Tonight’s sky of new research

Point spread function requirements for dark matter subhalo detection with the Habitable Worlds Observatory

Georgios N. Vassilakis, Susan F. Redmond, Jason D. Rhodes+2 more

• Instrumentation and Methods for Astrophysics

AstronomerThis simulation study forecasts HWO sensitivity to subhalo perturbations in strongly lensed galaxy images, targeting masses below about 10^8 solar masses where dark-matter theories predict different subhalo populations and morphologies. It simulates 2000-second HRI exposures under the fiducial EAC1 design, assuming known source structure and excluding lens-galaxy light. Selecting 50 of 965 lenses using only arc signal-to-noise and relative gradient power reduces the median mass threshold for 10% aperture coverage by roughly a factor of ten. The top 12 lenses reach a median threshold of 6.6 × 10^7 solar masses at that coverage; median thresholds at the most sensitive positions are 3 × 10^7 and 1.5 × 10^7 solar masses for the top 50 and top 12, respectively. Non-linear fits support the Fisher forecasts at the tested masses and positions. For the top 12, increasing physical wavefront error from 35 to 65 nm RMS raises median thresholds by only 0.1 dex if the PSF is correctly modelled. Mismodelling the reference PSF instead removes detectable positions, while false detections remain rare. Illustrative sensitive-area retention criteria imply a median tolerated wavefront mismatch of 5 nm RMS, ranging from 2 to 10 nm. These are conditional forecasts, not observed subhalo detections: selective HWO follow-up of Euclid or Roman lenses could constrain dark-matter models if PSF characterization preserves the predicted sensitivity.

PublicDifferent theories of dark matter predict different numbers and shapes of small dark-matter clumps around galaxies. These clumps could leave subtle distortions in images of galaxies magnified and stretched by gravitational lensing. The researchers simulated how the planned Habitable Worlds Observatory might detect those distortions. Choosing the 50 most promising systems from 965 simulated lenses improved the typical mass sensitivity by about tenfold under their chosen area-coverage criterion. The best 12 could reach a typical threshold of 66 million solar masses across 10% of the image aperture, with lower thresholds at especially sensitive locations. Accurate modelling of the telescope’s image response was crucial: an incorrectly modelled response reduced the area where clumps could be detected, even though false detections stayed rare. The simulations assumed the background galaxy’s structure was known and left out light from the lensing galaxy, so these forecasts are not demonstrated performance on real observations. Carefully selected follow-up of lenses found by Euclid or Roman could help distinguish dark-matter theories, provided the telescope’s image response is characterized accurately enough.

Young explorerDark matter is something scientists study even though it does not shine. Little clumps of it could make tiny changes in pictures of faraway galaxies stretched by gravity. Scientists made pretend telescope pictures on a computer to see whether a planned space telescope could spot those changes. Picking the most helpful pictures made smaller clumps easier to find. But the scientists also had to know exactly how the telescope would blur each picture, or some clues disappeared. This is a plan tested with pretend pictures, not a discovery of new clumps in the sky.

Distinguishing the origin of cosmic birefringence: dark energy, dark matter, and neutrino asymmetry

Lu Yin, Eiichiro Komatsu

• High Energy Astrophysical Phenomena
• High Energy Physics - Phenomenology
• High Energy Physics - Theory

AstronomerThe paper calculates the CMB EB power spectrum generated by a neutrino-asymmetry current and compares it with axion dark energy and dark matter within a common Chern–Simons framework. Although a single source’s net polarization rotation provides little information about its origin, the spectrum’s angular-scale dependence probes birefringence evolution: large- and small-scale CMB polarization correlations sample sources at approximately z = 10 and z = 1100, respectively. The calculations predict suppressed EB power at low multipoles, ℓ ≲ 20, for neutrino asymmetry, similar to axion dark matter but unlike axion dark energy. Large-scale measurements, including LiteBIRD, could therefore distinguish late-time dark energy birefringence from these higher-redshift mechanisms. Neutrino-density evolution during recombination also changes the predicted high-multipole spectrum, offering a potential way for ground-based experiments such as the Simons Observatory to separate neutrino asymmetry from axion dark matter. These are theoretical discriminants, not reported observational detections.

PublicLight arriving from across the universe may have its polarization—the orientation of its light waves—rotated by processes that violate a symmetry called parity. Measuring the total rotation from one source tells us little about what caused it. This study instead calculates how different possible causes would shape a particular polarization pattern in the cosmic microwave background. The predicted pattern is weakened on large angular scales for a neutrino imbalance and for axion dark matter, but not for axion dark energy. Future large-scale polarization measurements, including LiteBIRD, could use this difference to test the dark energy explanation against the other two. The calculations also predict a small-scale pattern caused by changes in neutrino density during recombination, which could help the Simons Observatory distinguish a neutrino imbalance from axion dark matter. The study presents theoretical predictions rather than a detection of any of these causes.

Young explorerLight from far away can have a direction, and that direction might turn as the light travels through space. Scientists calculated how three possible causes could turn very old light in different ways. Two causes would make a certain pattern weaker across big patches of the sky, while the third would not. Patterns in smaller patches might help tell the first two apart. Scientists hope to use sky measurements to check these ideas; this study does not show which cause is really at work.

Dark Energy Survey Year 6 Results: fast and interpretable posterior predictive checks for correlated cosmic probes

C. Doux, J. Muir, A. Ferté+59 more

AstronomerThe authors present a fast, numerically stable posterior predictive distribution (PPD) framework for testing internal consistency among correlated cosmological probes, developed for the DES Year 6 combined weak-lensing and galaxy-clustering analysis. A Gaussian-mixture model approximates the high-dimensional PPD, and the scalar metric Δ_PPD measures the fraction of that distribution at lower probability density than the observed data. Applied to DES Year 3 measurements, it recovers the inter-probe tensions identified by published calibrated PPD tests, requiring only minutes per test and avoiding calibration and numerical-stability challenges of the earlier methods. Tests using noise realizations of simulated DES Year 6 analyses show a coherent response to injected inconsistencies. However, nuisance-parameter shifts can absorb tensions and reduce detectability, while poorly constrained parameter directions can produce projection effects that flag tension between disjoint observable sets even for consistent data. The authors recommend the metric as a practical diagnostic for multiprobe unblinding alongside other validation checks and propose its use in forthcoming Stage-IV surveys, including LSST, Euclid, and Roman.

PublicThe researchers developed a faster way to check whether different kinds of cosmological measurements agree within a shared model. Designed for the Dark Energy Survey’s combined analysis of weak lensing and galaxy clustering, the method compares the measurements with a distribution of data expected under the model and summarizes how unusual the observations are. When applied to existing DES Year 3 measurements, it identified the same disagreements as earlier published tests, taking only minutes per test. In simulated Year 6 analyses, it also responded sensibly to deliberately introduced inconsistencies. The authors warn that the test is not a definitive verdict: adjustments to auxiliary model parameters can hide disagreements, and uncertainty in some parameters can make consistent measurements appear to disagree. They recommend using it with other checks and suggest it could help future surveys such as LSST, Euclid, and Roman.

Young explorerScientists have different ways to study space, and they want to check whether those ways tell a matching story. They made a faster computer check. When they tried it on older measurements, it found the same disagreements as earlier checks. They also tried it on pretend measurements, and it reacted when they added disagreements on purpose. But the check can miss a problem or warn about one that is not really there. So scientists need other checks too.

A novel, fast, and accurate code for cosmological loop calculations

Tjark Harder, Luca Amendola, Thiago S. Pereira+1 more

• Instrumentation and Methods for Astrophysics

AstronomerThe authors introduce neckar, a public FFTLog-based code for one-loop matter and galaxy power spectra and correlation functions in Eulerian EFTofLSS, designed for fast, high-dimensional Bayesian inference from galaxy surveys. It separates pre-computable and cosmology-dependent terms, treats the Alcock-Paczynski effect semi-analytically for power-spectrum multipoles, and implements symmetry-based bootstrap kernels to facilitate applications to a broader class of cosmologies. An improved infrared resummation scheme corrects previous implementation inaccuracies associated with errors of order 1% in the quadrupole and 10% in the hexadecapole at k ≳ 0.1 h Mpc⁻¹. An asymptotic treatment extends accurate predictions into mildly nonlinear scales around k ∼ 0.4 h Mpc⁻¹, with relevant corrections to the correlation function near the BAO peak. The authors report speedups of up to two orders of magnitude over similar codes, without emulators, alongside improved numerical accuracy. These are computational developments rather than new observational findings. The implementation is in C with a Python wrapper.

PublicThe authors present neckar, a publicly available program that calculates statistical patterns in the distribution of matter and galaxies. It is intended to help researchers compare cosmological models with galaxy-survey data while exploring many model parameters. The program reuses calculations where possible and improves how several physical and geometric effects are handled. The authors report that it corrects inaccuracies in earlier implementations, improves predictions on scales where matter clustering is becoming more complex, and changes predictions around a characteristic feature called the baryon acoustic oscillation peak. They also report that neckar can run up to 100 times faster than similar programs while improving numerical accuracy. This work introduces a calculation tool; it does not report new observations of the Universe.

Young explorerGalaxies make patterns across space. Scientists built a computer tool called neckar to work out what those patterns might look like and help compare their ideas with galaxy maps. They say it fixes some mistakes in older calculations and can work much faster. It is a new tool, not a new discovery in the sky.

Probing Early Phases of the Epoch of Reionization with the kSZ²×21cm² Cross-Correlation

Wen-Qing Guo, Yin-Zhe Ma, Adam Lidz+2 more

AstronomerThis study investigates the higher-order kSZ² × 21-cm² cross-correlation at z ≃ 9–16, emphasizing spatial fluctuations in the neutral-hydrogen spin temperature. Squaring the kSZ field avoids line-of-sight cancellations, while squaring the 21-cm field permits nonzero correlations involving equal-and-opposite high-k_parallel mode pairs accessible outside the foreground wedge. Forecasts incorporating instrumental noise yield cumulative signal-to-noise ratios of 5.89 for SKA-Low AA* × CMB-HD and 3.62 for HERA × CMB-HD under a fiducial heating history and the stated optimistic foreground-avoidance scenario, k_parallel ≤ 0.1 h Mpc⁻¹. With a horizon-extending wedge, these fall to 2.94 and 2.85, respectively. These are forecasts, not detections, and depend on the assumed heating and foreground scenarios. The statistic is sensitive to both IGM thermal evolution and ionization structure, offering complementary constraints on early heating and reionization.

PublicThe researchers explore a way to study the early universe, when the first luminous sources were changing the temperature and ionization of gas between galaxies. Their method compares squared patterns in two signals: the kinetic Sunyaev–Zel’dovich effect in the cosmic microwave background and 21-centimeter emission from neutral hydrogen. Squaring helps prevent parts of the first signal from canceling and allows useful combinations of hydrogen-signal modes beyond a foreground-contaminated region. The study predicts how clearly combinations of telescopes could measure this relationship, rather than reporting a detection. Under an assumed heating history and optimistic foreground conditions, forecast signal-to-noise ratios are about 5.9 for SKA-Low AA* with CMB-HD and 3.6 for HERA with CMB-HD; a larger foreground-contaminated region lowers both to about 2.9. The method could help reveal both how the early gas heated and how it became ionized.

Young explorerLong ago, the first bright things in space began changing the gas around them. Scientists want to learn how that gas warmed up and changed. They worked out a way to compare patterns in two faint signals from space, using a math trick to keep useful clues from disappearing. They predict that some telescope teams could spot these clues, but they have not spotted them in this study. Other signals in the way could make the clues harder to see.

Baryonic Imprints on DM Halos: the concentration-mass relation and its dependence on 28 model parameters in the CAMELS suite

Cami Delgado, Dhayaa Anbajagane

• Astrophysics of Galaxies

AstronomerUsing 2048 CAMELS simulations with the IllustrisTNG galaxy formation model, the authors quantify how 23 galaxy formation parameters or processes and five cosmological parameters affect the halo concentration–mass relation, which characterizes halos’ radial density distributions. They construct a simulation-informed nonlinear model of concentration as a function of halo mass, redshift, and these 28 parameters, covering M_vir = 10^11–10^14.5 M_sun/h and z = 0–3. The simulations show clear mass- and redshift-dependent imprints from the different feedback mechanisms. Based on these simulation measurements, the authors develop a three-component phenomenological model for incorporating astrophysical effects into the concentration–mass relation quickly and simply. These findings are simulation-based, not observational measurements.

PublicThe way galaxies form can affect how matter is distributed within large structures called halos. The researchers explored these effects using 2048 computer simulations, varying 23 settings related to galaxy formation and five related to cosmology. In the simulations, different feedback mechanisms left distinct patterns in how concentrated halos were, and those patterns depended on halo mass and cosmic time. The team used these results to build a relatively simple, fast model that includes galaxy formation effects when estimating halo concentration. The findings describe the simulated systems rather than direct observations of the universe.

Young explorerThe scientists made pretend universes on computers to study big clumps of matter called halos. They changed the rules for how galaxies grow and checked how tightly the matter gathered inside the clumps. In their computer worlds, the changes worked differently for clumps of different sizes and at different times. They then made a simpler way to describe those patterns. These clues come from computer models, not from looking directly at real clumps in space.

High Energy Neutrinos, Gravitational Waves, and Dark Matter from a Cosmological First Order Phase Transition

James M. Cline, Savas Stoica, Yong Xu

• High Energy Physics - Phenomenology

AstronomerThe study models high-energy neutrinos from the decay of superheavy dark matter produced through the filtered dark-matter mechanism during a cosmological first-order phase transition. The relic-abundance calculation incorporates updated hydrodynamic determinations of the bubble-wall velocity. A dark-matter mass of approximately 4.4 × 10^8 GeV can reproduce the observed relic abundance and accommodate ultra-high-energy neutrino events such as KM3-230213A; this is a model-based explanation, not an established origin for the event. The same transition predicts a stochastic gravitational-wave background peaking at 10^4 Hz, which is not yet observable in this example. For dark-matter masses at or below roughly 10^6 GeV, the predicted neutrino spectrum shifts into the range relevant to IceCube, while the gravitational-wave signal moves to lower frequencies and can reach the projected sensitivities of Cosmic Explorer, BBO, and DECIGO. The proposed multimessenger connection links both signals to dark-matter production in the phase transition.

PublicThe researchers explore whether an early-universe phase transition could have produced very heavy dark-matter particles whose later decay releases high-energy neutrinos. Their calculation updates how fast the boundaries of bubbles formed during the transition move. In one example, particles with a mass of about 4.4 × 10^8 GeV could account for the observed amount of dark matter and explain ultra-high-energy neutrino events such as KM3-230213A, but the study does not establish that this is their actual source. The same transition would produce a background of gravitational waves, peaking at 10,000 Hz in this example and not yet observable. With lower dark-matter masses, at or below about 10^6 GeV, the predicted neutrinos fall into an energy range relevant to IceCube, and the gravitational waves could fall within the projected sensitivity of Cosmic Explorer, BBO, and DECIGO. These are predictions connecting two possible signals, not detections of that connection.

Young explorerScientists are testing an idea about when the universe was very young. A big change, with bubbles forming and growing, might have made very heavy bits of invisible matter called dark matter. If those bits later broke apart, they could send out tiny particles called neutrinos. The same change could also make ripples in space called gravitational waves. Their math says this idea could explain some very energetic neutrinos, but they have not shown that it really happened. In one example, the ripples cannot be seen yet. Other examples with lighter dark matter might make signals that future experiments could find.

Multi-Band Constraints on Cosmic Strings: Unifying Harmonic and Burst Spectra

Hansong Zhang, Huai-Ke Guo, Mairi Sakellariadou+2 more

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

AstronomerThis study formally unifies the discrete harmonic expansion and continuous burst-superposition descriptions of the cosmic-string-loop gravitational-wave background. The two representations converge on the scale-invariant spectral plateau but diverge on the rising low-frequency branch, where the first few harmonics dominate and discreteness matters. The unified framework supports consistent multi-band spectral calculations. The authors perform joint Bayesian inference with NANOGrav, EPTA, and LIGO–Virgo–KAGRA datasets for four representative loop-distribution models, sampling string tension Gμ and average cusp and kink numbers to account for loop-radiation uncertainties. Using the harmonic expansion strengthens LVK bounds by 21%–31% for three models. The LVK constraints also preclude three of the four models from explaining the observed PTA common signal. For the remaining model, the multi-band analysis tightens the inferred limit on Gμ. These are model-dependent constraints, not a detection of cosmic strings.

PublicCosmic strings are hypothetical objects whose loops could produce gravitational waves across a broad range of frequencies. Researchers usually calculate these waves in two different ways. This study shows that those methods describe the same underlying process and agree over a flat part of the predicted spectrum, but differ at lower frequencies, where individual harmonics matter. The researchers then compare four models of cosmic-string loops with data from NANOGrav, EPTA, and LIGO–Virgo–KAGRA, allowing for uncertainty in how the loops emit waves. Using the harmonic calculation strengthens LIGO–Virgo–KAGRA limits by 21%–31% for three models. Those observations rule out three models as explanations of the shared signal seen in pulsar-timing data. The fourth remains possible, with a tighter limit on string tension. The study does not establish that cosmic strings exist.

Young explorerScientists wonder whether tiny loops of something called cosmic strings could make ripples in space. They have not shown that these strings are real. This study connects two ways of figuring out what the ripples might look like. Using telescope and detector data, the scientists find that three of four ideas about the loops cannot explain a signal they see. One idea is still possible, but it has stricter rules to follow.

Non-Gaussian timing residual skewness in pulsar timing arrays

Reginald Christian Bernardo, Rituparna Mandal, Kin-Wang Ng

• General Relativity and Quantum Cosmology

AstronomerMotivated by searches for weak primordial non-Gaussianity in the CMB, this theoretical study investigates perturbative non-Gaussian statistics of a stochastic gravitational-wave background in pulsar timing arrays. A quadratic ansatz generates three-point correlations at first order in the nonlinear coupling and covariance corrections at second order. Applied to gravitational-wave helicity amplitudes, it yields a timing-residual bispectrum that is not manifestly invariant under local polarization-basis rotations for tensor and vector modes. The authors instead construct a polarization-frame-invariant phenomenological model for detector-projected amplitudes and evaluate the one-pulsar timing-residual third moment using a simplified response. Numerical benchmarks yield very small Gaussian-rms-normalized skewness; this is a model calculation, not an observational detection.

PublicThe researchers explore whether a background of gravitational waves could produce small departures from Gaussian, or bell-curve-like, statistics in pulsar timing measurements. Their first mathematical model produces a three-way correlation whose independence from the chosen polarization reference frame is not evident for two types of gravitational-wave modes. They therefore develop an alternative model that does not depend on that choice. With a simplified model of the pulsar response, their numerical calculations find only a very small normalized asymmetry in the timing fluctuations of a single pulsar. This is a theoretical finding, not evidence that such an asymmetry has been observed.

Young explorerPulsars are stars that send out regular flashes, like space clocks. The researchers used math to ask whether a jumble of gravitational waves could make the clocks' timing wiggles a little lopsided. Their first recipe had a problem: it was not clear that the answer stayed the same when they changed the directions used to describe the waves. They made another recipe that avoids that problem. In simplified computer calculations for one pulsar, the lopsidedness was very tiny. They did not report finding it in real pulsar measurements.

Big Bang Nucleosynthesis Constraint on B-mesogenesis

James M. Cline, Jonas Frerick, Sebastian A. Naja+1 more

• High Energy Physics - Phenomenology

AstronomerThe study investigates Big Bang Nucleosynthesis constraints on B-mesogenesis, a low-temperature baryogenesis mechanism using Standard Model CP violation in B mesons to satisfy the Sakharov conditions. The scenario requires a late matter-dominated epoch driven by a scalar field Φ that decays into bottom quark–antiquark pairs and reheats the Universe below the QCD phase transition. The authors identify hadron injection altering neutron–proton interconversion as the dominant effect on nucleosynthesis, followed by neutrino heating from Φ decays. Their analysis requires a reheating temperature of approximately 10 MeV or higher for Φ masses of approximately 100 GeV or less. This is a constraint on the proposed mechanism, not an observational detection of it.

PublicThe researchers examine a proposed explanation for how the early Universe generated its matter: B-mesogenesis, which uses differences between the behavior of B mesons and their antimatter counterparts. This scenario requires a hypothetical field to dominate the Universe for a time, then decay into bottom quarks and antiquarks, reheating it. The study asks how those decays would affect the formation of light atomic nuclei. The largest effect comes from injected particles changing the balance between neutrons and protons; heating neutrinos is the next most important effect. The analysis finds that, if the field's mass is about 100 GeV or less, the reheating temperature must be about 10 MeV or higher. These findings restrict the proposed scenario rather than establish that it happened.

Young explorerScientists studied an idea about how the very young Universe made matter. In this idea, something called a field breaks apart, makes tiny particles, and warms the Universe. Those particles could change how many neutrons and protons were available to build the centers of atoms. The scientists found that their idea needs enough warming to work with the early making of atoms, at least for the field masses they describe. They have not shown that this is what really happened.

Higgsino dark matter compatible with the LUX-ZEPLIN high-energy nuclear-recoil event and IceCube constraints

Katherine Freese, Dionysios P. Theodosopoulos

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

AstronomerThe authors assess inelastic Higgsino dark matter as a possible explanation of LZ’s reported 248 keV nuclear-recoil event, subject to IceCube’s null searches for dark-matter annihilation in the Sun. Nearly pure Higgsinos have two neutral Majorana states with a small splitting and an off-diagonal Z coupling. A likelihood analysis identifies 90% confidence regions in mass and splitting, comparing the Standard Halo Model with possible LMC-induced enhancements of the high-speed tail, and including or omitting LZ’s empty high-energy sideband constraint. Four variants of IceCube bounds reflect assumptions about solar cooling channels, given severe theoretical uncertainty in Higgsino–nucleon elastic scattering, which is crucial for these bounds but unimportant for direct detection. The 1.1 TeV thermal Higgsino is only marginally compatible when the LMC-induced tail is included and both solar elastic cooling and the sideband constraint are neglected. Higher masses offer better compatibility: depending on the assumptions, allowed regions extend from roughly 2 TeV to hundreds of TeV or higher, with splittings of approximately 350–525 keV. These are conditional model interpretations, not a dark-matter detection.

PublicCould a particle called a Higgsino explain the 248 keV nuclear-recoil event reported by the LUX-ZEPLIN experiment? This study tests that possibility against IceCube searches, which found no signal from dark matter annihilating in the Sun. The answer depends on uncertain assumptions about how Higgsinos lose energy in the Sun, the speeds of dark-matter particles near us, and whether the absence of other high-energy LUX-ZEPLIN events is included as a constraint. A 1.1 TeV Higgsino is only marginally compatible under a particular set of assumptions. Heavier Higgsinos fit the combined constraints better, with compatible masses ranging from about 2 TeV to hundreds of TeV or more depending on the assumptions. The analysis identifies possible explanations; it does not establish that the event was caused by dark matter.

Young explorerA detector reported a tiny bump to the center of an atom. Scientists wondered whether an unseen particle called a Higgsino could have caused it. They checked that idea against another experiment that saw no dark-matter signal from the Sun. Heavier Higgsinos look more promising in their calculations, but the answer depends on things scientists are still unsure about. They have not shown that dark matter caused the bump.

Cosmological implications of tracker scalar fields: Testing the evidence for dynamical dark energy with recent data

Md. Wali Hossain, Afaq Maqsood

• General Relativity and Quantum Cosmology

AstronomerThe study examines non-phantom tracker scalar-field dark energy with inverse axionlike and inverse steep exponential potentials. Such models can alleviate the cosmic coincidence problem and approach cosmological-constant-like behavior at late times. Calculations of background evolution and perturbations yield mild suppression of the matter power spectrum relative to ΛCDM, but no distinguishing bispectrum features. Using combined CMB, BAO from DESI DR1 and DR2, Pantheon Plus, Hubble-parameter, and RSD datasets, the authors compare models with AIC and BIC. Within this non-phantom tracker framework, they find no evidence favoring dynamical dark energy, and ΛCDM remains the better fit to current observations. This conclusion does not rule out phantom-crossing models, which other studies have found to fit some datasets better.

PublicThe researchers tested models in which dark energy—the component associated with the Universe’s accelerating expansion—changes over time rather than remaining constant. Their chosen models could help explain why matter and dark energy have comparable importance today, while eventually behaving much like constant dark energy. The calculations predict slightly weaker matter clustering than the standard ΛCDM model, but no distinctive difference in another measure of clustering called the bispectrum. Comparing the models against several combined astronomical datasets, with statistical criteria that account for model complexity, the researchers found no evidence favoring changing dark energy within the particular class they studied. The standard model still fits current observations better in this comparison. Other kinds of changing dark energy, including models that cross a boundary known as the phantom divide, are not ruled out.

Young explorerThe Universe is getting bigger faster and faster. Scientists studied ideas where something called dark energy changes as time passes, instead of staying the same. Their calculations said matter might bunch together a little less in these ideas. But when they compared the ideas with information about the Universe, the usual idea with steady dark energy worked better. That does not mean every idea about changing dark energy is wrong—this study only tested certain kinds.

Dark Energy Survey Year 6 Results: Redshift Calibration of the MagLim++ Lens Sample

G. Giannini, A. Alarcon, W. d'Assignies+85 more

AstronomerThe study derives and calibrates the redshift distributions of the MagLim++ lens galaxy sample for the DES Y6 3x2pt analysis, which combines lens-galaxy clustering and weak gravitational lensing. SOMPZ combines deep-field multiband photometry, wide-field data, and the Balrog synthetic-source injection catalogue. Relative to DES Y3, improvements include a noise-weighted self-organizing-map metric, an expanded Balrog catalogue, and revised systematic-uncertainty propagation. Approximately 100 million redshift-distribution realizations span the dominant uncertainty sources and are combined with independent clustering-redshift measurements through importance sampling. The calibration yields typical mean-redshift uncertainties of 1–2%, an average reduction of 20–30% relative to Y3. Redshift-distribution uncertainties are compressed into a small set of orthogonal modes; marginalizing over these modes produces only a minor degradation of cosmological constraints. The authors conclude that MagLim++ is a robust lens sample for DES Y6 precision cosmology and present the framework as scalable to future surveys.

PublicResearchers calibrated how the galaxies in the Dark Energy Survey’s Year 6 MagLim++ sample are distributed in redshift, a measure used to locate galaxies along our line of sight. This calibration supports an analysis combining galaxy clustering with weak gravitational lensing. Their method brings together galaxy images, tests that insert synthetic sources into survey data, and independent measurements based on galaxy clustering. They generated about 100 million possible redshift distributions to represent the main sources of uncertainty; these are alternative calibration realizations, not additional observed galaxies. The resulting uncertainty in the average redshift is typically 1–2%, an average improvement of 20–30% over the Year 3 calibration. A compact way of carrying these uncertainties into the cosmological analysis only slightly weakens its constraints. The authors argue that the sample is suitable for precision cosmology and that the approach could be used by future surveys.

Young explorerScientists study lots of galaxies to learn about the universe. They worked on a better way to figure out how far away a group of galaxies is. They used pictures, added pretend objects to test their method, and checked clues from how galaxies gather together. They tried many possible answers to keep track of what they were unsure about. Their new method has less uncertainty than the older one, but it is not perfect. Keeping that uncertainty in their calculations only makes their answers about the universe a little less precise.

An Effective Theory for Biased Tracers via the Boltzmann-Equation Approach

Tomohiro Fujita, Tomo Takahashi, Sora Yamashita

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

AstronomerThe authors develop an effective theory of biased tracers at the Boltzmann-equation level, treating density and velocity bias within a unified framework. A general effective collision operator encodes tracer dynamics that differ intrinsically from dark-matter dynamics and introduces source terms into the continuity and Euler equations. At linear order, the framework predicts self-consistent time- and scale-dependent bias parameters, includes peak bias as a special case, and clarifies the origins of velocity bias and higher-derivative effects. The authors apply the model to redshift-space distortions and compare the tracer power spectrum with that obtained in the Effective Field Theory of Large-Scale Structure. The abstract does not report the outcome of that comparison or observational validation.

PublicObjects used to trace the universe’s large-scale structure need not be distributed or move exactly like dark matter. This work develops a mathematical framework that describes both differences together. It adds an effective term to an equation governing the tracers’ distribution and motion, allowing their dynamics to differ from those of dark matter. In a linear approximation, the theory predicts that these differences can change with time and with the scale being examined. The authors also apply the model to patterns affected by motion along our line of sight and compare its predictions for clustering with another theoretical framework. The abstract presents theoretical work, not an observational detection, and does not state how the comparison turned out.

Young explorerScientists use some things in space as clues to where matter is. But those clues might not spread out or move just like the dark matter they are meant to trace. These scientists made a math model to describe both differences at once. Their model says the differences can change over time and can depend on how big a patch of space you look at. They compared their model with another theory, but this summary does not say whether the two agreed. This is a new way to calculate things, not a report of something newly seen in the sky.

Dark Energy Survey Year 6 Results: Galaxy-galaxy lensing

G. Giannini, G. Camacho-Ciurana, A. Whyley+97 more

AstronomerThe study presents galaxy–galaxy lensing measurements from the full six-year Dark Energy Survey data set, covering 4031 square degrees, for the DES Y6 3×2pt cosmological analysis. It uses approximately 9 million MagLim++ lens galaxies in six redshift bins and 140 million Metadetection source galaxies in four bins. The mean tangential shear has a total signal-to-noise ratio of 173, a 17% improvement over DES Y3. Applying the cosmological scale cuts reduces this to 75 for the linear galaxy-bias model with R_min = 6 Mpc/h, or 90 for the nonlinear model with R_min = 4 Mpc/h. Validation tests support robustness against observational and astrophysical systematics at the statistical precision required for DES Y6. High-signal-to-noise geometric shear ratios extracted on small angular scales provide an internal consistency check on the photometric redshift distributions and shear calibration, but are not used in the main cosmological analysis.

PublicResearchers measured how foreground galaxies bend light from more distant galaxies, subtly changing their apparent shapes. Using all six years of Dark Energy Survey data across 4031 square degrees of sky, they analyzed about 9 million foreground galaxies and 140 million background galaxies. The combined lensing measurement has a signal-to-noise ratio of 173, 17% higher than in the survey’s three-year analysis. Restricting the measurement to the scales used for the cosmological analysis lowers that ratio to 75 or 90, depending on how the relationship between galaxies and matter is modeled. Extensive tests indicate that observational and astrophysical effects do not compromise the measurement at the precision needed for this analysis. Additional comparisons of lensing signals on small angular scales provide an internal check on estimated galaxy distances and shape-measurement calibration; these comparisons are not part of the main cosmological analysis.

Young explorerA galaxy’s gravity can bend light from galaxies farther away, making their shapes look a tiny bit different. Scientists used six years of sky pictures to measure this with millions of galaxies. Their measurement was clearer than the one made with three years of data. They checked carefully for things that could fool them, and the tests suggest the measurement is reliable enough for their study. They also made an extra check of their galaxy-distance estimates and shape measurements, but did not use that extra check in their main study of the universe.

Cosmology with Multi-Wavelength Line Intensity Mapping Synergies in the SKAO Era

Debanjan Sarkar, Suman Majumdar, Chandra Shekhar Murmu+21 more

AstronomerThis chapter explores the potential of joint line-intensity mapping analyses using SKAO 21-cm maps and complementary line maps of overlapping cosmic volumes. LIM measures spatial fluctuations in cumulative emission from unresolved sources or the intergalactic medium. Complementary tracers include far-infrared [CII], [OIII], [NII], and [OI] lines, mid- and high-J CO transitions, and hydrogen Lyα and Hα. Cross-correlations can mitigate uncorrelated systematics and improve sensitivity to the underlying matter distribution, while multi-line analyses can help disentangle cosmological and astrophysical parameters. The chapter also considers cross-bispectra, marked correlations, and morphological measures as probes of non-Gaussian structure and environmental dependence. These are opportunities for joint analysis, rather than reported observational measurements; the abstract provides no quantitative forecasts or simulation results.

PublicRather than identifying every source separately, line-intensity mapping measures how the combined light at particular spectral lines varies across space, revealing the Universe’s large-scale structure over cosmic time. This chapter explores how maps of neutral hydrogen’s 21-centimeter emission from SKAO could be combined with maps of other emission lines covering the same regions. Comparing these maps can reduce errors that are unrelated between them and help separate information about cosmic structure from information about the emitting material. More advanced comparisons could reveal patterns and environmental effects that simpler analyses miss. The chapter presents potential routes to learning about galaxy evolution and cosmology, not a new measured discovery.

Young explorerImagine making a map of space from the glow of lots of things that are too hard to see one by one. Different kinds of glow can make different maps of the same place. This chapter explores how comparing those maps could help scientists spot patterns and avoid some mistakes. It could help them learn how galaxies and the Universe change. It describes what scientists could learn, not a new discovery they have already measured.

Discovering Substellar Dark Matter Halos with Astrometric Weak Lensing of Multiply Imaged Quasars

Ken Van Tilburg, David E. Kaplan

• Astrophysics of Galaxies
• High Energy Physics - Phenomenology

AstronomerThe authors propose time-domain astrometric weak lensing of multiply imaged quasars to probe dark-matter microhalos; they report sensitivity forecasts, not a detection. In ΛCDM, microhalos along each macro-image’s light path produce stochastic centroid motion with a calculable red power spectrum. Halos whose crossing times exceed the survey duration contribute relative angular acceleration between image pairs. The response peaks for scale radii of 0.005–2 pc and masses of 3×10^-6–100 solar masses, reaching scales associated with the damping cutoffs of a 100 GeV thermal relic. Forecasts assume ten-year campaigns with 300 epochs: 0.1 microarcsecond per-epoch precision for the galaxy-lensed quadruple B1422+231, forecast for extended-path intensity correlation, and 1 microarcsecond for the cluster-lensed triple SDSS J1029+2623. Under the optimistic assumption that surviving microhalos contain 10% of the projected mass density at the image positions, the acceleration-channel variance signal-to-noise ratio is of order ten for the galaxy lens, falling to order unity after stellar microlensing subtraction, and 0.35 for the cluster lens. A positive detection would raise universal dark-matter particle-mass lower bounds to approximately 400 keV for fermions and 10^-12 eV for bosons, constrain the kinetic decoupling temperature to approximately 10 MeV or higher, and probe spectral-tilt running at the 0.01 level across 15–20 e-folds. A robust null result across well-characterized lenses would constrain microhalo survival and/or imply violations of those inequalities. The proposal requires extreme differential centroiding precision, rather than demonstrating that such observations have already succeeded.

PublicThis paper proposes a way to search for tiny clumps of dark matter by tracking the apparent positions of quasars whose light is split into multiple images by gravitational lensing. Dark-matter clumps along the different light paths are predicted to cause small, irregular shifts in those images. Slowly passing clumps could also produce a measurable difference in how the images’ motions accelerate. The authors forecast what ten years of observations, with 300 measurements per system, might reveal in two example lenses. The required position measurements are extraordinarily precise: 0.1–1 microarcsecond. Their forecasts optimistically assume that surviving small clumps hold 10% of the projected mass density at the image positions. The galaxy lens looks more promising than the cluster lens, but accounting for lensing by stars substantially weakens its expected signal. No dark-matter clumps are detected here. If the proposed signal were detected, it could tighten limits on dark-matter particle masses and reveal information about the early universe. A reliable absence of the signal could instead restrict how many clumps survive or challenge the stated dark-matter limits.

Young explorerGravity can bend light from one faraway bright object so we see it in several places. The scientists suggest watching those spots very carefully. Tiny clumps of invisible dark matter might make the spots shift a little. They worked out what years of watching might show, but they have not found the clumps this way yet. The shifts would be very hard to measure, and stars could make the search harder.

ξRϕ² non-minimal coupling, and the long range gravitational potential for different spin fields from 2-2 scattering amplitudes

Avijit Sen Majumder, Ayan Kumar Naskar, Sourav Bhattacharya

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

AstronomerThis theoretical study computes the long-range gravitational contribution of a non-minimal curvature–scalar coupling, ξRφ², within perturbative quantum gravity. Motivated by renormalisation of quartically self-interacting scalar theory in curved spacetime, the coupling generates vertices involving two scalars and gravitons without explicit scalar momenta, unlike standard minimal matter–graviton vertices. Assuming small dimensionless ξ and a vanishing cosmological constant, the authors calculate scalar 2-to-2 scattering amplitudes through order G²ξ and extract the potential in the non-relativistic limit. The long-range contribution has no tree-level term at order Gξ; its leading term arises at one loop, at order G²ξ, and scales as r⁻⁴. Extensions to scalar scattering with massive spin-1 and spin-1/2 particles demonstrate spin and polarisation dependence of the two-body potential. These are theoretical calculations, not observational findings; possible physical implications are discussed.

PublicThe paper explores a theoretical way that a scalar field could couple directly to the curvature of spacetime, changing the gravitational interaction between particles. The researchers assume this extra coupling is weak and set the cosmological constant to zero. They calculate particle-scattering amplitudes and use their slow-motion limit to derive an additional long-range gravitational potential. For this contribution, the simplest calculation gives no long-range term; the leading term instead comes from a quantum calculation with one loop and falls with the fourth power of distance. This describes the extra contribution, not a replacement for the usual gravitational potential. The authors also extend the calculation to interactions with massive particles of spin 1 and spin 1/2, finding dependence on spin and polarisation. The study presents theoretical results rather than measurements.

Young explorerScientists used maths to ask whether a special link between tiny particles and the bending of space could change how gravity works between them. In their calculation, they kept that extra link weak. They found an extra piece of gravity that gets smaller very quickly as the particles move farther apart. Their maths also showed that the particles’ spin can matter. This is a result from a calculation, not something they have seen in an experiment.

A Vector-Like Lepton Interpretation of the High-Energy Nuclear Recoil Candidate in LUX-ZEPLIN

Fatemeh Elahi, Pedro Schwaller

• High Energy Physics - Phenomenology
• High Energy Astrophysical Phenomena
• High Energy Physics - Experiment

AstronomerLZ reported a nuclear-recoil candidate at 248 keV, with statistical and systematic uncertainties of 23 keV each, in an exposure of 2.84 tonne-years. The authors propose an elastic spin-dependent interpretation motivated by the strongly suppressed spin-independent xenon response at this recoil energy. In their singlet-doublet Majorana dark matter model, a diagonal Z coupling generates the O4 = S_DM · S_N interaction and a harder recoil spectrum. A Higgs blind spot suppresses the otherwise excessive low-energy Higgs-mediated spin-independent signal while preserving a nonzero Z coupling. They identify a parameter region predicting order-one events in the LZ high-recoil window and reproducing the observed thermal relic abundance. Solar capture through the same spin-dependent interaction provides an independent test: current IceCube limits probe part of this thermal parameter space, but a viable region remains. Further xenon exposure and improved solar-neutrino searches could test this interpretation; the candidate is not established as a dark matter event.

PublicThe LZ experiment reported a possible collision with an atomic nucleus at an unusually high recoil energy. This is not a confirmed detection of dark matter. The authors explore a dark matter model whose spin-dependent interactions could produce such energetic recoils. The model would normally also predict too many lower-energy collisions, but a special region of its parameters suppresses those interactions. Their calculations identify a region that predicts roughly one high-energy event and matches the observed cosmic abundance of dark matter through a thermal-production scenario. The same interaction could trap dark matter in the Sun, making solar-neutrino searches another test. Existing IceCube limits constrain some, but not all, of the proposed region. More xenon data and better solar-neutrino searches could help assess this explanation.

Young explorerA detector saw something that might have given the middle of an atom a big bump. Scientists do not know if dark matter caused it. They worked out one way dark matter might make a bump like this without making too many smaller bumps. More detector observations and searches for tiny particles called neutrinos from the Sun could help check their idea.

Towards robust simulations of the galactic dynamo: a cross-code comparison between Eulerian and Lagrangian schemes

Mark Ivan Ugalino, Benedikt Diemer, Vadim A. Semenov+8 more

AstronomerThe study presents a systematic comparison of magnetic-field amplification in Milky Way-type galaxy simulations using Eulerian and Lagrangian codes with diverse MHD schemes: ART, RAMSES, AREPO, and SWIFT. With identical initial conditions and no star formation or stellar feedback, the simulated disk-field amplification histories depend strongly on the hydrodynamical scheme, differing by orders of magnitude between Eulerian and Lagrangian approaches. Reducing the mesh velocity in AREPO produces results consistent with the static-grid codes ART and RAMSES. These numerical findings underscore that dynamo saturation levels and amplification timescales remain poorly constrained across methods; they do not establish a code-independent amplification history for real galaxies.

PublicGalactic magnetic fields are thought to grow through dynamo action, which turns energy from turbulent and rotating gas into magnetic energy. This study compares four computer simulation codes modeling Milky Way-type galaxies from identical starting conditions. The simulations produce magnetic-field growth histories that differ by orders of magnitude depending on how the gas is modeled. Slowing the moving computational mesh in one code, AREPO, brings its results into agreement with two fixed-grid codes. These are simulation findings, not observations of galaxies, and the models omit star formation and energy input from stars. The comparison shows why numerical effects must be checked before drawing conclusions about how quickly galactic magnetic fields grow or how strong they become.

Young explorerGalaxies have magnetic fields. Scientists used four computer programs to see how those fields might grow as gas moves around. Even when the programs started with the same setup, they gave very different answers. When scientists slowed the moving grid in one program, its answer became more like those from two other programs. These pretend galaxies did not include new stars being made or stars stirring up the gas. Scientists still need to check how the programs work before knowing how magnetic fields grow in real galaxies.

Inferring magnetic field strengths in high-redshift lensing galaxies from Faraday rotation measure observations

Stefan Reissl, Ralf S. Klessen, Annalisa Pillepich+3 more

• Cosmology and Nongalactic Astrophysics

AstronomerFaraday rotation in the lensing galaxy of CLASS B1152+199 at z = 0.439 suggests that efficient dynamos had already amplified galactic magnetic fields by that epoch. To assess field-strength inference and the rarity of the observed differential rotation measure, the authors forward-model 64 mass- and redshift-matched star-forming disk galaxies from TNG50 using POLARIS polarized radiative transfer and RM synthesis. The simulated characteristic large-scale field strengths are B₀ = 1.9–15.6 μG for individual galaxies and 10.3 μG for the combined sample. Fields inferred from synthetic observations generally recover B₀ within a factor of three, with weaker sensitivity to assumed field geometry than to inclination and beam depolarization. RM-synthesis differential rotation measures remain correlated with directly integrated values, but beam depolarization systematically suppresses their magnitudes. Only 1.41% of directly integrated sightline pairs reproduce the observed ΔRM = 1040 ± 60 rad m⁻²; this rises to 3.16% when selecting galactocentric distances comparable to the observed 2.6 and 6.5 kpc. The study supports differential Faraday rotation of lensed sources as a robust large-scale field probe, while finding this system’s large ΔRM relatively rare within the selected TNG50 analogs.

PublicMagnetic fields can rotate the polarization of light passing through a galaxy. In CLASS B1152+199, a foreground galaxy bends a background source’s light along different paths, allowing astronomers to compare that rotation. The observed large difference suggests that processes amplifying galactic magnetic fields were already efficient at the galaxy’s observed epoch. The researchers tested this interpretation with synthetic observations of 64 similar galaxies in a computer simulation, rather than new observations of 64 real galaxies. Their method generally recovered the simulated magnetic field strengths within a factor of three. The galaxy’s viewing angle and polarization cancellation within the observing beam affected the estimates more strongly than the assumed field shape. Differences as large as the observed one appeared in only about 1.4% of simulated path pairs, or about 3.2% when the paths were selected to pass at comparable distances from galaxy centers. The results support the method’s usefulness, but show that this unusually large signal is rare among the simulated galaxies studied.

Young explorerA galaxy’s magnetic field can twist a special pattern in light passing through it. One galaxy bends light so it travels along different paths, and astronomers found a big difference in how much the light’s pattern was twisted. They made computer versions of similar galaxies to check what this could tell them. Their test showed that the light can help them estimate how strong a galaxy’s magnetic field is, though the answer is not exact and depends on how we see the galaxy. Such a big difference was unusual in their computer galaxies.

Collapse-accelerated small-scale dynamos in the first stars and galaxies

Muhammed Irshad, Pallavi Bhat

• Cosmology and Nongalactic Astrophysics
• Solar and Stellar Astrophysics

AstronomerThis theoretical study extends a supercomoving framework for small-scale dynamos in gravitational collapse from the kinematic to the nonlinear regime. Earlier work found super-exponential kinematic amplification as collapse increases the dynamo growth rate; here, collapse also accelerates nonlinear amplification and scale-by-scale saturation, allowing magnetic energy to reach progressively larger scales. Applications to first-star and first-galaxy formation show a strong dependence on dynamo efficiency: fast dynamos saturate before substantial collapse, while very slow dynamos yield weak dynamo amplification and flux freezing dominates. At intermediate efficiencies, collapse produces dynamo speed-ups exceeding a factor of 10 within the explored parameter space, allowing dynamically significant fields to develop within the collapse time. Nonlinear saturation yields correlation scales that are a non-negligible fraction of the system size. The authors provide estimates and scaling relations for final field strengths and correlation scales as functions of halo, turbulence, dynamo, and collapse parameters. These are theoretical findings, not reported observations; potential consequences include altered fragmentation, angular-momentum transport, and subsequent evolution.

PublicThe study explores how magnetic fields could grow while gas collapses to form the first stars and galaxies. Turbulent gas motions can strengthen magnetic fields through a process called a dynamo, and collapse changes both the speed and size of those motions. In the authors’ theoretical framework, collapse accelerates not only the early growth of weak fields but also the later stage, when the fields become strong enough to influence the gas and spread their influence to larger scales. The effect depends on how efficiently the dynamo works: a very fast dynamo reaches its limit before much collapse occurs, while a very slow one adds little amplification beyond that caused by compression. Between those extremes, the explored cases show dynamo acceleration by more than a factor of 10. The resulting fields could become strong enough to affect the gas before collapse finishes and remain correlated across an appreciable part of the system. The authors estimate field strengths and correlation sizes rather than report measurements. Such fields could change how gas breaks into pieces and redistributes its spinning motion, affecting the development of early stars and galaxies.

Young explorerLong ago, clouds of gas squeezed together to make the first stars and galaxies. The gas swirled around, and those swirls could help tiny magnetic fields grow stronger. The scientists used a mathematical model to explore this. They found that squeezing the cloud could help the magnetic fields grow faster, but not in every case: some grow quickly already, and others grow too slowly for much help. If the fields become strong enough, they could change how the gas moves and breaks into smaller pieces. This is an idea explored with a model, not something the scientists watched happening.

Separating the Optical to Near-Infrared Light of AGN and Their Host Galaxies

Callum Dewsnap, Pauline Barmby, Sarah C. Gallagher

• High Energy Astrophysical Phenomena

AstronomerThe study decomposes images of 96 X-ray-selected AGN in the Extended Groth Strip using Sérsic host-galaxy plus point-source fits with AstroPhot, across up to 13 JWST and HST bands. Parametric and nonparametric methods are examined together to characterize the hosts. After separating host and AGN light, independent CIGALE fits to their photometric spectral energy distributions estimate host stellar masses and star formation rates, and AGN disk luminosities. In the stellar-mass–star-formation-rate plane, the hosts align with massive non-AGN galaxies in the control sample across all redshifts studied. The inferred AGN disk luminosities yield bolometric-to-X-ray flux ratios in the expected range of 5–20:1. The work also evaluates limitations of Sérsic modeling and recommends best practices for multiband AGN–host decomposition with JWST; the physical properties are model-based estimates rather than direct measurements.

PublicResearchers studied 96 galaxies with active central supermassive black holes, selected because of their X-ray emission. Using images from the James Webb and Hubble space telescopes, they modeled and separated the light from each galaxy and its active center. They then used that separated light to estimate the galaxies' stellar masses and rates of forming new stars, along with the brightness of the black holes' accretion disks. Across the redshifts studied, these galaxies followed the same relationship between stellar mass and star formation rate as massive comparison galaxies without active nuclei. The inferred disk brightnesses also gave total-to-X-ray flux ratios within the expected range. These conclusions depend on the light-separation and fitting models, whose limitations the study examines; they do not establish that active black holes cause or prevent star formation.

Young explorerScientists looked at pictures of 96 galaxies with bright centers powered by matter falling toward giant black holes. They used computer models to tell apart the light from the galaxy and the light from its bright center. This helped them estimate how much stuff was in the stars and how quickly new stars were being made. The galaxies were similar to other big galaxies without active centers in how their star-making rates compared with their amounts of stars. Separating the light is tricky, so the scientists also checked where their models might fall short.

X-ray Characterization of Galaxy Groups and Hickson Groups in COSMOS-Web to z 3.8 I. X-ray Luminosity Function Evolution

Ghassem Gozaliasl, Günther Hasinger, Gavin Leroy+35 more

AstronomerThe study presents uniform X-ray aperture photometry using the combined Chandra and XMM-Newton COSMOS mosaic for 1,678 AMICO-selected COSMOS-Web groups (CW-All; approximately z = 0.08–3.7) and a parallel catalog of 993 Hickson compact groups (CW-HCG; approximately z = 0.08–3.82), covering 0.45 square degrees. The released catalogs include X-ray measurements and derived properties, including fluxes, luminosities, temperatures, halo masses and radii, upper limits, and quality flags. At SNR ≥ 2.0, 499 CW-All groups (29.7%) and 332 CW-HCG groups (33.4%) are detected. X-ray luminosity functions in four redshift bins show a monotonic increase in characteristic luminosity L* of approximately 1.9–2.1 dex from the lowest to highest bin in both catalogs. This trend survives two independent alternative binning schemes and is not explained by mass or richness selection within the detected population. A targeted search for diffuse emission from the AmicOne protocluster candidate at approximately 2.50 ≤ z < 3.09 yields no statistically significant signal at the current depth, rather than establishing an absence of emission.

PublicResearchers used Chandra and XMM-Newton observations to study X-ray light from two catalogs of galaxy groups in the COSMOS-Web survey: one containing 1,678 groups and another containing 993 compact groups. Using the same analysis method throughout, they detected X-ray emission from about 30% of the first catalog and 33% of the second, at their chosen signal-to-noise threshold. They found that the characteristic X-ray brightness of the group population increases strongly toward higher redshift, corresponding to earlier cosmic times. The trend remained when they changed how groups were divided into redshift ranges, and differences in the detected groups’ masses or numbers of galaxies did not explain it. These findings characterize the population but do not establish what causes the brightness trend. A separate search for spread-out X-ray emission from the AmicOne candidate forming galaxy cluster found no statistically significant signal; the available observations could still miss faint emission. The team publicly released its measurements and derived group properties.

Young explorerGalaxies can gather in groups. Scientists looked for a special kind of light called X-rays coming from many of these groups. They found it in some groups, but not in most at the level they could detect. When they compared groups from different times in the universe, they found that groups from earlier times had a higher typical X-ray brightness. That does not mean every earlier group was brighter. They also looked at one place where a big group of galaxies might be forming, but did not find a clear X-ray glow. A faint glow could still be there, too hard to see in these pictures.

Super-resolving Polarized Dust Emission with Transformer-Based Multi-Tracer Fusion

Minjie Lei, George Halal, S. E. Clark+3 more

AstronomerThe study develops a data-driven super-resolution framework for polarized Galactic dust foreground modeling in next-generation CMB B-mode experiments. Existing dust polarization templates are constrained only to approximately 1 degree. A transformer combines Planck dust optical depth tau_353, neutral-hydrogen-based Stokes templates, and coarse Planck GNILC Q and U maps. It is trained to recover native-resolution GNILC polarization from a version smoothed with a beam four times broader, learning tracer-informed deconvolution rather than generating structure to match a prescribed statistic. Applied to uniform-resolution GNILC maps, it predicts Q and U at 20 arcminutes across the high-latitude sky, where the absolute value of Galactic latitude exceeds 30 degrees. Scalar and tensorial Minkowski functionals and scattering transform statistics show that the predicted maps have more coherent, anisotropic, and filamentary small-scale structure than the latest PySM dust model. These are model predictions informed by observed tracers, not direct measurements of polarization at the predicted resolution. The results support learned deconvolution as a promising foreground-modeling approach, without establishing that all predicted small-scale features reproduce the true sky.

PublicPolarized emission from dust in our Galaxy complicates efforts to study B-mode patterns in the cosmic microwave background. Existing dust polarization templates are constrained only to about 1 degree, leaving finer detail uncertain. The researchers developed an artificial-intelligence model that combines Planck dust measurements, polarization templates based on neutral hydrogen, and coarse Planck polarization maps. During training, the model learned to reconstruct a sharper polarization map from a version blurred with a beam four times broader. It then predicted dust polarization at a resolution of 20 arcminutes for regions where the absolute value of Galactic latitude is greater than 30 degrees. Statistical comparisons found that these predictions contain more coherent, directionally organized, threadlike fine structure than the latest PySM dust model. The finer details are inferred from observations, not directly observed polarization at that resolution. The work offers a promising way to model Galactic foregrounds for future cosmic microwave background experiments, rather than proof that every predicted detail is correct.

Young explorerDust in our Galaxy makes polarized light that can get in the way when scientists study very old light from the universe. Their usual dust maps are reliable only for details about 1 degree across. The researchers taught a computer to make a blurry dust map sharper, using several kinds of sky maps as clues. For practice, they blurred a map with a beam four times broader and asked the computer to recover the sharper map. Then it predicted details 20 arcminutes across in parts of the sky more than 30 degrees above or below the Galaxy's middle. Compared with another computer-made dust model, its maps had more connected, threadlike patterns that tended to point in particular directions. These tiny patterns are the computer's predictions, not new pictures proving that the sky looks exactly that way.

DESI Interacting Dwarfs Survey: Multiple Evolutionary Channels of Dwarf Galaxies Driven by Major Dwarf Interactions

Marko Mićić, Sugata Kaviraj

AstronomerUsing the Dark Energy Spectroscopic Instrument Early Data Release, the study constructs what it reports as the largest dwarf-galaxy pair sample, spanning 6.5 ≤ log(M_star/M_sun) ≤ 9.5 and 0.015 ≤ z ≤ 1.5. It examines star formation rates and multiwavelength colors as functions of projected separation, stellar mass, and external tidal environment. Low-mass, low-redshift pairs show star formation enhancement attributed to interactions at intermediate separations. At projected separations of roughly 10 kpc or less, their behavior diverges: isolated pairs show signs of emerging dust-obscured star formation, pairs in weak external tidal fields show extended unobscured star formation, and pairs in strong fields show rapid quenching. High-mass, low-redshift pairs exhibit a more uniform pattern with weaker environmental dependence: intermediate-separation enhancement followed by increased dust obscuration and rapid quenching at the closest separations. At higher redshifts, high-mass dwarf pairs show initial suppression followed by renewed star formation at smaller separations. Early gas removal and subsequent interaction-driven inflows are offered as an interpretation of that pattern, not as directly established gas measurements. The reported separation-dependent trends support multiple interaction pathways rather than a single universal evolutionary sequence, with implications for compact, dusty, intensely star-forming systems.

PublicPairs of small galaxies do not all respond to close encounters in the same way. Using the Dark Energy Spectroscopic Instrument Early Data Release, researchers assembled what they describe as the largest sample of dwarf-galaxy pairs and compared their star formation and colors with their apparent separation, mass, and the gravitational influence of their surroundings. Among lower-mass pairs in the relatively nearby universe, star formation is enhanced at intermediate separations. For the closest pairs, the surroundings matter: isolated pairs show signs of star formation hidden by dust, pairs under weak outside gravitational influence show extended star formation unobscured by dust, and those under strong outside influence rapidly stop forming stars. Higher-mass nearby dwarf pairs show a more consistent pattern, with enhanced star formation followed at the closest separations by more dust obscuration and rapid shutdown. Higher-mass pairs seen farther back in cosmic history instead show suppressed star formation followed by renewed activity at smaller separations. The researchers interpret this last pattern as possibly reflecting gas removal followed by gas flowing inward, rather than directly demonstrating those gas movements. Overall, the findings suggest that encounters between dwarf galaxies can lead to several different outcomes.

Young explorerSmall galaxies are big groups of stars. Scientists looked at pairs of these galaxies to see how many new stars they were making. Some close pairs were making more stars, sometimes behind dust that hides them. Other close pairs were quickly stopping. Which pattern scientists saw depended on how big the galaxies were and how strongly things around them pulled on them. For some galaxies seen farther back in time, the scientists think gas moving away and then moving inward could help explain the pattern, but they have not shown that for sure. Small galaxies do not all act the same when they get close together.

The Largest Catalog of Dwarf Galaxy Groups: Transient Structures or Building Blocks of the Universe?

Marko Mićić

AstronomerThe authors present the largest catalog of isolated dwarf galaxy groups, identified using DESI: 74 systems with three to six members each. The median line-of-sight velocity dispersion is approximately 53 km/s, and the median crossing time is approximately 0.37 Gyr. Stellar mass alone is generally insufficient to bind the observed configurations. Including dark matter through independently inferred stellar-to-halo mass relations and NFW potentials favors a bound interpretation for 69 systems, or 93%, after propagating observational and halo-model uncertainties; this is model-dependent evidence rather than definitive confirmation of binding. For these 69 systems, dynamical-friction estimates suggest that substantial orbital decay within a Hubble time is plausible if members retain significant dark-matter subhalos. The authors interpret many groups as possible sites of ongoing hierarchical assembly into more massive descendants, providing nearby laboratories for an assembly mode expected to have been common at early cosmic epochs.

PublicUsing the DESI survey, researchers identified 74 isolated groups of small galaxies, each containing three to six members—the largest catalog of its kind. The central question is whether gravity holds these groups together or whether they are temporary arrangements. The mass in their stars generally cannot provide enough gravitational pull to bind them. When the researchers included estimated dark matter, their calculations favored gravitationally bound groups in 69 of the 74 cases, while accounting for uncertainties in the observations and models. This does not prove that those groups are bound. Further estimates suggest that their galaxies could move substantially closer together over the age of the Universe, provided they retain substantial dark matter around them. The researchers therefore suggest that many groups may be building toward more massive galaxies, offering a nearby way to study a process expected to have been common early in cosmic history.

Young explorerScientists found 74 little groups of small galaxies, with three to six galaxies in each group. They wondered whether gravity keeps the galaxies together or whether the groups will drift apart. The stars usually do not give enough pull to hold a group together. When scientists added their estimates of invisible stuff called dark matter, their calculations suggested that 69 groups could stay together—but they are not sure. If the galaxies keep plenty of dark matter around them, they might slowly move closer together and help build bigger galaxies.

Star Cluster Populations in 38 Spiral Galaxies: Evidence for Near-Universal Mass and Age Distributions from PHANGS

Rupali Chandar, Matthew R. Floyd, David A. Thilker+23 more

AstronomerThis study analyzes uniformly selected PHANGS-HST catalogs of more than 15,000 human-classified and 36,000 machine-classified compact clusters in 38 nearby spiral galaxies. Improved photometric SED age dating mitigates degeneracies with reddening and metallicity. The galaxies span approximately two orders of magnitude in SFR, star-formation surface density, and molecular-gas surface density. Cluster mass functions follow dN/dM ∝ M^β, with β = −1.9 ± 0.2, and show no significant dependence on these environmental measures across individual galaxies and eight SFR-based composite groups. Age distributions decline as dN/dt ∝ t^γ, with γ = −0.83 ± 0.24, showing little dependence on host properties or cluster mass. The reported independence of mass and age distributions implies a separable joint distribution, g(M,t) ∝ M^β t^γ. The authors interpret these findings as evidence that strong, mass-independent dissolution dominates spiral-disk cluster populations during their first approximately 1 Gyr, rather than as a direct measurement of individual clusters dissolving. The distributions provide a benchmark for cluster demographics and context for young-cluster studies at high redshift.

PublicA study of star clusters in 38 nearby spiral galaxies finds surprisingly similar population patterns despite large differences in the galaxies’ star formation and molecular gas. Using catalogs containing more than 15,000 clusters classified by people and 36,000 classified by machines, the researchers find that lower-mass clusters are more common than higher-mass ones, and that cluster numbers fall steeply with increasing age. These patterns vary little with the galaxy properties examined, and the age pattern also varies little with cluster mass. Improved estimates of cluster ages reduce uncertainties caused by dust reddening and chemical composition, but do not eliminate them. The authors interpret the patterns as suggesting that many clusters dissolve during their first roughly billion years, with the effect largely independent of cluster mass. This is an interpretation of the population statistics, not a direct observation of individual clusters breaking apart.

Young explorerStar clusters are groups of stars. Scientists studied lots of these groups in 38 nearby galaxies. They found more groups with less total star material than groups with more, and fewer old groups than young ones. The patterns looked much alike in different galaxies. The scientists think many groups spread apart as they grow older, whether they have more or less star material. That is their explanation for the patterns, not something they watched happen to each group.

No Convincing Evidence for Tidal Binary Clusters in the Galaxy

Juan Casado, Zahra Al

• Solar and Stellar Astrophysics

AstronomerThe authors reassess twenty star clusters cataloged as members of proposed tidal binary clusters, whose formation through tidal capture remains dynamically uncertain. Using Gaia DR3 astrometry and photometry, they simultaneously fit age, distance modulus, reddening, and metallicity for each candidate pair. None of the studied systems satisfies their age-based evolutionary criteria for independent formation followed by capture. They instead interpret the systems as coeval members of primordial cluster pairs or groups. The authors conclude that genuine tidal binary clusters, if present in the Milky Way, must be extremely rare, emphasizing robust age estimates and physically motivated selection criteria for future searches.

PublicCan two star clusters form separately and later become a gravitationally bound pair through tidal capture? Researchers revisited twenty clusters previously classified as members of such pairs, using Gaia data to estimate their ages and other properties consistently. None of the systems met the study's age requirements for that formation history. Instead, the researchers interpret them as clusters that formed at the same time as members of an original pair or group. They conclude that pairs assembled through tidal capture must be extremely rare in the Milky Way, if they exist, rather than claiming to have ruled them out entirely.

Young explorerStar clusters are groups of stars. Scientists checked twenty clusters thought to belong to pairs that joined up after forming separately. Their ages did not fit that story. The scientists think they formed at the same time as parts of a pair or group instead. Clusters that join up later may be very rare.

A two-stage settling of the Milky Way disk revealed by precise ChronoGal ages

David Mirabal, Carme Gallart, Tomás Ruiz-Lara+9 more

AstronomerUsing color–magnitude diagram fitting of Gaia data, the authors derive age–metallicity distributions for complete stellar samples in the solar neighborhood and isolate quasi-mono-age-metallicity populations with reported age resolution better than 5% (approximately 0.5 Gyr at old ages). Their absolute vertical density profiles show a clear age–scale-height correlation, with younger populations more confined to the Galactic plane. They find evidence for a sharp change in the scale-height–age relation at 10.85 (+0.13/−0.12) Gyr ago: the inferred early decline runs from over 1.26 kpc to approximately 0.5 kpc within 2 Gyr, followed by much more gradual thinning toward approximately 0.1 kpc for the youngest populations. The authors interpret this relation as strong support for early upside-down formation of the thick disk during a highly turbulent phase, followed by quieter secular evolution and gradual gas settling that formed the thin disk. This two-phase formation history is an interpretation of the observed population profiles, not a direct observation of the disk settling over time.

PublicThe researchers used Gaia data to estimate the ages and chemical makeup of stars in complete samples near the Sun, then measured how far different groups spread above and below the Milky Way’s disk. They found that younger stars occupy a thinner layer than older stars. The relationship between age and thickness suggests a major change about 10.85 billion years ago: the earliest part of the disk’s history shows a rapid decrease in thickness, followed by much slower thinning. The authors interpret this as strong evidence that the thick disk formed first in a turbulent environment, while the thin disk formed later as conditions became calmer and gas gradually settled. This history is inferred from stars seen today; the study did not directly watch the disk become thinner.

Young explorerThe Milky Way has a big, flat part filled with stars. Scientists studied stars near the Sun and found that younger stars stay closer to the middle of this flat part, while older stars spread farther above and below it. These clues make the scientists think our galaxy first made a thick layer of stars when things were very swirly, then made a thinner layer as things became calmer. They are figuring out what happened long ago by looking at stars today, not by watching it happen.

Merger remnant in TXS 1033+026 - I: Hα and HI 21-cm observations suggest counter-rotating gas

J. N. H. S. Aditya, Hyein Yoon, L. G. Dahmer-Hahn+5 more

AstronomereMERLIN and GEMINI IFU observations of the post-merger ultraluminous infrared galaxy TXS 1033+026 resolve radio continuum, H-alpha, and HI 21-cm structure on sub-kpc scales. The L-band (approximately 1.4 GHz) and C-band (approximately 4.8 GHz) continuum images show a symmetric, two-sided core-jet structure. A likely double-double radio morphology suggests possible recurrent AGN activity. The sub-arcsecond GEMINI IFU data suggest a rotating, kiloparsec-scale circumnuclear H-alpha disk with signs of warping. HI kinematics indicate two counter-rotating gas components orbiting the core-jet axis, one counter-rotating relative to the H-alpha disk, although the true morphology may be more complex than this interpretation. The estimated HI velocity-integrated optical depth is 90 ± 3 km s−1. These are the first sub-kpc-scale results probing H-alpha and cold neutral hydrogen in this galaxy.

PublicObservations with eMERLIN and GEMINI reveal jets and complicated gas motions near the center of TXS 1033+026, an exceptionally infrared-bright galaxy left after a merger. Radio images show two symmetric jets extending in opposite directions from the core. Their apparent double-double structure may indicate that the active galactic nucleus has gone through more than one episode of activity. Light from hydrogen suggests a rotating disk around the center, roughly a kiloparsec in scale, with signs of a warp. Measurements of cold neutral hydrogen suggest two gas components rotating in opposite directions; one also rotates opposite to the hydrogen disk seen in H-alpha light. This is an interpretation of the gas motions, and the actual arrangement could be more complicated. The study provides the first observations of H-alpha and cold neutral hydrogen in this galaxy on scales smaller than a kiloparsec.

Young explorerAstronomers looked closely at a galaxy that formed after galaxies joined together. They saw two jets reaching out in opposite directions from its middle. The jets may be clues that the galaxy's center has been active more than once. The observations also suggest that gas circles the middle in a disk that may be bent. Some cold gas seems to circle one way, while other gas circles the opposite way. The astronomers are not sure exactly how all the gas fits together—it could be more complicated than it looks.

Discovery of thermal radio recombination line emission toward the high-mass protostar IRAS18162-2048

R. Fedriani, J.F. Gomez, Y. Cheng+7 more

AstronomerArchival ALMA Band 6 observations at approximately 53 × 42 mas resolution yield the first detection of thermal H30α radio recombination-line emission in IRAS18162−2048, the high-mass protostar driving HH80–81. The emission is spatially unresolved, with an estimated emitting-region size of ≲50 au at a distance of 1.4 kpc. The spectrally resolved line has an LSR velocity of approximately −14 km/s, a blueshift of approximately 26 km/s relative to the cloud systemic velocity, and an FWHM of approximately 82 km/s. These findings suggest, rather than establish, that H30α traces blueshifted outflowing material in the known radio jet. The detection offers a route to future studies of ionised-jet kinematics and physical conditions.

PublicUsing archived ALMA telescope observations, researchers detected a particular radio signal from ionised gas for the first time around the massive young star IRAS18162−2048, which powers the HH80–81 jet. The emitting region is too small for these observations to resolve, but its estimated size is no more than about 50 times the Earth–Sun distance. The signal spans a broad range of velocities and is shifted toward us relative to the surrounding cloud. This suggests that it comes from gas flowing outward in the star’s known radio jet, although that interpretation is not established definitively. The detection could enable more detailed studies of how ionised jets move and what conditions they contain.

Young explorerAstronomers found a new radio signal from hot gas very close to a big star that is still growing. The gas looks too tiny and far away for their telescope to show its shape. The signal suggests that the gas is rushing toward us in a stream shooting away from the star, but the astronomers are not yet sure. Finding this signal may help them learn more about the stream.

A multi-scale view of molecular gas and magnetic fields in the Antennae galaxies

Akhil Lasrado, Enrique Lopez-Rodriguez, Claudia Cicone+5 more

AstronomerThis observational study examines the relationship between cold molecular gas and magnetic-field geometry in the Antennae merger, NGC 4038/4039, combining CO(3-2) observations from APEX/LAsMA and ALMA with archival 154 μm dust polarization from SOFIA/HAWC+. At kiloparsec scales, polarization measurements anticorrelate with CO intensity (ρ ≲ -0.6) and CO velocity dispersion (ρ ≲ -0.4), which the authors interpret as signatures of geometric depolarization. Because dust polarization averages density-weighted magnetic-field vectors along the line of sight and within the beam, ALMA channel maps are used as proxies for unresolved density structure. Geometric analysis identifies prominent kinematic structures in the overlap region aligned with the SOFIA-inferred field orientation. These structures might dominate the measured orientation through their density or high polarization fraction, but this interpretation assumes correspondence between molecular gas structures and magnetic fields. A modest correlation (ρ ~ 0.5) between small-scale gas coherence, used as a proxy for line-of-sight angular dispersion, and polarization fraction indicates that polarization measured on roughly 2 kpc scales is sensitive to structures on roughly 50 pc scales.

PublicThe researchers studied cold gas and magnetic fields in the Antennae, a nearby pair of merging galaxies. They combined observations of molecular gas with polarized light emitted by dust, which provides clues to magnetic-field direction. They found that stronger gas emission and a wider spread of gas velocities tend to accompany lower polarization. They interpret this as evidence that differently oriented magnetic fields partly cancel one another's polarization signals when averaged together. More detailed gas observations also revealed structures in the region where the galaxies overlap that line up with the inferred magnetic field. These structures may strongly influence the measured field direction, although that explanation assumes the gas structures trace the magnetic fields. A further, modest correlation suggests that gas structure on scales of about 50 parsecs affects polarization measured across regions about 2,000 parsecs wide.

Young explorerTwo galaxies are coming together, and scientists looked at their cold gas and clues to their magnetic fields. Dust gives off light that can help show which way those fields point. Some gas shapes lined up with the magnetic-field direction. The scientists think those shapes might help explain what they see, but they are not sure. They also found clues that smaller gas shapes matter even when they look at a much bigger area.

Searching for Green Pea Galaxies in the SFACT Survey

Kristin N. Baker, John J. Salzer, Brooke Kimsey-Miller+5 more

AstronomerThis study presents the first catalog of Green Pea galaxy candidates from the ongoing deep, narrowband SFACT survey. Approximately 120 candidates are selected from its [O III]-detected galaxy catalog using broadband gri colors and [O III] equivalent widths derived from narrowband imaging. All candidates have spectroscopically confirmed redshifts of z = 0.31–0.51, and the sample has a median apparent magnitude of g = 22.9. Comparison with samples of known Green Peas shows that SFACT's depth enables detection of candidates at lower luminosities. The objects remain classified as candidates; confirmed redshifts do not by themselves establish Green Pea status. Further candidates are expected as spectroscopic follow-up is completed. Green Peas are rare, extreme star-forming galaxies with physical properties resembling those of high-redshift Ly-alpha emitters.

PublicAstronomers have assembled about 120 candidates for a rare type of galaxy called a Green Pea, known for intense star formation and strong emission from doubly ionized oxygen. Using the SFACT survey, they selected the candidates by their colors and the strength of this oxygen emission. Spectra confirm that all have redshifts between 0.31 and 0.51, but they are still described as Green Pea candidates. Compared with existing samples of known Green Peas, SFACT's deep observations uncover candidates with lower intrinsic brightness. These galaxies are of interest because their physical properties resemble those of much more distant galaxies that emit Lyman-alpha light. This is SFACT's first candidate catalog, with more additions expected as follow-up observations are completed.

Young explorerSome galaxies make lots of new stars. A rare kind is nicknamed a Green Pea galaxy. Astronomers looked at galaxies' colors and a special kind of light from oxygen, and found about 120 that might be Green Peas. Their survey can spot dimmer possible Green Peas than the other groups they compared with. These are still possible Green Peas, not all confirmed ones. The astronomers expect to add more as they keep checking their observations.

Growth of Aromatic Hydrocarbon Dust Particles in the Extremely Metal-poor Galaxy Sextans A

Elizabeth J. Tarantino, Julia Roman-Duval, Karin M. Sandstrom+17 more

AstronomerJWST observations detect and spatially resolve PAH emission in Sextans A at 7% solar metallicity, the lowest-metallicity PAH emission detection reported to date. The emission occurs in compact clumps spanning 0.5–1.5 arcseconds, or 3–10 pc, explaining its nondetection with lower-resolution instruments. Ratios of the 3.3, 7.7, and 11.3 micrometer features indicate small, neutral PAH grains, with no evidence of significant radiation-field processing. These findings favor inhibited grain growth rather than enhanced destruction as the explanation for Sextans A's low PAH abundance. The authors interpret the clumps as likely sites of in-situ PAH growth in dense, well-shielded interstellar gas, rather than directly establishing that growth mechanism. The results show that PAHs can form and survive at extremely low metallicity, under conditions common early in cosmic evolution.

PublicUsing JWST, researchers detected infrared light from tiny carbon-rich dust grains called PAHs in the galaxy Sextans A. Its abundance of elements heavier than helium is only 7% of the Sun's, making this the lowest such abundance at which PAH emission has been detected to date. The light comes from small clumps, 3–10 parsecs across, that earlier, lower-resolution instruments could not distinguish. The pattern of infrared emission indicates that the grains are small and electrically neutral, with no evidence that radiation has substantially altered them. This favors the idea that PAHs are scarce because their growth is limited, rather than because they are destroyed more rapidly. The researchers suggest that the clumps may be sheltered places where PAHs grow, but that explanation remains an interpretation. The findings show that these grains can form and survive in environments poor in heavy elements, like those common early in the universe.

Young explorerScientists used the JWST telescope to find light from tiny bits of carbon dust in a galaxy called Sextans A. This galaxy has very little of the heavier ingredients that help make dust. The dust was hiding in little bunches that earlier telescopes could not see clearly. Its light suggests the tiny grains have not been changed much by strong light around them. Scientists think there may be so little of this dust because it has trouble growing, not because it gets broken apart more often. The bunches might be sheltered places where dust grows, but the scientists are not sure yet.

Learning to See Sharper: A Physics-Informed Artificial Intelligence Framework for Super-Resolving Galaxy Spectra

Aryana Haghjoo, Shoubaneh Hemmati, Bahram Mobasher+6 more

AstronomerThis proof-of-concept deep-learning framework reconstructs galaxy spectra at approximately ten times the input resolving power, from R≈100 to R≈1000. Training uses 2,858 paired JWST/NIRSpec observations from JADES, matching prism spectra to a unified G140M, G235M, and G395M reference spanning 1.0–5.3 micrometers. The three-stage architecture first produces a coarse reconstruction, estimates redshift, and then applies physics-informed residual refinement through attention across emission-line tokens, parametric line-profile prediction, and convolutional continuum corrections. On a 20% held-out sample, the authors report noise-limited residuals over most wavelengths and improved signal-to-noise ratios for [OII], Hβ, [OIII], and Hα. The reconstructions separate features unresolved in the prism data, including the [OIII] λλ4959,5007 doublet and Hβ, although line-flux recovery is described as modest. These are model-inferred spectra tested against medium-resolution observations, not new high-resolution measurements. Extension to Euclid and Roman low-resolution grism spectroscopy is proposed as a potential route to population-level diagnostics across millions of spectra, rather than demonstrated here.

PublicGalaxy spectra spread light into wavelength patterns that help astronomers study galaxies, but collecting finely detailed spectra for large samples is expensive. The researchers trained an AI model using 2,858 pairs of lower- and higher-resolution JWST spectra. It predicts a more detailed spectrum from a less detailed one, targeting roughly a tenfold increase in resolving power. In tests on a reserved 20% of the sample, the reconstructed spectra separated some blended features and improved the signal-to-noise ratio of several important emission lines. Errors were comparable to the noise over most of the wavelength range, though recovery of the light contained in individual lines remained modest. The added detail is inferred by the model, not directly measured anew. Applying this approach to future Euclid and Roman data could help study millions of galaxies, but that application has not yet been demonstrated.

Young explorerLight from a galaxy makes a pattern, but sometimes its little details blur together. Scientists taught a computer using pairs of blurry and clearer galaxy-light patterns. The computer then guessed clearer patterns from blurry ones. In tests, it could separate some details that had looked stuck together, but it did not get everything exactly right. Scientists hope this could help them study many more galaxies.

A New Record Census of Dwarf AGN and a Bimodal M(BH)-M(⋆) Scaling Relation with DESI DR1

Ragadeepika Pucha, S. Juneau, M. Mezcua+48 more

AstronomerUsing DESI DR1 spectroscopy, the authors systematically search approximately 1.7 million line-emitting galaxies at 0.001 ≤ z ≤ 0.45 for AGN signatures. The [NII]/Hα versus [OIII]/Hβ diagnostic selects 314,245 of 1,211,573 high-mass galaxies (25.9%) and 9,648 of 467,214 dwarf galaxies (2.1%), with the division at log(M★/M☉) = 9.5. The selected AGN fraction rises monotonically with stellar mass, from approximately 1.4% to 93.3%; these fractions apply to the line-emitting sample and this diagnostic. Among the selected AGN, 17,949 show broad Hα, enabling single-epoch virial black hole mass estimates. The sample extends the MBH–M★ relation to log(M★/M☉) ≈ 7.8 and log(MBH/M☉) ≈ 4.4. The authors find a bimodal distribution in this plane, described by two empirical relations. Extrapolating the high-stellar-mass, high-black-hole-mass relation overlaps the high-redshift overmassive black hole candidates; this is not a direct measurement of their evolutionary connection. The authors interpret the results as suggesting at least two broad evolutionary pathways for overmassive black holes and their hosts. They also release the EmFit value-added catalog, with emission-line fluxes and widths for approximately 7.4 million galaxies and decomposition into narrow, broad, and outflow components.

PublicThe researchers searched spectra from DESI’s first data release for signs of active galactic nuclei in about 1.7 million relatively nearby galaxies that show emission lines. Their spectral test identified such activity in 25.9% of the higher-mass galaxies and 2.1% of dwarf galaxies. The fraction increased with galaxy stellar mass, but these numbers describe this selected sample and detection method, not all galaxies. Nearly 18,000 of the identified active galaxies had a broad hydrogen emission line that the researchers used to estimate black hole masses. Comparing these estimates with the galaxies’ stellar masses revealed two groupings, described by different relationships. Extending the relationship for the more massive systems reaches the region occupied by distant candidates for unusually massive black holes. The authors suggest this may point to at least two broad evolutionary routes, rather than demonstrating how individual systems evolved. They also released a catalog of emission-line measurements for about 7.4 million galaxies.

Young explorerScientists looked at light from about 1.7 million galaxies to find signs of active black holes. They found these signs more often in galaxies with more stars. For some black holes, they used the light to estimate how heavy they are. Comparing black holes with their galaxies showed two groups. This hints that they might grow in different ways, but it does not prove how they grew.

Diverse Histories and Common Origins of Nitrogen-enhanced JWST Galaxies

Vadim Rusakov, Christopher J. Conselice, Thomas Harvey+2 more

AstronomerUsing public JWST surveys, the authors assemble 76 nitrogen-to-oxygen-enhanced galaxies (NOEGs) at 4 < z < 8.5, the largest high-redshift sample reported to date. The NOEG fraction increases from approximately 3% at z ≈ 4 to 18% at z ≈ 7, compared with approximately 2% locally; burstier, cluster-dominated star formation is proposed as a possible driver. Stacked spectra of the most nitrogen-rich systems show signatures of low-metallicity Wolf-Rayet (WR) stars, with young stellar UV and optical continua and Balmer jumps in some cases. WR stars are interpreted as a likely source of primary nitrogen during the first few Myr of a starburst. Secondary [O III] and Hα components occur in 40% of the sample, providing evidence for ionised outflows. Stacks of the remainder show broadened, offset Hα without forbidden-line counterparts, suggesting dust-attenuated or faded outflows; their weak continuum Balmer break indicates a post-burst phase. The authors propose that outflows dilute gas metallicity after initial enrichment, allowing low-metallicity asymptotic giant branch (AGB) stars to renew N/O enhancement. Their interpretation places NOEGs in brief post-starburst phases: within approximately 10 Myr for WR-wind enrichment, or after 30–40 Myr for AGB-wind enrichment following radiative- or supernova-driven outflows. This proposed sequence is consistent with recent chemical evolution models.

PublicJWST observations have revealed early galaxies with unusually high amounts of nitrogen relative to oxygen, challenging models of how galaxies build up chemical elements. Using public JWST surveys, the researchers identify 76 such galaxies. Their fraction rises from about 3% at redshift 4 to about 18% at redshift 7, compared with about 2% in nearby galaxies. More intense, cluster-dominated bursts of star formation could help explain this trend, but that explanation is not established. Combined spectra of the most nitrogen-rich galaxies show signs of low-metallicity Wolf-Rayet stars, which the researchers suggest could supply nitrogen soon after a burst of star formation. Gas-emission features in 40% of the galaxies provide evidence for outflows. Combined spectra of the remaining galaxies suggest additional outflows that may be obscured by dust or have faded. The authors interpret the findings as two short-lived stages: enrichment by Wolf-Rayet winds within roughly 10 million years of a burst, or enrichment by winds from asymptotic giant branch stars after 30–40 million years. In the proposed later stage, an intervening outflow dilutes the gas's heavy-element content. This explanation agrees with recent models, but the observations do not directly establish the whole sequence.

Young explorerScientists used the JWST telescope to study 76 galaxies from long ago that have lots of nitrogen compared with oxygen. They found clues that some stars might blow nitrogen into the gas around them. They also found signs of gas blowing out of many of these galaxies. The scientists think different kinds of stars could add nitrogen at different times after lots of new stars are born. That is their explanation for the clues, not something they watched happen from beginning to end.

Probing the molecular gas content of galaxies in an over-dense group at z 0.7: A test case for environmental quenching

Jonathan Freundlich, Benoît Epinat, Thierry Contini+14 more

AstronomerCO(2–1) observations with IRAM NOEMA and the 30m telescope probe molecular gas in COSMOS-Gr30 at z ≈ 0.7, a dense group at a cosmic-web filament intersection containing an extended ionized structure revealed by MUSE. Four galaxies are detected at S/N > 5; upper limits are obtained for the remaining members with secure spectroscopic redshifts. Stacked measurements indicate molecular gas contents approximately 0.5 dex below field scaling relations, with gas fractions 20–40% of those in typical main-sequence galaxies. Significant uncertainties remain, so environmental depletion is an interpretation of the measured deficit rather than a directly identified mechanism. The 30m data constrain molecular gas associated with the extended ionized structure to Mgas < 2 × 10^10 solar masses, implying that less than one-third of the intragroup gas is in a cold, star-forming phase. The findings support environmental removal or suppression of molecular gas and associated quenching in this group.

PublicAstronomers used two radio telescopes to study the cold molecular gas that supplies star formation in the galaxy group COSMOS-Gr30. They detected carbon monoxide emission, a tracer of molecular gas, in four galaxies and set limits for the others studied. Combining measurements suggests that the group’s galaxies have substantially less molecular gas than comparable galaxies outside dense groups: their gas fractions are about 20–40% of those in typical star-forming galaxies. The uncertainties are substantial, but the results suggest that the group environment reduces this fuel supply. Observations also limit the molecular gas in a large ionized gas structure around the galaxies, implying that less than one-third of the gas between them is cold and available for star formation. The study supports, but does not identify a specific mechanism for, environmentally driven suppression of star formation.

Young explorerGalaxies use cold gas to make new stars. Astronomers looked at a crowded group of galaxies and found signs that they have less of this gas than usual. Being in the group might make it harder for them to keep their star-making gas, but the scientists are not yet sure exactly how.

Supernovae Ia ejecta velocities and host galaxy environments: the role of survey-selection effects

L. V. Barkhudaryan, A. A. Hakobyan, M. H. Gevorgyan+6 more

AstronomerThis study re-examines whether near-maximum-light Si II λ6355 velocity diversity in spectroscopically normal SNe Ia reflects systematic host-environment differences. The sample contains 354 nearby events at z ≤ 0.04: 239 normal-velocity (NV) and 115 high-velocity (HV) SNe from targeted and untargeted surveys. The analysis characterizes host morphology, galactocentric distance, physical size, and homogeneous stellar masses while assessing survey selection. Two Gaussian components describe the Si II velocity distribution well, supporting the NV/HV division. No statistically significant subgroup differences are found in galactocentric distance, host size, or stellar mass. Previously reported environmental trends appear only marginally in the targeted subsample and nearly disappear in the untargeted subsample, consistent with a substantial role for selection effects. These findings weaken explanations based primarily on the global host properties examined. The authors instead favour intrinsic explosion asymmetries and viewing-angle effects as substantial contributors, an interpretation rather than a direct demonstration; local environments and progenitor properties remain possible contributors.

PublicWhy do otherwise normal Type Ia supernovae show different speeds in their silicon spectral signatures near peak brightness? This study compares 354 nearby supernovae, including 239 in the normal-velocity group and 115 in the high-velocity group. The researchers find no statistically significant differences between the groups in their distances from their galaxies' centres, their host galaxies' sizes, or their host galaxies' stellar masses. Environmental differences reported in earlier work are only weakly present among supernovae found by surveys targeting selected galaxies and largely vanish among those from untargeted surveys. This suggests that how surveys choose where to look may explain much of the earlier apparent difference. The results favour an explanation involving uneven explosions and the angle from which we see them, but do not establish that explanation directly. Nearby conditions within a galaxy or differences in the stars that explode could still play a role.

Young explorerSome exploding stars have signs in their light that show faster-moving material than others. Scientists compared 354 explosions to see whether the faster and slower groups happened in different kinds of galaxies or different places inside them. They did not find a clear difference in the galaxy sizes, the amount of stars in the galaxies, or how far the explosions were from the galaxies' middles. How scientists picked galaxies to search may have made earlier differences look stronger. The scientists think uneven explosions, seen from different sides, could explain much of the difference in speed. But they are not sure yet, and the stars themselves or things nearby could matter too.

Generation of UL-Axions by a Kerr Black Hole. Part III: The fate of its Axion Wind

Guy Pelletier

AstronomerThis theoretical study explores potentially observable interactions of axion winds from supermassive Kerr black-hole magnetospheres with baryonic matter and axionic dark matter around nearby active galactic nuclei. It assumes ultralight axions that form Bose–Einstein condensates described by a large-scale Schrödinger wave. The authors argue that the only efficient interaction considered with plasma and hydrogen gas is a gravitational Cherenkov–Vavilov-type effect coupling to acoustic waves through a streaming instability. They predict that the instability can operate efficiently in the host galaxy’s central region on scales up to parsecs, potentially enabling Lyman-alpha diagnostics and detection of hydrogen’s 21 cm hyperfine emission. They also argue that weak scattering permits winds to propagate through halos and potentially across other galaxies without significant loss until quantum thermalization. Conversion into gamma rays on Earth is proposed as a possible direct-detection route. Messier 87 is identified as a promising target for gamma-ray conversion searches and bulge Lyman-alpha diagnostics. The abstract reports theoretical possibilities, not observed axion winds or detections.

PublicCould hypothetical dark-matter particles flowing away from a galaxy’s central black hole leave detectable traces? This study explores that possibility for ultralight particles called axions, assumed here to make up dark matter. The authors argue that an axion wind could gravitationally excite sound waves in nearby hydrogen gas and plasma. Those waves might be studied using hydrogen’s Lyman-alpha light or its 21-centimeter radio emission. Their calculations also suggest that the wind could travel very large distances with little loss, potentially crossing other galaxies. They propose searching for axions through conversion into gamma rays on Earth and identify Messier 87 as a promising galaxy to investigate. These are theoretical predictions and proposed searches, not evidence that axions have been detected.

Young explorerScientists wonder if tiny, unseen particles called axions could stream away from a huge black hole. They think this stream might make waves in nearby gas, a bit like ripples. Special light from the gas might help reveal those waves. A galaxy called Messier 87 could be a good place to look, but the scientists have not found these particles in this study.

Testing internal dynamics in neutron stars with radio pulsar timing

Reginald Christian Bernardo

• Instrumentation and Methods for Astrophysics
• General Relativity and Quantum Cosmology

AstronomerThe study compares two crust–superfluid models using observed pulsar phases to assess whether angular-velocity fluctuations are stationary. Equal-and-opposite internal torques exchange angular momentum and produce stationary spin noise, whereas independent torques allow diffusive changes in total angular momentum and produce nonstationary noise. In three isolated pulsars with measurable timing noise, the inferences differ: PSR J1359-6038 favors independent torques with odds of 700:1, characterized in the abstract as mild support; PSR B1937+21 shows no clear model preference; and excess scatter and unexplained residual structure limit interpretation of Vela’s pre-glitch interval.

PublicPulsars show small irregularities in their rotation. This study uses observed pulse timing to compare two explanations: angular momentum being exchanged between a pulsar’s radio-emitting crust and its superfluid interior, or separate twisting forces that let its total angular momentum wander. The three pulsars do not give a uniform answer. For PSR J1359-6038, the model comparison favors separate forces by odds of 700 to 1, although the abstract describes that support as mild. PSR B1937+21 does not clearly favor either explanation. For Vela, observations from an interval before a sudden change in rotation contain extra scatter and unexplained patterns, limiting what can be concluded.

Young explorerPulsars are spinning stars that send out radio pulses. Their spinning can be a little uneven. Scientists checked three stars to compare two ideas: parts inside a star might trade spin with each other, or separate pushes might change the star’s spin overall. One star gave some support to the separate-push idea. Another did not help choose between the ideas. The third had messy timing patterns that the models could not explain well, so the scientists could not draw a clear conclusion.

Neutrino flavor instabilities intermediate between slow and fast

Nicolas Viaux, Lucas Johns

• Astrophysics of Galaxies
• Solar and Stellar Astrophysics

AstronomerThis theoretical study examines mixed neutrino flavor instabilities that combine attributes of slow, fast, and collisional instabilities, relevant to supernovae and neutron star mergers. Growth rates are analyzed in two-dimensional parameter-space phase diagrams whose axes correspond to pure instability types. The analysis finds critical curves connecting pure-type onset points and identifies qualitative trends in growth-rate spectra, including crossovers and phase transitions in the fastest-growing Fourier mode. It emphasizes the distinction between spatial-mean instabilities at zero wavevector and flavor-wave instabilities at nonzero wavevector. These results are presented as a step toward understanding instabilities beyond idealized pure-type limits, not as observations of their behavior in astrophysical events.

PublicNeutrinos in supernovae and neutron star mergers can change their mixture of types, called flavors, through processes that can become unstable. These instabilities are usually divided into slow, fast, and collision-related categories. This theoretical study explores what happens when their characteristics overlap. By mapping how quickly instabilities grow as two parameters vary, the researchers find boundaries linking the onset of different pure categories. They also identify changes in which pattern grows fastest, distinguishing changes in the spatial average from wave-like changes across space. The work moves beyond simplified categories toward understanding more realistic behavior, but does not report observations of these effects in a supernova or merger.

Young explorerTiny particles called neutrinos come in different kinds and can switch kinds. Scientists studied how those switches might grow together in exploding stars and when two neutron stars come together. They used a theoretical study to explore what happens when different ways of making the switches grow are mixed. They found that the pattern growing fastest can change, and that a change in the average is different from a wave-like change across space. This helps them think about what might happen in nature; they did not watch it happen in a real star.

Extending the Pulsar radio population through Quantum Vacuum Cherenkov Emission

Tales A. O. Gomes, Sergei V. Bulanov, Jaziel G. Coelho+3 more

AstronomerRadio pulsars observed within and below the conventional death valley in the period–period-derivative diagram challenge polar-cap pair-cascade models based on curvature radiation (CR) and resonant inverse Compton scattering (RICS). The authors identify quantum-vacuum Cherenkov radiation, enabled by strong-field QED vacuum polarization, as a distinct pair-creation channel in the vacuum gap model. Their model yields sufficiently short acceleration lengths for Cherenkov emission and subsequent photon mean free paths to support rapid electron–positron conversion, including regimes where the conventional channels are strongly suppressed. The resulting death lines partially overlap with and extend beyond the CR and RICS death valleys, expanding the modeled parameter space for radio-active neutron stars. This is a theoretical explanation for how long-period neutron stars could sustain the pair creation associated with coherent radio emission, not an observational detection of the proposed channel. Future facilities such as the Square Kilometre Array are suggested as opportunities to test the underlying non-linear QED physics.

PublicSome neutron stars emit radio pulses even though standard models place them in a region where the particle-production processes thought to support those pulses should struggle. This study offers a theoretical explanation: in a sufficiently strong magnetic field, quantum effects can allow Cherenkov radiation from the vacuum. In the authors’ model, the resulting photons rapidly produce electrons and their antimatter partners, providing an additional route when the usual processes are strongly suppressed. This changes the predicted boundaries for which neutron stars could remain radio-active, potentially explaining pulses from long-period stars previously considered inactive. The study does not report a detection of this mechanism; future radio facilities, including the Square Kilometre Array, could help test the idea.

Young explorerSome stars send us radio signals even when scientists’ usual ideas say they should have gone quiet. Scientists worked out another way these stars might make tiny particles that help them keep sending signals. It works in their model, but they have not seen this new process happening. Future radio telescopes could help test the idea.

Suppression of spiral density waves in collisionless accretion flows

Stephen Majeski, Matthew W. Kunz, Jason Dexter

• Plasma Physics

AstronomerSpiral density waves are non-modal, non-axisymmetric perturbations whose wavenumbers, frequencies, and amplitudes evolve under background shear. Global simulations of optically thin, low-luminosity black-hole accretion flows show spiral density patterns that affect emission morphology, but previous wave studies assumed local thermodynamic equilibrium (LTE). This study combines kinetic and fluid descriptions in a collisionless shearing sheet to better represent the expected non-LTE plasma conditions. The models find that microphysical plasma instabilities induce weak particle scattering that nevertheless produces appreciable viscous damping of the waves. Proposed observational implications are reduced emission-region variability and lower pattern speeds than in LTE simulations. These effects may improve agreement with Event Horizon Telescope observations and affect interpretation of eventual EHT movies; they are model-based implications, not reported observational detections.

PublicComputer simulations show that waves can make spiral patterns in the hot material flowing around a black hole, changing the shape of the region that emits light. Earlier studies of these waves assumed that the material always remained in local thermodynamic equilibrium, an assumption expected to be unsuitable for hot, diffuse flows around low-luminosity black holes. The researchers used models that account for particle behavior as well as fluid motion. They found that small-scale plasma instabilities can weaken the spiral waves through particle scattering and viscous damping. This could make the emitting region change less over time and its patterns move more slowly than earlier simulations suggest. These are possible observational consequences, not newly observed effects, and may help explain Event Horizon Telescope observations and future movies.

Young explorerHot stuff moving around a black hole can make spiral waves. Scientists used computer models to study how these waves behave when the tiny particles in the hot stuff do not act like a simple fluid. In their models, small disturbances scatter the particles and weaken the waves. That might make the bright patterns change less and move more slowly. Scientists have not shown this happening in real black-hole pictures yet.

A Refined Analytic Oblate--Schwarzschild Model for Thermal X-Ray Pulse Profiles of Rotating Neutron Stars

Xi Yang, Tong Zhao, Renxin Xu

AstronomerThe authors derive a refined analytic flux expression in the oblate–Schwarzschild approximation, combining approximate light bending, propagation delays, and lensing with a spheroidal emitting surface. Motivated by the precision anticipated from eXTP, they benchmark pulse profiles against numerical Schwarzschild and second-order Hartle–Thorne ray tracing on the same surfaces. Tests use a selected two-spot configuration rotating at 300 Hz, isotropic blackbody emission, and three prescriptions for surface eccentricity: a freely specified value, the Newtonian Maclaurin relation, and a rotating-neutron-star surface fit. Relative to Hartle–Thorne ray tracing, the refined model gives RMS flux differences of 1.76–1.98%, versus 6.50–21.39% for spherical Schwarzschild-plus-Doppler profiles; all differences are normalized to the phase-averaged reference flux. Schwarzschild and Hartle–Thorne ray-tracing differences remain below 1.1%. These computational comparisons distinguish analytic photon-transfer errors from surface-deformation and rotating-spacetime effects. For the configurations tested, including oblateness substantially improves agreement while preserving analytic calculation speed; the abstract does not establish performance across other configurations or report observational mass–radius measurements.

PublicThe changing X-ray brightness of a spinning neutron star can help scientists estimate its mass and size, because gravity bends the light leaving its surface. This study develops a fast mathematical model that includes the star’s flattened shape, along with approximations for light bending, travel time, and focusing. The researchers tested it against more detailed computer calculations, using a particular setup with two emitting spots and a star spinning 300 times per second. Across three choices for the star’s shape, the new model’s root-mean-square brightness differences were about 1.8–2.0%, compared with roughly 6.5–21.4% for a model that treats the star as spherical. These percentages are relative to the detailed model’s average brightness. The tests suggest that accounting for flattening can substantially improve these calculations without sacrificing speed. This is a modeling result for the setups examined, not a measurement of a real star; the work is motivated by the precision expected from the eXTP mission.

Young explorerA spinning neutron star can look brighter and dimmer as its glowing spots turn around. Its strong gravity bends the light, and its shape can be a little squashed instead of perfectly round. Scientists made a quick way to work out how bright it would look. In their computer tests, including the squashed shape matched the more detailed calculations better than pretending the star was round. They tested one kind of setup, so they have not shown that it works equally well for every star.

The Structure in the Structure Function of Black Hole Light Curves

Daniel C. M. Palumbo, Alejandro Cárdenas-Avendaño, Lena Murchikova

AstronomerThe study assembles heterogeneous 230 GHz light curves of Sgr A* from discrete observations spanning approximately 12 years, with differing instruments, durations, and cadences. It analyzes their structure function using three frameworks: analytic predictions for stationary random processes with Matérn covariance, lensed synthetic movies of optically thin accretion flows with spatial and temporal Matérn covariance, and a library of 72 general relativistic magnetohydrodynamic simulations. The synthetic-flow analysis identifies structure-function features attributable to black-hole geometry. In the simulation library, magnetically arrested disk (MAD) models generally yield smoother structure functions with steeper slopes than standard and normal evolution (SANE) models. The observed slope on 5–15-minute timescales more closely follows the MAD trend, but both model classes generally show greater variability than the data across sub-hour timescales. This comparison favors the MAD trend in that interval without establishing a definitive accretion-state identification.

PublicSgr A*, the black hole at the center of our Galaxy, changes in brightness on timescales shorter than an hour. Researchers gathered about 12 years of observations at 230 GHz to study these changes. Because the observations were taken at uneven intervals, they used a structure function, which describes how brightness differences depend on the time between measurements. They compared the observations with mathematical predictions, simplified simulated views of gas around a black hole, and 72 simulations of gas and magnetic fields. On intervals of 5–15 minutes, the measured pattern more closely resembles the trend in magnetically arrested disk models than in the alternative models studied. However, both kinds of simulations generally vary more strongly than the observations on timescales below an hour, so neither provides a complete match.

Young explorerScientists watched how the light from material around the black hole in the middle of our galaxy changes. They used observations collected over about 12 years and compared the changes with computer-made versions. For changes a few minutes apart, one kind of computer model looked more like the real pattern than the other. But both kinds usually changed more than the real light did. That means the models still do not match everything the scientists saw.

Study of the Ultra-Long GRB 220627A: Exploring a Possible Blue Supergiant Collapsar Origin

Ayush Garg, Amit Shukla, Dorottya Szécsi+1 more

AstronomerTime-resolved spectroscopy of the ultra-long GRB 220627A reveals spectral evolution across two bright emission episodes separated by about 600 s of quiescence. The burst has T90 > 1000 s and an isotropic-equivalent energy of approximately 10^54 erg. Using HOP-based time segmentation, the authors find that a Comptonized power-law model describes the prompt emission over approximately 10 keV–40 MeV across all analyzed timescales. Fermi-GBM spectra soften from a low-energy index of −0.70 in episode I to −1.29 in episode II, interpreted as a transition from slow- to fast-cooling synchrotron emission. Although this evolution resembles that of the magnetar-candidate GRB 091024A, the authors argue that the extreme isotropic-equivalent energy exceeds the maximum magnetar spin-down energy and strongly favors a blue-supergiant collapsar origin. Sustained accretion through an extended stellar envelope is the proposed explanation for the prolonged, multi-episode activity. The study emphasizes that spectral evolution alone may not distinguish progenitors and should be combined with energetic constraints.

PublicResearchers studied how the gamma-ray spectrum of GRB 220627A changed during a burst lasting more than 1,000 seconds. It contained two bright episodes separated by a quiet interval of about 600 seconds, and the second episode had a softer spectrum than the first. The authors interpret this change as a shift in how quickly the particles producing the radiation cooled. A similar pattern has been seen in a burst suspected of being powered by a magnetar, a highly magnetic neutron star, so the spectral pattern alone does not identify the power source. However, the authors argue that GRB 220627A’s enormous estimated energy strongly favors a collapsing blue supergiant over a magnetar. In their interpretation, material continuing to fall inward from the star’s extended outer layers could sustain the long burst and its separate episodes. This is a favored explanation, rather than a direct observation of the collapsing star.

Young explorerScientists watched a very powerful burst of light from space. It had two bright parts with a long quiet time between them, and the light changed from the first part to the second. That change alone did not tell them what made the burst. After also checking how much energy it seemed to have, they think a huge star collapsing is a better explanation than a special spinning star. They suggest that material falling inward could keep the burst going, but they have not proved that this is what happened.

Candidate X-ray Counterparts of Ultra-High-Energy Emission of the Galactic Microquasar V4641 Sgr Revealed by Einstein Probe

Yi-Heng Chi, Shao-Qiang Xi, Ping Zhou+20 more

AstronomerEinstein Probe's Follow-up X-ray Telescope (FXT) has detected diffuse X-ray structures spatially coincident with the northern and southern TeV gamma-ray emission regions associated with V4641 Sgr. Located approximately 20–40 pc from the microquasar and extending over several arcminutes, individual knots have 0.5–8 keV fluxes of approximately 1–3 × 10^-13 erg s^-1 cm^-2 and photon indices Γ ≈ 2–3. In a one-zone leptonic interpretation, the weak X-ray emission implies a magnetic field of order 1–2 microgauss. Stronger fields remain possible if inverse Compton scattering accounts for only part of the TeV–PeV emission and hadronic interactions supply the remainder. The observations support relativistic electrons on tens-of-parsec scales, but do not establish the origin of the ultra-high-energy gamma rays.

PublicUsing the Follow-up X-ray Telescope aboard Einstein Probe, researchers discovered faint, extended X-ray structures on both sides of the microquasar V4641 Sgr. These structures lie roughly 65–130 light-years from the system and overlap regions already seen in very energetic gamma rays. The observations support the presence of electrons moving at close to the speed of light far from the microquasar. In a model where electrons in a single region explain the emission, the faint X-rays suggest a weak magnetic field. A stronger field is still possible if interactions involving other particles produce some of the gamma rays. What produces the highest-energy gamma rays remains unresolved.

Young explorerScientists used a telescope in space to find faint patches of X-ray light far away on two sides of an object called V4641 Sgr. The patches are in places where scientists also see another kind of light called gamma rays. The new pictures give clues that tiny particles called electrons are moving very fast there. But scientists still do not know exactly what makes the most energetic gamma rays.

XMM-Newton Resolves Parsec-scale X-ray Jets in the PeVatron Microquasar V4641 Sgr

Naomi Tsuji, Caterina Tresoldi, Kaya Mori+34 more

AstronomerAn XMM-Newton survey during quiescence detected extended X-ray structures north and south of the Galactic PeVatron microquasar V4641 Sgr, aligned with its radio-jet axis and extending over several tens of parsecs. Knots n1 and s1 lie approximately 20 pc from the binary and spatially coincide with gamma-ray emission previously detected up to 0.8 PeV. Each knot has a photon index of 1.9 ± 0.1 (statistical) ± 0.5 (systematic) and a 2–10 keV energy flux of approximately (2–4) × 10^-13 erg cm^-2 s^-1. The spectra are interpreted as likely nonthermal synchrotron emission from accelerated electrons. The X-ray/gamma-ray morphological correspondence favors a leptonic gamma-ray origin, but the X-ray structures are more compact and a hadronic origin remains possible. Joint X-ray-to-gamma-ray modeling yields a magnetic field of 3–5 microgauss. The authors propose that the knots trace jet termination or recollimation acceleration sites, or downstream structures analogous to outer-jet knots in SS 433/W50; these identifications are not established. The discovery suggests extended jet-aligned X-rays may be an overlooked signature of PeVatron microquasars.

PublicV4641 Sagittarii is a microquasar in our Galaxy already identified as a powerful particle accelerator through its extremely energetic gamma-ray emission. Using XMM-Newton while the system was quiet, researchers discovered extended X-ray structures on both sides of it, aligned with its radio jets. Two bright patches lie about 20 parsecs from the central binary and overlap the gamma-ray emission on the sky. Their X-rays likely come from fast electrons radiating in a magnetic field. This overlap supports an electron-based explanation for the gamma rays, but does not prove it: the gamma-ray region is larger, and a competing explanation involving hadronic particles remains possible. Modeling indicates a weak magnetic field of 3–5 microgauss. The researchers propose that the patches could mark places where the jets accelerate particles, or structures farther downstream. Similar extended X-ray structures could help identify other microquasars that accelerate particles to very high energies.

Young explorerScientists looked at a space object called V4641 Sagittarii that sends out jets. They found two patches glowing in X-rays, a kind of light our eyes cannot see, far away on opposite sides of the object. The patches line up with the jets and overlap places glowing in another kind of light called gamma rays. Scientists think tiny particles called electrons may make the X-ray glow. The patches might be places where particles get a big boost of speed, but scientists are not sure yet. Finding more patches like these could help them learn about other powerful particle boosters in space.

Comparing the size evolution of GRB 221009A with afterglow models

S. Giarratana, O. S. Salafia, B. Marcote+10 more

AstronomerGlobal-network VLBI observations of GRB221009A at 5 GHz span 231–750 days after the burst. The source surface-brightness FWHM was measured at sub-milliarcsecond scales, with one-sigma-equivalent fractional errors of 13% and 30% at 231 and 391 days, respectively. A single-power-law fit combining these measurements with published 5 and 8 GHz sizes gives size proportional to t^a, with a = 0.52 (+0.14, −0.12). Modeling the 5 GHz size evolution with VegasAfterglow as forward-shock emission from a decelerating jet constrains the collimation-corrected energy-to-density ratio: log[(Ejet/n) erg^-1 cm^-3] = 54.2 (+0.4, −0.5) for a homogeneous ISM, or log[(Ejet/A_star) erg^-1] = 51.7 (+0.4, −0.2) for a wind-like medium. These are model-dependent constraints, not separate measurements of energy and density. Among published standard-afterglow light-curve and spectral fits reproducible with VegasAfterglow, none has best-fitting parameters compatible with these constraints within two sigma; their predicted size evolution is also incompatible with the observations. The results establish afterglow size measurements as an independent probe of dynamics, structure, and emission mechanisms.

PublicAstronomers used a global network of radio telescopes to measure the tiny apparent size of the afterglow of gamma-ray burst GRB221009A. Observations taken 231–750 days after the burst, combined with earlier published size measurements, show how the source expanded. The fitted growth follows approximately the square root of time, with uncertainty in the exact rate. The researchers then modeled a slowing jet moving through either uniformly distributed gas or gas with a wind-like density pattern. These models constrain the jet’s energy relative to the surrounding gas density, rather than measuring either quantity separately. Published models that fit the burst’s brightness and spectrum and could be reproduced with the researchers’ software failed to match the size constraints and observed growth. Measuring size therefore provides an important additional test of afterglow models.

Young explorerAfter a huge burst in space, radio telescopes watched its glow get bigger. Scientists measured how it grew and compared that with computer models of a jet slowing down in nearby gas. The older models they could test did not match the measured growth. Watching the glow’s size helps scientists check their ideas.

The 2015-2017 Large EVPA Rotation in OJ 287: Dominant Propagating Component in a Helical Magnetic Field with Time-Dependent Viewing Geometry

Wanchaloem Khwammai, Minchul Kam, Motoki Kino+11 more

AstronomerMonitoring of OJ 287 during 2012–2023 with KVN, ALMA, and Metsähovi, combined with published optical polarimetry, reveals an exceptionally large, smooth electric-vector position-angle (EVPA) rotation confined to 2015–2017. The millimeter EVPA changes by more than approximately 300 degrees over approximately 1.5 years; the optical rotation is comparably large but evolves faster. EVPAs are comparatively stable at other epochs. Concurrent radio flares across 37–343 GHz have increasing peak amplitudes toward March 2017, when the rotation ends. Modeling the ALMA 91.5 GHz light curve gives variability Doppler factors of approximately 8–11, without a systematic increase through the flare sequence, disfavoring progressively stronger relativistic beaming as the primary cause of the rising flare envelope. The authors interpret the event as a newly ejected disturbance temporarily dominating polarized emission while traversing structured inner-jet regions with a helical magnetic field and modest jet-direction changes. In this interpretation, large rotations occur intermittently when emission dominance and viewing geometry align favorably.

PublicA decade of observations of the blazar OJ 287 found an unusual change in the orientation of its polarized light during 2015–2017. At millimeter wavelengths, that orientation turned through more than about 300 degrees over roughly a year and a half; visible light showed a similarly large but faster change. Strong radio flares grew in peak brightness until the rotation ended in March 2017. Modeling did not show a steadily increasing boost from the jet’s relativistic motion, making that an unlikely main explanation for the growing flares. The researchers instead interpret the event as one moving disturbance temporarily dominating the polarized light while traveling through a jet with a spiral-shaped magnetic field. This explanation suggests that such rotations require a favorable combination of viewing angle and which part of the jet supplies most of the polarized light.

Young explorerScientists watched a bright space object called OJ 287. For a while, a special direction in its light slowly turned, and bursts of radio light grew brighter. That big turn did not happen throughout the years they watched. They think a moving patch in its jet, traveling through a spiral-shaped magnetic field, may explain it. That is their explanation, not something they directly saw.

Twins in the Shadow: Phase Transitions in Proto-Neutron Stars

Jannik Milthaler, Jan-Erik Christian, Pia Jakobus+1 more

• Nuclear Theory

AstronomerThis theoretical study examines how a first-order transition from hadronic to deconfined quark matter affects proto-neutron-star evolution. A highly parameterizable equation of state combines relativistic mean-field hadronic matter with constant-sound-speed quark matter, while cooling is approximated by decreasing entropy at fixed baryonic mass. Some parameterizations produce gravitational twins: stars with equal gravitational mass but different radii. Under the adopted evolutionary approximation, however, such twins are possible only if the hybrid star has no additional baryonic twin. This excludes most modeled twin pairs, especially for transitions at high densities, leaving an unpopulated hybrid branch “in the shadow” of the hadronic branch in the mass-radius diagram. The result is a model-dependent constraint on the accessibility of twin configurations, not an observational detection.

PublicResearchers modeled how newly formed neutron stars might change as they cool, including a possible transition from hadronic matter to quark matter. Some models allow two stars with the same gravitational mass but different sizes, known as twin stars. Finding such twins is regarded as strong evidence for this transition. But the modeled cooling paths suggest that most predicted twin pairs cannot actually be reached, especially when the transition requires high densities. The key condition is that the quark-containing star must not also have a twin with the same baryonic mass, a measure of its matter content distinct from gravitational mass. These conclusions rely on an approximate cooling model; the study does not report observed twin stars.

Young explorerScientists used a model to think about how a newborn neutron star cools down. They asked whether the matter inside could change into a different kind called quark matter. Some models allow two stars with the same mass but different sizes, like a matching pair that is not quite alike. But when the scientists followed how the stars could cool, most of those pairs seemed unable to form that way. This is an idea tested with models, not a pair of stars they found in the sky.

Guide field effects on particle acceleration in three-dimensional relativistic magnetic reconnection

Despina Karavola, Lorenzo Sironi, Maria Petropoulou

• Plasma Physics

AstronomerThis study tests whether the rapid particle-acceleration channel previously found in weak-guide-field relativistic reconnection survives when the guide field becomes comparable to the reconnecting field. The authors use 3D particle-in-cell simulations of pair plasmas, with corresponding 2D runs and open outflow boundaries that establish a quasi-steady state. Increasing the guide field reduces the reconnection rate and aligns energetic particles more closely with the local magnetic field. The fast channel, in which particles escape the reconnected plasma and gain energy from the large-scale upstream electric field, persists in 3D throughout the investigated guide-field range but is absent in 2D. Its participating particle fraction decreases with increasing guide field, yielding steeper energy spectra and lower maximum Lorentz factors. These are simulation findings, with persistence established only over the guide-field strengths tested.

PublicMagnetic reconnection—the rearrangement of magnetic fields in a plasma—can give particles large amounts of energy. This study uses three-dimensional computer simulations to ask whether a particularly fast way of energizing particles survives as an accompanying magnetic field, called the guide field, becomes stronger. In this fast route, particles escape the region of reconnected plasma and gain energy from an electric field outside it. The route survives at every guide-field strength tested in three dimensions, but fewer particles use it as the guide field strengthens. Stronger guide fields also slow reconnection and make energetic particles move more closely along the local magnetic field. The resulting particle populations have relatively fewer high-energy particles and lower maximum energies. Corresponding two-dimensional simulations do not show the fast route; these findings come from simulations rather than astronomical observations.

Young explorerScientists used a computer to study how changing magnetic fields can give tiny particles more energy. They found a fast way for some particles to gain energy after leaving the place where the fields had changed. When an extra magnetic field was stronger, fewer particles used that fast way, and the particles did not reach energies as high. The fast way still worked in all the three-dimensional computer tests they tried, but not in the flat, two-dimensional tests.

Forward Bayesian Inference for the Binary Black Hole Populations

Poulami Dutta Roy, Tanmaya Mishra, Achal Kumar+1 more

• General Relativity and Quantum Cosmology

AstronomerPopCWB is a Bayesian framework for forward inference of the binary black hole population using the unmodeled coherent WaveBurst (cWB) search pipeline. Instead of using individual-event posterior samples, it varies population models and constructs likelihoods from marginal probability distributions based on a large set of simulated events reconstructed by cWB, with total masses estimated by machine-learning regression. Applied to cWB detections from the LIGO–Virgo–KAGRA third observing run, it constrains an astrophysically motivated model incorporating pulsational pair-instability supernovae and dynamical mergers. The analysis predicts a maximum black hole mass from stellar evolution of 45.5 (+5.3/−6.5) solar masses and infers a local binary black hole merger rate of 23.1 (+11.3/−8.4) Gpc⁻³ yr⁻¹. These are population-model predictions and inferences, not direct measurements of a universal mass limit or merger rate. The results are compared with existing population models in the literature.

PublicThe researchers introduce PopCWB, a method for studying the population of pairs of black holes that merge. Rather than starting with detailed estimates for each detected merger, it compares observations with many simulated events processed by the coherent WaveBurst search method, using machine learning to estimate their combined masses. The team applies it to events detected during the third observing run of LIGO–Virgo–KAGRA. Their model includes effects from pulsational pair-instability supernovae and mergers driven by dynamical interactions. It predicts that black holes formed through stellar evolution reach a maximum mass of about 45.5 times the Sun’s mass, with a reported uncertainty of +5.3/−6.5 solar masses. It also estimates a local merger rate of 23.1 events per cubic gigaparsec per year, with an uncertainty of +11.3/−8.4. These conclusions depend on the population model and simulated events; they are not directly observed limits.

Young explorerScientists studied signals from pairs of black holes joining together. They made lots of pretend black hole events on a computer and compared them with the real signals to find which picture of the black hole family fits best. Their model suggests that black holes made from stars can grow to about 45 times the Sun’s mass, but that number is uncertain. They also used the model to estimate how often black holes join together. These are the model’s best estimates, not things the scientists know for sure.

Charged anisotropic white dwarfs in f(R, T) gravity

Zhe Feng

• General Relativity and Quantum Cosmology
• Solar and Stellar Astrophysics

AstronomerThis theoretical study investigates equilibrium models of charged, anisotropic white dwarfs in f(R,T) = R + 2βT gravity, where R is the Ricci scalar and T is the trace of the energy-momentum tensor. The authors derive the stellar structure equations and solve them numerically using the Chandrasekhar equation of state and a charge density proportional to the energy density, ρ_ch = αρ. They examine how charge, modified gravity, and anisotropy affect stellar structure across parameter combinations. The solutions exhibit super-Chandrasekhar configurations beyond the standard general-relativistic cases. The authors suggest that these models may help explain superluminous type Ia supernovae, but the abstract reports theoretical solutions rather than observational confirmation.

PublicThe researchers use mathematical models to study white dwarfs whose structure is affected by electric charge, pressure that differs with direction, and a modified theory of gravity. Their calculations assume a particular relation between charge density and energy density and use the Chandrasekhar equation of state to describe the stellar material. Under some modeled conditions, white dwarfs can exceed the usual Chandrasekhar mass limit. The authors suggest that such configurations might help explain exceptionally bright type Ia supernovae, but this study does not establish that real stars have these properties or that they cause those explosions.

Young explorerScientists used math to imagine small stars called white dwarfs. They tried changing gravity, adding electric charge, and letting the push inside a star be different in different directions. In their calculations, some stars could hold more stuff than the usual rules allow. This might help explain some very bright exploding stars, but the scientists have not shown that real stars work this way.

Chaotic signatures in extreme-mass-ratio systems surrounded by bosonic environments

Qi-Xuan Xu, Kyriakos Destounis, Yin-Da Guo+2 more

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

AstronomerThe study investigates conservative orbital dynamics around rotating black holes with scalar clouds using fully nonlinear numerical solutions and an analytical post-Newtonian model. Poincaré sections and rotation curves exhibit finite-width resonant islands, indicating non-integrability even for clouds containing a small fraction of the black-hole mass. For weak clouds, the post-Newtonian model reproduces the dominant resonance and its island width, but it underestimates the width for the stronger, more compact configurations examined. A cloud as massive as the black hole produces wider islands and scattered phase-space layers indicative of chaos. These theoretical results motivate studying resonance crossings and possible gravitational-wave signatures in extreme-mass-ratio inspirals after including radiation reaction; those signatures are not established here.

PublicResearchers used numerical calculations and an approximate mathematical model to study orbits around spinning black holes surrounded by scalar clouds. Their calculations suggest that even a relatively low-mass cloud can disrupt the orderly orbital structure of an isolated spinning black hole. The approximate model captures the main orbital resonance for weak clouds but underestimates its extent in the stronger, more compact clouds studied. When the cloud has the same mass as the black hole, the calculations also show signs of chaotic motion. These are theoretical findings, not observations. How the altered orbits might affect gravitational waves remains a question for future work that includes the effects of gravitational-wave emission.

Young explorerScientists used math and computers to study how a small object could move around a spinning black hole with a cloud around it. Even a small cloud could change the patterns of its path. A very heavy cloud showed signs that the motion could become harder to predict. The scientists have not yet worked out how this would change gravitational waves.

Kinetic Equilibrium between SIMP Dark Matter and Radiation via Internal Bremsstrahlung

Xiaoyong Chu, Ajay Kaladharan, Yassine El Mohtadi

• High Energy Physics - Phenomenology

AstronomerThis theoretical study proposes internal bremsstrahlung as an energy-dissipation mechanism for strongly interacting massive particle dark matter whose relic abundance is regulated by three- or four-body self-annihilation rather than standard two-body annihilation. Such freeze-out requires both particle-number reduction and efficient energy dissipation; the proposed radiation processes establish kinetic equilibrium between dark matter and radiation. The authors describe a natural realization in strong-dynamics models with flavor-universal quarks and a light axion. They demonstrate the mechanism in an Sp(4)_c dark-color model by computing the relevant interaction terms and numerically solving the full Boltzmann equations. They also state that the mechanism can apply to vector dark matter models. These are model-based theoretical results, not observational evidence for this dark matter scenario.

PublicThe researchers propose a way for a hypothetical kind of strongly interacting dark matter to lose energy as its abundance becomes fixed in the early universe. In this scenario, interactions involving three or four dark matter particles reduce their number, but a separate process is needed to dissipate energy. The proposed process, called internal bremsstrahlung, would allow dark matter to exchange energy with radiation and reach kinetic equilibrium. The team explores how this could arise in models containing dark-sector quarks with the same interaction properties and a light axion, and tests a specific model through interaction calculations and numerical evolution equations. They suggest that the mechanism could also work for vector dark matter. The study develops a theoretical possibility; it does not report a detection of these particles or processes.

Young explorerScientists have an idea about dark matter, a mysterious kind of matter. In their idea, groups of dark matter particles could turn into fewer particles when the universe was young. The particles would also need a way to lose energy. The scientists propose that they could share energy with radiation, a bit like letting heat escape. They used calculations to explore how this might work. It is an idea tested with math, not something they have seen happen.

Primitive recovery methods for binary neutron star mergers with tabulated equations of state in SPHINCS(B)SSN

Swapnil Shankar, Stephan Rosswog, Peter Diener

• General Relativity and Quantum Cosmology

AstronomerThis work develops conservative-to-primitive recovery algorithms for tabulated equations of state in SPHINCS_BSSN, a Lagrangian numerical relativity code that evolves spacetime on an adaptive mesh and the fluid with freely moving particles. Its evolution equations require recovery methods different from those used in conventional numerical relativity. The authors compare 3D and 2D Newton-Raphson schemes with a 1D scheme based on Ridders' method. In a neutron star merger simulation using the DD2 equation of state, the 3D method is fast and robust, with an average failure fraction well below 1%. The 2D method offers no obvious advantages, while the 1D method is slow but essentially fail-safe. They therefore adopt 3D Newton-Raphson as the default, with 1D Ridders recovery as a fallback. These are numerical performance findings, not observational results.

PublicSimulating colliding neutron stars requires descriptions of how extremely dense matter behaves, often stored in tables. Simulation programs must repeatedly convert the quantities they track into physical quantities needed to describe the matter, a calculation that can be costly or fail. The authors developed three ways to do this for SPHINCS_BSSN, a code that represents the fluid with moving particles while calculating spacetime on an adaptive grid. In a merger simulation using a matter model called DD2, their three-dimensional Newton-Raphson method was fast and failed in well under 1% of recovery attempts on average. A two-dimensional version showed no clear advantage. A slower, one-dimensional method based on Ridders' method was essentially fail-safe, so they use it as a backup when the faster method fails. The study improves a simulation tool; it does not report observations of an actual collision.

Young explorerScientists use computers to make pretend collisions between very dense stars called neutron stars. The computer has to keep solving tricky number puzzles to work out what the star stuff is doing. The scientists tried three ways to solve those puzzles. In their pretend collision, one way was quick and almost always worked. Another way was slow but worked very reliably. They chose the quick way first and the slow way as a backup. This helps their computer model, but it is not a collision they watched in the sky.

JWST Nebular Spectroscopy of SN 2023qov: Circumstellar Dust Emission in a Normal Type Ia Supernova

Colin W. Macrie, Conor Larison, Huei Sears+43 more

AstronomerPanchromatic observations of the normal Type Ia SN 2023qov span approximately two weeks before to one year after maximum light. JWST near- and mid-infrared spectra at +276 and +363 days reveal approximately 400 K dust emission, cooling by about 75 K between epochs—the first unambiguous spectroscopic detection of dust emission in a normal SN Ia. Carbonaceous-dust models reproduce the emission with approximately 10^-4 solar masses of dust within about one light-year of the SN. No evidence of active dust formation is found; an infrared light echo from pre-existing circumstellar dust is the favored interpretation. Nebular line profiles suggest asymmetric, stratified ejecta, with a slight double-horn structure in argon lines indicating a toroidal enhancement. The slightly red, fast-declining early light curve has Δm15(B) = 1.47 ± 0.05 mag and yields an inferred nickel-56 mass of 0.21 ± 0.04 solar masses and a distance of 36.0 ± 1.8 Mpc to the SN and its host, NGC 7029.

PublicObservations of the Type Ia supernova 2023qov, from about two weeks before its peak brightness to roughly a year afterward, reveal a clear infrared signature of warm dust. This is the first unambiguous spectroscopic detection of dust emission in a normal Type Ia supernova. Two JWST observations measured dust emission at about 400 kelvin, with cooling of roughly 75 kelvin between observations. Models fit the emission with carbon-based dust lying within about one light-year of the explosion and totaling around one ten-thousandth of the Sun’s mass. The researchers found no evidence that dust was actively forming, so they favor an infrared light echo: the explosion illuminated dust that was already nearby. Other spectral features suggest that the expelled material is layered and uneven, with a possible ring-like enhancement. The supernova’s early brightness faded relatively quickly; the researchers used its light curve to estimate its nickel-56 content and its distance, about 36 million parsecs.

Young explorerAstronomers watched an exploding star called 2023qov. With the JWST telescope, they clearly saw warm dust glowing in infrared light, a kind of light our eyes cannot see. The dust was cooler when they looked again later. They did not find signs that new dust was being made. They think the dust was already nearby and glowed after light from the explosion reached it—like an echo made of light. The light also gives clues that the stuff thrown out by the star was not spread evenly.

Reassessing the contribution of long-GRB high-energy afterglows to the isotropic gamma-ray background after GRB 221009A

S.V. Troitsky

AstronomerThe study updates estimates of the long-GRB contribution to the Fermi-LAT isotropic gamma-ray background using a time-integrated high-energy afterglow template for GRB 221009A, anchored by GeV–TeV observations and explicitly scaled with prompt energy and beaming. Absorption by the extragalactic background light partly reprocesses very-high-energy emission into a GeV cascade, whose estimated contribution reaches only 1.6e-4 of the IGRB. Adding direct GeV emission raises the maximum fraction to 1.1e-3, with greater dependence on the population-averaged broadband template. Tested variations in background light, propagation implementation, intrinsic spectral cutoff, and population prescription preserve the conclusion that long GRBs are not significant contributors to the IGRB despite the observed multi-TeV afterglow of GRB 221009A.

PublicSome of the highest-energy light from gamma-ray bursts is absorbed by light spread through intergalactic space, and part of its energy reappears as lower-energy gamma rays. Researchers used observations of the afterglow of GRB 221009A to estimate how much long-duration gamma-ray bursts contribute to the diffuse gamma-ray background measured by Fermi-LAT. Their model puts the reprocessed contribution at just 0.016% of that background. Including gamma rays emitted directly by the bursts raises the maximum estimate to 0.11%, although this depends more strongly on how a typical burst population is represented. Changing several modeling assumptions did not alter the main conclusion: long-duration gamma-ray bursts are not a major source of this background.

Young explorerGamma-ray bursts are flashes in space that give off very powerful light. Some of that light gets absorbed on its way to us, and part comes back as less powerful light. Scientists used measurements of one burst to work out how much these flashes might add to the gamma-ray glow across the sky. Their calculations suggest that long-lasting bursts add only a tiny bit of that glow. They tried different ways of doing the calculation, and the answer stayed much the same.

First Light of Neutron Star Mergers: Off-axis Cocoon Cooling X-ray Emission from Short Gamma-Ray Burst Jets

Jian-He Zheng, Wenbin Lu

AstronomerThe study models early cooling emission from jet-driven cocoons formed as short-GRB jets propagate through neutron star merger ejecta. Hydrodynamic simulations with radiative post-processing predict mildly relativistic cocoons producing off-axis soft X-ray transients with luminosities of 10^46–10^48 erg/s, durations of a few to ten seconds, and quasi-thermal spectra with characteristic temperatures of 0.1–1 keV. The modeled emission is less beamed than the GRB, offering a potential early counterpart for observers outside the narrow jet. Predicted Einstein Probe detectability extends to z ≈ 0.3 at a viewing angle of 10°, and to viewing angles of about 45° for nearby events like GW170817. The canonical model predicts an EP detection rate of 0.5 per year. These are simulation-based predictions, not reported cocoon detections; rapid UV, optical, and infrared follow-up is proposed to identify an associated kilonova and jet afterglow and confirm the merger origin.

PublicMerging neutron stars are confirmed sources of gravitational waves, but their narrow gamma-ray beams can miss observers looking from the side. This study uses computer simulations to investigate a potentially easier-to-see signal: a brief X-ray glow from a cocoon formed as a jet pushes through material thrown out by the merger. The models predict bright, soft X-ray flashes lasting a few to ten seconds across a range of viewing directions. They suggest that Einstein Probe could detect this glow out to a redshift of about 0.3 when viewed 10 degrees from the jet direction, or as far off-axis as about 45 degrees for a nearby event like GW170817. The standard model predicts roughly one detection every two years. No such detection is reported here. The authors propose rapid follow-up in ultraviolet, visible, and infrared light to find the associated kilonova and jet afterglow and confirm the flash's origin.

Young explorerWhen two neutron stars crash together, they can send out a narrow beam that we might miss if it points away from us. Scientists used computer simulations to study a hot cloud made when the beam pushes through material from the crash. Their models suggest this cloud could glow in X-rays for a few seconds, and we might see it even from the side. A telescope called Einstein Probe might catch that glow. This is a prediction, not a glow they have found yet. Looking quickly for other light afterward could help show that it came from a neutron star crash.

Physical properties of compact star-like systems harboring traversable wormholes: Effects of chaotic magnetic fields and anisotropic matter

Muhammad Lawrence Pattersons, Freddy Permana Zen, Hadyan Luthfan Prihadi+1 more

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

AstronomerThe authors construct theoretical compact star-like systems containing traversable wormholes supported by two scalar fields, incorporating chaotic magnetic fields and neutron-fluid pressure anisotropy. In all configurations considered, the null energy condition is violated near the throat, the Kretschmann scalar indicates regular spacetime, and the temporal metric function indicates no horizons; traversability persists with or without magnetization and anisotropy. Magnetized models can attain ADM masses above 8 solar masses and surface redshifts above approximately 1.5. Ultracompact configurations permit calculations of possible gravitational-wave echo times: approximately 0.01–0.1 ms without magnetization, versus approximately 0.1 microseconds–0.1 ms with magnetization, with the timing depending on magnetic configuration and fluid anisotropy. A separate explicit relation for a uniform magnetic field predicts decreasing echo time with increasing field strength. Radial-perturbation analysis finds all considered configurations with surface fields of 10^15 G stable against those perturbations. These are theoretical findings, not observations or a demonstration of stability against all perturbations.

PublicThis theoretical study explores star-like objects containing traversable wormholes: passages through spacetime supported in the model by two scalar fields. The researchers include magnetic fields and pressure that can differ by direction inside the neutron fluid. Their calculated objects have no horizons or spacetime singularities, and the wormhole passage stays open in every case studied. Near the passage’s narrowest point, the model violates a standard energy condition. With magnetic fields, some models exceed eight times the Sun’s mass and strongly shift escaping light toward redder wavelengths. Very compact versions could produce gravitational-wave echoes, whose calculated delays depend on the magnetic fields and internal pressure. Magnetic models span a wider range of delays, and a calculation using a uniform magnetic field predicts shorter delays as the field grows stronger. The tested models with surface fields of 10^15 gauss are stable against radial disturbances, but this does not establish stability against every kind of disturbance. No such objects or echoes are reported as observed.

Young explorerScientists used math to imagine a strange star with a tunnel through space inside it. In their model, special fields help keep the tunnel open, and magnetic fields can change how the star behaves. Some of these pretend stars could be very heavy. They might also make tiny delayed echoes of ripples in space. The scientists calculated how long those echoes might take, but they have not seen these stars or their echoes. Some models also passed a test of what happens when the star is disturbed inward and outward, though that does not mean they would pass every test.

Full orbital solution and dynamical masses for a new shell-Be + sdOB binary AN Col

R. Klement, Th. Rivinius, A. C. Carciofi+4 more

AstronomerNear-infrared GRAVITY interferometry confirms AN Col as a Be + stripped sdOB binary and maps its relative astrometric orbit. After characterizing the dominant disk-density oscillations, the authors identify spectral lines tracing both stars and combine their radial velocities with the astrometry to derive a full three-dimensional orbit, dynamical masses, and dynamical parallax. The disk has completed three oscillation cycles since 2010, with a period of approximately 5.1 years. The binary period is approximately 87.7 days; its orientation is nearly edge-on, but the absence of eclipses in TESS light curves constrains the inclination to at most 88.4 degrees. The inferred masses are 8.39 ± 0.67 solar masses for the Be star and 0.81 ± 0.22 solar masses for the sdOB companion. Weak He II 4686 absorption and other He I lines indicate a companion temperature near 30,000 K and slow rotation. The estimated efficiency of past mass transfer is unexpectedly high, making the system a useful dynamical constraint on binary-evolution models.

PublicAstronomers have confirmed that AN Col consists of a Be star, surrounded by a gas disk, and a hot, stripped companion. By combining measurements of the stars’ relative positions with changes in their spectral lines, they determined the pair’s three-dimensional orbit and masses. The stars circle each other about every 87.7 days. The larger star has about 8.4 times the Sun’s mass, while its companion has about 0.8 times the Sun’s mass, with greater relative uncertainty in the companion’s mass. Changes in the gas disk repeat roughly every 5.1 years and had to be separated from the orbital signals. Although we view the orbit nearly edge-on, no eclipses were detected. The companion’s spectrum suggests a temperature near 30,000 K and slow rotation. The authors interpret the system as the outcome of past gas transfer between the stars and estimate that this transfer was unexpectedly efficient.

Young explorerAN Col is two stars going around each other. One is much heavier, and the other is a small, very hot companion. Astronomers watched their positions and studied their light to work out how they move. They go around each other about once every 88 days. Gas around the bigger star also changes, but much more slowly. The scientists think the smaller star gave gas to the bigger star long ago. Studying this pair can help them understand how stars change when they live together.

The 200-300 GHz Survey for 18 Class II Disks in the Ophiuchus Star-Forming Complex

Chia-Ying Chung, Hauyu Baobab Liu, Chuan-Yung Lin+4 more

• Earth and Planetary Astrophysics
• Astrophysics of Galaxies

AstronomerSMA measurements of 18 Class II protoplanetary disks in Ophiuchus at 198–310 GHz yield spectral indices α200–300 = 2.3 (+0.2/−0.5), similar to those of 48 spatially compact Class II disks previously surveyed in Taurus-Auriga. In the combined sample, α200–300 has a weak positive correlation with 250 GHz flux density (Pearson r = 0.27, p = 0.02), but no convincing correlation with the R95% disk radius. The authors interpret indices near 2 in compact disks as evidence that optically thick thermal dust emission dominates at frequencies ≳200 GHz, regardless of flux density or radius. This interpretation explains the positive relationship between (sub)millimeter luminosity and apparent disk size reported by resolved surveys. In clusters aged approximately 1–2 Myr, smaller or less luminous Class II disks therefore need not have depleted or dispersed their dust reservoirs.

PublicAstronomers used the Submillimeter Array to measure emission from 18 dusty disks around young stars in the Ophiuchus star-forming region. Their emission changes with frequency much like that of 48 compact disks previously studied in Taurus-Auriga. Across both samples, this frequency dependence is weakly related to brightness, but shows no convincing relationship with disk radius. The researchers interpret the emission from compact disks as coming mainly from warm dust that is opaque at the measured frequencies, rather than revealing all the dust within each disk. This interpretation helps explain why disks that appear larger also tend to be brighter. It also means that, in clusters about one to two million years old, a small or faint disk does not necessarily have little dust left.

Young explorerYoung stars have dusty disks around them. Astronomers measured light from 18 of these disks and found that it behaved much like light from another group of disks. They think the dust in small disks may be hard to see through, so the light does not show all the dust inside. A disk that looks small or faint might still have plenty of dust—it does not necessarily mean the dust has gone away.

Mesoscale Turbulence in Type Ia Supernova Deflagrations II. Evidence for Fuel Preheat Due to Flame Thermal Expansion from Lagrangian Analysis

Ryan Learn, Andrey Zhiglo, Tomasz Plewa

• High Energy Astrophysical Phenomena
• Data Analysis, Statistics and Probability
• Fluid Dynamics
• Plasma Physics

AstronomerMultidimensional simulations and Lagrangian tracer analysis investigate ignition-time shortening ahead of Rayleigh–Taylor-unstable Type Ia deflagration fronts in partially degenerate carbon–oxygen fuel. The most strongly preconditioned parcels, a minority of the fuel layer, undergo approximately pressure-constrained expansion with modest density reductions and temperature increases ranging from about 2×10^8 K to 7×10^8 K across the low- to high-density models, or about 13–63% above the unperturbed fuel temperature. Carbon ignition’s strong temperature sensitivity makes these perturbations sufficient to substantially shorten inferred ignition times. The authors interpret the evolution as a two-step process: flame-driven expansion disrupts hydrostatic equilibrium, and weak acoustic waves restore pressure balance while redistributing internal energy from degenerate to thermal components. The simulations suggest that unsteady flames can thermodynamically precondition fuel over distances exceeding the laminar flame thickness. Secondary ignition and a contribution to deflagration-to-detonation transition remain untested because nuclear burning is disabled in the analyzed fuel.

PublicComputer simulations explore how a thermonuclear flame in a Type Ia supernova can warm nearby carbon–oxygen fuel before the flame reaches it. A small fraction of the fuel expands, becomes modestly less dense, and heats up. Because carbon’s ignition time depends very strongly on temperature, even these moderate changes can greatly reduce the time it would take to ignite. The researchers propose a two-step explanation: expansion driven by the flame disturbs the fuel’s pressure balance, then weak sound waves help restore that balance and shift internal energy into heat. Their results suggest that a changing flame can affect fuel farther ahead than the thickness of a smooth flame. However, these simulations do not show the warmed fuel igniting or triggering a transition to a detonation: nuclear burning was switched off in the fuel being studied.

Young explorerThe researchers used a computer to study a flame inside an exploding star. In the computer model, the flame made some nearby star fuel spread out a little and get hotter before the flame reached it. They think gentle sound waves helped warm that fuel. Hotter fuel could start burning sooner. But they did not test whether it really started a new fire, because they had turned off burning in that part of the model.

A New Analysis Tool for Radial Pulsations

Hiroyasu Ando

AstronomerThe study introduces a wave-energy relation for linear radial pulsations, incorporating kinetic, acoustic-potential, dynamical-potential, and entropy-potential energies. It accounts for energy changes due to non-adiabatic processes and wave-energy leakage. Applied to modal analysis of adiabatic pulsations in 10, 20, and 30 solar-mass Zero Age Main Sequence models, it finds ordinary modes well trapped in the interior cavity with no significant leakage. Strange modes instead show steep increases in eigenfunctions and kinetic energy toward the surface, together with significant wave-energy leakage; their kinetic energy is no longer confined to the exterior cavity. These findings concern stellar models, not reported observations.

PublicThe researchers introduce a tool for tracking the energy of a star’s inward-and-outward pulsations, including energy that escapes. They apply it to models of stars at the start of their main-sequence lives, with masses 10, 20, and 30 times the Sun’s. In these calculations, ordinary pulsations retain their wave energy deep inside the star, with no significant leakage. Pulsations called strange modes behave differently: their motion and kinetic energy increase sharply toward the surface, and significant wave energy leaks away. Their kinetic energy is therefore not confined to the star’s outer cavity. The results come from models rather than observations of actual stars.

Young explorerStars can pulse inward and outward. Scientists made a new way to keep track of the energy in those pulses and tried it on models of very big stars. Some pulses kept their energy deep inside. Other pulses, called strange modes, grew much stronger near the surface and let energy leak away. These are things the scientists found in their star models, not things they watched real stars do.

Formation and Eruption of a Vortex-driven Magnetic Flux Rope in the Simulated Quiet Sun

Zhizhen Ye, Feng Chen

AstronomerA radiative MHD simulation extending from the upper convection zone to the corona tracks the formation and eruption of a supergranular-scale magnetic flux rope in the quiet Sun. Connectivity-based clustering of closed field lines yields eight persistent cluster assemblies representing the rope and surrounding magnetic structures. A persistent counterclockwise vortex at the supergranular convergence point, coincident with the rope’s positive footpoint, injects helicity and wraps ambient structures around the central flux tube. Over approximately one hour, the tube becomes strongly twisted and erupts. The simulated eruption develops current-sheet structures similar to those inferred for active-region flux-rope eruptions, but its mass ejection and heating are much weaker, producing very weak observable signatures. Synthetic EUV images show mainly dimming from density rarefaction as the rope expands. The authors suggest that comparable quiet-Sun events may be underestimated because of their stealthy signatures; the study does not establish their occurrence rate on the real Sun.

PublicThe Sun’s magnetic field can form twisted bundles called flux ropes, which are important in solar flares and eruptions. This study uses a computer simulation, rather than direct observations, to explore how one could form in a quiet region of the Sun. In the simulation, a lasting swirl where large convection cells meet twists a magnetic tube and winds nearby magnetic structures around it. Within about an hour, the tube becomes a strongly twisted rope and erupts. Although some magnetic structures resemble those associated with eruptions in more active regions, the simulated event ejects much less material and produces much weaker heating. Images calculated from the simulation show mostly faint dimming as the expanding rope becomes less dense. The researchers suggest that similar eruptions on the real Sun could be easy to miss, but this simulation does not show how often they actually happen.

Young explorerScientists used a computer to explore what might happen in a quiet part of the Sun. In their model, a swirling motion twisted the Sun’s invisible magnetic field into a rope-like bundle. After about an hour, the bundle burst outward. It did not throw out much material or make much heat compared with eruptions in more active places. The pictures made from the model mostly showed a little darkening as the bundle spread out. The scientists think quiet eruptions like this might be hard to spot on the real Sun, but this one happened in a computer.

Plato benchmark stars I. The initial benchmark sample

T. Merle, P. F. L. Maxted, O. L. Creevey+22 more

• Earth and Planetary Astrophysics
• Instrumentation and Methods for Astrophysics

AstronomerThis work defines the PLATO benchmark stars (PBS) catalogue to support stellar parameter validation and exoplanet characterisation throughout the mission. It compiles 1090 FGKM main-sequence and subgiant stars using data from eclipsing and spectroscopic binaries, interferometry, asteroseismology, and large surveys. Stellar properties receive B1, B2, or B3 quality levels according to their model dependence. The catalogue includes 15 gold-tier stars with B1 mass, radius, and luminosity; 195 silver-tier stars with B1 mass and radius; and 416 bronze-tier stars with at least one B1 property. The remaining stars have well-characterised model-dependent B2 or empirical B3 properties. Homogenized ancillary data include Gaia DR3 bias-corrected parallaxes, metallicities, bolometric fluxes, extinction, rotation periods, and M-dwarf X-ray fluxes. About 40% of the sample falls within PLATO fields: 285 stars in LOPN1 and 143 in LOPS2. The authors describe PBS as the largest benchmark-star catalogue assembled to date, intended for pipeline validation, evolutionary-model testing, and cross-survey calibration. It is available online, with regular updates planned.

PublicTo understand a planet outside our Solar System, astronomers need reliable information about its host star. This study assembles a catalogue of 1090 well-characterised stars to support ESA’s PLATO mission, which aims to find and study Earth-size planets around bright stars. The researchers combined several kinds of stellar measurements and survey data, then classified the stars’ properties according to how much they depend on models or empirical relationships. Only 15 stars have top-level, model-independent estimates of all three key properties: mass, radius, and luminosity. Other stars have fewer such properties or rely on model-dependent or empirical estimates. About 40% of the catalogue’s stars lie within PLATO’s observing fields. The catalogue is intended to help check automated analysis tools, test models of how stars evolve, and align results from different surveys; the study does not report new planet discoveries. The authors describe it as the largest catalogue of benchmark stars assembled so far and plan to update it regularly.

Young explorerScientists made a list of 1090 stars that they know a lot about. They gathered information about how big, heavy, and bright the stars are. Some of that information comes from measurements that do not need star models, while other information depends on those models or on patterns seen in other stars. The list is meant to help a space mission called PLATO look for planets about the size of Earth. Knowing a star better helps scientists understand its planets better, too. This study made the star list; it did not announce new planets.

The origin of dispersion in the wind mass-loss rate--luminosity relation of massive O stars

Jiri Krticka, Iva Krtickova

AstronomerObserved O-star wind mass-loss rates show a clear dependence on luminosity, but with substantial scatter of uncertain origin. The authors test whether sensitivity to effective temperature, stellar mass, and metallicity can account for part of this dispersion. They calculate tailored wind models for selected Large Magellanic Cloud O stars using stellar parameters from a previous analysis and a global wind code that obtains the radiative force from comoving-frame radiative transfer. These models reproduce the observationally inferred mass-loss rates better than simple scaling relations derived from model grids, supporting the interpretation that parameters beyond luminosity contribute to the scatter. Residual dispersion remains; wind variability is suggested as another possible contributor, not established as its cause.

PublicHot stars lose material through winds pushed outward by their radiation, mainly through interactions with heavy elements. Observations of O stars show that brighter stars generally lose more material, but the relationship has considerable scatter. The researchers calculated wind models tailored to selected O stars in the Large Magellanic Cloud, using previously estimated properties of each star. These models matched the observationally inferred rates of material loss better than simpler brightness-based scaling rules. This suggests that temperature, mass, and heavy-element content may explain some of the differences between stars. They do not explain all of the scatter, and changes in the winds over time remain a possible additional explanation.

Young explorerVery hot stars blow some of their material into space, and their light helps push it away. Brighter stars usually lose more material, but they do not all follow the same pattern. Scientists made computer models for some stars, taking account of how hot and heavy they are and what they are made of. These models agreed better with what astronomers had worked out from observations than simpler rules did. That may explain some of the differences, but not all. Winds that change over time might explain more, though the scientists have not shown that yet.

First strength measurements of low-energy resonances in the ⁴⁵Sc(p,γ)⁴⁶Ti reaction and its astrophysical implications

R. S. Sidhu, R. J. deBoer, J. Görres+13 more

• Nuclear Experiment

AstronomerThe study reports measurements of 45Sc(p,γ)46Ti using the 5 MV accelerator at Notre Dame over laboratory proton energies of 526–1275 keV. It provides the first direct resonance-strength measurements for six resonances at 917.4, 1026.0, 1031.1, 1049.7, 1059.4, and 1257.5 keV, plus integrated resonance strengths at 555, 630, 700, 761, and 871 keV. Strengths below the lowest directly measured energy were estimated from available transfer-reaction data rather than measured directly. These inputs yield an updated thermonuclear rate for a reaction previously described by statistical-model calculations. The reaction regulates flow through the Sc–Ti region during massive-star oxygen and silicon burning, including C–O shell mergers, connects nuclei above Ca toward the Fe region in ONe novae, and influences 47Sc production in core-collapse supernovae. Astrophysical implications are discussed, but the abstract gives no quantitative abundance changes or rate comparison.

PublicResearchers measured a nuclear reaction in which scandium-45 captures a proton and becomes titanium-46. This reaction helps regulate how elements form inside massive stars and during stellar explosions. Using an accelerator at the University of Notre Dame, the team directly measured the strengths of six resonances—energies where the reaction is enhanced—and obtained additional integrated resonance strengths. For energies below those directly measured, they estimated strengths using earlier data from another type of nuclear experiment. They then calculated an updated reaction rate, previously based on theoretical models. The abstract does not specify how much the rate changed or quantify its effects on element production.

Young explorerStars can turn one kind of tiny building block into another. Scientists studied how a building block called scandium catches a tiny particle and becomes titanium. They tested this in a laboratory to help work out how often it happens in stars. Some parts were measured, and some still had to be estimated.

Non-adiabatic Effect on Convective Mode

Hiroyasu Ando

AstronomerThis theoretical analysis uses a wave-energy relation to investigate non-adiabatic effects on convective modes. For the adiabatic case, it proposes a propagation diagram as a tool for understanding mode behavior. In the strongly non-adiabatic regime, the analysis finds that a monotonically growing convective mode becomes oscillatory. The radial-displacement and wave-energy distributions each exhibit a single bump, with the entropy-energy distribution eS nearly overlapping the gravity-energy distribution eg. This suggests, rather than establishes, that entropy energy acts as the potential energy of oscillatory convection. The transition occurs abruptly, not gradually, as the non-adiabatic indicator changes.

PublicThe study uses mathematical analysis to explore how heat exchange changes convection, the motion of material that transports heat. It finds that when heat-exchange effects are strong, a convective disturbance that grows without oscillating becomes oscillatory. This change happens abruptly as a measure of those effects is varied. In the oscillatory state, the displacement and wave-energy patterns each have one peak, and the energy contributions associated with entropy and gravity have nearly matching patterns. The authors interpret this as a possible sign that entropy-related energy provides the potential energy for the oscillation. They also propose a diagram for understanding convection when heat exchange is neglected. These are theoretical findings and interpretations, not reported observations.

Young explorerThe researchers used math to study moving material that carries heat. Their math showed that, when heat can move around strongly enough, a motion that only gets bigger can start swinging back and forth. The change happens suddenly instead of little by little. They think energy connected to heat might help the swinging motion, a bit like a spring, but that idea is not certain.

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 interferometry at the CHARA Array provides uniform-disk and limb-darkened angular diameters for 27 nearby solar-type stars, including several known exoplanet hosts. The sample spans a broad metallicity range and evolutionary stages from the zero-age main sequence to mildly evolved subgiants. 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. These comparisons assess grid-to-grid systematics and highlight sensitivity to abundances, evolutionary stage, and proximity to grid boundaries. The measurements provide empirical benchmarks for stellar evolution models, surface brightness-color relations, and exoplanet host characterization.

PublicAstronomers measured the apparent sizes of 27 nearby stars similar to the Sun using PAVO at the CHARA Array. The stars have different chemical compositions and range from stars beginning their main-sequence lives to somewhat more evolved subgiants; several are known to host planets. Combining the size measurements with total received starlight and Gaia distance information allowed the team to determine stellar radii, surface temperatures, and luminosities without relying on stellar evolution models. Typical uncertainties are about 1% for radius and 1.5% for temperature. Estimates of mass and age do depend on such models, and comparisons showed that different model sets can give different answers depending on a star's composition and evolutionary stage or its position near the limits of a model set. These measurements can help test theories of how stars evolve and improve our understanding of planet-hosting stars.

Young explorerAstronomers looked carefully at 27 nearby stars that are a bit like our Sun. Some have planets around them. They measured how big the stars look in the sky, then used information about their distances and light to work out how big, hot, and bright they really are. The size and temperature measurements are very precise, but not perfect. To estimate how heavy and old the stars are, the astronomers compared them with computer models of how stars change. Different models can give different answers. These star measurements can help scientists check their ideas about stars.

TOI-1408: the limb darkening models, photometric and Doppler noises, and the exoplanetary system

Roman V. Baluev

• Instrumentation and Methods for Astrophysics

AstronomerA self-consistent analysis of available Doppler measurements and TESS and ground-based transit photometry broadly confirms the previously inferred configuration of TOI-1408: two planets near a 2:1 mean-motion commensurability and a distant companion. However, multiple local likelihood maxima span a wider parameter domain, increasing some model uncertainties relative to earlier estimates. Planet b's radius remains poorly constrained at approximately 1.2–3.5 Jupiter radii because of its near-tangential transit geometry. The inferred model also depends strongly on priors for the spectrum-derived stellar mass and radius. These constraints could substantially inform the fit, but require accurately specified prior distributions, including the mass–radius correlation, whose sufficiently precise characterization is currently unavailable in the literature.

PublicResearchers reanalyzed measurements of the star TOI-1408's motion and the dips in its light when planets pass in front of it. Their analysis broadly supports the previously inferred arrangement: two planets with orbital periods close to a two-to-one ratio, plus a distant companion. But several different model solutions fit the observations, making some properties less certain than earlier studies suggested. Planet b passes almost tangentially across the star, leaving its size especially uncertain: its estimated radius ranges from about 1.2 to 3.5 times Jupiter's radius. The results also depend strongly on assumptions about the star's mass and size. Estimates from the star's spectrum could help, but the information needed to use them reliably, including how their uncertainties are linked, is not yet adequately characterized in published work.

Young explorerScientists looked again at a star with two planets and another companion far away. The two planets go around the star so that one takes almost twice as long as the other. The new study mostly agrees with what scientists thought before, but shows that some answers are less certain. One planet passes near the edge of the star when we watch it, so it is hard to tell how big it is. Scientists also need better information about the star's size and mass to understand the planets more clearly.

Performance of AutoRegressive Planet Search methodology on simulated PLATO lightcurves

Eric D. Feigelson, Marco Montalto, Geert Jan Talens+4 more

• Instrumentation and Methods for Astrophysics

AstronomerThis simulation study evaluates PLATO sensitivity to transiting planets with radii of 0.5–2.0 Earth radii using the Autoregressive Planet Search (ARPS) pipeline. Several thousand PLATO-like light curves representing magnetically active stars expected in the LOPS2 field contain injected planetary transits. ARPS filters nonplanetary variability with autoregressive modeling and searches for transits with the Transit Comb Filter periodogram; thresholds on peak periodogram power and transit duration reduce false alarms. For simulated first-three-month observations of bright P1 and P2 stars, at least 50% of Earth-size planets are recovered at periods shorter than 40 days. For simulated two-year LOPS2 observations, 25% are recovered at periods below 240 days. The study discusses detrending, periodograms, false alarms, vetting, and catalog evaluation, and demonstrates a positive predicted value heat map after detection and vetting. These are simulated recovery results, not observed planet discoveries. ARPS is not entirely well-suited to PLATO analysis, but offers insight into detection sensitivity and reliability.

PublicResearchers tested how well a search method might help the PLATO mission find small planets through the dips in starlight produced when planets cross in front of their stars. They used several thousand simulated brightness records of magnetically active stars, adding signals from planets between half and twice Earth's radius. The method filters out nonplanetary changes and searches for repeating transit signals, with extra checks to reduce false alarms. In simulated three-month observations of bright stars, it recovered at least half of the Earth-size planets with orbital periods shorter than 40 days. In simulated two-year observations, it recovered 25% for periods below 240 days. These figures describe different orbital-period ranges, not a direct comparison of performance. The work does not report real planet discoveries, and the authors caution that the method is not an ideal fit for PLATO.

Young explorerA planet can make a star look a little dimmer when it passes in front. Scientists made pretend star-light records with small planets hidden in them to test a computer search for PLATO. The computer found some of the hidden planets, but missed others. It also needed checks so it would not mistake other changes in starlight for planets. This was a practice test, not a discovery of real planets, and the search method still has limits.

Joint RV-Astrometric Analysis of two-planet system HD 65216: Prospects for Gaia DR4

Alexander L. Wallace, Robert A. Wittenmyer, Jonathan Horner

AstronomerA joint analysis of new radial-velocity data and the Hipparcos-Gaia proper-motion anomaly updates the constraints on HD 65216, which hosts at least two giant planets on eccentric orbits. HD 65216 c most likely has an eccentricity of 0.42 ± 0.05 and a period of 7007 days (+192/−161), longer than previously determined. The proper-motion anomaly supports a bimodal inclination distribution with peaks at sin i approximately 0.5. Assuming coplanar planetary orbits, the inferred true masses are 2.23 Jupiter masses (+0.96/−0.77) for b and 3.32 Jupiter masses (+1.40/−1.16) for c. Simulations of Gaia DR4 epoch astrometry and the DR3–DR4 proper-motion anomaly indicate that these methods should be sensitive enough to further constrain orbital parameters and true masses; these are forecasts, not results from DR4 observations.

PublicHD 65216 has at least two giant planets following elongated rather than circular paths. Researchers combined new measurements of the star’s motion toward and away from us with Hipparcos and Gaia measurements of changes in its motion across the sky. Their analysis suggests that planet c takes 7007 days to complete an orbit, longer than earlier estimates. The orbital tilt remains ambiguous. If both planets orbit in the same plane, their estimated masses are about 2.23 and 3.32 times Jupiter’s mass, with substantial uncertainty. Computer simulations suggest that future Gaia measurements could sharpen the estimates of their orbits and masses, but that improvement has not yet been demonstrated with those observations.

Young explorerA star called HD 65216 has at least two big planets moving around it on stretched-out paths. By studying how the star moves, scientists think one planet takes longer to go around than they thought before. They are still unsure exactly how heavy the planets are. Computer tests suggest that future measurements could help them find out more.

Temporal Variability of Titan's Middle-Atmospheric Zonal Winds from Southern Fall to Late Winter (2016-2023)

Martin A. Cordiner, Yuan Lian, Juan M. Lora+10 more

AstronomerSpatially and spectrally resolved ALMA observations of CH3CN emission from 2016–2023 probe Titan’s zonal winds at approximately 200–490 km altitude, spanning late southern autumn to late winter (Ls = 81.6°–156.4°). The retrieved winds show substantial variability on timescales as short as about one Earth month. Variability is strongest near the equator, where speeds reach 240 ± 26 m/s, with repeated roughly 40 m/s fluctuations during Ls = 146.0°–156.4°. Two independent general circulation models qualitatively reproduce the broad-latitude decline in wind speeds through Ls = 146.0° and the subsequent more moderate increase. They also typically reproduce speeds around 45° south reasonably well, with discrepancies of about 30% or less. Equatorial winds, however, are up to roughly twice the predicted speeds, with the largest mismatch near solstice (Ls ≈ 90°). The authors interpret the rapid variability as evidence of strong atmospheric instabilities that the models do not reproduce well, motivating further model improvements.

PublicALMA observations from 2016 to 2023 show that Titan’s winds flowing around the moon at heights of about 200–490 kilometers can change substantially in as little as one Earth month. The strongest changes occur near the equator, where wind speeds reach 240 ± 26 meters per second and repeatedly fluctuate by about 40 meters per second during the later observations. Two computer models capture the overall pattern of winds slowing and then increasing more modestly as Titan moves from late southern autumn toward late winter. They also generally match the winds around 45 degrees south reasonably well. But the equatorial winds can be about twice as fast as the models predict, and the models do not reproduce the rapid changes well. The researchers interpret those changes as signs of strong instabilities in the atmosphere, suggesting that the models need improvement.

Young explorerScientists watched winds high above a moon called Titan. Near its middle, the winds were very fast and could change a lot in about a month. Two computer models got the slow changes over several years mostly right, but the winds near the middle were sometimes about twice as fast as the computers expected. The scientists think the quick changes are signs that the air is unstable in ways the models do not show well yet.

Post-Training Quantization of Autoregressive Weather Models

Ananyo Bhattacharya, Swastik Bhattacharya, Christiane Jablonowski

• Machine Learning

AstronomerThis computational weather study investigates post-training quantization (PTQ) of pre-trained global weather emulators, using Deep Learning Weather Prediction (DLWP) and FourCastNet (FCN) as proof-of-concept applications to geophysical fluid dynamics. PTQ offers a potential route to more efficient matrix computations in autoregressive inference. The authors systematically evaluate quantization configurations over short-range forecast horizons using simulated quantization. Their results suggest that qualitatively meaningful short-horizon forecasts may be retained, providing an initial benchmark for quantization-based optimization of dynamical-system emulators. The abstract does not establish measured speed or power improvements for these weather models, nor does it demonstrate quantized forecast quality at longer horizons.

PublicAI weather models can produce forecasts with much less computing effort than physics-based models. This study explores whether existing AI models can be made more efficient by reducing the numerical precision used in their calculations, a technique called post-training quantization. The researchers test this approach in two global weather models, DLWP and FourCastNet. Tests using simulated reduced precision suggest that the models can still produce qualitatively meaningful forecasts over short periods. This is an early benchmark, not a demonstration of measured energy savings or faster forecasts in these models, and it does not establish how well the approach works for longer forecasts.

Young explorerThe researchers tested two computer helpers that predict weather. They tried letting the helpers use less exact numbers, which might make their work easier for a computer. In tests that imitated this change, the helpers seemed able to make weather predictions that still made sense for a short time ahead. This is an early test: it does not yet show that these helpers use less power or work faster.

Quantitative Links between Formation and Atmospheric Composition for Giant Planets

Yayaati Chachan, Ruth Murray-Clay, Jonathan J. Fortney

AstronomerThe paper presents a quantitative framework for translating giant-exoplanet atmospheric abundances into constraints on the accretion of metals and primordial gas. It introduces simplified, generalized relations between atmospheric metallicity and metal mass fraction, methods to infer metal sources and their contributions, and comparisons of the derived quantities with formation-model expectations. It also derives an estimate of the minimum disk mass required to form a planetary system from a planet’s excess accreted metals, conditional on those metals originating from pebble drift and evaporation at condensation fronts. This is a methodological framework, not a report of new abundance measurements, and an accompanying open-source code implements the methods.

PublicThe chemicals in a giant planet’s atmosphere can offer clues to how it formed. This paper develops a mathematical toolkit for connecting atmospheric measurements to the amounts of gas and heavier elements the planet gathered, estimating where those heavier elements came from, and comparing those estimates with planet-formation models. It also develops a way to estimate the minimum mass of the disk of material needed to form a planetary system. That estimate assumes the planet’s extra heavy elements came from pebbles that drifted through the disk and evaporated at boundaries where materials condense. The paper provides methods and open-source software rather than new measurements of planets.

Young explorerA giant planet’s air can give clues about how the planet grew. The researchers made a number toolkit to help work out how much gas and heavier stuff a planet collected and where that stuff might have come from. They also made a way to estimate how much material was needed around a young star to build its planets. That part assumes some of the heavier stuff came from drifting pebbles that turned into gas. These are tools for studying planets, not new measurements of their air.

A Missing Latent, Not a Missing Simulator: Radius-Augmented Inference for Real JWST Retrieval

Angshuman Chakravertty, P V V Raj

• Earth and Planetary Astrophysics
• Machine Learning

AstronomerThe authors report that amortized simulation-based inference trained on radiative-transfer simulations succeeds on synthetic JWST spectra but fails on real reduced spectra. For WASP-39b, the flow posterior collapses to an importance-sampling effective sample size of 1, with best-fit chi-squared/N = 301. Nested-sampling tests of a temperature gradient, SO2 opacity, and a high-fidelity opacity set leave the fit unchanged; the authors instead attribute the failure to omitting planet radius as a latent inference parameter. Their MIRAGE method augments a flow-matching posterior with radius and calibrates it against an independent nested-sampling reference using importance sampling and an optimal-transport map. They report a physical, literature-consistent WASP-39b retrieval with chi-squared/N = 0.06, and unchanged-method transfer across two instruments and three real JWST targets, including one spectrum reduced end-to-end from raw MAST data. The broader interpretation is that omitting a latent variable represented in the simulator can mimic forward-model misspecification; the physics checks described address specific candidate explanations.

PublicA computer method for studying exoplanet atmospheres worked on simulated James Webb Space Telescope measurements but failed on real observations. The researchers investigated several possible shortcomings in their model of atmospheric physics, but those changes did not improve the fit for WASP-39b. They traced the problem instead to leaving the planet’s size out of the quantities the method could infer. Their revised method, MIRAGE, includes planet size and is calibrated against an independent analysis. They report a much better fit for WASP-39b and atmospheric properties consistent with earlier research. The same method also worked without changes across three planets observed with two instruments. The study suggests that a failed analysis can sometimes reflect a missing quantity in the inference method rather than missing physics in the simulation.

Young explorerScientists use computers to learn about the air around faraway planets from telescope light. One computer method did well with pretend telescope data but got confused by real data. The scientists say it needed to work out how big the planet was, too. They added that missing piece, and their new method matched the real light much better. They tried it on three planets. This shows why scientists check their computer methods with real observations, not just pretend ones.

Comment on: "The Preprint Evolution: The Rise of Unreviewed Drafts on arXiv and its Implications for Astronomy"

Noam Soker

AstronomerThis commentary argues against the proposal in arXiv:2609.35787 to separate astrophysics submissions into peer-reviewed papers and pre-review discussion drafts. The author contends that this split could constrain open discussion and encourage further categorization by journal impact factor or mainstream status. As an alternative, readers seeking only peer-reviewed work could filter submissions using AI or other tools. The author argues that posting before journal acceptance broadens feedback beyond referees, can expose errors and overlooked literature, and provides immediate access and a transparent record of priority despite delays or shortcomings in anonymous peer review. The concluding proposal is for astrophysics journals to require at least one week of arXiv posting before acceptance. These are arguments and policy recommendations, not demonstrated outcomes.

PublicThe author opposes splitting the arXiv research-sharing platform into separate sections for papers that have passed journal review and drafts that have not. They worry that this could limit open scientific discussion and lead to more restrictive divisions. Instead, they suggest that readers who want only reviewed papers use filtering tools. The author argues that sharing papers before acceptance lets more researchers spot mistakes or missing references, makes results available without waiting for journal review, and records who shared work first. They propose requiring astrophysics papers to be on arXiv for at least a week before journal acceptance. The abstract presents a viewpoint and a proposed rule, rather than evidence that these changes would have particular effects.

Young explorerScientists can share their papers on a website called arXiv before a journal finishes checking them. Someone suggested putting checked papers and not-yet-checked papers into two separate groups. This author thinks that could make it harder to share ideas freely. They say sharing early lets other scientists help find mistakes and lets people read the work sooner. They suggest that journals should wait until a paper has been on the website for at least a week before accepting it. This is their idea for how things should work, not something they tested.

Optimizing spectral-matching component separation for measuring CMB B-mode polarization with a satellite mission

Hoang Viet Tran, Guillaume Patanchon, Michele Citran+1 more

• Cosmology and Nongalactic Astrophysics

AstronomerThe authors modify SMICA to address spatially varying Galactic foreground emission, which its standard implementation does not adequately represent. Two complementary component-separation strategies add effective foreground components beyond the physical dust and synchrotron degrees of freedom and fit subsets of the sky independently. They also explore likelihood-level marginalization using internally reconstructed foreground templates. In simulated LiteBIRD-like observations with foreground models of increasing complexity based on d1s1 and d10s5, combining the component-separation improvements with template marginalization yields effectively unbiased estimates of the tensor-to-scalar ratio r, with statistical uncertainties of order 10^-3 or below. These are simulation results, not a detection of primordial CMB B-mode polarization.

PublicA faint polarization pattern in the cosmic microwave background is difficult to measure because brighter emission from our Galaxy gets in the way. The researchers improve a signal-separation method called SMICA so it can better accommodate foreground emission that changes across the sky. They add flexibility to its foreground model, analyze different sky regions separately, and account for foreground templates when estimating the desired signal. In simulated observations resembling those expected from LiteBIRD, the combined approach recovers the tensor-to-scalar ratio r with effectively no systematic offset and statistical uncertainties around 0.001 or smaller. The results demonstrate performance on the tested simulations, rather than a measurement of the primordial signal in real data.

Young explorerScientists want to find a very faint pattern in light left over from the early universe, but brighter light from our galaxy makes it hard to see. They improved a computer method to handle how that bright light changes in different parts of the sky. They tested it on pretend sky observations, and the improved method got very close to the answer used to make those tests. This is a promising test, not a discovery of the faint pattern in the real sky.

Learning Approximate Isometric Embeddings for Efficient Template Placement

Alexandra Wernersson, Jessica Irwin, Melissa Lopez+1 more

• High Energy Astrophysical Phenomena
• General Relativity and Quantum Cosmology

Astronomerisobank uses a normalizing flow to learn an approximately isometric coordinate transformation, allowing Euclidean distances in latent space to approximate metric-induced proper distances in physical parameter space. Template placement can then avoid repeated metric evaluations. In a five-dimensional eccentric-binary parameter space, isobank achieves 97% coverage at a maximum mismatch of 0.03 with 23% fewer templates than the stochastic placement code mbank, which achieves 94% coverage. These are computational benchmark results, not observational detections: coverage is evaluated on independent injections drawn uniformly over masses, spins, and eccentricity, using exact waveform matches rather than the metric approximation. Training takes about 2.5 hours and bank placement under 1 hour on 32 CPU cores. The software is publicly available on GitHub.

PublicSearching for gravitational waves involves comparing possible signals with a bank of model waveforms called templates. Building that bank efficiently is difficult because distances between models depend on where they lie in the space of possible source properties. The new software isobank learns a simpler coordinate map where ordinary distance checks approximately capture those more complicated distances. In a computational test involving binaries with eccentric orbits, it covered 97% of independent test signals while using 23% fewer templates than the comparison software, which covered 94%. Coverage was checked using actual waveform agreement, not just the approximate distances used to build the bank. This demonstrates improved performance in the tested parameter space, rather than a new gravitational-wave detection.

Young explorerScientists look for gravitational waves by comparing signals with lots of possible wave patterns. A new computer tool helps choose those patterns by learning an easier way to tell which ones are similar. In a computer test, its collection matched more test signals even though it used fewer patterns than another tool. Its shortcut is not perfect, so the scientists checked how well the wave patterns really matched. This was a test of the tool, not the discovery of a new wave.

Do Astronomical Foundation Models Know When They Will Fail?

Vaidehi Bulusu, Mehul Goyal, Md Rabius Sany Apu+2 more

AstronomerThe study audits cross-survey embedding transfer with a conformal framework applied to cross-matched Legacy Survey–HSC, HSC–JWST, and SDSS–HSC objects. Astronomy-specific AstroPT embeddings yield lower translation errors and tighter conformal regions than general-purpose visual backbones at comparable coverage, although different model families fail on different objects. Adaptive conformal prediction, using a ridge difficulty model fitted to source embeddings, tests whether those embeddings contain information about their subsequent transfer errors. This warning signal is consistent across tested backbones for Legacy→HSC, backbone-dependent for HSC→JWST, and largely absent for SDSS→HSC. Where informative, adaptation improves coverage for the hardest objects. Matched-control analysis identifies silent failures not explained by magnitude, apparent size, or nearest-neighbor distance. The results support conformal uncertainty as a practical transfer audit, but not as a universal advance warning of failure.

PublicThe researchers tested whether AI models represent the same astronomical object consistently when it appears in different sky surveys—and whether the models can give advance warning when that transfer will go wrong. In the tested survey pairs, the astronomy-specific AstroPT model made smaller transfer errors and produced narrower statistical uncertainty regions than general-purpose image models at comparable coverage. Different model families nevertheless struggled with different objects. A method that adjusts uncertainty using information in the original representation provided useful warning signals across the tested models for Legacy-to-HSC transfer, only for some models for HSC-to-JWST, and largely not at all for SDSS-to-HSC. When that signal was useful, the adjustment improved coverage for the hardest objects. Some failures were not explained by object brightness, apparent size, or similarity to nearby representations. The study therefore shows both the value and the limits of uncertainty-based checks: they can help assess transfer reliability, but failures can still occur without warning.

Young explorerDifferent sky surveys can take pictures of the same thing in space. Researchers checked whether computers could keep track of that thing when moving from one survey to another. A computer model made especially for astronomy did better than the general picture models they tested, but every kind of model had trouble with some things. The researchers also tested a way for computers to warn, “This might be hard for me.” The warning helped with some survey pairs, but often did not work with another pair. So these checks can help, but a computer can still make a mistake without warning.

Robust Bayesian non-linear pulsar timing and noise analysis using a sequential data-tempered ensemble sampler

Abhimanyu Susobhanan

• High Energy Astrophysical Phenomena

AstronomerThe authors develop a sequential ensemble MCMC scheme for Bayesian pulsar timing and noise analysis, using data size as the tempering parameter. Starting with small subsets, potentially orders of magnitude smaller than the full dataset, the method progressively increases sensitivity and narrows the target distribution toward the full-data posterior, allowing convergence from potentially uninformed initial points. Early computational costs are reduced further through approximate lower-rank models justified by the subsets’ reduced sensitivity. Inference uses the final chain sampling the true target distribution after appropriate burn-in, rather than the intermediate tempered chains. A demonstration with NANOGrav 12.5-year data for PSR B1855+09 shows progressive convergence to the target posterior, with most computational time spent sampling that target rather than on preceding tempered iterations.

PublicThe researchers developed a computer method for analyzing the timing of pulsar signals and the noise in those measurements. Instead of tackling all the data immediately, it begins with a small portion and gradually adds more, helping the calculation settle on the range of explanations supported by the complete dataset. The early stages save computing effort by using less data and simpler approximate models. The final analysis uses the full-data model, with the initial settling-in part of that final calculation discarded. A demonstration using NANOGrav’s 12.5-year dataset for the pulsar PSR B1855+09 showed the calculation progressively approaching the intended result. Most computing time went into the final, full-data stage rather than the preparatory steps.

Young explorerA pulsar is a star that sends us signals like a ticking clock. Scientists made a computer method to help understand those ticks, even when the measurements are messy. The computer starts with a little bit of information, then gets more and more. It can use simpler guesses at first, but its final answers use all the information and the full model. When the scientists tried it with measurements of one pulsar, it worked its way toward the answers they wanted to calculate.

Design, Fabrication, and Free-Space Characterization of a Two-Photon-Polymerized Nano-printed Photonic Lantern

Kyra Watts, Natasha Popenoe, Benjamin Gerard+6 more

• Optics

AstronomerThe authors designed, simulated, fabricated, and characterized a compact polymer photonic lantern intended to convert a multimode input into five nominally single-mode output waveguides at 1050 nm. Eigenmode-expansion simulations optimized the geometry to minimize insertion loss and output-channel power nonuniformity, and two-photon polymerization produced a standalone component. Preliminary free-space measurements at 635 nm assessed throughput, output intensity distribution, and light guiding. The abstract provides no numerical performance results. Possible simulation–measurement discrepancies include the wavelength mismatch, fabrication tolerances, material and surface-scattering losses, alignment errors, and departures from idealized simulation parameters. The work demonstrates an additively manufactured lantern platform; its use in future high-contrast exoplanet-imaging instrumentation remains a prospective application rather than a demonstrated result.

PublicResearchers made a tiny polymer device called a photonic lantern, designed to guide light from an input carrying several light patterns into five separate channels, each intended to carry a single pattern. Computer simulations helped shape the device to reduce light loss and make the channels' output powers more even. The team fabricated it using two-photon polymerization and tested its light transmission and output patterns with a laser and camera. An important limitation is that the preliminary tests used 635-nanometer light, while the device was designed for 1050 nanometers. That difference, along with manufacturing imperfections, light losses, and alignment issues, could explain differences between simulations and measurements. The abstract does not report numerical performance. This is a step toward optical components for future instruments that could image exoplanets, not a demonstration of planet imaging.

Young explorerThe researchers made a tiny piece of plastic that is meant to guide light from one bigger path into five little paths. They first used a computer to help plan its shape, then made it and shone a laser through it to see how the light came out. They tested it with a different kind of light from the kind it was designed for, so the test cannot tell them everything about how well it will work. Tiny bumps or imperfect aiming could also change what happens. Someday, devices like this might help telescopes take pictures of planets around other stars, but this study did not take those pictures.

FlashSinkhorn 2: Block-Sparse Entropic Optimal Transport

Felix X.-F. Ye, Yu Chin Fabian Lim, Naigang Wang+1 more

• Artificial Intelligence
• Numerical Analysis

AstronomerFlashSinkhorn 2 (FS2) is a single-GPU solver for discrete entropic optimal transport with squared-Euclidean cost on low-dimensional point clouds. Unlike streaming solvers that evaluate every point pair at each Sinkhorn iteration, FS2 combines coarse centroid updates with block-sparse fine updates. Centroid potentials are lifted to individual points; a failed sampled marginal check triggers further centroid iterations. The fine stage corrects remaining centroid error, using Morton-ordered blocks, screening, and fused tensor-core execution. Block-mass-dependent thresholds bound each omitted tile’s contribution to every row and column. In synthetic benchmarks, FS2 reaches the target marginal residual on all 32 problems, compared with 10 for GeomLoss multiscale. On one A100 GPU, it solves transport between two cosmological N-body simulation measures, each containing 134 million particles, with entropic blur equal to the mean interparticle distance, reaching an all-particle marginal residual below 0.01 in under 2.5 hours. The authors describe this as, to their knowledge, the largest discrete EOT problem solved to this accuracy within hours and release an open-source implementation. This is a computational result using simulation data, not an observational cosmological finding.

PublicThe researchers present a faster way to compute how weight can be distributed between two enormous collections of points while accounting for their separation and a smoothing term. Their program, FlashSinkhorn 2, first works with grouped points, then refines the answer at the individual-point level. It can skip some groups of calculations while bounding the contribution left out. In artificial test cases, it met the requested accuracy target in all 32 problems; a comparison method met it in 10. Using one A100 graphics processor, the new program also handled two sets of 134 million particles each from a computer simulation of the cosmos in under 2.5 hours. Its remaining mismatch with the required weight totals was below 0.01. The authors believe this is the largest problem of this type solved to that accuracy within hours. The achievement concerns computing with simulated particles, rather than discovering something new about the real universe.

Young explorerImagine two enormous pictures made of dots, and a computer working out how to move little amounts from one picture to the other. Looking at every possible pair of dots takes lots of work. The researchers made a program that first looks at groups of dots, then fixes the smaller details. It checks how closely its answer follows the rules. In a big test, it worked with dots from a pretend universe made by a computer and finished in less than two and a half hours on one special computer chip. This shows a faster way to do the calculation, not a new discovery about real stars.

SVOM/C-GFT: Instrumentation and Performances on the SVOM Alerts

Chao Wu, Zhe Kang, Xiao-Meng Lu+20 more

• High Energy Astrophysical Phenomena

AstronomerThis paper describes the Chinese Ground Follow-up Telescope (C-GFT), an optical facility at Jilin Observation Station upgraded to support SVOM by rapidly identifying and monitoring GRB optical counterparts. The 1.2-m telescope has two switchable focal-plane instruments: the prime-focus wide-field LATIOS camera and the Cassegrain-focus three-channel CATCH camera. The overview covers the observatory, telescope, instrumentation, Operations Center-managed automation, and data-processing pipelines. Performance results from more than one year of SVOM post-launch operations indicate that the system meets its design specifications and provides robust observational and operational performance. The abstract does not provide quantitative performance metrics or results for individual GRBs.

PublicThe Chinese Ground Follow-up Telescope at Jilin Observation Station was upgraded to help the SVOM space mission find and track visible-light counterparts of gamma-ray bursts. Its 1.2-m telescope can switch between a wide-field camera and a three-channel camera. The paper explains the facility, its automated operations, and how it processes observations. Based on more than a year of operations after SVOM’s launch, the authors report that the system works reliably and meets its design requirements, though the abstract gives no detailed performance measurements.

Young explorerA telescope in China helps a space mission called SVOM look for light from bursts called gamma-ray bursts and watch how that light changes. It can switch between two cameras, and an automatic system helps it work. The team checked how it worked for more than a year after SVOM launched. They report that it works reliably and does what it was built to do.

hyprfine: simulating the 21-cm signal from the Dark Ages through to the Epoch of Reionization on a GPU

Harry T. J. Bevins

• Cosmology and Nongalactic Astrophysics

Astronomerhyprfine is a publicly available analytic simulation of the sky-averaged 21-cm signal over z = 1100–6, implemented in JAX and Python with native GPU support. It models the mean signal temperature as a function of Λ-CDM cosmological parameters and the astrophysics of the first stars and galaxies. The authors report subsecond execution, efficient GPU parallelisation, and differentiability through the Dark Ages at z ≥ 35. To their knowledge, it is the first analytic GPU-native simulation of this signal. This is a computational tool, not an observational measurement.

PublicThe researchers present hyprfine, a publicly available computer model of how the average temperature of the sky’s 21-centimetre signal changes over cosmic history. Its calculations depend on cosmological parameters and on the properties of the first stars and galaxies. Written in Python using JAX, it is designed to run on graphics processors. The authors report that it runs in less than a second, efficiently handles parallel calculations, and can calculate how its output responds to input changes during the early period called the Dark Ages. They believe it is the first analytic model of this signal built for native graphics-processor use. It simulates the signal rather than measuring it.

Young explorerScientists made a fast computer program called hyprfine. It models how a special signal from the sky could change as the universe grows older, including when the first stars and galaxies appear. The scientists say it can finish a calculation in less than a second. It is a computer model, not a real picture or measurement of the sky, and they have made it available for others to use.

Deep Learning Search for Gravitational Waves from Compact Binary Coalescence

Lorenzo Mobilia, Tito Dal Canton, Gianluca Maria Guidi

• General Relativity and Quantum Cosmology

AstronomerThe study evaluates a hybrid compact-binary search combining matched-filtering concepts with convolutional neural networks, without the usual χ² rejection test. Tests use simulated signal injections in Gaussian noise, transient noise, and signals containing eccentricity, precession, or higher-order modes absent from the template bank. When glitches are present or injected signal physics is missing from the bank, the hybrid achieves detection efficiency comparable to or better than a standard matched-filtering search while using computational resources more efficiently. However, it loses some detection capability for standard binary-neutron-star and binary-black-hole searches in pure Gaussian noise. These simulation results suggest a complementary approach to managing future detector workloads, rather than demonstrating uniformly superior performance or performance on observed detector data.

PublicSearching for gravitational waves from merging compact objects often means comparing detector data with many predicted signal patterns, a process expected to become much more computationally demanding for future detectors such as the Einstein Telescope. This study tests a method that combines that approach with a neural network. In simulated data, it detected signals about as well as or better than a standard search, while using fewer computing resources, when the noise contained glitches or the signals included physical features missing from the comparison patterns. But it missed more signals in some standard searches with purely Gaussian noise. The results suggest a useful complementary tool, not a method that is better in every situation; the tests reported here used simulations rather than observed gravitational-wave events.

Young explorerScientists look for tiny ripples in space, but those ripples can be hidden in noise. They tested a computer helper using pretend ripples and noise. When the noise had sudden bumps, or the ripples were different from the patterns the search expected, the helper found ripples about as well as or better than the usual search and needed less computer work. But in some simpler tests, it missed more ripples. It might help scientists search in the future, but it was not better at every test.