThis theoretical study extends interacting-vacuum cosmology from Robertson-Walker geometry to anisotropic Bianchi type I models. A phenomenological energy-momentum transfer four-vector reduces the field equations to a four-dimensional autonomous system for expansion, total shear, fluid density, and vacuum energy. Potential-energy and phase-space analyses compare linear and nonlinear vacuum-fluid couplings. The linear coupling admits non-singular bouncing trajectories. For the nonlinear coupling, invariant phase-space boundaries constrain the expansion domain and rule out cosmological bounces for physical matter configurations, unlike in the Robertson-Walker case. These are model-dependent dynamical results, not observational evidence for a cosmic bounce.

PublicCould the universe pass from contraction to expansion without encountering a singularity? This theoretical study explores that possibility in a universe that can expand differently in different directions, with energy exchanged between vacuum energy and a matter-like fluid. The researchers compare two mathematical rules for that exchange. The linear rule allows smooth bouncing histories, while the nonlinear rule rules out bounces for physically allowed matter in the model. The latter result differs from the corresponding Robertson-Walker case, showing that the assumed cosmic geometry matters. The study analyzes possible mathematical histories; it does not establish that our universe underwent a bounce.

Young explorerImagine a universe that can stretch differently in different directions. Scientists used math to ask whether it could shrink and then grow again without running into a breakdown in the model. They tried two rules for how two parts of their pretend universe share energy. One rule lets it bounce from shrinking to growing. The other does not, when the matter follows the model's physical rules. This does not mean scientists have seen our universe bounce.

Origin of the red spectral tilt in Inflation without an Inflaton

Raul Jimenez, Daniele Bertacca, Mariam Abdelaziz+3 more

• General Relativity and Quantum Cosmology
• High Energy Physics - Theory

AstronomerInflation without an Inflaton (IWI) uses a de Sitter background to drive inflation and a graviton bilinear to generate second-order scalar perturbations, without an inflaton or another fundamental scalar field. The authors derive n_s − 1 = 2n_T from the scalar spectrum’s four tensor mode functions. The observed CMB scalar tilt, n_s ≃ 0.9649, therefore implies n_T ≃ −0.0175 within IWI, independently of the tensor-to-scalar ratio r, unlike the standard single-field slow-roll relation n_T = −r/8. Their full time-dependent calculation of φ₂ in exact de Sitter produces an almost scale-invariant scalar spectrum with a small blue infrared residual, n_s − 1 ≃ +4 × 10⁻⁴, rather than the observed red tilt. Introducing a slow Hubble drift ε = −Ḣ/H² gives n_T = −2ε and n_s − 1 ≃ −4ε at leading order. Matching the observed tilt requires ε_* ≃ 0.0088, whereas their classical graviton-backreaction calculation gives an absolute value of ε_self no greater than approximately 10⁻¹¹. They therefore investigate de Sitter quantum break-time as a proposed source of background evolution, obtaining n_s − 1 = −4C_q N_sp(H/m_pl)², where C_q is an order-one depletion coefficient and N_sp describes the particle content. Evolution of this drift further predicts positive running, α_s = +(1 − n_s)²/2 ≃ +6 × 10⁻⁴. The quantum origin of the drift is a proposed explanation, and the tensor tilt and running are model predictions rather than reported detections.

PublicThis theoretical study examines whether inflation, an early period of rapid cosmic expansion, could work without the hypothetical inflaton field. In the proposed model, called Inflation without an Inflaton, the expanding background drives inflation, while pairs of gravity-wave disturbances generate the small variations described by the scalar spectrum. Observations give a scalar spectral tilt of about 0.9649. The model links this to a predicted gravity-wave tilt of about −0.0175, regardless of the relative strength of gravity waves and scalar variations; this differs from the standard single-field prediction. However, the authors’ calculation for an exactly de Sitter background gives an almost unchanging spectrum with a small tilt in the opposite direction, about +0.0004. To match observations, they introduce a slow decline in the expansion rate, requiring a drift parameter of about 0.0088. Their calculation finds that classical graviton backreaction can sustain a drift with an absolute value no greater than about 10⁻¹¹, far too small. They therefore investigate a proposed quantum explanation that connects the tilt to the particle content of the expanding background. This picture also predicts a small positive change of tilt with scale, about +0.0006. Those gravity-wave and changing-tilt predictions are possible tests of the model, not measurements reported here.

Young explorerScientists are exploring an idea about how the universe grew very quickly when it was young, without needing a special field called the inflaton. In their idea, tiny ripples in gravity help make the small differences seen in the universe. But their simplest calculation does not quite match what astronomers see. They suggest that the universe’s expansion slowly changed, perhaps because of a quantum effect. That explanation is still a proposal, not something they have shown happened. It makes predictions that observations could test.

Joint Line Intensity Recovery from Multi-Tracer Cross-Correlations

Carlos E. Sierra, Kirit S. Karkare

• Instrumentation and Methods for Astrophysics

AstronomerThe authors present a joint likelihood for LIM and external galaxy-survey auto- and cross-spectra to disentangle overlapping emission lines and recover bias-weighted line intensities at fixed cosmology. They validate the framework on realistic mocks—not observations—of an extended SPT-SLIM-like survey covering 125–175 GHz over 100 square degrees, paired with an LSST Y1-like photometric galaxy catalog. In the presence of bright continuum foregrounds, the mock analysis recovers CO(2–1) through CO(6–5) and [CI](1–0) over approximately 0.3 < z < 4. Adding galaxy data tightens line constraints by a factor of about 3–4 within the galaxies’ redshift coverage and by about 20–50% beyond it, indirectly through improved constraints on low-redshift interlopers. The results motivate prioritizing overlap with external tracers when designing LIM frequency coverage and survey footprints.

PublicMaps of emission from the distant universe can mix together several kinds of light from gas at different distances, while bright foreground emission makes the signals harder to separate. The researchers developed a method that jointly analyzes these maps and a galaxy catalog, using shared spatial patterns to help untangle the signals. In realistic simulated surveys, rather than actual observations, the method recovered the strengths of several carbon monoxide and neutral-carbon emission lines, with those strengths still combined with a factor describing how the emitting material traces cosmic structure. Adding galaxy information made the constraints about 3–4 times tighter where the datasets covered the same distances. It also improved constraints by about 20–50% farther away, because better accounting for nearer emission helped separate the more distant signals. The tests assumed a fixed cosmological model and suggest that overlap with galaxy surveys should be an important consideration in planning future mapping experiments.

Young explorerLight from space can get mixed together, like several voices talking at once. The scientists made a way to use a map of galaxies to help sort out the mixed-up light. They tried it on pretend space maps made to be realistic, not on real observations. The galaxy map helped them separate the light better. It even helped with light from farther away than the galaxy map reached, because sorting out the nearby light made the faraway light easier to pick out.

Magnetically Charged Black Holes from Grand Unified Theory

Tanmay Vachaspati, Anja Wachowitz

• High Energy Physics - Phenomenology
• High Energy Physics - Theory

AstronomerThis theoretical study considers magnetic monopoles and transient, biased domain walls in Grand Unified models with a weakly broken discrete symmetry. For one range of the symmetry-breaking parameter, collapsing walls can form magnetically charged extremal black holes lighter than approximately 1 kg; Hawking evaporation and Schwinger monopole pair production are expected to prevent their survival to the present. Still smaller parameter values may yield astrophysical black holes with masses above 10^15 g and sub-extremal magnetic charge, Q ≃ 10^8 for the authors’ canonical parameters. The residual monopole energy density also depends on this parameter and can satisfy all observational constraints when it is sufficiently small. These are model-dependent possibilities, not reported detections.

PublicThe paper explores a theoretical way that temporary boundaries called domain walls could collapse into black holes carrying magnetic charge. Such walls can arise in particle-physics models that also predict magnetic monopoles. Depending on how strongly a particular symmetry is broken, the resulting black holes could be lighter than about a kilogram or far more massive. The light ones are not expected to survive to today because of Hawking evaporation and the production of monopole pairs. With sufficiently weak symmetry breaking, the models may also leave a population of monopoles consistent with observational limits. The abstract reports theoretical possibilities, not observations of these objects.

Young explorerScientists are exploring an idea in which temporary boundaries in the universe could shrink into black holes with a special magnetic charge. In their theory, changing one setting could make tiny black holes that would not last until today, or much heavier ones. Some versions of the idea fit the limits set by observations, but that does not mean scientists have found these black holes.

All Quiet on the Vector Front: Scalar Growth and Perturbative Control in Horndeski--Weyl-squared Gravity

Antonio De Felice, Guillem Domènech, Jan Tränkle

• General Relativity and Quantum Cosmology
• High Energy Physics - Theory

AstronomerThis theoretical study analyzes classical linear stability in Horndeski gravity augmented by a Weyl-squared term, using shift-symmetric de Sitter and power-law FLRW backgrounds. Vector modes avoid gradient and tachyonic instabilities when the Weyl-induced mass squared is positive. Tensor modes necessarily include a ghost, although their superhorizon branches remain bounded; a frozen-background analysis supplies a separate finite-momentum stability condition. Scalar perturbations have a growing long-wavelength branch on every expanding background considered, affecting at least one gauge-invariant Bardeen potential through an inverse-gradient factor a^2/k^2. Crucially, the dynamical scalar fields remain bounded on inflationary backgrounds, the growing shear's direct contribution to the clock-matched tidal field cancels, and the electric Weyl tensor decays. These distinctions inform questions of perturbative control and phenomenological viability, rather than establishing an observational verdict on the theory.

PublicThe researchers use mathematical calculations, not observations, to test whether small disturbances remain controlled in a modified theory of gravity. They study Horndeski gravity with an added term involving spacetime curvature, on two kinds of expanding-universe backgrounds. Some disturbances avoid particular instabilities under a stated condition, but the tensor disturbances necessarily contain a problematic mode called a ghost. The scalar disturbances also produce growth in at least one mathematical description of the gravitational field on large scales. That growth needs careful interpretation: on the inflationary backgrounds studied, the underlying scalar fields remain bounded, a direct contribution to a tidal effect cancels, and another measure of tidal curvature decreases. The results highlight potential difficulties for these theories without showing that every gravitational disturbance grows uncontrollably.

Young explorerScientists used math to try out a different set of rules for gravity in a growing universe. They asked what happens to tiny wiggles. Some stayed under control, but they found a troublesome kind of wiggle and some growing numbers. Growing numbers did not mean that every stretching or squeezing effect grew too: some stayed limited or faded away. This was a math test, not something they saw in the sky.

Correlation between gravitational wave frequencies as a signature of new black hole physics

Ngo Phuc Duc Loc

• High Energy Physics - Phenomenology
• General Relativity and Quantum Cosmology
• High Energy Physics - Theory

AstronomerThis theoretical study identifies a near correspondence between the peak of the coarse-grained graviton gravitational-wave spectrum and that of the binary-merger spectrum for black holes of the same mass. The predicted ratio, f_peak^graviton/f_peak^merger ≈ 2.3, is independent of black-hole mass or population. For black holes still evaporating, both peak frequencies scale as the inverse initial mass; after accounting for redshift, they scale as the square root of initial mass for evaporation during radiation domination and linearly with initial mass for evaporation during matter domination. The authors highlight 10^14–10^20 Hz as a promising range where both spectra are allowed to reach their maximum amplitudes, and propose departures from the ratio as a diagnostic of new black-hole physics. In a phenomenological self-similar regular Hayward black-hole model with one hair parameter, a measured ratio could infer that parameter and associated Hawking temperature, horizon size, and innermost stable circular orbit. These are theoretical predictions and proposed inferences, not reported detections. The study also discusses advantages and drawbacks of frequency correlations involving other gravitational-wave sources.

PublicThe researchers predict a surprising link between two very different ways black holes can produce gravitational waves: radiation associated with black-hole evaporation and the merger of two black holes. For black holes of the same mass, the evaporation spectrum should peak at about 2.3 times the frequency of the merger spectrum, regardless of the black-hole mass or population. How those peak frequencies depend on the original mass changes according to whether the black holes are still evaporating or evaporated during different stages of the universe’s expansion. The authors suggest looking for this relationship at extremely high frequencies, around 10^14–10^20 Hz. They propose that a different ratio could signal new black-hole physics, and illustrate how it could reveal properties of one alternative black-hole model. The abstract reports a theoretical relationship and a possible test, not an observed pair of signals.

Young explorerBlack holes can make ripples in space when they join together. Scientists also predict ripples linked to black holes slowly losing their mass. This study says that, for black holes with the same mass, the two kinds of ripples should have a special connection: one kind should wiggle about 2.3 times as fast at its strongest part. If scientists someday find a different connection, it might help them learn something new about black holes. This is a prediction, not something the study says people have already seen.

Dark Energy Survey Year 6 Results: improved mitigation of spatially varying observational systematics with masking for the MagLim++ lens sample

M. Rodríguez-Monroy, N. Weaverdyck, J. Elvin-Poole+63 more

AstronomerThe authors define the DES Y6 JOINT footprint by combining observational-systematics templates with artefact indicators and masking extreme values from an initial SEED footprint, where mitigation may be unreliable. Applying the MagLim++ lens sample to this footprint, they enhance Iterative Systematics Decontamination (ISD) to detect non-linear contamination and improve correction accuracy. The footprint mask affects angular clustering less than systematics decontamination does, but its impact is comparable to statistical uncertainties at some w(theta) scales and in some redshift bins. The final footprint covers 4,031.04 deg2 and provides a common basis for DES Y6 galaxy-clustering and cosmic-shear analyses, including 1x2pt, 2x2pt, and 3x2pt. The approach balances retained survey area against the reliability and complexity of systematic-error mitigation.

PublicWhen astronomers map how galaxies cluster, uneven observing conditions and image defects can create misleading patterns. This study defines which parts of the Dark Energy Survey’s sixth-year data to use, excluding regions with extreme problems that are difficult to correct reliably. The researchers also improve a correction method to identify contamination that does not follow a simple linear relationship with observing conditions. Their final usable region covers 4,031.04 square degrees. Excluding problematic areas changes the clustering measurements less than applying the corrections does, but the effect still matters: for some angular scales and distance ranges, it is comparable to the uncertainty from limited data. The work establishes a shared survey region for studies of galaxy clustering and distortions of galaxy images caused by gravity.

Young explorerImagine making a map of where galaxies are, but some parts of your pictures are blurry or have marks on them. Those problems can make galaxies look more bunched together than they really are. The researchers chose which parts of a big sky map to keep and improved a way to fix misleading patterns. Leaving out the troublesome parts mattered less than fixing the patterns, but it still made a difference worth paying attention to. Keeping more sky is useful, but so is making sure the map can be trusted.

Evidence of galaxy cluster rotation and intrahalo gas motions in the cosmic microwave background

Samuel Goldstein, J. Colin Hill

• Astrophysics of Galaxies

AstronomerThe authors report the first robust evidence for the rotational kinematic Sunyaev-Zel'dovich (rkSZ) effect, a dipolar CMB signal from Thomson scattering by intracluster gas in dynamically active systems, including rotation and mergers. Combining Planck CMB intensity and polarization data with SDSS spectroscopic member-galaxy redshifts for 25 X-ray cross-matched clusters at 0.02 < z < 0.09 and approximately 10^13.9–10^14.6 solar masses in M500c, they detect a dipole aligned with the clusters' estimated angular momenta. They report rejection of a chance fluctuation at 99.98% confidence (3.6 sigma), aided by methodological improvements that isolate the signal from primary CMB fluctuations and noise. The observed amplitude and shape agree qualitatively, rather than quantitatively, with hydrodynamical simulation predictions. The authors present the result as a new CMB-based probe of cluster dynamics.

PublicResearchers report evidence that moving gas inside galaxy clusters leaves a two-sided pattern in the cosmic microwave background, the ancient light that fills the universe. This rotational kinematic Sunyaev-Zel'dovich effect can arise from cluster rotation and mergers, so it is not necessarily a sign of simple spinning motion alone. Combining Planck satellite measurements with galaxy redshifts from the Sloan Digital Sky Survey, the team found a pattern aligned with the estimated rotation directions in a sample of 25 nearby clusters. They report a statistical significance of 3.6 sigma, ruling out a chance fluctuation at 99.98% confidence. Improved methods helped separate the pattern from background variations and noise. Its strength and shape broadly resemble predictions from computer simulations, suggesting a new way to study how galaxy clusters move internally.

Young explorerHuge groups of galaxies have gas moving around inside them. When very old light travels through that gas, the gas can give it a tiny two-sided pattern. Scientists studied 25 galaxy groups and found evidence of this pattern pointing the way they estimated the groups were turning. The pattern is unlikely to be just chance, but it does not mean every group is simply spinning: groups coming together can help make it too. It could give scientists a new way to learn how gas moves in these huge groups.

Probing scalar-tensor-induced gravitational waves in the nHz band: NANOGrav and SKA

William Iania, Angelo Ricciardone

• General Relativity and Quantum Cosmology
• High Energy Physics - Theory

AstronomerThis theoretical study computes scalar-tensor-induced gravitational waves (STGWs) in the Poisson gauge during a generic matter-dominated era and an early matter-dominated epoch ending in a sudden transition to radiation domination. The calculated STGW energy density rapidly dilutes in a purely matter-dominated era but remains non-vanishing for the short early matter-dominated phase. The authors assess whether STGWs could dominate the NANOGrav 15-year signal and forecast SKA detection prospects, considering production during early matter and radiation domination, including linear-order contributions. They also compare models with scalar-induced gravitational waves (SIGWs) as an additional component or the sole signal. SIGWs still appear to dominate, while avoiding primordial black hole overproduction tightly constrains the posteriors. Scalar-tensor mixing is identified as a viable target for future, more sensitive nanohertz observations, not as an established detection.

PublicThe study explores a possible source of the faint gravitational-wave background investigated with pulsar timing: waves produced by interactions between density fluctuations and gravitational waves in the early universe. The authors calculate how this signal would evolve if the universe passed through an early matter-dominated period that ended abruptly in radiation domination. In their model, the signal fades rapidly during prolonged matter domination but remains nonzero when that early period is short. Comparing possible signals with the NANOGrav 15-year dataset, they find that waves generated by density fluctuations alone still appear to contribute most. The models are also tightly limited by the need not to produce too many primordial black holes. Forecasts suggest that the mixed signal could be a target for future, more sensitive observations, including those with the Square Kilometre Array; the study does not establish that it has been detected.

Young explorerScientists are studying tiny ripples in space. They used maths to ask whether lumps of matter and other space ripples could have worked together to make some of them long ago. Their calculations say these mixed ripples could still be around if one early chapter of the universe was short. But another way of making ripples still seems to explain more of the signal being studied. Future, more sensitive observations might help scientists find the mixed ripples. They have not shown that they have found them yet.

Cosmo-PINN: A Physics-Informed Neural Network for Cosmological Reconstruction

Andronikos Paliathanasis

• General Relativity and Quantum Cosmology

AstronomerThe authors introduce Cosmo-PINN, a physics-informed neural network that reconstructs the dark-energy equation-of-state parameter w_DE(z) from late-time background observations. Training uses DESI DR2 baryon acoustic oscillations, cosmic chronometers, and three supernova compilations, with H0, Ω_m0, and r_drag jointly trained. Cosmological constraints are embedded in the loss function to enforce physical consistency during training, addressing a limitation of purely data-driven reconstructions. The reconstructed w_DE(z) crosses the phantom divide, w_DE = −1, around z = 0.5, consistent with the crossing obtained using the Chevallier–Polarski–Linder model. In the quintessence scenario considered, w_DE(z) is forced toward the ΛCDM limit of −1 in the past. These are reconstruction results, not direct measurements of w_DE; the abstract gives no uncertainty or significance for the crossing. A comparison with an otherwise identical, purely data-driven network illustrates the role of the physical constraints.

PublicThis study introduces an AI method for reconstructing how dark energy behaves over cosmic history. Rather than fitting observations alone, Cosmo-PINN also incorporates cosmological rules into its training. The researchers use measurements from DESI DR2, cosmic chronometers, and three supernova collections. Their reconstruction suggests that a parameter describing dark energy crosses a dividing value of −1 around redshift 0.5, agreeing with a separate model-based estimate. This is an inference from the method, not a direct observation of dark energy changing, and the abstract does not report how statistically certain the crossing is. In the quintessence case studied, the parameter is forced toward the standard ΛCDM value of −1 further back in cosmic history. The authors also compare their method with an AI network that fits the data without these physical constraints.

Young explorerScientists made a computer helper to study something called dark energy in the universe. They gave it clues from space and rules about how the universe works, so it would not just copy patterns in the clues. Its answer suggests that dark energy's behavior may have changed in the past. That is what the computer worked out, not something the scientists saw directly, and this short report does not say how sure they are. They also compared it with a computer helper that did not use those rules.

Time-reversed stochastic inflation in the quantum well

Chiara Animali, Baptiste Blachier, Nanoka Okada+3 more

• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology
• High Energy Physics - Theory

AstronomerThis theoretical study exactly solves time-reversed stochastic inflation for a flat, bounded potential, termed a quantum well. The formulation counts e-folds backward from the end of quantum diffusion toward an initial state, adopting the viewpoint of observers on the end-of-inflation hypersurface. At a given lifetime, the field evolution is either indistinguishable from that in a semi-infinite flat potential or exhibits enhanced stochasticity that erases memory of the initial state. The derived curvature-perturbation distribution matches the semi-infinite result for small fluctuations but develops exponential tails for large positive and negative fluctuations. These tails decay twice as fast as in standard forward stochastic inflation. The differences may affect tail-sensitive phenomena such as primordial black hole formation; the abstract does not establish a specific consequence for that formation process.

PublicThe researchers study a mathematical model of the early universe by working backward from the end of a phase dominated by quantum randomness. They solve the model exactly for a flat potential with boundaries, called a quantum well. Depending on the lifetime considered, the model either behaves like a comparison model with only one boundary or becomes more random and loses all memory of its starting state. Small fluctuations follow the comparison model, but large fluctuations in either direction have exponentially declining probabilities. Those probabilities fall off twice as fast as in the usual forward-time calculation. This theoretical difference could matter for the formation of primordial black holes, but the study does not demonstrate that such black holes formed.

Young explorerScientists used math to study a very young universe, starting at a later time and working backward. In their model, random wiggles can sometimes wipe away clues about how things started. They found that very big wiggles become rarer more quickly than in a usual forward-time calculation. This might matter for how black holes could form, but it does not show that any black holes actually formed.

Field-Level Baryon Acoustic Oscillation Reconstruction of the DESI DR1 Luminous Red Galaxies with Linear Field Transformer (LiFT)

Liam Parker, Uroš Seljak, Adrian E. Bayer+2 more

• Instrumentation and Methods for Astrophysics

AstronomerThe authors report the first application of neural field-level BAO reconstruction to real spectroscopic survey data. Their Linear Field Transformer (LiFT), a 3D vision transformer, uses the observed galaxy field, standard reconstruction, and line-of-sight, coverage, and redshift context to learn corrections toward the linear density field. It is trained on forward-modeled lightcones resembling the DESI DR1 luminous red galaxy sample. Tests on held-out simulations and alternative mocks spanning gravity solvers, halo finders, HOD, cosmology, fiber-assignment histories, and distorted distance–redshift relations yield unbiased dilation parameters and consistently tighter constraints than standard reconstruction within the tested cases. On real DESI DR1 data, uncertainties in alpha_iso decrease by 13%, 24%, and 30%, and those in alpha_AP by 5%, 22%, and 30%, for LRG1, LRG2, and LRG3, respectively. Central values remain consistent with DR1 and DR2. The reported Figure of Merit gains are factors of 1.2, 1.7, and 2.0, interpreted as equivalent effective-volume gains relative to standard reconstruction, not additional observed volume. The authors conclude that LiFT is survey-ready.

PublicResearchers have applied an AI method called LiFT to real galaxy-survey data to sharpen measurements of the baryon-acoustic oscillation pattern in galaxy positions. The method learns to improve an existing reconstruction technique using simulated galaxy surveys resembling the DESI Data Release 1 luminous red galaxy sample. In tests on several kinds of simulations, it produced tighter measurements without detectable bias in the parameters being tested. Applied to the real survey, it reduced uncertainties in one distance-related parameter by 13%, 24%, and 30% across three galaxy groups, and in a second parameter by 5%, 22%, and 30%. The measured values remained consistent with the earlier DESI DR1 and DR2 results: the advance is greater precision, not a conflicting measurement. The authors describe the method as ready for survey use, based on these simulation tests and its application to real data.

Young explorerScientists made a computer helper to study patterns in where galaxies are. First, they taught it with pretend galaxy maps made by computers. Then they tried it on a real galaxy map. It helped make their measurements less uncertain, and the answers still agreed with earlier ones. The pretend maps helped them check the helper, but the better measurements came from using it on real galaxies.

Evolving dark energy and a younger Universe from cosmic inhomogeneity

Jacky David Yang, Hans-Otto Carmesin

AstronomerJoint BAO, type Ia supernova and CMB analyses favor an evolving dark-energy equation of state. This study examines whether cosmic inhomogeneity can produce apparent evolution within general relativity by entering the expansion dynamics directly. With CMB-inferred parameters fixing the homogeneous limit, the framework produces redshift-dependent effective Hubble and dark-energy density parameters without an additional free parameter. The effective dark-energy density parameter rises toward the present from 0.679 to 0.735, about eight percent, while the inferred Hubble constant shifts from the Planck value toward local estimates. These model-derived trends are broadly consistent with published estimates from several probes, but a joint analysis of the underlying data remains future work. Integrating the expansion history gives a present age of 13.521 Gyr versus 13.827 Gyr in the homogeneous model; the authors interpret the 0.306 Gyr difference as global time dilation between descriptions. Separately, the framework yields a homogeneous-limit dark-energy density parameter of two thirds from volume formation alone. Its predicted redshift dependences await tests with forthcoming distance and expansion-rate measurements.

PublicSome combined astronomical observations favor the idea that dark energy changes over cosmic history, but that is not the only possible explanation. This study explores whether an uneven distribution of matter could make dark energy appear to change within general relativity. In the proposed framework, unevenness directly affects cosmic expansion without adding a new adjustable parameter. The calculations give a rising effective dark-energy density parameter toward the present and move the inferred present expansion rate toward estimates from nearby measurements. These trends broadly agree with published estimates, but the underlying observations have not yet been analyzed together to test the framework. The calculation also gives a younger universe than the uniform-matter comparison model. The authors interpret that age difference as a difference in time between the two descriptions, rather than reporting a direct measurement of time dilation. Future measurements could test the predicted expansion history.

Young explorerThe universe has clumps of matter and emptier places. Scientists used a mathematical model to ask whether those clumps could make dark energy, which helps explain how the universe expands, look as if it changes. Their calculations suggest this might happen, but they have not shown that this is what really happens. More measurements could help check the idea.

How much can shape degeneracies affect the Hubble constant measurement?

Ashish K. Meena, Prasenjit Saha, Liliya L. R. Williams+1 more

AstronomerCluster lens models constrained primarily by image positions admit shape degeneracies (ShaDes): mass perturbations that preserve every image position while altering time delays. The authors show that the delay shift equals the perturbing-potential difference between images, regardless of the number of source or lens planes. For MACS J0138.0−2155, perturbations constrained to preserve nonnegative convergence, image multiplicity, and parity can contribute at least about 7 days to the delay between detected SN-Encore images, or 17.5% of the measured 39.8-day delay. They can also contribute about 112 days to the predicted SN-Encore and SN-Requiem reappearance intervals of 3,000–4,000 days, corresponding to 2.8–3.7%. These are degeneracy-induced uncertainties, not measured delay shifts. The authors state that the fractional uncertainties transfer directly to H0 and remain invisible to comparisons of independent models.

PublicA galaxy cluster can bend light so that the same exploding star appears in several images, whose light arrives at different times. This study shows that different mass distributions can reproduce exactly the same image positions yet give different arrival-time delays. For the cluster MACS J0138.0−2155, the authors find that such hidden differences could contribute at least about 7 days of uncertainty to SN-Encore’s measured 39.8-day delay. They could also contribute about 112 days to the predicted 3,000–4,000-day waits for SN-Encore and SN-Requiem to reappear. These figures describe uncertainty in the lens models, not newly observed changes in arrival times. The uncertainty passes directly into estimates of the universe’s expansion rate and would not be revealed simply by comparing independent models.

Young explorerA big group of galaxies can bend a star’s light, making us see the same exploding star more than once, at different times. Scientists use maps of the galaxies’ matter to work out how long the light takes. This study shows that different maps can put the star’s pictures in exactly the same places but still give different waiting times. That means scientists may be less sure about when another picture will appear, and about how fast the universe is growing. The study finds a hidden uncertainty in the maps; it does not report seeing the star appear again.

Collider Probes of Dark Energy Microphysics

Chaitanya Bashyam, Alfredo Gurrola, Andres Florez+1 more

• High Energy Physics - Phenomenology
• General Relativity and Quantum Cosmology
• High Energy Physics - Experiment

AstronomerThe authors propose a collider probe of dark energy microphysics, motivated by the degeneracy of expansion histories among models with similar equation-of-state parameter w and the weak observational constraints on dark energy's perturbation sound speed. Their effective-field-theory framework couples a dynamical dark energy scalar to the pseudoscalar mediator of the 2HDM+a model through symmetry-motivated derivative interactions. Within this framework, the interactions induce invisible decays and modify mediator propagation in a dark energy background, making resonance widths, branching ratios, and kinematic structure sensitive to dark energy's sound speed. The proposed measurements at colliders such as the LHC could complement cosmological constraints and distinguish otherwise degenerate models. These are theoretical predictions within the constructed framework, not reported collider detections of dark energy effects.

PublicObservations of the universe's expansion do not uniquely reveal what dark energy is: different theories can predict the same expansion history. This paper proposes looking for additional clues in particle collisions. In the authors' theoretical model, a hypothetical particle interacts with a dark energy field, changing how that particle travels and decays. Those changes could reveal how quickly disturbances spread through dark energy, a property that current astronomical observations constrain poorly. Collider experiments such as the LHC might therefore help distinguish competing theories. The paper presents a proposed connection and its theoretical consequences, not an observed dark energy signal in collider data.

Young explorerScientists still do not know what dark energy is. It is linked to the universe growing faster and faster. This paper suggests that smashing tiny particles together might offer clues. In the scientists' model, dark energy could change how a new, not-yet-found particle moves and breaks apart. Looking for those changes might help, but scientists have not seen them yet.

Axion Misalignment Across First-Order Phase Transitions

Galymzhan Baltabay, Francesco D'Eramo, Ville Vaskonen

• High Energy Physics - Phenomenology

AstronomerLattice simulations in an expanding universe examine axion dark matter production when the axion mass turns on only inside expanding true-vacuum bubbles during a first-order phase transition. Two regimes modify standard misalignment production: rapid transitions delay the onset of oscillations until bubble percolation, enhancing the relic abundance, whereas slower transitions generate spatial gradients that suppress the effective misalignment angle through bubble misalignment. A derived semi-analytical relic-density expression unifies both regimes and accurately reproduces the simulations. The study also finds modifications to isocurvature perturbations and the small-scale matter power spectrum, with implications for axion minicluster formation. These are results within the modeled framework, not observational detections.

PublicThis theoretical study explores how axions, hypothetical dark matter particles, could have been produced during a bubble-forming transition in the early universe. In the scenario studied, axions acquire mass only inside the expanding bubbles. Computer simulations find that a fast transition delays when axions begin oscillating, leaving more axion dark matter than in the standard picture. During a slower transition, differences between neighboring regions instead weaken the initial displacement that drives those oscillations. The researchers derive an approximate formula that matches both simulation regimes. They also find changes in the predicted pattern of dark matter fluctuations on small scales, which could affect the formation of axion miniclusters. The study does not report observations of axions or these clusters.

Young explorerScientists used computers to imagine how a mysterious kind of matter might have formed when the universe was very young. In their idea, tiny particles called axions get mass only inside growing bubbles. When the bubbles grow and join quickly, the axions start wiggling later, leaving more of this matter. When the change takes longer, differences from place to place make the starting wiggles smaller. This could also change how the matter gathers into little clumps. It is something scientists studied in a computer, not something they have seen in the sky.

Quantum Field Theory Of Cosmological Perturbations Induced By Ultralight Dark Matter

Tomislav Prokopec, Marco Vecchioni

• High Energy Physics - Theory
• General Relativity and Quantum Cosmology

AstronomerThis theoretical study develops a first-principles quantum-field framework for linear cosmological perturbations during matter domination with ultralight scalar dark matter (ULDM). It derives a closed equation for graviton dynamics and computes regularized source terms for generic Gaussian initial states using the adiabatic WKB approximation and a middle-point working assumption for non-local terms. After gauge-fixing, the classical ULDM condensate does not affect gravitational-wave propagation, contrary to previous claims. Quantum pressure in a squeezed state can instead induce a time-dependent graviton effective mass and parametrically amplify particular primordial gravitational-wave modes. For non-relativistic ULDM at matter-radiation equality, however, the calculated growth is negligible for masses of roughly 10^-24 to 10^-21 eV under an assumed power-law squeezing spectrum. These are theoretical findings, not observational detections.

PublicDark matter helps small differences in the early universe grow, and extremely light particles described by a scalar field are one possible explanation for it. This study treats that candidate's quantum behavior explicitly rather than using only a classical description. Within the theoretical framework, the classical field does not change how gravitational waves travel, contrary to earlier claims. Quantum effects could amplify certain gravitational waves left over from the early universe. However, the calculated amplification is negligible for the very light particle masses studied at the transition between radiation and matter domination, assuming a particular distribution of the field's quantum squeezing. The work does not report an observed signal.

Young explorerScientists used math to study a possible kind of dark matter, the unseen stuff that helps tiny clumps in the universe grow. They asked whether it could change ripples in space. In their math, treating this dark matter in the usual way did not change how the ripples travel. Its tiny quantum effects could make some ripples grow, but with the conditions they tried, that growth was much too small to matter. This was a calculation, not something they saw in the sky.

How JWST is Revolutionizing Our View of Early Galaxy Formation

Rychard Bouwens

AstronomerThis review summarizes JWST’s first four years of constraints on early galaxy formation. Strong spectral breaks have enabled identification of hundreds of star-forming galaxies at z ≳ 8, within roughly 650 million years of the Big Bang, while sensitive spectroscopy has informed studies of stellar populations, gas, nebular continuum, enrichment, dust, and ionization. These systems are more numerous and brighter than pre-JWST models anticipated. The emerging physical picture includes compact, clumpy star formation, high gas fractions, and intense radiation fields, with implications for reionization, stellar mass and metal buildup, and luminosity-function evolution. Star-formation efficiency, intermittency, the IMF, ISM conditions, galaxy masses and structure, and reionization topology remain uncertain. The review identifies lensing magnification, sensitive spectroscopy beyond 5 microns including ALMA observations, higher-redshift exploration, and larger, more complete samples as necessary next steps.

PublicThe James Webb Space Telescope has identified hundreds of galaxies forming stars when the universe was less than about 650 million years old. They are brighter and more numerous than models made before JWST had predicted. By studying their light, astronomers are learning about their stars, gas, dust, and chemical enrichment. The findings suggest that early galaxies had tightly packed, patchy regions of star formation, large proportions of gas, and intense radiation. This review discusses what those discoveries could mean for galaxy growth and the transformation of the universe’s neutral gas into ionized gas. Important questions remain, including how efficiently and steadily stars formed and how massive these galaxies were. Answering them will require more sensitive observations and larger, more complete galaxy samples.

Young explorerWebb is a space telescope that helps us see galaxies as they were when the universe was very young. It has found hundreds of galaxies making stars, and they are brighter and more plentiful than scientists expected. Their stars seem to form in small, crowded patches. But scientists still have lots of questions about how these galaxies grew. They need more observations to find the answers.

EMRIs in Kerr Spacetime: The Role of Inclination Diffusion

Yael Alush, Nicholas C. Stone, Scott A. Hughes

• High Energy Astrophysical Phenomena
• General Relativity and Quantum Cosmology

AstronomerThis theoretical and Monte Carlo study models encounter-driven inclination evolution along Kerr geodesics to refine uncertain EMRI-to-plunge ratios in dense nuclear star clusters. Unlike earlier fixed-inclination treatments, its 3D diffusion framework allows initially prograde orbits to become retrograde, changing whether compact objects gradually inspiral or plunge directly. The simulations estimate that substantial massive-black-hole spin enhances the EMRI rate by about 2.5. Separately, even for a non-spinning black hole, relativistic geodesics yield about 2.5 times as many EMRIs as Newtonian trajectories. The modeled Kerr EMRI inclination distribution has a substantial prograde bias, which may help identify loss-cone EMRIs in future samples. These are modeling results, not detections; EMRI rates and orbital distributions remain highly uncertain.

PublicA small, compact object can spiral slowly into a massive black hole, emitting gravitational waves that the future LISA mission is expected to detect, or plunge straight in without a detectable signal. Predicting how often each happens is difficult. This study uses mathematical modeling and computer simulations to follow how encounters with surrounding stars change an object's orbit around a spinning black hole. The simulations show that an orbit can switch from moving with the black hole's spin to moving against it, potentially changing a slow inspiral into a plunge or the reverse. The researchers estimate that substantial black-hole spin increases the slow-inspiral rate by about 2.5 times. Separately, using relativistic rather than Newtonian orbits around a non-spinning black hole increases the simulated number of slow inspirals by a similar factor. The modeled preference for inspirals moving with the spin might help classify future detections, but these findings are predictions from simulations, not observations.

Young explorerA small, very squeezed object can circle a huge black hole and slowly fall closer, making ripples in space. Or it can fall straight in without ripples we could detect. Scientists used math and computer models to see how nudges from nearby stars change its path. In their models, an object could change from circling with the black hole's spin to circling against it. That could change how it falls in. The models suggest that a spinning black hole helps more objects take the slow, ripple-making path. Scientists have not watched this happen in this study; they are working out what a future space detector might find.

The Dance of the Little Red Dots: Spectroscopy of Two Blue Companions at z = 3.9 and 5.5 Reveals Young, Metal-Poor Starbursts Merging with Their LRDs within a Few Hundred Myr

Fabio Pacucci, Pierluigi Rinaldi

• Cosmology and Nongalactic Astrophysics
• High Energy Astrophysical Phenomena

AstronomerSpectroscopy confirms blue companions at nearly the same redshifts as two Little Red Dots (LRDs): Waltz at z = 3.9 and Tango at z = 5.5. Their projected separations are 3.6 and 2.5 kpc, with velocity offsets within 132 and 57 km/s, respectively. Despite being observed 524 Myr apart in cosmic time, the companions share similar properties: starbursts no older than about 50 Myr, metallicities of 0.2 times solar, no dust, dynamically cold gas, and rest-frame UV brightness comparable to their LRDs. Waltz's LRD hosts an approximately 3-million-solar-mass black hole accreting at half the Eddington rate, embedded in gas as metal-poor as its companion. Orbital modeling—not a direct orbital measurement—finds Tango bound in 81% of allowed orbits; Waltz is bound if its host halo exceeds 50 billion solar masses. In the bound configurations, the companions are predicted to merge with their LRDs within a few hundred Myr. The authors interpret these systems as evidence consistent with synchronized-pair heavy black-hole seeding, rather than a direct observation of seed formation.

PublicAstronomers have confirmed that two compact red objects in the early universe each have a nearby blue companion at essentially the same cosmic distance. The companions are young bursts of star formation, poor in elements heavier than helium, dust-free, and as bright in ultraviolet light as the red objects themselves. One red object, in the pair called Waltz, contains a black hole about three million times the Sun's mass. Computer modeling suggests that the other pair, Tango, is probably gravitationally bound; whether Waltz is bound depends on the mass of its surrounding halo. If bound, the companions are predicted to merge with their red neighbors within a few hundred million years. The authors interpret the pairs as possible examples of a proposed route to forming massive black-hole seeds beside young, metal-poor starbursts. The observations do not directly show those black holes being born.

Young explorerAstronomers found two little red objects in space, each beside a blue neighbor full of young stars. One red object has a very heavy black hole inside. The blue neighbors have very little of the heavier ingredients stars can make. Calculations suggest that each pair might join together someday. The scientists think these neighbors could help explain how big black holes first got started, but they did not see a black hole being born.

Wave Cold Dark Matter Can Reproduce the Radial Acceleration Relation in X-ray Elliptical Galaxies

Runyu Meng, Xiaobo Dong

AstronomerThe authors test wave cold dark matter against the empirical radial acceleration relation (RAR) in eight X-ray elliptical galaxies using 3D Schrödinger–Poisson simulations. For each galaxy and adopted ultralight-boson mass, they select the realization whose final, virialized quasi-stationary snapshot best matches the RAR. These selected realizations reproduce the relation without baryonic feedback or dark-matter self-interactions. At a boson mass of 10^-23 eV, the combined fit yields a0 = 1.19 × 10^-10 m s^-2, consistent with the canonical disk-galaxy value. Across masses of 3 × 10^-24 to 2 × 10^-23 eV, the best-fit a0 varies by about 11%, with no systematic mass trend. The authors attribute this weak dependence to velocity-field support dominating over quantum pressure across the relevant radii. The result demonstrates compatibility for selected simulated realizations in this sample, extending tests beyond solitonic cores rather than establishing wave CDM as the unique explanation.

PublicThis study asks whether a wave-like form of dark matter could explain an observed relationship between the distribution of ordinary matter and the total gravitational pull in eight elliptical galaxies studied in X-rays. The researchers simulated dark-matter halos and, for each galaxy and assumed particle mass, selected the simulation that best matched that relationship. Those selected simulations could reproduce it without including effects from ordinary matter feeding energy back into its surroundings or dark-matter particles interacting with one another. The fitted characteristic acceleration agreed with a value previously inferred from disk galaxies and changed by only about 11% over the particle masses tested, with no consistent upward or downward trend. The authors explain this weak mass dependence by finding that motions within the simulated halos matter more than wave-related quantum pressure at the distances examined. This supports wave dark matter as a possible explanation for this galaxy relationship, but does not prove that it is the correct one.

Young explorerAstronomers see a pattern in how strongly gravity pulls inside some galaxies. The researchers made computer galaxies with an invisible kind of matter that acts like waves. For eight galaxies, they picked the computer versions that matched the pattern best, and those versions could copy it. Changing the tiny particles’ mass did not change the match very much. That means this idea could work for these galaxies, but it does not mean we know the invisible matter really is like that.

GroArnold: A Framework for Constructing Action-based Models for Triaxial Galaxies and Dark Matter Halos

Jian-Yu Gu, Xiao-Bo Dong, Shi-Yan Zhong+1 more

AstronomerThe study presents GroArnold, a modular framework for constructing analytical action-based distribution functions, f(J), for axisymmetric and triaxial galaxies and dark matter halos. Its workflow combines N-body initial-condition generation, simulation, angle–action estimation, and distribution-function fitting. The Nbody-TACT module extends TACT’s triaxial Stäckel Fudge method to estimate actions directly from N-body gravitational potentials. The framework aims to produce distribution functions approximating dynamically stable, physically consistent states for user-specified systems. Tests comparing the fitted functions’ predicted spatial and velocity distributions with those of input N-body snapshots found reasonably accurate agreement; the abstract gives no quantitative accuracy measures. These are computational comparisons, not observational tests. The publicly available code supports varied density profiles and kinematics and is designed for future extensions.

PublicResearchers introduce GroArnold, a publicly available computer toolkit for building mathematical descriptions of how stars or dark matter are distributed and move within model galaxies and halos. It combines particle simulations with methods for estimating orbits and fitting formulas, including for systems with three unequal axes rather than only round or rotationally symmetric shapes. The goal is to create models that remain dynamically stable and are physically consistent. In computational tests, the fitted formulas reproduced the simulated particles’ positions and velocities reasonably accurately. That agreement supports their usefulness for modeling, but the abstract does not report numerical error estimates or tests against observations of real galaxies.

Young explorerScientists made a computer toolkit called GroArnold to build pretend galaxies and describe where their tiny moving pieces go. They checked its math against computer-made galaxies, and it matched reasonably well. They hope it can help build galaxies that keep a steady overall shape. These were computer tests, not checks of real galaxies in the sky.

A Nonlinear General Implicit Runge-Kutta Integrator for Multifluid Charged Dust and Gas

Mengxuan Chen, Hui Li, Chong-Chong He+3 more

AstronomerThe authors implement a two-stage general implicit Runge-Kutta source integrator in the GPU-accelerated quokka code for multifluid charged dust coupled to ideal MHD gas. A joint implicit update of drag and Lorentz forces avoids terminal-drift errors that can arise from splitting these forces. Comparing the timestep with a drag-Lorentz timescale selects either a resolved Gauss-Legendre branch or a stiff branch designed to recover the terminal drag-Lorentz balance. State-dependent stopping times and charge-to-mass ratios are evaluated at each implicit stage, with nonlinear equations solved by Picard iteration. The source update conserves total gas-dust momentum, and its cost scales linearly with the number of dust species. Numerical tests reproduce expected damping and terminal drift, confirm predicted gyromotion amplitude and phase errors, and recover expected wave, shock, and instability dynamics. These are computational validation results, not astronomical observations.

PublicThis work develops and tests a computer method for simulating electrically charged dust moving through magnetized gas. Gas drag and magnetic forces can change dust motion faster than a simulation's time steps can follow directly. The method handles both forces together, avoiding errors in the steady drift that can occur when they are calculated separately. It also allows dust properties to change as the simulated conditions evolve. Computer tests recover expected patterns of motion, including waves, shocks, and growing disturbances. The reported results validate a simulation method rather than describe observations of space.

Young explorerImagine tiny dusty specks moving through gas, with magnets pushing on them too. A computer can have trouble following their very quick moves. The researchers made a way to work out the gas and magnet pushes together. They tested it in computer experiments, and the dust moved in the ways they expected.

Substructure-enhanced Collisional Relaxation in Stellar Systems

Jian-Yu Gu, Xiao-Bo Dong, Run-Yu Meng

AstronomerThis theoretical study generalizes the classical Chandrasekhar calculation of two-body diffusion beyond a homogeneous stellar background with isotropic Gaussian velocities. Retaining hyperbolic two-body encounters, the authors explicitly integrate over the spatial density and full velocity distribution to obtain a separable diffusion tensor. In their models, spatial substructure dominates the enhancement: log ζr scales approximately as (1 − Dfrac/3)^q, with q ≈ 4.28. Enhancement is moderate at the observationally motivated Dfrac ≈ 1.5 and grows substantially at lower fractal dimensions. Anisotropic, power-law-tailed, and fractal-like velocity distributions change diffusion only by factors of order unity. Extrapolating particle-number trends in a representative model to N = 10^11 gives spatial and velocity enhancement factors of about 3.45 and 1.33, respectively, or about 4.6 overall; these are model extrapolations, not observed galactic measurements. Within the two-body framework and commonly used separable distribution functions, the authors conclude that this increase still has little effect on the mean-field character of typical galaxies.

PublicStars gradually change one another’s motions through gravitational encounters. Standard calculations estimate this effect by treating the surrounding stars as smoothly spread out, with a simple distribution of velocities. This study instead calculates what happens when stars have more complicated spatial patterns and motions. The models indicate that spatial clumping strengthens the effect more than changes in the velocity distribution do. More extreme spatial structure produces larger increases, while a case motivated by observations gives a moderate increase. For one representative model, extrapolating to 100 billion stars gives an overall increase of about 4.6 times the standard estimate—not a direct measurement of a galaxy. Even with that increase, the authors conclude that typical galaxies should remain governed mainly by their collective gravitational field rather than by individual stellar encounters, within the assumptions of their calculation.

Young explorerStars tug on each other with gravity. Scientists used math to ask what happens when stars are grouped unevenly instead of spread out smoothly. In their models, the uneven groups made little tugs change stars’ motions more strongly. Changing how the stars moved mattered less. This was a calculation, not something they watched happen in a galaxy. Their answer suggests that, in a typical galaxy, the pull of all the stars together still matters much more than little encounters between pairs of stars.

The convective-transition gap in 47 Tucanae with JWST

M. Scalco, L. R. Bedin, M. Libralato+3 more

AstronomerDeep JWST observations reveal a feature identified as the convective-transition gap on the lower main sequence of the Galactic globular cluster 47 Tucanae. Luminosity functions derived using two independent colour-magnitude diagrams both show a narrow gap followed by a discontinuous increase in stellar counts, with an overall morphology qualitatively consistent with previous studies. The authors use an empirical likelihood model to estimate the feature’s statistical significance, but the abstract gives no numerical significance. Similar signatures in additional JWST passbands provide further evidence for a discontinuity.

PublicUsing deep observations from the James Webb Space Telescope, astronomers report a narrow dip in the number of stars at certain brightnesses in the globular star cluster 47 Tucanae, followed by an abrupt increase in star counts. They identify this feature as the convective-transition gap among the cluster’s lower-main-sequence stars. Two independent colour–brightness diagrams show the pattern, and observations in additional wavelength bands offer further support. Its overall shape resembles findings from earlier studies. The team used a statistical model to assess the feature’s significance, though the abstract does not state how strong that significance is.

Young explorerAstronomers used the James Webb Space Telescope to look at a big group of stars called 47 Tucanae. When they counted stars by how bright they look, they found a small dip: fewer stars in one brightness range, followed by a sudden rise in the count. This is not an empty hole in the group. They saw a similar pattern in several ways of looking at the stars, which gives them more reason to think the dip is real.

The connection between massive galaxies and their dark matter haloes from z=0.25 to z ∼4 from the combined COSMOS, XMM-LSS and ECDF-S fields

Natalia Stylianou, Matt J. Jarvis, Rohan G. Varadaraj+4 more

• Cosmology and Nongalactic Astrophysics

AstronomerUsing optical and near-infrared UltraVISTA and VIDEO data spanning 9.3 square degrees across three fields, the authors measure angular two-point correlations for stellar-mass-selected galaxies at 0.25 < z < 4 to constrain halo occupation. The area is approximately five times that of comparable previous studies, and combining fields reduces cosmic variance by about a factor of two relative to individual fields. The stellar-to-halo mass ratio peaks near a halo mass of 10^12 solar masses and reaches its maximum around z = 1. For the most massive galaxies, the halo mass associated with this peak increases from z = 1 to the present, while the corresponding stellar mass remains approximately constant, interpreted as declining massive-galaxy formation efficiency below z = 1. A rising satellite fraction since z ≈ 1 supports the inference that massive haloes continue hierarchical growth while central stellar-mass growth is suppressed. The authors suggest AGN feedback, likely associated with low-power stochastic radio emission, as the explanation; this mechanism is proposed rather than established by the clustering findings.

PublicHow do galaxies grow inside the dark matter structures that surround them? Researchers studied galaxy clustering using two surveys covering three patches of sky, tracing galaxies out to a redshift of about four. Combining the patches reduced uncertainty caused by differences between cosmic regions. They find that the ratio of stellar mass to dark matter halo mass is highest for haloes around a trillion times the Sun’s mass, and that this ratio reaches its greatest value around redshift one. Since then, the most massive galaxies appear to have gained little stellar mass even as their haloes continued growing. An increasing proportion of satellite galaxies supports this interpretation. The researchers suggest that feedback from active galactic nuclei, likely linked to weak, intermittent radio emission, could limit the central galaxies’ growth. That explanation is not demonstrated by this study.

Young explorerGalaxies are huge groups of stars that live inside much bigger homes made of dark matter. Scientists looked at how galaxies bunch together. Their clues suggest that some big galaxies stopped adding many stars even while their dark matter homes kept growing and gathering smaller galaxies. The scientists think activity in the big galaxies’ centers might slow their growth, but they have not shown that this is the cause.

MOSS III: MeerKATs view on the galaxy populations in two massive galaxy clusters

Robert Kincaid, Mark Sargent, Pascale Jablonka+5 more

AstronomerThe ongoing MOSS project compares radio-selected galaxy populations in two clusters in the Saraswati supercluster core at z = 0.28: the more massive Abell 2631 and the more dynamically active, merging ZwCl2341. The analysis combines deep pilot MeerKAT L-band catalogs, obtained at 1.28 GHz with 8-arcsec resolution, with spectroscopic redshifts, mainly from DESI DR1 and SDSS DR16, and optical photometry. The authors use redshifts and reported 1.4-GHz flux densities to derive dust-free star-formation rates. They find up to four times more star-forming galaxies in ZwCl2341 than in Abell 2631 and report that star-formation-related radio processes dominate over AGN-related processes in ZwCl2341. They interpret this contrast as suggesting enhanced star-formation radio activity and larger star-forming populations in dynamically active environments; the comparison does not establish that mergers cause the enhancement. A survey of the entire supercluster remains planned.

PublicResearchers compared two galaxy clusters in the core of the Saraswati supercluster using radio observations, galaxy distance information, and optical data. The cluster undergoing active merging, ZwCl2341, contains up to four times more star-forming galaxies than the more massive Abell 2631. In ZwCl2341, the authors also report that radio activity associated with star formation dominates over activity associated with active galactic nuclei. Radio measurements let them estimate star-formation rates without dust obscuration. These findings suggest that the busy environments where clusters assemble may favor star formation, but they do not prove that merging causes it. The project is ongoing, with a broader survey planned.

Young explorerGalaxies are huge groups of stars, and they can gather in big groups too. Scientists compared two of these groups. The group where galaxies are coming together had up to four times as many galaxies making new stars as the other group. This hints that coming together might help galaxies make stars, but the scientists have not proved that yet.

Are Broad Mg II Galaxies Fading AGN?

Stephanie M. LaMassa, Michael Eracleous, Jessie Runnoe+2 more

AstronomerSpectral decomposition of 494 SDSS I–IV galaxies with broad Mg II λ2798 emission but weak or absent broad Balmer lines supports, but does not establish, a fading-AGN interpretation. These galaxies have lower AGN luminosities and Eddington ratios than typical SDSS Type 1 quasars. Their Eddington ratios resemble those of dim-state changing-look AGN, with an average of ≲1%. The proposed explanation relies on the greater responsiveness of Balmer emission to continuum changes: as the AGN fades, broad Hβ and then Hα weaken and disappear, while broad Mg II remains as evidence of earlier activity. The reported average Eddington ratio is near the threshold at which the inner thin disk is thought to evaporate into a geometrically thick, radiatively inefficient flow in stellar-mass black holes; this comparison does not demonstrate such a transition in these galaxies. Broad Mg II galaxies may be the penultimate stage of a changing-look AGN sequence before all broad lines disappear.

PublicResearchers studied 494 galaxies whose spectra show an unusual combination: broad emission from magnesium, but weak or missing broad emission from hydrogen. Their active central regions are less luminous and have lower relative black-hole feeding rates than typical quasars. These findings support the idea that the galaxies’ central activity is fading, although they do not prove it. In the proposed explanation, hydrogen emission responds more strongly to fading activity and disappears before the magnesium emission, which lingers as a clue to a brighter past. The galaxies’ average relative feeding rate is about 1% or less of the Eddington benchmark, similar to active galaxies observed in dim states. The authors suggest these objects may be near the end of a transition, just before all broad emission lines disappear.

Young explorerScientists looked at 494 galaxies and found a puzzle in their light. One kind of light signal was still broad, while other signals were weak or missing. The galaxies’ bright centers were also dimmer than those of typical quasars. Maybe the centers are fading, and one signal lasts longer than the others—like a clue that they used to shine more brightly. Scientists have not proved that explanation yet.

SQuIGGLE: Radio AGN Found Predominantly in Young, Gas-rich Post-starburst Galaxies at z 0.7

Vincenzo R. D'Onofrio, Justin S. Spilker, Krista L. Smith+13 more

AstronomerDeep, subarcsecond VLA 6 GHz observations detect continuum emission in 18 of 52 massive SQuIGGLE post-starburst galaxies at z≈0.7. The reported 1.4 GHz luminosities span log(L/[W Hz−1])≈23–25 and generally exceed expectations from ongoing star formation and the fading starburst, favoring an AGN origin. Limited evidence for luminous, radiatively efficient AGN at other wavelengths suggests comparatively weak, mechanically powered radio AGN. Radio activity is concentrated within roughly 200 Myr after the burst and predominantly occurs in galaxies retaining substantial molecular gas. Above a common radio luminosity threshold, the detection fraction is approximately 2.5 times the radio AGN candidate fraction in mass- and redshift-matched quiescent LEGA-C galaxies, mainly because of lower-power sources. If jet–ISM coupling is efficient, the inferred mechanical power could supply enough energy to unbind the molecular gas on timescales comparable to its observed decline. These findings suggest, but do not establish, that radiatively inefficient AGN help maintain inefficient star formation in young, gas-rich post-starburst galaxies.

PublicSome galaxies stop making stars rapidly even though they still contain plenty of molecular gas, the material needed to form stars. Researchers used sensitive radio observations to study 52 massive galaxies that had recently ended a burst of star formation, detecting radio emission in 18. The emission is generally stronger than expected from star formation alone, pointing instead to activity associated with central black holes. Other observations show little evidence for brightly radiating black holes, suggesting that these sources mainly release energy mechanically. Radio activity is most common soon after the starburst ends and in galaxies that still have substantial gas. It is also more frequent than in a comparison sample of similarly massive quiet galaxies at similar redshifts. If jets transfer their energy efficiently to the surrounding gas, their estimated power could be sufficient to remove it. The study therefore suggests a possible way to keep star formation inefficient, but does not demonstrate that the jets actually remove the gas or maintain the shutdown.

Young explorerA galaxy is a huge group of stars. Some galaxies stop making lots of new stars even though they still have gas to make them. Scientists looked for radio signals from 52 galaxies like this and found signals in 18. They think many of these signals come from activity around black holes, rather than from stars. That activity might send out jets that push on the gas and make it harder to form new stars. But the scientists have not shown that this is what keeps these galaxies from making many new stars.

Emergence of high-mass stars in complex fiber networks (EMERGE) VII. Multi-Tracer Column Density Synthesis

Alvaro Hacar, Andrea Socci, Mario Tafalla+1 more

• Instrumentation and Methods for Astrophysics

AstronomerThe paper introduces Multi-Tracer Column Density Synthesis (MT-CDS), an empirical method for estimating high-dynamic-range H2 column density maps from complementary molecular tracers. Using IRAM-30m HNC (1–0) and N2H+ (1–0) integrated intensities and Herschel column density estimates in seven Orion star-forming regions, the authors derive temperature-corrected conversion factors for each tracer. They apply these low-resolution calibrations to ALMA data, using HNC and N2H+ to estimate lower- and higher-column-density components, respectively, and combine them into total column density maps at 4.5 arcsec resolution spanning approximately 10^21.5–10^23.5 cm^-2. Comparison with independent ArTeMiS maps at 8 arcsec resolution yields typical deviations of no more than about 0.2 dex. Maps are obtained for five targets with available ALMA data at approximately 2000 au resolution, about five times finer than the calibration resolution. The results support the technique’s potential, although the independent comparison is at an intermediate rather than the finest resolution.

PublicThe researchers developed and tested a way to map how much molecular gas lies along each line of sight through star-forming clouds. Their method combines emission from two molecules that trace different gas conditions. They first calibrated the method against existing gas maps in seven star-forming regions in Orion, then applied it to sharper ALMA observations available for five targets. The combined maps cover roughly a hundredfold range in gas column density and reveal detail about five times finer than the original calibration maps. A check against independent maps at an intermediate resolution found typical differences of about 0.2 on a base-10 logarithmic scale or less. These findings suggest that combining molecular tracers can produce detailed gas maps over a wide range of column densities, though the independent check does not test the maps at their finest resolution.

Young explorerSpace has clouds of gas where stars can grow. The scientists made maps to estimate how much gas is stacked along the direction we look. They used signals from two kinds of molecules: one helps show places with less gas in the way, and the other helps show places with more. They used less detailed maps to learn how to read those signals, then made sharper maps of five places. When they compared their work with another set of maps, the answers were usually close. That is a good sign, but this check could not test the very smallest details.

Galactic Outflows and Star-Formation Quenching: A JWST Perspective

Rebecca L. Davies, Sirio Belli

AstronomerThis review examines JWST evidence connecting neutral outflows and quenching in massive galaxies at cosmic noon, z ≈ 2. Balmer absorption constrains star formation histories, while blueshifted Na I D absorption traces neutral outflows. Such outflows occur in approximately 25–50% of galaxies with log(M*/M☉) > 10, independent of star formation rate. In star-forming systems, the outflows are consistent with star formation and/or AGN driving; in quiescent systems, they are generally attributed to current or past AGN activity. Growing evidence associates recent rapid quenching with powerful AGN-driven outflows having mass-loading factors η ≳ 1–10, but this is not a definitive demonstration of causation. Neutral gas dominates the outflow mass budget, yet its velocity is usually below the halo escape velocity, suggesting a galactic fountain rather than permanent gas removal. Neutral inflows and residual cold gas in quiescent galaxies suggest that additional feedback, such as AGN heating, is needed to maintain quenching. The review discusses systematic uncertainties in mass outflow rates, the potential of multiphase measurements to constrain feedback models, and implications for the earliest massive quiescent galaxies.

PublicCan winds from active galaxy centers stop galaxies from making stars? This review brings together recent James Webb Space Telescope observations of massive galaxies at an era called cosmic noon. The observations trace both past star formation and neutral gas moving outward. These outflows appear in about 25–50% of the massive galaxies studied, regardless of their star formation rate. Winds in galaxies still forming stars could be powered by star formation, activity in the galaxy center, or both; winds in galaxies with little star formation are generally linked to present or past central activity. Evidence increasingly connects powerful winds from active centers with a recent, rapid shutdown of star formation, although the connection does not establish that the winds caused the shutdown. Most of the neutral gas moves too slowly to escape its galaxy’s surrounding halo, so it may eventually fall back. Gas flowing inward and cold gas remaining in quiet galaxies suggest that something else, such as heating by the active center, is needed to keep star formation suppressed. The review also explains uncertainties in estimating how much gas these winds carry.

Young explorerGalaxies use gas to make new stars. Scientists used the James Webb Space Telescope to study big galaxies and found gas blowing outward in many of them. Some galaxies that recently stopped making many stars also have strong winds that scientists think come from their active centers. That is a clue, but it does not prove the winds made the star-making stop. Much of the gas may fall back instead of leaving forever, like water in a fountain. Scientists think extra heating may help keep these galaxies from making lots of new stars again.

The Contribution of Mergers and Accretion to Dark Matter Halo Assembly: An Excursion Set Theory Approach

Hamed Kameli

• Cosmology and Nongalactic Astrophysics

AstronomerThis theoretical study extends a variance-discretized Excursion Set Theory merger-tree algorithm to reconstruct all branches and distinguish mergers from accretion using a merger-ratio threshold. Model progenitor distributions agree closely with the analytical conditional first up-crossing distribution across a wide range of halo masses and redshifts. The inferred accretion fraction is strongly classification-dependent: for massive haloes it reaches approximately 70% at thresholds MR = 0.1–0.25, but falls to approximately 40% when all resolved mergers down to MR = 10^-6 are included. These fractions agree well with previous N-body simulations; they are not observational measurements. Accreted mass has a nearly self-similar distribution in the mass–redshift plane, dominated by progenitors with 10^-3 M0 ≲ M ≲ 10^-1 M0, predominantly at 0.5 ≲ z ≲ 2. The authors conclude that EST-based trees offer an accurate, computationally efficient framework for quantifying halo assembly.

PublicHow much do dark matter haloes grow by merging, rather than by gathering material counted as accretion? This theoretical study builds complete branching histories of haloes and shows that the answer depends strongly on where researchers draw the line between those two categories. For massive haloes, accretion supplies up to about 70% of growth when only relatively large combinations count as mergers. Counting much smaller resolved combinations as mergers lowers that share to about 40%. These are model findings, not observations, and they agree well with earlier computer simulations. The method also closely reproduces an analytical prediction for the distribution of earlier halo building blocks. The authors present it as an accurate and computationally efficient way to study how haloes assemble.

Young explorerScientists used a computer model to make family trees for big clumps of dark matter. They asked how much each clump grew by joining other clumps and how much by collecting material. The answer changed depending on how small a joining clump could be and still count as a merger. Counting more tiny joinings as mergers left less growth called collecting. This came from a model, not from watching real clumps grow.

Deep X-ray View of a Distant Protocluster Anchored by a Quasar at z=6.63: No Evidence for Enhanced X-ray AGN Activity

Shouyi Wang, Feige Wang, Jinyi Yang+22 more

• High Energy Astrophysical Phenomena

AstronomerUsing approximately 865 ks of Chandra observations, the authors present the first systematic X-ray AGN census in a z>6 protocluster, targeting J0910-0414 at z=6.63. None of 21 spectroscopically confirmed members, excluding the central quasar, is individually detected. Stacking the members provides approximately 17 Ms of total exposure but no significant signal, constraining the mean rest-frame 2–10 keV luminosity to ≤9.54×10^42 erg s^-1. The null result yields a central 90% Jeffreys upper bound of f_AGN<0.09. Accounting for spatially varying sensitivity, the field Compton-thin X-ray luminosity function predicts 0.0356 AGN; assuming AGNs follow the galaxy overdensity profile raises the expectation to 0.131. Zero detections give a one-sided 90% upper limit of η_rel<17.5 on additional enhancement beyond that associated with the galaxy overdensity. Thus, no significant excess of X-ray-detectable AGN is found, but more than an order-of-magnitude enhancement remains allowed. Heavily obscured, intrinsically X-ray-weak, or intermittently accreting SMBHs could escape detection, so these data do not establish whether dense environments accelerate SMBH growth during reionization.

PublicResearchers used Chandra X-ray observations to look for signs of growing supermassive black holes in a dense group of galaxies in the early universe. They examined 21 confirmed galaxies in the J0910-0414 protocluster, leaving out its central quasar. No galaxy was detected individually, and combining their X-ray measurements also produced no significant signal. The observations therefore set limits on average X-ray brightness and on how common X-ray-detectable active black holes could be. A comparison with expected counts found no significant excess, but it assumed that active black holes follow the same concentration pattern as the galaxies, and the limits still allow a substantial enhancement. Black holes hidden by material, unusually faint in X-rays, or active only intermittently could have been missed. The study does not settle whether crowded surroundings help black holes grow faster.

Young explorerScientists looked at a crowded group of galaxies far away to see whether their big black holes were feeding. They searched for a kind of light called X-rays in 21 galaxies, but did not find a clear signal, even after putting the measurements together. That does not mean the black holes are not there or never feed. They might be hidden, too faint, or feeding only sometimes. We still do not know whether living in a crowded group helps black holes grow faster.

A JWST View of Cosmic Star Formation from z∼0 to 9 with Hydrogen Recombination Lines in the COSMOS and GOODS-N fields

Shuqi Fu, Linhua Jiang, Christopher J. Conselice+9 more

AstronomerCombining wide-area COSMOS-3D and deeper GOODS-N JWST/NIRCam F444W slitless spectroscopy, the authors use 9,146 galaxies to trace star formation over z≈0–9. Six Brackett, Paschen, and Balmer lines are dust-corrected and converted to equivalent Hα luminosities assuming Case B recombination, with line-detection completeness accounted for. COSMOS constrains luminous emitters, while GOODS-N extends the luminosity functions to fainter sources. Schechter fits indicate increasing characteristic Hα-equivalent luminosity toward cosmic noon. Integrating the inferred star formation rate functions above 0.24 solar masses per year yields cosmic star formation rate densities broadly consistent with canonical UV- and IR-based histories at z≲6. However, fixed-slope tests show that the Hβ-based estimate at z≈8 remains sensitive to an external photometric faint-end constraint and extrapolation below the spectroscopic limit.

PublicAstronomers used JWST spectra of 9,146 galaxies to estimate how the universe’s rate of star formation changed across cosmic history. A wide survey captured bright emitters, while deeper observations added fainter galaxies. The team corrected hydrogen emission lines for dust and used a model of hydrogen emission to translate different lines into a common measure of star formation. Their estimates broadly agree with earlier ultraviolet- and infrared-based histories out to a redshift of about 6. An estimate for the earlier universe, at redshift about 8, is less secure: it depends on additional imaging-based information about faint galaxies and on extending the calculations below what the spectra can detect.

Young explorerScientists used the Webb telescope to study light from thousands of galaxies and work out how quickly they were making new stars at different times. Their answers mostly match earlier studies. But one answer about the very young universe is harder to pin down, because some galaxies are too faint for these observations and the scientists must estimate their contribution.

Hot Molecular Hydrogen in Galaxies at Redshift 0.2-1.5 Revealed by JWST

Jie Chen, Linhua Jiang, Shuqi Fu+5 more

AstronomerUsing JWST slitless spectroscopy of ro-vibrational H2 emission, including 1-0 S(1), this study selects 144 H2-luminous galaxies at z ≈ 0.2–1.5 to investigate hot molecular gas (≳1000 K). Approximately 96.5% and 80% are detected in radio and far-infrared emission, respectively, and hot H2 emission correlates strongly with both. Radio-excess, X-ray, and optical diagnostics identify significant AGN activity in 62 sources (43%). H2 line luminosity scales sublinearly with radio luminosity, whereas its relation to total infrared luminosity is approximately linear after radio-excess sources are excluded. The authors interpret these relations as evidence for a baseline contribution from star formation plus additional AGN-related excitation in radio-excess sources, potentially through jet- or wind-driven shocks; the specific excitation mechanisms are inferred rather than directly established.

PublicResearchers used JWST to study light from hot molecular hydrogen in 144 galaxies at redshifts of about 0.2–1.5. This gas is part of the molecular reservoir that supplies star formation and black hole growth. Its emission is strongly linked to the galaxies’ radio and far-infrared emission, and 43% of the sample show evidence of active galactic nuclei. The measured relationships suggest that star formation contributes to energizing the hot hydrogen. Galaxies with excess radio emission appear to need an additional energy source associated with their active nuclei, possibly shocks driven by jets or winds. These are interpretations of the observed patterns, not direct proof of a particular heating mechanism.

Young explorerScientists used the JWST telescope to look at glowing hot gas in 144 faraway galaxies. They found that galaxies with more of this gas light also tended to shine more in other kinds of light. The patterns suggest that making stars helps give the gas energy. In some galaxies, activity near a black hole may give it extra energy, perhaps by sending out jets or winds that jolt the gas. The scientists have clues, but they have not proved exactly how the gas gets its energy.

Large-scale Environmental Dependence of AGN Activity Revealed by JWST Paα Emitters

Danyang Jiang, Linhua Jiang, Shuqi Fu+7 more

AstronomerThe study examines the large-scale environments of 70 AGNs at z = 1.1–1.5 using a highly complete sample of 3,419 Paα emitters with accurate spectroscopic redshifts from a JWST slitless survey. Eighth-nearest-neighbor surface densities probe approximately 1.5 proper Mpc scales. Environmental density correlates weakly positively with radio luminosity, and radio-bright AGNs occupy statistically denser environments than radio-faint AGNs. Density also correlates positively with Eddington ratio and weakly negatively with central black hole mass, which the authors interpret as evidence for more efficient accretion in denser environments. Paα luminosity functions around AGNs are systematically elevated relative to the field and have shallower faint-end slopes, suggesting accelerated galaxy growth and enhanced star-formation quenching. Because Paα emitters trace gas-rich, star-forming galaxies, these observations support—but do not establish causally—a scenario in which large-scale cold gas promotes AGN activity at cosmic noon.

PublicResearchers used a JWST survey to study the galactic neighborhoods of 70 active galactic nuclei: bright centers powered by matter falling toward central black holes. They mapped these neighborhoods with 3,419 gas-rich, star-forming galaxies identified through their Paα emission. Active nuclei with brighter radio emission tended to have denser surroundings, although the correlation was weak. Denser neighborhoods also tended to contain black holes accreting more strongly relative to their Eddington limit, while black hole mass showed a weak trend in the opposite direction. The distribution of Paα brightnesses around active nuclei was elevated compared with the general galaxy population and less steep at the faint end. The authors interpret this as suggesting faster galaxy growth alongside increased shutdown of star formation. Overall, the findings support the idea that cold gas in the wider neighborhood helps fuel black hole activity, but they do not prove that the environment causes it.

Young explorerSome galaxies have very busy black holes in their middles. These black holes get bright as nearby stuff falls toward them. Scientists used the Webb telescope to look at the neighborhoods around 70 of these busy centers. The ones that were brighter in radio waves tended to have more neighboring galaxies, but the pattern was not very strong. Other clues suggested that black holes in busier neighborhoods were feeding more strongly. The scientists think cold gas in those neighborhoods may help feed them, but they have not proved that yet.

Simulations of Dust Content and Attenuation in z=5-15 Galaxies

Dhruv T. Zimmerman, Jed McKinney, Desika Narayanan+10 more

AstronomerThis theoretical study predicts high-redshift dust attenuation laws using 107 cosmological zoom-in simulations with SMUGGLE, including a multiphase ISM and an evolving dust grain size distribution. POWDERDAY radiative transfer produces synthetic spectra and attenuation curves for galaxies at z=5–15 with stellar masses of approximately 10^6.5–10^10 solar masses. The simulated curves show evidence for flatter attenuation than commonly adopted locally calibrated laws, and the vast majority lack the 2175 Å absorption feature. Attenuation laws evolve little across z=15–5; the authors attribute this to relatively constant small-grain fractions through z=4 in the simulations. Galaxy mass anticorrelates with attenuation-curve slope and correlates positively with A_V. The authors interpret these trends in terms of efficient dust growth in galaxies above roughly 10^9 solar masses whose ISM exceeds a critical metallicity threshold. They propose simulation-informed priors for attenuation-law parameters in SED fitting. These are model predictions, not observational constraints on high-redshift dust.

PublicDust changes how much light escapes a galaxy at different wavelengths, affecting estimates of its growth and physical properties. Because dust in the very early universe is poorly constrained, the researchers used 107 galaxy simulations to predict its effects. Their simulated galaxies generally show less variation in dimming with wavelength than commonly used models based on nearby galaxies, and most lack a particular ultraviolet absorption feature. The predicted wavelength dependence changes little over the early periods studied. More massive simulated galaxies also tend to have greater visible-light dimming, which the authors link to more efficient dust growth under suitable conditions. They offer these predictions as guidance for interpreting galaxy light, not as measurements of real early galaxies.

Young explorerDust in a galaxy can block some of its light. Scientists made computer models of very young galaxies to see how that dust might change the light we see. The models suggest that dust may dim different colors more evenly than people often assume. These are computer predictions, not things scientists have confirmed in real young galaxies.

Barflow: Modeling Gas Kinematics of Bar-Driven Flows

Seungwon Baek, Woong-Tae Kim, Taehyun Kim+2 more

AstronomerSelf-consistent N-body/hydrodynamical simulations of isolated Milky Way-like disk galaxies show that increasing the initial gas fraction delays bar formation and suppresses it in the most gas-rich model through higher-order spiral modes and early central mass growth. After bar formation, gas inflow and gravitational torques weaken the bar and inhibit its secular slowdown: gas-bearing bars remain shorter and predominantly in the fast-bar regime, whereas the gas-free bar enters the slow-bar regime. Stellar mean velocities are approximately bisymmetric, but cold and warm gas follow elongated, x1-like streamlines with shock-driven transitions, yielding sawtooth-like radial and archlike tangential velocity profiles. Their azimuthally averaged tangential velocities nevertheless track the circular velocity over most of the disk. Hot gas is largely decoupled from ordered bar-driven flow because of stellar feedback and thermal pressure. The proposed phenomenological barflow model incorporates non-sinusoidal streaming and a radially varying shock-front phase. In mock line-of-sight velocity fits, it recovers the intrinsic rotation curve, bar-driven perturbations, and radial gas transport more accurately than a conventional bisymmetric model; this comparison is based on simulations, not observations.

PublicComputer simulations of isolated galaxies resembling the Milky Way suggest that gas can delay the formation of a central, elongated structure called a bar—and prevent it in the most gas-rich case studied. Once a bar forms, gas flowing inward and gravitational forces weaken it and limit how much its rotation slows. The simulations also show that stars and gas move differently around a bar. Stars have a relatively smooth velocity pattern, while cold and warm gas undergo sharp changes in velocity at shocks. Even so, their average rotation speeds around the galaxy closely follow the speed expected for circular orbits across most of the disk. Hot gas behaves differently, responding mainly to energy from stars and thermal pressure. The researchers introduce a model called barflow to describe the sharper gas motions. Tests using simulated measurements recover the galaxy's rotation curve, bar-related motions, and inward or outward gas transport more accurately than a conventional model. Whether that advantage holds for real observations remains untested in this abstract.

Young explorerThe scientists made pretend galaxies inside a computer to see how stars and gas move. Some galaxies grow a long shape in the middle called a bar. In these computer galaxies, more gas made the bar appear later, and the galaxy with the most gas did not grow one. When a bar did grow, gas helped weaken it and kept its turning from slowing as much. Stars moved in a smoother pattern, but cooler gas had sudden changes in speed. The scientists made a new way to describe those gas movements. It worked better than an older way in their pretend measurements, but these were computer tests, not measurements of real galaxies.

Microcaustics: Fast GPU-Accelerated Dynamical Microlensing of Time-Dependent Extended Sources

Joshua Fagin, Connor Stone, James Hung-Hsu Chan+7 more

• Instrumentation and Methods for Astrophysics

AstronomerMicrocaustics is a GPU-accelerated PyTorch package for dynamical microlensing of time-dependent extended sources in strong lenses, addressing the computational cost that usually motivates static magnification maps. It combines local-exact/far-field deflections, source-directed lens-plane scouting with temporal reuse, biquadratic inverse polygon mapping (IPM), and accelerated rasterization, with binary labels identifying source-centred caustic crossings. Benchmarks across three simulated quadruply lensed quasars produce 10-year, 147-frame multiband light curves in an amortized median of 0.68 s on a consumer GPU, or 0.88 s with labels. Median light-curve RMSE is 0.35 mmag, and every reference source-centred caustic crossing is recovered. At comparable map accuracy, measured batched throughput is 780 times that of a recent CUDA IPM implementation; the claimed millions-fold advantage over classic GPU-D is extrapolated, not directly benchmarked. Demonstrated convergence scales as N_ray^-0.84, compared with idealized piecewise-affine IPM scaling of N_ray^-1 and inverse ray-shooting scaling of N_ray^-1/2. The authors also introduce a GPU-resident general relativistic, reverberating quasar source model and demonstrate an evolving supernova source. These are computational demonstrations, not observational findings; the authors conclude that fully dynamical stellar fields become practical for Bayesian and simulation-based inference.

PublicStars in a foreground lens galaxy can change the apparent brightness of a distant quasar through gravitational microlensing. Modeling those changes helps researchers investigate the quasar’s unresolved light-emitting disc and compact objects in the lens galaxy, and account for effects on cosmological measurements. Because tracking moving lenses is expensive, many analyses use static simulations. The new Microcaustics software instead models changing lenses and sources using a graphics processor. In tests involving three simulated quasars, each appearing as four lensed images, it generated a decade-long brightness sequence in less than a second on a consumer graphics processor, with small errors relative to reference calculations. It also recovered every reference crossing of the sharp magnification features called caustics. Its measured throughput was 780 times that of one comparison implementation; a much larger claimed advantage over another method is an extrapolation. The work demonstrates faster simulations, including a changing supernova source, rather than reporting new sky observations.

Young explorerGravity from stars can act a little like a magnifying glass, making a faraway bright object look brighter or dimmer. Scientists made a fast computer program to pretend how this happens as things move and change. In computer tests, it closely matched the answers they checked against. These were pretend skies, not new pictures of real ones.

Large dust grains escaping from a supernova remnant

Evgenii O. Vasiliev

AstronomerThis one-dimensional gas-dynamical study, including dust destruction, models the survival and escape of supernova-ejecta grains for power-law size distributions with different maximum grain sizes. Large grains can overtake the forward shock through inertia. At late remnant ages, the surviving and escaping mass fractions closely track one another, indicating that nearly all surviving dust escapes into the ambient interstellar medium. For solar metallicity and ambient density n ≈ 1 cm⁻³, both fractions reach about 0.7–0.8 at 30 kyr, the onset of the radiative phase, when the maximum grain size is several microns. Most of this dust consists of grains larger than 1 μm, initially located at radii ≳0.2 times the ejecta core radius. Escaping grains moving at several hundred km/s undergo further kinetic sputtering, although grains several microns across suffer little destruction. After deceleration, the modeled surviving fraction of the original dust mass falls from approximately 0.5 to 0.3 as ambient density increases from 1 to 100 cm⁻³, for a maximum grain size of 10 μm. Smaller maximum sizes yield lower survival fractions; these are model findings, not observational measurements.

PublicDust made in an exploding star can be partly destroyed by hot gas in the expanding remains. This study uses a one-dimensional computer model to estimate how much dust survives and escapes. Larger grains can carry enough momentum to pass the expanding shock front. In the modeled late stages, almost all dust that survives inside the remnant eventually escapes. For one set of conditions, with a maximum grain size of several microns, about 70–80% of the original dust mass survives and escapes by 30,000 years. Escape does not guarantee lasting survival: collisions with interstellar gas continue to erode the grains. With a maximum grain size of 10 microns, the model predicts that roughly half to one-third of the original dust mass remains after the grains slow down, depending on the surrounding gas density. Denser gas and smaller maximum grain sizes reduce survival.

Young explorerWhen a star explodes, it can make tiny bits of dust. Scientists used a computer model to see what might happen to them. Hot gas destroys some dust, but bigger bits can rush out of the star’s expanding leftovers. Gas outside can wear them down too. In the model, bigger dust bits survive better, while thicker gas leaves less dust behind.

Strong gravitational lensing with Euclid

Alessandro Sonnenfeld

AstronomerThis forward-looking paper anticipates discoveries from Euclid’s strong-lens sample, projected to add approximately 100,000 lenses and increase the known population by a factor of 30. The first quick data release has already revealed hundreds of lenses, with deflectors ranging from isolated galaxies to clusters and from early-type galaxies to edge-on disks. Four double-source-plane systems, in which a foreground object lenses two galaxies at different redshifts, have already been discovered. The larger sample is expected to broaden the parameter space of lenses and sources and uncover rare configurations. Detecting strong-lensing signatures of dwarf galaxy satellites and finding systems with unusually many images remain possibilities for future data, not reported results.

PublicEuclid’s first quick data release has already revealed hundreds of strong gravitational lenses: systems in which foreground objects bend the light of more distant galaxies. The objects doing the bending include isolated galaxies, galaxy clusters, and disk galaxies seen edge-on. Four systems have been found in which one foreground object lenses two galaxies at different distances. Looking ahead, the paper anticipates about 100,000 new lenses from Euclid, increasing the known total roughly thirtyfold. That larger collection could reveal rare systems, perhaps including lensing signatures of dwarf galaxy satellites or lenses producing unusually many images; these are possibilities, not discoveries reported here.

Young explorerObjects in space can bend light from galaxies far behind them, a little like a funny window. Euclid has already found hundreds of these space lenses. In four of them, one thing in front bends light from two galaxies, one farther away than the other. Scientists expect Euclid to find many more. They hope some future pictures might show signs of tiny galaxies or lots of images of the same faraway galaxy, but they do not know yet.

A heterogeneous set of unusual quasars selected from astrometry and broad-band photometry

C. Cheng, K. Valeckas, L. Christensen+7 more

AstronomerThis observational study tests a method for finding quasars with unusual broad-band colours, including those affected by reddening or broad absorption from outflows. Sources are pre-selected using Gaia parallaxes and proper motions consistent with zero within uncertainties, then matched to wide-area photometry and selected for spectroscopy using colour-colour diagrams. SPHEREx observations are also used to establish redshifts. Of 24 spectroscopically observed sources, 21 are classified as quasars at z=0.139–3.732 and three as stars. Most sources lying away from the normal quasar locus are broad-absorption-line quasars. The lowest-redshift source resembles the high-redshift Little Red Dots found with JWST, although this resemblance does not establish that they are the same type of object. The procedure successfully identifies previously undiscovered quasars, particularly those with broad absorption lines or unusual extinction.

PublicResearchers tested a way to find quasars whose unusual colours can make them stand out from typical quasars. They first used Gaia measurements to select objects with no detectable parallax or motion across the sky within measurement uncertainties, then used colour comparisons from wide-area surveys to choose targets for spectroscopy. SPHEREx observations also helped establish redshifts. Of 24 objects examined with spectroscopy, 21 were quasars and three were stars. Most of the objects outside the usual quasar colour pattern showed broad absorption features associated with outflowing material. One nearby-in-redshift example, at z=0.139, resembled the distant objects called Little Red Dots seen with JWST; the study does not establish that it is the same kind of object. The results show that this approach can uncover previously unknown quasars with unusual light absorption or reddening.

Young explorerScientists looked for quasars, bright objects far out in space, by picking things that did not seem to move in their measurements and then checking their colours. They spread the light out to learn what each object was. Of 24 things they checked, 21 were quasars and three were stars. Many with unusual colours had signs of material flowing outward and blocking some of their light. One looked a little like faraway objects called Little Red Dots, but looking alike does not mean they are the same. This way of searching helped scientists find quasars they had not known about before.

PDRs4All XXIII. JWST-MIRI template spectra of PAHs in the Orion Bar obtained with blind signal separation

P. Amiot, O. Berné, J. Roux-Morin+12 more

AstronomerUsing JWST MIRI-MRS observations of the Orion Bar photodissociation region from PDRs4All, the authors isolated aromatic infrared band (AIB) emission through multi-component fitting and applied non-negative matrix factorization to extract two template spectra, AIBirrad and AIBshield. Their spatial distributions and spectral characteristics suggest two chemically distinct populations. The authors interpret AIBirrad as emission from strongly UV-exposed PAHs, predominantly large, compact, and ionized. AIBshield is interpreted as emission from PAHs embedded more deeply in the cloud and less exposed to UV, consisting of small, asymmetric, mainly neutral molecules with bonded aliphatic side groups. These population assignments are interpretations of the extracted spectra, rather than direct identification of individual molecules. The templates are intended to support analysis of PAH emission and inference of PAH properties in other objects observed with MIRI-MRS.

PublicResearchers used James Webb Space Telescope observations of the Orion Bar to separate two patterns of infrared emission. These emission bands are generally attributed to carbon-based molecules called polycyclic aromatic hydrocarbons, or PAHs. After separating the bands from other contributions to the observations, the team extracted two reference spectra. Their locations and features suggest different molecular populations: one exposed to strong ultraviolet light, interpreted as mostly large, compact molecules carrying an electric charge; the other more sheltered inside the cloud, interpreted as smaller, less symmetrical, mostly uncharged molecules with additional chemical side groups. These descriptions are interpretations, not direct identifications of the molecules. The reference spectra could help researchers study PAHs in other objects observed with the same Webb instrument.

Young explorerScientists used the Webb telescope to study light from a cloud in space. They found two patterns that they think come from tiny molecules. One pattern may come from molecules in strong ultraviolet light. The other may come from molecules tucked farther inside the cloud, where less of that light reaches them. Scientists can use these patterns as guides when studying other places in space.

Sleeping or Dead? Probing the Quenching Mechanism of JWST Dormant Galaxies at z > 3 with ALMA

Mengyuan Xiao, Songnan Qi, Pascal A. Oesch+16 more

AstronomerThe study combines JWST/NIRSpec prism spectrophotometric fitting with archival ALMA [CII] 158 μm and CO constraints to examine 7 dormant and 15 quiescent galaxies at z>3 and log(Mstar/Msun)>9.5. Molecular gas constraints are mostly 3σ upper limits. Dormant galaxies have systematically lower SFRs averaged over 10 Myr than over 100 Myr, supporting a recent rapid decline. For the approximately 70% of the sample with sufficiently constraining ALMA data, molecular gas fractions are at least approximately 0.3–2 dex below main-sequence expectations. Dormant and quiescent galaxies show no systematic difference in gas fraction. These findings favor rapid quenching associated with molecular gas depletion or removal over suppressed star formation efficiency in a substantial retained reservoir, but do not establish the depletion or removal mechanism. A lasting transition to quiescence is favored only if substantial future gas replenishment does not occur.

PublicSome distant galaxies seen by JWST appear to have slowed their star formation only recently. Researchers asked whether these galaxies are merely taking a break or are running out of the material needed to make stars. They combined JWST observations with existing ALMA observations for 7 recently slowed galaxies and 15 already quiet galaxies. The recently slowed galaxies formed stars less rapidly over the past 10 million years than over the past 100 million years. For about 70% of the full sample, the ALMA observations constrain their molecular gas supplies to be well below those expected in typical star-forming galaxies. Most gas measurements are upper limits rather than detections, and the recently slowed galaxies show no systematic difference in gas fraction from the quiet ones. The findings favor an explanation in which star formation shuts down as molecular gas is used up or removed, rather than simply becoming harder to turn into stars. Whether these galaxies remain quiet depends on whether they acquire substantial new gas.

Young explorerGalaxies make stars from gas. Scientists looked at faraway galaxies that seem to have recently slowed down their star-making. They found clues that many have very little of the gas used to make stars, though usually they could only tell how much gas there could be at most. This suggests the galaxies may have used up or lost their gas, not just paused while keeping lots of it. They might stay quiet—but new gas could help them make stars again.

The Role of Environment in Shaping the Assembly Timelines of Massive Quiescent Galaxies at Cosmic Noon

Tianmu Gao, J. Trevor Mendel, Letizia Bugiani+10 more

AstronomerThe study examines whether the diverse star formation histories of massive quiescent galaxies at z~2 depend on host dark matter halo mass. For 12 galaxies selected from the JWST Blue Jay survey, the authors infer star formation histories by modelling deep NIRSpec medium-resolution spectra and multi-band photometry, then compare formation and quenching epochs with host halo masses from 3D-HST. After accounting for the quiescent sample's redshift range of 1.8<z<2.5, galaxies in more massive haloes are found to have formed at significantly earlier cosmic epochs. They also quenched earlier overall, but the scatter in quenching epochs at similar halo masses suggests that halo mass alone does not determine quenching.

PublicResearchers studied 12 massive galaxies that had largely stopped forming stars to ask whether their surroundings are linked to when they formed and stopped making stars. They reconstructed the galaxies' star formation histories using JWST spectra and images in multiple wavelength bands, and compared those histories with estimates of the masses of their surrounding dark matter haloes. After accounting for differences in the cosmic times at which the galaxies are observed, they found that galaxies in more massive haloes formed earlier. Those galaxies also tended to stop forming stars earlier, but galaxies in similarly massive haloes did not all stop at the same time. This suggests that other factors besides halo mass help determine when star formation shuts down.

Young explorerScientists looked at 12 big groups of stars called galaxies that had mostly stopped making new stars. They used the galaxies' light to work out their stories. Galaxies inside bigger clouds of invisible matter tended to have formed earlier and stopped making stars earlier. But galaxies with similar-sized clouds did not all stop at the same time, so the scientists think other things matter too.

The physical and chemical structure of TMC-1. The spatial distribution and excitation conditions of carbon, oxygen, and sulfur bearing species: Depletion of CO and CS

J. Cernicharo, B. Tercero, N. Marcelino+3 more

AstronomerSpatially resolved molecular emission in TMC-1 reveals chemical differentiation across its filamentary structure. The authors favor a single cloud with a velocity gradient perpendicular to the filament over a chance alignment of three independent clouds, and conclude that the three velocity components are dynamically connected. The main emission contribution from the studied C-bearing species occurs at 5.83 km/s, whereas O-bearing species peak at 5.7 and 6.25 km/s and occupy different locations from the carbon chains and radicals. Matching 13C18O, C18O, and C17O line profiles rule out self-absorption or foreground absorption as the explanation for the CO emission dip at 5.83 km/s, supporting significant CO depletion where carbon-chain and radical emission occurs. The authors interpret the O-bearing emission as arising in the filaments' external layers. CS, CCS, HCS+, and H2CS are also inferred to be significantly depleted in the CO-depleted zone, where several molecules show enhanced deuteration.

PublicObservations of the filament-shaped cloud TMC-1 show that different molecules concentrate in different places and move at different speeds along our line of sight. The researchers favor one cloud with a systematic change in velocity across the filament rather than three unrelated clouds overlapping in our view. Where carbon-chain molecules and radicals emit, carbon monoxide is significantly depleted. Observations of three isotopic forms of carbon monoxide rule out the possibility that its weaker emission there is simply caused by gas absorbing the signal. The researchers suggest that oxygen-bearing molecules mainly emit from the outer layers of the carbon-rich filaments. Several sulfur-bearing molecules are also depleted in the carbon-monoxide-poor region. In those depleted regions, several molecules more often contain deuterium, a heavy form of hydrogen.

Young explorerA long cloud in space called TMC-1 has different tiny molecules in different places. Scientists found less carbon monoxide in places where some chains of carbon atoms give off signals. They think some oxygen-containing molecules are around the outside of those places. Where carbon monoxide and some sulfur-containing molecules are scarce, other molecules more often contain a heavier kind of hydrogen.

Galactic Morpholography: Linking present-day galaxy compactness to assembly history and relic formation in the COLIBRE simulations

Maximilian Zemsch, Claudia D.P. Lagos, Chiara Spiniello+11 more

AstronomerUsing COLIBRE cosmological hydrodynamical simulations, the authors test compactness as a statistical tracer of assembly history rather than treating it as sufficient evidence of relicness. Six tracers—stellar age, metallicity, [Mg/Fe], sSFR, velocity dispersion and ex-situ mass fraction—vary coherently across the stellar mass–size plane and independently indicate log10[Σ1.5,crit/(M☉ kpc^-1.5)] = 9.75 ± 0.10. They call this structure–history mapping morpholography. Combining the compactness threshold with Degree of Relicness > 0.6, a measure of early, rapid star formation, selects 267 simulated relic candidates. Ancient galaxies nevertheless span nearly the full ex-situ-fraction range, so old populations alone do not imply little merger growth. Candidates concentrate at stellar masses of approximately 10^10–10^11 M☉, have black holes approximately 0.25–2.5 dex above the median black-hole–stellar-mass relation, and are predominantly satellites (76%), preferentially in clusters. Only approximately 3% show strong tidal stripping, suggesting environmental preservation rather than creation of relic-like systems. Of the candidates, 87 are direct descendants of the simulation’s z = 2 massive quiescent galaxies. These simulation results support a statistical, not one-to-one, link between present-day structure and assembly history.

PublicA small, tightly packed galaxy is not necessarily an untouched survivor of the early Universe. Using the COLIBRE computer simulations, researchers tested how well a galaxy’s present-day size and mass reveal its past. Six indicators of its stars, motions and growth pointed to a common compactness threshold. Combining that threshold with a measure of how early and quickly stars formed identified 267 simulated relic candidates. Simply having ancient stars was not enough: some ancient galaxies had gained substantial mass through mergers. Most candidates were satellites of larger systems, with a preference for galaxy clusters, and their black holes were unusually massive relative to their stellar mass. Only about 3% showed evidence of strong tidal stripping, suggesting that their surroundings mostly help preserve these systems rather than make them compact by stripping them down. About one third were direct descendants of massive galaxies that had already stopped forming stars at an early cosmic epoch. The findings suggest that galaxy structure can preserve clues to growth history, but they come from simulations and do not make compactness alone proof of an untouched past.

Young explorerCan a tightly packed group of stars tell us what it was like long ago? Scientists explored this with a computer model of galaxies. They found 267 pretend galaxies that were both tightly packed and had made their stars early and quickly. These might be like galaxies that have changed very little for a long time. But being small and crowded, or having old stars, was not enough to be sure. Many of the candidates lived near bigger galaxies, and the model suggests those places may help keep them from changing. These are clues from a computer model, not discoveries of 267 real galaxies in the sky.

Uncovering the origin of complex velocity distributions in edge-on disc galaxies

Sophie Townson, Marie Martig, Robert J. J. Grand+3 more

AstronomerUsing an edge-on simulated spiral galaxy, the authors extract stellar line-of-sight velocity distributions (LOSVDs) across the disc. Multiple-peaked LOSVDs occur mainly near the midplane and arise from spiral-arm overdensities, rather than significantly different arm and disc kinematics. The number of peaks varies with the number of arms intersected along a sightline. The authors propose using this structure to quantify arm strength above the midplane and variations in arm thickness across the disc. In the simulation, the fourth-order Gauss–Hermite moment h4 is negative in multiple-peaked regions and thus traces the arms. Their observability assessment suggests that MUSE may lack the spectral resolution to separate the arm-induced peaks but should identify negative-h4 regions, while higher-resolution instruments such as KOALA and WEAVE may recover multiple peaks. These are simulation-based findings and observational prospects, not detections in real galaxies.

PublicA computer simulation suggests a way to study spiral arms in galaxies seen edge-on, where their shape is difficult to make out. Researchers examined the distribution of stars’ speeds toward or away from the viewer. Near the simulated galaxy’s central plane, these distributions often had several peaks. The peaks came from concentrations of stars in spiral arms, not from the arms moving very differently from the surrounding disc. Their number varied with how many arms lay along the viewing direction. This pattern could help reveal how strong the arms are away from the central plane and how their thickness changes across the galaxy. The team also found a related signal in a measure of the distributions’ shape, called h4. They suggest that MUSE should detect this shape signal even if it cannot separate the individual peaks; higher-resolution instruments such as KOALA and WEAVE may distinguish the peaks themselves. The method remains a prospect based on a simulated galaxy, rather than an observed result in a real one.

Young explorerScientists made a pretend galaxy on a computer and looked at it from the side. They counted how many stars were moving toward or away from them at different speeds. The counts made little hills on a graph. Extra hills mostly appeared where they looked through the galaxy’s spiral arms, because the arms held more stars—not because those stars moved very differently from the others. The scientists think these hills could help us learn how thick spiral arms are. Some tools might see the hills, while another might only see a gentler clue in the graph’s shape. They have tried this in a computer galaxy, not yet shown it in a real one.

Constrain the Size of Broad Line Region in NGC 1068 Using Sub-millimeter Excess

Qi Guo, Junzhi Wang, Lingrui Lin+3 more

AstronomerThe authors propose constraining AGN broad-line region (BLR) sizes using millimeter-to-submillimeter spectral energy distributions. A possible submillimeter excess, interpreted as free-free continuum from dense BLR gas that is optically thick at these wavelengths, could constrain the emitting solid angle. Applying this analysis to the central source S1 in the nearby type II AGN NGC 1068 yields a reported BLR solid-angle upper limit of (4.94 ± 0.61) × 10^-6 arcsec^2, corresponding to a radius no greater than 0.085 pc. This is an upper bound under the proposed emission interpretation, not a direct size measurement, and could help constrain central supermassive black hole mass estimates.

PublicThe authors propose a way to estimate how large a region of fast-moving gas near an active galaxy’s central black hole can be. Their method uses the spectrum of millimeter and submillimeter radiation: a possible extra contribution at submillimeter wavelengths could reveal the apparent area of dense gas, if that radiation comes from the broad-line region as proposed. Applied to the central source S1 in the nearby active galaxy NGC 1068, the analysis places an upper limit of 0.085 parsecs on the region’s radius, rather than measuring its exact size. Such limits could help astronomers estimate the masses of supermassive black holes.

Young explorerA black hole in the middle of a galaxy has gas nearby. Scientists suggest using a special kind of light from that gas to work out how big its home could be. They tried this idea on a galaxy called NGC 1068 and found a limit on how big the gas region could be, not its exact size. The idea depends on the light coming from the gas in the way they think it does. This could help scientists work out how heavy the black hole is.

The ringing Large Magellanic Cloud: evidence for a recent dwarf-dwarf collision

Slater J. Oden, Bethany Garver, Joshua Povick+2 more

AstronomerRecent red clump distance maps reveal that the Large Magellanic Cloud’s (LMC’s) stellar periphery is vertically displaced from its central disk plane by approximately 1.2 kpc at a radius of 8.5 kpc, with an S-shaped warp reaching approximately 3.6 kpc at 11.5 kpc. An N-body simulation of a direct LMC–Small Magellanic Cloud collision produces outer-disk vertical oscillations with amplitudes of approximately 1 kpc and a period of approximately 600 Myr. The closest match to the observed vertical structure occurs approximately 260 Myr after the simulated collision, although this timing depends on the adopted LMC model. The simulation reproduces the offset’s sign and radial onset and the warp’s orientation, but underpredicts the warp amplitude by a factor of approximately 4–5. The comparison supports, rather than establishes, a collision-driven origin for the LMC’s large-scale vertical structure.

PublicDistance maps of stars in the Large Magellanic Cloud reveal that its outer stellar disk is displaced from the plane of its central disk and bends into an S-shaped warp. The measured displacement is about 1.2 kiloparsecs at a distance of 8.5 kiloparsecs from the center, while the warp reaches about 3.6 kiloparsecs at 11.5 kiloparsecs. To investigate the cause, researchers compared these observations with a computer simulation of a direct collision with the Small Magellanic Cloud. The simulated collision sends the outer disk oscillating above and below its plane. Its shape most closely resembles the observations about 260 million years after the collision, though that timing depends on the model. The simulation matches several features of the observed bending, but its warp is roughly four to five times too small. The findings support a past collision as an explanation, without establishing it conclusively.

Young explorerThe Large Magellanic Cloud is a galaxy full of stars. Scientists mapped where its stars are and found that the outer part bends into an S shape instead of lying flat. They used a computer to try out what might happen if a smaller galaxy bumped into it. In the computer, the bump made the stars move up and down and bent the galaxy in a similar way. But the pretend bend was much smaller than the real one. A galaxy bump could explain the shape, but the scientists are not sure yet.

IRAC-Excess Galaxies in the NIRSpec Wide Survey: physical properties of bright EELGs at z∼7 and implications for Reionization

Katherine Ormerod, Renske Smit, Joris Witstok+4 more

AstronomerNIRSpec PRISM spectroscopy of 23 Spitzer/IRAC-excess galaxies at 5.66 < z < 7.64 yields a median rest-frame [OIII]+Hβ equivalent width of 1583 Å, consistent with pre-JWST selection predictions. Seventeen galaxies (74%) meet the EELG criterion of EW ≥ 1000 Å. Line widths, line ratios, and the absence of high-ionization lines favor star formation as the dominant power source, although AGN contributions remain possible in a few objects. The luminous EELGs have mean M_UV = −20.7, subsolar oxygen abundances of 7.38 < 12 + log(O/H) < 8.12, stellar ages around 20 Myr, and median log10(ξ_ion/[erg⁻¹ Hz]) = 25.62. At fixed [OIII]+Hβ EW, roughly L* UV-luminous EELGs have lower O32 than roughly 0.1 L* EELGs, interpreted as less extreme radiation fields and/or lower gas densities. Low neutral-hydrogen columns are consistent with a largely ionized CGM, but Lyα escape fractions below 2% suggest small IGM ionized regions, ≲0.25 proper Mpc. The authors tentatively interpret this as evidence that bright galaxies may contribute only modestly to reionization.

PublicSpectra of 23 galaxies in the early universe reveal that 17 have exceptionally strong emission from oxygen and hydrogen gas. Their properties point mainly to vigorous star formation rather than activity from central black holes, although black-hole contributions cannot be ruled out in a few cases. These bright galaxies contain young stars, with typical ages around 20 million years, and gas less enriched in heavy elements than the Sun. They also efficiently produce radiation capable of ionizing hydrogen. Compared with fainter galaxies with similarly strong emission lines, their gas shows signs of less extreme radiation and/or lower density. The observations are consistent with these galaxies having ionized much of the gas immediately around them. Yet less than 2% of their Lyman-alpha light escapes, suggesting that the ionized regions in the wider intergalactic gas remain small. The authors cautiously suggest that bright galaxies may therefore play only a minor part in reionization, the transformation of intergalactic hydrogen from neutral to ionized.

Young explorerScientists studied light from 23 galaxies from long ago. In 17, gas shines especially strongly, mostly because of young stars. The light gives clues that the stars have changed much of the gas close around their galaxies. But one special kind of light hardly gets out. That suggests the changed spaces farther around them may still be small. These bright galaxies might have played only a small part in changing the gas across the universe, but scientists are not sure.

The contact frontier in Galactic civilization networks: radial structure and the Galactic habitable zone

Kohji Tsumura

• Earth and Planetary Astrophysics
• Instrumentation and Methods for Astrophysics

AstronomerThis theoretical study models Galactic technological civilizations as nodes connected when their separation is less than the distance a signal can travel during a communicative lifetime. It replaces a uniform stellar disc with an exponential disc and allows the civilization-hosting fraction to vary radially through a factorized Galactic Habitable Zone model. Isolation, contact, and network transitions occur across frontiers several kiloparsecs wide. The contact frontier is set entirely by the disc scale length; gradient percolation broadens the network frontier, which remains near 1.5 scale lengths. Their overlap includes the Sun. Within this model, the civilization-density peak radius depends only logarithmically on supernova sterilization strength, yet varying that parameter primarily reproduces published peak radii from the Galactic centre to 12 kpc. Under the adopted normalization, zone location only modestly affects local contact probability, while Galactic connectivity is minimized when the density peak lies near the solar Galactocentric radius, where the abstract reports current determinations place it. These are model-dependent findings, not detections of civilizations.

PublicCould civilizations communicate across the Milky Way? This study explores that question with a mathematical model, rather than observations of extraterrestrial societies. It connects hypothetical civilizations if a signal could travel between them during the time they remain communicative. Accounting for the Galaxy’s declining stellar density produces broad regions of transition from isolation to contact and wider networks, rather than sharp borders. In the model, the Sun lies where the contact and network transitions overlap. Assumptions about how strongly supernovas prevent civilizations from surviving help explain differing estimates of where civilizations might be most concentrated. With the study’s chosen normalization, moving that concentration changes our local contact chances only modestly, but Galaxy-wide connectivity is lowest when the concentration peaks near the Sun’s distance from the Galactic centre.

Young explorerImagine possible space neighbors scattered around our galaxy. Scientists made a math model that links two neighbors if a message could reach them while they can still talk. In their model, lonely places slowly turn into connected places, with no sharp edge. Our Sun sits where two of these changes overlap. This is an idea about possible neighbors, not neighbors the scientists found.

A Step-Like Transition Underlying the Life and Death of Galaxies

Zhicheng He, Enci Wang, Luis C. Ho+6 more

• Cosmology and Nongalactic Astrophysics

AstronomerThe authors derive a step-function quenching response from gas mass conservation, governed by competition between gas-supply and gas-depletion timescales. Within this framework, the observed quenched fraction permits inference of the gas-supply timescale. Application to approximately 350,000 galaxies yields a characteristic supply timescale of about 1 Gyr and identifies inside-out and outside-in quenching signatures associated with supermassive black holes and dark matter halos, respectively. The authors also identify galaxies at intermediate stellar surface mass densities as occupying a critical state for quenching and rejuvenation. They interpret these findings within a unified framework in which diverse physical processes affect the balance of gas supply and depletion; the inferred timescale and physical associations should be understood in that framework rather than as direct measurements of gas delivery or demonstrations of causation.

PublicGalaxies need gas to keep making stars. This study develops a mathematical framework in which star formation shuts down through a sharp, switch-like response determined by the competition between how quickly gas arrives and how quickly it is depleted. Applying the framework to observations of about 350,000 galaxies, the researchers infer a typical gas-supply timescale of roughly one billion years. They find patterns of shutdown progressing from the center outward associated with supermassive black holes, and from the outskirts inward associated with dark matter halos. These associations do not by themselves establish cause and effect. The authors also identify galaxies with intermediate amounts of stellar mass per unit area as being in a critical state for stopping or restarting star formation. They propose that the gas-supply-versus-depletion balance provides a common explanation for these different behaviors.

Young explorerGalaxies use gas to make new stars. If their gas gets used up faster than more arrives, they can stop making stars. Scientists made a math rule for this balance and used it to study lots of galaxies. They found signs that some galaxies stop making stars first in the middle, while others stop first near the edges. They think the balance between getting gas and using it up can help explain why galaxies stop making stars and sometimes start again.

Binary-lens amplification of starlight: from magnification flares to quasi-periodic tracking of orbital evolution

Hanxi Wang, Bence Kocsis, Miguel Zumalacárregui

• Cosmology and Nongalactic Astrophysics
• General Relativity and Quantum Cosmology

AstronomerThis theoretical study extends a proposed gravitational-lensing method for identifying supermassive black hole binaries in non-active galactic nuclei, developing the phenomenology of binary-lens amplification of starlight (BLAST). The binary's extended caustic geometry rotates with its orbital period; caustic crossings can yield magnifications up to a factor of one million. The calculations account for relative source proper motion, single or binary stellar sources, binary eccentricity and precession, and relative inclination. Rapid stellar motion across caustics produces single- or double-peaked flares, whereas the zero-relative-proper-motion limit produces quasi-periodic lensed starlight whose repeated peaks track orbital evolution. The authors calculate magnification curves, their Fourier transforms, and expected peak magnifications and durations under different conditions. These predicted signatures may inform electromagnetic time-domain search pipelines; the abstract reports no observational identification of a binary.

PublicPairs of supermassive black holes are expected to form when galaxies merge. This study explores a proposed way to find them, even in galaxies without active centers: look for their gravity to bend and greatly magnify a star's light. The calculations predict that a star moving quickly across regions of strong magnification would produce a flash with one or two brightness peaks. With no relative motion of the star, the orbiting black holes could instead produce repeated peaks that follow changes in their orbit. Magnification can reach a factor of one million in the described lensing scenario. These are theoretical predictions, not reported detections, and may help researchers design searches through surveys that monitor changing brightness.

Young explorerTwo giant black holes moving around each other can bend a star's light, a bit like a magnifying glass. Scientists calculated that this could make the star look much brighter for a little while, or brighten again and again. They hope these flashes could help them find hidden black hole pairs. This study predicts the flashes; it does not report finding a pair.

The stellar-to-halo mass relation of central galaxies across three orders of halo mass

Victoria Toptun, Paola Popesso, Ilaria Marini+9 more

• High Energy Astrophysical Phenomena

AstronomerThe authors measure the brightest central galaxy (BCG) stellar-to-halo mass relation across halo masses of approximately 10^12–10^15 solar masses, combining SDSS-based stellar masses with halo masses inferred from eROSITA eRASS1 X-ray data. Stacking spectra of optically selected groups yields average gas temperatures in bins, which are converted to halo masses using the mass–temperature relation rather than measured directly. The BCG stellar-to-halo mass ratio peaks near 10^12 solar masses and declines toward higher halo masses. The measurements agree with previous observational constraints across the sampled range. Hydrodynamical simulations agree well at low masses but show significant normalization discrepancies at cluster scales. The authors interpret the declining ratio in terms of AGN feedback, reduced cooling efficiency, and an increasing contribution from ex-situ stellar assembly as halos continue growing; these processes are interpretations, not separately established by the measurements. They present the study as the first X-ray-based observational SHMR spanning three orders of magnitude in halo mass and as a benchmark for galaxy formation models.

PublicThis study compares the mass in stars in the brightest central galaxy with the mass of its surrounding dark matter halo. The researchers used optical observations to estimate stellar masses and combined X-ray signals from groups of galaxies to estimate average gas temperatures, then inferred halo masses from those temperatures. Across halos ranging from about a trillion to a thousand trillion times the Sun’s mass, the central galaxy’s share of the halo mass is highest near the low-mass end and decreases in more massive halos. The findings agree with earlier observations. Computer simulations match the lower-mass measurements well but differ significantly for galaxy clusters. The authors suggest that heating by active galactic nuclei, less efficient gas cooling, and changes in how galaxies assemble their stars help explain the trend; the measurements do not separately establish those explanations.

Young explorerGalaxies live inside huge clouds of dark matter. Scientists used starlight and X-rays to estimate how much mass is in a bright middle galaxy’s stars and in its surrounding cloud. They found that, in bigger clouds, those stars make up a smaller share of the total mass. Their computer models matched the smaller clouds better than the biggest ones. Scientists have ideas about why, but this study does not prove which idea is right.

The DESIRED strong-line calibrations: I. New empirical metallicity relations for the local and high-redshift universe

F. F. Rosales-Ortega, J. E. Méndez-Delgado, J. U. Guerrero-González+16 more

AstronomerUsing DESIRED, the authors derive 27 empirical optical strong-line metallicity calibrations, including four previously uncalibrated diagnostics, from 2,392 spectra with direct electron-temperature determinations: 1,029 extragalactic HII regions, 1,296 local star-forming galaxies, and 67 galaxies at z > 2. Homogeneously derived abundances span 12 + log(O/H) = 6.79–9.07; typical intrinsic dispersions are approximately 0.15–0.35 dex. Oxygen-, nitrogen-, sulphur-, argon-, and neon-based relations are provided with validity ranges for both uniform-temperature conditions (t² = 0) and an adopted temperature-inhomogeneity scenario (t² > 0), the latter reconciling recombination-line and collisionally excited-line abundances within that framework. Comparisons with independent high-redshift relations support using a subset of diagnostics at z > 2 within their intrinsic scatter; others show systematic offsets associated with elevated N/O or harder ionising conditions. High-redshift applicability is therefore diagnostic-dependent.

PublicThe researchers assembled 2,392 spectra of glowing gas regions and star-forming galaxies to improve estimates of oxygen abundance from strong features in their light. They produced 27 calibration relationships, including four for indicators not previously calibrated, using consistently analysed temperature and abundance measurements. The relationships cover a broad range of oxygen abundances but retain appreciable scatter. The team also provides separate calibrations assuming either a uniform gas temperature or temperature variations; the temperature-variation scenario brings two types of abundance measurement into agreement. Comparisons involving distant galaxies show that some indicators remain useful, while others give systematically different answers associated with different nitrogen-to-oxygen ratios or more energetic ionising radiation. No single calibration should therefore be assumed to work equally well for every distant galaxy.

Young explorerGlowing space gas makes patterns in its light. Scientists used many of these patterns to make better recipes for telling how much oxygen the gas contains. They made recipes for gas with an even temperature and for gas with warmer and cooler patches. The patchy-temperature idea helps two ways of counting oxygen agree. Some recipes also work well for very faraway galaxies, but others can give different answers, so scientists must choose carefully.

Astrophysical Parameters of 5056 Open Star Clusters from Bayesian Nested Sampling with PARSEC Isochrones

Olcay Plevne, Furkan Akbaba

AstronomerThe authors uniformly infer ages, metallicities, distances, and reddenings for 5,056 UCC open clusters by fitting Gaia DR3 colour-magnitude diagrams with PARSEC isochrones using Bayesian nested sampling. Metallicity is free for every cluster; Gaia XP spectrophotometric metallicities inform 1,201 fits, while the remaining clusters use broad constraints from Gaia parallaxes and the Schlegel-Finkbeiner-Davis dust map. No external open-cluster parameter catalogue anchors the fits, and no per-cluster manual intervention is applied. Their fit-quality metric identifies 3,807 clusters (75%) with reliable colour-magnitude solutions, spanning 0.004–5.9 Gyr and distances to 17 kpc. Comparison with independent OCCAM DR19 high-resolution spectroscopy for 132 clusters yields a metallicity median absolute deviation of 0.054 dex and a reported mean offset of −0.021 ± 0.132 dex, with agreement comparable to the intrinsic systematic uncertainty of isochrone-based metallicities. The XP-informed sample gives a radial metallicity gradient of −0.064 dex kpc−1; the highest-quality subset steepens toward the spectroscopically calibrated benchmark of −0.079 dex kpc−1. The authors interpret this as evidence that their photometric pipeline recovers a physically meaningful abundance scale. The catalogue and posterior chains are publicly released.

PublicResearchers have produced a catalogue estimating the ages, chemical compositions, distances, and dust reddening of 5,056 open star clusters. They used the same automated method throughout, comparing Gaia measurements of stellar colours and brightnesses with models of stars of different ages and compositions. Unlike many earlier large catalogues, they allowed each cluster’s metal content to vary in the fit rather than fixing it beforehand. Their quality check judged 75% of the clusters to have reliable fits. For 132 clusters with independent, high-resolution measurements of chemical composition, the estimates agreed closely, although the modelling method still has systematic uncertainty. The catalogue also recovers a decrease in metal content with distance from the Galaxy’s centre, with the highest-quality results moving closer to a benchmark based on spectroscopy. These are model-based estimates, not direct measurements of every property. The catalogue and its detailed statistical results are publicly available.

Young explorerScientists studied thousands of groups of stars. They compared the stars’ colours and brightnesses with computer models to work out how old the groups might be, how far away they are, and what they are made of. They also estimated how dust changes the colours we see. About three out of four groups passed their check for a good fit. For some groups, they checked the ingredients against a different kind of measurement and found close agreement. The answers are useful estimates, but they are not perfect. The scientists have shared their star-group list so others can use it.

WaveDM.jl: An Adaptable Simulation Framework for Dynamics of Baryonic and Wave Dark Matter on Galaxy Scales

Runyu Meng, Xiaobo Dong

AstronomerThe authors present WaveDM.jl, an open-source Julia package for galaxy-scale simulations of wave dark matter. It solves the time-dependent Schrödinger–Poisson equation with a pseudo-spectral Fourier method coupled to N-body gravitational force solvers, allowing wave dark matter and baryonic components to evolve together. A multilevel parallelization framework supports shared-memory, distributed-memory, and GPU execution, with workflows designed to scale from single-node to multi-node systems without major code changes. Tools include flexible initial-condition generators, trajectory lookback, tidal-force calculations, and real-time visualization. Its modular nonlinear Schrödinger framework also supports applications in nonlinear optics and cold-atom physics. The abstract describes software capabilities rather than observational findings or new physical conclusions.

PublicWaveDM.jl is a freely available simulation program for studying how wave dark matter—a model in which dark matter has wave-like dynamics—could behave within galaxies. It can simulate this dark matter together with ordinary matter and is designed to run on computing setups ranging from a single node to multiple nodes, including systems using graphics processors. Built-in tools help researchers set up simulations, examine trajectories and tidal forces, and visualize changes as calculations run. The software is also adaptable to studies of light and cold atoms. This work introduces a research tool; it does not report observations establishing that dark matter behaves this way.

Young explorerScientists made a computer tool called WaveDM.jl to explore an idea about dark matter, a mysterious kind of matter in space. The tool lets them pretend that dark matter acts like waves and see how it might move with ordinary matter in a galaxy. It can also show pictures while the pretend galaxy changes. These are computer experiments, not proof that real dark matter acts like waves.

Continuum Variability in AGN: Evidence for Systematically Suppressed Fluctuations in the BAL Population

A. Aliaga, P. Arévalo, M.L. Martínez-Aldama+2 more

AstronomerUsing SDSS DR16 and ZTF g- and r-band light curves, the authors compare BAL and non-BAL quasar variability at 1.57 ≤ z ≤ 2.00 and 18.5 ≤ rmag ≤ 19.8. Here, g includes C IV emission and BAL absorption, while r probes the continuum; Mg II provides black hole mass estimates. BAL quasars have consistently lower excess variance and DRW variability amplitude, while both populations vary more in g than in r. The variability suppression persists within bins of estimated black hole mass and Eddington ratio, arguing against differences in these properties as its sole explanation. Its presence in the continuum-probing r band supports an intrinsic continuum difference rather than line contamination. The samples could agree if BAL black hole masses were systematically overestimated by a factor of ≳4, implying higher Eddington ratios. Other proposed explanations connect the suppression to lower X-ray luminosities or preferential obscuration of a more variable inner accretion disc; these possibilities are not established by the comparison.

PublicQuasars with broad absorption features in their spectra show smaller long-term brightness changes than quasars without those features, according to this comparison of survey observations. The difference remains when the researchers compare objects with similar estimated black hole masses and Eddington ratios, a measure of their relative feeding activity. It also appears in a colour band that measures the underlying light rather than the spectral features, supporting the interpretation that the reduced variability belongs to the underlying emission. The cause remains uncertain. A large systematic overestimate of black hole masses in the absorption-feature group could reconcile the samples. Alternatively, the weaker variability might be connected to their lower X-ray luminosities or to obscuration hiding a particularly variable inner region of the disc around the black hole.

Young explorerScientists watched faraway lights called quasars to see how much their brightness changed. One group changed less than the other, even when the scientists compared quasars with similar estimated properties. They do not yet know why. One idea is that something hides the part that changes most, but that has not been shown.

The Study of Detailed Morphology of Milky Way Dwarf Galaxies: Draco and Boötes I

Kyosuke S. Sato, Masafumi Yagi, Sakurako Okamoto

AstronomerDeep, wide-field photometry uses old main-sequence stars to map the outer distributions of the dwarf spheroidals Draco and Boötes I. Draco shows no prominent extended component, apart from weak eastern and northwestern elongations, and its ellipticity decreases with radius. Its compact distribution relative to its estimated Jacobi radius of 57.2 (+13.5/−11.1) arcmin suggests a tightly bound stellar component. Boötes I instead shows directional number-density excesses above the best-fit exponential profile beyond roughly 20 arcmin, near its estimated Jacobi radius of 21.6 (+9.3/−7.6) arcmin, together with increasing ellipticity and a prominent S-shaped structure approximately aligned with its orbit. These observations suggest, but do not establish, that Boötes I has tidal tails from Milky Way interactions. The contrast further suggests that dwarf galaxies’ tidal responses may depend on dark-matter halo structure as well as orbital history.

PublicImages covering wide areas around two small Milky Way satellite galaxies, Draco and Boötes I, reveal contrasting arrangements of their old stars. Draco remains relatively compact, with only faint extensions in two directions, and becomes rounder farther from its center. Boötes I becomes more stretched out toward its outskirts and has more outer stars than a simple model of its distribution predicts. It also shows a striking S-shaped structure roughly aligned with its path around the Milky Way. Together, these features suggest that the Milky Way’s gravity may be pulling stars into tails around Boötes I, although the study does not confirm that interpretation. The difference between the galaxies also suggests that their responses to the Milky Way’s gravitational pull may depend both on their past orbits and on the internal arrangement of their dark matter.

Young explorerAstronomers looked at old stars in two little galaxies near our Milky Way. In one, called Draco, the stars mostly stay in a snug bunch. In the other, called Boötes I, the outside stars spread out into a shape like the letter S. The Milky Way’s gravity might be tugging those stars into tails, but the astronomers are not sure yet.

Rotational excitation of SiC₆ by collisions with helium: cross sections, rate coefficients and non-LTE modeling

Liman Tian, Ziyu Xiang, Chuangang Ning+1 more

AstronomerFollowing detections of SiC6 rotational transitions at j=26–40 in IRC+10216, this study calculates previously unavailable SiC6–He rotational excitation rates using a two-dimensional RCCSD(T)-F12 potential energy surface under the rigid-rotor approximation. Close-coupling (CC) calculations treat lower rotational levels, while the coupled-states (CS) approximation provides rates through j=40 at 3–100 K. Individual CC and CS rates differ by up to about a factor of two, particularly for transitions affected by weak coupling and resonances. Nevertheless, the examined high-j transitions have nearly identical modelled excitation and brightness temperatures, and CS-based line fluxes agree with CC results within 6.5% for H2 densities of at least 10^3 cm^-3. This supports CS for the high-j non-LTE modelling considered, where fully converged CC calculations are computationally impractical. Using reduced-mass scaling of the He rates to estimate H2 rates, the modelling finds subthermal excitation of j=40→39 at an H2 density near 10^4 cm^-3, emphasizing the importance of non-LTE effects. The H2 rates are estimates, not direct collision calculations.

PublicRotational emission from the molecule SiC6 has been detected in IRC+10216, but interpreting it requires knowing how collisions change the molecule’s rotation. This study calculates those collision rates for helium and uses a scaling approximation to estimate rates for molecular hydrogen. A less computationally demanding method gives modelled emission close to that from a more detailed method for the transitions tested, even though some individual collision rates differ by about a factor of two. The calculations also indicate that, at a low density typical of IRC+10216, one high-rotation transition is not excited as strongly as thermal equilibrium would imply. This is a modelling result rather than a new observation, and it shows why interpreting the detected emission requires accounting for departures from thermal equilibrium.

Young explorerAstronomers have seen light from a molecule called SiC6 in a place called IRC+10216. To understand that light, scientists used computers to work out how bumps from helium change the molecule’s spinning. They also used those answers to estimate what bumps from hydrogen would do. A simpler calculation gave almost the same light predictions as a harder one for the examples they checked. Their model suggests that, when there are few molecules around to bump into, one kind of spinning does not get as much energy as it would if everything had settled into balance.

Identity Crisis: Untangling Mass-Ordering Artifacts from Compact-Object Pairing in Gravitational-Wave Populations

Soumendra Kishore Roy, Asad Hussain, L. A. C. van Son+3 more

• Cosmology and Nongalactic Astrophysics
• General Relativity and Quantum Cosmology

AstronomerThe authors examine how the convention m1 ≥ m2 folds physically labeled binary black hole mass distributions across the equal-mass line. They show that ordering alone can make the secondary-mass distribution decline faster than the primary-mass distribution and create an apparent concentration near equal masses, without intrinsic component differences or correlations favoring equal-mass pairing. Distinct physically labeled populations can also yield identical ordered distributions. In contrast, a preferred companion mass that stays fixed as m1 increases requires an intrinsic characteristic mass scale. Applying their model to mergers in the fifth Gravitational-Wave Transient Catalog, the authors recover such a scale near m2 ≈ 50 solar masses. The inferred merger-rate density falls more steeply above this scale than below it, ruling out an equal or weaker high-m2 decline at 99.45% credibility. They conclude that models of the observed high-mass merger population must include a characteristic scale in at least one physically labeled component, although masses alone cannot identify which component carries it.

PublicWhen describing two merging black holes, researchers usually call the heavier one the primary and the lighter one the secondary. This study shows that sorting by weight can create misleading population patterns: it can make lighter companions appear to become rarer more quickly with increasing mass, or make similar-mass pairs appear especially common, even without those underlying physical tendencies. But not every pattern can be explained by sorting. Using a model applied to gravitational-wave observations in the fifth Gravitational-Wave Transient Catalog, the authors infer a distinctive companion-mass scale around 50 times the Sun’s mass. The merger rate drops much more sharply above that scale than below it. They conclude that this scale must reflect a real feature of the underlying population, though the masses alone cannot reveal which physically distinct component is responsible.

Young explorerScientists study pairs of black holes and always call the heavier one first. This sorting rule can make some patterns look real when they are only caused by sorting. But the researchers found evidence for one pattern that sorting cannot explain: a special weight around 50 Suns. Their study says this weight matters for these black hole pairs, but it cannot tell which member of the pair gives the pattern its special weight.

The Second Catalog of Low-Energy Fermi-LAT Sources

Fermi-LAT Collaboration

AstronomerUsing 14 years of Fermi-LAT observations, the authors construct the Second Catalog of Low-Energy Fermi-LAT Sources (2FLE), with 450 sources detected at TS greater than 25 between 20 and 200 MeV. The catalog provides localization, spectral, and association information; its median energy flux is 1.9 × 10⁻¹¹ erg cm⁻² s⁻¹ over this band. Bayesian and likelihood-ratio methods associate 377 sources with known counterparts: 325 extragalactic objects, with flat-spectrum radio quasars the dominant source class, and 52 Galactic objects. Three associated sources are new gamma-ray detections of known origin, absent from previous gamma-ray catalogs. Positional cross-matches with 4FGL-DR4 exist for 387 sources, and spectra are compared with the corresponding 4FGL spectral energy distributions. Of 73 sources without multi-wavelength associations, 13 have unclassified 4FGL counterparts and 60 are newly discovered gamma-ray sources. Among those 60, 51 have absolute Galactic latitude greater than 10 degrees and 38 are detected at greater than 10 sigma. Of all 450 sources, 45 are TeV emitters and six are spatially coincident with a 1LHAASO source; spatial coincidence alone does not establish a physical association. The authors describe 2FLE as the most sensitive 20–200 MeV catalog to date and a step toward reducing the MeV gap.

PublicAstronomers analyzed 14 years of observations from the Fermi Large Area Telescope to catalog 450 gamma-ray sources in the 20–200 MeV energy range. They statistically linked 377 sources to known objects: 325 outside our Galaxy and 52 within it. Flat-spectrum radio quasars are the leading source class in the catalog. Three sources linked to known objects had never appeared in an earlier gamma-ray catalog. Separately, 73 sources have no identified counterpart at other wavelengths: 13 match previously cataloged but unclassified gamma-ray sources, while 60 are newly discovered gamma-ray sources. Of those 60, 51 lie more than 10 degrees from the Galactic plane and 38 have detections stronger than 10 sigma. Overall, 387 catalog entries positionally match sources in 4FGL-DR4, 45 are also TeV emitters, and six overlap the positions of 1LHAASO sources. These positional matches are not all equivalent to identifying the objects responsible for the emission. The authors describe this as the most sensitive catalog yet in this energy band, helping fill a poorly covered part of gamma-ray astronomy.

Young explorerScientists used 14 years of pictures from a space telescope called Fermi to make a list of 450 places shining in gamma rays, a kind of light our eyes cannot see. They found likely matches to known space objects for 377 of them, but some still have no identified match. They also found 60 new gamma-ray sources whose identities remain unknown. Three other objects were already known, but had not been listed as gamma-ray sources before. This new list helps scientists study a kind of space light that has been hard to explore.

Search for Sub-Solar Mass Binaries in the First and Second Part of LIGO's Fourth Observing Run O4a-O4b

Keisi Kacanja, Kanchan Soni, Alexander H. Nitz

• General Relativity and Quantum Cosmology

AstronomerThe first sub-solar-mass compact-binary search combining Advanced LIGO O4a and O4b data finds no statistically significant candidates. It covers primary masses of 0.1–2 solar masses and secondary masses of 0.1–1 solar mass, accounting for tidal effects in extremely low-mass neutron stars. At a chirp mass of 0.5 solar masses, the 90% confidence merger-rate upper limit is 5.2 × 10^2 Gpc^-3 yr^-1, a factor of 2.2 lower than previous O1–O4a limits. The inferred effective local dark-matter fraction satisfies f̃_PBH < 0.6% at M_PBH = 0.8 solar masses, improving previous constraints by approximately a factor of 1.5. Under the authors’ model assumptions, the fraction limits are 2–7 times lower than OGLE microlensing constraints for M_PBH ≥ 0.6 solar masses. A detection of sub-solar-mass neutron stars or black holes would indicate a new class of objects not expected from standard stellar evolution; this search does not establish their existence.

PublicResearchers searched Advanced LIGO data from both parts of its fourth observing run for merging pairs containing unusually lightweight neutron stars or black holes. Objects of these kinds weighing less than the Sun are not expected to form through standard stellar evolution, so finding them would reveal a new class of astronomical objects. The search found no statistically significant signals. Instead, it tightened limits on how often such mergers could occur, improving the merger-rate limit by a factor of 2.2 at the specified reference mass. The authors also used the search to constrain how much local dark matter could consist of the black holes considered in their model: the effective fraction must be below 0.6% for black holes weighing 0.8 times the Sun’s mass. These dark-matter conclusions depend on the model assumptions, and the lack of a detection does not prove that these objects do not exist.

Young explorerScientists looked for tiny ripples in space from pairs of very small black holes or super-squished stars coming together. Some of these objects would weigh less than our Sun, and the usual story of how stars grow old does not explain how to make them. The scientists did not find a clear sign of any. That does not mean there are none, but it helps scientists work out how often they might come together.

A possible evolutionary connection between high-mass X-ray binary pulsars and isolated rotation-powered pulsars

Jun Yang

AstronomerArchival spin periods and period derivatives from XMM-Newton, Chandra, and RXTE reveal an approximately linear log-log relation between spin period and the absolute value of its derivative for high-mass X-ray binary pulsars in the Small Magellanic Cloud, with slope 1.02 ± 0.11. This resembles the trend for the youngest isolated rotation-powered pulsars. However, ATNF comparison slopes depend strongly on the characteristic-age selection: 1.10 ± 0.16 below 10,000 years and 0.72 ± 0.08 below 100,000 years; the full non-recycled population has no significant correlation. The binary pulsars occupy approximately the same characteristic-age range, 1,000–10,000 years, as the youngest rotation-powered pulsars, but their spin periods are two to three orders of magnitude longer. Reference characteristic-age contours are roughly parallel to the binary-pulsar relation, which is consistent with, but does not establish, a continuous evolutionary sequence.

PublicResearchers used existing measurements from XMM-Newton, Chandra, and RXTE to study how the rotation of pulsars in high-mass X-ray binary systems in the Small Magellanic Cloud changes over time. They found a pattern linking rotation period to the absolute value of its rate of change: on a logarithmic graph, the trend is approximately a straight line with slope 1.02 ± 0.11. A similar pattern appears among the youngest isolated pulsars powered by rotation, but the comparison depends strongly on which characteristic ages are included. The slope is 1.10 ± 0.16 for characteristic ages below 10,000 years and 0.72 ± 0.08 below 100,000 years; the full non-recycled comparison population shows no significant correlation. The binary pulsars have characteristic ages of approximately 1,000–10,000 years, similar to the youngest isolated pulsars, yet take about 100–1,000 times longer to rotate once. These characteristic ages are not established actual ages. Lines marking characteristic age roughly follow the observed trend, supporting a possible continuous evolutionary sequence rather than proving one.

Young explorerScientists looked at old measurements of spinning stars called pulsars. Some have a big companion star nearby. They found a pattern connecting how long these stars take to turn once with how much their turning speed changes. The pattern looks like one seen in some very young pulsars that are alone, but it changes depending on which stars scientists compare. The stars with companions take about 100–1,000 times longer to turn once. The pattern might help explain how their spinning changes as time passes, but it does not prove that explanation.

Correlation of galactic very-high-energy gamma-ray sources detected by LHAASO with high-energy neutrinos

Long-Yu Zhang, Kai Wang

• High Energy Physics - Phenomenology

AstronomerThe study tests spatial associations between 90 VHE gamma-ray sources in the First LHAASO catalog and 348 track-like neutrino events in IceCat-1. Monte Carlo correlation tests yield best p-values of 0.237 for all LHAASO sources, 0.312 for KM2A sources, and 0.115 for WCDA sources, providing no compelling evidence for an association. Assuming exclusively hadronic gamma-ray production, the authors also estimate optimistic theoretical neutrino fluxes and compare them with IceCube observations; this conditional analysis disfavors most catalog sources as counterparts to the detected neutrinos. LHAASO sources remain possible Galactic neutrino emitters, but establishing a connection requires greater sensitivity, such as that anticipated from IceCube-Gen2.

PublicResearchers compared the sky positions of 90 sources of very-high-energy gamma rays detected by LHAASO with 348 neutrino events recorded by IceCube. Using computer simulations to assess the apparent matches, they found no convincing evidence that the two sets are connected. They also estimated optimistic neutrino emissions under the assumption that all the gamma rays come from interactions involving particles such as protons. Comparing those estimates with IceCube observations suggested that most of the gamma-ray sources are unlikely to explain the detected neutrinos. These sources could still emit neutrinos within our galaxy, but more sensitive instruments, such as IceCube-Gen2, are needed to test the connection more strongly.

Young explorerScientists checked whether bright gamma rays and tiny particles called neutrinos might come from the same places in space. They compared their directions and used computer tests, but did not find a strong match. They also worked out how many neutrinos the bright places might send us if the gamma rays were made in a certain way. That calculation suggested most of those places probably did not make the neutrinos they detected. Some might still send out neutrinos, but scientists need more sensitive detectors to look for clearer clues.

Constraint on particle mass of dark matter based on XTE J1814-338 observation and DANS model

Lin Wang, Dehua Wen

• Solar and Stellar Astrophysics
• High Energy Physics - Phenomenology

AstronomerThe reported mass and radius of XTE J1814-338, 1.21 ± 0.05 solar masses and 7.0 ± 0.4 km, challenge conventional neutron-star models composed of normal nuclear matter. This theoretical study explores dark-matter-admixed neutron stars using self-interacting fermionic dark matter, varying its particle mass, self-interaction strength, and stellar mass fraction. Within this model, jointly satisfying the small stellar radius and dark-matter self-interaction cross-section limits inferred from colliding galaxy clusters constrains the dark-matter particle mass to sub-GeV through a few GeV. This is a model-dependent constraint, not a detection of dark matter in the star.

PublicThe neutron star XTE J1814-338 has a reported mass about 1.21 times the Sun’s but a radius of only about 7 kilometres, with uncertainties of 0.05 solar masses and 0.4 kilometres. Its small size is difficult to explain with traditional models made of normal nuclear matter. The researchers investigate a possible explanation: a neutron star containing dark matter whose particles interact with one another. In their model, matching the star’s small radius while respecting limits on dark-matter interactions inferred from colliding galaxy clusters restricts the dark-matter particle mass to below one to a few gigaelectronvolts. The study constrains this proposed explanation; it does not establish that the star contains dark matter.

Young explorerScientists have measured a very heavy star that seems surprisingly small. Their usual ideas about what is inside such stars have trouble explaining its size. So researchers tried a model with some dark matter mixed into the star. They found that, for this idea to fit both the small star and clues from crashing groups of galaxies, the dark-matter particles would need to have masses in a certain range. That does not mean they found dark matter inside the star—it is still a possible explanation.

Linear Polarization of Synchrotron Radiation from Very-small-pitch-angle Electrons

Meng Nie, Jirong Mao

AstronomerThis theoretical study calculates the linear polarization of very-small-pitch-angle synchrotron radiation, with alpha much smaller than 1/gamma, in contrast to conventional synchrotron radiation with alpha much larger than 1/gamma. It considers power-law, Maxwellian, and hybrid thermal–nonthermal electron energy distributions across radio, optical, X-ray, and gamma-ray bands. The calculations yield generally lower linear polarization degrees than in the conventional case, although both thermal and nonthermal electrons can still produce significant linear polarization. Polarization behavior varies with the physical parameters. The authors suggest that this regime is important for interpreting synchrotron polarization and offer a framework for application to synchrotron sources; the abstract reports calculations rather than observational tests.

PublicElectrons moving through magnetic fields can emit synchrotron radiation, whose light can be linearly polarized: its electric field preferentially vibrates in one direction. This study calculates that polarization when the electrons move at exceptionally small angles to the magnetic field. The researchers consider thermal electrons, nonthermal electrons, and mixtures of the two, for radiation ranging from radio waves to gamma rays. Their calculations indicate that polarization is generally weaker than in the conventional synchrotron case, but can still be substantial. Its behavior depends on the physical conditions. The authors argue that this small-angle case deserves attention when studying synchrotron sources, but these are theoretical results, not reported observations.

Young explorerTiny particles called electrons can give off light as they move through a magnetic field. The light's wiggles can line up in a favorite direction. The scientists used math to work out what happens when the electrons move almost along the field. They found that the wiggles usually line up less than in the usual case, but they can still line up a lot. The answer changes with the conditions. This was a math study, not a report of seeing it happen in the sky.

Black Hole Binary Mergers in Galactic Nuclei: Combined Effects of Secular Dynamics and Stellar Flybys

Hao Wang, Bin Liu, Johan Samsing

• Astrophysics of Galaxies

AstronomerNumerical simulations model the long-term evolution of black hole binaries in galactic nuclei, including the central SMBH’s tidal field, the nuclear star cluster potential, SMBH-induced relativistic precession, and stochastic stellar flybys. SMBH-driven ZLK dynamics dominate the evolution, but repeated flybys alter binary angular momentum and energy, substantially reshaping trajectories toward merger or disruption. Population synthesis estimates a merger rate of approximately 16 Gpc⁻³ yr⁻¹, significantly above predictions from dynamical channels that omit flybys. The study also predicts that a non-negligible fraction of mergers retain detectable eccentricity near 5 Hz, potentially offering a signature for next-generation ground-based gravitational-wave detectors. These are simulation-based estimates and predictions, not observational detections; the proposed channel may account for a major fraction of observed mergers.

PublicThis study uses computer simulations to explore how pairs of black holes evolve near a galaxy’s central supermassive black hole, amid a dense cluster of stars. The central black hole largely controls their long-term orbital changes, but repeated close passes by stars can change the pairs’ orbital energy and motion, helping send them toward either a merger or separation. A simulated population gives an estimated merger rate of about 16 per cubic gigaparsec per year, higher than predictions from models that leave out these stellar encounters. The researchers also predict that an appreciable fraction of merging pairs would still have noticeably elongated orbits when their gravitational waves reach frequencies around 5 hertz. Future ground-based detectors might identify this signature. The suggestion that this process could explain a major share of observed mergers remains a modeling-based interpretation.

Young explorerScientists used computers to imagine two black holes moving around each other near a much bigger black hole, with lots of stars nearby. In their computer models, the big black hole mostly guides how the pair’s paths change. But stars passing close by can give the pair little gravitational nudges. Many nudges can help the black holes come together or pull their partnership apart. The scientists think some pairs that come together might still follow stretched-out paths, leaving clues that future detectors could notice. They have predicted these clues, not seen them yet.

Optical constraints on intranight variability in TeV HBLs from a two-year Asiago Schmidt monitoring campaign

Domenico Impiombato, Giacomo Bonnoli, Elisa Prandini+2 more

AstronomerA two-year homogeneous optical campaign with the Asiago Schmidt 67/92 cm telescope monitored three TeV-emitting high-synchrotron-peaked BL Lac objects: 1ES 1959+650, H 1426+428, and PG 1553+113. More than 17,000 R- and I-band measurements span 957 source-filter sessions and about 420 hours between February 2024 and January 2026. Uniform differential photometry and classical F-tests using two independent comparison-star pairs identify robust intraday variability only in H 1426+428: 15 of 43 analysed R-band sessions and 5 of 40 I-band sessions. No significant intraday variability is detected in the other two sources under the adopted framework. For H 1426+428, duration-weighted duty cycles are 28.0% in R and 7.0% in I, calculated using only variable sessions with a measured local characteristic timescale. Local extrapolated doubling/halving timescales are approximately 5–15 minutes in the observer frame, rather than necessarily directly observed full flux doublings or halvings. The authors interpret the findings as evidence that rapid optical synchrotron variability is intermittent and state-dependent, and highlight the value of dense, uniform optical monitoring for high-energy programmes.

PublicAstronomers spent two years monitoring visible light from three blazars, objects whose powerful jets also emit very-high-energy gamma rays. Using the Asiago Schmidt telescope, they collected more than 17,000 brightness measurements. Their statistical tests found clear changes within a single observing session only in H 1426+428, not in 1ES 1959+650 or PG 1553+113. Those non-detections do not establish that the other two never vary. For H 1426+428, extrapolating local brightness trends gave estimated doubling or halving times of roughly 5–15 minutes as seen by the observer; this does not mean complete doublings or halvings were directly recorded over those intervals. The authors interpret the results as showing that rapid visible-light changes in these jets occur intermittently and depend on their activity state. The campaign also demonstrates how smaller optical telescopes can provide sustained support for high-energy observations.

Young explorerScientists used a telescope for two years to watch light from three faraway objects with powerful jets. They found clear, quick changes in brightness in just one of them. Their tests did not find clear quick changes in the other two, but that does not mean those objects always stay the same. The scientists think these fast changes happen only sometimes. Watching often with smaller telescopes can help them learn what the jets are doing.

Search for High-Energy Neutrinos from Infrared Flares

R. Abbasi, M. Ackermann, J. Adams+97 more

AstronomerThe study tests infrared flares as contributors to IceCube’s diffuse astrophysical neutrino flux. Previous neutrino detections from TXS 0506+056 and NGC 1068 motivate supermassive black hole accretion as a candidate production mechanism, while several candidate transient counterparts show strong dust echoes: infrared emission delayed relative to optical outbursts. A time-dependent stacking analysis of 393 Northern Sky infrared-flare sources using 10 years of IceCube through-going-track data finds no significant neutrino emission. The authors derive catalog-level upper limits and extrapolate them to the population, finding that infrared flares contribute less than 2.7% of the diffuse neutrino flux at 100 TeV for a spectral index of 2.5. This population constraint depends on the extrapolation and assumed spectrum; the null detection does not establish that individual infrared flares emit no neutrinos.

PublicIceCube has detected high-energy neutrinos from space, but the sources of its widespread background of these particles remain unknown. Matter falling toward supermassive black holes is one possible explanation. Earlier studies identified several possible neutrino-associated outbursts with delayed infrared light, known as dust echoes. Researchers searched for neutrino signals associated with 393 infrared-flare sources in the northern sky using 10 years of IceCube data, but found no statistically significant emission. They used this result to set limits rather than to rule out neutrino production entirely. Extrapolating those limits to the wider population, they estimate that infrared flares supply less than 2.7% of the background neutrino flux at an energy of 100 TeV, assuming a particular neutrino spectrum.

Young explorerTiny particles called neutrinos reach us from space, and scientists are trying to learn where they come from. Some bright space outbursts have a later glow from dust, so scientists wondered whether these outbursts also send us neutrinos. They checked 393 places against 10 years of neutrino records and did not find a clear signal. That does not mean these outbursts never make neutrinos. Using some assumptions, the scientists worked out that outbursts like these probably explain only a small part of the neutrinos at the energy they studied.

Rotochemical heating of neutron stars in 2D

Mikhail V. Beznogov, Jerome Novak, Dany Page+1 more

AstronomerThe authors simulate rotochemical heating in spinning-down neutron stars using fully relativistic, 2D axisymmetric models without the slow-rotation approximation, following coupled thermal, mechanical, and chemical evolution with radial and angular structure. Their simplified microphysics assumes nucleonic matter, non-equilibrium modified Urca reactions as the main heating/cooling mechanism, and no superfluidity. They explore magnetic field strength, heat-blanketing envelope properties, initial spin frequency, mass, and core equation of state (EOS). Most simulated trends agree with earlier work, but cooling curves during rotochemical heating show a strong core-EOS dependence, previously regarded as weak. The authors suggest that earlier studies sampled too narrow a range of density-dependent symmetry energy; this explanation remains an interpretation, not an established result.

PublicAs a neutron star spins more slowly, its interior slowly compresses. This can upset its chemical balance and trigger nuclear reactions that heat it. The researchers modeled this process on a computer, accounting for the nonspherical shape of rapidly spinning stars and using general relativity. Unlike most earlier models, theirs follows changes both with depth and around the star. Most findings agree with previous calculations, but the simulated temperature histories during this heating depend strongly on the assumed properties of dense matter in the core. The authors suggest earlier studies explored too little variation in one aspect of those properties. These are simulation results, not observations, and the models use simplified particle and reaction physics and omit superfluidity.

Young explorerA neutron star is a very tightly packed star that spins. As it slows down, the stuff inside can get squeezed and start reactions that warm it up. Scientists used a computer to explore this, letting their pretend star have a squashed shape instead of being a perfect ball. They found that changing their ideas about how the stuff deep inside behaves could change how the star cools a lot. This is what their simplified computer stars did, not something they measured in a real star.

LHAASO Constraints on New-Source Cosmic Rays:Abundance Scenarios and Injection Spectral Indices

Xu-Lin Dong, Pei-Pei Zhang, Qi-Ling Chen+2 more

AstronomerRecent LHAASO observations indicate that microquasars and massive star clusters contribute to Galactic cosmic rays and likely to pre-knee spectral hardening. The study models these new-source contributions with two abundance prescriptions: Case-1, an SNR-like composition enhanced in heavy nuclei, and Case-2, microquasar companion-star surface abundances. Injection indices are constrained using LHAASO proton, helium, and all-particle spectra, while mean logarithmic mass, <lnA>, discriminates between models. Assuming a common injection index for heavy elements, Case-2 fits <lnA> significantly better, but requires large, physically unmotivated differences between heavy-element and helium injection indices. This tension motivates relaxing the common-index assumption or considering other abundance patterns, rather than establishing Case-2 as the correct composition. The models predict nearly consistent pre-knee elemental spectral indices for Case-1, versus significantly softer Mg, Si, and Fe spectra than He, C, and O for Case-2. Future element-resolved spectra from HERD and LHAASO are proposed as a decisive test.

PublicLHAASO observations suggest that microquasars and massive star clusters help supply the Milky Way's cosmic rays and probably contribute to a change in their energy distribution below a feature called the knee. Because these sources differ from supernova remnants, they may produce a different mixture of elements. Researchers compared two possible mixtures: one resembling that associated with supernova remnants, enriched in heavier elements, and another based on the surfaces of microquasar companion stars. With an assumption that heavy elements share the same injection spectral shape, the companion-star mixture better matches LHAASO's composition data. However, that fit requires large differences between the heavy-element and helium injection spectra that lack a physical motivation, so it does not settle which mixture is correct. The models make different predictions: the first mixture gives nearly matching spectral slopes across elements, while the second makes magnesium, silicon, and iron decline more steeply with energy than helium, carbon, and oxygen. Future HERD and LHAASO measurements could test this distinction.

Young explorerSpace has tiny, speedy particles called cosmic rays. Observations suggest that microquasars and big groups of stars help send them through our galaxy. Scientists tried two possible recipes for the kinds of particles these places send out. One recipe matched the clues better, but only by making the particles behave differently in a way the scientists cannot yet explain well. So they do not know which recipe is right. The recipes also predict different patterns: in one, the different kinds follow almost the same pattern as energy goes up; in the other, some heavier kinds fade away faster than some lighter kinds. Future measurements could help tell the recipes apart.

A Parsec-Scale Transient High-Frequency-Peaked Radio Source in the Very Large Array Sky Survey Brightening and Fading over a Decadal Timescale

Yuyang Chen, B. M. Gaensler, Maria R. Drout+10 more

• Astrophysics of Galaxies

AstronomerVT J1823-2345 is a VLASS radio transient resembling a peaked-spectrum (PS) source, a population generally interpreted as young radio jets. It brightened threefold at 1.4 GHz between 1996 and 2021, shows observed spectral peaks at approximately 6 GHz or higher, and has a peaked 3 GHz light curve declining since 2023. In 2024, its resolved Gaussian major-axis size was 0.4 mas. At 8.8 GHz, its linear polarization fraction is approximately 0.73%, with an extreme observed Faraday rotation measure of about +12,000 rad m^-2. It coincides on the sky with a supernova remnant and an F-type star, but no background galaxy is detected. The authors use its multi-wavelength properties to disfavor Galactic transients, explosive extragalactic transients, and blazar variability. They interpret it as consistent with a short-lived, parsec-scale PS source containing a decades-old jet that does not develop into a large-scale radio galaxy. Comparisons with other VLASS nuclear-transient light curves motivate speculation about a broader transient-jet population, possibly associated with episodic AGN activity or jetted tidal disruption events; these connections are not established.

PublicAstronomers report an unusual radio source, VT J1823-2345, that became three times brighter at one radio frequency between 1996 and 2021 and has been fading at another frequency since 2023. Its radio spectrum and tiny measured angular size resemble sources commonly interpreted as young jets from active galaxy centers. Its polarized radio signal also undergoes an unusually strong rotation. Although it overlaps a stellar explosion remnant and a star on the sky, no background galaxy is visible. The authors consider several alternative explanations unlikely and suggest it could be a decades-old jet that remains small rather than growing into a large radio galaxy. They speculate that similar radio transients might share this origin, but neither that connection nor the source's proposed identity is confirmed.

Young explorerAstronomers found a tiny spot in the sky sending out radio signals. It got brighter, and later some of its signals began getting weaker. They think it might be a small stream of material called a jet, like ones found in the centers of active galaxies. This jet might stay small instead of growing very big, but the astronomers are not sure yet.

Can bosenovae deplete the galactic dark matter?

Samuel Gómez Gómez, Joshua Eby

• Cosmology and Nongalactic Astrophysics
• Astrophysics of Galaxies
• High Energy Physics - Phenomenology

AstronomerThis theoretical analysis bounds galactic dark-matter depletion by bosenovae, assuming all dark matter consists of ultralight bosons with attractive self-interactions. It considers gravitational atoms around stars and compact objects, and self-gravitating boson stars fed by the halo; collapse converts some mass into relativistic radiation that escapes the galaxy. Combining per-object ejection bounds with realistic galaxy models, stellar populations, and stellar evolution gives a Milky Way stellar gravitational-atom depletion fraction of at most about 3 × 10^-9, with similarly negligible depletion in other galaxies. Sgr A* could nominally reach about 10^-3, but only at a boson mass disfavoured by ultrafaint dwarf galaxies and outside perturbative validity, where only a geometric dark-matter flux bound is available. Boson stars radiate at most about 3 × 10^-5 of the Milky Way halo and 0.1% of a DF2-like halo. These model-based bounds argue against either channel substantially depleting galactic dark matter.

PublicCould collapsing dark-matter clouds drain dark matter from galaxies? This theoretical study finds that the two mechanisms examined would remove very little. It assumes dark matter is made entirely of extremely light particles that attract one another. These particles could collect around stars and compact objects or form self-gravitating clumps. When such systems collapse, some mass could become fast-moving radiation that escapes the galaxy. Calculations using galaxy models put extremely small limits on the loss: ordinary stars would remove at most about three billionths of the Milky Way’s dark-matter halo, while self-gravitating clumps would radiate at most about 0.003%. For a DF2-like galaxy, the latter limit is 0.1%. A potentially larger contribution from the Milky Way’s central black hole relies on a particle mass disfavoured by dwarf-galaxy evidence and falls outside the calculation’s reliable range. These are theoretical limits, not observed losses.

Young explorerGalaxies have mysterious stuff called dark matter. Scientists asked whether, if it is made of a certain kind of tiny particle, it could gather into clouds, collapse, and send some of its energy racing out of a galaxy. They used calculations rather than watching this happen. Their answer is that the kinds of collapsing clouds they studied would let only a very tiny bit escape—not enough to empty a galaxy of its dark matter.

GRB 181201A: Spectropolarimetric Constraints on Prompt Emission and Magnetic Field Structure

Dhruv S. Bal, Nikita S. Khatiya, Philippe Laurent+3 more

AstronomerTime-integrated and time-resolved INTEGRAL/IBIS analyses identify GRB 181201A as its fourth polarized GRB, reporting a polarization degree of 81.5% (+17.2/−15.7 percentage points) over the three highest-signal-to-noise time bins and modest temporal evolution of the polarization angle. The photon index evolves from hard to soft without crossing the synchrotron line-of-death. The high polarization tends to disfavor photospheric emission, for which cited studies predict polarization below 20%. Under standard synchrotron assumptions, the authors interpret the measurements as favoring a non-axisymmetric, multi-patch jet with locally coherent magnetic fields but no global structure, with one or a few patches dominating. The measured polarization overlaps the intrinsic synchrotron maximum within 3σ uncertainties. Compton drag also remains possible under restricted conditions, such as viewing near the jet edge. Measurement uncertainties and scope for pipeline improvement prevent a strong preference between synchrotron and Compton drag.

PublicObservations of gamma-ray burst GRB 181201A show that its light was strongly polarized: its waves had a pronounced preference for a particular orientation. The researchers report about 82% polarization, with substantial uncertainty, and a modest change in its orientation over time. The burst's spectrum also shifted from harder to softer. The strong polarization makes an explanation based on emission from a photosphere less likely. One interpretation is that the burst's jet contained several magnetic patches, with only one or a few contributing most of the light, rather than a single globally organized magnetic field. However, another mechanism, called Compton drag, could also produce strong polarization under particular viewing conditions. The uncertainties and possible improvements to the analysis mean the observations do not strongly favor either mechanism.

Young explorerScientists studied a bright flash from space. Much of its light waved in a similar direction, and that direction changed a little as the flash went on. This could mean that a few patches with organized magnetism made most of the light. But another way of making the light could also fit what they saw. The measurements are not exact enough to tell which explanation is right.

Nonlinear Perturbations of Relativistic Stars

K. J. Kwon, Abhishek Hegade K. R., Tejaswi Venumadhav+2 more

• General Relativity and Quantum Cosmology
• Solar and Stellar Astrophysics

AstronomerThis theoretical study extends the Friedman–Schutz general-relativistic Lagrangian perturbation formalism beyond linear order while retaining full time dependence, and gives relations between Lagrangian and Eulerian perturbations at arbitrary perturbative order. As a proof of principle, it reduces the second-order field and conservation equations for tidally perturbed relativistic stars in Regge–Wheeler gauge to master equations with a nonlinear source. Projection onto stellar eigenmodes yields nonlinear mode-amplitude equations and coefficients describing mode–mode and mode–tidal-field couplings. With approximations to the tidal field and coupling coefficients, the quadrupolar fundamental mode alone reproduces the direct metric-matching static quadratic Love number to about 4%, subject to a further correction from the Hamiltonian and momentum constraints of the second-order tidal field.

PublicThe researchers developed a mathematical framework for calculating how a star responds to gravity that stretches and distorts it, including effects beyond a simple linear response and allowing the disturbances to change over time. Their equations describe how the star’s natural vibrations interact with one another and with the external gravitational pull. In a theoretical test using approximations and just one vibration pattern, they calculated a measure of the star’s nonlinear deformation that agreed with a direct calculation to about 4%. That comparison remains subject to an additional correction required by constraints in the gravitational equations. This is a calculation, not an observation of a star.

Young explorerGravity can pull on a star and change its shape. The researchers made math rules to describe how the star’s wiggles can affect one another while it is being pulled. They tried a simpler calculation using just one kind of wiggle, and its answer was close to another calculation. But their answer still needs an extra correction. They worked this out with math, not by watching a real star.

Spinformation: do gravitational-wave events carry information beyond effective spins?

Cailin Plunkett, Jack Heinzel, Noah E. Wolfe+2 more

• General Relativity and Quantum Cosmology

AstronomerThe study quantifies whether component-spin posteriors contain information beyond constraints implied by the effective inspiral spin χ_eff and effective precession spin χ_p, then applies the method to GWTC-5. Using an information-loss threshold of approximately 0.25 bits or greater, more than 80% of catalog events have component-spin posteriors described by χ_eff alone. Only about 3% contain substantial spin information beyond both χ_eff and χ_p, making the catalog’s component-spin information effectively two-dimensional in these parameters. Simulated signals show that different noise realizations can create or destroy more than one bit of information beyond χ_eff; apparent structure in real data may therefore be noise-driven. At current sensitivity, the authors conclude that component spins offer an interpretive rather than informational advantage over effective parameters.

PublicThe spins of merging black holes can offer clues to how these pairs formed, but gravitational waves measure combined spin properties more precisely than each black hole’s individual spin. This study tests how much information is lost by using those summaries. In the GWTC-5 catalog, more than 80% of events are adequately described by one combined spin measure under the study’s information-loss criterion. Only about 3% provide substantial extra spin information beyond two combined measures. Tests with simulated signals show that noise can add or erase apparent extra information, so some detail in real observations may come from noise. With current sensitivity, describing individual spins mainly helps interpret the measurements rather than revealing additional information.

Young explorerWhen two black holes join together, they make ripples that can give us clues about how they spin. Scientists checked whether studying each black hole’s spin tells us more than a short summary of their spins together. For most events they studied, the short summary was enough. In pretend signals, they found that noise could make extra clues appear or disappear. So, with today’s measurements, more detail does not always mean we know more.

Strong-Field Gravitational-Wave Lensing from Ray-Traced Arrival-Time Surfaces

Luka Vujeva, João S. Santos, Brian C. Seymour

• General Relativity and Quantum Cosmology

AstronomerThis theoretical work develops a formalism for wave-optics gravitational-wave lensing when a source lies near a massive black hole, where assumptions underlying the conventional diffraction integrand break down. Motivated by a binary source near a black hole lens, the method uses the Hamilton–Jacobi equations for null geodesics to construct a time-delay surface without the thin-lens approximation, then evaluates its diffraction integral directly to obtain low-frequency corrections. For a stationary source at 10M, comparison with a relativistic wave-scattering model yields reported agreement at the 6.5% level for peak amplification and the 0.3% level for the first diffractive fringe. At a weak-field source location of 10^4 M, amplitude agreement with the point-mass lens is better than 1%, although noticeable dephasing appears between amplification peaks at higher frequencies. The authors describe the framework as valid for source locations from approximately 6M outward to infinity, connecting strong- and weak-field regimes. These are theoretical model comparisons, not observational measurements.

PublicA massive black hole can bend gravitational waves, changing how strongly they arrive and producing wave-interference patterns. Standard calculations become unreliable when the waves originate very close to the black hole. This study presents a new theoretical method that follows paths through curved spacetime to calculate travel-time delays without treating the lens as a thin layer. Tests using a stationary source close to the black hole show agreement with another relativistic model at the 6.5% level for maximum amplification and the 0.3% level for the first interference feature. Farther away, amplitudes agree with a simpler model to better than 1%, but the positions of amplification peaks differ at higher frequencies. The work connects calculations near and far from a black hole; it does not report an observed gravitational-wave signal.

Young explorerA black hole can bend waves that are ripples in space, making them stronger or weaker. Working out what happens is especially tricky when the waves start very close to it. Scientists made a new way to calculate this and checked it against other calculations. The answers were close, but not exactly the same. This was a study using math, not a wave they watched arrive.

Black Hole Fine Structure

Adrian Ka-Wai Chung, Richard Dyer, Tomasz Kinowski+1 more

• General Relativity and Quantum Cosmology

AstronomerIn General Relativity, axial and polar black-hole perturbations have identical quasinormal-mode spectra, a property called isospectrality. The authors conduct a theory-agnostic search for frequency splitting between these modes in gravitational-wave observations and find no evidence of isospectrality breaking. They report a combined 90% upper limit of <28.5% on the relative frequency splitting. Mapping these constraints onto several modified-gravity theories yields coupling-length bounds of approximately 28 km or less. These are upper bounds, not detections of new physics.

PublicGeneral Relativity predicts that two types of black-hole vibrations have matching characteristic frequencies. Some new physics could separate those frequencies, much as atomic fine structure splits spectral features. The researchers searched gravitational-wave observations for this separation and found no evidence of it. Their combined 90% upper limit puts the relative frequency difference below 28.5%. Interpreting the limit within several alternative theories of gravity constrains their coupling-length parameters to about 28 kilometres or less. The findings limit possible departures from General Relativity rather than establish that such departures exist.

Young explorerA black hole can wobble in two different ways. Einstein’s gravity theory says those wobbles should have matching notes. Scientists looked at ripples in space to see whether the notes were different, but they found no sign that they were. They could put a limit on how different the notes might be, but that does not prove they match exactly.

The WDM time-frequency transform in gravitational-wave data analysis II: Evolutionary spectrum and noise covariance

Aaron D. Johnson, Katerina Chatziioannou, Robert Rosati

• General Relativity and Quantum Cosmology

AstronomerThe authors develop a time-frequency description of nonstationary gravitational-wave detector noise, relevant over minutes for upcoming ground-based detectors and months for space-based detectors. Within the oscillatory-process framework, they introduce evolutionary power spectra in the Wilson-Daubechies-Meyer basis that, to leading order in the ratio of Meyer-filter to nonstationarity timescales, can be estimated from a single noise realization. The corresponding leading-order covariance is band tri-diagonal, whereas the exact, all-orders covariance is positive semidefinite by construction and may be dense depending on the noise. They derive a time-frequency tiling that minimizes diagonal-approximation error and show that coarse-graining suppresses correlations quadratically. Simulations incorporating a LISA Galactic foreground and a drifting power-law spectrum demonstrate signal-to-noise ratio loss and severe inference bias when stationarity is assumed. For realistic LISA data, their assessment supports a diagonal time-frequency covariance for narrow-band analysis of one resolved Galactic binary, but not for broad-band analysis. They also provide strategies to mitigate wraparound correlations when the spectrum differs between the data endpoints.

PublicNoise in gravitational-wave detectors changes over time, so treating it as constant can distort the signals researchers hope to study. This work develops a mathematical description that tracks noise in both time and frequency, including correlations that simpler methods can miss. In simulated data containing a model of the LISA Galactic foreground and a changing noise spectrum, assuming unchanging noise reduced signal-to-noise ratios and strongly biased the inferred signal properties. The authors find that a simplified version of their method is accurate for studying one resolved Galactic binary over a narrow frequency range under realistic LISA conditions, but is insufficient over a broad frequency range. They also propose ways to reduce artificial correlations between the beginning and end of a data segment. These are mathematical and simulation-based findings, not a report of new gravitational-wave observations.

Young explorerImagine trying to hear a quiet tune while the background hum keeps changing. Scientists made a new math tool to keep track of that changing hum when searching for tiny ripples in space. In pretend detector data made by a computer, ignoring the changes made the signals harder to pick out and led to wrong answers about them. A simpler version of the tool worked for one kind of small search, but was not good enough for a wider search.

Radion/Dilaton portal freeze-in dark matter in extra-dimensional theories

Amrita Mukherjee, George Sanamyan, Dipan Sengupta

• High Energy Physics - Phenomenology
• High Energy Physics - Theory

AstronomerThis theoretical study calculates freeze-in dark matter production through a radion/dilaton portal in stabilized warped extra-dimensional models. The authors treat scalar, vector, and fermion dark matter coupled conformally through the radial mode. Their calculations indicate that particles with masses from keV to TeV can account for the full relic abundance when the reheating temperature is much lower than the radion mass. They also identify Lyman-alpha constraints in the keV–GeV range, which they describe as a model-independent probe of this sector. The work emphasizes consistent matrix-element calculations, explicit assumptions, and cosmological constraints; it does not report a dark matter detection.

PublicCould dark matter have formed through a connection to hypothetical extra dimensions? This paper explores that possibility mathematically, using a process called freeze-in to calculate how dark matter could accumulate in the early universe. In the proposed models, a field called the radion provides the connection. The calculations suggest that dark matter particles spanning a broad mass range could account for all of today's dark matter, provided the universe's reheating temperature was much lower than the radion's mass. Lyman-alpha observations restrict some of the possibilities. These are theoretical results within the proposed framework, not evidence that extra dimensions or these dark matter particles have been discovered.

Young explorerScientists are trying to understand dark matter, the invisible stuff in space. They used math to explore an idea: perhaps it slowly formed with help from an extra direction in space that we cannot see. Their math says this might make enough dark matter, but only under certain conditions in the young universe. Clues from light in space limit which versions of the idea could work. They have not shown that this is how dark matter really formed.

Testing Charged Black Holes Embedded in Anisotropic Matter and Surrounded by Plasma through Gravitational Lensing: Bounds from the Sloan Lens ACS Survey

Ritesh Pandey, Shubham Kala, Amare Abebe+2 more

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study models a charged black hole with anisotropic surrounding matter using the two-component Kiselev metric in a homogeneous plasma. After examining the geometry and horizons, the authors derive the weak-deflection angle from Hamiltonian light propagation using a fixed-turning-point expansion, checked against direct numerical integration. They calculate Einstein-ring angles, image positions and magnifications, then compare the model with observed Einstein radii for the galaxy-scale SLACS lenses J0008−0004 and J0029−0055. Within this model, the minimum Einstein angle imposed by the reduced deficit deflection yields mass-independent bounds of K<6.5×10^-6 and K<4.2×10^-6, respectively. The charge correction is suppressed by r_s/R_E≈5×10^-6 and is deemed unobservable; the optical plasma parameter is of order 10^-22 and cannot be constrained. The authors conclude that these data tightly limit anisotropic matter within the model, while probing plasma effects requires low radio frequencies.

PublicThe researchers calculate how light would bend around a charged black hole surrounded by matter whose properties depend on direction, with a uniform plasma also present. They check their approximate calculation against a direct numerical calculation and predict the locations and brightnesses of lensed images. Comparing the model with observed light-ring sizes around two galaxy-scale gravitational lenses places tight limits on the model's surrounding-matter parameter. This comparison does not establish that the lenses contain the proposed matter or measurable black-hole charge: the predicted charge effect is too small to observe, and the optical images cannot constrain the plasma effect. The authors conclude that plasma effects would need to be investigated at low radio frequencies instead.

Young explorerGravity can bend light and make faraway things look like rings. Scientists used math to imagine a black hole with an electric charge and special material around it. They compared their math with two rings seen in space. If their model is right, the special material must stay below a small limit. The pictures cannot reveal the tiny effects of the electric charge or the surrounding gas. The scientists say low-frequency radio waves are needed to look for the gas effect.

Biases in Ringdown Tests of General Relativity from Gravitational-Wave Microlensing

Sreelakshmi Mundakkal Dasan, Anuj Mishra, Apratim Ganguly

• General Relativity and Quantum Cosmology

AstronomerUsing GW150914-like simulated signals, the authors investigate lensing across the long-wavelength, wave-optics, and geometric-optics regimes with unlensed waveform models in time-domain post-merger and frequency-domain full inspiral–merger–ringdown analyses. Wave-optics lensing can substantially bias inferred remnant mass, spin, and ringdown modal content. It can spuriously favor the first overtone, with log10 Bayes factor approximately 40 despite no support for that overtone in the injected signal. Parameterized ringdown tests can also falsely favor departures from the Kerr QNM spectrum, with log10 Bayes factor approximately 8. Evidence for higher-order modes remains largely unchanged for the simulations considered. A parameterized full-signal analysis additionally finds that microlensing can bias the inferred dominant (2,2,0) QNM frequency. These simulation results identify unmodeled microlensing as a potential systematic in precision Kerr tests, not an observed departure from GR.

PublicAfter two black holes merge, the remaining black hole produces fading gravitational waves called ringdown. Researchers simulated signals resembling GW150914 to test how gravitational lensing—the distortion of waves by gravity along their path—could mislead analyses that ignore it. In the wave-optics regime, lensing could make the final black hole appear to have the wrong mass or spin, create false evidence for an extra ringdown tone, and mimic a departure from the behavior predicted for a Kerr black hole. An analysis of the complete simulated signal also found that microlensing could shift the inferred frequency of the main ringdown tone. Evidence for higher-order modes changed little in the simulations studied. These findings warn of a possible source of error in tests of general relativity; they are not observations of gravity breaking its predicted rules.

Young explorerWhen two black holes join, they send out space ripples that fade away, a little like a bell’s sound. Scientists used pretend signals to see what happens if gravity bends those ripples on their way to us. They found that ignoring the bending could make us guess the black hole’s size or spin wrongly, or think it made an extra note. It could even make gravity’s rules look wrong when the pretend signal did not show that. This was a computer test, not something they found happening to a real black hole.

Transient PULSE: Code for the Transient Propagation of UltraLight (pseudo)Scalars to Earth

Jason Arakawa, Charles Cheung, Muhammad Hani Zaheer+2 more

• High Energy Physics - Phenomenology
• Instrumentation and Methods for Astrophysics
• Computational Physics

AstronomerTransient PULSE numerically implements a previously developed source-to-detector framework for transient ultralight bosonic signals from astrophysical bursts. It discretizes a user-supplied emission energy spectrum into momentum modes, propagates them through a specified matter-density profile, and constructs the time-frequency energy-density distribution at Earth, including dispersion and in-medium screening. The package accommodates non-Gaussian source spectra and supplies inputs for detector-specific analyses. A complementary analytical module estimates coupling sensitivities, arrival-time delays, and screening thresholds from parameterized source and detector properties. These are modeling capabilities, not reported detections; their outputs depend on the supplied source, propagation, and detector assumptions.

PublicTransient PULSE is software for calculating how possible signals made of ultralight bosonic particles could travel from an astrophysical burst to a detector on Earth. Starting with an assumed distribution of emitted particle energies and a specified distribution of matter along the route, it models how the signal spreads out in arrival time and how matter can screen it. The resulting predictions describe how the signal's energy density at Earth varies with time and frequency, providing information for detector-specific studies. A separate analytical component estimates arrival delays, screening thresholds, and sensitivity to the particles' interaction strength. The work presents a modeling tool, not an observation of these particles.

Young explorerScientists made a computer tool to imagine how a burst in space might send very tiny particles toward Earth. They tell the computer what the burst might send out and what matter the particles would pass through. The tool works out how the signal might spread out on its journey and what a detector on Earth might receive. It helps scientists plan what to look for; it does not mean they have found these particles.

A Very Rich Bimodal Galaxy Cluster Merger: RXC J0032.1+1808

David Wittman, Rodrigo Stancioli, Christopher Hopp+3 more

• Cosmology and Nongalactic Astrophysics

AstronomerRXC J0032.1+1808, previously found to be elongated north–south in optical imaging and lensing mass maps, shows bimodal X-ray morphology suggestive of a merger. Together with a previously reported radio relic, this supports the authors’ interpretation that the system is observed after first pericenter. Archival XMM-Newton data yield a global temperature of 8.5 keV, with uncertainties of +1.1 and −0.9 keV, and an unabsorbed 0.5–10 keV luminosity of (1.04 ± 0.03) × 10^45 erg/s, both at 90% confidence. A member-galaxy redshift survey gives a line-of-sight subcluster relative velocity of 1002–1785 km/s at 68% confidence; the brightest cluster galaxies differ by 2466 km/s. Comparisons with publicly available hydrodynamic simulations rule out a head-on merger within the tested simulation set and are consistent with impact parameters of 0.5 or 1 Mpc. These comparisons provide initial constraints of approximately 315–550 Myr since pericenter and a range of possible viewing directions.

PublicThe galaxy cluster RXC J0032.1+1808 appears to contain two groups of galaxies in the process of merging. Its X-ray emission has two distinct components, while earlier optical images and gravity-based mass maps show a north–south stretch. The researchers interpret these features, together with a previously reported radio relic, as evidence that the groups have already made their first closest approach. Archival X-ray observations indicate extremely hot, luminous gas, and galaxy measurements show substantial relative motion along our line of sight. Comparing the observations with computer simulations, the researchers find that a direct, head-on encounter does not fit the tested models. Instead, an off-center encounter is consistent with them, with initial estimates placing the closest approach roughly 315–550 million years ago. The timing and possible viewing directions are simulation-based constraints, not direct measurements.

Young explorerScientists studied a huge gathering of galaxies and found that its X-ray glow has two parts. They think two groups of galaxies are joining together and have already passed closest to each other once. They compared what they saw with computer-made models. Those models suggest the groups passed a little to the side, rather than meeting straight in the middle. Scientists are still working out when that happened and which way we are looking at it.

Identifying heating processes in simulations with an entropy-based scheme: A single jet episode in a galaxy cluster

Moun Meenakshi, Rainer Weinberger, Christoph Pfrommer+1 more

• Astrophysics of Galaxies

AstronomerThis simulation study separates AGN jet heating channels in the intracluster medium using passive entropy scalars in MHD calculations. The method is validated against idealized tests covering turbulent heating, anisotropic Braginskii viscosity, dissipative and adiabatic shock heating with in-situ shock detection, and cosmic-ray heating through Alfvén-wave excitation and damping. Simulations of single-epoch, high-power outbursts show that light jets inflate wider bubbles and displace more core gas, while denser jets propagate farther with less central disturbance. Shocks dominate early heating at all jet densities studied. Later, light jets heat mainly through turbulent processes, including vortex dissipation and mixing of different-temperature gas, and through compressible dissipation of sound waves and very weak shocks; denser jets remain shock-dominated. Solenoidal-shear heating dominates within the cocoon, whereas shocks and acoustic compressions dominate outside. Light-jet forward shocks weaken rapidly, while dense jets sustain strong bow shocks to large distances. These findings concern the simulated outbursts, rather than direct observations or a demonstrated outcome for cooling and star formation.

PublicJets launched by active galactic nuclei can heat the gas in galaxy clusters, potentially helping regulate its cooling and the formation of stars. This study uses computer simulations, not direct observations, to investigate how that heating happens. After testing a method for separating heating processes, the researchers simulate individual powerful jet outbursts with different densities. Lower-density jets make wider bubbles and push aside more gas near the cluster’s center; denser jets travel farther while disturbing the center less. Shock waves dominate heating at first. Later, lower-density jets mainly heat through turbulent motions, mixing, sound waves and very weak shocks, while denser jets continue heating mainly through shocks. The results describe these simulated outbursts, not every possible jet.

Young explorerSpace between galaxies contains gas. Scientists used a computer to study how powerful jets could warm it. In their pretend space world, lighter jets blew wider bubbles, while denser jets traveled farther. Both made strong waves that heated gas at first. Later, lighter jets warmed gas more by stirring and mixing it, while denser jets kept making strong waves.

Delayed Radio Flares in Neutrino-associated Blazars: The Case of TXS 0506+056

S. I. Stathopoulos, C. Yuan, G. Vasilopoulos+4 more

AstronomerTXS 0506+056 showed a GHz radio maximum 2–3 years after the 2017 IceCube-170922A/gamma-ray flare. The authors test whether this delay can arise as the compact neutrino/gamma-ray production region expands downstream and its synchrotron self-absorption decreases. Starting from the 2017 flare blob parameters, they use fully time-dependent LeHaMoC simulations and compare modeled 1.2–22 GHz light curves with RATAN-600 data, exploring continuous injection and parsec-scale energy re-dissipation. A simple expanding blob fails to reproduce the observations; an optically thin downstream particle-dissipation episode followed by jet deceleration successfully describes the radio evolution. In this modeling, leptonic synchrotron emission powers the radio flare, with little sensitivity to the proton population relevant to neutrino production. The interpretation is therefore that, in certain jet configurations, delayed radio flares mainly probe downstream dissipation and beaming rather than directly tracing radiation from the compact neutrino-production zone.

PublicThe object TXS 0506+056 reached its radio peak 2–3 years after a 2017 event involving a neutrino detection and a gamma-ray flare. Researchers tested whether the same small emitting region could explain the later radio flare as it expanded along the jet and became more transparent to radio waves. Their computer models were compared with radio observations. Expansion alone did not reproduce the data. A model with a later episode of energy release farther along the jet, followed by the jet slowing down, did describe the radio changes. In that model, the radio emission depends little on the protons involved in neutrino production. The results suggest that, for some jet arrangements, a delayed radio flare reveals later activity in the jet rather than directly revealing the original neutrino-producing region.

Young explorerA faraway object had a burst of gamma rays linked to a tiny particle called a neutrino. Its radio waves reached their biggest peak 2–3 years later. Scientists used computer models to ask why. Just letting the burst spread out did not match what they saw. A model with energy released farther along a stream of material, which then slowed down, worked better. So the later radio burst may tell us about a different part of the stream, not directly about where the neutrino came from.

Probing the 3D Structures of Supernovae through IR Signatures of CO and SiO

T. Mera, P. Hoeflich, C. R. Burns+12 more

AstronomerMOFAT is a new public-domain tool for fitting near- and mid-infrared molecular features in supernovae with observation-constrained, time-independent radiative-transfer simulations containing multidimensional clump-like structures. These structures are required in the modeling to reproduce fundamental-to-overtone band flux ratios, addressing limitations of one-zone models. Tests with CO and SiO constrain model parameters, but detecting small-scale structure requires optically thick bands. Applied to SN2024ggi at 285 and 385 days after explosion, the analysis infers that CO formation triggers SiO formation in the inner CO-rich region. The inner boundary of SiO emission shifts from 1500 to 1000 km/s, interpreted as continued SiO formation, while the inferred SiO mass declines by roughly an order of magnitude from about 0.002–0.006 solar masses, suggesting ongoing evaporation. SiO features indicate clumping, although most flux comes from optically thin regions. SiO cooling is negligible, and no evidence for dust formation is found. The authors also discuss observing strategies for linking molecular evolution to dust formation.

PublicThe researchers introduce MOFAT, a freely available tool that compares infrared observations of exploding stars with simulations to study where molecules form. Its models include clumps rather than treating the emitting material as a single uniform region. Applied to supernova SN2024ggi at two times after its explosion, the analysis suggests that carbon monoxide formation triggers silicon monoxide formation farther inside the carbon-monoxide-rich material. The changing emission points to continued silicon monoxide formation, yet the estimated total amount of that molecule drops substantially, suggesting evaporation is also occurring. Its infrared features indicate clumps, although most of its light escapes from regions that are relatively transparent. Silicon monoxide contributes negligibly to cooling in this analysis, and the researchers find no evidence of dust formation. They also discuss how future observations could follow the relationship between molecules and dust.

Young explorerAfter a star explodes, tiny groups of atoms called molecules can form in the material it leaves behind. Scientists made a new computer tool to compare the molecules’ invisible light with pretend explosions that include little clumps. For one exploded star, their work suggests that one kind of molecule helps another kind form. The second kind seems to keep forming in some places even while its total amount gets smaller, perhaps because some is breaking apart. The light gives clues that the material is clumpy. The scientists did not find signs that dust was forming.

Diocotron Modes in Pulsar Magnetospheres: Charge Diffusion and Implications for Radio Emission Variability

Matthew Goodbred, Anatoly Spitkovsky

AstronomerThree-dimensional particle-in-cell simulations of aligned and oblique pulsars investigate the diocotron instability, expected to arise generically in differentially rotating equatorial magnetospheric plasma. In the simulations, the instability grows on rotation-period timescales and develops a strong, stable m=1 mode: a rotating dipolar charge asymmetry in the equatorial disk. Stochastic variations in mode amplitude and pattern speed drive cross-field diffusion that can rapidly transport charge through the closed zone toward the light cylinder. Nonlinear electric-field perturbations can modulate the polar-cap potential drop and emission-beam angle. Connections to nulling, periodic amplitude modulation, and drifting subpulses are suggested possibilities, not established observational results.

PublicComputer simulations explore an instability in the charged material around pulsars, where different parts of an equatorial disk rotate at different rates. In the simulations, a strong, persistent, rotating imbalance of charge develops on a timescale comparable to one pulsar rotation. Random changes in this pattern can move charged particles across magnetic-field boundaries toward the light cylinder. The resulting changes in electric fields could alter the voltage near the pulsar’s polar cap and the direction of its emission beam. The researchers suggest this mechanism might help explain some changes in pulsar signals, including temporary pauses and shifting pulses, but the abstract does not establish that connection through observations.

Young explorerThe researchers used a computer to explore how tiny charged particles move around something that spins, called a pulsar. In their computer experiments, the particles made a lopsided pattern that turned around and helped move particles outward. This pattern could also change where the pulsar’s beam points. It might help explain why some pulsar signals change or pause, but the researchers have not shown that this is what happens in real pulsars.

Hyperaccreting Magnetised Neutron Stars inside Rotating Massive Envelopes: Low-Power Jets and Precursor Flares

Patrick Chi-Kit Cheong, Christopher L. Fryer, David Radice

AstronomerThis simulation study investigates whether rotation and magnetic feedback can delay the collapse of a neutron star undergoing hypercritical accretion inside a massive companion during common-envelope evolution. The authors use fully coupled, axisymmetric GRMHD simulations with energy-integrated two-moment neutrino transport and a 13-isotope nuclear reaction network, varying envelope rotation and neutron-star surface fields from approximately 5 × 10^10 to 5 × 10^13 G. In non-magnetised models, envelope rotation produces a centrifugal barrier and thick accretion disk, reducing the accretion rate and neutrino luminosity; the neutron star’s intrinsic spin has negligible global influence. In magnetised models, differential rotation amplifies the toroidal field through the Ω-effect and drives expanding magnetic towers. For initial surface fields above approximately 2.3 × 10^13 G, magnetic pressure can halt surface accretion and evacuate a low-density polar funnel. The authors conclude that this strongly magnetised engine delays prompt black-hole formation, but cannot supply enough energy to unbind the envelope. Low-power precursor jets reaching approximately 10^46 erg/s, observable X-ray flares, and a later black-hole-driven explosion remain possible outcomes rather than observational findings. The results are based on axisymmetric simulations.

PublicWhat happens when a massive star swallows a neutron star, the dense remnant of another star? Gas falling onto the neutron star could make it collapse into a black hole. This study uses computer simulations—not observations—to explore whether rotation and magnetic fields can slow that process. Rotating gas forms a thick disk that reduces how quickly matter reaches the neutron star. Strong magnetic fields can become amplified and, in some models, stop gas from reaching its surface while clearing a low-density channel near its poles. The researchers conclude that this magnetic protection can delay black-hole formation, but does not provide enough energy to blow away the surrounding stellar envelope. It might also produce relatively weak jets and detectable X-ray flares. A later explosion powered by a black hole is another possibility, not an established result. The simulations assume symmetry around a central axis.

Young explorerImagine a huge star swallowing a tiny, very heavy star called a neutron star. Scientists used a computer to see what might happen. Gas could pile onto the tiny star until it becomes a black hole. In their pretend stars, swirling gas and strong magnetic fields could slow or stop the gas from falling in, helping the tiny star last longer. There was not enough energy to blow away the big star’s outer layers. Small jets and X-ray flashes might happen, but this study did not see them in the sky.

Scaling Up: A Global Optical/X-ray Correlation For Reprocessing Across Black Hole Masses

Changhyun Cho, David M. Russell, Aaryan Sharma+9 more

• Astrophysics of Galaxies

AstronomerThe study tests whether the optical/X-ray scaling associated with thermal reprocessing in black hole low-mass X-ray binaries extends to AGN. Using quasi-simultaneous optical and X-ray flux data, it adopts reverberation-mapping optical/X-ray lags as a proxy for the reprocessing radius, a_R, to compare the two populations. The reported global relation is log L_V = 0.48 log L_X + 0.96 log a_R + 6.5, with approximately 0.20 dex scatter, reduced to 0.18 dex by a disk-inclination correction involving cos i. The fitted exponents are close to the XRB expectation L_V ∝ L_X^0.5 a. The correlation suggests, rather than establishes, scale-invariant X-ray reprocessing from stellar-mass to supermassive black holes and provides constraints on models of their X-ray-emitting regions.

PublicResearchers compared visible light and X-rays from disks of material around both stellar-mass and supermassive black holes. They used the delay between changes in X-rays and visible light to estimate the size of the disk region that absorbs high-energy light and re-emits it as visible light. Across their sample, visible brightness followed a tight relationship with X-ray brightness and this estimated size. Accounting for the disk's viewing angle made the relationship slightly tighter. The findings suggest that the same light-reprocessing process operates around black holes of very different masses, although the correlation alone does not prove that interpretation.

Young explorerBlack holes can have disks of stuff around them that shine. Scientists compared X-rays and light we can see from disks around small and very big black holes. They used how long the visible light took to respond to X-rays as a clue to the size of the glowing part. They found a shared pattern: the visible light was linked to both the X-rays and that size. This suggests that X-rays may warm the disks and make them shine in a similar way around both small and big black holes.

Any colour you like: The diverse chromaticities of white dwarfs

Mark A. Hollands, Boris T. Gaensicke, Pier-Emmanuel Tremblay+1 more

• Instrumentation and Methods for Astrophysics

AstronomerThe study investigates white dwarf chromaticity as a function of temperature and atmospheric composition. Most white dwarfs have colours similar to blackbodies, but in ultra-dense atmospheres, reaching about 1 g/cm3 in the coolest known objects, metals such as carbon, calcium, or sodium can produce extremely broadened atomic and molecular opacities and substantial departures from blackbody optical spectra. The authors demonstrate that some known white dwarfs would appear yellow, green, cyan, pink, or purple if viewed close enough to resolve their stellar discs; these are inferred appearances, not reports of close-up visual observations. The volume-limited local 20 pc sample has a median correlated colour temperature of approximately 6800 K, supporting the conclusion that white dwarfs are white on average. The study also shows how spectral models can generate colour-accurate images of their predicted close-up appearance.

PublicWhite dwarfs are usually white, but their atmospheres can give some of them surprising colours. This study finds that most have colours close to those expected from their temperature alone. In some very dense atmospheres, however, elements such as carbon, calcium, or sodium change the light strongly enough that known stars would look yellow, green, cyan, pink, or purple from close enough to see their round faces. These colours describe their inferred close-up appearance, not what someone has directly seen from nearby. A study of white dwarfs within 20 parsecs finds a median colour temperature of about 6800 kelvin, supporting the idea that they are white on average. The researchers also show how models of their light can make images representing these close-up colours.

Young explorerStars called white dwarfs usually look white, but some could look yellow, green, blue-green, pink, or purple! The thick gas around some of these stars changes their light and can give them unusual colours. Scientists worked out how known stars would look if we could get close enough to see them as round balls instead of tiny dots. Nobody went close to look. The scientists also showed how computer models can make pictures of those colours.

JWST observations of 47 Tucanae: I. The low-mass main sequence down to the hydrogen-burning limit

M. Scalco, R. Gerasimov, L. R. Bedin+4 more

• Astrophysics of Galaxies

AstronomerCombining new and earlier JWST/NIRCam observations of 47 Tuc over roughly three years, the authors derive high-precision proper motions and select cluster members down to F444W ≈ 24.25 mag, corresponding to an estimated 0.077 solar masses, slightly above the cluster’s estimated hydrogen-burning limit of 0.074 solar masses. The previously identified low-mass main-sequence kink is not significantly detected in F090W–F444W photometry, consistent with, but not establishing, its proposed origin in a transition toward methane-dominated carbon chemistry. Isochrone comparisons suggest that oxygen-poor stars dominate near the bottom of the main sequence. Artificial-star tests show that proper-motion membership requirements substantially reduce faint-end completeness; the current observations cannot reliably trace the brown dwarf cooling sequence. The mass function has a break near 0.15 solar masses, not associated with the onset of convection, and mild systematic radial variation consistent with mass segregation. Its shape is more complex than a simple power law; an unrecognised formation or dynamical mechanism is suggested as a possible explanation, not demonstrated.

PublicUsing JWST images taken roughly three years apart, astronomers measured the motions of stars in the globular cluster 47 Tucanae to distinguish cluster members from other objects. Their sample reaches stars with estimated masses just above the minimum needed to sustain hydrogen burning. A bend previously seen among the faintest main-sequence stars was not significantly detected with the filters used here, which is consistent with a proposed explanation involving changes in carbon chemistry. Comparisons with theoretical models also suggest that stars near the bottom of the main sequence are mostly oxygen-poor. Tests show that requiring motion measurements makes the faintest objects harder to include, so these observations are not deep enough to reliably map the cluster’s brown dwarf cooling sequence. The distribution of stellar masses changes character near 0.15 times the Sun’s mass and varies slightly with distance from the cluster’s centre, consistent with stars becoming sorted by mass. The authors suggest that the complicated mass distribution could reflect an as-yet unrecognised process in how low-mass stars form or evolve within clusters.

Young explorerAstronomers used pictures from the Webb telescope to watch tiny movements of stars in a big group called 47 Tucanae. This helped them tell which stars belong to the group, even some very small, faint ones. They counted stars of different masses and found that the pattern was not as simple as expected. They do not yet know exactly why. They also checked for a bend seen before in a picture chart of the stars, but it did not clearly show up with these kinds of pictures. The pictures are still not good enough to reliably follow the group’s brown dwarfs—objects too small to shine by burning hydrogen the way stars do.

The mass functions of multiple stellar populations in 47 Tucanae

M. Scalco, J. Bruce, E. Vesperini+1 more

• Astrophysics of Galaxies

AstronomerCombined JWST and HST observations were used to measure separate present-day mass functions for the first and second stellar populations in 47 Tucanae (NGC 104) across a wide mass interval. The lower-main-sequence populations were identified using JWST photometry alone, with colour combinations sensitive to oxygen-abundance variations. At low masses, the first population has a significantly steeper mass function than the second, whose mass function appears nearly flat. In the authors’ dynamical model, reproducing this behaviour requires different initial mass functions for the two populations over 0.1–0.4 solar masses. This birth-mass difference is a model-based inference, rather than a direct observation, and provides a constraint on multiple-population star formation in globular clusters.

PublicUsing the James Webb and Hubble space telescopes, researchers studied how stars of different masses are distributed between two stellar populations in the globular cluster 47 Tucanae. Webb measurements sensitive to differences in oxygen abundance helped distinguish the populations among low-mass stars. The observations show that the first population’s star counts change more steeply with mass than the second population’s, which appear nearly flat. A model of the cluster’s dynamical evolution indicates that reproducing this pattern requires the populations to have started with different distributions of stellar masses between 0.1 and 0.4 times the Sun’s mass. That conclusion depends on the model and offers a new clue to how these populations formed.

Young explorerScientists used two space telescopes to study a big bunch of stars called 47 Tucanae. They sorted small stars into two groups and found different patterns in how many stars each group has at different masses. A model suggests the groups needed different mixes of small stars when they formed. That is a clue from the model, not something the telescopes watched happen.

First L-type substellar object discovered in the vicinity of the embedded cluster NGC 2023

Styliani Tsilia, Carlos Dominguez-Tagle, Maruša Žerjal+8 more

AstronomerThe authors report J054158.70-021031.4 as the first substellar object in a star-forming region spectroscopically confirmed with Euclid. Selected photometrically in Euclid Early Release Observations and examined using slitless 2D spectro-images, the young source has spectral type L3, extinction Av = 3 mag, and a Euclid optical magnitude of approximately 24.5. It lies near the embedded open cluster NGC 2023, while its proper motion is consistent with the nearby cluster NGC 2024; this does not establish cluster membership. At an adopted distance of 403 pc, its inferred mass is close to the planetary-mass boundary. The discovery demonstrates Euclid's potential to reveal very low-mass populations in obscured star-forming regions.

PublicAstronomers report the first spectroscopic confirmation with Euclid of an object below stellar mass in a region where stars are forming. The young, faint object, J054158.70-021031.4, was found by screening Euclid images and then examining its spectrum. It lies near the star cluster NGC 2023, and its motion across the sky is consistent with that of the nearby cluster NGC 2024, though membership is not established. Using a distance of 403 parsecs, the researchers infer a mass near the boundary associated with planetary masses, rather than definitively identifying it as a planet. The finding highlights Euclid's ability to uncover faint, very low-mass objects in dusty stellar nurseries.

Young explorerAstronomers used a space telescope called Euclid to find a very faint, young object in a place where stars are being born. They studied its light to check that it is an object with less mass than a star. Their estimate puts its mass near the dividing line for planet-sized masses, but that does not mean they know it is a planet. This discovery shows that Euclid can help find tiny, faint neighbors hidden in dusty places.

SPICY 30021: an embedded bona fide FUor with a mid-infrared precursor

Zhen Guo, Calum Morris, Vitor Fermiano+37 more

AstronomerMulti-wavelength photometry and outburst spectroscopy confirm SPICY 30021, discovered in the NEOWISE mid-infrared time series, as a bona fide, optically obscured FUor. The observations separate the source from nearby companions and show a spectrum closely resembling classical FUors. The inferred total interstellar and circumstellar extinction is Av = 12.5 mag; multiple methods give a distance of approximately 1.7 ± 0.4 kpc. Its accretion luminosity of 32 solar luminosities is moderate among FUors. Quiescent near-infrared photometry is consistent with a young, 0.9-solar-mass progenitor, but this mass estimate depends on the adopted evolutionary model and distance. A mid-infrared precursor suggests, rather than establishes, an outside-in outburst trigger.

PublicAstronomers have confirmed that the dust-obscured young star SPICY 30021 is undergoing a FUor event, one of the strongest and longest-lasting types of outbursts associated with a young star gathering material. The eruption was discovered in infrared monitoring, and follow-up observations showed a spectrum closely matching those of established FUors. The star is estimated to lie about 1.7 kiloparsecs away, with an uncertainty of 0.4 kiloparsecs. Its light from infalling material amounts to about 32 times the Sun’s luminosity, moderate for this kind of outburst. Before the eruption, its infrared brightness was consistent with a young star of roughly 0.9 times the Sun’s mass, although that estimate depends on models and distance. An earlier mid-infrared signal hints that the eruption was triggered farther out and progressed inward, but does not prove this explanation.

Young explorerA young star called SPICY 30021 is hidden behind lots of dust. Scientists used infrared light to spot it getting much brighter and confirmed that it has a special kind of big outburst as it gathers more material. They also saw an earlier infrared hint that the change might have started farther from the star and moved inward. That is a possible explanation, not something they know for sure.

Velocity-field estimation techniques for on-disk solar coronal bright fronts (CBFs) and shock-wave propagation

Oleg Stepanyuk, Kamen Kozarev

AstronomerThe study discusses practical parameter settings for Lucas–Kanade, Horn–Schunck, FLCT, and Farneback velocity-field algorithms, combining analytic reasoning with empirical measurements from a single event. It demonstrates their potential for tracking on-disk coronal shock-wave propagation during the X1.5-class event of 10 May 2022, processed using the wavelet-based Wavetrack technique. Spatially resolved velocity maps can characterize variations in front speed and possible deformation beyond an overall propagation speed. Such information is relevant to SEP forecasting. However, the abstract does not establish improved forecast accuracy or parameter generalizability across events; better automated pipeline performance remains a prospective benefit.

PublicLarge eruptions from the Sun can drive shock waves, and understanding their motion matters for forecasting energetic particles reaching Earth. This study explores image-analysis methods that map how different parts of a bright front move, rather than assigning the whole front one speed. The researchers discuss settings for four methods, using mathematical reasoning and measurements from one solar event on 10 May 2022. Their demonstration suggests these tools could help track expanding shock fronts and improve automated analysis. The study is limited to one event, and the abstract does not report a demonstrated improvement in particle forecasts.

Young explorerThe Sun sometimes sends out huge bursts that push waves ahead of them. Scientists tried computer tools on pictures of one Sun event to help track how the waves move. These tools could help show which parts move faster. They might help with predictions, but this study does not show that the predictions got better.

Understanding the Complex Morphology of a Coronal Mass Ejection. III: How to Create a Severe Geomagnetic Storm

Cecilia Mac Cormack, Abril Sahade, Erika Palmerio+4 more

AstronomerThe April 21, 2023 filament eruption launched an Earth-directed CME that triggered the first severe geomagnetic storm of solar cycle 25. To investigate its geoeffectiveness, the authors use the thermodynamic MHD model CORHEL-CME, representing the pre-eruptive structure as two intertwined magnetic flux ropes. They test the modeled early evolution against extreme-ultraviolet and white-light observations through synthetic observables, then compare the simulated CME with in situ measurements. From this model-data analysis, they infer that the CME merged with a stream interaction region before reaching Earth. They attribute storm initiation to compression of the CME sheath, which produced sustained negative B_n alongside enhanced solar wind density and velocity, and infer that a sustained southward field within the flux rope intensified the storm to severe levels. The study illustrates the diagnostic value of observation-validated MHD modeling; it does not report a demonstrated improvement in forecast performance.

PublicA solar eruption on April 21, 2023 sent a cloud of magnetized material toward Earth, triggering the first severe geomagnetic storm of the Sun’s current activity cycle. Researchers investigated why it had such a strong effect by comparing a computer simulation with telescope observations and measurements taken within the passing material. Their analysis suggests that the cloud merged with a region where solar wind streams interact before reaching Earth. They conclude that this encounter squeezed the cloud’s outer sheath, sustaining a southward magnetic component while increasing the solar wind’s density and speed. These conditions triggered the storm, while a persistent southward magnetic field inside the cloud made it severe. This explanation comes from combining modeling with observations, rather than directly observing every stage of the interaction.

Young explorerThe Sun sent a big cloud of material with magnetic fields toward Earth, and it caused a strong storm in Earth’s magnetic field. Scientists used a computer model and real observations to work out why. They think the cloud met a place where winds from the Sun interact, squeezing the cloud’s outer layer. The squeezed layer helped start the storm, and the way the magnetic field pointed inside the cloud made the storm stronger. The model helps explain what happened, but scientists did not watch every part of it directly.

A Distinct Type of Standstill in Ultra-Compact White Dwarf Binaries

Jan Kára, Liliana Rivera Sandoval, Iwona Kotko+3 more

• High Energy Astrophysical Phenomena

AstronomerThe study analyses post-superoutburst behaviour in three AM CVn-type systems, ultra-compact, semi-detached binaries with white dwarf primaries and hydrogen-poor secondaries. In MGAB-V270, superoutbursts are followed by echo-outburst series that evolve into standstill-like phases before a return to quiescence. ZTF18aaxuusk shows similar activity, with one echo-outburst series developing into a standstill-like phase. ASASSN-19ct exhibits comparable echo outbursts but no standstill-like phases. Periodicity analysis of TESS data shows that superhumps can persist during both echo outbursts and standstill-like phases. Although standstills have previously been observed in AM CVn stars, the authors interpret these phases as apparently distinct phenomena associated with post-superoutburst activity. They also compare the findings with other AM CVn systems that may show similar behaviour.

PublicResearchers studied three tightly orbiting pairs of stars called AM CVn systems, each containing a white dwarf and a companion poor in hydrogen. After major brightenings called superoutbursts, these systems show smaller repeat brightenings, or echo outbursts. In MGAB-V270, these echoes develop into a relatively steady phase before the system becomes quiet again. One echo sequence in ZTF18aaxuusk also develops into such a phase, while ASASSN-19ct shows echoes but no comparable steady phase. TESS observations reveal that repeating brightness patterns called superhumps can continue during both the echoes and the steady phases. The researchers suggest that these steady phases differ from previously observed standstills because they are associated with activity following superoutbursts.

Young explorerScientists watched three very close pairs of stars. After a big burst of light, the pairs had smaller bursts, like echoes. In two pairs, some echoes led to a time when the light stayed more steady. The third pair had echoes but no such steady time. The scientists think these steady times may be different from ones seen before.

Chandra-JWST Probing the Effects of Moderate X-Ray Superflares on Protoplanetary Disks

Konstantin V. Getman, Kevin L. Luhman, Bayron Portilla-Revelo+17 more

• Earth and Planetary Astrophysics
• High Energy Physics - Phenomenology

AstronomerThis pilot Chandra-JWST/NIRSpec study compares two-epoch infrared spectra of 10 X-ray-flaring and 12 matched non-flaring disk-bearing pre-main-sequence stars in Orion, drawn from 84 observed targets. Six Chandra/ACIS-I observations and three NIRSpec-MOS visits probe narrow 2.8–4.3 micron features, HI Br-alpha, and the CO fundamental band. The flaring sample shows tentative evidence for relatively fewer variable narrow features at longer wavelengths than the controls. Feature incidence decreases strongly with projected distance from Theta1 Ori C, and most classifiable features are in absorption. The authors interpret these properties as suggesting that some features originate in externally irradiated disk atmospheres and/or photoevaporative flows; apparent variability could reflect spatial sampling of structured material rather than temporal changes. Br-alpha shows systematically stronger variability in flare stars, which alone exhibit absorption-core profiles, suggesting a role for magnetospheric accretion and stellar magnetic processes rather than disk irradiation. No significant flare-associated CO variability is detected, consistent with models predicting weak responses to moderate X-ray superflares. Larger coordinated monitoring samples, including rare X-ray mega-flares, are proposed rather than demonstrated.

PublicResearchers used Chandra and the James Webb Space Telescope to investigate whether X-ray flares from young stars are associated with changes in the infrared light from their planet-forming surroundings in the Orion Nebula. They compared spectra taken at two times for 10 flaring stars and 12 similar non-flaring stars. A hydrogen feature varied more strongly in the flaring group, and only those stars showed profiles with an absorption dip at the center. The researchers suggest that this behavior is linked to gas falling onto the stars and their magnetic activity, rather than radiation affecting the disks. Other narrow features showed only tentative differences between the groups. Their connection to a nearby powerful star suggests that some may come from disk surfaces or escaping gas illuminated by that star; apparent changes could result from sampling different patches rather than material changing over time. Carbon monoxide showed no significant flare-related variation, in line with models predicting a weak response to moderate X-ray superflares. This small initial study motivates further monitoring, especially of rarer, more extreme flares.

Young explorerYoung stars can have big bursts of X-ray light. Scientists looked at stars with disks of material where planets can form, comparing stars that had bursts with similar stars that did not. They found that one clue in the light from hydrogen changed more around the bursting stars. They think this might be connected to the stars’ magnetism and gas falling onto them. Some other clues might only look different because the telescopes saw different patches of gas, not because a burst changed the gas. They did not find a clear burst-related change in the light from carbon monoxide. They need to watch more stars and bigger bursts to learn what happens.

Tracing Accretion and Inner-Disk Gas Evolution in the Orion Nebula via Br-alpha and CO

Konstantin V. Getman, Maria Claudia Ramirez-Tannus, Jenny Frediani+17 more

• Astrophysics of Galaxies

AstronomerA systematic JWST/NIRSpec-MOS study of 0.2–1.5 solar-mass pre-main-sequence stars in Orion uses 73 hydrogen Br-alpha and 46 CO fundamental-band spectra, with censored correlation and regression analyses accounting for multiple testing. Br-alpha luminosity correlates strongly with accretion luminosity, including after excluding sources within 2 arcminutes of Theta1 Ori C, whose irradiation may bias proplyd accretion estimates. This supports Br-alpha as an empirical accretion tracer. Br-alpha also correlates with visual extinction and, more weakly, stellar bolometric luminosity and mass. CO luminosity correlates with accretion luminosity and extinction, including in a larger combined NIRSpec+MIRI sample across multiple star-forming regions, but shows no significant dependence on basic stellar properties. The authors interpret this as evidence that accretion and local disk conditions primarily govern warm molecular emission. Weaker correlations involving the Spitzer/IRAC spectral slope suggest, but do not establish, that warm inner-disk gas evolves or disperses faster than optically thick dust. Declining CO emission with disk evolution remains tentative; accretion-powered thermal and ultraviolet excitation and inherited differences in emitting area may contribute.

PublicInfrared spectra from the James Webb Space Telescope reveal links between warm gas and the growth of young stars in the Orion Nebula. The study analyzed 73 hydrogen spectra and 46 carbon monoxide spectra. Brighter hydrogen emission is strongly associated with higher estimated rates of material falling onto the stars, supporting its use as a way to track this growth. The relationship remains after excluding stars near Orion’s main ionizing star, whose radiation could bias some growth estimates. Carbon monoxide emission also increases with the energy released by infalling material and with the amount of obscuring dust, a pattern that persists in a larger sample covering several star-forming regions. Unlike hydrogen emission, carbon monoxide emission has no significant link to basic stellar properties such as mass. The authors suggest that warm gas in the inner disks around these stars may fade or disappear faster than thick dust does, but this interpretation is tentative. Heating associated with material falling inward and differences in the size of the emitting regions could also influence the results.

Young explorerYoung stars grow by taking in material from disks around them. Researchers used the James Webb Space Telescope to study light from warm gas near young stars in the Orion Nebula. Stars estimated to be taking in more material tended to have brighter hydrogen and carbon monoxide light. The hydrogen light looks especially useful for spotting stars that are growing. The researchers also think warm gas might fade away sooner than the thick dust in the disks, but they are not sure yet.

Twisted Pseudodisk and Asymmetric Mass Accretion on the Circumstellar Disk II: Parameter Survey

Masahiro N. Machida, Shingo Hirano, Shantanu Basu

• Astrophysics of Galaxies

AstronomerThree-dimensional magnetohydrodynamic simulations including ohmic dissipation follow infalling-envelope evolution for approximately 100,000 years after protostar formation, varying the initial rotation–magnetic-field misalignment from 0 to 90 degrees. Every misaligned model develops a distorted pseudodisk and discrete, asymmetric accretion streams. Protostellar outflows coexist with strongly interwoven inflow regions; anisotropic angular-momentum transport by outflows leads to evolving disk orientations and outflow directions, further enhancing envelope asymmetry. Stream–field orientations exhibit statistical tendencies but cannot be classified uniquely as parallel or perpendicular, especially for strong misalignment. Most infalling gas moves at nearly free-fall velocity, with only a minor fraction substantially slowed within the pseudodisk. Asymmetric accretion and stream-like structures persist beyond 10,000 au. These simulation results demonstrate that magnetized core evolution can intrinsically generate large-scale asymmetry without initial turbulence or external gas accretion; they are not observational measurements.

PublicComputer simulations explore how gas falls toward a newly forming star over roughly 100,000 years. The researchers varied the angle between the gas cloud’s spin axis and its magnetic field. Whenever these directions were initially misaligned, the surrounding gas developed a complex, uneven shape and fed the star’s disk through separate streams rather than flowing inward evenly. Outward flows still formed and intertwined with the incoming gas. By carrying away rotational motion unevenly, these outflows changed the disk’s orientation and their own direction over time. The incoming streams did not consistently follow or cross the magnetic field, especially when the initial misalignment was large. Most infalling gas moved nearly as fast as it would in free fall, and uneven streams extended beyond 10,000 times the Earth–Sun distance. The simulations show that such patterns can arise without initial turbulent motions or extra gas arriving from outside; this study does not report direct observations of these effects.

Young explorerScientists used computers to imagine gas falling toward a baby star. They tried pointing the gas cloud’s spin and its magnetic field in different directions. When those directions did not match, the gas came in twisty, uneven streams instead of falling in evenly all around. Some gas also flowed outward, and the disk around the star changed which way it pointed. Most of the falling gas was hardly slowed down. In these computer experiments, the messy streams could form even without starting with jumbled gas motions or adding gas from outside. These are computer results, not things the scientists watched happen to a real star.

Transients and Stellar Activity as Revealed by Ultraviolet Diagnostic Tracers

Richard de Grijs, Martin A. Barstow, Deepak Chahal+5 more

• Astrophysics of Galaxies

AstronomerThis review surveys UV diagnostics of transient and variable phenomena from solar and stellar activity to supernovae and star-forming galaxies, placing them in the historical context of UV missions. It emphasizes Mg II h and k, C II, Si IV, C IV and N V resonance lines as probes of chromospheric and transition-region conditions, magnetic heating, shocks and mass loss. Topics include stellar flares, pre-main-sequence activity, rotation–activity correlations and their relevance to exoplanet irradiation and habitability; supernova shock breakout and early emission; and far-UV mapping of young populations and hierarchical star formation in the Magellanic Clouds. This is a synthesis rather than a report of new measurements. Instrument availability and observing cadence remain limitations; the anticipated gains from forthcoming missions are prospective.

PublicUltraviolet light helps astronomers investigate changing events that range from activity on the Sun and other stars to exploding stars and the formation of new stars in galaxies. This review explains how features in ultraviolet spectra reveal physical conditions, heating, shocks and material escaping from stars. It also discusses how stellar activity relates to the radiation reaching planets, how ultraviolet observations probe the earliest stages of supernova explosions, and how they map young stars in the Magellanic Clouds. The article brings together existing work rather than presenting a new discovery. Limited access to ultraviolet instruments and gaps between observations still make fast events difficult to follow; future missions are expected to improve that coverage.

Young explorerSpace can change very quickly: stars can flare, and some stars explode. A kind of light our eyes cannot see, called ultraviolet light, helps astronomers learn about these changes and find groups of young stars. This article explains what scientists have learned using that light. They cannot always look often enough to catch fast changes, so they hope future space telescopes will help.

Magnetic Reconnection Governs the Entire Lifecycle of Solar Eruptive Magnetic Flux Rope

Xinkai Bian, Chaowei Jiang, Qingjun Liu+3 more

• Plasma Physics
• Space Physics

AstronomerHigh-resolution three-dimensional MHD simulations investigate an erupting magnetic flux rope formed self-consistently by flux cancellation driven by converging motions and photospheric diffusion after an initial shearing phase. The rope remains quasi-static even after reaching a height where the decay index exceeds the classical torus-instability threshold. Eruption begins only when the underlying current sheet thins sufficiently for reconnection. Higher numerical resolution delays onset while leaving the onset decay index nearly unchanged, supporting reconnection, rather than torus instability, as the trigger in this simulated system. Reconnection subsequently converts surrounding sheared arcades into twisted flux that joins the erupting rope. A component-resolved analysis of Lorentz-force work attributes the predominant contribution during the main acceleration phase to this newly reconnected flux. These simulation results support a central role for reconnection in rope formation, eruption onset, and acceleration; they do not establish that this mechanism governs all solar eruptions.

PublicWhat starts a solar eruption remains debated. In three-dimensional computer simulations, researchers followed a twisted bundle of magnetic field as it formed and rose slowly. It passed a threshold commonly associated with an instability thought to trigger eruptions, but still did not erupt. Instead, eruption began when a thin layer beneath the bundle allowed magnetic field lines to reconnect, changing their connections. Increasing the simulation's resolution delayed the eruption, supporting reconnection as the trigger in this model. As the eruption continued, reconnection added more twisted magnetic field to the bundle, and the researchers' analysis indicated that this added field supplied most of the driving during the main acceleration stage. The findings give reconnection a leading role in this simulated eruption, rather than merely a supporting one, but do not show that every solar eruption works this way.

Young explorerScientists used a computer to study how a twisted bundle of the Sun's magnetic field might burst upward. In their model, the bundle rose slowly and did not burst when one usual rule suggested it might. It burst only when magnetic lines underneath changed how they were joined. More lines then joined the bundle and helped push it faster. This is what happened in the computer model; it does not mean every burst on the Sun happens this way.

Post-merger rotational evolution of magnetised single hot subdwarfs results in slow rotation due to magnetic braking

Facundo D. Moyano, Zhengwei Liu, Zhanwen Han+3 more

AstronomerHelium-core white dwarf mergers are a proposed formation channel for single hot subdwarfs, but their inherited orbital angular momentum poses a challenge to explaining the slow rotation observed in these stars. Motivated by recent detections of 200–500 kilogauss surface magnetic fields in hot subdwarfs, this study uses rotating stellar evolution models to investigate magnetic braking. The models find that stable, large-scale fields can efficiently remove angular momentum through coupling to stellar winds, producing slowly rotating hot subdwarfs. This offers a possible explanation for both long asteroseismic rotation periods and low spectroscopic rotational velocities, and suggests magnetic braking may influence the rotational evolution of low-mass stellar merger products.

PublicSome single hot subdwarfs are thought to form when two white dwarf stars with helium cores merge. Such a merger could leave the resulting star spinning rapidly, yet observations show slow rotation that earlier models struggled to explain. Prompted by detections of strong surface magnetic fields in hot subdwarfs, researchers modeled how magnetism could change their spin. Their models show that stable, large-scale magnetic fields can help stellar winds carry away spin, slowing the stars down. This is a possible explanation for the observed slow rotation, rather than direct evidence that magnetic braking caused it.

Young explorerWhen two small stars join together, the new star might spin fast. But astronomers see stars of this kind spinning slowly. The researchers used computer models to try an idea: a strong magnetic field could help wind blowing away from a star slow its spinning. The models show this could work, but they do not prove that this is what slowed the real stars.

Evidence for Suppressed Non-thermal Broadening in a Flare Ribbon from Stereoscopic Observations

Ziwen Huang, L. P. Chitta, L. Teriaca

AstronomerCoordinated SDO, IRIS, and Solar Orbiter observations of a remote flare ribbon near a sunspot during the M7.7 flare of 30 September 2024 reveal atypical small-scale downflow signatures. Stereoscopic imaging resolves motions on 200 km scales, with apparent speeds of 85–130 km/s in Solar Orbiter’s limb view and plane-of-sky speeds of 70–85 km/s in IRIS’s disk view. Despite these rapid apparent motions, Si IV profiles at the brightest ribbon pixels are well approximated by single Gaussians, with minimal Doppler shifts and non-thermal widths of only 10 km/s. Peak Si IV emission coincides with a deeper Mg II central reversal, and electron densities exceed typical quiet-Sun values by one to two orders of magnitude. These findings differ from the strong line-of-sight flows and enhanced non-thermal broadening commonly associated with flare ribbons. They are consistent with, but do not establish, plasma flowing along nearly horizontal chromospheric canopy fields without strong turbulence or wave motions. The study highlights magnetic geometry as a potentially important influence on ribbon energy deposition and lower-atmospheric response.

PublicBright ribbons in solar flares mark the bases of newly reconnected magnetic loops, but how energy reaches them remains uncertain. Observations of a ribbon near a sunspot showed small features apparently moving downward rapidly. Yet the light from its brightest patches showed little motion toward or away from the observer and unusually little extra spectral broadening, unlike many flare ribbons. The plasma was also much denser than in the quiet Sun. The researchers interpret these findings as consistent with plasma moving along nearly horizontal magnetic fields without strong turbulence or wave motions. This is a possible explanation, not a demonstrated mechanism, and suggests that magnetic-field direction helps shape how the Sun’s lower atmosphere responds to flares.

Young explorerScientists watched a bright ribbon on the Sun during a flare. Tiny patches looked like they were moving down fast, but their light did not show much rushing toward or away from us, or much extra stirring. The scientists think the Sun’s magnetic fields might guide the hot gas along nearly sideways paths. That idea fits what they saw, but it is not proved.

High-Frequency Transverse Waves in Chromospheric Fibrils Revealed by DKIST

Qifan Dong, Xiaoli Yan, Zhike Xue+4 more

AstronomerHigh-resolution DKIST/VBI observations of Hα fibrils in quiet-Sun and active regions reveal prevalent high-frequency, small-amplitude transverse oscillations across different magnetic environments. Reported typical periods are 56 ± 49 s, displacement amplitudes 37 ± 25 km, velocity amplitudes 6 ± 4 km/s, and phase velocities 21 ± 13 km/s. The oscillation characteristics are consistent with Alfvénic kink-mode waves. Assuming typical chromospheric conditions, the estimated wave energy flux is 20–200 W/m². These observations constrain the waves’ possible contribution to chromospheric and coronal heating, rather than establish how much heating they provide.

PublicSharp images from the Daniel K. Inouye Solar Telescope show that thin structures called fibrils in the Sun’s chromosphere frequently sway sideways, both in quiet areas and in active regions. The measured oscillations typically have periods of 56 ± 49 seconds and displacement amplitudes of 37 ± 25 kilometres. Their behavior is consistent with a type of magnetic wave called an Alfvénic kink wave. Using assumed typical conditions in the chromosphere, the researchers estimate that these waves carry an energy flux of 20–200 watts per square metre. The findings help constrain how these waves might contribute to heating the Sun’s atmosphere, but do not establish how much heat they actually supply.

Young explorerA powerful telescope saw thin strands in the Sun’s atmosphere wiggle from side to side. These little wiggles were common in both quiet and active parts of the Sun. They look like waves that could carry energy along the strands. That energy might help heat the Sun’s atmosphere, but the pictures do not show how much heating the wiggles do.

Nova shells in 3D: I. A catalog of integral field spectroscopic observations

Janis B. Rodríguez-González, Edgar Santamaría, Martin A. Guerrero+1 more

• Astrophysics of Galaxies

AstronomerThe authors present the first integral-field-spectroscopy-based 3D catalog of nova shells, compiling observations of 19 shells from MUSE at the VLT, complemented by new MEGARA/GTC and WEAVE/WHT observations. Selected emission-line visualizations reveal ellipsoidal or spherical shells, rings, bipolar features, and clumpy or irregular components, including structures obscured in 2D projections. Approximately 60% of the sample is predominantly ellipsoidal or spherical, while about 30% exhibits ring-like or bipolar structures. In several shells, [O III] or [N II] traces kinematic components distinct from Hα, highlighting varied excitation mechanisms and physical conditions within the ejecta. Integral field spectroscopy reveals a larger fraction of bipolar or toroidal shells than imaging studies. Comparing sky-plane and line-of-sight expansion velocities suggests low intrinsic aspect ratios, consistent with projected-shape estimates; the intrinsic 3D structures nevertheless remain poorly constrained overall.

PublicNova eruptions on white dwarf stars throw material into space, creating expanding shells. Researchers assembled observations of 19 such shells into what they describe as the first three-dimensional catalog based on a technique that records spectra across each shell. These reconstructions reveal shapes that ordinary flat images can hide: roughly 60% of the sample is mainly spherical or oval, while about 30% has rings or two-lobed structures. Some shells also contain clumps or irregular features. Light emitted by different elements sometimes traces material with different shapes and motions, pointing to varied physical conditions within a single shell. The technique reveals a larger share of two-lobed or doughnut-shaped shells than imaging studies do. Comparing expansion motions toward or away from us with motions across the sky suggests that the shells have relatively modest differences between their intrinsic dimensions, although their true three-dimensional shapes remain difficult to establish.

Young explorerWhen a small star called a white dwarf has a nova eruption, it throws stuff into space like an expanding bubble. Scientists studied 19 of these bubbles and used their light to make three-dimensional pictures. Many looked round or oval, while some had rings, two big lobes, or little clumps. A flat picture can hide these shapes. Different kinds of light sometimes showed different parts moving differently. The new pictures help scientists see more, but figuring out the bubbles’ true shapes is still tricky.

Stationary Resistive MHD Solutions Near an Isolated Three-Dimensional Magnetic Null

Kuljeet Singh Saddal, Dieter H. Nickeler, Rodrigo Meneses Pacheco+1 more

• High Energy Astrophysical Phenomena
• Plasma Physics
• Space Physics

AstronomerThis theoretical study constructs stationary, resistive, incompressible 3D MHD solutions near an isolated magnetic null colocated with a velocity stagnation point, using first-order local expansions of both fields. Each magnetic-null configuration admits a two-parameter solution family with multiple velocity-topology branches, including positive-radial, negative-radial, and spiral stagnation flows. Velocity-null polarity can change at bifurcations where the flow becomes effectively 2.5D. Pressure and resistivity are determined self-consistently and vary with flow topology. Magnetic and velocity separatrices need not coincide, permitting flow across the magnetic fan and yielding a local reconnective flow. Within this local model, nonuniform resistivity allows the same magnetic topology to support different stationary flow, pressure, and resistivity structures. Previously identified constant-resistivity solutions are recovered as special cases; these are analytical findings, not observations.

PublicA magnetic null is a point where the magnetic field vanishes. Such points occur in magnetic environments around stars and planets and are often associated with magnetic reconnection. This theoretical study examines steady plasma motion close to a magnetic null, assuming that the plasma also comes to rest at that point. The equations allow several different flow patterns around the same magnetic configuration, with different inward, outward, and swirling motions. Pressure and electrical resistivity—the plasma’s resistance to electric current—change together with those patterns rather than being set independently. The solutions also allow plasma to cross a magnetic boundary, providing a local flow associated with reconnection. The result is a mathematical finding within a local model: when resistivity varies, knowing the magnetic pattern alone is not enough to determine the surrounding flow and pressure.

Young explorerImagine a tiny spot in hot space gas where the magnetic field is zero. Scientists used math to study how the gas could move nearby, assuming it stops right at that spot. They found that the same magnetic pattern could go with different gas movements, including flowing inward, flowing outward, or swirling. So knowing the magnetic pattern does not tell you everything about how the gas moves. This came from a math model, not from watching gas in space.

Tracking a solar energetic eruption and associated energetic particles from Sun to spacecraft

D. E. Morosan, M. Baumgartner-Steinleitner, K. Bhandari+17 more

• Space Physics

AstronomerThe study combines radio and X-ray observations of the 10 March 2024 solar eruption with in situ particle measurements and an MHD model of the corona to investigate remote-to-in-situ connections. Multiple spacecraft detected a high-energy SEP event, including >25 MeV protons and 1 MeV electrons, despite its association with a slow white-light CME. Remote observations revealed a fast, large-scale coronal wave at 1400 km/s and type II radio bursts indicating multiple electron-acceleration regions around the wave. Strong coronal dimming away from the main flare region is interpreted as evidence that magnetic field lines opened into interplanetary space away from the flare site; it is not a direct measurement of that opening.

PublicAn eruption on the Sun on 10 March 2024 was associated with high-energy particles detected by several spacecraft. Although the accompanying outward-moving cloud of solar material was slow, observations showed a large wave moving through the Sun’s outer atmosphere at 1400 kilometres per second. Radio signals indicated that electrons were being accelerated in several regions around the wave. A pronounced dimming away from the main flare suggests that magnetic field lines there opened into space. The researchers combine observations of the Sun and spacecraft particle measurements with a computer model to investigate how the eruption and the detected particles are connected.

Young explorerSpacecraft spotted very speedy particles from the Sun. When scientists looked at the Sun, they saw a fast wave and radio signals showing where tiny particles called electrons were speeding up. They also saw a place grow dim, away from the main burst. That may mean the Sun’s magnetic paths opened out into space. A computer model helps them study how these clues fit together.

Flares and flux ropes: an entangled story

Rony Keppens, Yang Guo, Wenzhi Ruan

• High Energy Astrophysical Phenomena
• Plasma Physics
• Space Physics

AstronomerThis review treats solar flares as reference cases for magnetic-reconnection-driven energy release and discusses first-principles modeling of their heliospheric consequences. It surveys recent multidimensional magnetohydrodynamic models of flares and associated flux-rope expulsions, emphasizing self-consistent efforts in standard-flare configurations. Observationally established ingredients beyond single-fluid thermal plasma evolution are incorporated to varying degrees; the abstract does not specify those ingredients or report quantitative model validation.

PublicThis review describes advances in computer models of solar flares and the magnetic structures expelled with them. The models follow how hot, electrically charged gas and magnetic fields evolve together, aiming to describe effects extending into the region around the Sun. Some models include additional physics supported by observations, but the extent varies. The abstract highlights modeling progress rather than presenting a new observation or a measured test of model accuracy.

Young explorerThe Sun can have big bursts called flares. Scientists make computer models to study these bursts and the magnetic shapes pushed out with them. This review explains improvements to those models. Some include more clues from what scientists have seen, but they do not all include the same details.

HD 152384: A 5 Myr old debris disk system showing a gaseous ring of refractory elements at the dust sublimation radius

Mario van den Ancker, Daniela Iglesias, Olja Panić+2 more

• Earth and Planetary Astrophysics

AstronomerNew high-resolution VLT/UVES and VLT/CRIRES spectra of HD 152384, a 5 Myr A0 V star in Sco-Cen with hybrid-disk traits, reveal 74 narrow, double-peaked Fe, Mg, Si, and Ca emission lines with similar profiles and a peak separation of 103 km/s. Keplerian modelling locates the emitting gas in a geometrically thin ring at 0.09–0.12 au, close to the estimated dust sublimation radius of 0.10–0.14 au for a sublimation temperature of about 1500 K, rather than the previously suggested broad, gas-rich disk. Fe I emission is optically thick; optically thin Mg I lines imply a magnesium gas mass of 2.2 × 10^22 kg, or 3.6 × 10^-3 Earth masses. The dust and gas properties are consistent with, but do not establish, a secondary origin from rocky planetesimal collisions. The authors propose that collision-generated small grains spiral inward and sublimate, accumulating atomic gas near the sublimation radius, and interpret the system as a young analogue of gas-bearing debris disks and gaseous debris disks around metal-polluted white dwarfs.

PublicAstronomers studied light from HD 152384, a star about five million years old, and detected 74 emission features from iron, magnesium, silicon, and calcium gas. Modelling the shapes of these features suggests that the gas occupies a thin ring very close to the star, near where dust becomes hot enough to vaporize, rather than a broad gas-rich disk as previously suggested. The magnesium emission implies about 0.0036 Earth masses of magnesium gas; this is not a measurement of the ring’s total gas mass. The findings are consistent with rocky bodies colliding and producing dust. The researchers propose that small dust grains then spiral toward the star and vaporize, supplying the gas ring, but this origin has not been established.

Young explorerScientists looked at light from a young star and found signs of metal gas nearby. Their calculations suggest that the gas goes around the star in a thin ring, close to where dust gets so hot it can turn into gas. They think rocky pieces might crash together and make tiny bits of dust that move toward the star and heat up. That could explain the gas, but they do not yet know for sure.

Revisiting the Optical F-corona from the Artemis II Total Solar Eclipse with RAW Data: How Far Can Consumer JPEG Images Be Trusted for Astronomical Photometry?

Kohji Tsumura, Ko Arimatsu

• Earth and Planetary Astrophysics
• Instrumentation and Methods for Astrophysics

AstronomerA reanalysis of consumer-camera eclipse images from the Artemis II lunar flyby uses RAW data as the reference for assessing earlier JPEG-based results. Field-star calibration shows that lens vignetting and pixel-solid-angle variation suppress diffuse-light signals by up to approximately 70% at the field edge. The signal over the Moon’s dark side is most likely foreground light, not an instrumental offset. At elongations of 10–15 degrees, F-coronal radial power-law indices are −2.0 to −2.3 eastward, −2.5 westward, and −2.4 to −2.7 northward and southward, consistent with space-based observations. Ecliptic surface brightness at 10 degrees is approximately 26 MJy sr−1, with ±7% uncertainty. Isophote flattening indices are approximately 0.6–0.7, with superellipse indices of approximately 1.5–1.6. Comparison with ZodiSURF supports a radial dust-density index α ≃ 1.3 down to approximately 0.2 au and suggests a dust distribution that broadens vertically toward the Sun. Contrary to its metadata, the JPEG retains nearly all the vignetting, and its tone response is not a single power law. These effects, together with zero-point treatment, explain the previously reported steep, asymmetric profiles; the flattened morphology and α ≃ 1.3 remain supported. The study also identifies JPEG-robust quantities and demonstrates reconstruction of the tone response from field stars.

PublicResearchers revisited solar-eclipse photographs taken with a consumer camera during the Artemis II lunar flyby, comparing the original RAW data with a previously analyzed JPEG. Calibration using stars revealed that camera effects reduce the recorded diffuse light by as much as about 70% near the picture’s edges. Light seen over the Moon’s dark side is most likely foreground light rather than a camera offset. After accounting for the image effects, the measured fading of the Sun’s surrounding F-corona agrees with space-based observations. Comparison with a zodiacal-light model supports the inferred increase in dust density toward the Sun and suggests that the dust distribution becomes vertically broader closer in. That broadening is a model-based interpretation, not a direct measurement. The earlier JPEG analysis made the brightness decline appear too steep and asymmetric, although its finding of a flattened overall shape survives. The work also shows how stars can help recover the JPEG’s brightness response.

Young explorerScientists looked again at eclipse pictures taken near the Moon. They found that the camera made the edges look much darker than they should. Using stars as a guide helped them work out how the faint light really changes across the picture. The light still has a flattened shape. Comparing it with a model also gave them clues about dust near the Sun.

HD 120678: a classical Be star with a tilting heartbeat disk

Dietrich Baade, Jonathan Labadie-Bartz, Thomas Rivinius

AstronomerThe ASAS-3 V-band light curve of the classical Be star HD 120678 showed an inverse-P-Cygni-like event between March 2005 and November 2008, with a peak-to-valley amplitude of about 0.9 mag; the event may have been unique. Before and after it, Balmer emission profiles and variability were consistent with an intermediate- to low-inclination decretion disk, whereas shell profiles observed at the sharp photometric minimum implied an edge-on view. The authors interpret this Be–Be-shell–Be sequence as a change in disk orientation, analogous to interpretations of historical activity in gamma Cas and 59 Cyg. They identify HD 120678 and a few other Be stars as exhibiting 'heartbeat' light curves and attribute them to disks gravitationally tilted by an additional star, drawing on modeling of Pleione. This disk interpretation can explain Be-star variations roughly ten times larger than the few-hundredths-of-a-magnitude amplitudes typical of heartbeat stars; the abstract does not establish a companion-driven tilt observationally for HD 120678.

PublicHD 120678 is a star surrounded by a disk of gas. Between 2005 and 2008, its recorded brightness underwent a striking change, spanning about 0.9 magnitudes. Observations of the gas before and after the event suggested that the disk was viewed at a relatively open angle, but observations at the sharp brightness minimum indicated an edge-on view. The researchers interpret this as the disk changing its tilt. They propose that the gravity of another star could produce a 'heartbeat' pattern in the disk's brightness, drawing on earlier modeling of another star, Pleione. Such changing disks could explain brightness swings much larger than those typical of heartbeat stars. The event in HD 120678 may have happened only once, and the proposed gravitational explanation is not directly established by these observations.

Young explorerA star called HD 120678 has a ring of gas around it. Astronomers saw its light change a lot. Clues in the light suggest that the ring looked tilted toward us differently when the star was dimmest. The scientists think another star might pull on the ring and tip it, changing how bright it looks. They call this a 'heartbeat' disk, but it is not a real heart, and they have not proved that another star caused this change.

Modelling the 6.7 GHz Methanol Flaring in G358.93-0.03 Using the Maxwell-Bloch Framework

Ningyan Fang, Toktam Rashidi, Yoshinori Yonekura+4 more

AstronomerThe study models selected 6.7 GHz methanol light curves from the 2019 non-periodic flare in G358.93-0.03, associated with an accretion burst, using a one-dimensional Maxwell–Bloch framework. For six representative velocity channels, the observed sharp rises, multiple peaks, secondary structure, and extended decays are represented as sums of scaled responses from effective emitting systems. These systems are driven by phenomenological pump pulses with fixed width but component-dependent background rates, amplitudes, and arrival times. Inferred initial inverted column densities yield characteristic superradiance timescales of 0.3–1.4 days, shorter than the adopted dephasing and relaxation timescales of 6.9 and 144.4 days, respectively, placing the fitted components in the fast-transient superradiance regime. Existing VLBI observations motivate possible blending of multiple unresolved flaring regions within a single-dish velocity channel but do not directly constrain the fits. The non-unique decomposition offers a physically motivated description of the flare morphology, rather than a unique identification of its emitting components.

PublicRadio observations of methanol in G358.93-0.03 recorded a complex flare in 2019, associated with a burst of accretion. The signal rose sharply, showed several peaks, and faded over an extended period. Researchers modeled six selected portions of the radio signal as combinations of emissions from several effective sources responding to pulses of excitation. Their fitted sources fall into a theoretical regime called fast-transient superradiance, in which excited molecules can emit cooperatively. Higher-resolution observations suggest that several flaring regions could blend together in the measured signal, but those observations were not used to constrain the fits directly. The model provides a physically motivated explanation of the flare’s complicated shape, but the data do not determine a unique combination of sources.

Young explorerScientists saw a radio signal from a place in space grow quickly, brighten several times, and then slowly fade. They used a math model to see whether several little bursts together could make that wiggly pattern. In their model, tiny molecules can give off radio waves together, like a group singing together. The model can explain the pattern, but scientists cannot yet tell exactly which little bursts made it.

Dynamics of a switchback-like magnetic deflection induced by a propagating coronal jet

Jade Touresse, Etienne Pariat, Clara Froment+1 more

AstronomerA 3D magnetohydrodynamic simulation tests whether a reconnection-driven solar jet can yield switchback-like in-situ signatures when sampled along a virtual trajectory based on Parker Solar Probe’s 22nd-perihelion orbit. Synthetic signatures have durations and profiles consistent with PSP observations, extending earlier results from simplified trajectories. The simulated magnetic topology contains two field-line families, with either one deflection or two sequential deflections along a field line; both are outward-propagating Alfvénic structures. Deflection amplitudes increase substantially in low-plasma-beta regions but evolve more moderately where beta is near unity. Complete magnetic reversals would require longer residence times in low-beta environments. The results support jets as a possible solar source of a fraction of switchbacks, rather than establishing the origin of all observed events.

PublicParker Solar Probe has observed widespread sharp bends in the magnetic field carried by the young solar wind. This study tests one possible source: brief, narrow solar jets launched by magnetic reconnection. Researchers simulated a jet in three dimensions and sampled it with a virtual spacecraft following a path based on the probe’s actual orbit. The simulated signals resembled observed magnetic bends in their duration and shape. The model also revealed magnetic field lines with either one bend or two successive bends. Bends grew more strongly where magnetic pressure dominated plasma pressure; producing complete reversals would require more time in those conditions. These are simulation results, not direct observations of a jet producing a switchback, and they support jets as a possible explanation for some, not necessarily all, of the observed bends.

Young explorerA spacecraft near the Sun has found sharp bends in the Sun’s invisible magnetic field. Scientists wondered if quick jets shooting out from the Sun could make some of them. They made a pretend Sun jet on a computer and sent a pretend spacecraft through it. It picked up bends that looked like the real ones in how long they lasted and how their signals changed. Some magnetic paths bent once, and others bent twice. The bends grew more in some surroundings than in others. This suggests Sun jets could make some of the real bends, but it does not prove that they do.

¹⁶O(p,γ)¹⁷F Reaction and the C and O Isotopic Ratios in Red Giant Branch Stars

D. Robb, P. McGlynn, M. Aliotta+55 more

• Nuclear Experiment

AstronomerThe authors measured the cross section of 16O(p,γ)17F at LUNA over center-of-mass energies of 200–380 keV, a previously unexplored experimental range. Prompt gamma-ray detection and activation yielded results consistent within experimental uncertainties. Combining these measurements with literature data, they evaluated a new thermonuclear reaction rate and applied it to interpreting isotopic ratios in red giant branch stars. Their analysis indicates that 12C/13C is primarily sensitive to the maximum temperature reached during mixing, whereas 16O/17O is highly sensitive to initial stellar mass. Joint measurements of these ratios can therefore disentangle and tightly constrain initial mass and mixing temperature. The authors find that the remaining uncertainty is dominated by stellar abundance measurements rather than nuclear-physics inputs.

PublicA new laboratory measurement helps scientists interpret how material mixes inside red giant stars. At the underground LUNA laboratory, researchers measured a reaction in which oxygen-16 captures a proton and produces fluorine-17. They explored an energy range not previously studied experimentally, using two methods that agreed within their uncertainties. Together with earlier data, the measurements provided an updated reaction rate. The team's analysis shows how comparing different forms of carbon and oxygen in a red giant can help separate two clues: the carbon ratio mainly probes how hot the mixed material became, while the oxygen ratio is especially sensitive to the star's starting mass. For this analysis, uncertainties in measuring stellar abundances now matter more than uncertainties in the nuclear reactions.

Young explorerBig red stars mix the material inside them. Scientists want to know how hot that material gets and how much stuff the star started with. They tested a tiny reaction involving oxygen in a laboratory, using two methods whose answers agreed within the uncertainty of the tests. Their study shows that comparing two kinds of carbon and two kinds of oxygen in a star can help answer both questions. The carbon gives a clue about heat, and the oxygen gives a clue about the star's starting size by mass. The answers are still not exact, mostly because measuring the star's ingredients is tricky.

Probing the magnetic field of a coronal mass ejection with PSR J1022+1001

El Mehdi Zahraoui, Hannah T. Rüdisser, Golam M. Shaifullah+24 more

• High Energy Astrophysical Phenomena
• Instrumentation and Methods for Astrophysics

AstronomerSimultaneous LOFAR and NenuFAR observations captured a CME crossing the line of sight to PSR J1022+1001 on 20 August 2021 at a projected heliocentric distance of 24.6 solar radii. Using time-resolved LOFAR dispersion and rotation measures, with estimated interstellar, solar-wind and ionospheric backgrounds removed, the authors infer a density-weighted, line-of-sight-averaged magnetic field from the ratio of the CME contributions. This inferred component rises from approximately −9 nT to a peak near 63 nT. Synthetic line-of-sight signatures from a semi-empirical 3DCORE reconstruction, fitted to Solar Orbiter in-situ magnetic field data at 0.65 au, depend strongly on the assumed flux-rope configuration. Only the South-West-North configuration, independently confirmed by the Solar Orbiter data, reproduces the observed sign and overall evolution; alternative configurations are incompatible. However, modeled amplitudes exceed the pulsar-derived values by roughly a factor of five. The study demonstrates a way to estimate CME line-of-sight magnetic fields and test data-constrained three-dimensional magnetic structures, without achieving agreement in field amplitude.

PublicA cloud of material expelled by the Sun passed between Earth and a pulsar, a star whose radio pulses can act as a probe of intervening material. The researchers used changes in the pulses’ arrival times and polarization to estimate the cloud’s average magnetic field along the viewing direction, weighted toward denser material. That inferred field changed from negative to positive during the observations. They compared these estimates with a three-dimensional model constrained by Solar Orbiter measurements. Only one tested arrangement of the cloud’s twisted magnetic structure reproduced the field’s direction and overall change over time, and Solar Orbiter data supported that arrangement. But the model predicted fields about five times stronger than the pulsar-based estimates. The observations therefore help test the cloud’s magnetic structure, while leaving a substantial mismatch in field strength.

Young explorerA cloud from the Sun moved in front of a star that sends out radio flashes. By seeing how the cloud changed those flashes, scientists estimated the cloud’s magnetic field along the path to us. They also made computer models of the cloud. Only one kind of magnetic twist matched the field’s direction and how it changed. But the computer model said the field was about five times stronger than the flashes suggested, so the two answers did not fully agree.

Diameters and Temperatures VII: High-angular resolution measurements of Solar-type stars with the CHARA Array

Tabetha S. Boyajian, Ashley A. Elliott, Emelly D. Tiburcio+8 more

• Earth and Planetary Astrophysics
• Instrumentation and Methods for Astrophysics

AstronomerPAVO/CHARA interferometry provides uniform-disk and limb-darkened angular diameters for 27 nearby solar-type stars spanning a broad metallicity range and evolutionary stages from the zero-age main sequence to mildly evolved subgiants, including several known exoplanet hosts. Combining these measurements with bolometric fluxes and Gaia parallaxes yields model-independent radii, effective temperatures, and luminosities, with typical uncertainties of approximately 1% in radius and 1.5% in effective temperature. Masses and ages are instead estimated through comparisons with multiple stellar evolutionary grids; grid-to-grid systematics depend on abundances, evolutionary stage, and proximity to grid boundaries. The measurements provide empirical benchmarks for evolutionary models, surface brightness-color relations, and exoplanet-host characterization.

PublicAstronomers measured the apparent sizes of 27 nearby Sun-like stars using PAVO at the CHARA Array. Combining those measurements with the stars’ total received light and Gaia distance measurements, they determined stellar sizes, temperatures, and luminosities without relying on stellar evolution models. Typical uncertainties are about 1% for radius and 1.5% for temperature. The sample includes stars at different stages of life and several known to host planets. Estimates of stellar mass and age do rely on evolutionary models, and comparing different models reveals sensitivity to chemical composition, life stage, and the limits of the model grids. These measurements offer benchmarks for testing how stars evolve and improving our understanding of stars with planets.

Young explorerAstronomers measured how wide 27 nearby stars like our Sun look in the sky. Using those measurements, how much starlight reaches us, and how far away the stars are, they worked out how big and hot the stars are and how much light they give off. Some of these stars have planets. The astronomers also used computer models of how stars change to estimate their ages and masses, but different models can give different answers. The measurements can help scientists check their ideas about stars.

A forest of emission lines observed by Sunrise III/SUSI above the solar limb

J. S. Castellanos Durán, F. A. Iglesias, S. K. Solanki+31 more

• Instrumentation and Methods for Astrophysics

AstronomerLow-straylight spectroscopy with SUSI aboard the Sunrise III stratospheric solar observatory detected 174 off-limb emission lines between 407.6 and 410.25 nm, 2.5 times the number in previous reports. A spatial scan with the slit nearly parallel to the local limb extended from on-disc to 6.5 Mm off-limb. Of the detected lines, 122 begin appearing in emission on-disc near the limb. One-fifth of the relatively prominent emission lines are attributed to rare-earth and heavy elements and molecules; the corresponding absorption lines are typically weak on-disc.

PublicAstronomers used the SUSI instrument aboard the Sunrise III stratospheric solar observatory to study light near and beyond the Sun’s visible edge. In the wavelength range examined, they detected 174 emission lines—distinct wavelengths where material gives off light—2.5 times as many as previously reported. Surprisingly, 122 of these lines already appear in emission just inside the Sun’s visible edge. Among the relatively prominent emission lines, one in five comes from rare-earth and heavy elements and molecules, whose corresponding dark absorption lines are usually weak when viewed against the Sun’s disc.

Young explorerScientists used a special instrument to split sunlight into tiny pieces of color near the Sun’s edge. Just beyond the edge, they found 174 bright lines of color, more than people had reported before. They were surprised that 122 of those lines also start to shine just inside the edge. Some of the stronger lines come from rare-earth and heavy elements and from molecules—tiny groups of atoms.

Axial-Dipole and Equatorial-Dipole Coronal Holes: Congruent Magnetic Geometry, Divergent Evolution

Olga A. Panasenco, Yi-Ming Wang, Samuel T. Badman+2 more

AstronomerThe study tests whether coronal magnetic geometry explains the acceleration of wind from equatorial-dipole coronal holes (EDCHs). Parker Solar Probe observed fast EDCH wind deeply sub-Alfvénic at 9.9 solar radii, reaching only 60% of an asymptotic speed comparable to polar wind. Potential-field models of synthetic and observed fields at three cycle phases show that pure axial and equatorial dipoles are exactly congruent, with identical open areas and core expansion factors; differences therefore require orientation relative to differential rotation or surrounding multipoles. The analysis finds stationary axial-dipole coronal holes (ADCHs), sustained by converging meridional flow, whereas active-region emergence builds the equatorial dipole and flux transport dismantles it. Across 18-day sequences, axial-dipole strength at minimum is steady to 1%, while equatorial-dipole strength varies by 21% at maximum and 8% during decline. Most EDCH open flux expands less than ADCH flux, but EDCH boundaries are dominated by pseudostreamers and show non-monotonic expansion. Geometry alone does not predict slower EDCH acceleration. The authors propose extended heating by reflection-driven Alfvén-wave turbulence, perhaps supplied differently at the boundaries, as an explanation if the acceleration difference is real; potential-field models cannot test this mechanism. Low latitude alone does not identify an EDCH: the 2024 maximum was quadrupole-led.

PublicParker Solar Probe observed fast solar wind from a coronal hole associated with a strong equatorial magnetic dipole. Close to the Sun, that wind had reached only 60% of its eventual speed, even though its eventual speed matched wind from the poles, which is usually thought to accelerate faster. Researchers tested whether magnetic structure could explain this using models based on artificial and observed solar magnetic fields. Idealized equatorial and polar dipoles have exactly the same shape when reoriented, although their surroundings and evolution differ. Equatorial-dipole holes were more changeable, and their magnetic boundaries had more complicated expansion patterns. Nevertheless, magnetic geometry alone did not predict slower acceleration. The authors suggest that prolonged heating by turbulence involving magnetic waves could explain a genuine difference, but their models cannot capture that process. They also caution that not every low-latitude coronal hole belongs to this equatorial-dipole category.

Young explorerThe Sun sends out a wind. A spacecraft found fast wind from a place near the Sun’s middle, but close to the Sun it still had much more speeding up to do. Scientists used computer models to ask whether the shape of the Sun’s magnetism could explain this. The shapes alone did not give the answer. The scientists think waves might keep giving the wind extra energy, but their models cannot show whether that idea is right.

Thermodynamically consistent equation of state tables for use in giant planet and brown dwarf interior modeling

Emily Sandford, Yamila Miguel

• Solar and Stellar Astrophysics

AstronomerThe authors address first-law inconsistencies in equation-of-state (EOS) tables used for giant-planet evolution, generally arising from smooth interpolation across physical discontinuities or between domains described by different physical models. They construct a Helmholtz free energy F(ρ,T) over the EOS domain and derive the other required thermodynamic quantities from it, improving consistency by roughly a factor of 1,000 according to three first-law-based metrics. In controlled MESA evolution experiments, models using the original versus F-derived tables differ by up to 5% in radius at 5 Gyr and up to 25% in luminosity at earlier stages. These are model comparisons, not observed planetary discrepancies, and highlight the importance of thermodynamic consistency when characterizing young directly imaged planets. The revised tables and example MESA inlists are provided for download.

PublicComputer models of giant planets rely on tables describing how matter behaves under different conditions. Some parts of these tables do not consistently obey the first law of thermodynamics, which can create artificial gains or losses of energy or entropy in a model. The researchers developed a way to rebuild the tables from a single underlying thermodynamic function, making them roughly 1,000 times more consistent by three measures. In computer experiments, using the original or revised tables produced planet radii differing by as much as 5% at an age of 5 billion years, and brightnesses differing by as much as 25% at earlier ages. These differences come from simulations, not observations of planets. The work suggests that this modeling issue matters especially when interpreting images of young giant planets.

Young explorerScientists use computers to work out how giant planets change as they grow older. The computers use tables of rules, but some rules do not fit together properly and can make pretend energy appear or disappear. The researchers made the rules fit together much better. When they tried the old and new tables, their computer planets could have different sizes and brightnesses. They did not see real planets change this way. Better tables can help scientists understand young giant planets.

Science-Driven Performance Requirements for UV Coronagraph Design: Implications for O₃ Detection in Earth-like Atmospheres

Amber V. Young, Giada Arney, Shawn Domagal-Goldman+6 more

• Instrumentation and Methods for Astrophysics

AstronomerPhotochemical-climate models and atmospheric retrieval simulations establish fiducial near-ultraviolet requirements for detecting ozone as an indirect oxygen proxy in Proterozoic Earth-like exoplanet atmospheres. In the simulations, ozone abundance can be constrained within an order of magnitude at 1σ for oxygen levels as low as 0.1% of the present atmospheric level, using three adjacent 15%-wide photometric bands, a signal-to-noise ratio of 10 at 0.366 μm, and a short-wavelength cutoff near 0.26 μm. Self-consistent steady-state models indicate that sulfur dioxide, a potential spectral false positive, is difficult to accumulate in habitable atmospheres with appreciable water vapor: volcanic outgassing at least 100 times present-day Earth's is needed to reach surface abundances comparable to the modeled Proterozoic-like ozone abundances. Even at these high sulfur dioxide fluxes, its abundance remains largely unconstrained by the recommended configuration. These modeling results, not exoplanet detections, support near-ultraviolet coverage and UV-optimized optics and detectors for the Habitable Worlds Observatory.

PublicThis study uses computer models, rather than observations of planets, to explore how a future telescope could search for ozone on worlds resembling Earth during its low-oxygen Proterozoic era. Ozone can provide an indirect clue to oxygen when oxygen itself is hard to detect. The simulations suggest that three carefully chosen near-ultraviolet color bands could roughly constrain ozone abundance even when oxygen is only 0.1% of today's Earth level, provided the measurements meet the proposed sensitivity requirements. The researchers also modeled sulfur dioxide, which could mimic ozone's spectral features. In their modeled habitable atmospheres containing appreciable water vapor, building up comparable amounts required volcanic gas release at least 100 times today's Earth rate. However, the proposed measurements still poorly constrain sulfur dioxide, leaving an important limitation. The authors recommend ultraviolet-sensitive optics and detectors for the Habitable Worlds Observatory to support searches for possible signs of life, not to establish that life has been found.

Young explorerScientists used computer models to ask how a future telescope might look for a gas called ozone around faraway worlds like Earth long ago. Ozone could give a clue that another gas, oxygen, is there even when it is hard to see. The models suggest that looking at three special ultraviolet colors could help. Another gas from volcanoes might look similar, though the models say making enough of it would take much stronger volcanic activity than on Earth today. The suggested telescope measurements would still have trouble telling how much of that other gas was there. This is a plan for looking for clues, not a discovery of life.

Paleo-heat flux estimates across Enceladus derived from flexural response of the ice shell

Chelsea Eakins, Francis Nimmo, Paul Schenk

AstronomerThe study models flexural deformation of chasmata and dorsae on Enceladus to estimate effective elastic shell thickness and infer past heat fluxes. Model-derived paleo-heat fluxes range from 60 to at least 350 mW m−2, mostly clustering at 125–200 mW m−2. Estimates outside the South Polar Terrain are comparable to present-day measured south-polar fluxes but substantially exceed present-day fluxes inferred for those same non-polar locations from shell-thickness maps. This suggests past heating episodes followed by cooling and shell thickening outside the south-polar region. Similar inferred paleo-fluxes across terrains with different crater-density ages support, but do not establish, resonance locking through dissipation in Saturn and possibly a long-lived Enceladus–Dione resonance. The authors interpret the results as evidence for consistent tidal heating over time; sustained peak heating could support a long-lived subsurface ocean, with implications for habitability.

PublicEnceladus, a moon of Saturn, has active plumes, but its earlier heating history is poorly understood. Researchers modeled how its icy crust bends around fractures and ridges to estimate how much heat escaped in the past. Most estimates fall between 125 and 200 milliwatts per square metre. Outside the south-polar region, these past estimates are much higher than estimates of today's heat flow at the same locations, suggesting that those areas cooled and their ice thickened after earlier heating. The past estimates are comparable to heat flow measured at the south pole today. Similar estimates for landscapes of different ages support an explanation involving lasting orbital interactions, possibly including a long-lived resonance with the moon Dione, though they do not prove it. The authors suggest that consistent heating could have helped an ocean beneath the ice survive for a long time, which matters for assessing whether such environments could support life.

Young explorerSaturn's moon Enceladus sprays material into space and has an icy outside. Scientists used a model of how its ice bends to look for clues about how warm it used to be. Their model suggests that some places once let out more heat than they do now, then cooled and grew thicker ice. The clues also suggest that heating may have lasted a long time. That could help an ocean under the ice stay liquid, but this study does not show that anything lives there.

The Limits of Tidal Circularization and Atmospheric Escape for Mini-Neptunes and Super-Earths: The Case of TOI-2257 b

M. K. A. Olohoy, Y. A. D. Gelani, R. Barnes

AstronomerTOI-2257 b has a 35-day orbital period and an eccentricity of approximately 0.5, placing it in a sparsely populated region of transiting mini-Neptune parameter space. Coupled stellar, tidal, and atmospheric evolution simulations place it near the boundary where tides and atmospheric escape become negligible, whether or not it formed with a primordial hydrogen envelope. In the mini-Neptune models, all cases retain at least 0.02 Earth masses of envelope for 8 billion years, although envelopes initially exceeding 0.2 Earth masses can lose half their mass. Tidal evolution occurs only for initial envelope masses above 0.02 Earth masses, because those planets have radii large enough to produce significant torques. In the rocky super-Earth scenario, the models allow loss of approximately 10 Earth ocean masses of surface water during the roughly 75-million-year pre-main-sequence phase; the authors suggest possible habitability if the planet formed with at least roughly twice Earth's surface water mass. Predicted tidal heating fluxes tend to resemble Io's and never reach the runaway-greenhouse threshold in the simulated cases. Present-day eccentricities above 0.62 are strongly disfavored for rocky models, so a higher measured eccentricity could support a gaseous nature. These model-dependent results suggest potential constraints on mini-Neptune properties and the eccentricity dependence of the radius valley.

PublicTOI-2257 b circles its star every 35 days on a noticeably stretched orbit. Researchers used computer simulations, rather than direct measurements of its long-term evolution, to explore whether it is a planet with a hydrogen envelope or a rocky world. The simulations place it near the distance where tidal effects and atmospheric loss become negligible. In the gas-envelope models, the planet keeps some atmosphere for 8 billion years, although an initially more massive envelope can lose half its mass. Rocky models suggest substantial early water loss, but the authors leave open the possibility of habitability if the planet began with enough water. Predicted heating from tides does not reach the level needed to trigger a runaway greenhouse in any simulated case. The rocky models strongly disfavor a present-day orbital eccentricity above 0.62, so measuring a value above that could help establish that the planet is gaseous. Its composition and habitability remain uncertain.

Young explorerTOI-2257 b is a planet that goes around its star on a stretched-out path. Scientists used computers to imagine how it might change over a very long time. If it has a blanket of gas, their models say it could keep some of that blanket. If it is rocky, it might lose lots of water early on. We still do not know which kind of planet it is, or whether it could be a home for life.

ExoEcho: Exoplanet Ephemerides Change Observations. III. A JWST Survey for Transit Timing Variations of 37 Exoplanets

Yunke Wu, Zixin Zhang, Xinyue Ma+6 more

AstronomerThe ExoEcho analysis incorporates JWST transit observations into a sample of 84 light curves for 37 exoplanets: 20 hot Jupiters, 11 Neptune-like planets, and 6 super-Earths. Updated ephemerides and a systematic search for long-term and periodic transit timing variations identify two strong candidates. HATS-6 b shows a long-term trend with a positive period derivative of 230.5 ± 46.8 ms per year, potentially attributable to tidal interactions with its host star; this mechanism is an interpretation, not a confirmed cause. HAT-P-18 b shows a periodic timing signal with an amplitude of 92.9 ± 13.7 seconds. New timing data are inconsistent with the previously claimed positive period derivative for WASP-121 b. Continued monitoring is needed to confirm the candidate signals. The work demonstrates JWST’s potential for precise transit timing and extends these studies to lower-mass planets.

PublicAstronomers studied 84 records of planets passing in front of their stars, covering 37 planets and including observations from the James Webb Space Telescope. They found two strong candidates whose crossings do not follow a steady schedule. For HATS-6 b, the measured trend suggests that its orbital period is increasing by about 0.23 seconds per year; tidal interactions with its star are a possible explanation, not an established cause. HAT-P-18 b shows a repeating timing shift with an amplitude of about 93 seconds. The new observations also conflict with an earlier claim that WASP-121 b’s orbital period is increasing. More monitoring is needed to confirm the candidate signals, but the study highlights Webb’s potential to track subtle timing changes in planets of different sizes.

Young explorerWhen a planet passes in front of its star, the star looks a little dimmer. Scientists used these little dips in light, including some watched by the Webb telescope, to check when planets came around. Two planets seem to be changing their schedules: one may be taking longer to go around its star, and another seems to pass early and late in a repeating pattern. The scientists need to keep watching to make sure.

Emission spectroscopy of KELT-2A b with Gemini-North/IGRINS-2: hints of a stellar C/O ratio and sub-stellar metallicity

Yuya Hayashi, Stevanus K. Nugroho, Shota Notsu+13 more

AstronomerHigh-resolution H- and K-band emission spectroscopy of KELT-2A b with IGRINS-2/Gemini-North spans five nights before and after eclipse at R ~ 45,000. After singular value decomposition removes stellar and telluric contamination, H2O is detected at S/N = 6.57, confirming an earlier result at higher significance. A 12CO likelihood feature lies near the expected planetary velocity but does not constitute a definitive detection. Retrievals using IGRINS-2 alone and jointly with archival Spitzer/IRAC photometry favor a non-inverted temperature–pressure profile. The joint free-chemistry fit gives log(H2O) = -3.78 (+0.27/-0.20); the equilibrium-chemistry fit gives C/O = 0.19 (+0.12/-0.07), [C/H] = -0.81 (+0.41/-0.34), and [O/H] = -0.37 (+0.27/-0.17). C/O agrees with the host-star value, while carbon and oxygen appear moderately depleted but remain consistent with stellar abundances at approximately 2 sigma. If confirmed, this composition would challenge gas accretion between the H2O and CO snowlines. The authors instead interpret it as evidence for metal-depleted gas accretion beyond the CO snowline, limited planetesimal enrichment, and subsequent disk-free, high-eccentricity migration; this history is not established by the observations.

PublicFive nights of observations with IGRINS-2 on Gemini-North reveal water vapor in the atmosphere of the hot giant planet KELT-2A b, strengthening an earlier detection. There is also a possible carbon monoxide signal, but the data are not good enough to confirm it. Atmospheric models fitted to these observations and archival Spitzer measurements indicate that temperature does not rise with altitude over the atmospheric region probed. The models suggest a carbon-to-oxygen ratio similar to the host star’s, with somewhat lower carbon and oxygen abundances, although those abundances remain statistically compatible with the star’s. If that chemical pattern is confirmed, the authors argue that the planet may have gathered chemically depleted gas in a cold, distant part of its birth disk and later moved inward through a highly elongated orbit after the disk disappeared. This is a proposed formation and migration history, not a directly observed result.

Young explorerAstronomers studied light from a very hot giant planet called KELT-2A b. They found water vapor in its air, making an earlier finding more certain. They also saw a possible sign of a gas called carbon monoxide, but they are not sure it is really there. Models help them work out what the planet’s air might be like. The clues suggest the planet may have grown far from its star and moved closer later, but that story still needs checking.

LiDO: The Large inclination Distant Objects Survey

Mike Alexandersen, Rosemary E. Pike, Ying-Tung Chen+20 more

• Instrumentation and Methods for Astrophysics

AstronomerThe LiDO survey addresses the under-representation of high-inclination TNOs in ecliptic-focused surveys by observing two blocks 14–21 degrees north and south of the ecliptic. It detected 148 objects, all with i>14 degrees by survey design; 125 meet the characterized magnitude and rate limits and are suitable for comparison with survey simulations. Detections include 62 resonant TNOs: 21 Plutinos, of which 12 are securely Kozai resonators with consistently off-ecliptic pericenters, nine objects in the 5:2 resonance, and several mixed inclination–eccentricity resonators. No objects were detected beyond 63 au despite sensitivity extending to 150 au. Adding LiDO's 38 characterized hot classical TNOs makes the previous OSSOS model's i>14-degree orbital distribution statistically rejectable. A proof-of-concept model based on long-term stability sculpting is statistically acceptable for both LiDO and OSSOS and estimates 21,000 ± 3,000 hot classicals with H_r<8.3, consistent with OSSOS population estimates. Statistical acceptability does not establish this model as a unique explanation; the sample provides constraints on population models and Solar System migration history.

PublicEarlier searches for objects beyond Neptune concentrated near the plane of Earth's orbit, missing many objects on strongly tilted paths because they spend little time there. The LiDO survey instead searched above and below that plane, finding 148 objects. Of these, 125 form a carefully characterized sample suitable for testing population models. Many discoveries occupy orbital resonances, including 21 Plutinos. Nothing was detected beyond 63 times the Earth–Sun distance, although the survey could detect objects as far away as 150 times that distance; this is a nondetection, not evidence that the region is empty. The new data challenge an earlier model for the tilted orbits of a population called hot classical objects. A preliminary replacement model, based on how long-term stability shapes orbits, fits both this survey and an earlier one. Its population estimate agrees with previous estimates, but it remains a proof of concept rather than a confirmed history of the Solar System.

Young explorerSome objects beyond Neptune travel on paths tilted away from the flat area where people usually look. Scientists searched above and below that area and found 148 objects. They carefully checked which discoveries could help test their ideas. An old model did not match the new clues well. A new model fits, but that does not mean it is the only possible answer.

On-sky performance and prospects of near-infrared CMOS detectors in exoplanet detection: first year of SPIRIT

Clàudia Janó-Muñoz, Matthew J. Hooton, Peter P. Pedersen+8 more

• Instrumentation and Methods for Astrophysics
• Solar and Stellar Astrophysics

AstronomerThe paper reports first-year on-sky performance of SPIRIT, an InGaAs CMOS imager on the Callisto telescope at the SPECULOOS Southern Observatory, from mid-2022 to 2023. Ultracool dwarfs emit most strongly in the near-infrared, beyond the wavelength cutoff of silicon CCDs used by surveys such as SPECULOOS. Using 328 visits to 73 targets, the authors optimise CMOS-specific reductions, including glow correction and bad-pixel handling. Measured photometric precision agrees with their theoretical noise model, reaching sub-part-per-thousand precision under good observing conditions for targets spanning J = 10–13. Case studies include simultaneous SPIRIT zYJ and CCD I + z observations of a TRAPPIST-1 h transit and monitoring of the fast-rotating dwarf LP 944-20. The authors conclude that InGaAs CMOS detectors are cost-effective and competitive for ground-based transit photometry of cool stars; their wider role in next-generation instruments remains a prospect.

PublicVery cool dwarf stars are promising places to search for temperate, rocky planets, but their light is strongest in the near-infrared, beyond the reach of the silicon detectors used by surveys such as SPECULOOS. Researchers tested SPIRIT, an infrared camera on the Callisto telescope, during its first year of operation. Across 328 observing visits to 73 targets, they refined how they processed the images and found that the camera's measurement precision matched their noise model. Under good observing conditions, it measured stellar brightness with a precision better than one part in a thousand. They also demonstrated its capabilities by observing a transit of the known planet TRAPPIST-1 h and monitoring the rapidly rotating dwarf LP 944-20. The authors judge this detector technology to be a cost-effective, competitive option for measuring the small brightness changes caused by planets crossing cool stars, with promise for future instruments.

Young explorerSome stars are so cool that they shine brightest in light our eyes cannot see. Scientists tested a special camera called SPIRIT that can see some of that light. When observing conditions were good, it measured tiny changes in how bright the stars looked. It also watched a known planet pass in front of its star. The tests suggest cameras like this could help scientists look for planets around very cool stars.

Probing Planet Formation within 10 au: Dust Substructures in Extremely Compact Protoplanetary Disks

Pietro Curone, Gijs D. Mulders, Nienke van der Marel+1 more

• Solar and Stellar Astrophysics

AstronomerALMA Band 7 continuum observations at 0.9 mm resolve 11 compact Class II disks in Lupus with R68 < 10 au at 0.02 arcsec (2 au) resolution. Substructures are detected in four disks, including a clear 1.6 au-radius inner cavity, with tentative features in three more; two disks have faint outer rings beyond bright inner cores. Combining these observations with ALMA disk demographics, and requiring at least three resolution elements across each disk diameter, the study finds substructure detection rates of ≳95% for disk sizes above 30 au and approximately 50% between 3 and 30 au. Optical depth likely contributes to the lower detection rate in smaller disks. The authors interpret persistent millimeter emission as evidence that pressure traps have halted radial drift. Estimated planet masses needed to open gaps within 5 au lie in the super-Earth to mini-Neptune regime; these are not planet detections. The results support widespread disk substructure and extend probes of planet-forming conditions to a few au.

PublicSharp ALMA observations reveal features in some of the smallest planet-forming disks around young stars in Lupus. Of 11 disks examined, four show clear structures and three more show possible ones. The findings include a small central cavity and faint outer rings in two disks. A broader comparison finds structures in nearly all well-resolved disks larger than 30 Earth–Sun distances, versus about half of those spanning sizes of 3 to 30 Earth–Sun distances. The lower rate in smaller disks may partly reflect dust hiding features, rather than their absence. Estimates suggest planets in the super-Earth to mini-Neptune mass range could open gaps close to the stars, but no planets are reported as detected.

Young explorerYoung stars can wear little disks of dust where planets might grow. Scientists looked closely at 11 tiny disks. They saw clear patterns in four and possible patterns in three more, including rings and a small hole. Planets might make some gaps, but the scientists did not spot planets. Some patterns may still be hidden by dust.

Revealing the Spatial Distribution of Dust and Plasma Solitary Waves in Jupiter's Innermost Magnetosphere Using Juno Waves Observations

Wenyu Zhang, Hao Cao, William S. Kurth+6 more

• Space Physics

AstronomerThe study analyzes nearly a decade of in-situ Juno Waves electric-field measurements with a two-stage convolutional neural network that distinguishes dust impacts, solitary waves, and other plasma waves. Dust-impact detections trace a radially evolving structure extending well inside the optically observed halo: a compact, equatorially symmetric inner layer broadens vertically into a halo and then contracts toward the main ring, directly revealing the halo's toroidal morphology. Dust number density is enhanced within the halo and near the main-ring–halo transition. Radially varying hemispheric asymmetries in the vertical distribution are consistent with magnetic-geometry effects on charged dust, rather than establishing a unique cause. Solitary waves occur predominantly at high latitudes, and their mapped magnetic footprints correspond closely to auroral structures, particularly the main auroral oval. These measurements extend the optical picture of the rings and show that the optical inner boundary is not the end of the dust population.

PublicJupiter's faint rings contain tiny dust grains that are difficult to study close to the planet. Researchers used a neural network to sort nearly a decade of electrical measurements from the Juno spacecraft, separating signals from dust impacts from different kinds of plasma waves. The detected dust extends closer to Jupiter than the halo seen in optical observations. Moving outward, it forms a thin layer around the equator, spreads into a broad, doughnut-shaped halo, and narrows again toward the main ring. Dust is more concentrated within the halo and near its transition to the main ring. Differences between the dust above and below the equator change with distance from Jupiter; these patterns are consistent with an influence from the planet's magnetic field, but do not prove that explanation. Separately, solitary plasma waves are found mostly at high latitudes, with mapped magnetic footprints closely matching Jupiter's auroral structures.

Young explorerJupiter has faint rings made of tiny bits of dust. Scientists studied signals recorded by the Juno spacecraft when dust hit it. They found dust closer to Jupiter than pictures had shown. The dust makes a thin layer near the planet, spreads into a thick doughnut shape farther out, and then becomes thinner again near the main ring. Jupiter's magnetic field may help shape where the dust goes. Juno also detected waves in the charged gas around Jupiter, mostly near its polar regions, with a pattern that matches places where Jupiter's glowing auroras appear.

Testing the prevalence of hydrogen-silicate miscibility in young sub-Neptunes

James G. Rogers, Hilke E. Schlichting

AstronomerThis modeling study examines how hydrogen–silicate miscibility interacts with stellar-driven atmospheric escape in sub-Neptunes. The models find that most hydrogen resides in miscible interiors for approximately the first 100 Myr, shielding it from escape. As atmospheric hydrogen is lost, hydrogen exsolves from the interior, replenishing the envelope and delaying contraction relative to models without miscibility. The authors construct a population-level Bayesian hierarchical inference framework to test the prevalence of fully miscible sub-Neptunes. Assuming conservative measurement uncertainties and no completeness corrections, they predict that roughly 100–200 observed planets with measured radii, masses, and ages of about 1 Gyr or less would distinguish fully miscible from immiscible models. Better measurement precision reduces the required sample. They also find that underlying distributions of planetary initial conditions can be reliably inferred if completeness corrections are included. These are model findings and survey forecasts, not an observational detection of miscibility.

PublicCan hydrogen mixed into a planet’s rocky interior help it keep its atmosphere? This study’s models suggest that sub-Neptunes store most of their hydrogen inside for roughly their first 100 million years, protecting it from loss driven by their stars. As hydrogen escapes from the atmosphere, some stored hydrogen comes out of the interior and replenishes it, slowing the planet’s shrinkage. The researchers also develop a statistical test for how common fully mixed interiors might be. They estimate that measurements of size, mass, and age for about 100–200 sub-Neptunes younger than roughly a billion years could distinguish fully mixed from unmixed models. That forecast assumes conservative measurement uncertainties and does not correct for planets a survey misses; more precise measurements would reduce the sample needed. Correcting for missed planets also enables reliable estimates of the population’s starting conditions. The study does not establish that real planets have fully mixed interiors.

Young explorerImagine a planet keeping hydrogen tucked inside its rocky middle. The scientists’ models suggest that when its star makes hydrogen escape from the outside, some hidden hydrogen can come out and replace it. That could help the planet stay big for longer. The scientists think measuring many young planets could test this idea. They have not shown that real planets work this way yet.

Volcanic Satellites and Ion Escape in the Magnetospheres of Ultra-Cool and Brown Dwarf Stars

A. F. Lanza, A. V. Oza

AstronomerGigahertz radio emission from ultra-cool and brown dwarfs suggests Jupiter-like radiation belts. Using indirect estimates of magnetospheric plasma mass flow from auroral radio emission, the authors assess possible plasma sources for LSR J1835+3259. Their modeling finds ionospheric outflow of order 10^5 kg s^-1 viable if the effective Pedersen conductance is below approximately 0.003 mho. Alternatively, a tidally heated volcanic satellite with Io's mass and radius could supply the plasma at a semimajor axis below about 10 stellar radii, with eccentricity near 10^-3 maintained by perturbations from other planets, without strong restrictions on ionospheric conductance. Neither source is established observationally. The authors interpret the volcanic-satellite scenario as consistent with the reported higher radio-detection likelihood of ultra-cool dwarfs with distant substellar or stellar companions.

PublicRadio signals suggest that some ultra-cool stars and brown dwarfs have belts of electrically charged particles, similar to Jupiter's. This study explores where those particles might come from in the object LSR J1835+3259, using indirect estimates based on its auroral radio emission. The calculations allow two possibilities: particles escaping from the object's upper atmosphere under restrictive electrical conditions, or material supplied by a nearby, volcanically active satellite. The satellite would need to resemble Jupiter's moon Io in size and mass, with other planets maintaining a slightly elongated orbit that enables tidal heating. These are possible explanations, not detections of an escaping flow or a satellite. The authors also note that the satellite explanation fits with reports that ultra-cool dwarfs with distant companions are more likely to be detected emitting radio waves.

Young explorerSome very cool stars and star-like objects give off radio signals that hint at belts of tiny charged particles around them, like Jupiter has. Scientists used calculations to explore where the particles around one such object could come from. Maybe they escape from its upper air, but only if certain conditions are right. Or maybe a nearby moon with volcanoes supplies them. The calculations say both ideas could work under the right conditions, but they do not show that the volcanic moon is really there.

Physical Characterization of Moon Impactor 2025-010D

Tanner Campbell, Adam Battle, Bill Gray+4 more

• Instrumentation and Methods for Astrophysics

AstronomerGround-based physical and dynamical characterization identifies 2025-010D as a Falcon 9 upper stage predicted to strike the lunar farside on 2026 August 05. Backward orbital propagation independently links it to the “Ghost Riders in the Sky” launch. Visible and near-infrared spectra distinguish it from natural objects and show absorption bands consistent with spacecraft thermal-control materials. Photometric lightcurves confirm an elongated shape and reveal an unexpected change exceeding 8 s in its approximately 7 min rotation period during observations. The authors predict an impact between Bell and Einstein craters at approximately 2.4 km/s, producing a roughly 40 m crater; these are predictions, not observed outcomes. Its independently known provenance makes it a benchmark for characterizing cislunar objects of uncertain origin.

PublicResearchers used ground-based observations and orbit calculations to study 2025-010D, a discarded Falcon 9 rocket stage predicted to hit the Moon’s far side on August 5, 2026. Tracing its orbit backward independently connected it to the “Ghost Riders in the Sky” launch. Its reflected-light spectrum distinguishes it from natural objects and contains features consistent with materials used to control spacecraft temperatures. Changes in brightness confirm its elongated shape and show that its roughly seven-minute spin period unexpectedly changed by more than eight seconds during observations. The team predicts a collision between Bell and Einstein craters at about 2.4 kilometers per second, making a crater roughly 40 meters wide. The impact has not been reported as observed. This object’s known origin offers a useful test case for identifying other poorly tracked objects near the Moon.

Young explorerScientists studied a used-up rocket part traveling near the Moon. They worked backward along its path to check which launch it came from. Its light gives clues about spacecraft materials, and its changing brightness shows that it is long and spinning. They also found that the time it takes to spin around changed unexpectedly. They predict it will hit the side of the Moon we cannot see from Earth on August 5, 2026, and make a new crater. That crash is a prediction, not something they have seen happen. Studying this rocket part can help scientists recognize other mystery objects near the Moon.

3D Global Climate Simulations of Synthetic Mars Warming

Tom N. Landefeld, Harald Lesch

AstronomerThis modeling study tests aerosol-induced warming of modern Mars using the Generic Planetary Climate Model over one Martian year (669 sols). The scenario completely replaces natural dust with a single injection of radiatively active aluminium nanoparticles, without continuous replenishment, and includes a regional water-ice sheet of 3400 kg/m² in Hellas Basin. Comparison with an unperturbed control examines surface temperatures, sublimation fluxes, and atmospheric water vapour to assess whether infrared greenhouse forcing can overcome ice-albedo cooling and initiate a self-sustaining water-vapour greenhouse. The abstract describes the simulation framework and questions but provides no numerical outcomes or verdict on feasibility; it reports no observational demonstration.

PublicCould engineered particles help warm Mars despite a shortage of materials available to build a warming atmosphere? Researchers investigate this possibility with a three-dimensional climate simulation lasting one Martian year. Their scenario replaces natural airborne dust with a single injection of aluminium nanoparticles rather than continually adding particles. It also includes a large regional water-ice sheet in Hellas Basin, whose reflection of sunlight could counteract warming. The study tests whether particle-induced warming could release enough water vapour to sustain further greenhouse warming. The abstract does not state whether this succeeds: this is a computer-model investigation, not evidence that Mars has been warmed.

Young explorerScientists used a computer model to ask whether tiny aluminium particles in Mars's air could help keep the planet warm. In their pretend Mars, they replaced the dust with these particles just once. They also included a big patch of ice, which could bounce sunlight away and make warming harder. They wanted to see whether warming could turn some ice into water vapour that would help keep Mars warm. This summary does not tell us whether it worked, and they did not try it on the real Mars.

Correlative Microstructural Analysis of a Weathered Nantan Meteorite Fragment

Graeme J. Francolini, Brendan V. Dyck, Paul Mack+1 more

• Geophysics
• Materials Science

AstronomerA correlative study of a naturally weathered Nantan meteorite fragment used XPS, EDS and XRF to characterize chemistry and composition, and XRD and EBSD to identify phases and microstructure. The analyzed matrix was predominantly magnetite, with secondary goethite and maghemite. Two distinct regional contrasts were observed: one in Ni content, and another in grain size and Cl distribution. High-Ni (≥2.6 at%) and low-Ni (≤0.9 at%) regions are interpreted as weathered remnants of plessite and kamacite, respectively, from a former Widmanstätten pattern; distinct weathering mechanisms for kamacite and taenite within plessite are suggested rather than established. A visible boundary 100–200 μm wide marked a rapid transition from fine to elongated grains and from low, dispersed Cl to concentrated Cl spots. A brecciated phase was identified as a large cohenite grain showing weathering features, including vein-like matrix extensions composed of NiO and magnetite, plus iron and nickel carbonate deposits. These findings characterize one naturally weathered fragment within a process whose evolution depends on local conditions and exposure time.

PublicA study of a naturally weathered fragment of the Nantan meteorite shows how iron-rich meteorite material can change after reaching Earth. Several complementary chemical and structural methods found that the fragment’s main matrix consisted mostly of magnetite, with smaller amounts of goethite and maghemite. Researchers also observed regions with different nickel contents, and regions differing in crystal-grain size and chlorine distribution. They interpret the nickel-rich and nickel-poor areas as traces of the meteorite’s earlier metal structure, but the proposed differences in how its original metals weathered remain an interpretation. A large cohenite grain showed further evidence of alteration, including vein-like features containing nickel oxide and magnetite, and deposits of iron and nickel carbonates. The study describes changes in this particular fragment; weathering depends on both the conditions where a meteorite lands and how long it is exposed.

Young explorerA meteorite is a rock that falls to Earth from space. Scientists studied a piece of one called Nantan to see how its iron-rich parts had changed after landing. They found several kinds of minerals, mostly one called magnetite. Different parts had different amounts of nickel, and some had tiny grains while others had longer grains. The scientists think some of these differences are clues to what the meteorite looked like before it changed, but they are not sure exactly how all the changes happened. Where a meteorite lands and how long it stays there can affect how it changes.

Unveiling photometric transients with the ILMT and their follow-up using DOT

Priyanshi Kumari, Bhavya Ailawadhi, Talat Akhunov+10 more

• High Energy Astrophysical Phenomena

AstronomerThe study presents selected photometric transients, specifically supernova candidates, discovered with the 4-m International Liquid Mirror Telescope (ILMT) at Devasthal, India. ILMT continuously surveys a 22.3′ × 22.3′ strip of zenith sky, using the PyLMT pipeline with optimised image subtraction and convolutional neural networks for transient detection and classification. The authors investigate the candidates’ photometric and spectroscopic properties through ILMT light curves supplemented by ZTF data and spectra from the complementary 3.6-m Devasthal Optical Telescope (DOT). Spectroscopy is needed to confirm transient types; the abstract does not report confirmed classifications or specific characterisation results.

PublicTwo telescopes at Devasthal in India work together to study objects whose brightness changes. The International Liquid Mirror Telescope searches a strip of sky overhead, while software compares images and uses a neural network to find and classify possible events. The Devasthal Optical Telescope provides spectra, which separate light by wavelength and are needed to confirm what kind of event has occurred. This study examines a selection of possible supernovae using brightness measurements from ILMT and ZTF together with DOT spectra. The abstract describes the investigation but does not state which candidates were confirmed as supernovae or what their detailed properties were.

Young explorerOne telescope in India looks for things in the sky that change how bright they are. Another telescope helps scientists study their light to find out what they might be. The scientists are checking some things that could be exploding stars, called supernovae. They watch how the light changes and look at its different colors for clues. This short report does not say which ones were shown to be exploding stars.

jax-SNANA: A GPU-accelerated Supernova Framework for the SBI Era

Matthew Grayling

• Cosmology and Nongalactic Astrophysics

AstronomerThe authors present jax-SNANA, a JAX reimplementation of SNANA for GPU-accelerated transient simulation, light-curve fitting, supernova standardisation and cosmological inference. In single precision on an NVIDIA A100 GPU, after JIT compilation, it simulates more than 100,000 supernovae per second with LSST observing conditions and fits 5,000 light curves per second, reporting a roughly two-orders-of-magnitude speedup over current tools. These are computational benchmarks, not measurements of an observed supernova sample. Comparisons with SNANA show excellent consistency across the tasks tested. Supported models include SALT, BayeSN, physical models from redback-jax and various supernova SED templates; fitting accommodates photometric and spectroscopic redshifts. The modular pipeline also supports simulations of generic supernova–host relationships and multiple event sub-populations. It is designed for future simulation-based inference applications, including compiled simulations within training loops, rather than presenting a new cosmological result. The code is publicly available and installable through pip.

PublicResearchers have developed jax-SNANA, a faster software package for simulating stellar explosions called supernovae and fitting models to how their brightness changes over time. It also supports using supernovae to study cosmology. In a reported test on an NVIDIA A100 graphics processor, using single-precision calculations after an initial compilation step, the software simulated more than 100,000 supernovae per second as they would be observed by LSST and fitted 5,000 brightness records per second. The authors report speeds about 100 times those of current tools and excellent agreement with the existing SNANA software in the tasks compared. These results concern software performance and simulated events, not newly observed explosions or new findings about the universe. The package can model different kinds of supernovae and their relationships with host galaxies, and is designed to support future methods that learn from simulations. It is publicly available and can be installed through pip.

Young explorerScientists made a fast computer tool to pretend that stars are exploding and work out how their light changes. They checked it against an older tool and say the answers matched very well in their tests. The new tool can make lots of pretend star explosions very quickly. These are computer-made explosions, not new explosions found in the sky. Scientists can use the tool to help study real star explosions and the universe.

Neural networks applied to forecasting the astroclimatic and meteorological parameters in an operational context

C. Weinberger, E. Masciadri, M. De Sepibus+4 more

AstronomerThis study investigates neural-network algorithms for operational forecasting of atmospheric and astroclimatic parameters, motivated by potential applications to ground-based telescope operations, adaptive optics, and free-space optical communication. The abstract cites prior research identifying the AR technique as the best-performing approach for one-hour forecasts, with a seeing RMSE of 0.1 arcseconds. Neural networks are explored as possible alternatives that could improve on AR or serve where AR cannot be applied; no demonstrated superiority over AR or Random Forest is reported. The study also examines training-data gaps associated with the absence of daytime optical-turbulence measurements. Tests here use wind speed and provide evidence suggesting that measurements spanning the full 24 hours might improve forecast performance. The work is conducted within the LBT ALTA Center and VLT FATE operational forecasting efforts.

PublicForecasting atmospheric conditions helps ground-based telescopes plan observations and adjust systems that correct atmospheric image distortion. It also matters for communication using light through the atmosphere. This study explores neural networks as possible forecasting tools, but does not report that they outperform the existing AR method, which earlier research found best for one-hour forecasts. The researchers also examine how missing daytime measurements affect the data used to train forecasting algorithms. Their tests use wind speed and suggest that measurements covering both day and night might improve predictions; the abstract does not establish the same improvement for optical turbulence itself. The work is part of operational forecasting efforts for the LBT and VLT telescopes.

Young explorerAir can make the view through a telescope blurry. Scientists are trying computer tools that learn from measurements to help guess what the air will do next. In this study, they tested guesses about how fast the wind would blow. Their tests suggest that collecting measurements during both the day and the night might help the tools make better guesses. They have not shown that these new tools are better than the method already used.

Studying the Near-horizon Jet of M87 using Millimeter Balloon-borne VLBI stations

Felix M. Thiel, Dominic W. Pesce, Mayukh Bagchi+2 more

AstronomerSynthetic VLBI observations test a near-future EHT configuration augmented by one or three 2.5 m-class balloon-borne stations on a northern transatlantic trajectory from Kiruna, Sweden. The simulations assume frequency phase transfer between 230 and 86 GHz. Balloon stations would operate above 99.5% of the atmosphere, with their motion providing efficient uv-plane sampling. The simulated arrays add baselines down to 0.2 Gλ with one balloon and 0.07 Gλ with three, enabling Bayesian image reconstructions to recover M87 jet structures extending to 150 and 300 microarcseconds, respectively. Relative to EHT-only simulations, the authors report jet NRMSE improvements by factors of 1.2 and 1.3. These are simulation results under the stated assumptions, not observations from deployed balloon stations.

PublicComputer simulations suggest that adding balloon-carried radio telescopes to a near-future Event Horizon Telescope array could improve images of the base of M87's jet. The study models one or three balloons flying across the northern Atlantic from Kiruna, Sweden, above 99.5% of the atmosphere. Their movement would help fill gaps in the information collected by the telescope network. In the simulations, one balloon allowed reconstruction of jet structures extending to 150 microarcseconds, while three allowed structures extending to 300 microarcseconds. Both configurations improved an image-error measure compared with simulations using the EHT alone. These improvements have not been demonstrated in real balloon observations and depend on assumptions, including a technique that uses signals at one observing frequency to help calibrate another.

Young explorerScientists used a computer to try out an idea: send radio telescopes high into the sky on balloons to work with telescopes on the ground. In the computer test, the balloons helped make better pictures of a stream of material called a jet in M87. Three balloons showed more of the jet than one. This was a computer test, not pictures taken by real flying balloons, so scientists still need to find out how well it would work in the sky.

Optimal Design of Shaped Pupil Lyot Coronagraph for China's Large Segmented Telescope

Kaining Yang, He Sun, Bin B. Ren+7 more

AstronomerThe study optimizes a Shaped Pupil Lyot Coronagraph (SPLC) for the planned EAST and LOT telescopes, whose segmented, centrally obscured apertures produce diffraction that limits contrast at small inner working angles. The architecture combines a binary shaped-pupil apodizer, focal-plane occulting mask, and Lyot stop with two deformable mirrors for atmospheric and residual-aberration correction. End-to-end simulations using Lenghu site parameters and assuming idealized extreme adaptive-optics correction yield raw contrasts of order 10^-6–10^-7 in V, H, and K. These are upper-bound performance estimates, not on-sky measurements. The simulations suggest that the design can mitigate aperture diffraction while retaining a small inner working angle and practical throughput, making it a promising option for future high-contrast exoplanet imaging.

PublicResearchers investigated a way to block bright starlight so that China's planned EAST and LOT telescopes could more readily image planets and disks around other stars. Gaps between mirror segments and structures supporting the telescope optics scatter light, making nearby faint targets difficult to see. The proposed design combines light-blocking masks with two mirrors that change shape to correct distortions. Computer simulations using conditions for the Lenghu site suggest that it could reach raw contrast levels of about 10^-6 to 10^-7 in visible and infrared bands. However, the simulations assume idealized correction of atmospheric distortions, so they represent an optimistic performance limit rather than demonstrated telescope results.

Young explorerA star is so bright that it can hide a little planet beside it. Scientists are testing a design for future big telescopes that uses special masks to block starlight and two mirrors that change shape to help make the view clearer. Their computer tests suggest the design could help reveal faint planets. But the tests assume the system works extremely well, so they do not yet show how well it will work with a real telescope.

Development and characterization of a millimeter-wave circular polarization observation method using a quarter-wave plate with Simons Array

Kana Sakaguri, Darcy R. Barron, Yuji Chinone+17 more

AstronomerThe authors demonstrate a 90 GHz circular-polarization measurement technique on the Simons Array, combining a quarter-wave plate installed ahead of the receiver with a continuously rotating half-wave plate. The quarter-wave plate converts incident circular polarization into linear polarization accessible to the existing detectors; laboratory tests yield 99.0% conversion efficiency. Observations of Jupiter and Tau A establish the calibration and characterize instrumental leakage. The adopted measured Stokes V polarization efficiency is 46±2%, and U-to-V leakage is −11.7±5.1%. For Tau A, the measured circular-polarization fraction is V/I = 0.78±0.42%, which is not a significant detection. This measurement serves as a consistency check on calibration and systematic-uncertainty treatment. The work establishes the instrument response model and calibration parameters for a companion circular-polarization source search.

PublicResearchers demonstrated a way to measure circular polarization—a property describing how a light wave’s electric field rotates—at a frequency of 90 GHz using the Simons Array. They added an optical plate that converts circular polarization into linear polarization, which the instrument’s detectors can already measure, and used it together with another continuously rotating plate. The conversion plate achieved 99.0% efficiency in laboratory tests, but the calibrated instrument’s overall efficiency for measuring circular polarization was 46±2%. Observations of Jupiter and Tau A helped calibrate the system and measure how linear polarization can leak into the circular-polarization signal. The circular-polarization fraction measured for Tau A was 0.78±0.42%, not a statistically significant detection. The main outcome is a tested instrument model and calibration for a companion search, rather than evidence of circular polarization from Tau A.

Young explorerLight can wiggle in different ways. Scientists added a special plate to a telescope so it could look for light whose wiggle turns around in a circle. The plate changes that wiggle into a kind the telescope can measure. They tested the plate in a laboratory and used Jupiter and a bright space source called Tau A to check the telescope. They did not find a clear circular-wiggle signal from Tau A. These checks help them understand the telescope and prepare to search for such signals.

Identifying Planetary Nebulae Candidates from IPHAS and VPHAS+ Surveys via YOLO Deep Learning Models

Titouan Sérandour, Anne-Laure Méalier, Bruno Colicchio+5 more

• Astrophysics of Galaxies

AstronomerThe authors present a YOLO-based planetary-nebula detection pipeline for IPHAS and VPHAS+, using HiPS-preprocessed r, i, and Hα RGB images and HASH labels for approximately 2,600 PNe. Two datasets use 640 × 640-pixel images at full resolution and 1,280 × 1,280-pixel images designed to capture objects extending up to 0.2°. With metrics adapted to diffuse, low-contrast emission and a very permissive 1% intersection-over-union threshold, k-fold cross-validation of YOLOv12m on the first dataset yields an average precision of 0.979; at a confidence threshold of 0.15, precision is 98.7% and recall is 97.4%. The pipeline was deployed on larger images across approximately 3,755 square degrees, but the survey-wide detection analysis is preliminary. The authors report robustness against CCD corner defects and HiPS tile joints, and test-set performance comparable to or better than a recent Swin Transformer approach. Distinguishing PNe from mimics such as H II regions in crowded Galactic fields remains an unresolved challenge; the strong validation metrics do not establish equivalent survey-wide performance.

PublicThe researchers developed an artificial-intelligence system to identify planetary nebulae in images from two sky surveys. They trained it using images labelled with about 2,600 known planetary nebulae. In cross-validation on one image dataset, the system achieved 98.7% precision and recovered 97.4% of the labelled nebulae at a chosen confidence setting. These scores used a very lenient rule for how closely a detection had to overlap a labelled object, reflecting the nebulae’s faint, fuzzy appearance. The team also ran the system across about 3,755 square degrees of sky, but its analysis of those detections is still preliminary. The system handles some image defects well, yet it still struggles to distinguish planetary nebulae from similar-looking objects in crowded parts of our Galaxy. Its strong test results therefore do not mean that every survey detection is a genuine planetary nebula.

Young explorerThe scientists taught a computer to look for fuzzy space clouds called planetary nebulae in sky pictures. They showed it lots of labelled examples, and it did very well in tests that allowed loose matches around the fuzzy clouds. Then they used it to search many more pictures, but they are still studying what it found. Some other space clouds look almost the same, so the computer can still get confused.

RPCA: a Resolved PSF reconstruction method for undersampled images

Lin Nie, Huanyuan Shan, Guoliang Li+11 more

AstronomerThe authors introduce Resolved Principal Components Analysis (RPCA), an EMPCA-based method that explicitly accounts for pixel integration to reconstruct resolved PSFs from undersampled stellar images. Tests use simulated China Space Station Telescope (CSST) PSFs incorporating observational and detector-induced effects, rather than on-sky observations. In these tests, RPCA achieves higher precision in PSF shape parameters than MCCD, RCA, and PSFEx; the authors report that it could reduce the fractional squared-size bias, ΔR²/R², by approximately an order of magnitude relative to those methods. It also shows stability across varying signal-to-noise ratios and contamination by cosmic rays and bad pixels. These simulation results suggest RPCA is a promising candidate for future CSST PSF modeling, not an established performance result from telescope operations.

PublicA telescope spreads the light from a star into a small pattern called its point-spread function, or PSF. Modeling this pattern accurately matters for studying galaxy shapes, estimating distances from their light, and measuring weak gravitational lensing. The researchers developed a method called RPCA to recover a more detailed PSF when images have too few pixels to show its structure clearly. It accounts for how each pixel collects light across its area. In simulated images for the China Space Station Telescope, RPCA estimated the pattern's shape more precisely than three comparison methods and could reduce one measure of size bias by roughly a factor of ten. It also remained stable in tests with different noise levels, cosmic-ray contamination, and defective pixels. The findings are promising, but they come from simulations rather than observations with the telescope.

Young explorerWhen a telescope takes a picture of a star, the star looks like a little blurry spot. Scientists want to understand that blur so they can study space more carefully. They made a new computer method to work out the blur even when the picture has too few little squares, called pixels, to show it clearly. In pretend telescope pictures made by a computer, the new method did better than three other methods, even when the pictures had noise or some spoiled pixels. It might help a future space telescope, but it has not yet been shown to work in that telescope's real pictures.

R&D activity in INAF on light instrumentation for continuous optical turbulence monitoring

Camilo Weinberger, Elena Masciadri, Luca Carbonaro+5 more

• Atmospheric and Oceanic Physics

AstronomerThe authors present an automated, portable station designed for continuous night-time seeing and optical-turbulence measurements, integrating Cyclope, RINGSS, and scintillometer sensors. An on-site automation system monitors operational status and sensor conditions, provides real-time measurements, and synchronizes with data storage. The RINGSS turbulence profiler has been installed and programmed in collaboration with the LBT team; comparisons of the lower-cost Cyclope and scintillometer with RINGSS are planned, not reported as results. The station is intended to support local data generation, turbulence analysis, R&D, and on-site testing of forecasting methods. This work complements the Arcetri team's operational ALTA and FATE forecast systems above LBT and VLT, respectively. The abstract states that reliable forecast training requires at least two years of continuous data, but does not report such a dataset or quantitative performance results for the station. A dedicated instrument for both night-time and daytime measurements is planned.

PublicUnsteady air affects observations from ground-based telescopes and the transmission of light signals through open air. The authors describe a portable, automated station that combines three sensors to monitor these atmospheric effects at night. It checks the sensors, supplies real-time information, and coordinates data storage. The goal is to build local records that can support research and tests of forecasting methods, helping observers plan and optimize systems that correct atmospheric distortion. The team plans to compare two lower-cost sensors with a turbulence-measuring instrument already installed, but the abstract gives no comparison results or numerical accuracy measurements. It says reliable forecast training needs at least two years of continuous data. An instrument for measurements during both day and night is also planned.

Young explorerMoving air can make stars look blurry through a telescope. Scientists describe a portable station with three tools to watch what the air does at night. It can check its tools and help save their measurements. They hope these records will help them predict when the air will be better for looking at the sky. They still plan to compare the tools, and they have not shared those results here. A tool that works in daytime too is planned.

Geometrical and Optical Design of the GUEST Laser-Ranged Test Masses for the Detection of Gravitational Waves in the μHz range

Dario Vetrano, Giada Bargiacchi, Nicolò Burzillà+5 more

AstronomerThis study proposes an optical architecture for GUEST, a mission intended to detect gravitational waves in the largely unexplored microhertz band through precise orbital tracking. Its highly eccentric orbit requires operation at low velocity and long range near apogee, and high velocity and short range near perigee. The proposed spherical layout combines corner-cube retroreflectors with 1-inch and 2-inch apertures, aiming for an isotropic, homogeneous optical response and efficient packing. Optical cross-section is evaluated with a custom reduced-order model calibrated by reconstructing the optical response of LARES-2. The model assesses each reflector type’s contribution along the orbit. Sensitivity analyses explore reflector proportions, laser wavelength, spacecraft diameter, dihedral angle offsets, and mechanical configurations. The abstract reports a design and modeling study, not a gravitational-wave detection, and gives no quantitative performance outcomes.

PublicThe proposed GUEST mission aims to search for very slow gravitational waves by tracking a satellite’s orbit with high precision. This paper focuses on designing its reflective surface to work under two very different conditions: when the satellite is far away and moving slowly, and when it is closer and moving quickly. The design mixes two sizes of corner-cube reflectors across a spherical spacecraft, aiming for a consistent optical response in different directions. The researchers evaluated the design with a simplified computer model calibrated by reconstructing another satellite’s optical response, and explored how design choices affect it. The abstract does not report gravitational-wave detections or numerical performance results.

Young explorerScientists want to track a satellite very carefully to look for slow ripples in space called gravitational waves. They propose covering it with two sizes of special reflectors that send light back. These need to work when the satellite is far away and slow, and when it is closer and fast. The team used a computer model to study the design. They have not reported finding the ripples.

Updates to STIS NUV Dark Calibration

Jacqueline Brown, Sean Lockwood, TalaWanda Monroe+2 more

AstronomerNew superdark reference files (DARKFILEs) and a dark correction table (TDCTAB) have been produced for HST STIS NUV-MAMA observations from Cycle 19 onward. The superdarks combine 12 years of near-ultraviolet dark exposures and use an updated temperature-scaling equation developed in 2013 to characterize the detector dark rate more accurately. In tested datasets, they yield an average 3% increase in signal-to-noise ratio and smooth out a ring artifact caused by previous dark-rate oversubtraction. The reference files have been delivered to CRDS, and all affected datasets in MAST have been recalibrated; the reported performance gain is specific to the tested datasets.

PublicThe team has improved calibration files used to remove detector-generated background from near-ultraviolet observations made with Hubble’s Space Telescope Imaging Spectrograph. The new files draw on 12 years of background exposures and an updated description of how the background changes with temperature. In the datasets tested, the correction improved signal-to-noise ratio by an average of 3% and smoothed out a ring-shaped artifact left by subtracting too much background. The new files are now in the calibration reference system, and all affected observations from Hubble Cycle 19 onward in the telescope’s archive have been recalibrated. The tests do not establish that every observation improves by the same amount.

Young explorerOne of Hubble’s cameras adds a little unwanted background to its pictures, even when no light is reaching it. Scientists used 12 years of checks to make a better way to clean that background away. In the pictures they tested, the new cleanup made the useful information a little clearer and smoothed out a ring mark caused by taking away too much background before. They have already used the new cleanup on all the stored observations that needed this update.

Refurbishment and Cryocooler Upgrade of the CPAPIR Wide-Field Near-Infrared Camera: Design, Integration, and Lessons Learned

Philippe Vallee, Jonathan St-Antoine, Lison Malo+5 more

AstronomerCPAPIR, a wide-field near-infrared imager operating at the Observatoire du Mont-Mégantic since 2004, has undergone a major refurbishment following detector degradation, including the loss of one quadrant, and operational constraints from liquid-nitrogen cooling. The detector was replaced and a Sunpower CryoTel DS30 cryocooler integrated to extend instrument lifetime and reduce maintenance requirements. The paper describes the thermal and mechanical redesign using finite element analysis, three-dimensional CAD modeling, hardware selection, and laboratory validation, with emphasis on vibration mitigation and cryogenic integration. It discusses performance improvements and lessons learned, but the abstract provides no quantitative performance metrics. On-sky commissioning is scheduled for summer 2026, rather than reported as completed.

PublicA wide-field camera that detects near-infrared light at the Observatoire du Mont-Mégantic has been refurbished after more than two decades of use. Its aging detector had lost a quarter of its detecting area, and its liquid-nitrogen cooling system created operational difficulties. The team replaced the detector and installed a new cooling machine, aiming to keep the camera working longer with less maintenance. The paper describes engineering models, laboratory testing, and challenges such as limiting vibrations. It discusses improved performance without giving numerical results in the abstract. Testing the upgraded camera on the sky is scheduled for summer 2026.

Young explorerA special camera at an observatory helps people look at the sky using light our eyes cannot see. After many years, part of its light-catching piece stopped working, and keeping it very cold was difficult. The team put in a new light-catching piece and a new cooling machine. They tested it in a laboratory and worked on keeping it from shaking too much. They plan to try the fixed-up camera on the sky in summer 2026.

International Astrophysical Consortium for High-energy Calibration: Summary of the 18th IACHEC Workshop

K. K. Madsen, C. E. Grant, V. Burwitz+14 more

AstronomerThis report summarizes the 18th International Astronomical Consortium for High Energy Calibration (IACHEC) Workshop in Pelham, Germany, where 56 scientists involved in calibrating operational and future high-energy missions met for four days. Working Group reports cover the status of cross-calibration among current X-ray observatories and possibilities for improvement, including standard calibration sources, multi-observatory campaigns, statistical methods, instrument calibration, background characterization, and knowledge preservation. The abstract describes the scope of these activities but provides no specific calibration measurements or quantified improvements.

PublicScientists need to understand how different X-ray observatories measure signals so that their observations can be reliably compared. This report summarizes a four-day meeting in Pelham, Germany, where 56 scientists discussed the current agreement between observatories and ways to improve it. Topics included reference sources, coordinated observations, statistical methods, instrument behavior, background signals, and preserving calibration expertise. The abstract outlines the discussions rather than reporting specific improvements in accuracy.

Young explorerScientists use special telescopes to study light called X-rays. They want to understand how each telescope measures that light, so they can compare what the telescopes see. This report is about a meeting where scientists shared ways to check their telescopes and make those comparisons better. It does not tell us that they have already made the telescopes work better.

Quantum noise and torque correlations in a torsion-bar Sagnac speed meter

Yuki Inoue, Mario Onglao, Daiki Tanabe+3 more

• General Relativity and Quantum Cosmology

AstronomerAn input-output model of the CHRONOS torsion-bar Sagnac speed meter predicts that vacuum fields entering behind the end and middle test masses can dominate low-frequency quantum noise despite strong cancellation of opposing torques. For a reference configuration with mirror power transmissions of 10^-7, these fields contribute 89.7% of the quantum-noise power spectral density at 0.1 Hz; neglecting them underestimates the amplitude spectral density by a factor of 3.11. The model links correlations from successive optical interactions to bar forces and the measured signal, showing why torque cancellation alone does not guarantee improved sensitivity. Replacing transmission with absorption at fixed reflectivity leaves the excess noise essentially unchanged at the two operating points studied. Predicted signal response and quantum noise agree with independent FINESSE 3 calculations as recycling detuning and homodyne angle vary. These are modeling results, not detector measurements, and identify rear vacuum fields as a design-limiting noise source in this configuration.

PublicCalculations for CHRONOS, a detector design for low-frequency gravitational waves, identify an important source of quantum noise: fluctuations entering through mirrors from behind its sensing masses. The optical arrangement cancels opposing twisting forces, but the study predicts that this cancellation does not necessarily make the signal easier to detect. In one reference configuration, the extra fluctuations account for 89.7% of the quantum-noise power at 0.1 Hz, even with extremely small mirror transmission. Ignoring them would make the predicted noise amplitude too small by a factor of 3.11. Independent computer calculations support the predictions. For the two operating conditions tested, replacing mirror transmission with absorption did not substantially reduce the excess noise. The findings guide mirror and signal-readout design; they are not measurements from an operating detector.

Young explorerScientists used computer calculations to study a machine designed to listen for tiny ripples in space. Tiny quantum wiggles can sneak through its mirrors and make the ripples harder to hear. Even when pushes on its bars cancel, the unwanted noise can remain. The calculations help scientists understand what the mirrors and listening system need to do.

Validation of Satellite Lifetime Predictions at Leonid Space

Scott Shambaugh

AstronomerThe authors backtest Leonid Space’s satellite lifetime prediction pipeline against the final year of flight of 878 deorbited satellites spanning six decades. The pipeline combines orbit propagation, ballistic coefficient estimation from on-orbit TLE data, assimilated atmospheric density corrections, custom space weather forecasts, and Monte Carlo uncertainty analysis. Four validation stages progressively replace historical inputs with forecasts, moving from hindsight-assisted “perfect knowledge” to a fully predictive setup analogous to forecasting for a satellite flying today. Using probabilistic scoring and calibration metrics, the study reports median one-year prediction accuracy of 3.9 days (1.1%) with perfect knowledge and 44.9 days (12.3%) in the fully predictive case. Solar flux forecasts account for 89% of prediction variance. These are retrospective validation results, not prospective tests on currently orbiting spacecraft. The authors also propose using operationally relevant satellite lifetime predictions as a framework for scoring solar cycle forecasts.

PublicHow well can we predict when a satellite’s time in orbit will end? The researchers tested Leonid Space’s prediction system using records from 878 satellites that had already left orbit. They reconstructed forecasts for each satellite’s final year, progressively removing information that would only have been available afterward. With that hindsight included, the reported median accuracy was 3.9 days; when using forecasts instead, it was 44.9 days, or 12.3% of a year. Forecasts of the Sun’s activity accounted for 89% of the variation in the predictions. The study tests the system on past events under increasingly realistic forecasting conditions; it does not report a test that waited for future satellite lifetimes to unfold.

Young explorerScientists want to guess when a satellite will finish its time going around Earth. They tested their guessing tool with old records of 878 satellites. To make the test fairer, they stopped giving the tool clues that people would only learn later. Its guesses then were typically about 45 days off. Guessing what the Sun would do was the biggest source of differences in its answers. This was a test using the past, not a promise about the future.

CHRONOS Science Program

Yuki Inoue, Masashi Hazumi, Hsiang-Yu Huang+5 more

• Cosmology and Nongalactic Astrophysics
• General Relativity and Quantum Cosmology

AstronomerThis White Paper proposes CHRONOS, a cryogenic torsion-bar interferometer targeting precision measurements at 0.1–10 Hz. Its optical design combines a Sagnac speed-meter readout, power and signal recycling, and balanced homodyne detection. Reference sensitivity projections combine classical noise with a multi-input quantum model that includes rear-mirror vacuum fields and measurement-back-action correlations. Two operating points are optimized for complementary power-law-integrated sensitivity objectives. Gravitational-wave forecasts share this noise budget and specify source and observing assumptions; science targets include intermediate-mass black-hole binaries and stochastic backgrounds, alongside quantum measurement and terrestrial gravity perturbations. Dark-matter applications remain response and feasibility studies. A differential gravitational calibrator is proposed for a Yukawa-gravity test, with auxiliary-harmonic subtraction intended to lower its systematic floor. The paper outlines calibration and staged development, not demonstrated performance: all projected reach depends on validating noise, transfer functions, environmental backgrounds, and systematic uncertainties.

PublicCHRONOS is a proposed very cold instrument that would use laser light to measure tiny twisting motions in the 0.1–10 Hz frequency range. Its planned science includes searching for gravitational waves from intermediate-mass black-hole pairs and background gravitational-wave signals, as well as studying quantum measurement and changes in Earth's local gravitational field. The paper describes the design, calibration, and step-by-step development plan. Its sensitivity estimates and gravitational-wave forecasts are calculations, not measured performance. Dark-matter possibilities are explored only as feasibility studies, and a separate gravity test is proposed. Whether the instrument can achieve these goals depends on checking its noise, response, environmental disturbances, and measurement errors experimentally.

Young explorerScientists have a plan for a very cold machine called CHRONOS. It would use light to measure tiny twists and look for tiny ripples in gravity. This paper explains how they hope to build and test it. They have calculated what it might do, but still need experiments to find out whether it works as hoped.

Investigation and Mitigation of a Prominent Off-Axis Stray Light Path in Rubin Observatory Commissioning

Alex Drlica-Wagner, Alessio Taranto, Gabriele Rodeghiero+12 more

• Cosmology and Nongalactic Astrophysics

AstronomerThe “scratched tape” feature was the most prominent and prevalent stray-light artifact identified during Vera C. Rubin Observatory commissioning. Light arriving from large off-axis angles, approximately 20 degrees, passes between the mid-level and center-section baffles, reflects from the primary mirror, and illuminates the LSST Camera focal plane. Delayed integration of the dome slit light-wind screen left this path unobstructed to the sky during commissioning. The document describes the artifact’s identification, modeling, characterization, and mitigation, but the abstract gives no quantitative mitigation results.

PublicDuring commissioning of the Vera C. Rubin Observatory, unwanted light produced an image artifact nicknamed “scratched tape,” the most prominent and common stray-light feature identified at that stage. Light entering from about 20 degrees away from the telescope’s pointing direction slipped between light-blocking structures, bounced off the main mirror, and reached the camera’s detectors. A delay in installing the dome slit’s light-wind screen had left this route open to the sky. The report describes how the team identified, modeled, studied, and addressed the artifact, without specifying how effective the mitigation was.

Young explorerWhile people were getting the Rubin telescope ready, light sneaked in through a gap, bounced off its big mirror, and reached its camera. It made an unwanted mark called “scratched tape.” A screen that would help block the light was not in place yet. The report tells how people found and studied the mark and worked on ways to stop it, but this short description does not say how well those ways worked.

Enhanced Astrometry of the Rapid ASKAP Continuum Survey: Mid and High Frequency Epochs

Akhil Jaini, Adam T. Deller, Yuanming Wang+3 more

AstronomerThe authors extend their RACS astrometric correction framework to RACS-Mid1 and RACS-High1, using hierarchical crossmatching with high-precision external catalogues to remove large-scale systematic positional errors. Median offsets are effectively eliminated. For source-position residuals averaged over approximately one-square-degree regions, the 68% confidence interval decreases from at least about 0.4 arcseconds to at most about 0.18 arcseconds across most of both surveys. Independent comparisons with multiple radio astrometric references establish approximately 0.25-arcsecond individual-source accuracy at the 1-sigma level over the bulk of the sky, with slightly poorer performance in the Galactic plane. Motivated primarily by ASKAP fast radio burst localisation, the corrections also support transient identification, multiwavelength host association, and radio-population studies. Combined with earlier low-frequency corrections, the authors identify RACS as the highest-precision arcsecond-resolution all-sky astrometric reference in the southern hemisphere at decimetre wavelengths.

PublicResearchers have improved the positions of radio sources in two parts of the Rapid ASKAP Continuum Survey by comparing them with precise external catalogues and correcting systematic errors. Independent checks show that corrected positions have a typical uncertainty of about 0.25 arcseconds at the one-standard-deviation level across most of the sky. Accuracy is slightly worse along the plane of our Galaxy. More reliable positions should help astronomers match radio sources to objects seen at other wavelengths and identify the origins of brief radio events, including fast radio bursts. The study improves the survey’s positional reference system; it does not report new burst discoveries or host identifications.

Young explorerAstronomers have a map of places in the sky that send out radio waves. Some dots on the map were a little out of place. They compared the map with other very careful maps and fixed those mistakes. Checks show that the dots are now much closer to where they should be, though some parts of the map are still a little less exact. This can help astronomers work out where a quick radio flash came from.

pynucastro 3: A community library for nuclear astrophysics

Zhi Chen, Khanak Bhargava, Eric T. Johnson+8 more

AstronomerThis release report describes updates to pynucastro, a community Python library for nuclear astrophysics. The project aims to support interactive exploration of nuclear properties, reaction rates, and reaction networks, and export of those networks to simulation codes. Additions since the previous major release include new rate approximations, a stellar equation of state, support for StarLib and rate uncertainties, and new network-exploration tools. The abstract reports software capabilities rather than observational findings or simulation results.

PublicThe authors describe an updated version of pynucastro, a community-built Python software library for studying nuclear reactions in astrophysics. It is designed to help researchers explore nuclear properties, reaction speeds, and linked sets of reactions, and transfer those reaction networks into simulation programs. Updates include new ways to approximate reaction speeds, a description of how stellar matter behaves, support for a reaction-rate library called StarLib and for uncertainty in reaction rates, and new exploration tools. This is a software update, not a report of a new astronomical discovery.

Young explorerScientists have updated a computer toolkit called pynucastro. It helps them explore how tiny pieces of matter can change and how those changes connect, when studying stars. The update adds more ways to describe these changes and how sure scientists are about how fast they happen. It also helps prepare instructions for computer simulations. The paper describes better tools, not something new spotted in the sky.

Modelling Fourier filtering wavefront sensors for PSD-based methods: the AOPERA tool

Romain Fétick, Vincent Chambouleyron, Lisa-Marie Mazzolo+6 more

AstronomerThe authors develop a power-spectral-density (PSD) based method for predicting adaptive-optics phase PSDs and point spread functions while accounting for wavefront-sensor sensitivity and nonlinear response. PSD methods offer speed and an interpretable error budget, but nonlinear sensors such as pyramid and Zernike wavefront sensors are challenging to represent. The new formalism incorporates Fourier-filtering wavefront-sensor sensitivity and treatment of nonlinearity into PSD-based numerical tools. Its implementation is compared with high-fidelity end-to-end simulations using OOPAO. Agreement in fitting, temporal, and noise errors supports the method’s treatment of sensor sensitivity and nonlinearity in these numerical comparisons. The reported validation is simulation-based, not an on-sky demonstration; the abstract gives no quantitative accuracy or runtime benchmarks.

PublicAdaptive optics helps large telescopes counteract atmospheric turbulence, bringing images closer to the sharpness their optics can theoretically achieve. Predicting how well these systems will work requires computer simulations. Faster simulation methods can break down the sources of image blur, but they struggle to describe some sensors whose response does not change in simple proportion to the incoming distortion. The researchers develop a method that includes these more complicated responses and predicts the resulting image shape. They compare it with detailed computer simulations and find similar results for three sources of error: imperfect correction, correction delays, and noise. This supports the method in those tests, but the abstract does not report tests on the sky or numerical measures of its accuracy or speed.

Young explorerMoving air can make a telescope’s pictures blurry. Special equipment helps make them sharper, and scientists use computers to work out how well it will help. These researchers made a new way for computers to describe tricky parts of that equipment. Its answers were similar to those from more detailed computer tests. That is encouraging, but they did not report testing the new method on real sky pictures.

Vector field dark matter search with Sagnac interferometer

Yuki Inoue, Quynh Lan Nguyen, Ippei Obata

• General Relativity and Quantum Cosmology
• High Energy Physics - Experiment
• Optics

AstronomerThis calculation forecasts improved quantum-noise-limited sensitivity to B-L vector dark matter using a material-asymmetric, dual-ring Sagnac speed meter rather than a Fabry–Perot Michelson position meter. Material contrast enables sensitivity to composition-dependent B-L forces. The comparison holds incident power, input-mirror transmissivity, and cavity round-trip length equal. For sapphire mirrors and a one-week benchmark, the quantum-noise-only median expected 95% confidence upper limit is 1.2 × 10⁻²⁷ at m_A = 4.1 × 10⁻¹⁴ eV/c² (10 Hz), a factor-57 improvement. The material-induced displacement is essentially unchanged; the gain comes from reduced low-frequency quantum backaction. The broader calculation indicates nearly two orders of magnitude improvement at the low-mass end. These are sensitivity forecasts, not a detection or demonstrated instrument performance: classical noise is assumed negligible, and achievable sensitivity at 10 Hz with realistic suspension and isolation remains unestablished.

PublicThe researchers calculate that a different way of reading a laser-based detector could make searches for low-mass vector dark matter much more sensitive. Their design uses contrasting materials to respond to a possible dark-matter force that depends on material composition, and measures motion with a Sagnac speed meter rather than a Michelson position meter. In a one-week benchmark, the predicted sensitivity improves by a factor of 57 at 10 Hz under matched operating conditions. The improvement comes not from a larger dark-matter signal, but from reducing quantum disturbances caused by the measurement. This is a theoretical forecast, not a dark-matter discovery. It assumes other noise is negligible; whether realistic supports and vibration isolation can deliver that sensitivity at 10 Hz is not yet established.

Young explorerScientists worked out a new way to use light and different materials to look for dark matter, something they are trying to find. Their idea could make tiny movements easier to notice because the light would disturb the mirrors less. But this is a calculation, not a discovery. Real equipment can shake too, and they have not yet shown that it can stay quiet enough.

Searching for Ultra-Light Axions with Twisted Cavity Resonators of Anyon Rotational Symmetry with Bulk Modes of Non-Zero Helicity

J. F. Bourhill, E. C. I. Paterson, M. Goryachev+1 more

• High Energy Physics - Phenomenology
• Instrumentation and Detectors
• Quantum Physics

AstronomerThe authors present twisted hollow resonators with equilateral triangular cross-sections and anyon rotational symmetry. Unlike conventional cavities, these structures permit bulk resonant modes with a nonzero complex overlap between the electric field and the complex-conjugated magnetic field. For axion searches using a pumped resonator, the analysis must retain both positive- and negative-frequency components of the real axion field: their Maxwell equations produce distinct upper and lower mixing branches. Including both branches shows that the real overlap produces amplitude-modulated sidebands, while the imaginary helicity of the studied modes produces phase-modulated sidebands through the axion–photon chiral anomaly. The authors therefore propose an ultralight-dark-matter experiment using an ultrastable oscillator and phase-sensitive readout, rather than report a detection. Crucially, the calculated sensitivity curves assume a phase-modulation noise floor, not an amplitude-modulation noise floor, and require sufficiently low residual oscillator phase noise at the axion Fourier frequency. The proposed scheme avoids an external magnetic field and permits superconducting resonators, offering reduced surface loss and enhanced axion sensitivity.

PublicThis work proposes a way to search for axions, a possible form of ultralight dark matter, using twisted hollow cavities with triangular cross-sections. Their unusual geometry allows the electric and magnetic fields of a resonant mode to overlap in a way conventional cavities do not. The analysis predicts that an axion interacting with a driven cavity could produce small changes in the timing, or phase, of its oscillation, distinct from changes in its amplitude. A very stable oscillator and a phase-sensitive detector might reveal these signals without an external magnetic field. That could allow superconducting cavities with lower surface losses and greater sensitivity. This is a proposed search method, not a dark-matter discovery. Its calculated sensitivity depends on achieving sufficiently low oscillator phase noise at the frequency of the possible axion signal.

Young explorerScientists have an idea for finding something invisible that might be dark matter. They would use a hollow, twisted shape where electric and magnetic fields wiggle. If tiny things called axions are there, they might change the timing of those wiggles just a little. The scientists would need a very steady wiggle and a careful way to watch it. They have worked out how this might work, but have not found dark matter with it.

Cosmic Rays as an Interdisciplinary Earth Observation Tool: From Particle Physics and Atmospheric Processes to Geosciences and Urban Science

Bugra Bilin, Nuhcan Akçit

• High Energy Physics - Experiment
• Atmospheric and Oceanic Physics

AstronomerThis review surveys how cosmic rays—high-energy particles originating in space and the atmosphere—have become tools for Earth observation over the past 20 years. It covers cosmic-ray-induced cascades and ionization, including effects on atmospheric chemistry and radiation; cosmogenic radionuclides for dating geological materials; cosmic-ray neutrons for large-scale soil-moisture and snow-water-equivalent monitoring; and muons for non-invasive subsurface imaging and urban monitoring with distributed sensors. Particular emphasis is placed on integration with remote sensing and geographic information systems to bridge the scale gap between point measurements and satellite observations and enable three-dimensional subsurface representations. The abstract presents a synthesis of applications, not new measurements or simulation results, and closes with discussion of data standards, operational Earth-observation integration, and future research.

PublicHigh-energy particles from space and the atmosphere are useful not only for studying physics and astronomy but also for observing Earth. This review describes how scientists use radioactive isotopes produced by cosmic rays to date geological materials, neutrons to monitor soil moisture and the amount of water stored in snow, and muons to image below the surface without digging. Muon measurements combined with networks of sensors also support city monitoring. The review emphasizes combining these methods with remote sensing and geographic mapping systems to connect local measurements with satellite observations and build three-dimensional views of what lies underground. It summarizes existing uses and discusses data standards and future work rather than reporting a new experiment.

Young explorerTiny, speedy particles come from space and are also made in the air. Scientists can use them as clues to learn about Earth: how old rocks are, how wet the soil is, how much water is in snow, and what is hidden underground without digging. This paper gathers ways scientists use those clues. It also talks about joining them with maps and pictures taken from far away to make better pictures of what is under our feet.