Tonight’s sky of new research

And Then There WEre Baryons (ATWEB): The Baryon Budget of the Universe in Halos and the IGM over 13 Billion Years of Cosmic Time

Mohammadreza Ayromlou, G. Mark Voit, Thomas H. Reiprich+2 more

• Astrophysics of Galaxies

AstronomerLocal observations indicate that halo baryon fractions lie below the cosmic mean except in the most massive clusters. Using TNG, EAGLE, and SIMBA, this study investigates the spatial and temporal divergence of baryonic and dark matter distributions. At z=0, the simulations place less than 30% of cosmic baryons within galaxy-hosting halos, versus approximately 45% of dark matter, leaving over 70% of baryons in the intergalactic medium. Alongside the established closure radius, where the enclosed baryon fraction reaches the cosmic mean, the authors define a compensation radius, where enclosed total mass recovers its gravity-only value, and closure and compensation envelopes, the largest median radii across halo mass. At z=0, the compensation radius typically lies inside the closure radius. Galaxy groups contribute most per dex of halo mass to IGM enrichment by halo-associated baryons and redistribute baryons over the greatest distances, setting a model-dependent closure envelope of approximately 2–6.5 Mpc. Closure radii usually grow with cosmic time at fixed halo mass. Individual halo histories reveal open baryon cycles and substantial redistribution beyond halo boundaries at all masses; even progenitors of today's most massive clusters have subcosmic baryon fractions. The compensation envelope grows toward low redshift, reaching approximately 1.5–5.5 Mpc today. Across cosmic time, it coincides with the scale where the matter power spectrum recovers its gravity-only form, linking baryon redistribution to feedback's impact on large-scale structure.

PublicObservations show that most galaxy halos contain a smaller share of ordinary matter than the Universe-wide average; the most massive galaxy clusters are the exception. This study uses three simulations, TNG, EAGLE, and SIMBA, to investigate where ordinary matter goes and how its distribution differs from dark matter. In the simulations today, less than 30% of ordinary matter lies inside galaxy-hosting halos, compared with about 45% of dark matter. More than 70% of ordinary matter is in the space between galaxies. The researchers measure how far from a halo one must look to recover either the Universe's average proportion of ordinary matter or the total mass expected in a gravity-only calculation. Those two distances are generally different. Galaxy groups redistribute ordinary matter over the greatest distances, setting a characteristic outer scale of roughly 2–6.5 million parsecs, depending on the simulation. The simulated redistribution extends beyond halo boundaries throughout their histories. A separate scale for recovering the gravity-only total mass also tracks where the statistical pattern of matter clustering returns to its gravity-only form, connecting matter redistribution with feedback's effects on cosmic structure.

Young explorerGalaxies sit inside big regions called halos. When astronomers look at most halos, they find less ordinary matter than the Universe's usual share. Scientists used three computer models to explore this. In the models, most ordinary matter is outside galaxy halos, and groups of galaxies spread it especially far. Looking farther out can recover the usual share. The models do not all agree on exactly how far.

Lensing in the Blue IV: The First Weak Gravitational Lensing Maps from the Stratosphere

Sayan Saha, Maya Amit, Jacqueline E. McCleary+42 more

AstronomerSuperBIT completed its science flight in April 2023, acquiring imaging of 30 galaxy clusters. This work presents the first weak-lensing convergence maps from those observations for a selected subset of six clusters. Background-galaxy catalogs are constructed from three-band photometry using color-color foreground/background separation. Galaxy shapes calibrated in Lensing in the Blue III are then used to reconstruct the convergence field via Kaiser-Squires inversion. The convergence signal-to-noise maps are compared with independent tracers: X-ray emission and red-sequence cluster-member number-density maps. The authors report the first successful weak-lensing mass mapping using imaging from a sub-orbital astronomical observatory; the abstract does not specify the degree of agreement between tracers or quantitative map uncertainties.

PublicThe balloon-borne SuperBIT telescope collected images of 30 galaxy clusters during its April 2023 science flight. Researchers used observations of six of these clusters to produce maps of their mass through weak gravitational lensing, which detects subtle distortions in the shapes of background galaxies. They used images in three color bands to help distinguish background galaxies from foreground ones, then reconstructed the lensing maps from calibrated galaxy shapes. They compared these maps with X-ray emission and maps showing where cluster-member galaxies are concentrated, although the abstract does not say how closely these tracers agree. The study reports the first successful weak-lensing mass mapping from a sub-orbital astronomical observatory.

Young explorerA telescope carried by a balloon took pictures of big groups of galaxies. Scientists studied six of those groups. The groups bend light from galaxies behind them, making those faraway galaxies look a little stretched. Scientists used those tiny stretches to make maps of where the groups' mass is. They also compared the maps with other pictures of the groups. This was the first time scientists successfully made this kind of map using pictures from a telescope flying below orbit.

Stochastic Bubble Completion in de Sitter Space: Power Spectrum, Bispectrum, and Infrared Moment Hierarchies

Hyukjung Kim, Alp Kagan Ozmen, Heeseung Zoe

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

AstronomerThis theoretical study develops a first-arrival framework for the spatially random completion time of a first-order phase transition, calculating its power spectrum and equilateral bispectrum in Minkowski and de Sitter backgrounds. In eternally extended de Sitter histories, rare ancient bubbles produce an infrared-sensitive tail: the first finite-k correction to the two-point function becomes tail sensitive at H/β = 1/5, and its leading moment becomes singular at 1/3; the corresponding three-point thresholds are 1/8 and 1/6. Thus, the bispectrum is more infrared sensitive. A finite starting time cuts off the tail, keeps all spatial moments finite, and restores the strict infrared white-noise scalings Pτ ∝ k³ and Bτ,eq ∝ k⁶. The eternal-history thresholds instead govern the duration dependence of moment coefficients and an intermediate tail-sensitive regime, consistent with numerical calculations. Temporal localization of nucleation also smoothly regulates the tail and restores these limits. The results clarify possible implications for curvature perturbations and non-Gaussianity; they are not observational findings.

PublicThe researchers theoretically study a transformation that spreads through randomly appearing bubbles, so different places finish changing at different times. They examine how these timing differences are related across space, including patterns involving pairs and triples of locations. In a model of an expanding universe whose history extends indefinitely into the past, rare very old bubbles can strongly affect the largest-scale patterns, with three-location patterns more sensitive than two-location patterns. But if bubble formation begins at a finite time, that old-bubble contribution is cut off and the largest-scale behavior returns to a regular, white-noise form. Numerical calculations support the predicted transition between these behaviors. Restricting bubble formation to a localized period also removes the problematic old-bubble contribution. These are theoretical results relevant to understanding cosmic fluctuations, not measurements of a real transition.

Young explorerImagine a big change spreading through space in bubbles that pop up at random. Some places finish changing before others. Scientists used math to study the pattern of those finishing times. In their pretend expanding universe, bubbles from a very, very long time ago can make a big difference. But if the bubbles only started appearing a limited time ago, the biggest patterns behave more simply. This is a math study, not something the scientists watched happen in the sky.

Fast and accurate differentiable code of the galaxy power spectrum based on Eulerian and Lagrangian one-loop perturbation theories

Yosuke Kobayashi, Kazuyuki Akitsu

AstronomerThe paper presents elf, a publicly available JAX-Python implementation of the one-loop galaxy power spectrum in the effective field theory of large-scale structure, using both Eulerian and Lagrangian perturbation theory (EPT and LPT). Automatic differentiation with respect to cosmological parameters, galaxy bias, and counterterm coefficients supports gradient-based parameter inference, including Hamiltonian Monte Carlo. After just-in-time compilation, both spectra can be evaluated in a few milliseconds on a GPU. The authors analyze discretization errors and report relative errors of order 0.01% for k ≲ 1 h Mpc⁻¹ compared with brute-force numerical integration; this is a numerical accuracy benchmark, not a comparison with observations. They describe elf as the first auto-differentiable one-loop LPT galaxy power-spectrum implementation. LPT’s natural resummation of long-wavelength displacements makes it well suited to applications involving features beyond standard BAO, including primordial features, but the abstract reports no observational detection or completed inference application.

PublicThe researchers introduce elf, a freely available program for calculating how galaxies cluster at different scales using two theoretical approaches. It can automatically calculate how its predictions change when model parameters change, which can help methods that estimate those parameters from data. After an initial compilation step, the calculations take only a few milliseconds on a graphics processor. Against a more direct numerical calculation, the authors report differences of about 0.01% over the stated range of scales. That tests the program’s numerical accuracy, not its agreement with the real Universe. One approach, called Lagrangian perturbation theory, accounts for large-scale shifts in position in a way that could help studies of patterns beyond the usual baryon acoustic oscillation feature, including possible patterns originating in the early Universe. The paper presents a computational tool, not a detection of such patterns.

Young explorerGalaxies make patterns in space. The scientists made a computer tool called elf that quickly works out what those patterns might look like using two kinds of math. It can also work out how its answers change when you change the settings. They checked it against a slower calculation and found very small differences. This checks the computer math, not whether it matches real galaxies. The tool could help scientists study more kinds of patterns later, but this paper does not say they found a new one.

Third-order scalar induced gravitational waves during a matter-dominated era: secular growth and implications for primordial black hole domination

Jing-Zhi Zhou

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

AstronomerThis theoretical study derives closed-form kernels for third-order scalar-induced gravitational waves during matter domination, separating sources into three first-order scalars and a first-order scalar coupled to second-order tensor, vector, or scalar perturbations. Unlike the radiation-dominated kernels, these kernels grow secularly, giving Ω_GW^(3) ∝ x^6 rather than Ω_GW^(2) ∝ x^2 for x = kη ≫ 1. The general third-order power spectrum is expressed as a five-fold integral and evaluated numerically for a monochromatic primordial spectrum, for which all second-order-vector-source contributions vanish. For an early matter-dominated era driven by primordial black holes before evaporation, imposing ∫d ln k Ω_GW^tot < 1 to avoid backreaction yields Ω_PBH,f ≲ 4.6 × 10^−7 (m_PBH/10^7 g)^−0.48, about three orders of magnitude tighter than the second-order-only bound. These are theoretical results, not observational constraints; they indicate that higher-order contributions become nonperturbative if matter domination lasts sufficiently long.

PublicThe researchers calculate how disturbances in the early universe could generate gravitational waves during a period when matter dominated its evolution. Their theoretical calculation includes third-order effects and finds that these contributions grow much faster than the previously considered second-order contributions. In a scenario where primordial black holes drive this period before evaporating, requiring the waves not to feed back on the cosmological disturbances gives an upper limit on the initial black-hole abundance about a thousand times tighter than the second-order-only calculation. This is not a measurement of black holes or gravitational waves. The results indicate that, if matter domination lasts long enough, treating the higher-order wave contributions as small corrections stops being valid.

Young explorerThe researchers used math to study how little bumps in the young universe might make ripples in space. In their calculations, some extra ripple effects grow much faster than the simpler ones. If a time when matter was in charge lasted long enough, those extra effects would become too big to treat as little changes. They also calculated a limit on how many tiny black holes could have been there in one possible story of the early universe; they did not find or count those black holes.

Probing beyond the Cosmic Horizon

Tarun Souradeep

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

AstronomerThe abstract considers whether the observable region of approximately uniform curvature is only a small patch of a much more complicated global manifold. It interprets the cited supernova results as suggesting that the horizon scale may be comparable to or larger than the curvature radius, with nontrivial global structure also expected on roughly the local curvature scale. It proposes CMB anisotropy as a potential probe of global structure near or slightly beyond the horizon. As a theoretical illustration, it describes a high CMB anisotropy signal for Elliptical topology across a large fraction of the revised parameter space of closed, spherical FRW models reported as preferred by those supernova observations. This is an argument for possible detection or constraints, not a reported detection of cosmic topology.

PublicThe part of the universe we can observe might be just a small patch of a much more complicated whole. The abstract interprets supernova observations as suggesting that the universe’s curvature could become important on distances comparable to, or smaller than, our observable horizon. It argues that patterns in the cosmic microwave background could help reveal or constrain how space is connected on enormous scales, potentially even slightly beyond that horizon. One theoretical example, called Elliptical topology, is described as producing a strong signal in many of the curved-universe models considered. The abstract does not report finding this global structure.

Young explorerWe can see only part of the universe, and the whole thing might have a very surprising shape. Scientists think tiny patterns in the old light filling space might give clues about how faraway parts of space fit together. This paper says one possible shape could leave a strong clue. It does not say scientists have found that shape.

Evolution of neutrino distributions under repeated electron scattering

Jens Chluba, Bryce Cyr, Michiru Uwabo-Niibo+1 more

• High Energy Astrophysical Phenomena
• High Energy Physics - Phenomenology

AstronomerThis theoretical and numerical study treats neutrino energy redistribution through repeated elastic scattering in an isotropic thermal bath of free electrons. A redistribution-kernel formulation retains recoil, relativistic kinematics and Pauli blocking while reducing the collision calculation to a one-dimensional integral over outgoing neutrino energy. Two independent derivations of the Fokker–Planck limit show how the weak cross section’s energy dependence modifies drift and diffusion relative to the photon Kompaneets equation, making the high-energy distribution evolve faster than the low-energy part. The authors discuss fermionic spectral-distortion analogues, obtain approximate solutions in limiting cases, and derive a relativistic neutrino Sunyaev–Zeldovich analogue when Doppler terms dominate and scattering is inefficient. Comparisons with the full collision calculation and controlled numerical line-injection tests assess the approximations: diffusion works in some regimes, but non-local redistribution remains essential in others. Conservative numerical schemes are developed for both formulations; no observational measurements are reported.

PublicThe paper uses mathematics and computer calculations to study how neutrinos exchange energy with a warm population of electrons through repeated collisions. The calculations indicate that the higher-energy part of a neutrino population changes faster than the lower-energy part, unlike the corresponding behavior described by the standard photon equation. The researchers develop both a detailed collision model and a simpler approximation that treats energy changes as gradual spreading and shifting. They also explore neutrino counterparts of several effects studied for light. Computer tests identify when the simpler approximation is accurate and when the full treatment of energy redistribution is needed. These are theoretical and numerical findings, not observations of neutrinos in space.

Young explorerNeutrinos are tiny particles. This study uses math and computers to imagine them bumping into other tiny particles called electrons and trading energy. The calculations say that the neutrinos with more energy change faster than those with less energy. The scientists try a simpler way to do the math, but their computer tests show that sometimes they need the more detailed version. They did not watch these bumps happen in space.

ApPolLO: Apertif counterparts of Polarised LOFAR sources

A. Berger, B. Adebahr, H. Dénes+1 more

• Astrophysics of Galaxies

AstronomerThe study compares polarisation data from the LOFAR RM grid at 144 MHz and new Apertif observations at 1.4 GHz, compiling a catalogue of 598 polarised radio components, mostly in low-density environments. For sources common to the two datasets, the authors derive a depolarisation ratio to distinguish source-local effects from contributions along the line of sight. Fractional polarisation decreases with redshift at both frequencies. The authors attribute the dominant depolarisation at 1.4 GHz to regions near the sources, while interpreting the 144 MHz depolarisation as most likely arising in intervening cosmic filaments. These environmental assignments are interpretations rather than direct identifications. The analysis provides a first redshift-dependent upper-limit estimate of RM dispersion in cosmic-web filaments, not a measured dispersion value.

PublicResearchers compared the polarisation of radio waves observed by LOFAR at 144 MHz and Apertif at 1.4 GHz to investigate cosmic magnetic fields. Their catalogue contains 598 polarised radio components, most in relatively sparse environments. They found that the fraction of radio emission that is polarised decreases with increasing redshift at both frequencies. Comparing the two frequencies helps separate effects near the radio sources from effects encountered along the waves' journey. The team attributes most depolarisation at 1.4 GHz to material near the sources and considers cosmic-web filaments the most likely explanation at 144 MHz. This interpretation yields an initial, redshift-dependent upper limit on rotation-measure variations in those filaments, rather than a definite measurement.

Young explorerRadio waves from space can have a special pattern called polarisation. Scientists compared that pattern using two kinds of radio observations. They found less of it in sources with higher redshift. They think some changes happen near the sources, and others may happen as the waves cross long threads of matter in space. Those explanations are not certain.

The impact of feedback and cosmology on Cosmic Infrared Background cross-correlations

Sara Maleubre, David Alonso, Reggie Dunsdon+3 more

• Astrophysics of Galaxies

AstronomerThe study uses the FLAMINGO hydrodynamical simulations to examine the evolution and clustering of star formation rate density and assess whether Cosmic Infrared Background (CIB) cross-correlations can constrain stellar feedback, AGN feedback, and cosmology. It considers tomographic measurements of bias-weighted SFR density and CIB–cosmic shear correlations, the latter probing the SFR-density–matter correlation. Most models calibrated to the z=0 galaxy stellar mass function predict similar distributions and clustering of star-forming systems, limiting clean inferences about AGN feedback or cosmology from CIB statistics. Nevertheless, comparisons with current measurements clearly disfavour models with strong stellar feedback and simulations with strong kinetic, jet-driven AGN feedback, even under the fiducial stellar mass function calibration. The results support the potential of CIB cross-correlations as probes of star and galaxy formation physics, rather than establishing a unique feedback prescription or cosmology.

PublicThe researchers used computer simulations from the FLAMINGO project to study how star formation changes over cosmic history and how star-forming galaxies cluster. They compared simulation predictions with measurements linking the Cosmic Infrared Background to the distribution of matter, including measurements of how matter bends light from distant galaxies. These comparisons clearly disfavor simulated models in which stellar feedback is strong, or in which jets from active galactic nuclei provide strong feedback. However, most models adjusted to match the present-day distribution of galaxy stellar masses make similar predictions, making it difficult to isolate the effects of active galactic nuclei or cosmology. The study shows that these infrared-background comparisons offer a promising way to test galaxy-formation physics, but do not identify a single correct model.

Young explorerScientists made pretend universes on computers to study where new stars form. They checked their ideas against measurements of infrared light from space and how matter bends light. Pretend universes with very strong effects from stars, or very strong jets from active galaxy centers, did not match the measurements well. But many other pretend universes looked alike, so scientists still cannot tell exactly which explanation is best.

Stochastic effect on ultralight dark matter searches with astronomical polarized sources

Kyohei Yamada

AstronomerThe authors present a unified statistical framework for polarization-oscillation searches for ultralight axion-like particle (ALP) dark matter, rather than reporting a detection. In the standard halo model, the ALP field is treated as a stochastic Gaussian random field, inducing polarization-angle oscillations proportional to the field difference between observer and source. The signal statistics depend on source size and distance relative to the ALP Compton and coherence lengths, and hence on ALP mass. The framework identifies four amplitude-statistics regimes and describes their transitions, recovering previously known models for laboratory-scale, pulsar, and cosmic microwave background searches. A likelihood prescription incorporates signal stochasticity. The authors show that source-distance uncertainties can change inferred ALP-photon coupling constraints by up to a factor of three, making their treatment important for consistent interpretation and comparison of searches.

PublicUltralight axion-like particles are possible constituents of dark matter, but this work does not report finding them. Under the dark-matter model used here, these particles would make the orientation of polarized light oscillate randomly as the light travels to us. The expected pattern depends on the size and distance of the light source and on the particle mass. The researchers developed a statistical framework that covers four types of oscillation behavior and the transitions between them, bringing together earlier descriptions used for laboratory experiments, pulsars, and the cosmic microwave background. Their method accounts for the signal's randomness when assessing searches. They also show that uncertainty about a source's distance can change the inferred limits on how strongly the particles interact with light by as much as a factor of three. This provides a common basis for comparing searches, not evidence that the particles exist.

Young explorerScientists wonder whether tiny particles we have not found could make up dark matter. If they do, they might make the direction in which light wiggles turn back and forth in a random way. This team made a math tool to describe what that could look like for light coming from things of different sizes and distances. They also showed that not knowing exactly how far away something is can change what a search tells us. They did not find the particles; their tool helps scientists understand searches for them.

Boosted Odds: Lower-Point Probes of Parity Violation with Momentum Fields

Yong Sheng Yap, William R. Coulton, Jiamin Hou+1 more

• High Energy Physics - Phenomenology

AstronomerThe authors propose the density-density-momentum bispectrum, with momentum field p = (1 + δ)v, as a probe of primordial parity violation associated with inflationary dynamics beyond single-field slow roll. This three-point statistic complements density four-point searches while reducing data-vector dimensionality and covariance-analysis complexity. They show that sensitivity to parity violation survives projection of the momentum onto the line of sight. A Fisher forecast for the parity-violating amplitude of an ultra-squeezed template in the galaxy-galaxy-kSZ cross bispectrum yields projected constraints competitive with existing methods; this is not an observational detection. The approach could be incorporated into existing pipelines and benefit from ongoing work on systematics mitigation and covariance modelling for galaxy-galaxy-kSZ analyses.

PublicThe researchers propose a new way to search for signs that the early universe treated mirror-image patterns differently. Such a discovery could point to physics beyond the simplest models of inflation, the universe’s early expansion. Their method combines information about where matter is concentrated and how it moves, using a three-part statistical pattern rather than the four-part patterns used in traditional searches. They show that the method remains sensitive even when only motion along our viewing direction is available. A calculation forecasting its performance with galaxy clustering and kinetic Sunyaev-Zel’dovich signals suggests it could compete with existing approaches. These are predictions of the method’s sensitivity, not a detection of mirror asymmetry. Existing work on measurement errors and statistical modelling could help put the proposal into practice.

Young explorerImagine looking at the universe and its reflection in a mirror. Scientists want to know whether the universe’s very early patterns followed the same rules as their mirror images. They suggest a new way to look for clues by studying where space’s matter gathers and how it moves. Their calculations suggest this could work about as well as other ways of searching, but they have not found such a clue yet.

When, Why, and How CMB Compression Fails

Davide Pedrotti, William Giarè, Hanyu Cheng+1 more

AstronomerThis study tests CMB likelihood compression calibrated in ΛCDM against the full Planck-CMB likelihood across extensions involving late-time dark energy, interacting or decaying dark matter, and persistently non-standard dark-matter redshift evolution. In the cases studied, compression remains accurate for late-time dark-energy extensions that preserve the dark-matter background evolution and introduce no significant additional perturbative effects. Modified dark-matter evolution instead breaks the mapping between present-day matter density and matter density at CMB-relevant epochs, invalidating the compressed constraints even for exclusively late-time modifications. The resulting posterior distortions include shifts, anisotropic deformations, reordered principal modes, and mixing and rotation of eigendirections. These propagate into incorrect marginalized parameter constraints, with differences between full and compressed analyses approaching an order of magnitude in some cases. These are findings from comparisons of inference methods within the tested models, not evidence that dark matter actually interacts or decays.

PublicA shortened statistical summary of cosmic microwave background data can make it easier to test theories about the universe, but this study finds that the shortcut is not reliable for every theory. The researchers compared analyses using the full Planck-CMB likelihood with analyses using a compressed version calibrated to the standard cosmological model. In the models tested, the shortcut worked for changes to late-time dark energy that left dark matter's background evolution unchanged and added no substantial effects on cosmic fluctuations. It failed when dark matter evolved differently, even if the change occurred only late in cosmic history: today's matter density then no longer connects to the density relevant to the microwave background in the assumed way. The shortcut could shift and reshape the inferred parameter ranges, with differences approaching a factor of ten in some cases. The study identifies limitations of the analysis method; it does not establish that these alternative dark-matter models describe the real universe.

Young explorerScientists use very old light from space to learn about the universe. Sometimes they use a short summary instead of the full information. This study checked whether that shortcut gives the same answers when scientists try different ideas about how the universe changes. For some ideas, it worked well. For ideas where dark matter changes differently over time, it could give very different answers, even if the change happened only much later. That does not mean those ideas are true. It means scientists need to be careful about when they use the shortcut.

Halo Mass Function Constraints on Early Galaxy and AGN Populations in the JWST Era

Elan Yogeswaren, Robert Schaefer

• Astrophysics of Galaxies

AstronomerMotivated by JWST observations of massive galaxies and luminous AGN at high redshift, the authors develop a framework linking the linear matter power spectrum to halo statistics and observable populations. They adopt the Sheth-Tormen halo mass function as a baseline and compare it with an illustrative Bolshoi-Klypin-calibrated modification to assess sensitivity to simulation-based calibration. Applications test galaxy baryonic and stellar mass reservoirs, the abundance of potential luminous AGN hosts, and the rest-frame UV luminosity function. In the rare, high-peak tail, modest changes in inferred host mass, baryonic conversion efficiency, black-hole occupation or duty cycle, and halo mass function calibration can substantially alter predicted abundances. The model comparison indicates that calibration uncertainty materially affects the inferred host supply, especially around redshift 10. Comparisons with representative JWST measurements emphasize that reproducing individual source properties does not establish population consistency: sufficiently numerous host halos are also required. The observations thus stress-test both cosmological halo abundances and baryonic and black-hole physics, rather than establishing a unique explanation.

PublicJWST has discovered massive galaxies and bright active galactic nuclei in the early universe. The authors build a theoretical framework to ask whether enough dark matter halos—the structures that can host these objects—are available to account for the observed populations. They examine the material available for forming massive galaxies, possible hosts for bright active nuclei, and the numbers of galaxies at different ultraviolet brightnesses. Comparing two prescriptions for halo abundance shows that predictions can depend strongly on how the models are calibrated against simulations, especially around redshift 10. Assumptions about host masses, how efficiently material becomes stars, and how often black holes are present or active also matter. The central point is that explaining one remarkable object is not enough: a model must supply enough hosts for the whole population. The observations provide increasingly demanding tests, but the abstract does not establish a single explanation or a failure of cosmology.

Young explorerA telescope called JWST has found big galaxies and very bright centers of galaxies from when the universe was young. Scientists made a model to ask whether there were enough invisible dark matter homes for all these galaxies. It is not enough to explain how one galaxy could fit in a home—there must be enough homes for all the galaxies we see. Different ways of counting the homes give different predictions, and scientists are still unsure how galaxies and their bright centers grew.

Mitigating prior-volume effects in galaxy clustering by adopting Mpc over Mpc/h units

Andrea Pezzotta, Alejandro Pérez-Fernández, Giosuè Gambardella+4 more

AstronomerThis study investigates prior-volume effects in Bayesian galaxy-clustering analyses using models including EFT and VDG∞. The authors identify priors on parameters defined in Mpc/h units as a major source of spurious correlations with the Hubble parameter h, and find that a physically motivated formulation in Mpc substantially mitigates the resulting marginalisation-induced shifts. Tests use synthetic clustering data designed to represent a Stage-IV survey for ΛCDM, KCDM, wCDM, and w0waCDM, rather than observations from such a survey. Discrepancies from fiducial values decrease from several standard deviations to well within 1σ, including in the challenging w0waCDM case. Performance is comparable to invariant priors and nuisance-parameter reparametrisation using growth and geometrical amplitudes. For the latter approach, replacing σ8 with σ12 improves performance even at high redshift, where dark-energy equation-of-state constraints are weaker. The conclusions also hold when additional BAO constraints are included and when statistical power is reduced. These tests support using Mpc-based formulations without explicit h dependence, although the reported constraints are largely, not completely, free of marginalisation-induced shifts.

PublicWhen scientists use the pattern of galaxy clustering to estimate properties of the universe, their starting assumptions can unintentionally pull the answers away from the values supported by the data. This study finds that much of this problem comes from setting those assumptions for model parameters in distance units tied to h, a parameter describing the universe’s expansion rate. A more physically motivated formulation using megaparsecs without that explicit dependence greatly reduces the problem. The researchers tested the method on artificial data representing signals expected from a Stage-IV galaxy survey, across several cosmological models; these are not findings from an observed survey. In those tests, estimates moved from several standard deviations away from the input values to well within one. The method performed comparably to other ways of addressing the problem, and the improvement persisted with extra information about cosmic distances and with less statistically powerful data. The results suggest a useful way to make future galaxy-survey analyses less sensitive to unintended effects of their assumptions.

Young explorerScientists look at how galaxies are grouped to learn about the universe. But the rules they choose before doing the sums can accidentally tug their answers the wrong way. The researchers tried a different way of setting up those rules, using a distance ruler that does not depend on how fast the universe expands. They tested it with pretend galaxy data where they already knew the right answers. Their new method got much closer to those answers. That could help scientists study real galaxy maps, but these tests used pretend data.

Lunar radio emission from dark photon dark matter

Ariel Arza

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

AstronomerThis work proposes searching for dark-photon dark matter through its conversion into radio waves at the Moon’s dielectric surface, using standard radio telescope antennas to collect the emission. Detailed sensitivity projections indicate that current and future observatories, including ALMA, SKA, FAST, and GBT, could probe substantial, previously inaccessible dark-photon parameter space. These are projected search capabilities, not a reported detection of dark matter or lunar radio emission from this mechanism.

PublicResearchers propose using the Moon to help search for dark matter in the form of hypothetical particles called dark photons. The idea is that the Moon’s surface could convert these particles into radio waves that radio telescopes could pick up. Their calculations suggest that existing and future telescopes could test possibilities that have previously been beyond reach. The study presents a proposed search and estimates of its sensitivity, not evidence that dark photons have been detected.

Young explorerScientists have an idea for looking for invisible stuff called dark matter. If it is made of tiny things called dark photons, the Moon’s surface could turn them into radio waves. Special telescopes could look for those waves. The scientists’ calculations suggest this could be a useful way to search, but they have not found dark photons in this study.

Coherent versus incoherent amplification: from parametric resonance to the kinetic regime in stimulated axion decay

Clemente Smarra, Elisa Todarello

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

AstronomerThis theoretical study reconciles the photon growth exponent s proportional to g_aγ in coherent-field parametric resonance with the s proportional to g_aγ² behavior expected from a kinetic treatment of stimulated axion decay. Starting with finite axion momentum dispersion, the authors derive an effective evolution equation whose kernel incorporates dephasing among momentum modes. For a continuous Maxwell-Boltzmann velocity distribution, they obtain an implicit growth exponent that recovers both asymptotic regimes and approximately describes the crossover. Amplification on scales shorter than the axion coherence length yields the linear coupling dependence; the opposite limit yields effectively kinetic, quadratic behavior. The crossover depends on the momentum distribution, while the authors expect, rather than establish generally, that the asymptotic coupling scalings are largely distribution-independent. These are theoretical results, not an observational detection.

PublicAxions are proposed particles that could decay into light, although their spontaneous decay would be extremely slow on cosmic timescales. Under suitable conditions, this process could be strongly amplified. This theoretical study explains why two ways of calculating that amplification appear to disagree: the answer depends on how coherently the axion waves act together. When amplification develops over distances shorter than those over which the waves stay coordinated, the light's growth rate scales with the axion-light interaction strength. In the opposite limit, it scales with the square of that strength. The researchers derive a formula that approximately connects these behaviors for a particular distribution of axion velocities. The transition depends on that distribution, though they expect the limiting behaviors to be more general. The work does not report an observation of axions or their light.

Young explorerScientists are thinking about possible tiny particles called axions that could turn into light. They used math, not a sighting of these particles, to study how that light might grow. Imagine waves moving together: if they stay in step while the light grows, they can help it grow in one way. If the waves get out of step, the light grows in a different way. The study helps explain why two kinds of math gave different answers. Exactly how the change happens depends on how the axions are moving.

Spectator Dark Matter and the Higgs Portal

Stephen E. Henrich, Yann Mambrini, Keith A. Olive

• High Energy Physics - Phenomenology

AstronomerThis theoretical study examines how a very weak Higgs portal can suppress the inflationary memory of a light scalar spectator, whose stochastic fluctuations could otherwise produce an excessive dark-matter abundance if its primordial condensate persists. For sub-freeze-in couplings of approximately 10^-28 to 10^-9, portal-induced radiative self-interactions and a thermal mass can trigger earlier oscillations and efficient redshifting of the condensate energy without thermalizing the spectator or destroying the condensate. The portal also suppresses the spectator's equilibrium field variance relative to an isolated field. The authors explicitly consider inflation too short to establish stochastic equilibrium; in that scenario, isocurvature supplies the major constraint, requiring approximately N ≥ 10^10 e-folds. Adding a non-minimal gravitational coupling substantially enlarges the viable parameter space. The model generally favors light, especially sub-GeV, dark matter, with a quoted mass range of approximately 0.1 eV to 10 GeV, and favors low reheating temperatures when non-minimal gravity is absent. The mechanism can account for the entire relic abundance at sub-freeze-in portal couplings or provide a suppressed initial condition for standard Higgs-portal freeze-in. These are model-based findings, not reported observations.

PublicA light field present during inflation, an early period of rapid cosmic expansion, could retain fluctuations that later produce far too much dark matter. This theoretical study finds that an extremely weak connection to the Higgs field could reduce that problem. The connection changes the light field's behavior so that it can begin oscillating earlier, allowing cosmic expansion to dilute its stored energy more efficiently without destroying it or bringing it into thermal equilibrium with its surroundings. It also reduces the fluctuations expected if the field reaches statistical equilibrium during inflation. The authors examine cases where equilibrium was not reached and find a strong constraint from differences in the relative distributions of cosmic components, requiring an exceptionally long inflationary period. An additional coupling to gravity broadens the model's possibilities. Depending on its parameters, the mechanism could produce all of the dark matter or set a reduced starting abundance for another production process. No observational confirmation is reported.

Young explorerScientists think an invisible field in the very young universe might have left behind too much dark matter, the unseen stuff in space. Their calculations suggest that a tiny connection to another field, called the Higgs field, could help. It could make the first field wobble sooner, so its energy becomes more spread out as the universe grows. This might leave the right amount of dark matter, but it is a possible explanation, not something they have seen happen.

Axion Pyramid

Chan-Gyung Park, Dahee Lee, Hyerim Noh+1 more

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

AstronomerThe abstract identifies a pronounced pyramid-shaped enhancement in the axion density power spectrum induced by the QCD phase transition. It occurs near the horizon scale at the transition, with a characteristic comoving length comparable to the size of the Solar System. Under hilltop initial conditions, coupling to radiation triggers the enhancement, amplifying axion density perturbations by factors exceeding 3.5 × 10^13 relative to the cold dark matter case. The connection between the initial condition and axion mass suggests that a future cosmological observation of this feature may constrain the QCD axion mass; the abstract does not report an observational detection.

PublicThe study describes a possible pyramid-shaped peak in the pattern of density variations of axions. The feature arises from the QCD phase transition and appears on a characteristic scale comparable to the size of the Solar System, measured in coordinates that account for cosmic expansion. With a particular starting condition called the hilltop condition, interaction with radiation makes the axion density variations more than 35 trillion times larger than in the cold dark matter comparison. This is not a reported observation: the authors suggest that detecting the pattern in the universe could help constrain the axion's mass.

Young explorerImagine a graph showing how bumpy the spread of tiny particles called axions might be. The study describes a peak shaped like a pyramid on that graph—not a real pyramid in space. With a special starting setup, radiation and a change called the QCD phase transition make the bumps much bigger. Scientists have not reported seeing this pattern in the sky here, but finding it might help them learn how much an axion weighs.

Flavor decoherence and washout timing in nonthermal leptogenesis after inflation

Boliang Yu, Ruixin Zhou

• High Energy Physics - Phenomenology

AstronomerThis theoretical study examines a sign reversal of the baryon asymmetry in nonthermal leptogenesis after hilltop inflation. Along the investigated mass trajectory, lowering the lighter heavy-neutrino mass, N1, delays its washout relative to electron–muon flavor decoherence while leaving the dominant N2-decay injection nearly unchanged. With source and background fixed, shifting the washout history without changing its shape or integrated strength reproduces more than 99% of the N2-source yield changes at two physical target masses. A decomposition of the N2 CP source finds that its projector-aligned component remains positive, whereas its initially trace-free component reverses its propagated contribution and accounts for about 99.7% of the fixed-source timing contrast. Rapid damping of electron–muon coherence largely suppresses this contrast; rapid chemical equilibration does not. The interpretation is that later washout encounters a more decohered flavor state, weakening the positive electron–muon contribution enough for negative diagonal contributions to set the final sign. At a mass recalculated to match the observed baryon yield, increasing the muon collision operator by 10% flips the sign in a fixed-input sensitivity test. These results concern the studied model and controlled comparisons, not an observed reversal of the cosmic asymmetry.

PublicWhy might an early-universe model switch from producing an excess of matter to an excess of antimatter? This theoretical study finds that timing can be decisive. In the model, decays of a heavier neutrino state supply most of the initial imbalance, while processes involving a lighter state later erase parts of it. Lowering the lighter state's mass mainly delays that erasing process rather than changing the initial supply. By then, quantum coherence between electron and muon flavors has faded further, so the erasing process acts on a different mixture: positive contributions weaken, and negative ones can dominate. Controlled calculations reproduce nearly all of the studied change by shifting the timing alone. The outcome is also sensitive to collision physics: a 10% increase in the modeled muon collision operator reverses the sign in one fixed-input test. This is a result within the model, not evidence that the universe's actual matter excess reversed.

Young explorerScientists used a model to explore why the young universe might make more matter than antimatter, or the other way around. Imagine adding two kinds of blocks, then taking some away. The model says that taking blocks away later can change which kind is left over, because the mixture changes while you wait. This is an idea tested with calculations, not something scientists watched happen.

Gravitational Waves and Nambu-Goldstone Bosons from Infrared-Finite Cosmic Strings

Hajime Fukuda, Shuailiang Ge, Keisuke Harigaya

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

AstronomerThe abstract presents a theoretical argument concerning skyrmion lines and semi-local strings, infrared-finite cosmic strings arising in theories with spontaneously broken global symmetries. Unlike global U(1) strings, these defects lack the long-range Nambu–Goldstone boson (NGB) profile that produces a logarithmically infrared-divergent string tension. The authors argue that NGB emission from low-frequency oscillations is strongly suppressed, suggesting that their gravitational-wave signals may be comparable to those of local strings. This is a theoretical possibility, not a reported observational detection.

PublicSome theories predict cosmic strings: threadlike structures associated with broken symmetries. This abstract considers two types, called skyrmion lines and semi-local strings. Unlike another type known as global U(1) strings, they lack an extended field pattern that makes the string tension grow logarithmically with the distance scale considered. The authors argue that slow oscillations of these strings would emit very little energy as Nambu–Goldstone bosons. Their gravitational-wave signals might therefore be comparable to those of local cosmic strings, but the abstract reports a theoretical argument rather than an observation.

Young explorerSome science theories say space could have things like very thin threads. The scientists think two special kinds of these threads would give off very little energy as tiny particles when they wiggle slowly. They might make ripples in space like another kind of space thread does. This is an idea from a theory, not something the scientists report seeing.

Universal Relations Meet Causality: Bounding the Dynamical Love Number of Neutron Stars

Alex Kehagias, Antonio Riotto

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

AstronomerThis theoretical study derives an upper bound on the leading, second-order-in-frequency correction to neutron-star tidal deformability. Under suitable conditions, causality, reality and passivity make a rescaled response a holomorphic self-map of the upper complex frequency half-plane, allowing application of the Schwarz–Pick theorem. Comparison with recent published dynamical-response calculations, which also show a tight correlation between static deformability and its second-order correction, finds saturation of the bound to within a few per cent. The authors interpret this as quantitative confirmation of f-mode dominance in the relativistic regime. Static deformability combined with an independent f-mode frequency determination may therefore provide an equation-of-state-independent upper limit on the dynamical tide; this possibility is not presented as an observational result.

PublicA neutron star changes shape under tidal forces, and its response depends on how quickly those forces vary. Using physical constraints and a mathematical theorem, this study places an upper limit, under suitable conditions, on the leading correction to its response to steady tides. Recent published calculations come within a few per cent of that limit. The authors interpret this agreement as confirmation that a characteristic stellar vibration called the f-mode dominates the changing tidal response. They suggest that knowing both the steady tidal response and the f-mode frequency independently may let researchers limit the dynamical response without specifying the star’s equation of state—the relationship describing its matter. These findings come from theory and calculations, not new observations.

Young explorerA neutron star can change shape when something pulls on it. Scientists used math to find a limit on how much its response can change when the pulling changes speed. Other calculations came very close to that limit, suggesting that one kind of star vibration does most of the work. This is a math result, not something newly seen in the sky.

Black Holes in the Red-sequence Elliptical Galaxies at Redshifts ∼0.7-2.5: Not Dark Energy Source but Remnants of Little Red Dots

Lei Lei, Ze-Fan Wang, Yi-Ying Wang+2 more

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena
• General Relativity and Quantum Cosmology

AstronomerThe authors test the proposal that black holes supply dark energy through cosmological coupling, for which strong evidence had previously been claimed from black-hole mass growth in red-sequence elliptical galaxies at z ≤ 2.5. Using a sample of very-high-redshift AGNs detected by JWST in red-sequence elliptical galaxies, they report rejecting this possibility at a confidence level exceeding 10σ. They further argue that JWST’s Little Red Dots, characterized by low accretion rates, can evolve into red-sequence elliptical galaxies hosting relatively low-mass black holes at z ≈ 0.7–2.5 without cosmological coupling. This evolutionary connection is an interpretation, rather than a directly observed sequence, and the abstract does not detail the assumptions behind the reported rejection.

PublicOne proposed explanation for mysterious dark energy is that black holes produce it through a connection with the expansion of the universe. Earlier research had claimed strong support for this idea. By analyzing very distant active galactic nuclei detected by the James Webb Space Telescope, the authors now report evidence against it, with a statistical confidence exceeding 10 sigma. They also suggest that objects called Little Red Dots, whose black holes take in material slowly, could grow into galaxies containing relatively low-mass black holes without needing that connection to cosmic expansion. This proposed evolutionary path is not a directly watched transformation, and the abstract does not explain the assumptions underlying the statistical claim.

Young explorerScientists wonder whether black holes could make something mysterious called dark energy. They studied faraway galaxies seen by the James Webb Space Telescope and say their results strongly disagree with that idea. They also think tiny-looking objects called Little Red Dots could become galaxies with smaller black holes without that special connection to the growing universe. That is an explanation of how the objects might change, not something the scientists watched happen.

A dense dark matter core of the subhalo in the strong lensing system JVAS B1938+666

Lei Lei, Yi-Ying Wang, Qiao Li+7 more

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena
• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology

AstronomerA non-parametric mass reconstruction of the previously identified dark subhalo in the strong-lensing system JVAS B1938+666 yields a cored density profile, with core radius approximately 0.5 kpc and central density approximately 2.5 × 10^7 solar masses per cubic kiloparsec. Both self-interacting dark matter (SIDM) and fuzzy/wave dark matter (ψDM) fit the reconstructed profile significantly better than the standard Navarro–Frenk–White profile. The ψDM fit gives mψ = 1.32^{+0.22}_{-0.31} × 10^-22 eV, while a Bayes factor of 14.44 favors SIDM over ψDM. The inferred core is consistent with core–halo mass scaling relations observed in Local Group dwarf spheroidals. These model comparisons may help address the core–cusp discrepancy in ΛCDM substructure predictions, but do not establish the nature of dark matter.

PublicResearchers used gravitational lensing—the bending of light by gravity—to reconstruct how mass is distributed in a previously discovered dark-matter clump in the system JVAS B1938+666. The reconstruction indicates a central core rather than the sharply rising central density described by the standard profile used for comparison. Two alternative dark-matter models fit this inferred structure significantly better: one in which dark matter interacts with itself, and another in which it behaves like a wave. The comparison favors the self-interacting model over the wave model. The core also agrees with relationships found in nearby dwarf galaxies. This could help explain a mismatch between predicted and inferred dark-matter structures, but it does not settle what dark matter is.

Young explorerDark matter is something we cannot see directly, and scientists still do not know what it is. They studied how a hidden clump bends light to work out where its matter is. Their picture suggests that the middle is spread out instead of rising into a sharp peak. They tried two ideas about dark matter: that it can interact with itself, or that it acts like a wave. Both matched the picture better than the usual comparison, and the first matched best. That is a clue, not proof of what dark matter really is.

Euclid: Impact of halo mass-conversion model assumptions on galaxy cluster number-count analyses

T. Gayoux, P.-S. Corasaniti, T.R.G. Richardson+97 more

AstronomerThis study tests how halo-mass conversions affect cosmological constraints from cluster number counts, motivated by the large cluster catalogues expected from Euclid. Halo mass function fits can be calibrated using N-body haloes with spherical masses defined at the virial overdensity, but a conversion is needed when the mass function and scaling relation use different mass definitions. Tests with synthetic N-body data show that conventional conversions assuming a concentration–mass relation can produce systematic shifts exceeding 2σ, depending on the mass definition and assumed relation. Conversions based on halo sparsity statistics yield systematic biases smaller than the statistical errors in every case examined. These are simulation-based findings, not results from observed Euclid cluster counts, and their scope is limited to the cases tested.

PublicCounting galaxy clusters can help scientists study the universe, and the Euclid survey is expected to provide large catalogues for this purpose. But the theoretical predictions and the relationships used to estimate cluster masses may define mass differently, requiring a conversion. Using simulated data, the researchers found that a standard conversion based on how concentrated a cluster's dark-matter halo is can noticeably distort the inferred properties of the universe. In some tested cases, the shift exceeded twice the statistical uncertainty. An alternative conversion using a measure called halo sparsity kept these distortions below the statistical uncertainty in all cases studied. This is a promising simulation result, not yet a finding from Euclid observations or a guarantee for every possible case.

Young explorerScientists want to count big groups of galaxies to learn about the universe. But they can use different rules to say how heavy each group is, so they need a way to change from one rule to another. They tried this with pretend groups made in computer simulations. One usual way sometimes made the answer about the universe wrong by more than the expected uncertainty. Another way kept that mistake smaller than the uncertainty in every test they tried. They still need to be careful: these tests used computer-made groups, not real groups seen by Euclid.

Banana Split: Improved Cosmological Constraints with Two Light-Curve-Shape and Color Populations Using Union3.1+UNITY1.8

David Rubin, Taylor Hoyt, Greg Aldering+1 more

AstronomerThe authors apply UNITY1.8 to the updated Union3.1 compilation, replacing the usual single-population SN Ia treatment with a two-mode model. They find evidence for distinct light-curve-shape and color distributions, different shape–magnitude standardization relations, and differing population distributions with host stellar mass and redshift. The residual host-mass luminosity step is consistent with zero for unreddened SNe, while the constraint on the difference in red-color standardization between low- and high-mass hosts tightens significantly. Fitting the same SNe with two modes yields smaller estimated cosmological uncertainties than a single-mode fit; tests on two-mode simulations show similar trends. Under flat ΛCDM, SNe alone give Ω_m = 0.334 (+0.025, −0.024). Under a flat w₀–wₐ model, combining SNe, BAO, and CMB gives w₀ = −0.760 (+0.084, −0.082) and wₐ = −0.79 (+0.28, −0.30). Relative to single-mode UNITY, the two-dimensional w₀–wₐ tension with flat ΛCDM decreases by only 0.1 sigma, remaining approximately 3 sigma.

PublicType Ia supernovae help researchers measure cosmic expansion and constrain dark energy, but their brightness must first be calibrated. This study updates that calibration by treating the explosions as two populations rather than one. The analysis finds evidence that the populations differ in how their brightness changes over time, their colors, their brightness-calibration relationships, and their distribution among galaxies and across cosmic history. For supernovae whose colors are not reddened, a leftover brightness difference associated with host-galaxy mass is consistent with zero in the new analysis. The two-population model gives smaller estimated uncertainties on cosmological parameters, and tests using simulated two-population data show similar trends. When supernovae are combined with baryon acoustic oscillation and cosmic microwave background data, the results remain about 3 sigma away from a flat cosmological model with constant dark energy—only slightly closer than in the earlier, single-population analysis. This is a model-dependent statistical tension, not proof that dark energy changes over time.

Young explorerScientists use exploding stars to learn how the universe grows. To do that, they need to work out how bright the stars really are. This study finds clues that these explosions come in two groups, with different colors and different ways of getting brighter and dimmer. Treating them as two groups makes the scientists’ answers less uncertain. They also tried this idea with pretend star data made on a computer and saw a similar pattern. The new answers still do not quite match one usual picture of how the universe grows, but that does not prove the picture is wrong.

Simulation-based inference from the Lyman-alpha forest 1D power spectrum with CAMELS

Francesco Sinigaglia, Patricia Iglesias-Navarro, Matteo Viel

AstronomerThe authors present the first full simulation-based inference analysis of the Lyman-alpha forest 1D power spectrum, using CAMELS hydrodynamic simulations with IllustrisTNG and SIMBA at 2.0 < z < 3.5. A normalizing flow estimates posteriors for two cosmological parameters, Omega_m and sigma_8, and four supernova and AGN feedback parameters. With training and testing on the same galaxy formation model, inferred cosmological values deviate from the simulation inputs by less than 10% in at least approximately 75% of cases for Omega_m and 90% for sigma_8, with precision better than 10% for both. The feedback parameters instead converge to their prior means because of the limited simulated volume. Cross-model testing substantially worsens accuracy and precision and produces an approximately 10% positive bias in sigma_8. Training jointly on both simulation models recovers unbiased constraints in these tests. These are simulation-validation results, not cosmological measurements from observed forest data; they support joint-model training as a promising way to mitigate model-dependent inference.

PublicThis study tests whether artificial intelligence can infer cosmological properties from the Lyman-alpha forest's statistical patterns in computer simulations. When the AI learns from and is tested on simulations using the same model of galaxy formation, it recovers the two cosmological inputs accurately in most cases. But when it learns from one galaxy formation model and is tested on the other, its estimates become less accurate and less precise, with one cosmological parameter, sigma_8, biased about 10% too high. Training on both models together removes that bias in the simulation tests. The method does not meaningfully constrain the four parameters describing feedback from supernovae and active galactic nuclei, because the simulated volume is too limited. The results suggest a promising approach for future cosmological studies, but they are not measurements of the real Universe.

Young explorerThe scientists taught an AI helper using computer-made universes. They asked it to work out two numbers used to make those universes. It usually did well when the practice universes and the test universes were made the same way. When they were made differently, the helper made bigger mistakes and guessed one number too high. Practicing with both kinds helped fix that problem in the tests. Some other numbers were still too hard to work out because the computer-made universes were too small. This is a promising practice test, not yet a measurement of our real Universe.

Alleviating the Hubble Tension Using Coupled Dark Energy - Dark Matter Interaction

Yismaw Wassie Ambelu, Amare Abebe, Solomon Belay Tessema+1 more

AstronomerThe authors constrain two interacting dark-energy models using DESI DR2 BAO, Planck 2018 CMB, Pantheon+ SNe Ia, and KiDS-1000/DES-Y3 weak lensing. In ξCDM, with free coupling ξ and fixed equation-of-state parameter w₀, Planck alone gives H₀ = 71.59 (+1.69/−2.30) km s⁻¹ Mpc⁻¹; the full combination gives 69.72 (+0.50/−0.41), reducing the reported H₀ tension from approximately 5.0σ to 2.8σ. Allowing both ξ and w₀ to vary in ξwCDM gives 72.46 (+4.05/−3.66) from Planck alone and 70.22 (+0.45/−0.40) from the full dataset, with residual tension of approximately 2.5σ. The latter fit favors phantom w₀ = −1.116 ± 0.043 and ξ = −0.107 (+0.012/−0.023), corresponding under the stated convention to energy transfer from dark energy to dark matter. These are model-dependent inferences, not direct detections of energy transfer. Model selection is mixed: for ξwCDM, Planck+BAO+SN gives Δχ² = −14.60 and ΔAIC = −10.60, but ΔBIC = +0.30 weakly favors ΛCDM. Adding weak lensing reduces the fit improvement to Δχ² = −6.67 and yields ΔBIC = +8.23, strongly favoring ΛCDM. The models therefore alleviate rather than resolve the tension, with their added freedom insufficient to overcome the BIC penalty.

PublicDifferent ways of estimating how fast the universe expands give disagreeing answers. This study tests whether models in which dark energy transfers energy to dark matter could ease that disagreement. The researchers fit two versions of this idea to observations of the early universe, galaxy-distance patterns, supernovae, and the bending of light by matter. Combining all the data, both models raise the inferred expansion rate and reduce—but do not eliminate—the discrepancy. The more flexible model favors dark-energy behavior that includes energy transfer to dark matter, but this is an inference within the model, not a direct observation of that transfer. Whether the extra complexity is justified depends on the statistical test: one comparison favors the flexible model without the light-bending data, while another strongly favors the standard ΛCDM model when those data are included. The interaction remains a possible explanation, not an established solution.

Young explorerScientists use different clues to work out how fast the universe is growing, but their answers do not quite match. They tested an idea where something called dark energy gives energy to dark matter. With this idea, the answers get closer, but they still do not match. The clues do not prove that this sharing really happens, and some checks favor the usual explanation instead.

Whispers of Supergravity in Gravitational Wave Backgrounds: Determining the Gravitino Mass from Cosmic Thermal History

Angus Spalding, Stephen F. King

• High Energy Physics - Phenomenology

AstronomerThe authors propose using a stochastic gravitational-wave background to probe gravitinos with masses above the electroweak scale, beyond collider reach. In their scenario, gravitinos decay before Big-Bang Nucleosynthesis (BBN) but first generate an early matter-dominated epoch. This epoch imprints two characteristic frequencies, marking its onset and end, on a primordial gravitational-wave spectrum. The analysis indicates that both the gravitino mass and initial abundance can be inferred if matter domination occurs while the background is freely propagating; the mass can still be determined more generally, including when the background is sourced during that epoch. Future gravitational-wave observatories could probe masses from the BBN bound of order 100 TeV to order 10^10 TeV. The reported NANOGrav signal could potentially probe masses of 500–10^4 TeV, but only if its origin is primordial. These are proposed inference capabilities, not a detection of gravitinos or a measurement of their mass.

PublicGravitinos could be too massive for particle colliders to investigate, but this study proposes another route: looking for their effects on gravitational waves from the early universe. In the proposed scenario, gravitinos briefly make matter dominate the universe before they decay, ahead of the formation of light elements. That period would leave two characteristic features in the gravitational-wave background, marking when it began and ended. The authors argue that these features could reveal the gravitino mass and, under particular conditions, how abundant gravitinos initially were. Future observatories could test a very wide range of masses. A gravitational-wave signal already reported by NANOGrav might also provide a test, but only if it originated in the early universe. The study does not establish that gravitinos exist or that they caused the reported signal.

Young explorerScientists wonder whether tiny particles called gravitinos were around when the universe was very young. If they were, they could have changed the universe for a little while before disappearing. That change might have left two clues in old ripples in space. Scientists propose looking for those clues to learn about the particles. They have not found gravitinos this way yet.

PHANTOM: A MATLAB and Octave Toolbox Connecting Linear Field Statistics to Dark Matter Halo Observables

Mohammad Abu Thaher Chowdhury

• Instrumentation and Methods for Astrophysics

AstronomerThe authors present phantom, a public MATLAB toolbox and Octave package connecting the linear density field to theoretical dark matter halo observables. It combines background cosmology and linear power-spectrum, variance, and correlation-function calculations with halo mass functions, linear bias, density profiles, and concentration–mass relations for cold, warm, and fuzzy dark matter models. A cosmology structure constructed once and passed through the routines keeps halo statistics and structure calculations consistent. Outputs on user-defined grids include enclosed mass, circular velocity, projected density, and lensing convergence. Core routines agree at the sub-percent level with colossus, hmf, and halomod for shared models across the tested quantities; this is code-to-code validation, not observational confirmation of the dark matter scenarios. The package fills a stated gap in native MATLAB/Octave implementations and is released under the MIT licence.

PublicThis work introduces phantom, freely available software for calculating how theoretical models of dark matter relate to the properties of dark matter halos. Written for MATLAB and Octave, it supports cold, warm, and fuzzy dark matter models and calculates quantities such as halo abundance, mass distribution, and effects on gravitational lensing. It uses one shared description of the universe so that its calculations remain consistent with one another. In tests using models shared with existing software packages, its answers differed by less than one percent. That agreement checks the software calculations; it does not establish which dark matter model describes the real universe.

Young explorerThe researchers made a computer toolbox called phantom to help study dark matter, which we cannot see directly. It works out what different ideas about dark matter say about big clumps of it called halos. They checked its answers against other computer tools, and the answers were very close when the tools used the same models. That means the tools agree, not that we know which idea about dark matter is right.

The Treble Clef radio phoenix and its old nonthermal filaments

A. Botteon, M. Brienza, K. Rajpurohit+15 more

• High Energy Astrophysical Phenomena

AstronomerLoTSS inspection identified a bright, filamentary radio source near the Galactic plane (b ≈ 0.5°), previously considered a pulsar and subsequently associated with an obscured galaxy cluster. Chandra and SRG/eROSITA observations provide the first characterization of the host cluster’s redshift, mass, temperature, X-ray luminosity, and dynamical state. Spatially resolved, multifrequency analysis using new uGMRT data and LoLSS observations leads the authors to classify VLSS J0318.9+5755, nicknamed the Treble Clef, as a radio phoenix in a massive, merging cluster in the Zone of Avoidance. Its spectrum is extremely steep, reaching α > 4 between 400 and 650 MHz. The authors speculate that merger-driven intracluster gas motions shape its complex filaments and may also generate a candidate central radio halo, whose detection remains tentative. Its filamentary structure and brightness below roughly 1 GHz motivate proposed high-resolution, very-low-frequency LOFAR2.0 follow-up.

PublicAstronomers studied a bright, threadlike radio source nicknamed the Treble Clef because of its shape. Once thought to be a pulsar, it is now interpreted as a radio phoenix belonging to a massive cluster of galaxies undergoing a merger, largely hidden behind the plane of the Milky Way. X-ray observations allowed the team to characterize the cluster, while observations at several radio frequencies mapped how the source’s radio emission changes across it. The emission falls very sharply with increasing frequency. The researchers suggest that gas stirred by the merger could be shaping the tangled radio threads and could also explain a possible diffuse radio halo near the cluster’s center. Those explanations remain uncertain, and the halo detection is tentative. The team recommends sharper observations at very low radio frequencies to investigate further.

Young explorerScientists found a bright, twisty pattern using telescopes that detect radio waves our eyes cannot see. They nicknamed it the Treble Clef because it looks like a music symbol. They think it belongs to a huge group of galaxies that is joining with another group, behind our own galaxy. Moving gas might be making the twisty shapes, but the scientists are not sure. They also spotted hints of a faint radio glow in the middle of the group. They want to take a closer look with a radio telescope.

Analytic Approximations for Fermionic Preheating

Heather E. Logan, Daniel Stolarski, Fazlul Yasin

• High Energy Physics - Phenomenology

AstronomerThis theoretical study examines non-perturbative production of non-thermal fermions during coherent scalar-field oscillations in λφ⁴ inflation. The momentum distribution depends on the coupling parameter q: for q ≳ 0.01, an approximately half-filled Fermi sphere generated by non-adiabaticity dominates the total number density, whereas for q ≲ 0.01, higher-momentum resonance peaks provide the main contributions. The authors obtain a simple relation predicting resonance-peak momenta for any q and numerical approximations to the number-density integrals. They find number-density scalings proportional to q^(1/2) for q ≲ 0.01 and q^(3/4) for q ≳ 10. Lower bounds on the fermion mass are estimated under the assumption that these particles constitute all dark matter; this is not an observational identification of dark matter.

PublicThe researchers study a theoretical way that an oscillating field in the early universe could create particles called fermions. Their calculations show that the particles’ momentum distribution changes with a parameter controlling their interaction with the field. Above roughly q = 0.01, most particles occupy a broad region of lower momenta; below roughly that value, concentrations at particular higher momenta dominate. The study provides a rule for predicting where those concentrations occur and approximations for how the total particle density grows with q. If these particles account for all dark matter, the authors estimate limits on how light they could be. The work does not establish that dark matter was actually produced this way.

Young explorerThe scientists used math to study how a field wobbling in the very young universe might make tiny particles. In their model, changing how strongly the particles interact with the field changes how much motion the particles have and how many are made. They also asked how light the particles could be if they made up all of the mysterious stuff called dark matter. They have not shown that these particles really are dark matter.

Detector orientation matters: Consequences for gravitational-wave background detectability

Nelson Christensen, Joseph D.Romano, Mairi Sakellariadou+1 more

• General Relativity and Quantum Cosmology
• Instrumentation and Methods for Astrophysics
• High Energy Physics - Theory

AstronomerUsing standard cross-correlation techniques on a few simple examples, the authors illustrate how the relative orientation of two Earth-based L-shaped laser interferometers can strongly affect sensitivity to gravitational-wave backgrounds, both isotropic and anisotropic. Such searches depend on detector geometry, including physical separation and relative orientation. The abstract describes illustrative analyses, not an observed background detection, and gives no quantitative sensitivity estimates.

PublicSearching for a background of gravitational waves involves comparing signals from different detectors. How far apart the detectors are and how they are turned relative to each other affects the search. Using a few simple examples, the authors show that the relative orientation of two L-shaped detectors on Earth can make a large difference in how detectable a background would be, whether it is the same in every direction or varies across the sky. This is an illustration of how searches work, not a report of detecting such a background.

Young explorerScientists use big L-shaped tools to look for tiny ripples in space. They compare what two tools pick up. In a few simple examples, the scientists show that turning one tool compared with the other can make the ripples much easier or harder to find. They are showing how to look, not saying they found the ripples.

Stochastic template banks for GW searches using low-discrepancy sequences

Tarun Kumar, Anand S. Sengupta

• General Relativity and Quantum Cosmology
• Computational Physics

AstronomerThis computational study tests low-discrepancy sequences as an alternative to uniform random proposals in stochastic template-bank construction for matched-filter searches for compact binary coalescences. The tested banks achieve comparable recovery fractions with 27.5% fewer proposal points in two dimensions, about 12% fewer in three dimensions, and 17% fewer in a four-dimensional eccentric equal-spin toy bank. Final template counts are much less sensitive to proposal sampling, consistent with metric-volume constraints on coverage. A slab-wise coarse prefilter for candidate rejection under strongly anisotropic metrics yields an approximately 1.28-fold total construction speed-up in the 4D toy bank. The main benefit is a smaller initial proposal set, reducing memory use and bookkeeping rather than substantially reducing the final bank size. These are bank-construction results, not new gravitational-wave observations; the four-dimensional test uses a toy bank.

PublicGravitational-wave searches compare data with banks of predicted signals. Building these banks requires choosing enough patterns to cover the possible signals without unnecessary duplication. In computational tests, the researchers replaced random trial choices with sequences that spread the choices more evenly. This achieved comparable signal-recovery performance with fewer trial points, although the number of patterns ultimately kept changed much less. A separate shortcut made construction about 1.28 times as fast in a simplified four-dimensional test. The main improvement is less memory use and administrative work while building the banks, not evidence of new gravitational-wave detections.

Young explorerScientists look for tiny ripples in space by checking lots of possible ripple patterns. This study tried a more orderly way to choose which patterns to test, instead of choosing them randomly. In computer tests, it needed fewer tries and did about as well at finding matching patterns. It mostly made the preparation easier, rather than making the finished pattern collection much smaller. It did not report finding new ripples in space.

Building a Better Beta: Nucleation and Timescales in Cosmological Phase Transitions

William Searle, Csaba Balázs

• High Energy Physics - Phenomenology

AstronomerThis theoretical study examines bubble nucleation and transition timescales in first-order early-universe phase transitions that can generate a stochastic gravitational-wave background. Rather than characterizing the transition through a Taylor expansion of the false-vacuum decay rate, the authors propose using the bubble-lifetime distribution and define a new timescale, beta_nu, as its first moment. They show that it recovers previous timescale definitions in appropriate limits while avoiding their pathologies. Using this definition shifts the predicted gravitational-wave peak amplitude by up to an order of magnitude relative to earlier definitions. These are theoretical predictions, not an observed gravitational-wave signal.

PublicA sudden change in the state of the early universe could have produced expanding bubbles and a background of gravitational waves. This study proposes a new way to describe the timing of that change, based on how long the bubbles last rather than the usual mathematical approximation to their formation rate. The authors find that their approach agrees with earlier descriptions in suitable limits while avoiding some of their problems. It can change the predicted strength at the peak of the gravitational-wave signal by as much as a factor of ten. The work aims to improve predictions for future detectors; it does not report a detection.

Young explorerThe very young universe might have changed by making bubbles. Those bubbles could have made tiny ripples in space. Scientists tried a new way to describe how long the bubbles last. Their calculations show that this can make a big difference to how strong they expect the ripples to be. They have not found those ripples in this study; they are working out what to look for.

Power-law Coupling and Mock Validation of a Surface-density Anisotropy Diagnostic for 85 Rich Galaxy Clusters

Sardor Sharipbayevich Kutlimuratov, Ikram Uralbayevich Tadjibayev

AstronomerReanalysis of 20-annulus profiles for 85 optically rich clusters finds that the surface-density anisotropy diagnostic A_ani is poorly constrained: 24 fits hit the canonical grid ceiling of 1.92, 12 hit the extended ceiling of 1.99, 69 upper Δχ²=1 bounds remain open, and only four clusters have two-sided intervals. For 40 preselected power-law fits, the observed Spearman correlation between profile slope α and A_ani is 0.616. Model-native forward-recovery tests recover all 935 noiseless inputs within 0.02, but 46,750 Poisson realizations matched to observed count and background conditions yield RMSE 0.992 and recovery correlation ρ=0.093; 40.0% hit the canonical ceiling and 81.4% have open upper intervals. Fixing background and radial scale reduces RMSE to 0.564 in a separate sensitivity test. Power-law-generated Poisson controls reproduce the observed slope association, with median mock correlation 0.608 and a 95% range of 0.453–0.731. These tests indicate numerical recoverability without noise, but unreliable identification for individual clusters with the available photometry. The slope association can reflect shared projected profile shape rather than independent evidence for orbital anisotropy.

PublicThe researchers tested whether a number calculated from the distribution of galaxies in a cluster can reliably diagnose differences in their orbital directions. In observations of 85 clusters, the number was usually poorly constrained, often reaching the maximum allowed by the fitting procedure. Among 40 selected clusters, it correlated with how steeply galaxy density changes with distance from the cluster center. Simulations clarified the limitations: perfectly noise-free model profiles recovered the intended number accurately, but simulated galaxy counts with realistic statistical fluctuations did not. Other simulations, built from simple power-law profiles, reproduced the observed correlation. The authors therefore conclude that the available observations cannot reliably determine this diagnostic for individual clusters. The correlation may arise from the shape of the galaxy distribution itself and is not independent evidence about orbital directions.

Young explorerScientists looked at groups of galaxies and tested a number that might help tell how the galaxies move. But the real pictures did not pin down that number well. In pretend galaxy groups, the test worked when the information was perfect, but not when the counts were noisy like the real ones. A pattern they found could come from where the galaxies are, rather than how they move.

EMIR confirmation of the high-z Lyα blob SHARDS20018464

S.Zarattini, F. Garzón, C. Muñoz-Tuñón

• Cosmology and Nongalactic Astrophysics

AstronomerKs-band spectroscopy of the Lyα blob SHARDS20018464 with EMIR on the 10.4 m GTC, using its upgraded H2RG detector, identified the [OIII] doublet at the positions of both the blob and its companion galaxy. A 4-hour exposure yielded line fluxes of order 10^-17 erg s^-1 cm^-2. Analysis of the two lines individually gives a mean redshift of z = 3.59 ± 0.01, higher than but consistent within uncertainties with the published photometric estimate of z = 3.49. The measured doublet flux ratio, R = 2.92, is close to the theoretical value of 2.98, strongly supporting the line identification. The redshift is consistent with the previously inferred physical properties. The blob's small size, 5–8 kpc compared with roughly 100 kpc for typical samples, and its position beside the companion support the proposal that it could represent a new class of compact Lyα emitters. The data also support, rather than establish, photoionisation by a cluster of young, massive stars.

PublicAstronomers used the EMIR infrared spectrograph on the 10.4-metre GTC telescope to study a glowing cloud called SHARDS20018464 and a nearby companion galaxy. In a four-hour observation, they detected two emission lines from oxygen. The relative strengths of these lines closely match the theoretical expectation, giving strong evidence that the lines were correctly identified. The spectra indicate a redshift of 3.59 ± 0.01, consistent within uncertainties with the earlier estimate of 3.49 based on photometry. The cloud is unusually compact: about 5–8 kiloparsecs across, compared with roughly 100 kiloparsecs for typical clouds in the samples discussed. Its size and location beside the galaxy strengthen the suggestion that it may be the first example of a new class of compact hydrogen-emitting clouds. The observations also support the idea that a group of young, massive stars supplies the radiation that makes the gas glow, but do not prove that explanation.

Young explorerAstronomers used a big telescope to look at a glowing cloud in space beside a galaxy. They found two special marks in its light that match what they expect from oxygen. The light also agrees with their earlier estimate of how far away the cloud is. This cloud is much smaller than many others like it, so it might be an example of a new kind of glowing cloud. A group of young, big stars may be making the gas glow, but the astronomers are not sure yet.

Probing departures from Schwarzschild geometry with the S301 star and kilometre-baseline interferometry

Rodrigo P. Silva, Alexandre C. M. Correia, Paulo J. V. Garcia

• General Relativity and Quantum Cosmology

AstronomerS301 has a pericentre one tenth that of S2, offering a closer probe of Sgr A*’s spin and departures from Schwarzschild geometry. The authors develop a post-Newtonian secular Hamiltonian framework for bound geodesics in stationary, axisymmetric spacetimes and calculate the maximum projected astrometric deviation over one orbit. They forecast that the expected GRAVITY+ precision could distinguish several nonrotating geometries and sizeable spin-induced deviations, while kilometre-baseline interferometry could probe substantially smaller departures. These are theoretical sensitivity forecasts, not reported detections of spin or non-Schwarzschild geometry.

PublicThe star S301 passes the black hole Sgr A* at one tenth the closest-approach distance of the star S2, making it a promising way to test how the black hole shapes space and time. Researchers developed a mathematical model to calculate how different spacetime geometries, including effects of black-hole rotation, could shift the star’s apparent position during an orbit. Their calculations suggest that GRAVITY+, at its expected precision, could detect some of these differences, while interferometry with telescopes separated by kilometre-scale distances could reveal smaller ones. The study predicts what these measurements could test; it does not report that such differences have been observed.

Young explorerA star named S301 swings much closer to a black hole than another star named S2 does. Scientists used math to work out how the black hole might change the path we see the star follow. Very careful telescope measurements could help them learn whether the black hole is spinning and test how it bends space and time. They have worked out what we might be able to see, but they have not seen those changes yet in this study.

Cracking open the "dragon egg": ALMA 1.3mm observations of a compact, young high-mass core candidate at 30mas resolution

A. T. Barnes, J. D. Henshaw, Á. Sánchez-Monge+14 more

• Solar and Stellar Astrophysics

AstronomerNew ALMA Band 6 observations test the proposed massive prestellar core candidate C2c1a, the “dragon egg,” at 0.035–0.078 arcsec resolution, corresponding to approximately 175–400 au at 5 kpc. Although the region fragments, its brightest component, C2c1a(a), remains a single continuum peak down to approximately 175 au, with a deconvolved radius of approximately 87 au and a nearest neighbouring fragment approximately 2400 au away in projection. Its approximately 40 K peak brightness temperature exceeds the approximately 10 K gas temperature inferred from lower-resolution NH3 data, indicating a strong radial temperature gradient. Temperature-dependent continuum mass estimates span approximately 2–30 solar masses, implying H2 number densities above 10^9 cm^-3; lower-resolution observations indicate an approximately 110-solar-mass reservoir on approximately 10^4 au scales. No strong hot-core tracers are seen, H2CO and CO emission is weak and spatially extended, and no high-velocity outflow is unambiguously associated with C2c1a(a). The observations establish an exceptionally compact core within a massive cold reservoir, but neither additional unresolved fragmentation nor its evolutionary status is settled. The authors interpret it as potentially tracing the earliest formation of a central protostellar seed, rather than establishing it as a massive prestellar core.

PublicAstronomers used new high-resolution ALMA observations to examine the “dragon egg,” a cloud core proposed as a possible birthplace of a massive star before a star has formed. The surrounding region contains several fragments, but its brightest component remains a single compact peak at the resolution achieved. That component has an estimated radius of about 87 times the Earth–Sun distance and sits inside a much larger, cold reservoir containing about 110 times the Sun’s mass. The compact component’s own estimated mass ranges from about 2 to 30 solar masses because it depends strongly on temperature. Its peak brightness temperature is about 40 K, higher than the roughly 10 K gas temperature measured at lower resolution, indicating that temperature changes substantially within the core. The researchers found no strong chemical signatures of a hot core and could not clearly link a fast gas outflow to this component. They suggest that it may contain a star’s earliest forming seed, but this is an interpretation, not a confirmed detection of a young star. Smaller fragments could also remain undetected within the observations’ resolution and sensitivity limits.

Young explorerAstronomers looked closely at a space cloud nicknamed the “dragon egg.” They saw several clumps, but the brightest little clump still looked like one piece in their pictures. It sits inside a much bigger, cold cloud and appears warmer toward its middle. The scientists think a baby star might just be starting to form there, but they are not sure yet. Their pictures also cannot rule out smaller pieces that are too tiny or faint to see.

DIGging into HII regions: the role of ionizing photon leakage and spectral hardening in coupling HII regions and diffuse ionized gas

Dalya Baron, Kathryn Kreckel, Gwen C. Rudie+15 more

AstronomerUsing PHANGS-MUSE observations of 19 nearby galaxies at 50–100 pc resolution, the authors analyze thousands of HII regions and diffuse ionized gas (DIG) sightlines. Both populations trace continuous sequences in optical line-ratio diagnostic diagrams: progressively fainter regions exhibit elevated high- and low-ionization ratios, with the DIG extending into the composite–LINER regime. The dependence on global specific star formation rate suggests harder ionizing radiation at greater star formation activity, contrary to expectations for increasing dominance by older stellar populations. Line-of-sight mixing accounts for only part of the trends. The authors develop a leakage model incorporating geometric dilution, attenuation, and spectral hardening as ionizing photons propagate through the diffuse interstellar medium. It predicts that fainter HII regions receive an increasing contribution from neighboring luminous regions. Joint modeling reproduces the HII-region luminosity distribution and DIG surface brightness with escape fractions of approximately 0.4–0.6 and ionizing-photon mean free paths of approximately 0.5–1 kpc; it reproduces the line-ratio sequences and their specific-star-formation-rate dependence qualitatively. These model-dependent results suggest, rather than establish, a non-local radiative feedback channel connecting compact star-forming regions to galaxy disks.

PublicObservations of 19 nearby galaxies show a continuous pattern linking bright clouds of ionized gas around young stars with the fainter, more spread-out ionized gas between them. As the gas becomes fainter, the relative strengths of its emission lines change systematically. The changes also suggest that galaxies with greater star formation activity relative to their stellar mass have more energetic ionizing radiation. Overlapping gas along the viewing direction explains some, but not all, of these patterns. The researchers therefore develop a model in which radiation escapes star-forming clouds and travels through the surrounding gas, becoming weaker and changing its mix of photon energies. The model predicts that faint clouds increasingly rely on radiation leaking from brighter neighbors. It matches the distribution of cloud luminosities and the brightness of diffuse gas when roughly 40–60% of ionizing photons escape their source regions and their average travel distance before absorption is about 0.5–1 kiloparsec. These are model-inferred values, not direct measurements. The model also broadly reproduces the emission-line patterns, suggesting that escaping radiation may connect local star-forming sites to gas across galaxy disks.

Young explorerStars can shine on gas and make it glow. Scientists looked at 19 galaxies and found that bright gas clouds and faint gas between them have linked patterns in their light. They made a model in which some light escapes a bright cloud and travels to other gas. The model suggests that dim clouds can get help glowing from brighter neighbors. It matches some things the scientists saw, but they have not proved that escaping light explains everything.

Molecular hydrogen formation on dust: The impact of gas-dust drift on formation efficiency

Stefan Reissl, Simon C. O. Glover, Ralf S. Klessen+2 more

• Earth and Planetary Astrophysics
• Mesoscale and Nanoscale Physics
• Computational Physics

AstronomerThis simulation study examines how gas-dust drift changes H2 formation through competition between enhanced H-atom collision rates and reduced sticking at higher impact energies. An event-driven kinetic Monte Carlo model tracks adsorption, migration, thermal desorption, and Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) reactions on spherical silicate and carbonaceous grains, using a shifted Maxwellian velocity distribution. Increasing drift makes adsorbed-H and H2-production distributions more anisotropic. With constant sticking probability, drift enhances formation, with efficiencies reaching ε = 0.3–0.4; with impact-energy-dependent sticking, strong drift suppresses formation on both materials, reducing efficiencies to ε = 0.01–0.03. Carbonaceous grains remain efficient at higher dust temperatures than silicates. ER reactions dominate most of the investigated parameter space and gain importance under strong drift as declining surface populations suppress LH reactions. These are model results, not observational measurements: their contrasting outcomes highlight the importance of treating both relative velocities and energy-dependent sticking in models of dynamically active environments.

PublicHydrogen molecules form mainly when hydrogen atoms meet on dust grains in interstellar space. This study used computer simulations to investigate what happens when gas moves relative to that dust. Faster relative motion brings more atoms to a grain, but higher-energy impacts can also make atoms less likely to stick. When the model kept the sticking chance constant, faster motion increased molecule formation. When sticking depended on impact energy, strong relative motion instead reduced it. The simulations also found that atoms and molecule formation became more unevenly distributed across grain surfaces, and that carbon-based grains remained effective at warmer temperatures than silicate grains. The findings show that more collisions do not necessarily mean more hydrogen molecules; the outcome depends on how readily atoms stick.

Young explorerTiny dust grains in space help hydrogen atoms join in pairs to make molecules. Scientists used a computer model to see what happens when the gas moves past the dust faster. More atoms hit the dust, but they may be less likely to stick. In the model, faster motion could help or hinder making pairs, depending on how sticking worked.

Spectroscopic Confirmation of the Milky Way Satellites Boötes V and Leo Minor I and the LMC Satellite DELVE 2: Three Small Ultra-Faint Dwarf Galaxies

W. Cerny, M. Geha, J. D. Simon+22 more

AstronomerThe first multi-object spectroscopy of Boötes V, Leo Minor I, and DELVE 2 identifies 13, 7, and 7 member stars, respectively, using at least two observing epochs per system with Keck/DEIMOS or Magellan/IMACS. These compact, ultra-faint outer-halo systems have half-light radii of 20–26 pc and heliocentric distances of 71–102 kpc. DELVE 2 has a tentatively resolved velocity dispersion of 2.1 (+1.5/−0.9) km/s; only upper limits are obtained for Boötes V (<2.7 km/s) and Leo Minor I (<7.8 km/s). All three are very metal-poor, with mean [Fe/H] between −2.85 and −2.15. Resolved metallicity dispersions of 0.46 (+0.18/−0.12) dex and 0.57 (+0.23/−0.18) dex underpin confident dwarf-galaxy classifications for Boötes V and Leo Minor I. DELVE 2 is most likely a dwarf galaxy, but its metallicity spread of 0.52 (+0.29/−0.25) dex is only modestly significant and rests on three stars. Orbital analysis in a joint Milky Way–LMC potential supports the first confirmation of DELVE 2 as a long-term bound LMC satellite. An empirical review finds that nearly every spectroscopically characterized Milky Way satellite with azimuthally averaged half-light radius >15 pc and half-light surface brightness >26.5 mag/arcsec² is likely a dwarf galaxy, offering a probabilistic classification guide for future Rubin, Roman, and Euclid discoveries.

PublicAstronomers measured the motions and iron content of stars in three tiny, faint stellar systems near the outskirts of the Milky Way: Boötes V, Leo Minor I, and DELVE 2. The clearest evidence comes from differences in iron abundance among their stars. These measurements lead the researchers to confidently classify Boötes V and Leo Minor I as dwarf galaxies. DELVE 2 is probably a dwarf galaxy too, although its evidence for an iron-abundance spread is less secure and comes from only three stars. The researchers tentatively measured a spread in stellar speeds in DELVE 2, while obtaining only upper limits for the other two systems. Their orbital analysis, which includes the gravity of both the Milky Way and the Large Magellanic Cloud, also identifies DELVE 2 as a long-term satellite of the latter. A broader review suggests that a combination of size and faint surface brightness can help estimate whether newly discovered stellar systems are dwarf galaxies, but this is a probabilistic guide rather than a definitive test.

Young explorerScientists studied three very faint groups of stars to find out what they are. They checked how the stars move and how much iron they contain. Differences in the stars’ iron helped show that two groups, called Boötes V and Leo Minor I, are tiny galaxies. The third, DELVE 2, probably is too, but the scientists are less sure because the iron clues come from just three stars. By working out its path through space, they also found that DELVE 2 stays tied by gravity to a galaxy called the Large Magellanic Cloud. These clues may help scientists recognize other tiny galaxies they find later.

Hierarchical Black Hole Mergers at High Redshift: Predictions for LISA and LGWA from SEEDZ

Daxal H. Mehta, Lewis R. Prole, John A. Regan+13 more

• Cosmology and Nongalactic Astrophysics

AstronomerThe SEEDZ cosmological zoom-in simulations investigate hierarchical black-hole assembly at z ≥ 10 in two independent regions, Rarepeak and Normal1, using no, weak, and standard thermal isotropic black-hole feedback. Stronger feedback substantially suppresses repeated mergers. In the no-feedback runs, some black holes undergo more than 50 mergers within a few hundred million years and acquire over 10^8 solar masses through mergers alone; with standard feedback, black holes rarely undergo more than three mergers. The authors treat the no-feedback case as an upper limit exceeding expected merger-driven growth in the Universe. Galaxy assembly, black-hole occupation fractions, and seed abundances remain broadly similar across the suites. Instead, the simulations attribute merger suppression to feedback disrupting dense gas around newly formed seeds, limiting early accretion and preventing runaway hierarchical merger growth. These are simulation findings, not observed merger populations. Feedback, seeding choices, and other subgrid prescriptions introduce degeneracies that must be disentangled ahead of LISA and other next-generation gravitational-wave facilities.

PublicComputer simulations suggest that energy released around growing black holes can strongly limit how often black holes merge in the early Universe. The researchers simulated two regions with three different treatments of this feedback. Without feedback, some black holes merged more than 50 times within a few hundred million years. With standard feedback, they rarely merged more than three times. The simulations indicate that feedback disrupts nearby dense gas, slowing young black holes' growth and preventing a chain of repeated mergers. The no-feedback case is an extreme upper limit, not what the authors expect in the real Universe. These predictions are not observations, and uncertainties in feedback and how black holes first form complicate their use for future gravitational-wave studies.

Young explorerScientists used computer models to see how black holes might grow when the Universe was very young. In some models, black holes joined together again and again. But when the models included energy released around growing black holes, that energy disturbed nearby gas. The black holes grew less and joined together less often. This is what the computer models suggest, not something scientists have watched happen.

Multiple H I 21-cm absorbers towards blazar PKS 1158+007

Abhisek Mohapatra, R. Srianand, R. Dutta

AstronomerMeerKAT observations toward the blazar PKS 1158+007 (J1201+0028; z_em = 1.369) reveal two intervening H I 21-cm absorbers separated by only Δz ≈ 0.04. The stronger system at z_abs = 0.5653 has integrated optical depth 1.31 ± 0.04 km/s and associated Mg II λ2796 absorption, with rest-frame equivalent widths of 1.40 ± 0.07 Å in SDSS and 1.21 ± 0.11 Å in DESI. The weaker system at z_abs = 0.5305 has integrated optical depth 0.31 ± 0.04 km/s but no detectable associated optical metal absorption. The authors describe it as a metal-poor absorber, although the reported metal-line nondetection is not a direct metallicity measurement. HSC PDR3 and DESI Legacy Surveys DR10 photometric redshifts identify a broad galaxy overdensity at z ≈ 0.53 ± 0.06. This suggests, but does not confirm, that the sightline intersects a complex large-scale structure or filament; follow-up observations are needed. The detections illustrate how blind H I 21-cm surveys can reveal cold gas missed by optical/UV metal-line selection.

PublicAstronomers used the MeerKAT radio telescope to detect two clouds of neutral hydrogen along the same line of sight to a distant bright source called a blazar. Such a pair within a small redshift interval is rare. One cloud also produces a clear magnesium absorption signature in optical spectra, while the other has no detectable optical absorption from heavier elements. The researchers interpret the second cloud as metal-poor, but not detecting those signatures does not directly measure its chemical abundance. Galaxy estimates from imaging suggest that both clouds may lie within a larger crowded region of galaxies, possibly a filament, though further observations are needed to confirm that connection. The discovery shows how radio searches can find cold gas that searches relying on optical or ultraviolet signatures of heavier elements may overlook.

Young explorerScientists used a radio telescope to look toward a very bright object far away. They found two clouds of hydrogen gas in front of it because the clouds absorbed a little of its radio signal. One cloud also left a mark from magnesium in ordinary light, but the other did not leave any marks from heavier elements that the scientists could detect. That does not mean those elements are completely missing. The clouds might be near a big group of galaxies, but scientists need to check. Looking with radio waves helps them find gas that other kinds of searches can miss.

Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VII. First interstellar detection of fully deuterated methanol

A. Belloche, S. Spezzano, A. Coutens+12 more

AstronomerAn ALMA COMPASS imaging spectral survey of IRAS4A in NGC1333 yields the first reported interstellar detection of fully deuterated methanol, CD3OD, toward the binary component IRAS4A2, alongside several other methanol isotopologs. Column densities derived assuming local thermodynamic equilibrium show an increase in apparent D/H from singly to multiply deuterated methanol, similar to patterns in other low-mass protostars. Prestellar and protostellar deuteration models do not reproduce this pattern quantitatively, and CD3OD further exacerbates the discrepancy. The LTE analysis gives low methanol-to-13C and methanol-to-18O isotopolog column-density ratios, whereas the 13C-to-18O and 18O-to-17O ratios agree with expectations for the local ISM. The authors suspect that the methanol column density is underestimated; clumpy rather than monolithic emission is a possible explanation, not an established result. The detection highlights deuterium fractionation as a diagnostic of organic-molecule formation and inheritance during star formation.

PublicUsing an ALMA survey, researchers report the first detection in interstellar space of methanol with all its hydrogen replaced by deuterium, a heavier form of hydrogen. They found this molecule, called CD3OD, around the young star-forming component IRAS4A2, along with other forms of methanol. The pattern of deuterium enrichment resembles that seen around other young, low-mass stars, but chemical models cannot reproduce it quantitatively; the new detection makes that mismatch more pronounced. The estimated molecular amounts depend on an assumed thermal equilibrium, and the researchers suspect they have underestimated ordinary methanol. Emission coming from clumps is one possible explanation. Such measurements can help investigate how organic molecules form and are passed along during star formation.

Young explorerScientists used a telescope called ALMA to look at a place where a star is forming. They report finding a special kind of molecule called methanol, with all its hydrogen swapped for a heavier kind called deuterium. This is the first reported discovery of that special methanol in the space between stars. Their chemistry models do not yet explain the pattern they found, and they may have counted too little ordinary methanol. The discovery gives them a new clue about how molecules form as stars are born.

The universal thickness of mid-infrared bubbles

Michael M. Schulreich, A. Beate C. Patzer

AstronomerThe study investigates the nearly constant fractional thickness of 8-micron rings in the Spitzer GLIMPSE surveys using analytic constraints and catalogs containing 591 objects, 91 with kinematic distances. Equilibrium grain temperatures of 20–35 K would underproduce the required emission by more than 20 orders of magnitude, leading the authors to identify stochastically heated PAHs and very small grains in photon-dominated regions as the emitters. In this interpretation, the ring width traces the far-ultraviolet penetration depth, giving ΔR/R = A_V(PDR)/A_V(cloud), whereas a swept-up shell predicts ΔR/R proportional to (R/R_S)^(3/2). Angular resolution inflates the measured thickness ratio for the smallest bubbles. After accounting for this systematic, the authors obtain ΔR/R = 0.217 and a residual physical-radius dependence of 0.03 ± 0.05, consistent with zero. They report excluding fixed ambient density at 20 sigma and the swept-up-shell scaling at 9–28 sigma. The inferred cloud column is approximately 8.7 × 10^21 cm^-2, with 0.112 dex scatter. They attribute the near-universal morphology to nearly invariant ultraviolet-shielding and parent-cloud columns, without invoking stellar winds.

PublicHundreds of infrared rings have surprisingly similar proportions despite spanning a factor of 40 in size. This study compares calculations with Spitzer survey measurements to investigate why. The authors find that limited image resolution makes the smallest rings look relatively thicker; after accounting for this effect, the ring width is about 22% of its outer radius, with no statistically significant remaining dependence on physical size. Their calculations indicate that ordinary dust at a steady temperature is far too cold to produce the observed infrared light. Instead, they infer that tiny grains and aromatic molecules emit after absorbing individual photons, in a layer whose depth is set by how far ultraviolet light penetrates. The authors argue that similar shielding properties and similar material columns in the surrounding clouds explain the rings' proportions. Their comparison strongly disfavors a swept-up-shell explanation, and their proposed explanation does not require stellar winds.

Young explorerAstronomers looked at hundreds of glowing rings in space. Big rings and small rings seemed to have almost the same shape. They found that blurry pictures made the smallest rings look too thick. Even after allowing for that, the rings still had similar shapes. Their calculations suggest that tiny bits of dust glow when they catch light, and that the glowing layer ends where the light cannot reach any farther. They think this helps explain why so many rings look alike.

Occam's Razor and a Three-Family Ultralight Fermionic Dark Matter Model

Fabian Hernandez-Gutierrez, Juan Barranco

• High Energy Physics - Phenomenology

AstronomerThe authors propose a dark matter model comprising three ultralight fermion species that interact only gravitationally, inspired by the Standard Model’s three generations. They fit SPARC galaxy rotation curves using self-gravitating, gravitationally coupled fermion components with degenerate cores and either perfect-fluid-like or NFW halo descriptions. A preliminary single-fermion analysis identifies characteristic mass regions near 20, 40, and 65–70 eV for both halo prescriptions; these regions inform the three-component model’s priors rather than constituting particle detections. The three-component model improves goodness of fit for 94.9% of the galaxies considered, while AICc and BIC comparisons favor it over the single-fermion model for more than 50% of the sample despite its additional parameters. Preference is strongest for galaxies with greater radial extent and more complex rotation curves. These results support the model’s descriptive flexibility across diverse rotation curves, not confirmation that dark matter consists of three fermion species.

PublicCould dark matter consist of three kinds of extremely light particles rather than one? The authors propose this possibility and test it against measurements of how galaxies rotate in the SPARC catalog. In their model, the three particle types interact through gravity and together form a galaxy’s dark matter halo. Compared with a one-particle-type model, the three-type model fits the rotation data better for 94.9% of the galaxies studied. Because adding adjustable parameters can improve a fit, the authors also use statistical tests that penalize extra complexity; these favor the three-type model for more than half of the galaxies. It is especially favored for galaxies measured over larger radial ranges and those with more complicated rotation patterns. The findings show that the proposed model can describe varied galaxy rotation curves, but they do not establish what dark matter particles actually are.

Young explorerGalaxies turn, and scientists study how fast different parts move. These scientists tried an idea: maybe the invisible stuff called dark matter is made of three kinds of tiny particles that pull on each other with gravity. Their three-kind model matched the turning patterns of most galaxies they studied better than a one-kind model. Even after checking whether the extra parts made matching too easy, the three-kind idea was preferred for more than half of the galaxies. But matching a pattern does not prove the idea is true. Scientists still do not know whether dark matter really has these three kinds of particles.

BRAHMa: Bar Recognition And Hatching using Machine learning -- a framework for oriented bounding box detection of galactic bars

Rajit Shrivastava, Narendra Nath Patra, Keerthi K

AstronomerThe paper introduces BRAHMa, a publicly available galactic-bar detection tool using an oriented-bounding-box YOLO11x model, intended to avoid the computational and post-processing burdens of pixel-wise segmentation. Initial training used synthetic data; subsequent training used Galaxy Zoo 3D bar masks and DESI Legacy Survey images. Comparing GZ-3D-derived and Hoyle measurements for 586 shared galaxies gives a mean absolute discrepancy of 0.99 kpc. BRAHMa achieves an L1 error of 1.1 kpc against the Hoyle dataset for 3,150 galaxies, close to that catalogue-disagreement benchmark. Although the authors describe this as approaching a fundamental limit, the benchmark measures disagreement between catalogues rather than error against independently established ground truth. The authors also report validation on distinct datasets, but the abstract supplies no dataset-specific performance metrics. BRAHMa is presented as a scalable method for bar extraction and large-scale morphological studies, accessible through a web interface.

PublicResearchers introduce BRAHMa, a machine-learning tool that identifies bar-shaped structures in galaxies. It was first trained on artificial images, then on real survey images using bar outlines supplied by Galaxy Zoo 3D volunteers. Tested against an existing catalogue of 3,150 galaxies, its reported measurement error was 1.1 kiloparsecs. For comparison, two existing catalogues disagreed by an average of 0.99 kiloparsecs for 586 galaxies they shared. This suggests the tool performs close to the level of agreement between those catalogues, but does not establish that either catalogue gives the exact true measurements. The researchers also report successful testing on other datasets. The publicly available tool is intended to make studies of galactic bars easier to scale to large surveys.

Young explorerSome galaxies have shapes like bars inside them. Researchers taught a computer tool to find these bars, first using made-up pictures and then real galaxy pictures. Its measurements were close to people's measurements, but people do not always agree either. The tool could help researchers study lots of galaxies.

Life in the Cosmic Neighbourhood: Galactic Habitable Zones in the EAGLE Simulations

Luke A. Barnes, Geraint F.Lewis, Jaime Salcido+3 more

AstronomerThis study uses the EAGLE cosmological hydrodynamical simulations to model galactic-scale habitability, rather than observe life or habitable planets. Its observer-occurrence model incorporates main-sequence stars, metal production and distribution, and habitable-planet formation, alongside five potentially life-extinguishing processes: core-collapse and Type Ia supernovae, star-star interactions, gamma-ray bursts, and quasars. It quantifies habitable-planet time per unit baryonic and stellar mass as a function of galaxy mass and galactocentric distance. Within this framework, early-universe, newly formed galaxies with high star-formation rates are the most dangerous environments. The present-day Milky Way is characterized as typical of habitable galaxies, efficiently producing habitable time with a low modeled probability of cosmic catastrophes. These conclusions depend on the adopted habitability and hazard model.

PublicResearchers used computer simulations to explore which galaxies might offer favorable conditions for life. Their model considers stars, the production and spread of heavier elements, and the formation of potentially habitable planets. It also accounts for threats such as exploding stars, interactions between stars, gamma-ray bursts, and quasars. The study compares how much time planets could remain habitable relative to the amount of matter in galaxies. In the model, young galaxies in the early universe that are rapidly forming stars are the most dangerous. Today's Milky Way appears typical of life-friendly galaxies, providing substantial habitable time with a low modeled risk of cosmic catastrophes. This is a simulation-based assessment, not evidence that life exists elsewhere.

Young explorerScientists used a computer to explore which big groups of stars might be good places for life. In their model, young groups making lots of new stars were more dangerous because space disasters could harm life. Our own group of stars, the Milky Way, looked like a fairly safe place, but the scientists did not find living things on other planets.

Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) III. CH₃OH isotopic fractionation in the low-mass protostar BHR71-IRS1

A. Coutens, F. Cruz-Sáenz de Miera, J. K. Jørgensen+26 more

• Solar and Stellar Astrophysics

AstronomerThe COMPASS ALMA spectral survey of the low-mass protostar BHR71-IRS1 detects CH3OH, 13CH3OH, CH3(18)OH, CH3OD, CH2DOH, CHD2OH, and CD3OH at the continuum peak. CH3(17)OH is tentatively detected; CD3OD is not detected, although a few faint lines may be present at a position redshifted from the continuum peak. Line identification and column-density constraints were obtained with CASSIS assuming local thermodynamic equilibrium. Main-isotopologue column densities inferred from 13CH3OH and CH3(18)OH agree when adopting nominal 12C/13C and 16O/18O ratios of 68 and 557. The CH2DOH/CH3OD column-density ratio is 7 ± 2, with statistically corrected D/H ratios of 1.9 ± 0.6% and 0.8 ± 0.2%, respectively. Statistically corrected deuteration increases with the number of D atoms in the methyl group, reaching 23 ± 5% for CD3OH/CH3OH. These trends resemble those in IRAS 16293–2422 and HOPS 373SW but appear to differ from V883-Ori. Comparable studies of other COMPASS sources are planned to test possible environmental and evolutionary influences; those influences are not established here.

PublicAstronomers used an ALMA survey to study methanol around the young, low-mass star BHR71-IRS1. They detected ordinary methanol and several versions containing different isotopes, including deuterium, a heavier form of hydrogen. Their analysis, which assumes local thermodynamic equilibrium, found that deuterium enrichment depends on where the deuterium sits in the molecule. After statistical corrections, the inferred enrichment also increases for versions with more deuterium atoms in methanol’s methyl group. One additional isotope variant is only tentatively detected, and a version containing four deuterium atoms was not detected, despite a few possible faint lines away from the main measurement position. The pattern resembles those reported for some other low-mass young stars but seems different from that of the eruptive young star V883-Ori. Future comparisons are intended to test whether a star’s surroundings or stage of development affect this chemistry; this study does not yet establish the cause.

Young explorerScientists looked near a young star called BHR71-IRS1 and found a molecule called methanol. Molecules are tiny groups of atoms joined together. Some of this methanol has a heavier kind of hydrogen in it. The scientists found several of these heavier versions. Their calculations suggest that the heavier hydrogen is more strongly enriched in versions that have more of it in one part of the molecule. Some very faint clues are still uncertain. They plan to look near more young stars to learn whether the surroundings or how far the stars have grown help explain the differences.

The Rogue One: A Dark Matter-Dominated Dwarf in the Trail of Dark Matter-Deficient Galaxies

Daniel Vaz, Arsen Levitskiy, Duncan Forbes+6 more

AstronomerThe first stellar velocity-dispersion measurement for LEDA 4014647, a compact dwarf spatially aligned with the NGC 1052 trail, gives σ = 15.8 ± 2.0 km/s within the half-light radius using KCWI integral-field spectroscopy. The inferred dynamical mass within the 3D half-light radius is (1.5 ± 0.4) × 10^8 solar masses, approximately three times the enclosed stellar mass, implying a dark matter fraction of 0.7 ± 0.1. Full-spectrum fitting indicates an old, metal-poor population, with age approximately 13 Gyr and [M/H] approximately −1.2 dex, consistent with independent photometric estimates. These findings identify LEDA 4014647 as dark matter dominated and rule out formation from the dark-matter-free, shock-compressed gas invoked for DF2, DF4, and DF9 in the proposed collision approximately 8 Gyr ago. Its origin remains unresolved: it could be a chance projection or a surviving collisionless remnant of a progenitor dwarf. Deeper spectroscopy and targeted N-body and hydrodynamical simulations are needed to distinguish these interpretations.

PublicLEDA 4014647 appears along a chain of galaxies that has been proposed to originate in a high-speed collision about 8 billion years ago. Measurements of its stars’ motions indicate that, unlike the dark-matter-deficient galaxies associated with that proposal, this compact galaxy is dominated by dark matter: the inferred dark matter share is about 70%, with an uncertainty of 10 percentage points, within its three-dimensional half-light radius. Analysis of its starlight also suggests that its stars are about 13 billion years old and contain relatively few elements heavier than helium. These findings mean it could not have formed from the dark-matter-free gas described in the collision proposal. It might simply appear along the chain by chance, or it might be a surviving remnant of one of the galaxies involved in the proposed collision. More detailed observations and computer simulations are needed to decide.

Young explorerThis little galaxy looks like it sits in a line of other galaxies. Scientists measured how fast its stars move and found signs of lots of dark matter—stuff we cannot see but whose gravity affects the stars. Its stars also seem very old. Scientists have suggested that a crash between galaxies made some galaxies in the line, but this little one could not have been made from the gas in that idea. It might only look like it belongs in the line, or it might be a leftover piece of a galaxy from the possible crash. Scientists need more clues to find out.

Barium and europium abundances from the Gaia-ESO Survey using The Cannon

Pradosh Barun Das, Francesca Primas, Gayandhi De Silva+3 more

• Solar and Stellar Astrophysics

AstronomerThe authors applied The Cannon to 36,263 Gaia-ESO FLAMES/GIRAFFE HR15N spectra at R≈19,200, training on 782 stars with high-quality reference labels from the homogenised DR5 catalogue. The model infers Teff, log g, [Fe/H], v sin i, A(Ba), and A(Eu). Multidimensional quality flags and feature-detection criteria yield approximately 21,000 reliable Ba abundances but only 400 reliable Eu abundances, alongside stellar parameters for all spectra. Reported median uncertainties are approximately 38 K, 0.08 dex, 0.04 dex, 0.06 dex, and 0.02 dex for Teff, log g, [Fe/H], A(Ba), and A(Eu), respectively. External comparisons with Gaia Benchmark Stars, GALAH DR4, and multiple open clusters show good agreement. The catalogue complements previous abundance analyses and enables studies of s- and r-process enrichment in open clusters; it does not itself establish a particular enrichment history. Adaptation to 4MOST, WEAVE, and WST is presented as a future capability, not a demonstrated result.

PublicBarium and europium in stars help astronomers trace how slow and rapid neutron-capture processes have enriched our Galaxy over time. Measuring these elements reliably from moderately detailed stellar spectra is difficult. The researchers trained a computer model on 782 well-characterised stars and applied it to 36,263 spectra from the Gaia-ESO Survey. After quality checks, they obtained about 21,000 reliable barium abundance estimates but only about 400 reliable europium estimates. Comparisons with independent reference datasets showed good agreement. The new catalogue provides material for studying the chemical histories of groups of stars called open clusters, rather than reporting a specific history already uncovered. The authors also suggest that the method could be adapted to future large surveys.

Young explorerA star’s light has clues about what it is made of. The researchers taught a computer to read those clues using stars that had already been carefully studied. Then it looked at lots of star-light records for two ingredients called barium and europium. Many records gave trustworthy clues about barium, but far fewer did for europium. Checks against other studies looked good. These clues can help scientists learn how groups of stars got their ingredients, but they have not told that whole story yet.

Stirred, not shaken: Dislodging ω Centauri from the Sausage galaxy through bar resonances

Axel Mannu, Chervin F. P. Laporte, Matthew D. A. Orkney+2 more

AstronomerThe study tests the proposal that ω Centauri was the nuclear star cluster of Gaia-Sausage-Enceladus (GSE), subsequently displaced by the galactic bar. Simulations with time-evolving, slowing bars show that the retrograde 3:2 resonance can substantially change orbital energy and angular momentum over approximately 0.5–1 Gyr, comfortably within the assumed 8–10 Gyr bar lifetime. The authors report that this behavior is independent of their choice of potential or modeling. Observationally, they identify nitrogen-rich stars with −2.0 < [Fe/H] < −1.0 and aluminium enrichment consistent with ω Centauri. These stars form a trailing corridor in energy–angular-momentum space between ω Centauri and the GSE debris centroid, matching the cluster’s predicted past track. The authors interpret this agreement as their strongest evidence yet for the proposed association, rather than a definitive identification. Separately, chemical comparisons involving M54 and ω Centauri show that neither first- nor second-generation populations follow general galaxy-wide enrichment trends, supporting the interpretation that globular-cluster chemical trends arise from cluster-scale physics.

PublicWas ω Centauri once the central star cluster of the Gaia-Sausage-Enceladus galaxy? This study tests that idea with simulations and stellar chemistry. The simulations suggest that a slowing galactic bar could shift the cluster’s orbit enough within the bar’s lifetime. The researchers also identify nitrogen-rich stars whose aluminium enrichment resembles that of ω Centauri. In a map of orbital energy and angular momentum, these stars trace a corridor linking the cluster to debris from Gaia-Sausage-Enceladus, consistent with the cluster’s predicted earlier path. The authors call this their best evidence yet for the connection, but it does not prove the proposed history. A separate comparison of chemistry in ω Centauri and M54 suggests that chemical patterns in globular clusters depend on processes within the clusters, rather than on enrichment across whole galaxies.

Young explorerω Centauri is a big bunch of stars. Scientists think it might once have been at the middle of a galaxy called Gaia-Sausage-Enceladus. Their computer experiments show that a galactic bar could have moved it away. They also found stars with chemical clues like ω Centauri’s, arranged along a path that fits this idea. That is a helpful clue, but it does not mean they know the story for sure. Other chemical clues suggest that what happens inside star bunches matters, not just what happens across a whole galaxy.

Radiation pressure powers quasar broad absorption line winds but fails to drive galaxy feedback

Braden Seefeldt-Gail, Lluís Mas-Ribas, Norman Murray

AstronomerUsing 81,388 broad absorption line troughs from the SDSS-IV DR16 quasar catalog and detailed mock trough spectra, the authors detect line locking in 60–70 percent of troughs. They interpret this radiation-pressure signature as evidence that radiative line driving dominates wind acceleration, ruling out alternative mechanisms. Their direct wind-energy measurement gives a median kinetic luminosity of 0.01 percent of bolometric luminosity, reported to be 50 times below the level required for effective feedback. They conclude that line-driven quasar winds cannot quench star formation. This challenges the common cosmological-simulation prescription in which quasar winds provide the primary quenching mechanism, with momentum flux assumed to approach L/c.

PublicMany galaxy-formation simulations assume that winds from quasars can stop massive galaxies from making stars. The researchers examined 81,388 absorption features in quasar spectra, alongside artificial spectra used for comparison. They found a pattern called line locking in 60–70 percent of those features and interpret it as showing that radiation pushes the winds through interactions with spectral lines. But their measured median wind power is only 0.01 percent of the quasars’ total light output—50 times below the level they say is needed to stop star formation. They conclude that these radiation-driven winds are too weak to do the job assigned to them in many simulations.

Young explorerScientists thought winds from very bright places called quasars could stop galaxies from making new stars. They studied the light and found clues that the light pushes these winds. But the winds they measured were much weaker than needed. The scientists say these winds cannot stop new stars from forming, so computer models that rely on them may need changing.

The Role of the Cosmic Web in Galaxy Evolution Across 0.4<z<4

Sina Taamoli, Bahram Mobasher, Hossein Hatamnia+12 more

AstronomerUsing mass-complete COSMOS2020 galaxy samples in four redshift bins spanning z = 0.4–4, the study identifies clusters, filaments, and field environments with the Multiscale Morphology Filter and assigns central, satellite, and isolated classifications using Friends of Friends. At z < 1, stellar mass increases toward denser structures, primarily among centrals and satellites, with field-to-cluster differences up to approximately 0.35 dex. Cluster SFR is approximately 0.1 dex lower than in the field, particularly for centrals; the much weaker environmental dependence among star-forming galaxies indicates that quenched galaxies primarily drive this trend. Cluster centrals also show the strongest sSFR decline, consistent with enhanced environmental quenching. At 1 < z < 2, star formation activity is largely environment-independent. At z > 2, mild field-to-cluster increases in SFR and sSFR of approximately 0.1 and 0.13 dex suggest, but do not establish, a reversal of the environmental trend.

PublicThe researchers used the COSMOS2020 galaxy catalog to examine how galaxies’ stellar masses and star formation differ between crowded clusters, connecting filaments, and less crowded regions across a broad span of cosmic history. In the more recent period studied, galaxies in denser environments tend to have greater stellar masses and lower star formation rates. The star formation difference appears to come mainly from galaxies whose star formation has been shut down, rather than large differences among galaxies still actively making stars. In an intermediate period, star formation shows little dependence on environment. At the earliest times studied, cluster galaxies show a small increase in star formation, including relative to their stellar mass. This hints that the relationship between a galaxy’s surroundings and its star formation may have reversed over cosmic time, but the early-time reversal remains tentative.

Young explorerGalaxies are big groups of stars. Some have lots of other galaxies nearby, and some have fewer neighbors. Scientists looked at galaxies from different times in the universe. In the later times they studied, galaxies in crowded places tended to have more stars but make fewer new ones. Many had stopped making stars. In the earliest times they studied, crowded galaxies seemed to make a little more new stars instead. That is a clue that a galaxy’s neighborhood may matter differently at different times, but scientists are not sure about that switch yet.

A Graph Attention Network Framework for Simultaneous Prediction of Galaxy and Dark Matter Halo Properties in GAMA DR4

Sandeep Aashish, Abhay V Hegde, Aditya Prakash Gupta+4 more

• General Relativity and Quantum Cosmology

AstronomerThe authors develop GAMANet, a graph-based model using a unified sample of 19,469 galaxies assembled from GAMA DR4 catalogues. Inputs include photometric, spectroscopic, morphological, and environmental features. Galaxies form graph nodes, with edges defined by spatial proximity and group membership; GATv2 attention layers weight information from neighbouring galaxies. The model jointly predicts halo mass, stellar mass, and a specific star formation rate proxy. Test-set R² values are 0.958, 0.985, and 0.982, respectively, with a halo-mass RMSE of 0.237 dex. These are predictive-performance results using observational catalogues, not new direct measurements of the target properties. The star formation target is explicitly a proxy. The results support the usefulness of graph-based learning incorporating encoded environmental relationships, although the abstract does not report a comparison isolating the benefit of those relationships.

PublicResearchers developed an artificial intelligence model called GAMANet using observational catalogues containing 19,469 galaxies. Instead of treating each galaxy separately, the model links galaxies that are close together or belong to the same group, then learns how much attention to give each neighbour. It predicts the mass of a galaxy’s halo, its stellar mass, and an indicator of star formation relative to stellar mass. On a held-out test sample, its predictions closely matched the target values. This is a result about predicting properties from catalogue information, rather than measuring those properties directly. The star formation prediction concerns a proxy, not the star formation rate itself.

Young explorerScientists taught a computer to look at galaxies and their neighbours. The computer used nearby galaxies and galaxy groups as clues to guess how much mass galaxies and their halos have, plus a clue about star-making. Its guesses matched the test answers closely, but they are still predictions, not direct measurements.

COSMOS-3D: Spectro-photometric Confirmation of Shabgard, a Cool, Metal-poor Brown Dwarf in the COSMOS Field

Bahareh S. Salmasi, Priyanka Jalan, Tomotsugu Goto+19 more

• Earth and Planetary Astrophysics
• Solar and Stellar Astrophysics

AstronomerJWST/NIRCam slitless spectroscopy, photometry, and multi-epoch imaging support classifying COSMOS2025 ID639188, nicknamed Shabgard, as a cool, metal-poor Galactic brown dwarf. The authors compare its background-subtracted 4.05–4.85 micrometer spectrum with six atmosphere-model families. A LOWZ fit using PCA interpolation and MCMC yields an effective temperature of 718.6 (+10.6/−10.2) K and [M/H] = −1.00 (+0.07/−0.08), favoring an atmosphere near the late-T/Y transition. A fixed-atmosphere opacity test strongly favors methane contributing to the spectral shape, but the limited wavelength coverage precludes molecule-by-molecule abundance determinations. Physical estimates remain model-dependent, spanning approximately 23–52 Jupiter masses and 140–180 pc; LOWZ flux scaling gives 176.2 (+18.4/−17.8) pc. The measured proper motion is 89.2 ± 0.4 milliarcseconds per year. The study demonstrates how JWST deep-field surveys can identify and characterize faint substellar objects.

PublicResearchers used James Webb Space Telescope observations to investigate a faint object nicknamed Shabgard, previously identified as a possible brown dwarf. Its infrared spectrum, brightness measurements, and measured movement across the sky support its classification as a cool brown dwarf in our Galaxy. Comparing the observations with atmosphere models favors a temperature near 719 kelvin and a relatively low abundance of elements heavier than helium. A separate model test strongly favors methane helping shape the spectrum, although the narrow wavelength range does not allow individual molecular abundances to be determined. Estimates of its mass, about 23–52 times Jupiter’s, and distance, about 140–180 parsecs, depend on the models used. The work shows that Webb surveys can uncover and study faint brown dwarfs.

Young explorerScientists studied a faint object called Shabgard with the Webb telescope. Its light and movement suggest it is a cool brown dwarf in our Galaxy, a kind of object between stars and giant planets. Computer models help estimate how warm and heavy it is. Its light also gives a strong clue that methane gas is there, but scientists cannot yet tell how much.

Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS): I. Overview of the ALMA Large Program

J. K. Jørgensen, A. Coutens, M. N. Drozdovskaya+27 more

AstronomerThis paper introduces COMPASS, an unbiased ALMA spectral survey of 11 line-rich Class 0 and I protostellar sources covering 279.0–311.7 GHz at 0.15–0.5 arcsecond resolution, probing roughly the inner 100 au in radius. The program aims to inventory complex organic molecules and assess the influence of environment and evolutionary stage on protostellar chemistry. Alongside the observing strategy and source selection, the paper presents qualitative comparisons of selected molecular spatial distributions and complex-organic line fluxes. These suggest possible source-to-source chemical differences, including in the abundances of oxygen- versus nitrogen-bearing species, with variations smaller than an order of magnitude. These are not yet quantitative abundance determinations: forthcoming analyses will use the survey’s broad bandwidth and carefully account for excitation and the strengths of the several thousand lines detected toward each source.

PublicAstronomers are using ALMA to survey complex organic molecules in the hot gas around 11 young, still-embedded stars. The COMPASS survey examines regions roughly 100 times the Earth–Sun distance in radius, with the aim of understanding how a young star’s surroundings and stage of development influence its chemistry. This paper describes the survey and compares where selected molecules appear and how strongly they emit. Those preliminary comparisons suggest that the sources may differ chemically, including in their relative amounts of oxygen-containing and nitrogen-containing molecules, but by less than a factor of ten. Measuring those differences reliably will require detailed analysis of the thousands of detected spectral lines in future papers. The chemistry of these early stages may influence later planet-forming disks and potentially planets, but this paper does not establish that connection.

Young explorerScientists used a telescope called ALMA to study warm gas around 11 very young stars. They are looking for different kinds of molecules, the tiny pieces that make up things. The telescope’s signals hint that the stars may have somewhat different mixtures of molecules. But the scientists still need to check those signals carefully to know how much of each kind is there. They hope this will help them understand the ingredients around stars before planets form.

Chaotic accretion can (still) explain early supermassive black hole growth

Kastytis Zubovas, Matas Tartėnas

• Cosmology and Nongalactic Astrophysics

AstronomerThe authors test whether chaotic accretion can account for the most extreme SMBH masses at z > 7 by comparing a predicted exponential growth timescale with compiled mass estimates, implied seed masses, and expected halo feeding and feedback conditions. In their scenario, uncorrelated inflows in slowly spinning dark matter haloes keep black-hole spins and radiative efficiencies low. They infer that the most massive SMBHs at 7.6 < z < 10.6 likely grew with an exponential timescale of about 32 Myr, consistent with chaotic accretion if growth was almost continuous. All high-redshift SMBHs with virial mass estimates could, within this scenario, have grown from seeds of roughly 100 solar masses or less. Their proposed reservoir evolution suggests that wind-driven feedback removes most of the feeding gas and changes the growth mode around z ~ 7.5. Predictions for spins, host-galaxy correlations, and observable counterparts offer future tests. The analysis supports chaotic accretion from stellar-mass seeds as a viable explanation without massive seeds or super-Eddington growth, but does not establish it as the origin of these objects.

PublicHow did enormous black holes grow so early in the universe? This study evaluates a possible explanation: gas arriving from changing directions could keep a black hole spinning slowly, allowing it to grow efficiently because less of the incoming material's energy is radiated away. Comparing this model with estimates of early black-hole masses, the authors infer that the most massive ones likely grew exponentially on a timescale of about 32 million years. The model can match that pace only if feeding was almost uninterrupted. In this scenario, all the early black holes whose masses were estimated using the virial method could have started from seeds no heavier than roughly 100 Suns. The authors also suggest that winds eventually clear away much of the gas, changing how the black holes grow. These are model-based interpretations, not direct observations of their growth histories. Future tests of black-hole spin, relationships with host galaxies, and observable counterparts could distinguish this explanation from alternatives.

Young explorerScientists are trying to understand how some black holes became very big when the universe was still young. One idea is that gas came to them from many different directions. That could keep them from spinning too fast and help them grow quickly. The scientists compared this idea with estimates of how big early black holes were. They found that small starting black holes could have grown big enough, but only if they kept eating gas almost all the time. They also think winds might later push much of that gas away. This idea could work, but scientists still need to test whether it is what really happened.

Early galactic heavy element production - a phenomenological approach

B. Wehmeyer, D. Blaschke, F.K. Röpke+1 more

• Nuclear Theory

AstronomerHigh heavy-element abundances in early, extremely metal-poor Galactic stars remain an unresolved problem in Galactic Chemical Evolution. The authors propose pre-enriched inflow as a possible explanation, noting difficulties with standard neutron-star-merger scenarios and ongoing discussion of non-merger channels. They apply a heavy-element freeze-out approach to characterize the conditions needed for such inflow, describing the initial distribution with Lagrange parameters that generalize temperature and chemical potentials to nonequilibrium settings. They speculate that the required conditions might occur in early-Universe cosmological fluctuations and might be connected to primordial black-hole formation; neither connection is established.

PublicSome early stars in our galaxy contain unexpectedly large amounts of heavy elements despite being extremely poor in metals overall. Explaining this remains difficult, including for standard ideas involving merging neutron stars. The authors suggest that matter flowing into the galaxy might already have contained heavy elements before the stars formed. They use a mathematical approach to describe the conditions this incoming matter would require. They also speculate that those conditions could have arisen from fluctuations in the early universe, possibly linked to the formation of primordial black holes. This is a proposed explanation, not a demonstrated origin for the elements.

Young explorerSome very old stars have heavy ingredients that scientists find hard to explain. The scientists suggest that material coming into our galaxy might already have carried those ingredients. They use math to explore what conditions this idea would need. They also wonder whether changes in the very young universe, perhaps linked to black holes forming back then, could be part of the story. They have not shown that this is what really happened.

Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VI. Discovery of a class I methanol maser transition and its association with acetaldehyde

Jae-Hong Jeong, Jeong-Eun Lee, Jes K. Jørgensen+16 more

AstronomerUnbiased COMPASS ALMA surveys of 11 sources spanning 279.0–311.7 GHz reveal a newly detected collisionally pumped class I CH3OH maser transition at 302.9 GHz. Rotation-diagram departures from LTE robustly establish masing in seven sources, with peak brightness temperatures from a few to approximately 1,000 K. The brightest detection, toward HOPS 108, is likely associated with the outflow from the nearby intermediate-mass protostar HOPS 370. Excluding that case, detections occur in six of ten low-mass protostars (60%); all six are Class 0 sources interacting with dense ambient material. Non-detections are three Class I protostars and one isolated Class 0 core, suggesting a preference for early evolutionary stages and gas-rich outflow interaction environments. Maser emission coincides with thermal CH3OH along outflow cavity walls and bow shocks but is more compact and knot-like. Of the surveyed complex organic molecules, only CH3CHO closely follows the maser's shocked morphology, and only around HOPS 108. The sample supports a higher incidence of these masers than previously recognized, but more sensitive CH3CHO observations are required to test whether the apparent connection to shock-driven complex chemistry extends to low-mass systems.

PublicAstronomers used ALMA to find methanol gas acting as a natural microwave amplifier, called a maser, around forming stars. They detected a newly identified maser signal at 302.9 GHz in seven of 11 surveyed sources. The strongest signal, toward HOPS 108, probably relates to an outflow from a nearby, more massive young star. Leaving that case aside, six of ten low-mass protostars showed the signal. All six were in the earliest protostellar stage and were interacting with dense surrounding gas, suggesting that young stars in gas-rich environments especially favor this emission. The signals form compact knots along locations where stellar outflows encounter surrounding material. The researchers also looked for links to complex chemistry in these shocks. Only one surveyed complex molecule, CH3CHO, closely matched the maser pattern, and only around HOPS 108. More sensitive observations are needed to see whether this chemical connection also holds around low-mass protostars.

Young explorerBaby stars can send gas rushing into gas around them. Scientists found tiny bright spots where a kind of molecule called methanol makes a special signal. Six of ten small baby stars they checked had it, and those six were very young and surrounded by thick gas. One extra, brighter spot may be caused by a bigger baby star nearby. Scientists still need to look more carefully to learn how these spots connect to other molecules.

The [OIII]λ5007 Equivalent Width as an Ionization-Parameter Diagnostic Across Cosmic Time

Dian P. Triani, Lisa J. Kewley

AstronomerThis study uses MAPPINGS photoionization models with BPASS single-star and binary-inclusive spectra to investigate the equivalent width of [O III] λ5007 (EWO3) as an ionization-parameter diagnostic. Unlike O32, EWO3 offers an alternative when broad wavelength coverage and dust corrections are unavailable. In the models, binary-inclusive populations maintain harder ionizing spectra and strong [O III] emission to later ages. EWO3 is highly sensitive to ionization parameter but also depends systematically on metallicity, gas pressure, and stellar population age. Its dependencies broadly resemble those of O32, although its weaker pressure sensitivity at low metallicity and high ionization makes it promising for metal-poor and high-redshift galaxies. Model comparisons with observations favor lower pressures for local galaxies and higher pressures for intermediate- and high-redshift galaxies, suggesting evolving ISM conditions. The authors present metallicity- and pressure-dependent calibrations; validation against O32-derived ionization parameters favors log(P/k)=6 for local galaxies and log(P/k)=7 for intermediate- and high-redshift galaxies.

PublicThe researchers investigate whether the strength of an oxygen emission line relative to the surrounding starlight can help measure how strongly gas in galaxies is ionized. This could provide an alternative to a commonly used oxygen-line ratio that needs wider wavelength coverage and corrections for dust. Their computer models show that populations including binary stars can sustain strong oxygen emission longer than populations modeled with single stars alone. The proposed diagnostic also depends on the gas’s metal content and pressure, and on the stars’ age, so those factors must be considered. Comparisons with observed galaxies favor lower-pressure models nearby and higher-pressure models at intermediate and high redshift, suggesting that interstellar gas conditions change over cosmic time. The researchers provide calibrations and check them against the existing oxygen-line diagnostic.

Young explorerStars can make gas in galaxies glow. Scientists used computer models to see whether one kind of oxygen glow could tell them about the gas. In their models, stars in pairs kept that glow strong for longer. But the glow also depends on the gas and the stars’ ages. Comparing models with real galaxies suggests that gas pressure was different at different times in the universe.

Galaxy merger-driven signatures in massive black hole pair hosts across cosmic time

Pranav Satheesh, Aklant K. Bhowmick, Laura Blecha

AstronomerThis simulation study compares merger-associated signatures in candidate massive black hole pair hosts in IllustrisTNG-50 and two BRAHMA runs with different black hole seeding models. Post-merger galaxies whose progenitors both contain massive black holes are compared with matched non-merging controls. In TNG50, at 0 ≤ z < 3.3, specific star formation rates reach about 1.4 times control values, while specific black hole accretion rates reach about 1.5–1.7 times control values. BRAHMA seeds black holes in lower-mass galaxies and at higher redshifts than TNG50. Its merger-associated enhancements in specific star formation rate and gas fraction are comparable to TNG50 at z ≲ 3.3 and persist to z ≈ 6, but it shows no significant enhancement in specific black hole accretion rate across its full redshift range. TNG50 also yields an enhanced AGN fraction, whereas BRAHMA shows only a weak excess among the most rapidly accreting massive black holes. These are simulated findings, and the black hole activity signatures differ between the models despite similar star formation enhancements.

PublicComputer simulations suggest that galaxies formed by mergers can make stars faster without necessarily feeding their central black holes faster. The researchers compared recently merged galaxies, whose two parent galaxies each contained a massive black hole, with similar galaxies that were not merging. In the TNG50 simulation, mergers increased both star formation and black hole feeding, and a larger fraction of the galaxies had active central black holes. In two BRAHMA simulations, mergers similarly boosted star formation and gas content, including at earlier cosmic times, but did not significantly increase black hole feeding. BRAHMA also showed only a weak excess of activity among the fastest-feeding black holes. The simulations use different assumptions about how black holes first form, so the predicted signs of black hole activity are not consistent across these models. These are computer-model results, not observations of real galaxies.

Young explorerScientists used computers to pretend that two galaxies joined together. Each galaxy started with a big black hole. In the computer stories, the joined galaxies made stars faster than similar galaxies that were not joining. But the black holes did not always gobble up more stuff: that happened in one computer model, but not clearly in the other two. Different ways of building the pretend galaxies gave different answers.

Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) -- IV. Methyl cyanide isotopologues toward BHR71-IRS1

P. Nazari, A. Coutens, J. K. Jørgensen+16 more

AstronomerThe authors analyze approximately 33 GHz of ALMA COMPASS spectral coverage toward BHR71-IRS1 to characterize methyl cyanide isotopologues. They detect CH3CN, its v8=1 vibrationally excited state, 13-CH3CN, CH3-13-CN, CH3C-15-N, CH2DCN, and CHD2CN, deriving column densities and excitation temperatures through spectral fitting under a local thermodynamic equilibrium assumption. The column density ratio 13-CH3CN/CH3-13-CN is approximately unity, consistent with previous observations. Across the compared low-mass objects, CH2DCN/CH3CN ratios are similar and approximately an order of magnitude above those in Sgr B2(N2b); a warmer pre-stellar phase or different formation timescale for Sgr B2(N2b) are possible explanations. Methyl cyanide D/H ratios agree with those of methanol in BHR71-IRS1, supporting, but not establishing, formation and deuteration during a similar pre-stellar phase. Increasing inferred D/H with the number of deuterium substitutions suggests that deuterated isotopologues may form later within that phase. Future COMPASS analyses are intended to enlarge the low-mass sample and potentially test these trends statistically.

PublicAstronomers used ALMA observations to study methyl cyanide, a complex nitrogen-containing molecule, around the forming star BHR71-IRS1. They detected several versions of the molecule containing different isotopes, including deuterium, a heavier form of hydrogen. Their estimates of molecular amounts and excitation temperatures assume local thermodynamic equilibrium. Comparing sources, they found similar proportions of singly deuterated methyl cyanide in the low-mass systems studied, roughly ten times the proportion in Sgr B2(N2b). That difference might reflect warmer conditions before star formation or a different formation timescale in Sgr B2(N2b). In BHR71-IRS1, methyl cyanide and methanol show similar deuterium enrichment, suggesting that both acquired their deuterium during the phase before the star formed. The enrichment pattern also hints that deuterated methyl cyanide may have formed later in that phase. These are interpretations rather than established histories; future observations could test the trends in a larger sample.

Young explorerScientists looked at gas around a star that is still forming. They found a molecule called methyl cyanide and several slightly different versions of it. Some have a heavier kind of hydrogen. The scientists compared how much of these versions they found. The clues suggest that some molecules may have been made before the star began forming, with the heavier-hydrogen versions possibly made later during that time. They are not sure yet, and studying more young stars could help them check.

Unraveling the mysteries of Jets in peculiar NLSy1 galaxies through multi-wavelength variability

Vineet Ojha, Xue-Bing Wu, Luis C. Ho+4 more

• High Energy Astrophysical Phenomena

AstronomerThe study investigates seven radio-quiet narrow-line Seyfert 1 galaxies with recurring 37 GHz flares detected by Metsahovi, combining ZTF optical variability, WISE mid-infrared variability, and broadband spectral energy distribution modeling. All sources show statistically significant long-term optical variability, with larger amplitudes at shorter wavelengths. Three exhibit bluer-when-brighter behavior and optical variability patterns interpreted as evidence for a non-thermal contribution. Intrinsic mid-infrared variability is detected in three of four sources examined in that regime. Significant optical–mid-infrared and mid-infrared intra-band lags are reported, whereas optical intra-band lags are insignificant. Optical variability amplitudes anti-correlate with Eddington ratio and correlate positively with black hole mass. These observations, supported by spectral modeling, suggest that weak or intermittent jets contribute to the optical and mid-infrared emission in a subset of the sample; they do not establish jets as the unique explanation. Coordinated multi-wavelength monitoring is needed to better constrain the variability's origin.

PublicThese seven galaxies are classified as radio-quiet, and their light is generally thought to come mainly from hot material swirling around their central black holes. Yet repeated radio flares prompted researchers to investigate whether other processes contribute. Optical observations show that all seven change brightness over long periods, with stronger changes at bluer wavelengths. Three become bluer as they brighten. Mid-infrared brightness changes were detected in three of the four galaxies examined at those wavelengths, and some brightness changes occur with measurable delays between wavelength bands. Together with models of the galaxies' emission, the findings suggest that weak or intermittent jets may contribute light in some cases. The origin remains uncertain, and coordinated observations across wavelengths are needed.

Young explorerScientists watched seven galaxies whose middles sometimes flash in radio light. They found that the galaxies also get brighter and dimmer in light our eyes can see. Some change in invisible infrared light, too. Hot stuff around their black holes makes light, but little jets might help. Scientists need more watching to find out.

A homogeneous three-dimensional view of Molecular Cloud kinematics out to 2.5 kpc. Using Young Stellar Objects and Open Clusters as complementary tracers

Xabier Pérez-Couto, Santiago Torres, Nuria Miret-Roig+4 more

• Instrumentation and Methods for Astrophysics
• Solar and Stellar Astrophysics

AstronomerUsing Gaia DR3 astrometry and complementary spectroscopic radial velocities, the study combines 24,732 stellar tracers to derive homogeneous 3D kinematics for 15 molecular-cloud complexes within 2.5 kpc. Proper-motion clustering identifies co-moving young stellar objects, and Monte Carlo sampling yields cloud-averaged motions for comparison with open clusters younger than 30 Myr. The populations have strongly consistent kinematics, with a median spatial velocity offset of approximately 2 km/s, supporting young open clusters as complementary tracers of parent-cloud bulk motion. The complexes have a median peculiar velocity of approximately 8.7 km/s relative to Galactic rotation. The analysis detects expansion in Orion and Ophiuchus at 5σ and coherent rotation in at least seven complexes. Orbital integrations in a realistic Galactic potential reconstruct the Solar System's passage through the Orion cloud and a common origin for Lupus, Ophiuchus, and Corona Australis in Sco-Cen; these past histories are model-based reconstructions rather than direct observations.

PublicResearchers used the motions of 24,732 young stars and stars in young clusters to map how 15 nearby complexes of star-forming gas clouds move through space. The two kinds of stellar tracers move very similarly, supporting the use of young clusters alongside young stars to track their parent clouds. The clouds also depart from the motion expected from the Galaxy's rotation. The analysis finds that Orion and Ophiuchus are expanding and that at least seven cloud complexes show organized rotation. By calculating orbits in a model of the Galaxy, the researchers reconstruct a past passage of the Solar System through the Orion cloud and a shared origin for three other cloud complexes. These accounts of the past depend on the orbital model, rather than direct observations of those events.

Young explorerBig clouds in space are places where stars form. Scientists watched how young stars and groups of young stars move to work out how nearby clouds move. Both kinds gave very similar answers. Some clouds are spreading out, and some are turning. A computer model also helped scientists work out where the clouds and our Solar System might have been long ago.

Probing Direct Contributions of Galaxies and AGN to Cosmic Reionization in a Quasar Field J0226+0302 with JWST NIRCam and NIRSpec

Xiangyu Jin, Jinyi Yang, Feige Wang+19 more

• Cosmology and Nongalactic Astrophysics

AstronomerNew JWST Cycle 2 NIRCam and NIRSpec observations of the z=6.5412 quasar field J0226+0302 identify 65 additional line-emitting galaxies at 5.3<z<6.4, beyond eight [OIII] emitters previously detected by ASPIRE. The IGM–galaxy cross-correlation shows a roughly 2-sigma excess in transmission at separations of about 10–40 cMpc, suggesting that regions traced by star-forming galaxies contribute to the local ionizing background. The correlation is consistent with THESAN simulations having a 5%–7% IGM neutral fraction and a mean galaxy ionizing-photon escape fraction of 6%; substantial cosmic variance in this single field prevents independent constraints on these quantities. Four of 49 NIRSpec-observed line emitters show broad H-alpha emission and are identified as AGN, giving an AGN fraction of (8±4)%. IGM effective optical depths and the IGM–AGN cross-correlation indicate higher transmission within 5 cMpc/h of these AGN than around most [OIII] emitters. The authors interpret this excess as local radiation enhancement by AGN; an illustrative cross-correlation model yields an estimated AGN escape fraction of approximately 50%–100%, rather than a direct measurement. Future NIRSpec observations in additional quasar fields are expected to tighten the IGM–AGN correlation constraints.

PublicUsing the James Webb Space Telescope, researchers found 65 additional galaxies emitting distinct spectral lines in a distant quasar field, where eight such galaxies had previously been found. They are studying how galaxies and active galactic nuclei, or AGN, affected the gas between galaxies during cosmic reionization. The gas showed a modest, roughly two-sigma tendency to transmit more light in regions around galaxies, suggesting that star-forming galaxies help supply radiation that ionizes this gas. Comparisons with simulations are compatible with particular amounts of neutral gas and escaping radiation, but one observed field cannot reliably determine these quantities separately. Among 49 galaxies examined with NIRSpec, four had broad hydrogen emission lines indicating AGN. The gas close to these four transmitted more light than the gas around most of the other galaxies. The researchers interpret this as an effect of extra radiation from the AGN. Their illustrative model estimates that about 50%–100% of the AGN's ionizing photons escape, but this is not a direct measurement. More observations are needed to establish how much galaxies and AGN contributed to reionization.

Young explorerScientists used the Webb telescope to find more galaxies far away. They looked at how easily light could pass through the gas between those galaxies. Near four galaxies with very bright, active centers, the gas let more light through than it did near most of the other galaxies. The scientists think light from those bright centers may help make the gas more see-through. They also found a smaller hint that ordinary star-making galaxies help. But they have studied only one patch of space, so they need to look at more patches to be more sure.

The New Dark Matter Density Profile from JWST JADES Galaxies

Aritra Sanyal, Farook Rahaman

• General Relativity and Quantum Cosmology

AstronomerThe authors present what they describe as the first dark matter density profile derived directly from JWST JADES DR3 NIRSpec observations of 587 galaxies at cosmic noon, spanning 1.5 ≤ z ≤ 3.5. They measure Hα velocity dispersions from G235M/G395M spectra, stack galaxies into four Δz = 0.5 bins, and reconstruct representative group rotation curves within general relativity. A four-parameter modified exponential fit yields an exact relativistic energy density, represented by a compact [2/3] Padé approximant with coefficients determined in closed form from the observations. The resulting model profile is analytic, cusp-free, and redshift-dependent; the authors report that it satisfies energy conditions, causality, and orbital stability. Its inferred central density changes by less than 15% across the redshift range despite a 35% decline in asymptotic rotation velocity. They interpret this as a universal dark matter core saturation density decoupled from baryonic evolution. These density profiles and the universality interpretation follow from the reconstruction and modeling, rather than being direct measurements of dark matter density.

PublicResearchers used James Webb Space Telescope spectra of 587 galaxies from an era called cosmic noon to study how dark matter may be distributed. They measured the spread of velocities traced by glowing hydrogen, combined galaxies into four groups by redshift, and used a model based on general relativity to infer rotation curves and dark matter density profiles. The model has a smooth central core rather than a sharp density spike. Its central density varies by less than 15% across the studied epochs, even though its outer rotation speed declines by 35%. The authors interpret this as evidence for a common central dark matter density that is separate from the evolution of ordinary matter. That conclusion depends on their reconstruction and model; the telescope did not measure dark matter density directly.

Young explorerScientists used the Webb telescope to look at light from lots of galaxies. The light helped them learn how gas was moving. Then they used a math model to work out where invisible dark matter might be. Their model showed smooth centers with nearly the same amount of dark matter packed inside. They think this could be a shared pattern, but they did not see the dark matter itself.

A Systematic Assessment of Total Stellar Mass Measurements with Spatially Resolved Photometry and Medium Bands at 1 < z < 9: The Impact of Mass-to-Light Variations and Outshining

Naadiyah Jagga, Adam Muzzin, Visal Sok+16 more

AstronomerUsing JWST NIRCam data from CANUCS, Technicolor, and JUMPS, together with HST UV–IR photometry, the study compares spatially resolved and integrated stellar-mass estimates for approximately 3,000 galaxies at photometric redshifts 1 < z_phot < 9. Resolved parameter maps show spatial variations in stellar populations and mass, while integrated photometry systematically yields lower stellar masses. The bias is small at sSFR < 10^-9 yr^-1 and increases above 10^-8.5 yr^-1, where the median signed offset reaches approximately -0.36 dex; the largest bias occurs at M_* ≤ 10^9.5 solar masses. This is consistent with, but does not independently establish, outshining of older populations by recent star formation. The abstract also reports a negative association between the signed mass bias and spatial scatter in log10(M_*/L_V), with a strongest Spearman correlation of -0.37. However, the stated sSFR intervals for these correlations have reversed bounds, so their precise bin assignments cannot be interpreted as written. When only wide bands are used, the reported mass-offset dispersion is 0.33 dex for integrated photometry versus 0.15 dex for resolved photometry, suggesting that spatial resolution reduces sensitivity to missing medium-band coverage.

PublicThe researchers used James Webb and Hubble space telescope observations to compare two ways of estimating the mass in stars in about 3,000 galaxies: measuring each galaxy as a whole, or examining its different regions separately. Whole-galaxy measurements systematically gave lower stellar-mass estimates. The difference was small for galaxies forming stars slowly relative to their existing stellar mass, but larger for those forming stars rapidly, especially lower-mass galaxies. For the rapidly star-forming group, the typical offset was about -0.36 dex on a logarithmic mass scale. The authors interpret this pattern as consistent with bright, recently formed stars masking the contribution of older stars, rather than as direct proof of that explanation. Examining separate regions also reduced the spread in mass offsets when medium-band measurements were omitted. The abstract's numerical ranges for one additional correlation are inconsistently written, so that detail requires clarification.

Young explorerA galaxy is a huge group of stars. The researchers looked at many galaxies in two ways: all at once, and in smaller pieces. Looking at the pieces usually made them estimate more mass in the stars. The difference was bigger in galaxies making lots of new stars. They think bright new stars may make older stars harder to notice, like a bright lamp making a dim light hard to see. Looking at the pieces also helped when some kinds of light measurements were missing.

Discovery of the Lyman-α Forest in a Star-Forming Galaxy at z ≈7.57: Implications for the Timing and Topology of Cosmic Reionization

Jakob M. Helton, Joris Witstok, Marta Laska+15 more

AstronomerJWST/NIRSpec PRISM spectroscopy detects flux blueward of Lyα at approximately 7σ in JADES-GS-z7-LAF, a star-forming galaxy at z≈7.57 with M*≈10^9.1 solar masses and MUV≈−21.5. Independent NIRCam F090W imaging confirms the flux at approximately 10σ; it is spatially coincident with the galaxy but offset by approximately 0.4 proper kpc from its rest-frame 1500 Å UV centroid. No evidence supports foreground contamination, although the existing data cannot formally exclude it. If the flux originates from this galaxy, its transmission implies an exceptionally transparent IGM sightline, with xHI≪0.1% over z≈5.5–7.5. Numerous galaxy overdensities coincide spatially and kinematically with the sightline and may explain its transparency. The gradual Lyα-break turnover is consistent with either an extreme damping wing, NHI≈10^23.3 cm−2, or strong nebular continuum contributing approximately 60–70% of the rest-frame 1500 Å flux. The galaxy is substantially brighter than the faint sources commonly invoked as reionization drivers. If such systems are common, massive galaxies could contribute more to the ionizing photon budget than other indirect constraints suggest; their prevalence and contribution are not established here.

PublicAstronomers report unusually clear passage for light from JADES-GS-z7-LAF, a massive, star-forming galaxy in the early Universe. Neutral hydrogen between galaxies is normally expected to absorb this light at wavelengths shorter than the Lyman-alpha transition. Instead, two independent JWST observations detect it. The light appears at the galaxy’s location, slightly offset from its ultraviolet center. A nearer object could potentially account for the signal, although the researchers find no evidence for one and cannot rule it out completely. If the light really comes from the distant galaxy, it implies that the intervening gas along this particular path contains exceptionally little neutral hydrogen. Several concentrations of galaxies along the path might help explain that transparency. The spectrum also has a gradual change that could reflect either strong hydrogen absorption or substantial light emitted by gas within the galaxy. If similarly bright galaxies are common, they may have played a larger role in making the early Universe’s hydrogen transparent, but this study does not establish that broader contribution.

Young explorerLong ago, gas in space usually blocked a certain kind of light from faraway galaxies. Scientists used the Webb telescope to spot that light near one big galaxy. If it really came from that galaxy, the gas along its path must have let it through unusually easily. Other galaxies nearby might have helped clear the way. The scientists still cannot completely rule out light from something closer to us.

Deep radio characterization of the supernova remnant G343.1-00.7

S. Loru, A. Ingallinera, C. Trigilio+20 more

• High Energy Astrophysical Phenomena

AstronomerCombining 0.944 GHz ASKAP-EMU imaging with 0.088–0.200 GHz MWA-GLEAM data, the authors present the first sensitive spatially resolved radio spectral analysis of G343.1−00.7. Its integrated spectral index, α = −0.50 ± 0.01, confirms the previously reported value with improved precision. Revised morphology and spectral measurements provide the first evidence linking filaments projected onto the nearby H II region G343.147−00.44 to the SNR. Brightness-brightness analysis identifies flatter-spectrum filaments along the southeastern shell, consistent with a possible thermal bremsstrahlung contribution from radiative or partially radiative shocks. H I and CO components are kinematically consistent with the remnant’s distance, but show no clear morphological evidence of interaction. Gas around the H II region suggests an expanding H I shell partially embedded in its parent molecular cloud. Theoretical models place the remnant between the late Sedov and early pressure-driven phases, suggesting spatially varying evolutionary stages rather than establishing a uniform phase.

PublicRadio observations have given astronomers a clearer picture of G343.1−00.7, the expanding remains of an exploded star. Combining ASKAP and MWA survey data, the team measured how its radio emission changes with frequency, confirming an earlier overall measurement more precisely and mapping local differences sensitively for the first time. The images and radio spectra provide evidence that thin strands overlapping a nearby region of ionized gas belong to the remnant. Some southeastern strands have a different radio spectrum that could include emission from hot gas associated with shocks that are losing energy through radiation. Nearby gas has motions consistent with the remnant’s distance, but its shape does not clearly show that the remnant is interacting with it. The gas pattern around the ionized region also suggests an expanding shell of atomic hydrogen partly inside a molecular cloud. Theoretical models suggest the remnant is transitioning between stages of expansion, with different parts potentially at different stages.

Young explorerWhen a star explodes, it can leave a big, spreading cloud. Scientists used radio pictures to study one of these clouds and found clues that some thin strands belong to it, even though they look mixed up with another cloud nearby. Some strands give off different radio signals, which might partly come from hot gas. The scientists also looked at gas nearby, but did not see a clear sign that the leftover star cloud was bumping into it. Their models suggest that different parts of the cloud may be changing in different ways.

Relaxation of a Vlasov gas to an inhomogeneous state due to phase space mixing in an axisymmetric potential: A Newtonian analogy of the Kerr orbital motion

Ana Laura Garc\a'ia-Perciante, Merce Guerrero, Daraío Naúañez+1 more

• Astrophysics of Galaxies
• General Relativity and Quantum Cosmology
• Mathematical Physics

AstronomerThe study models a Vlasov gas in an external axisymmetric potential combining a central term with a quadrupolar component that creates two potential wells along the symmetry axis. Independent N-particle simulations and statistical methods show that an initially homogeneous, isotropic distribution evolves into an inhomogeneous state with overdensities at the wells. The quadrupolar term is chosen to make the Hamiltonian integrable, enabling an analytic calculation of the final state, comparison with late-time simulations, and interpretation of relaxation through phase-space mixing. The model is a Newtonian analogue of particle motion in Kerr spacetime; possible astrophysical applications are discussed, not established observationally.

PublicUsing computer simulations and mathematical methods, the researchers explore how a gas of particles moves in a prescribed force field with two trapping regions along its symmetry axis. In the model, particles that begin evenly distributed and moving without a preferred direction develop concentrations around these regions. The force field is specially chosen so that the final distribution can also be calculated analytically, allowing comparison with the simulations and helping explain how the particles' motions mix into a settled distribution. The model offers a Newtonian counterpart to particle motion in Kerr spacetime. Possible connections to recently observed astrophysical phenomena are discussed, but the abstract does not establish those connections.

Young explorerThe researchers used computers and math to study lots of tiny particles moving in an invisible landscape with two dips. In their model, the particles start spread out evenly, but later more of them gather near the dips. The researchers chose a special landscape so they could also work out the ending with math. They discuss whether this model might help explain things seen in space, but they have not shown that it does.

Classification of X-ray Binaries in NGC 6946 with the use of Multiwavelength Data

Senay Avdan, Hasan Avdan, Eda Sonbas+1 more

AstronomerArchival Chandra observations of NGC 6946 yielded 98 X-ray binary candidates in the 0.3–8 keV band, with luminosities of 10^36–10^40 erg s^-1. X-ray color-color classification identified 57 HMXB and 8 LMXB candidates. Temporal analysis found 40 variable sources and classified 26 as transients. HST imaging provided possible optical counterparts for 57 sources; color-magnitude diagrams placed 40 above 8 solar masses, classified as HMXBs, and 17 between 5 and 8 solar masses, classified as IMXBs. Sources without identified optical counterparts were assumed, rather than established, to be LMXBs. HMXB and LMXB luminosity functions derived using the X-ray and optical classifications were best described by single power laws with α approximately 1.3–1.6. A machine-learning classifier using multiwavelength photometry assigned a significant population to AGN, whereas traditional methods identified no AGN candidates. These ML classifications remain limited in reliability by instrumental spatial resolution and the training database.

PublicResearchers used archived Chandra X-ray observations to identify 98 possible X-ray binary systems in the galaxy NGC 6946. Forty sources changed in brightness, and 26 were classified as transient sources. Two classification methods gave different breakdowns: X-ray colors identified 57 high-mass and 8 low-mass candidates, while possible counterparts in Hubble images suggested 40 high-mass and 17 intermediate-mass systems. Sources lacking an identified optical counterpart were assumed to belong to the low-mass group, so that assignment is not a confirmed finding. The brightness distributions of the high- and low-mass groups were best described by a single power-law pattern. A machine-learning method also identified a substantial group of possible active galactic nuclei that the traditional methods did not find. However, limited image resolution and limitations in the machine-learning training data make those classifications uncertain.

Young explorerScientists looked at X-ray pictures of a galaxy called NGC 6946 and found 98 bright spots that might be pairs of stars. Some spots changed how bright they were. Pictures from another telescope helped the scientists sort possible star partners into heavier and lighter groups, but they could not find a partner for every spot. A computer also sorted some spots into a different group called active galaxy centers. The pictures and the computer’s learning examples were not good enough to make every answer certain, so the scientists still need to be careful about what these spots really are.

Uncovering the Physical Origins of Black Holes in the Milky Way for Astronomical Surveys

Ilia Kiato, Pierson Lipschultz, Vicky Kalogera+5 more

• Astrophysics of Galaxies
• Solar and Stellar Astrophysics

AstronomerUsing POSYDON binary population synthesis, the authors predict the present-day Milky Way stellar-mass black-hole population and test sensitivity to core-collapse prescriptions, natal kicks, common-envelope efficiency, metallicity, and initial binary distributions. Across their models, isolated black holes predominate, with stellar mergers contributing most and binary disruptions second; detached BH-BH systems dominate surviving binaries. Wind-driven evolution of massive Wolf-Rayet progenitors produces a narrow higher-mass feature near 13 solar masses in the fiducial model, especially prominent in detached BH-BH binaries. It persists under the tested variations in binary-evolution and black-hole-formation physics but depends strongly on metallicity. Lower-mass BH-BH systems predominantly follow stable mass transfer before black-hole formation. The authors also embed synthetic populations in a Galactic model, evolve their kinematics, and make first-order BH-BH microlensing calculations. For systems with luminous companions, they predict a robust stable-mass-transfer population largely absent from rapid synthesis predictions. These are model predictions, not new observational detections, intended to inform interpretation of emerging surveys.

PublicThis study uses computer simulations to predict how stellar-mass black holes in the Milky Way formed and what kinds of systems they occupy today. Across the tested models, most black holes are alone, mainly because their histories involved stars merging or binary systems breaking apart. Among binaries that survive, pairs of black holes dominate. The simulations also predict a narrow concentration near 13 times the Sun's mass in the reference model, linked to winds from massive progenitor stars. This feature survives several changes to the model assumptions but is strongly affected by the stars' chemical composition. The researchers also model how black-hole pairs could magnify background light through gravitational lensing and predict a population of black holes with shining companion stars shaped by stable transfer of stellar material. These are predictions rather than newly observed discoveries, offering a framework for interpreting current and future observations, including those expected from Gaia DR4 and Roman.

Young explorerThe scientists used a computer to imagine how black holes from stars might be spread around our galaxy. In their models, most black holes are alone. Some became alone after two stars joined together or a pair split apart. Others have another black hole or a shining star as a partner. The computer's answers change with some of its rules, so these are ideas to help scientists understand what they find in the sky—not new black holes they have already seen.

Power-Law Injection Spectrum from an Ensemble of Reconnecting Current Sheets

Omar French

• Plasma Physics

AstronomerThe abstract presents a theoretical model of particle injection by a hierarchy of reconnecting current sheets expected in collisionless, low-beta plasma with strong sub-Alfvénic turbulence and a strong guide field. If the reconnecting field scales with sheet length as L^κ and the number of sheets per unit length interval scales as L^(-x), the injected nonthermal spectrum is proportional to γ^(-s), with s = 1 + (x - 2)/(1 + κ). Longest-sheet dominance of the injected energy requires x < 3 + κ and produces a hard spectrum, s < 2. Earlier numerical studies found approximately 2 ≤ x ≤ 3.3, while intense-sheet scalings support κ ≥ 0, giving an estimated range of approximately 1 ≤ s ≤ 2.3. The proposed injection mechanism may account for flat or mildly steep radio spectra in optically thin sources and hard ion spectra in active galactic nucleus coronae; these applications are possibilities, not demonstrated observational results.

PublicThis theoretical study considers how turbulent, magnetized plasma could give particles unusually high energies. It assumes that turbulence creates thin regions called current sheets, where magnetic fields reconnect, across a broad range of sizes. The predicted distribution of particle energies depends on how common large sheets are and how their magnetic strength changes with size. When the longest sheets supply most of the energy, high-energy particles make up a relatively large share of the injected population. Earlier computer studies provide ranges for the model’s inputs, but the abstract does not report a new observational test. The mechanism could help explain certain radio spectra and energetic ions in the hot plasma around active galactic nuclei.

Young explorerImagine a swirling cloud of tiny particles with magnetic fields running through it. Scientists think the swirling can make thin patches where the magnetic fields reconnect and give particles energy. Their idea says that if the biggest patches give most of the energy, quite a lot of particles could get a big boost. Earlier computer studies help them work out what might happen. This could help explain some radio signals from space, but it is not yet shown here to be the explanation.

Radial Modes of Hot Neutrino-Trapped Hybrid Stars

Peter B. Rau, Andrea Sabatucci, Armen Sedrakian

• Nuclear Theory

AstronomerThis theoretical study computes the fundamental radial mode of hot hadronic and hybrid stars under conditions relevant to proto-neutron stars and neutron-star merger remnants. Finite-temperature stellar models combine a covariant density functional for hadronic matter with three-flavor 2SC quark matter. Two isentropic configurations are examined for neutrino-transparent matter and matter with trapped electron neutrinos at fixed electron-lepton fraction. For trapped matter, the authors compare a Gibbs-type construction with global electron-lepton-number conservation against a locally constrained Maxwell-type prescription. Both fixed-entropy equations of state have extended coexistence regions, without sharp interfaces requiring conversion rate-dependent junction conditions. The hybrid-star mode frequency tracks the purely hadronic sequence until deconfinement begins, then decreases relative to it. Neutrino trapping shifts this signature to higher stellar masses and central pressures; the Maxwell-type prescription further raises the onset pressure and yields a steeper frequency decrease near the stability limit. Fractional frequency shifts are evaluated at equal gravitational mass. These model results identify the fundamental radial mode as a sensitive probe of entropy, lepton trapping, and the treatment of quark deconfinement, rather than reporting an observed stellar signal.

PublicThe researchers used theoretical models to study how hot, dense stars expand and contract in their simplest radial vibration. Such conditions are relevant to newly formed neutron stars and the remnants of neutron-star mergers. They compared stars made entirely of hadronic matter with stars whose dense interiors also contain quark matter. In the models, the vibration frequency follows the hadronic-star pattern until quark matter appears, then becomes lower by comparison. Trapping neutrinos inside the star delays the appearance of quark matter, moving this change to greater stellar masses and central pressures. The way the transition between matter types is modeled also affects when the change begins and how rapidly the frequency drops near the stability limit. These calculations suggest that radial vibrations could help probe the interiors of hot compact stars; the study does not report an observed vibration or detection of quark matter.

Young explorerScientists made computer models of very hot, tightly packed stars to study how they puff in and out. In the models, when a different kind of matter called quark matter appears inside, the star's puffing becomes slower than in a similar star without it. Tiny particles called neutrinos can delay this change when they are trapped inside. This is a prediction from models, not something the scientists watched a real star do.

Chana: A GPU-Accelerated AMR GRRMHD Code

Tianshu Wang

• Instrumentation and Methods for Astrophysics

AstronomerChana is a GPU-accelerated, block-structured adaptive-mesh code coupling general relativistic magnetohydrodynamics, multigroup M1 neutrino transport, and dynamical spacetime evolution with Z4c. Spatial discretizations and ghost-zone widths are chosen independently for each physical module to balance accuracy and cost. Stiff radiation–matter interactions use an implicit treatment with analytically calculated Jacobians. Implemented in C++20 with MPI and Kokkos 5, the code is validated through GRMHD, radiation-transport, and dynamical-spacetime tests. For a representative core-collapse supernova configuration with three neutrino species and 12 energy groups per species, four-stage RK4 integration achieves approximately 1.1 million cell updates per GPU second on NVIDIA A100 GPUs. Reported weak-scaling efficiency exceeds 85% through 256 GPUs on Perlmutter. These are code-validation and performance results, not observational findings or new supernova predictions.

PublicThe paper introduces Chana, a computer simulation tool for modeling magnetized matter, neutrinos, and changing spacetime under general relativity. It uses graphics processing units (GPUs) and a grid that can be refined to balance accuracy with computing cost. The authors report testing the software's treatment of matter, radiation, and spacetime. In a benchmark setup representative of a collapsing star, it processed about 1.1 million grid-cell updates per GPU per second on NVIDIA A100 hardware. Its efficiency stayed above 85% as the workload and computer resources grew together, up to 256 GPUs on the Perlmutter system. These results describe the software's tests and speed, rather than observations of a real exploding star.

Young explorerScientists made a computer program called Chana to help model what happens when a star collapses. It works out how star material, tiny particles called neutrinos, and space itself can change. The program divides its model into little boxes and uses powerful computer chips to do the calculations quickly. The scientists tested its different parts and measured how fast it worked. This paper is about testing a computer tool, not watching a real star explode.

Investigating X-ray Emission from Radio-detected Broad- and Narrow-line Seyfert 1 Galaxies

Minhua Zhou, Minfeng Gu, Lei Xu+2 more

AstronomerThis statistical comparison of radio-detected narrow- and broad-line Seyfert 1 galaxies (NLS1s and BLS1s) combines XMM-Newton spectral fits with SDSS and FIRST data. The samples show no significant difference in fitted soft X-ray blackbody temperatures, but NLS1s have steeper hard X-ray photon indices and optical-to-X-ray slopes, αox. At comparable optical luminosities, NLS1s have higher αox, indicating relatively weaker X-ray emission. The samples also show marginally distinct radio-luminosity–black-hole-mass dependencies in the fundamental plane and different αox–radio-loudness correlations. Relative to the UV-luminosity–αox relation for radio-quiet AGN, estimated X-ray excess correlates positively with radio loudness in both samples. Radio-quiet BLS1s generally show an X-ray excess, whereas radio-quiet NLS1s tend to show a deficiency; the latter also have lower Eddington ratios inferred from X-rays than from optical luminosity. The authors interpret these findings as evidence for intrinsically weaker X-ray emission in NLS1s and suggest, without establishing, that an earlier evolutionary stage may explain the differences. Multivariate fits involving radio luminosity, X-ray luminosity, and radio loudness support a jet-associated multi-wavelength radiative connection.

PublicResearchers compared X-ray emission from two groups of radio-detected active galaxies: narrow-line and broad-line Seyfert 1 galaxies. Using X-ray spectra alongside optical and radio data, they found no significant difference in the temperatures used to describe the galaxies’ soft X-ray emission. However, the narrow-line group had steeper hard X-ray spectra and, at similar optical brightness, relatively weaker X-ray emission. Comparisons with a reference relation for radio-quiet active galaxies showed that radio-quiet broad-line galaxies generally had more X-ray emission than expected, while radio-quiet narrow-line galaxies tended to have less. In both groups, estimated X-ray excess increased with radio loudness. The authors suggest that the narrow-line galaxies’ weaker X-ray emission may reflect an earlier stage of evolution, but this explanation is not established. Statistical links between radio and X-ray properties also support a connection involving jets.

Young explorerScientists looked at two groups of galaxies that send out radio signals and a kind of light called X-rays. When the galaxies were about equally bright in ordinary light, one group tended to shine less brightly in X-rays. Not every galaxy was the same. The scientists think this group might be at an earlier stage of growing, but they are not sure. They also found clues that the radio signals and X-rays may be linked to jets coming from the galaxies.

A spatially resolved view of Fast Radio Burst host metallicities with Integral-field Spectroscopy

Sunil Simha, Hsiao-Wen Chen, Wen-fai Fong+15 more

• Astrophysics of Galaxies

AstronomerThe study uses spatially resolved IFU spectroscopy and the O3N2 index to map gas-phase metallicity in five FRB hosts at z < 0.05, including the burst locations. Four hosts were observed with Magellan/LLAMAS, while FRB 20250316A was studied using archival Keck/KCWI data. Most hosts exhibit internal ISM metallicity variations of at least 0.3 dex, with host median abundances spanning 12 + log(O/H) ≈ 8.5–8.7. Four burst sites have abundances of approximately 8.5–8.9 on this scale; the fifth is below 8.5. These observations show that global longslit metallicity estimates do not always represent burst-site conditions. Magnetars motivate the investigation as the leading proposed FRB progenitors, but the study does not establish a metallicity preference for FRB occurrence or magnetar formation. The authors advocate IFU observations of larger host samples to constrain such preferences.

PublicScientists mapped the chemical composition of gas in five nearby galaxies where fast radio bursts occurred. Their observations reveal substantial differences in metallicity—the abundance of elements heavier than helium—both within individual galaxies and among the burst locations. This means a galaxy-wide metallicity estimate does not always describe the environment where a burst happened. Magnetars are the leading proposed sources of these bursts; if their formation favors particular chemical environments, that preference might also appear at burst sites. This small study does not establish such a preference. The researchers recommend mapping more host galaxies to test it.

Young explorerScientists looked at five galaxies where quick flashes of radio waves happened. They found that the gas has different amounts of some ingredients in different places. So measuring a whole galaxy does not always tell us what the gas is like right where a flash happened. They want to look at more galaxies to learn whether these flashes happen more often in places with certain ingredients.

Adaptive proposals for nonparametric equation-of-state inference with RIFT: iterative Gaussian-process refinement in a compressed sequence representation

R. O'Shaughnessy, Z. Zhu

• Instrumentation and Methods for Astrophysics

AstronomerThe study develops and validates adaptive proposals for nonparametric neutron-star EOS inference while keeping the base functional prior fixed. Reweighting a finite prior ensemble remains sufficient for binary-neutron-star detections to date; effective sample size becomes problematic when the likelihood concentrates with third-generation catalogues or additional electromagnetic and nuclear-theory constraints. Data-informed generations are combined through multiple importance sampling, with a calibrated Gaussian projection used when that approach degenerates at large catalogue size. Implementations use either compressed principal components of the neutron-star sequence, requiring no stellar-structure solve for draws, or a sound-speed parametrization with a differentiable Tolman–Oppenheimer–Volkoff solver, both on a constrained low-density-to-pQCD bridge. Separately, replacing the wide nuclear-metamodel anchor with a crust-plus-chiral-EFT anchor leaves the maximum-mass prior unchanged but imposes a hard radius-prior ceiling at the measured NICER value, highlighting the anchor's role in fixing the low-density prior. GW170817 combined with the specified NICER and radio factors yields a calibration-conditional R(1.4 solar masses) = 11.7 ± 0.4 km. In a synthetic 1,000-event catalogue, the method reproduces the mean fixed-prior Λ(1.4 solar masses) to 0.4%, with a result 1.5 times wider, while the fixed archive's effective sample size falls from approximately 470 to 22.

PublicThe researchers developed and tested a way to learn how matter behaves inside neutron stars without relying on a single prescribed equation. Existing detections can still be analysed by adjusting the weights of a fixed collection of possibilities. Much larger future catalogues, or added information from electromagnetic observations and nuclear theory, can make that collection less useful. The new method generates better-targeted possibilities while preserving the original starting assumptions. Those assumptions still matter: changing the model used to anchor low-density matter introduces a strict upper limit on the radius in the starting distribution, without changing its maximum-mass distribution. Combining GW170817 with specified NICER and radio information gives a radius of 11.7 ± 0.4 kilometres for a neutron star with 1.4 times the Sun's mass, conditional on the calibration used. A separate test with 1,000 simulated events closely reproduces a reference mean for the star's tidal response, but gives a result 1.5 times wider. This simulated test is not a finding from 1,000 observed events.

Young explorerNeutron stars are stars packed very tightly. Scientists use clues to work out what their insides might be like. This study tested a new way to find useful guesses when there are lots of clues, while keeping the same starting rules. It worked well in a test with pretend star events, though its answer was less narrow than the comparison answer. The starting rules still matter, so the answers are not completely certain.

Scalable and sequential inference of the neutron star equation of state with the Einstein Telescope

Thibeau Wouters, Thomas C. K. Ng, Hauke Koehn+4 more

• General Relativity and Quantum Cosmology

AstronomerThe authors introduce a GPU-accelerated hybrid sequential Monte Carlo algorithm for hierarchical inference of the neutron-star equation of state from binary neutron star mergers. Combining data and likelihood tempering, it adaptively updates the posterior in batches while reusing previous inference results, rather than restarting from a wide prior as existing methods do. In a simulated month containing around 1500 mergers, the method infers the equation of state in a few hours on a single GPU. Processing a full year of detections in a few days on current hardware is a projection, not a demonstrated result. The approach offers a practical route toward real-time inference for future observatories such as the Einstein Telescope, which are expected to detect tens of thousands of mergers annually.

PublicFuture gravitational-wave observatories, such as the Einstein Telescope, are expected to detect tens of thousands of neutron star mergers each year. These signals could help scientists understand how matter behaves inside neutron stars, but combining information from so many mergers poses a computing challenge. The authors present a method that updates its conclusions as new batches arrive, preserving earlier work instead of starting over. Using simulated data for about 1500 mergers, representing one month, it completed the analysis in a few hours on a single graphics processing unit. The authors estimate that a year's detections could be analyzed in a few days on current hardware. That yearly performance is a projection; the reported test used simulations rather than observations.

Young explorerWhen two neutron stars crash together, they make tiny ripples in space. Scientists hope future machines will hear lots of these ripples and help us learn what neutron stars are like inside. This study shows a new computer method that keeps what it has already learned when more information arrives, instead of starting again. The researchers tested it with pretend signals from about 1500 crashes, and it took a few hours. They think it could handle a whole year's signals in a few days, but they have not shown that yet.

X-ray spectral scaling of black hole mass in quasi-periodic eruptive source RX J1301.9+2747

Lev Titarchuk, Elena Seifina, Vadim Arefiev+2 more

• Astrophysics of Galaxies

AstronomerThe authors analyze X-ray spectra and timing of the accreting SMBH in RX J1301.9+2747 using ASCA, ROSAT, XMM-Newton, and NICER observations; NICER detected renewed quasi-periodic eruption activity in 2024. Fits with the Bulk Motion Comptonization model yield a photon index that increases with inferred mass accretion rate and saturates at Γ = 2.7 ± 0.1 near outburst peaks. Applying Γ–accretion-rate scaling to this source for the first time, with HLX-1 ESO 243-49, OJ 287, and 1H 0707-495 as references, gives a mass estimate of 4 × 10^5 to 7 × 10^6 solar masses. This range depends on an assumed inclination of 0°–70°, adopted as plausible under the AGN unified model. Separately, a quasi-periodic oscillation frequency near 10^-4 Hz is used to infer a Compton cloud size of approximately 10^11 cm and a black hole mass of order 10^6 solar masses. These model-dependent estimates are consistent with previous mass measurements using other methods.

PublicResearchers studied X-rays from matter falling toward the supermassive black hole in RX J1301.9+2747, which produces bright eruptions at roughly repeating intervals. NICER observations detected renewed eruptions in 2024. By modeling how the X-ray spectrum changes as the inferred rate of infalling matter rises, the team estimated the black hole's mass at between 400,000 and 7 million times the Sun's mass. The broad range depends on assumptions about the viewing angle and comparisons with other black hole systems. A separate estimate based on the timing of X-ray oscillations points to roughly a million solar masses. The estimates agree with earlier measurements, but depend on models rather than a direct weighing of the black hole.

Young explorerScientists watched X-rays coming from hot stuff falling toward a huge black hole. The light has bursts that happen again and again, though not like a perfect clock. They saw the bursts return in 2024. By studying the light and how it changes, they estimated that the black hole could weigh as much as hundreds of thousands to millions of Suns. They cannot weigh it directly, so their answer depends on how they think the hot stuff behaves and which way we are looking at it.

Probing turbulence in the ionized interstellar medium using young pulsars. I. Dispersion measure variations

S. J. I. Melfor, A. Parthasarathy, S. Johnston+9 more

AstronomerThe study characterizes temporal dispersion-measure (DM) variability in 364 young pulsars using 18 years of Murriyang/Parkes timing observations from the 21 cm Multibeam and ultra-wideband low-frequency (UWL) receivers. Epoch-wise DMs were derived from sub-banded pulse arrival times, with variability assessed through linear trends and structure functions compared against Kolmogorov-turbulence expectations. Significant DM variations were detected in 89 pulsars in the UWL data and 23 in the multibeam data; 16 pulsars in the combined dataset show significant trends. These receiver-specific counts should not be treated as disjoint populations. The authors find tentative evidence that the observed variations are predominantly consistent with Kolmogorov turbulence in the ionized interstellar medium. For PSRs J1105-6107 and J1829-1751, variations in the estimated DM are attributed to periodic pulse-profile variability. A further finding is that 21 bright, slow pulsars exhibit short-term DM variations exceeding expectations from the ionized interstellar medium; the abstract does not establish their physical origin.

PublicPulsars send out radio pulses that can reveal changes in the electrically charged gas between them and Earth. Researchers examined 18 years of observations of 364 young pulsars with the Murriyang/Parkes radio telescope, measuring changes in dispersion measure, a quantity that traces free electrons along the signal’s path. They detected significant changes in many pulsars and found tentative evidence that most of the observed variability fits a standard model of turbulence in interstellar gas. Not every measured change necessarily reflects that gas: in two pulsars, periodic changes in pulse shape were identified as driving the estimated dispersion changes. They also found 21 bright, slow pulsars with short-term variations larger than expected from the interstellar medium, without establishing the cause in the abstract.

Young explorerPulsars are stars that send us radio pulses. Scientists watched 364 young pulsars over 18 years to learn about the gas their signals travel through. Many signals changed. The changes mostly seem to fit the idea of swirly gas, but scientists are not sure yet. For two pulsars, changing pulse shapes affected the measurements. Some other changes were bigger than expected, and their cause is still unclear.

Predicting High-Energy neutrino emission from X-ray absorption in CSM-interacting SNe

Silvia Gagliardini, Simone Dall'Osso, Dafne Guetta

AstronomerThe study develops an X-ray-driven framework for predicting high-energy neutrino emission from core-collapse supernovae interacting with dense circumstellar material. It uses the time-dependent hydrogen-equivalent absorbing column, N_H(t), and shock velocities inferred from X-ray plasma temperatures to reconstruct the circumstellar density profile and shock-velocity evolution. Applied to SN 2023ixf and SN 2024ggi, the framework estimates shock-breakout epochs and neutrino emission, and computes expected event rates for IceCube and KM3NeT/ARCA. The calculations predict that neutrino production is concentrated near shock breakout, when hadronic interactions are most efficient, defining short, source-specific search windows that maximize signal-to-background ratio. These are predictions informed by X-ray observations, not reported neutrino detections; the method reduces reliance on prescribed density profiles and progenitor mass-loss histories.

PublicExploding stars surrounded by dense gas are promising sources of high-energy neutrinos. This study uses X-ray observations to help predict when and how strong those neutrino signals might be, rather than relying mainly on assumed histories of gas loss from the stars. For SN 2023ixf and SN 2024ggi, the researchers use changing X-ray absorption and temperature to reconstruct the surrounding gas and the motion of the explosion’s shock. They then estimate the expected neutrino signals for IceCube and KM3NeT/ARCA. Their calculations place most neutrino production near shock breakout, suggesting a short search period tailored to each explosion that would best separate a possible signal from background events. The study predicts signals and search windows; it does not report detecting neutrinos from these supernovae.

Young explorerWhen a star explodes, its blast can run into gas around it. Scientists used X-ray clues from two exploding stars to work out what that gas and blast might be like. Then they predicted when tiny particles called neutrinos might come from them. Their calculations suggest a short time near when the blast breaks out is the best time to look. They have not reported finding those neutrinos.

The Potential Contribution of Radiative Supernova Remnants to the Local Cosmic Ray Spectrum

P. Cristofari, V. H. M. Phan, S. Recchia+1 more

AstronomerVery-high-energy gamma-ray observations of massive stellar clusters and microquasars have renewed questions about the dominant Galactic cosmic-ray sources. This study computes the cosmic-ray proton content of typical supernova remnants from diffusive shock acceleration and reacceleration of pre-existing cosmic rays through the adiabatic and early radiative phases. The calculations indicate that, if both mechanisms persist into part of the radiative phase, the accumulated energized-particle content can quickly exceed the typical budget needed to explain most Galactic cosmic rays. The authors infer that the instantaneous efficiency, defined as the fraction of fluid ram pressure converted into cosmic rays, would then need to remain below roughly 1% for most of the remnant’s evolution. They also find that radiative-phase acceleration can shape the injected spectra and illustrate how differences between thermonuclear and core-collapse remnants could help explain the measured local interstellar helium–proton spectral difference. These are conditional calculations and proposed explanations, not observational confirmation of extended acceleration.

PublicWhat supplies most of the energetic particles called cosmic rays in our Galaxy remains debated. Gamma-ray observations show that massive star clusters and microquasars can accelerate particles to very high energies, challenging the long-standing emphasis on supernova remnants. Here, researchers calculate how supernova remnants could accelerate particles and further energize existing cosmic rays as the remnants expand and begin cooling through radiation. If these processes continue into part of that cooling stage, the calculated particle energy budget can exceed what is needed to explain most Galactic cosmic rays. This suggests that the remnants would need to transfer only a small fraction, roughly 1% or less, of their fluid ram pressure into cosmic rays for most of their evolution. The calculations also suggest possible effects on particle spectra, including a potential explanation for measured differences between helium and proton spectra; they do not establish that explanation.

Young explorerWhen a star explodes, the expanding leftovers can give tiny particles a big energy boost. Scientists calculated what could happen if those boosts keep going while the leftovers cool. Their sums suggest that the boosts might add up to more than needed to explain most of these speedy particles in our Galaxy. If so, each boost would need to be quite gentle. This is an idea from calculations, not something they have proved by watching.

Assessing transitional pulsar candidates through a quantitative estimation of their light-curve similarity

D. F. Torres, C. R. García, F. Coti Zelati+5 more

AstronomerThe study introduces a Dynamic Time Warping (DTW) framework for assessing transitional millisecond pulsar (tMSP)-like X-ray light-curve morphology. Moving-window similarity distributions calibrate candidate–prototype distances against the internal heterogeneity of PSR J1023+0038 across observations, replacing qualitative comparison with a single prototype observation. Applied to confirmed and candidate tMSPs and a non-tMSP control sample, the measure yields a reproducible ranking suitable for candidate triage and archival searches. The controls show that short-timescale accretion variability can partly mimic tMSP-like morphology, so light-curve shape remains a screening diagnostic rather than a definitive classification.

PublicAstronomers often identify possible transitional millisecond pulsars by visually comparing their changing X-ray brightness with that of a reference source, PSR J1023+0038. This study introduces a repeatable comparison method called Dynamic Time Warping. Rather than matching just one observation, it checks whether a candidate's brightness patterns fit the range seen in the reference source across observations. Tests on confirmed pulsars, candidates, and other systems produced a ranking that can help prioritize promising candidates and search existing observations. However, the other systems sometimes showed similar patterns as material fell onto them. The method can therefore flag candidates, but brightness patterns alone cannot establish their identity.

Young explorerScientists watch how some things in space get brighter and dimmer in X-rays. They made a new way to compare those patterns with a special pulsar, using many of its patterns instead of just one. Their tests helped them rank which things looked most alike. But other things in space can make similar patterns too, so looking alike is only a clue—not proof that they are the same kind of thing.

It Takes Two: nucleosynthesis in core-collapse supernova simulations of binary-star progenitors

Gaétan Jalin, Almudena Arcones, Evan P. O'Connor+2 more

AstronomerThis study presents one- and two-dimensional neutrino-driven core-collapse supernova simulations of single- and binary-star progenitors, examining how binary interaction changes pre-supernova core structure and explodability. The models predict that binary-evolved progenitors are generally more explodable than single stars of the same initial mass, suggesting that initial mass alone does not correlate well with the supernova outcome. This trend still requires confirmation through a systematic comparison of self-consistent single- and binary-star explosion simulations. The study also compares in-situ nuclear reaction networks with post-processing approaches. A small alpha-chain network approximates nuclear energy generation and the abundances of key isotopes such as nickel-56 well, but titanium, chromium, and iron isotope production shows notable discrepancies and remains sensitive to network size and thermodynamic history.

PublicInteractions between massive stars in a pair can change their internal structure and composition before they explode. Using one- and two-dimensional computer simulations, the researchers predict that stars altered by a companion are generally more likely to explode than single stars that began with the same mass. This suggests that a star’s starting mass alone is not a reliable guide to its supernova outcome, although a systematic comparison of self-consistent simulations is still needed to confirm the trend. The researchers also tested ways of calculating nuclear reactions during and after the simulations. A compact reaction model can approximate the energy released and the amount of some isotopes, including nickel-56, but predictions for titanium, chromium, and iron isotopes depend on how many reactions are included and on the material’s temperature and density history. These are simulation findings, not observations of supernovae.

Young explorerSome very big stars have a star companion that can change what they are like inside. Scientists used computer models to see how these stars might explode. The models suggest that a star changed by a companion may explode more easily than a star that started just as heavy but had no companion. Scientists still need more careful computer comparisons to check this idea. They also tried a simpler way to work out the energy and kinds of atoms made in an explosion. It worked well for some things, but not for every kind of atom.

Unveiling the Accretion Architecture of GS 1354--64: A Broadband X-ray and Polarimetric Study of its 2025--2026 Outburst

Kaushik Chatterjee

AstronomerA multi-satellite study of the black hole candidate GS 1354-64 during its 2025–2026 outburst combines broadband spectroscopy, fast timing, and X-ray polarimetry. In the Compton-dominated hard-state rise, narrow Type-C QPOs increase from 0.08 to 1.73 Hz with approximately 8–10% fractional RMS. Their anti-correlation with inferred inner disk radius and linear correlation with coronal photon index support an interpretation involving inward disk migration, increasing precession frequency, and coronal cooling. An observed highly ionized Fe XXVI equatorial wind is interpreted as evidence for strong localized radiation pressure before the transition. In the thermal-dominated soft state, individual-epoch reflection fits give a* approximately 0.94–0.99 and inclination approximately 45–53 degrees; joint spectral fits favor a* approximately 0.998 and inclination approximately 51 degrees, with the disk at the ISCO. QPO frequencies rise to approximately 4.7–6.2 Hz while fractional RMS falls to approximately 3–6%. Joint spectro-polarimetric modeling uses the steep rise of polarization degree with energy to reject spherical and lamppost geometries in favor of a radially extended, highly asymmetric slab-like corona. The abstract also interprets weaker QPOs and an energy-independent polarization angle as stabilization into an extended, symmetric slab, consistent with collapse of a puffed-up hard-state corona; the differing symmetry descriptions remain unresolved in the abstract.

PublicDuring the 2025–2026 outburst of the black hole candidate GS 1354-64, researchers tracked changes in its X-rays, including repeating brightness variations and polarization, which describes how light’s vibrations are oriented. Early in the outburst, the repeating variations became faster as the estimated inner edge of the surrounding disk moved inward. These relationships support, rather than directly prove, a picture in which the disk’s motion changes the behavior of nearby hot gas and helps cool it. The observations also revealed a highly ionized wind from the disk, possibly driven by locally strong radiation pressure. Later, the disk dominated the X-ray emission, and modeling favored a black hole spinning very close to the maximum allowed rate. The brightness variations became faster but weaker. Polarization modeling favored a broad, flattened region of hot gas over spherical or compact lamppost models. The authors interpret the changes as a collapse and stabilization of the earlier puffed-up hot gas, although the abstract describes the later flattened region as both asymmetric and symmetric without explaining that difference.

Young explorerScientists watched X-rays from hot gas around a possible black hole as it became very active. The light had a repeating wiggle that got faster and later became smaller. They also found a wind blowing from the disk of gas. By comparing the light with models, they think the black hole spins very fast and the hot gas changed from a puffy shape to a flatter, wider shape. That shape is an explanation of the clues, not something they photographed directly.

Parameter degeneracy and information loss in inverse flavor mapping for high-energy astrophysical neutrinos

Zi-Qiang Chen, Zhi-zhong Xing, Ye-Ling Zhou

• High Energy Physics - Phenomenology
• High Energy Physics - Experiment

AstronomerThe study examines the inverse mapping from detected astrophysical neutrino flavor fractions f to source fractions η, related by f = Pη, where P depends on four lepton mixing parameters. Recovering η encounters parameter degeneracy and information loss, particularly near or at det P = 0, a limit allowed by current oscillation data. The authors explore the parameter correlations yielding this singular limit, including μ–τ reflection symmetry, and formulate constraints relating the electron and muon fractions at detection and production. They use recent IceCube all-sky flux data spanning 5 TeV to 10 PeV to illustrate how far the source composition can be mapped, assuming the relevant sources share a common flavor composition. The abstract does not report a uniquely recovered source composition.

PublicNeutrinos come in three types, or flavors, and their flavor mixture changes as they travel from cosmic sources to Earth. This study examines how reliably scientists can work backward from the detected mixture to the mixture at the sources. Uncertainty in the mixing parameters and loss of information can make that reconstruction ambiguous; in a limiting case still allowed by current data, the mapping cannot be uniquely reversed. The authors investigate the conditions behind this problem and illustrate the reconstruction limits using recent IceCube measurements from 5 TeV to 10 PeV. Their analysis assumes that the contributing sources all produce the same flavor mixture, rather than establishing that they do.

Young explorerTiny particles called neutrinos travel to us from space. They come in three kinds, and the mix of kinds can change on the way. Scientists want to use the mix that arrives to figure out the mix that started the trip. This study explains why different starting mixes can be hard or impossible to tell apart. The scientists use measurements from IceCube to show what they might learn, assuming all the places sending the neutrinos start with the same mix.

The pseudospectrum for gravitational perturbations in Kerr spacetimes

Hongsheng Zhang, Zong-Kuan Guo, Rong-Gen Cai

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

AstronomerThis mathematical and numerical study examines the Kerr gravitational pseudospectrum for spin weight s=2, rather than reporting gravitational-wave observations. A hyperboloidal formulation with two-dimensional Chebyshev collocation casts the quasinormal-mode problem as a non-self-adjoint eigenvalue problem. Because the fields with spin weights s and −s are independent for nonzero s, the conserved-current method does not provide a single-field energy norm. The authors instead use the Teukolsky–Starobinsky identities, relating the s=−2 field to a fourth-order operator acting on the s=+2 field, to obtain an H² energy norm after symmetrization. Together with the known H¹ norm for s=0, this suggests an H norm of order the absolute value of s; the pattern is verified only for s=0 and s=2. All results use a frequency-independent two-field hierarchy. The pseudospectrum tightens by 1.1–3.5 decades at each transition from L² to H¹ to H², but remains large. The s=+2 and s=−2 operators are isospectral, not isopseudospectral: in H², the ψ₀ resolvent exceeds the ψ₄ resolvent by 0.19–0.82 decades at twelve of fourteen probes, while the ordering reverses by 0.18–0.19 decades at the two probes furthest along the QNM line. The gravitational pseudospectrum exceeds the scalar one by 0.5–5.2 decades in the window minimum and by 5.9 decades in L² at ωM=0.47−0.17i. Along the damping direction, the s=2 resolvent is non-monotonic whereas the s=0 resolvent is smooth. The authors interpret these results as showing universal Kerr QNM spectral instability, stronger for gravitational perturbations.

PublicThe researchers use mathematical calculations to study how sensitive a rotating black hole’s characteristic ringing frequencies are to changes in the equations describing them. These are numerical findings, not measurements of a real black hole. They develop an energy-based way to assess gravitational disturbances and compare three mathematical measures, called L², H¹ and H². Each successive measure narrows the region of sensitivity by 1.1–3.5 decades, meaning orders of magnitude, but the region remains large. Two descriptions of the gravitational disturbance have the same ringing frequencies yet different sensitivities: one has a larger response at twelve of fourteen tested points, by 0.19–0.82 decades, while the other is larger at the remaining two, by 0.18–0.19 decades. Compared with a simpler scalar disturbance, the gravitational case is larger by 0.5–5.2 decades in the minimum across the studied frequency window, and by 5.9 decades for a particular frequency using L². Its response also varies less smoothly along the direction associated with damping. The authors conclude that sensitivity of ringing frequencies is a general feature of rotating Kerr black holes and is stronger for gravitational disturbances. Their proposed pattern for the appropriate energy measure has been checked for spin weights 0 and 2, not for every spin weight.

Young explorerScientists used math and computers to study how a spinning black hole might ring, a little like a bell. They did not listen to a real black hole in this study. They asked whether tiny changes in the math could change the ringing notes. Different ways of checking made the notes look less sensitive, but they still looked sensitive. Two ways of describing the same ringing gave the same notes, yet reacted differently to changes. The scientists think this sensitivity is a general feature of spinning black holes, and their calculations found it was stronger for gravitational disturbances than for a simpler kind of disturbance.

Magnus: neutrino oscillation probabilities for any Hermitian Hamiltonian, any number of flavors, and any matter profile

Mauricio Bustamante

• High Energy Physics - Phenomenology
• High Energy Physics - Experiment
• High Energy Physics - Theory
• Quantum Physics

AstronomerThe authors present Magnus, an open-source Python code for computing neutrino flavor-transition probabilities through varying-density media. Unlike constant-density stepping, whose error decreases quadratically with step width, Magnus uses a high-order Magnus expansion; its computational cost is governed by density variation rather than the number of oscillations along the path. The code accepts arbitrary density profiles, flavor counts, and Hermitian Hamiltonians, including models with non-standard interactions, sterile neutrinos, Lorentz-invariance violation, or pseudo-Dirac neutrinos. It automatically selects cheaper methods where applicable: for slowly varying profiles such as the Sun’s, it follows instantaneous eigenstates and uses the expansion at resonances. It returns both oscillating and phase-averaged probabilities, the latter relevant to solar and astrophysical neutrinos. The authors report typical evaluations taking a few milliseconds and batched scans costing one to two orders of magnitude less per point. Among the public codes they compared, Magnus was fastest at high accuracy for a varying profile. These are computational performance findings, not new neutrino observations; the comparisons do not establish superiority over every possible solver.

PublicNeutrinos can be detected as a different type, or flavor, from the one they started with. Predicting the chances becomes computationally demanding when the density of matter changes along their route, as it does inside Earth, the Sun, or a supernova. The authors introduce Magnus, a freely available Python program designed to make these calculations faster at high accuracy. It adapts its approach to the density profile and can handle a range of neutrino models, including proposed extensions to standard physics. The authors report that a typical calculation takes a few milliseconds and that processing many cases together reduces the cost per case further. In their comparisons, it was the fastest public code tested for high-accuracy calculations with changing density. This is a new calculation tool, not evidence that any proposed neutrino model is correct.

Young explorerNeutrinos are tiny particles that can change from one type to another as they travel. Scientists want to work out how likely each change is, even when the stuff along the way gets thicker or thinner. They made a computer program called Magnus to help. Their tests say it can do these calculations quickly. It calculates what might happen; it does not watch the particles itself.

The neutrino magnetic moment and supernovae with strong magnetic fields

Clément Ehrhardt, Maria Cristina Volpe, Miguel Ángel Aloy+1 more

• High Energy Physics - Phenomenology

AstronomerThis theoretical study explores how a non-zero magnetic moment could affect Majorana neutrinos in strong core-collapse supernova magnetic fields. The neutrino magnetic moment remains unknown. A schematic model illustrates the effects of resonant spin-flavor precession on the signal from a future Galactic supernova. Detailed simulations then consider a 17-solar-mass neutrino-driven supernova leaving a neutron star and a 26-solar-mass magnetorotational supernova leaving a black hole. The authors predict neutrino fluxes and event rates for the running JUNO and upcoming Hyper-Kamiokande experiments. In these models, transition magnetic moments of 10^-14 Bohr magnetons significantly affect the neutronization burst and accretion phase of the neutrino-driven case, while moments as small as 10^-15 Bohr magnetons significantly affect early times in the magnetorotational case. These are conditional simulation predictions, not measurements of a neutrino magnetic moment or an observed supernova signal.

PublicNeutrinos are particles released by exploding stars, but scientists still do not know their magnetic moment—the property that would let them interact with a magnetic field in the way studied here. The researchers explored whether strong magnetic fields in some stellar explosions could alter the neutrino signals reaching detectors. They used a simplified model and detailed simulations of two explosions: one leaving a neutron star and another leaving a black hole. Assuming neutrinos are of the Majorana type, the calculations predict that even very small magnetic moments could substantially change parts of the signal. The study predicts what JUNO and the upcoming Hyper-Kamiokande experiment might detect from a future supernova; it does not report a detection or establish that neutrinos have such magnetic moments.

Young explorerWhen a star explodes, it sends out tiny particles called neutrinos. Scientists do not know whether these particles can act like tiny magnets. They used computer models to ask what might happen if they can. In the models, a very strong magnetic field could change the neutrinos coming from the explosion, even if their magnet-like effect is very small. This could change what special detectors see when a star explodes in the future. It is a prediction, not something scientists have seen happen.

Line-of-sight Acceleration Driven Effects in Eccentric Compact Binary Coalescences

Mohd Asim Ansari, Avinash Tiwari, Sajad A. Bhat+2 more

• General Relativity and Quantum Cosmology

AstronomerExternal gravitational potentials can imprint line-of-sight acceleration (LOSA) on compact-binary inspiral signals, potentially probing their environments event by event. LOSA and orbital eccentricity can mimic one another when waveform templates include only one effect. The authors present the frequency-domain phase correction for the (2, 2) mode’s leading eccentric harmonic in an accelerating eccentric binary and discuss inconsistencies in the literature. They demonstrate that jointly modeling both effects can resolve the degeneracy in a simulated GW170817-like injection with added LOSA and eccentricity, assuming an A+-like noise power spectral density for the LVK network. The injected LOSA, eccentricity, and other binary parameters are recovered within their 90% credible intervals. This is a simulation result, not a measurement of LOSA or eccentricity in GW170817, and supports incorporating LOSA into eccentric waveform models.

PublicGravitational waves from two compact objects spiraling together may carry clues about gravity in their surroundings. But acceleration caused by that surrounding gravity can alter the signal in ways that resemble an elongated, rather than circular, orbit. The researchers developed a mathematical description that includes both effects and tested it using a simulated signal resembling GW170817, with both acceleration and orbital elongation added. Under assumed detector-noise conditions, their analysis recovered the input values within 90% credible intervals. The test supports modeling both effects together to avoid confusing them; it does not establish that either effect was observed in GW170817.

Young explorerWhen two objects in space go around each other, they make tiny ripples in space. A stretched-out path and a pull from gravity nearby can change those ripples in similar ways. Scientists made a pretend ripple signal with both changes. When they looked for both changes together, they could tell them apart and got answers that agreed with what they had put in, allowing for uncertainty. This was a pretend-signal test, not a discovery of those changes in a real pair.

Line-of-Sight Acceleration-driven waveform corrections for unequal-mass compact binary coalescences

Mohd Asim Ansari, Avinash Tiwari, Sajad A. Bhat+2 more

• General Relativity and Quantum Cosmology

AstronomerA constant line-of-sight acceleration (LOSA) of a quasi-circular compact binary’s centre of mass introduces gravitational-wave waveform modulations at −4 post-Newtonian order. Extending their earlier treatment of the dominant (2,2) mode, the authors derive phase and amplitude corrections for higher modes and implement LOSA self-consistently in a higher-mode waveform model. They show that these corrections are essential for asymmetric binaries such as GW190814 and that omitting them biases parameter inference. They also discuss inconsistencies in published higher-mode LOSA derivations and implementations. Although GW190814 has been suggested to provide evidence for nonzero LOSA, this abstract does not establish that interpretation as an observed detection.

PublicIf a pair of compact objects changes its motion toward or away from us at a constant rate while spiralling together, that acceleration alters its gravitational-wave signal. Some analyses account for this effect only in the signal’s dominant component, even when their models include additional components. The authors derive corrections for those additional components and show that leaving them out can skew the inferred properties of unequal binaries such as GW190814. They also identify inconsistencies in earlier treatments. GW190814 has been proposed as evidence for this acceleration, but the abstract does not confirm that it occurred.

Young explorerTwo heavy objects circling each other in space can make waves in space itself. If the pair’s motion toward or away from us keeps changing, the waves change too. Scientists worked out how to include that change in the main part of the waves and in extra parts. They found that leaving out the extra changes can give wrong clues about pairs whose objects are very different in size. Some scientists think a signal called GW190814 may show this kind of motion, but this work does not prove that it does.

Constraining the gravitational-wave breathing mode with LVK antenna patterns and GWTC data

Hong-Bo Jin, Yanyan Zheng

• General Relativity and Quantum Cosmology

AstronomerThe study assesses LVK sensitivity to a massless scalar breathing polarization in addition to the plus and cross tensor modes. Many scalar–tensor models predict a much smaller breathing amplitude, whereas gravitational quantum field theory allows an amplitude comparable to the tensor amplitudes. PyCBC antenna-pattern calculations include Michelson suppression: at the H1 zenith at the GW150914 epoch, F_b is approximately 5 × 10⁻⁶. Across 72 GWTC events with packaged strain, the median inclination gain in network breathing power S_b is approximately 34-fold. Ranking multi-detector events with network SNR at least 8 and at least two sites by SNR times the square root of S_b* identifies loud O4 triggers and GW170817 as geometric targets, not breathing-mode detections. PE-weighted calculations for twelve events show that the inferred sky position can suppress this geometric ranking, notably for GW170817; GW200129_065458, GW150914, and GW190814 have the highest PE-weighted S_b. The amplitude model is h_b = ξ h_+, with ξ = 0 in GR. In an HLV design-noise injection grid, an inclined sky with S_b approximately 0.18 gives log Bayes factors ln B(GR+b/GR) approximately 13 and 4 for injected ξ = 1 and 0.5, respectively; near zenith, with S_b approximately 0.016, the ξ posterior remains unconstrained. These are simulated sensitivity results. The catalog analysis is semi-joint: masses and spins are fixed at PE medians, while luminosity distance, inclination, sky position, and ξ vary within PE-informed priors. Eleven events are analyzed, with GW170817 omitted because its PE sky lies on the breathing null. None favors GR+b. Reported 90% bounds on the absolute value of ξ are approximately 0.15 for GW150914, 0.18 for GW200129_065458, and 0.23 for GW200311_115853, disfavoring order-unity amplitudes under this analysis. Weaker bounds, including that for GW190814, still allow order-unity amplitudes.

PublicGravitational waves could contain an extra ‘breathing’ pattern beyond the two tensor patterns described by general relativity. Many alternative gravity models predict this extra pattern to be weak, while gravitational quantum field theory allows it to be comparably strong. This study calculates how well the LIGO–Virgo–KAGRA network could respond to it and examines recorded events. Detector geometry matters greatly: for 72 catalog events, the median calculated gain in breathing sensitivity from inclination is about 34-fold. A preliminary ranking highlights loud O4 triggers and GW170817, but accounting for uncertainties in event parameters changes the priorities; GW170817’s inferred sky position makes it unsuitable for this test. Computer simulations, not detections, show that favorable geometry could provide evidence for an injected breathing signal: simulated breathing amplitudes of 1 and 0.5 times the plus-polarization amplitude give log Bayes factors of about 13 and 4. An unfavorable simulated direction leaves the breathing amplitude unconstrained. In the actual catalog analysis, none of the eleven tested events favors adding a breathing signal. The reported 90% bounds limit the absolute value of the breathing-to-plus amplitude ratio to about 0.15, 0.18, and 0.23 for GW150914, GW200129_065458, and GW200311_115853, respectively. These bounds disfavor a breathing signal comparable to the plus signal for those events, but weaker bounds for other events, including GW190814, still allow it. The limits are conditional: masses and spins were held fixed at previously estimated median values while distance, orientation, sky position, and breathing amplitude were allowed to vary within informed ranges.

Young explorerScientists listen for tiny waves that stretch and squeeze space. Some ideas say there might also be an extra kind of wiggle, like space taking a breath. Whether the detectors can notice it depends on where the wave comes from. The scientists made pretend signals on computers and found that some directions make this extra wiggle easier to spot, while another tested direction leaves its size uncertain. Pretend signals are not real discoveries. They also checked eleven real wave events, and none favored adding the extra wiggle. Three events gave tighter limits on how big it could be, but other events still allowed a bigger wiggle. For these checks, the scientists kept some properties of the sources fixed, so the limits depend on those choices. They have not shown that the extra wiggle exists or that it is impossible.

Extreme superluminal expansion traces an ultra-narrow GRB jet across relativistic regimes

Jin-Jun Geng, Ying-Kang Zhang, Hao-Xuan Gao+20 more

AstronomerVLBI observations of GRB 221009A, the brightest GRB ever detected, trace its radio angular size from 5 to 299 days after the burst. VLBA data at 8.4 and 15.2 GHz were characterized using circular-Gaussian fits to the complex visibilities. The inferred apparent expansion speed declines from about 90c at 5 days to about 6c near 300 days, tracing deceleration from ultra-relativistic to mildly relativistic dynamics and placing the source beyond the luminosity–velocity envelope of AGN and microquasar jets. Joint modeling of the size and multi-wavelength afterglow within a two-shell collision scenario supports an ultra-narrow jet with a half-opening angle of about 0.01–0.03 radians and an external density profile transitioning from wind-like at small radii to interstellar-medium-like farther out. The modeling favors two-phase size evolution, with only tentative observational evidence for lateral spreading; a hydrodynamic simulation confirms spreading for such an ultra-narrow jet.

PublicAstronomers used radio imaging to follow the growing radio source left by GRB 221009A, the brightest gamma-ray burst ever detected, from 5 to 299 days after the burst. Its apparent expansion slowed dramatically: the measured rates correspond to about 90 times the speed of light early on and about six times near day 300. These are apparent expansion rates, not claims that matter travels faster than light. Combining the radio sizes with observations at other wavelengths, the researchers infer an extremely narrow jet that slows as it moves through surrounding material whose distribution changes farther out. Their model favors two stages of growth. A computer simulation shows that such a narrow jet spreads sideways, but evidence for sideways spreading in the observations remains tentative.

Young explorerA huge flash in space left a growing radio glow. Scientists watched it with radio telescopes and found that its growth slowed down. Their best explanation is a very thin stream of fast-moving material pushing through the stuff around it. A computer model shows that the stream can spread sideways, but the telescope clues are not yet strong enough to be sure it did.

Exploring a Cosmic-Ray Inverse-Compton Origin to the SZ-to-X-Ray Pressure Deficit in the Cool Core Cluster ZwCl 3146

Emily M. Silich, Jack Sayers, Philip F. Hopkins+4 more

• Cosmology and Nongalactic Astrophysics

AstronomerThe study tests whether inverse-Compton scattering of cosmic microwave background photons by approximately GeV cosmic rays injected by a central AGN contributes appreciably to cool-core cluster X-ray continua, potentially biasing thermal bremsstrahlung interpretations and inferred cooling rates. In the relaxed cool-core cluster ZwCl 3146 at z = 0.291, the measured thermal SZ-to-X-ray pressure ratio is 25% below unity within 100 kpc of the center, at approximately 3-sigma statistical significance. Because thermal SZ measurements probe thermal ICM electrons, additional cosmic-ray inverse-Compton emission could inflate the X-ray-inferred pressure. The deficit agrees with predictions from reasonable AGN-driven cosmic-ray injection models, and two-component thermal plus inverse-Compton spectral fits are consistent with this interpretation, but do not establish it uniquely. The leading systematics considered, halo triaxiality and AGN-driven cavities, could lower the ratio by approximately 5% on average, with approximately 5% object-to-object variation; the average bias is half the measurement uncertainty. Non-negligible inverse-Compton emission is therefore plausible in this cluster, but detailed studies of larger samples are needed to establish its relevance to the cooling flow problem.

PublicA proposed explanation for a long-standing galaxy-cluster puzzle is that some X-rays attributed to hot gas actually come from energetic particles supplied by the central active galaxy. These particles could boost photons from the cosmic microwave background to X-ray energies, making the gas appear to have higher pressure and a faster cooling rate than it really does. This might help explain why clusters form fewer stars than their X-ray-inferred cooling rates suggest. In the cluster ZwCl 3146, researchers compared pressures inferred from X-rays with those measured through the hot gas's effect on the cosmic microwave background. Within 100 kiloparsecs of the center, the latter pressure was 25% lower, a difference with about 3-sigma statistical significance. Models and X-ray spectral fits are consistent with the proposed extra emission, but do not prove it. Cluster shape and cavities made by the active galaxy could also affect the comparison, though their estimated average effect is smaller. More clusters must be studied before drawing a firm conclusion.

Young explorerScientists studied a big group of galaxies filled with hot gas. They used two ways to check the gas, and the answers did not quite match. Maybe speedy particles from the galaxy in the middle give faint light an extra boost, turning it into X-rays. Those extra X-rays could fool scientists into thinking the gas is cooling faster than it really is. This idea fits what they found, but they are not sure it is right. They need to check more galaxy groups.

Impact of Magnetic Field Topology on Electromagnetic and Gravitational Waves from Binary Neutron Star Merger Remnants

Inês Rainho, Jamie Bamber, Davide Guerra+4 more

• General Relativity and Quantum Cosmology

AstronomerGRMHD simulations of binary neutron star mergers compare four magnetic topologies: a pulsar-like dipole, an internally confined poloidal–toroidal mixture, and two configurations transitioning smoothly from a mixed core to a pulsar-like exterior at 0.95 or 0.5 stellar radii. The transition configurations are explored for the first time in BNS merger studies. Models use the SLy and WFF1 equations of state, with an additional lower-mass SLy binary probing long-lived remnants. The analysis covers electromagnetic and gravitational-wave emission, remnant oscillations, rotation, temperature, and convective stability; the authors report the first assessment of convective stability in magnetized merger remnants. Pulsar-like configurations show a clear secondary gravitational-wave spectral peak, absent in the other topologies and consistent with nonlinear coupling between the m=0 and m=2 modes. The simulated topology dependence suggests that future gravitational-wave detectors could distinguish field structures for events within 50 Mpc. All models yield luminosities compatible with short gamma-ray bursts, with purely poloidal configurations most efficient at driving possible relativistic jets. These are simulation results and observational prospects, not detected signatures or confirmed jets.

PublicComputer simulations explore how different magnetic-field arrangements affect collisions between two neutron stars. The researchers tested four arrangements and two descriptions of how neutron-star matter behaves, and examined the merged objects and their light and gravitational-wave emission. In simulations with pulsar-like magnetic fields, the gravitational-wave spectrum contains an extra peak that is missing from the other arrangements. The authors interpret this as consistent with two kinds of stellar oscillation interacting. Their results suggest that future gravitational-wave detectors might distinguish magnetic arrangements in mergers closer than 50 million parsecs. The simulated luminosities are compatible with short gamma-ray bursts, but this does not establish that such bursts or jets were produced. Fields arranged purely in the poloidal direction were most efficient at driving possible jets.

Young explorerScientists used computers to pretend that two very dense stars crashed together. They tried different shapes for the stars’ magnetic fields. Some shapes made an extra wobble in the simulated ripples through space, while others did not. Better detectors might someday use those ripples from a nearby crash to tell the magnetic shapes apart. This was a computer experiment, not a crash they watched.

Gravitational self-lensing of Fast Radio Bursts in neutron star magnetospheres: II. Applications to strong repeaters and the CHIME population

Riccardo La Placa, Simone Dall'Osso, Luigi Stella+1 more

AstronomerThe authors test a model in which magnetospheric hotspots on highly magnetic neutron stars produce seed radio bursts that are strongly amplified by gravitational self-lensing. In this framework, orientation-dependent amplification can account for repeating versus non-repeating sources, high luminosities, and power-law burst-energy distributions. Comparison with FAST repeater data shows that FRB 20121102A’s energy distribution can be explained by two antipodal hotspots sharing a log-normal seed-energy distribution. This interpretation requires near alignment of the rotation axis, line of sight, and hotspot sites, with angular separations ≲2°. Similar geometric constraints are inferred for FRB 20201124A and FRB 20220912A; constraints for FRB 20190520B are weaker because its burst sample is smaller. Neutron-star precession can also explain FRB 20121102A’s evolving energy distribution and temporary disappearance within the model. For a randomly oriented cosmological population, predicted distance and fluence distributions agree well with a completeness-selected subsample of the first CHIME/FRB catalogue, provided seed-burst energies span approximately 10^35–10^38 erg. These are model-dependent explanations and predictions, not direct detections of hotspots, self-lensing, or precession.

PublicFast radio bursts are brief flashes of radio waves. This study tests the idea that bursts from hotspots near a highly magnetic neutron star become much brighter because the star’s gravity acts as a lens. In the model, viewing angle helps determine whether a source appears to repeat and how bright its bursts look. Radio telescope data for FRB 20121102A can be explained by two hotspots on opposite sides of the star, with the star’s spin axis, our viewing direction, and the hotspot locations aligned to within about two degrees. Two other repeating sources give similar constraints, while a source with fewer recorded bursts gives less precise ones. A changing direction of the spin axis could also explain changes in FRB 20121102A’s burst energies and its temporary disappearance. Predictions for a wider population agree well with selected catalogue data if the initial bursts have a suitable range of energies. The agreement supports the model’s plausibility but does not establish that this is how fast radio bursts are produced.

Young explorerScientists are testing an idea about quick flashes of radio waves from space. A tiny star might have spots that send out flashes, and its gravity might make those flashes look much brighter. Which way the star points could change what we see. The idea fits some telescope records, but scientists have not shown that these spots and this brightening really cause the flashes.

Simulating the jittering-jets explosion mechanism: circum-jet rings account for observed core-collapse supernova remnant morphologies

Muhammad Akashi, Noam Soker

AstronomerThree-dimensional hydrodynamical simulations within the jittering jets explosion mechanism produce opposite circum-jet rings resembling structures observed in some core-collapse supernova remnants. In a stripped-envelope stellar model, two successive jet pairs share an axis: wide jets first compress the core into a dense, rapidly expanding shell, and narrow jets subsequently overtake and penetrate that shell, compressing gas sideways into two rings. The projected morphology depends on viewing angle. At high inclinations of the jet axis to the line of sight, each ring produces two bright zones where it crosses the plane of the sky, which the authors identify with the morphology of G46.8-0.3. At intermediate inclinations, the rings appear as opposite bright elliptical rims, matching the two prominent outer-shell rings of G11.2-0.3. These are simulation-based explanations of observed structures; the authors interpret the results as strengthening the claim that jittering jets are the primary core-collapse explosion mechanism.

PublicComputer simulations suggest how jets from an exploding star could create two opposite rings like those seen in some supernova remains. The researchers modeled a star stripped of its outer envelope. First, broad jets pushed material into a dense, fast-expanding shell. Later, narrower jets caught up with the shell, broke through it, and squeezed gas sideways into rings. Depending on the viewing angle, the simulated rings appear either as separate bright patches or as complete oval rims. The authors use these patterns to explain structures observed in the remnants G46.8-0.3 and G11.2-0.3. They interpret the resemblance as support for the idea that jittering jets drive core-collapse supernova explosions, rather than as a direct observation of how those explosions happened.

Young explorerScientists used a computer to imagine a star exploding. In their model, wide streams of gas made a shell. Then skinny streams broke through the shell and pushed gas sideways, making two rings. From different directions, the rings looked like bright spots or ovals. They look like shapes seen around some exploded stars. The scientists think this is a clue that jets help stars explode.

Detection of relativistic orbital deformation from improved timing of PSR J1757-1854

Jaikhomba Singha, Vivek Venkatraman Krishnan, Marisa Geyer+12 more

AstronomerHigh-precision timing of PSR J1757−1854, a 21.5 ms pulsar in a double neutron star system with eccentricity 0.61 and a 4.4 hr orbital period, provides improved strong-field tests of general relativity (GR). Combining archival Murriyang and Green Bank Telescope data with new MeerKAT and additional Green Bank observations improves the precision of previously measured post-Keplerian parameters by roughly a factor of two or more. The authors report the first detection of relativistic angular deformation, δθ, in this system, making it the third double neutron star system with this parameter measured. The detection required nine years of timing, compared with decades for the double pulsar and Hulse–Taylor binary. Using δθ to constrain the spin-orbit geometry rules out two of four previously identified geometric solutions while remaining consistent with GR. An evaluation of second post-Newtonian and Lense–Thirring contributions to periastron advance finds a measurable systematic effect on the inferred total mass; this is not presented as a separate detection of either contribution. The observed orbital period derivative remains consistent with GR’s prediction for gravitational-wave damping over a wide range of plausible distances.

PublicAstronomers have improved their tests of Einstein’s theory of gravity using PSR J1757−1854, a pair of neutron stars that orbit each other every 4.4 hours along a strongly elongated path. One star is a pulsar, whose radio pulses allow researchers to track the orbit precisely. Combining observations from three radio telescopes roughly doubled or better the precision of previously measured relativistic orbital parameters. The team detected a relativistic distortion of the orbit called angular deformation for the first time in this system. Only two other double neutron star systems have had this effect measured. The new measurement rules out two of four previously proposed arrangements of the pulsar’s spin relative to the orbit. The researchers also evaluated smaller relativistic effects that influence the mass inferred from the orbit. The measured shortening of the orbital period agrees with Einstein’s prediction for energy lost through gravitational waves across a broad range of plausible distances, rather than depending on one assumed distance.

Young explorerTwo tiny, very heavy stars race around each other. One sends out radio flashes, like a lighthouse. Scientists used telescopes to time those flashes and follow the stars more carefully. They spotted a small change in the shape of their path that they had not measured in this pair before. It helped them rule out two ideas about how one star spins. The stars also take less time to go around each other, and the measurements fit Einstein’s ideas about gravity.

Beta-Particle Transport and Thermalization in Kilonova Ejecta with Detailed Atomic Microphysics

Zachary L. Andalman, Christopher L. Fryer, Christopher J. Fontes+2 more

AstronomerThis modeling study investigates beta-particle thermalization and transport in kilonova ejecta. The authors use evaluated atomic data to estimate species-dependent energy deposition, scattering, and electron-impact ionization, and make those data available online. They develop a fully relativistic transport framework for spherically symmetric, homologously expanding ejecta under two limiting magnetic-field geometries. In their calculations, non-local deposition and particle escape reduce thermalization efficiency, particularly in the innermost and outermost ejecta, yielding lower temperatures and ionization states than local-deposition models. Coulomb scattering partially counteracts these effects through particle trapping at approximately 3–30 days, while secondary electrons substantially enhance the total ionization rate. The authors provide spatially dependent analytic thermalization prescriptions for future light-curve calculations and argue for incorporating evaluated atomic data and charged-particle transport into next-generation models. These are modeling results under the stated assumptions, not observational measurements.

PublicWhen two neutron stars collide, they throw out material containing heavy atomic nuclei. Radioactive decay in this material powers a bright glow called a kilonova. This study models how electrons released by the decay move through the expanding debris and transfer their energy to it. Unlike simpler models that deposit energy where the electrons are produced, these calculations allow electrons to travel elsewhere or escape. That makes heating less efficient, especially near the center and outer edge of the debris, leaving it cooler and with fewer electrons stripped from atoms than simpler models predict. Collisions that temporarily trap the moving electrons partly offset this effect around 3–30 days, and additional electrons produced in collisions increase the rate at which atoms lose electrons. The calculations assume a spherical expansion and examine two limiting magnetic-field arrangements. The researchers offer formulas for future predictions of kilonova brightness; the findings come from modeling, not new observations.

Young explorerWhen two neutron stars crash together, they throw out material that can glow. Tiny particles called electrons help warm that material. The scientists made a model to follow where those electrons go. In the model, some travel away or escape instead of warming the place where they started, so parts of the material stay cooler. Other electrons get held up by bumps along the way and help keep it warm. This is a model of what could happen, not something the scientists watched directly.

Radio and X-ray Observations of the Transitional Supernova 2019yvr: Insights into the Progenitor Mass-Loss History

Raphael Baer-Way, Poonam Chandra, Maryam Modjaz+7 more

• Solar and Stellar Astrophysics

AstronomerRadio observations with GMRT and VLA and X-ray observations with Swift and Chandra cover SN 2019yvr from 18–1786 days after explosion. Initially a type Ib event, with strong helium and little or no hydrogen, it transitioned to type IIn at approximately 100 days, showing shock-driven hydrogen features from circumstellar interaction. The radio evolution is best fit by a synchrotron self-absorbed model with a CSM density profile proportional to r^(-1.54 ± 0.31), suggesting declining progenitor mass loss in the years before explosion. The radio-inferred early shock speed exceeds 30,000 km/s, suggesting a compact progenitor. Together, the radio and X-ray data probe CSM radii of 1.7 × 10^16 to approximately 2.0 × 10^17 cm and imply mass-loss rates of approximately (1–6) × 10^-5 solar masses per year, assuming a CSM speed of 100 km/s. The combined data rule out a dramatic CSM density jump associated with the appearance of optical hydrogen emission, unlike the optical analog SN 2014C. The progenitor’s stripping history remains an open question.

PublicAstronomers followed supernova SN 2019yvr in radio waves and X-rays from 18 to 1,786 days after it exploded. Its early spectrum showed strong helium but little or no hydrogen. About 100 days after the explosion, hydrogen emission appeared as the explosion’s shock interacted with surrounding gas. A model fitted to the radio observations suggests that the star’s rate of shedding material decreased in the years before it exploded. The inferred early shock speed, more than 30,000 kilometers per second, also suggests that the star was compact. Estimates of how much material it shed depend on an assumed speed for the surrounding gas. Importantly, the radio and X-ray data rule out a dramatic increase in gas density coinciding with the new hydrogen emission. These observations help constrain the star’s final years, but do not settle when or how extensively it lost its outer material.

Young explorerA star exploded, and scientists watched it using radio waves and X-rays. Later, they saw signs that the explosion was hitting hydrogen gas around the star. The clues suggest that the star had been letting out less gas as it got closer to exploding, and that it was small for its kind. The new hydrogen signs did not come with a huge jump in how tightly the gas was packed. Scientists still do not know exactly how the star lost its outside layers.

Pulsations and constraints on time lags in two distinct ULXs: NGC 5204 X-1 and NGC 55 ULX-1

Rajath Sathyaprakash, Matthew J. Middleton, Chris Done

AstronomerThe study examines the timing properties of NGC 5204 X-1 and NGC 55 ULX-1, two ULXs generally interpreted within the super-Eddington X-ray binary framework. Both have relativistic winds inferred from photo-ionisation modelling of emission-line spectra. Differences in their X-ray continuum hardness ratios suggest, but do not establish, slightly different viewing inclinations. The authors report new timing constraints on accretion-disc size and structure, although the abstract gives no quantitative constraints. An accelerated pulsation search, including correction for orbital modulation, identifies spin-periodic signals in both sources at greater than 3-sigma significance. These reported detections do not, in the abstract, establish the identity of either compact accretor. Reverberation lags and lag-energy spectra are discussed as diagnostics of optically thick, super-Eddington discs, alongside multi-wavelength and covariance spectral modelling.

PublicResearchers studied how the X-ray brightness of two exceptionally luminous sources, NGC 5204 X-1 and NGC 55 ULX-1, changes over time. Such sources exceed the conventional Eddington luminosity limit for a black hole with ten times the Sun’s mass, but their exact nature remains uncertain. Modelling of their emission-line spectra indicates that both launch relativistic winds. Their different X-ray spectral shapes suggest they may be viewed from slightly different angles. The timing analysis is reported to constrain the size and structure of the discs feeding these sources, though the abstract supplies no sizes. After accounting for how orbital motion could affect a repeating signal, the researchers report signals attributed to rotation in both sources, each above a statistical significance threshold of 3 sigma.

Young explorerScientists watched two very bright places in space that give off X-rays, a kind of light our eyes cannot see. They looked for patterns in how the brightness changes. They found repeating signals that they think come from spinning. Those patterns can help them learn about the swirling material around each source, but they still do not know exactly what these bright sources are.

Einstein ring fingerprint around supermassive black holes illuminated by broad line region spectral lines

Konstantinos Kostaros, George Pappas, Padelis Papadopoulos+1 more

• General Relativity and Quantum Cosmology

AstronomerStrongly lensed continuum emission from hot, ionized inner accretion-disk regions is superimposed on local plasma emission near the innermost stable circular orbit, obscuring strong-gravity signatures. The authors propose the more distant, cooler, neutral gas reservoir underlying the broad line region as an alternative illumination source, potentially producing cleaner strong-lensing brightness distributions against a nonluminous background. For sightlines near the disk plane, this scenario predicts an hourglass-like brightness distribution around the SMBH and an additional inner double-peaked feature within the disk’s global double-horned line profile. The spectral feature could be discerned even in unresolved sources. Spectral-line interferometry could reveal both signatures and provide SMBH mass estimates for edge-on systems. These are proposed observational diagnostics of the illumination scenario, not reported detections.

PublicBright gas close to a supermassive black hole can hide the patterns created when the black hole’s gravity bends light. The authors suggest using light from cooler gas farther away to make those patterns easier to distinguish against a dark background. In this proposed setup, a disk viewed nearly edge-on would show an hourglass-shaped brightness pattern. Its spectrum—the light separated by wavelength—would also have an extra pair of peaks within its broader two-peaked line shape. That spectral clue could be visible even if the source is too small to resolve into an image. The authors argue that interferometers observing spectral lines could reveal these features and help estimate the black hole’s mass. The abstract presents expected signatures, not observations confirming them.

Young explorerA black hole can bend light into strange shapes, but bright gas nearby can hide them. Scientists suggest looking at light from cooler gas farther away. They think this could make a shape like an hourglass when we look along the edge of the gas disk. It might help them learn how heavy the black hole is. They have not reported seeing this pattern here.

Rotation of the polarization plane in axion fields: application to neutron star polar cap regions

Iver H. Brevik, Moshe M. Chaichian, Tiberiu Harko+1 more

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

AstronomerThis theoretical study examines possible polarization effects as electromagnetic waves propagate through an axion field treated as a special magnetoelectric medium. A Casimir-type geometric model yields the polarization-plane rotation angle to lowest order. The authors discuss the result under neutron-star conditions, where a locally inhomogeneous axion region is predicted in the polar cap. The abstract reports a model-derived effect, not an observational detection of polarization rotation or an axion region.

PublicThe researchers use a mathematical model to explore whether an axion field could rotate the orientation of light’s polarization as light passes through it. They derive an approximate expression for this rotation and discuss how it might apply near a neutron star, where an axion region that varies from place to place is predicted near a magnetic pole. These are theoretical calculations and predictions, not reported observations of axions or their effects.

Young explorerLight has a direction in which it wiggles. The scientists used math to explore whether something called an axion field could turn that wiggle direction. They considered a place near the pole of a neutron star. This is an idea worked out with math, not something they report seeing.

Implications of the LISA stochastic signal from eccentric stellar mass black hole binaries in vacuum

Ran Chen, Rohit S. Chandramouli, Federico Pozzoli+2 more

• General Relativity and Quantum Cosmology

AstronomerThis modeling study examines how early-inspiral eccentricity affects the stochastic gravitational-wave background from unresolved stellar-mass binary black holes, with implications for future LISA observations. The authors improve a model with a Dirac-delta eccentricity distribution and extend it to a thermal distribution. Their Bayesian analysis finds that a population in which all binaries have initial eccentricity e0 ≳ 0.9 at orbital frequency 10^-4 Hz would produce a background robustly distinguishable from a quasi-circular population. For a thermal distribution, the background is consistent with a circular model if binaries form at 10^-5 Hz, whereas formation at 10^-4 Hz leads to significant systematic biases under circular modeling. Accounting for eccentricity also allows environmental effects such as dynamical friction to be distinguished from vacuum evolution, but only for sufficiently dense gas environments, with density ≳ 10^-7 g cm^-3. A LISA detection of this background would additionally place an upper bound on the population’s maximum eccentricity in the ground-based detector band, informing waveform templates and data analysis. These are model-based findings and conditional detection prospects, not reported observational detections.

PublicPairs of black holes can orbit along stretched-out paths rather than nearly circular ones. This study models how those orbital shapes would change the combined gravitational-wave signal from many pairs too difficult to distinguish individually. The calculations suggest that LISA could tell a population of very elongated orbits apart from one with nearly circular orbits. For a population with a range of orbital shapes, the outcome depends on the orbital frequency at which the pairs form: one modeled case resembles a circular population, while another would systematically distort conclusions drawn using a circular-orbit model. The study also predicts that effects from surrounding gas could be recognized, but only if the gas is sufficiently dense and orbital shape is properly included. A future LISA detection could limit how elongated these binaries’ orbits remain at frequencies studied by ground-based detectors. The paper presents modeling, not a detection.

Young explorerTwo black holes can go around each other in paths that are round or stretched out. They make tiny ripples in space. Scientists used a model to study the ripples from lots of black-hole pairs mixed together. They think a future space detector called LISA could sometimes tell whether the paths are very stretched out. But not every kind of path is easy to tell apart. This study is a prediction, not something LISA has already seen.

Polarization Analysis of Ringdown Signals

Nicole Khusid, Will Farr, Maximiliano Isi

• General Relativity and Quantum Cosmology

AstronomerThe study fits black-hole ringdowns with a polarization model constrained by equatorial reflection symmetry, which reduces each Kerr quasi-normal mode’s four amplitude-and-phase degrees of freedom to two. This symmetry applies to mergers with spins aligned or antialigned with the orbital angular momentum and fixes polarization relations through the viewing inclination. The authors show that circular polarization and handedness can be measured for GW150914-like ringdowns using only the two LIGO detectors; interpreting these measurements as source inclination requires the symmetry assumption. They also fit precessing systems, including GW190521, for which the restricted model cannot adequately capture the polarization structure. Tests with simulated GW190521-like injections show weaker predictive accuracy than an arbitrary-polarization model and potentially significant systematic biases in mode frequencies and amplitudes. Appropriate polarization modeling will become increasingly important as detector sensitivity improves.

PublicAfter two black holes merge, the remaining black hole emits fading gravitational waves in a phase called ringdown. This study examines the waves’ polarization—the pattern of their distortion. For mergers whose spins line up with, or point opposite to, the orbital motion’s axis, a symmetry simplifies that pattern. The authors show that the two LIGO detectors alone can measure how circularly polarized GW150914-like ringdowns are and which way that polarization turns. Assuming the symmetry holds, this also gives an estimate of the viewing angle. But the simplified model does not adequately describe mergers whose orbital orientation wobbles. Tests using simulated signals resembling GW190521 found poorer predictions and potentially substantial errors in the inferred ringdown frequencies and strengths. Better detectors will make choosing the right model more important.

Young explorerWhen two black holes join, they send out waves that fade like the sound of a ringing bell. Scientists study the patterns in those waves. For some black holes, a simple pattern can help them work out which way we are looking at the pair—but only if a special rule fits. Black holes that wobble need a more flexible pattern. When scientists tested made-up waves like those from a wobbling pair, the simple pattern could give wrong answers. As the wave detectors get better, using the right pattern will matter even more.

Deriving the Continuous β-FPUT Model for Decayless Solar Coronal Oscillations Directly from Resistive MHD

D. Tsiklauri

• Plasma Physics
• Space Physics

AstronomerThe authors develop an analytical explanation for observed persistent, decayless transverse oscillations in solar coronal loops, deriving a fluid-continuum beta-FPUT system from a third-order resistive MHD expansion. For waves propagating along a longitudinal magnetic field with cross-field density structure, out-of-plane polarization symmetry eliminates quadratic advective and Maxwell-tension terms. A quadratic longitudinal ponderomotive force nevertheless induces field-aligned density modulations whose feedback produces a cubic transverse restoring force. In the long-wavelength limit, the equations reduce to a fluid-continuum modified Korteweg-de Vries system, with cross-field profile variation supplying nonlinear dispersion. Within this framework, the authors prove stable, amplitude-dependent frequency self-focusing that phase-locks adjacent fluid elements and prevents phase-mixing attenuation without a prescribed steady external driver. They propose closed-form inversions of observed decayless wave-packet durations for the unresolved cross-field density-gradient scale length and internal volumetric filling factor. The abstract reports an analytical derivation, not observational validation of the mechanism or these diagnostic inversions.

PublicSome loops in the Sun’s outer atmosphere show sideways oscillations that persist without fading. This study offers a mathematical explanation: the waves alter the plasma’s density along the magnetic field, and those changes feed back on the waves. In the model, this feedback keeps neighboring parts of the loop oscillating together, preventing the weakening caused when they fall out of step, without prescribing a continuous outside driver. The authors also propose using the duration of these oscillations to infer otherwise unresolved density structure and how much of the loop’s volume is filled. These are theoretical findings and proposed diagnostics; the abstract does not report observational tests of them.

Young explorerLoops around the Sun can wiggle sideways without their wiggles fading away. Scientists made a math model in which the wiggles change the Sun’s hot gas, and the gas helps nearby wiggles stay together. They think timing the wiggles could reveal tiny details inside the loops. This idea still needs to be checked against observations.

The variable mass-loss in low-mass red giant stars: Chromospheric motion across stellar evolution in 47 Tuc

Ian Baeza, L. Monaco, H. Frelijj+8 more

• Astrophysics of Galaxies

AstronomerTemporal FLAMES/GIRAFFE spectroscopy of red giants in NGC 104 (47 Tuc) characterizes chromospheric variability through H-alpha, addressing uncertain atmospheric processes expected to power mass loss in cool, low-mass giants. The mean amplitude and range of H-alpha variations increase with luminosity. Above approximately log(L/L_sun) = 2.4, systematic line-core blueshifts indicate outflows, while deeper cores are consistent with increased chromospheric optical depth. Detectable profile changes typically require about one day, with little luminosity dependence. Shorter-timescale variations remain consistent with statistical uncertainties, although a possible increase toward dimmer stars is reported. The trends correlate similarly with luminosity and effective temperature; no additional correlation with cluster population or significant AGB–RGB differences is found. Outflow trends resemble previous observations across a wide metallicity range. The observations do not distinguish among changing H-alpha sensitivity to winds, a heating-efficiency-driven atmospheric transition, and continued chromospheric expansion with geometrically dominated H-alpha formation.

PublicResearchers repeatedly observed red giant stars in the cluster 47 Tuc to study changes in their chromospheres, atmospheric regions thought to help drive the loss of stellar material. They tracked the H-alpha spectral line and found that brighter giants generally show larger and more widely varying changes. In sufficiently luminous stars, shifts in the line indicate outward-moving gas, and deeper line cores are consistent with the chromosphere becoming more opaque. About a day is typically needed to detect a change, with little dependence on brightness. Possible faster changes in dimmer stars remain uncertain. The patterns also relate to surface temperature, but no significant differences were found between the two giant-star evolutionary stages examined. The study leaves open whether these patterns reflect changing sensitivity of H-alpha to winds, changes in atmospheric heating, or expansion of the chromosphere.

Young explorerScientists watched big stars to see how their outer layers change. Brighter stars usually showed bigger changes, and some clues suggest gas is moving away from them. The scientists usually needed to watch for about a day to notice a change. They still do not know exactly why the stars' outer layers behave this way.

Unlocking new information in stellar circular polarisation with second-order least-squares deconvolution

Oleg Kochukhov

AstronomerThe authors extend least-squares deconvolution beyond the weak-field approximation by retaining two odd wavelength-derivative terms in the Stokes V absorption coefficient. A second line weight, based on the third Zeeman-pattern moment, produces a second mean Stokes V profile through multiprofile LSD. Its proportionality to the second derivative of the first profile provides a longitudinal-flux-weighted mean-square field modulus, separating field strength from covering area. Polarised spectrum synthesis at realistic signal-to-noise ratios indicates reliable detection of the second component from about 500 G and constraints on the modulus up to several kG. Applications to archival spectra of two Ap stars yielded moduli consistent with known strengths; for two active M dwarfs, the inferred moduli were close to Zeeman-broadening measurements and much larger than the large-scale fields recovered by Zeeman-Doppler imaging. The authors interpret this as a measurement of field strength in regions contributing circular polarisation and identify infrared observations of cool active stars as especially promising.

PublicA standard way to measure stellar magnetism uses circularly polarised light, but assumes that the magnetic response remains linear and measures only the field component along our line of sight. This study extends that method to extract information about field strength from departures from the linear response, helping distinguish stronger fields from fields covering larger areas. Computer simulations suggest the extra signal can be detected from about 500 gauss and can constrain strengths up to several thousand gauss. Tests on existing spectra of four stars gave strengths consistent with earlier measurements. For the two active M dwarfs, the results were close to measurements based on magnetic broadening of spectral lines and much stronger than estimates of their large-scale fields. The method probes regions contributing circularly polarised light; the authors see particular promise for infrared studies of cool, active stars.

Young explorerStars can act like magnets, and their light carries clues about those magnets. Scientists tried a new way to read the clues and tell how strong the magnetic patches are, not just how much space they cover. They tested it with computer-made starlight and real light from four stars. The answers agreed with earlier measurements. The method looks promising, especially for cool, active stars.

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

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

AstronomerEquatorial-dipole coronal holes (EDCHs) form at the magnetic poles of a strong equatorial dipole when the axial dipole is weak, but not all low-latitude holes belong to this class: the 2024 maximum was quadrupole-led. Parker Solar Probe observed fast wind from an EDCH that was deeply sub-Alfvénic at 9.9 solar radii and had reached only 60% of an asymptotic speed comparable to polar wind, which is generally expected to accelerate faster. Potential-field models using synthetic and observed fields at three cycle phases show that pure axial and equatorial dipoles are exactly congruent, with identical open areas and core expansion factors. Differences must therefore involve orientation relative to differential rotation or surrounding multipoles. The analysis finds stationary axial-dipole coronal holes (ADCHs), sustained by converging meridional flow, whereas active-region emergence builds the equatorial dipole and flux transport dismantles it. Across 18-day sequences, axial-dipole strength at minimum is steady to 1%, while equatorial-dipole strength varies by 21% at maximum and 8% during decline. Most EDCH open flux expands less than ADCH flux, but EDCH boundaries are pseudostreamer-dominated and exhibit non-monotonic expansion. Magnetic geometry alone does not predict slower EDCH acceleration. The authors interpret any real acceleration difference as pointing to extended heating by reflection-driven Alfvén-wave turbulence, possibly supplied differently at these boundaries; this mechanism is not captured by the potential-field models.

PublicCoronal holes are regions where the Sun's magnetic field opens outward, allowing solar wind to escape. Some holes near the equator form when a strong, sideways-oriented magnetic dipole dominates, but not every low-latitude hole has this origin. Parker Solar Probe observed fast wind from one such hole close to the Sun, where it had reached only 60% of its eventual speed, comparable to that of wind from polar holes. The researchers tested whether magnetic structure could explain this relatively gradual acceleration. Their models show that an isolated sideways dipole has exactly the same geometry as a pole-aligned dipole, simply reoriented. In more complex fields, equatorial holes change more over time and differ in how their magnetic fields spread outward. Even so, magnetic geometry alone does not predict slower acceleration. The authors suggest that, if the acceleration difference is real, prolonged heating involving magnetic waves and turbulence may explain it. That remains an interpretation, not a result demonstrated by these models.

Young explorerThe Sun sends a stream of tiny particles into space. Scientists watched a fast stream coming from an opening in the Sun's magnetic field near its middle. Close to the Sun, the stream was still speeding up. Computer models of the magnetic field did not explain why it might speed up more slowly than streams from near the Sun's poles. Waves might keep heating it along the way, but that idea is not proven.

High-Angular-Resolution Survey of Stars within 18 pc of the Sun: Part I

F. Carolina Rojas-Galindo, Valeri G. Orlov, Rene A. Mendez+1 more

AstronomerThis paper describes the rationale, sample construction, methodology, and facilities for a volume-limited, high-angular-resolution survey of 2047 stars within 18 pc, compiled from Gaia eDR3 and complementary catalogs. Speckle imaging with high-speed cameras covered 703 stars with V < 14 mag at the OAN-SPM 2.1-m telescope and 645 with I < 16 mag at the 3.58-m NTT; 140 targets overlap, giving 1208 unique stars observed. The survey aims to obtain astrometry of known binaries and establish secondary-component detection limits for each observed star, with possible discovery of previously unresolved companions subject to the techniques’ limitations. A control sample of 70 known binaries with separations below 1 arcsecond shows that selection using Gaia RUWE, ipd_frac_odd_win, and ipd_frac_multi_peak can miss a significant fraction of binaries, supporting the volume-limited approach rather than preselection by these indicators. The paper also presents July 2022 OAN-SPM pilot observations; full analysis of the complete sample is deferred to forthcoming papers.

PublicAstronomers assembled a catalog of 2047 stars within 18 parsecs of the Sun and have observed 1208 of them using high-speed cameras on telescopes in the northern and southern hemispheres. The survey aims to measure the relative positions of known double stars and determine how faint or close an additional star could be before escaping detection. It may also reveal companions that were previously unresolved, but the abstract does not report new companion discoveries. Testing commonly used Gaia catalog indicators against 70 known close double stars showed that those indicators can miss a significant fraction of binaries. This supports surveying nearby stars without requiring those warning signs first. The paper presents the survey design and pilot observations; the full analysis is still forthcoming.

Young explorerSometimes two stars look like one because they are very close together in the sky. Astronomers have taken special pictures of 1208 stars near our Sun to help study star pairs and look for hidden partners. They found that some clues used to choose stars for a closer look can miss pairs already known to exist. They have shared their plan and some early observations, but the full study is not finished yet.

Does Diffusive Shock Acceleration Reach Steady State? Insights from a Near-Sun Shock Observed by Parker Solar Probe

Immanuel Christopher Jebaraj, Mikhail Malkov, Nicolas Wijsen+7 more

• High Energy Astrophysical Phenomena
• Plasma Physics
• Space Physics

AstronomerParker Solar Probe observed a fast, near-parallel interplanetary shock at 0.24 au, four hours after eruption, recording upstream waves and scattered protons on the same magnetic field line. From the wave spectra alone, the authors derive the parallel mean free path of 0.05–30 MeV protons as a function of energy and distance from the shock. They identify mirror forces from measured compressive fluctuations as supplying scattering across pitch angles inaccessible to gyroresonance. The mean free path increases with distance approximately as the steady self-generated solution predicts, but steady balance holds only near 1.3 MeV. Proton intensity profiles are a factor of two shallower than predicted from the derived diffusion coefficient, which the authors attribute to continuing wave growth. Confinement fails between 2.3 and 6 MeV, beginning at an energy a factor of two below the age-based expectation. The authors conclude that, for this evolving shock, growth of particle-driven waves—not shock age or size—limits the energy of confined particles.

PublicParticles accelerated by a shock in space generate waves that scatter them and help keep them near the shock. Theory describes this process once it reaches a steady balance, but an evolving shock need not have reached that balance. Parker Solar Probe observed one fast shock four hours after its eruption, measuring both the waves ahead of it and protons along the same magnetic field line. The researchers used the wave measurements to calculate how far protons travel along the field between scattering events. Although that distance changed with distance from the shock roughly as steady-state theory predicts, the full balance held only for protons near one energy, 1.3 MeV. The authors attribute the mismatch in the proton intensity profiles to waves that were still growing. Higher-energy protons also lost confinement sooner than the shock’s age would suggest. Their conclusion is that wave growth, rather than the shock’s age or size, limited the energies of particles this shock could keep confined.

Young explorerA spacecraft watched a fast-moving shock in space. Tiny particles near the shock make waves, and those waves help keep the particles nearby. Scientists found that the waves and particles had mostly not settled into a steady balance. They think the waves were still growing and could not keep some of the more energetic particles close. For this shock, how fast the waves grew mattered more than how old or big the shock was.

Exploring an X1.8 flare and associated quasi-periodic pulsations using SDO and Aditya-L1 observations, alongside NFFF extrapolation

Pawan Kumar, Sanjay Kumar, Sadashiv+2 more

AstronomerA multi-wavelength analysis using SDO and Aditya-L1 examines the initiation of the X1.8 flare SOL2024-10-09T0124 in NOAA active region 13848 and its associated quasi-periodic pulsations. Observations show a sigmoidal brightening at flare onset and evolving, complex brightenings and ribbons near the peak. Impulsive-phase pulsations have a dominant period of approximately four minutes in the hard X-ray light curve. A pre-flare non-force-free-field extrapolation identifies a magnetic flux rope, a 3D null, a sheared arcade, and quasi-separatrix layers. The authors propose that recurrent reconnection at these modeled magnetic features contributes to both flare initiation and the pulsations; the abstract does not establish this mechanism observationally.

PublicResearchers used observations from SDO and Aditya-L1 to study how a powerful solar flare began and why its brightness pulsed. They observed an S-shaped brightening at the start, followed by complex patterns of bright patches and ribbons near the flare’s peak. During its rapid energy-release phase, the hard X-ray brightness showed approximately repeating pulses with a dominant interval of about four minutes. A model of the magnetic field before the flare revealed several complex structures, including a magnetic flux rope. The researchers suggest that repeated magnetic reconnection at these structures helped start the flare and produce the pulses, but this explanation remains a proposal rather than a confirmed cause.

Young explorerScientists watched a big bright flash on the Sun. It began with an S-shaped glow, and its X-ray light pulsed roughly every four minutes for part of the flash. They also made a computer model of the Sun’s magnetic patterns. They think repeated changes in those patterns might help explain the flash and its pulses, but they have not shown that for sure.

Starspots on weak-lined T Tauri stars in the sigma Orionis cluster

Andrew J. Wilson, Darryl J. Sergison, Tim Naylor+1 more

AstronomerOptical spectral fits for young stars in the 4 Myr-old sigma Orionis cluster favour two-temperature photospheres, whereas an older field-star control sample shows no preference over single-temperature models. Independent infrared photometry tests for nine probable single K-type weak-lined T Tauri stars confirm large cool components, testing the predicted infrared excess of heavily spotted photospheres. The authors rule out binarity for all but one WTTS, accretion on the basis of small observed H-alpha equivalent widths, and gravity darkening because its predicted temperature contrasts are too small. They interpret the cool components as starspot-like regions covering 30–95% of the surface. No significant difference in cool-component temperature is found across covering fractions of 0.30–0.75, suggesting a common mechanism. Such coverage would cause significant age and mass overestimates when fitting unspotted isochrones in colour–magnitude diagrams. Variation in coverage could also explain lithium equivalent-width dispersion among coeval zero-age main-sequence stars; this remains a proposed explanation.

PublicSome young stars appear to have enormous cool patches on their surfaces. Researchers compared models with one surface temperature against models with two temperatures using optical spectra of stars in the young sigma Orionis cluster. The young stars favoured two temperatures, while older comparison stars did not. Infrared measurements of nine selected young stars independently supported the presence of large cool regions. The authors argue that starspot-like patches covering 30–95% of the surface are the most plausible explanation. They reject accretion and gravity darkening as alternatives, and rule out a companion star for all but one of the stars tested. If these patches are ignored, estimates of stellar ages and masses would be too high. Differences in patch coverage might also explain differences in lithium signatures among stars of the same age, but that explanation is not established.

Young explorerYoung stars may have huge cool patches, a bit like spots. Scientists studied their light and found that a warm surface with cooler patches fit better than a surface with just one temperature. Other light measurements also supported big cool areas. The scientists think starspots are the best explanation, though a second star could still explain one case. Missing these patches could make a star seem older and heavier than it really is.

Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) II. Approach to data reduction and products for line-rich broadband (sub)millimeter spectra

Adele L. Plunkett, Sébastien Maret, Daniel Harsono+26 more

• Astrophysics of Galaxies
• Instrumentation and Methods for Astrophysics

AstronomerThis paper documents the observing setup, reduction workflow, and primary data products of COMPASS, an ALMA spectral-survey program covering 11 protostellar regions to investigate how environment and evolutionary stage affect the chemistry of warm gas around embedded solar-type protostars. It provides infrastructure for forthcoming scientific analyses and archival research rather than reporting chemical conclusions. Calibration used CASA with the standard ALMA Pipeline, followed by self-calibration and imaging with IMAGER. Python post-processing handled continuum subtraction, primary-beam correction, and spectral extraction. The authors discuss data-volume and continuum-subtraction challenges, report computing-efficiency advantages from IMAGER that enabled benchmarking of imaging choices, and demonstrate scientifically comparable imaging outcomes with IMAGER and CASA. Products include image cubes for 36 spectral windows per source, extracted spectra, and continuum images.

PublicThe COMPASS project used ALMA to observe 11 regions containing young stars, with the goal of studying the chemistry of the warm gas around them and how it depends on their surroundings and stage of development. This paper explains how the observations were made and processed; it does not yet present conclusions about that chemistry. The team describes how it calibrated the data, made images, separated spectral-line signals from the underlying continuum emission, and extracted spectra. It also explains how it handled large data volumes and processing challenges. The authors found that the IMAGER software offered computing-efficiency advantages while producing imaging results scientifically comparable to those from CASA. The resulting image cubes, spectra, and continuum images are intended to support later COMPASS studies and research using archived observations.

Young explorerScientists used a telescope called ALMA to look at 11 places where young stars are growing. They want to learn what the warm gas around those stars is made of. This paper is like a guide to how they collected and cleaned up the telescope's information and turned it into pictures and signals that other scientists can study. Two computer tools made pictures that were scientifically comparable, and one helped the team work more efficiently. The paper does not yet tell us what they learned about the gas's ingredients.

Mapping of interstellar ices with JWST in protostellar envelopes: Spatial variations of ¹³CO₂, ¹²CO₂, CO, OCN⁻ and H₂O ice

N. G. C. Brunken, E. F. van Dishoeck, A. C. A. Boogert+16 more

AstronomerJWST NIRSpec IFU spectra extracted at every spatial pixel map 13CO2, 12CO2, CO, OCN−, and H2O ice in the protostellar envelopes of L1527 and IRAS 20126+4104. Using the 13CO2 ice feature as a thermal tracer, the study finds nonuniform ice distributions, localized temperature zones, and substructure in both sources. L1527 shows CO2 ice segregation and enhanced OCN− relative to CO2 in the warm central disk region. In IRAS 20126+4104, warm zones occur mainly near the central source and the shocked northwest outflow region, where dense material interacts with the precessing jet; these locations show CO2 ice segregation and CO ice sublimation. Crystalline H2O ice is also detected at a few envelope locations. The findings indicate that ice distribution and structure are linked to envelope temperature structure. IRAS 20126+4104 is interpreted as the more complex system, with interactions producing localized heating alongside denser regions containing cooler ices, whereas L1527 appears more organized, with warm ices concentrated toward the central disk. These observations help characterize the early chemical environments relevant to planet formation; they do not directly measure planetary compositions.

PublicThe chemistry available to future planets begins taking shape while their parent star is still forming. Researchers used the James Webb Space Telescope to map several kinds of ice around two young stars, L1527 and IRAS 20126+4104. The maps show that the ice is not spread evenly: different areas have different temperatures and ice structures. Around L1527, signs of heating are concentrated near the central disk, where carbon dioxide ice has separated from its surrounding ice mixture and cyanate is enhanced relative to carbon dioxide. Around IRAS 20126+4104, warm patches occur near the star and where its jet interacts with dense material in an outflow. There, carbon dioxide ice has also separated, and carbon monoxide ice is turning into gas. Crystalline water ice is detected at a few locations in that envelope. The researchers interpret these patterns as evidence that local temperatures shape the ice chemistry, with IRAS 20126+4104 showing a more complex mixture of warm and cool regions. The study examines potential planet-forming environments, not planets themselves.

Young explorerScientists used a space telescope to look at ice around two stars that are still growing. The ice was not the same everywhere. Around one star, called L1527, the warmer ice was mostly near the middle. Around the other star, warm spots were near the middle and where a stream of material from the star bumped into other material. In some places, one kind of ice was turning into gas. The scientists think warmer and colder places help explain why the ice looks different. Studying this ice can help us learn about the material that may someday make planets.

Coronal Mass Ejections from the Young Sun: Deceleration-Powered Solar Energetic Particles as a Self-Extinguishing Forcing of the Early Earth

Olga A. Panasenco

• Earth and Planetary Astrophysics

AstronomerA semi-analytic model chain follows young-Sun coronal mass ejections (CMEs) to Earth's atmosphere at about 3.9 billion years ago, when the Sun was approximately 0.6 billion years old. For launch speeds of roughly 3,000–4,000 km/s, the model gives about 6 × 10^25 J of kinetic-energy dissipation during deceleration, with about 10% converted into solar energetic particles (SEPs) through diffusive shock acceleration. Atmospheric deposition depends mainly on the spectral break energy, Eb. The model places the Alfvén surface at roughly 40–60 solar radii rather than 10–25, and predicts CME-shock particle fluences more than ten times those from flares. Using the measured wind-history scaling of mass loss with stellar age as t^-2.3, the modeled deceleration-powered forcing declines approximately as t^-3: it is about 50–100 times stronger at 3.9 billion years ago than at 2 billion years ago, and several hundred times today's level. This provides a physical basis for declining forcing often imposed in faint-young-Sun greenhouse scenarios, but not enough warming to solve the problem: SEP-produced nitrous oxide contributes at most a few W/m² toward a 20–40 W/m² requirement, and only if fractal organic haze prolongs its lifetime. Counting deposition below a survival level near 1 hPa yields modeled nitrogen fixation of about 4 × 10^10–4 × 10^11 mol N/year, potentially supplying surface prebiotic feedstock. Major uncertainties are Eb, eruption frequency, survival depth, and nitrous oxide lifetime.

PublicThe researchers model how powerful eruptions from the young Sun could have affected Earth's atmosphere about 3.9 billion years ago. Their calculations suggest that eruptions slowing down in the Sun's denser, more strongly magnetized wind could transfer substantial energy to fast particles that reach Earth. Using the measured history of the solar wind, the model predicts that this atmospheric influence weakened sharply as the Sun aged. That timing is useful for ideas about how Earth stayed warm when the young Sun was faint, but the calculated warming is limited. Nitrous oxide made through these particle-driven processes would provide only a small part of the greenhouse warming needed, and even that requires an organic haze to help the gas last longer. The model also estimates that the particles could turn atmospheric nitrogen into material potentially useful for chemistry preceding life in surface pools. These are modeled possibilities, not observations of ancient Earth. Important uncertainties include particle energies, eruption frequency, how deeply useful products must survive, and how long nitrous oxide lasts.

Young explorerWhen the Sun was young, it sent out many big bursts. Scientists used a model to work out how tiny, speedy particles from those bursts might have changed Earth's air. They might have helped make ingredients for the chemistry that came before life. They might also have helped warm Earth a little, but not enough on their own. Scientists are still unsure how much of this really happened.

High-Precision Differential Radial Velocities of C₃PO Wide Binaries: A Test of Modified Newtonian Dynamics (MOND)

Serat M. Saad, Yuan-Sen Ting

• Astrophysics of Galaxies
• Instrumentation and Methods for Astrophysics

AstronomerThe study introduces differential radial-velocity measurements from high-resolution, high-signal-to-noise spectra to extend wide-binary MOND tests beyond two-dimensional kinematics. For 85 C3PO wide binaries, it achieves approximately 8–15 m/s precision per pair, improving on Gaia DR3 by approximately 10–100 times, with a median improvement of 24 times. A scaled-velocity selection retains 57 systems classified as gravitationally bound. Combining these measurements with Gaia astrometry, a hierarchical Bayesian model infers orbital elements and the MOND acceleration scale a₀. The canonical a₀ is excluded at 2.5σ for the simple interpolating function, μ=x/(1+x), and at 1.5σ for the standard function, μ=x/√(1+x²). These results indicate tension rather than a decisive rejection of MOND; systematic uncertainties in the treatment of the external field effect, especially in the transition regime, may affect the conclusions.

PublicWidely separated pairs of stars offer a test of MOND, a theory that predicts departures from ordinary Newtonian gravity when accelerations are very small. The researchers used detailed stellar spectra to measure differences in the stars’ motions toward or away from us for 85 pairs, reaching a precision of about 8–15 metres per second—substantially better than Gaia’s radial-velocity measurements. They selected 57 pairs as gravitationally bound and combined the new measurements with Gaia’s measurements of positions and motions to model their orbits and test MOND. The results show some disagreement with MOND’s commonly accepted acceleration scale, stronger for one tested version than the other, but do not decisively rule out the theory. Uncertainty in how gravity from the surrounding environment is treated could change the conclusions.

Young explorerSome stars travel together even though they are very far apart. Scientists measured how differently the two stars in each pair move toward or away from us, using their light. They made much more precise measurements than before and used them to test an idea about how gravity works when its pull is very gentle. The results did not match that idea perfectly, but this does not mean the idea is definitely wrong. The scientists still need to account carefully for gravity from around the stars.

Searching for outbursts from Symbiotic Binaries in GOTO and ATLAS data

G. Ramsay, K. Ackley, S. Belkin+46 more

AstronomerA search of GOTO photometry from 2023 onward identified ten candidate outbursting symbiotic binaries, in which a white dwarf accretes material from a red giant, typically via a wind. Using ATLAS photometry to examine their pre-2023 behaviour, the authors retained five systems with photometric behaviour consistent with an outburst. ATLAS colours also provide insight into the nature of the events. They report LMC N67 as the first reported Z And-type outburst in an LMC symbiotic binary, and identify previously unreported outbursts in OGLE SMC-LPV-4044 and HK Sco. QW Sge and V4141 Sgr have previously reported outbursts that began in 2024 and remained ongoing at the time of the study. The authors argue that identifying and characterising more Z And-type events could help clarify their still incompletely understood physics.

PublicThese paired-star systems contain a white dwarf drawing material from a red giant, usually through gas flowing away from the giant. Researchers searched GOTO sky-survey observations taken from 2023 onward for episodes of brightening. They initially found ten candidates; comparison with earlier ATLAS observations left five whose brightness changes were consistent with outbursts. The study reports the first Z And-type outburst from such a system in the Large Magellanic Cloud, along with previously unreported outbursts in two other systems. Two further outbursts began in 2024 and were still underway when studied. These events are not yet fully understood, and studying more of them could help explain what drives them.

Young explorerSome stars live in pairs: a small star called a white dwarf takes gas from a big red star. Scientists looked for pairs that became brighter than usual. They found ten possible examples, then checked older pictures and found that five looked like they were having a brightening burst. Some bursts had not been reported before. Scientists still do not fully understand why these bursts happen.

Homogeneous stellar parameters for 717,807 TESS FGK stars using Gaia DR3

Francesca Waines, Angharad Weeks, Vincent Van Eylen

• Earth and Planetary Astrophysics

AstronomerThe authors present a homogeneous catalogue of 717,807 TESS FGK dwarfs and early subgiants, fitting isochrones using Gaia DR3 photometry, parallaxes, and spectroscopic temperatures and metallicities. They infer distances, surface gravities, metallicities, effective temperatures, radii, masses, and ages. Reported absolute median errors for radius, mass, temperature, and age are 0.06 solar radii, 0.05 solar masses, 104 K, and 2.1 Gyr, respectively. The catalogue is compared and validated against literature estimates using other isochrone grids and asteroseismology. The authors also identify 278 TESS exoplanet hosts and 915 candidates and recalculate planet radii for these systems. These model-based stellar estimates provide a consistent sample for investigating links between stellar properties and planetary characteristics and architectures; the abstract does not report findings about those links.

PublicResearchers have assembled a consistently analysed catalogue of 717,807 stars studied by TESS. They combined Gaia measurements with models of stellar evolution to estimate each star’s distance, size, mass, temperature, chemical composition, and age, and checked the estimates against previous studies. The ages are model-based estimates rather than direct measurements, with a reported median error of 2.1 billion years. The team also identified 278 stars hosting TESS exoplanets and 915 candidates and recalculated planet sizes in these systems. The catalogue can help researchers investigate how a star’s properties relate to its planets, but this study does not yet establish those relationships.

Young explorerScientists made a big list of stars to help them learn about planets around them. They used measurements and computer models to work out how big, hot, heavy, and old the stars might be. Those answers are not exact, especially the ages. They also worked out planet sizes again using the new information about the stars. The list can help scientists ask whether different kinds of stars have different kinds of planets.

Neutron star-companion interaction in core collapse supernovae. Population synthesis based on detailed binary evolution models

Andrea Ercolino, Norbert Langer, Avishay Gal-Yam+6 more

• High Energy Astrophysical Phenomena

AstronomerThis study predicts the rates and observables of companion–compact-object interactions following supernovae in binaries. It combines detailed binary evolution models, analytic prescriptions for ejecta-driven companion inflation, and SN-ORACLE population synthesis, exploring different explodability and neutron-star birth-kick distributions. The models predict periodic interactions in more than half of hydrogen-poor core-collapse SN binaries that remain bound, but a small occurrence rate for hydrogen-rich SN systems. Predicted periods span a broad range, peaking around 20–50 days, with interactions lasting 0.5–10 years. Specific binary models reproduce the observed light-curve modulation periods of SN2022jli, SN2015ap, and SN2022esa; this agreement does not establish the interaction mechanism observationally. The periodic emission of the Type Ic SN2022jli is interpreted as evidence for such an interaction. Companion inflation is also predicted to increase luminosity and detectability, with best-fit SN2022jli models predicting a J-band magnitude of 21–23 for up to 10 years. Up to 27% of hydrogen-poor SNe could exhibit periodic light curves, although only a few such events have been identified. These are model-based predictions that may guide searches in future and archival observations.

PublicMost massive stars have a companion star. When one explodes, material from the explosion can strike its companion and make it swell. The swollen star may then interact with the compact object left by the explosion, potentially producing repeated changes in the system’s light. Researchers modeled how often this might happen and what observers could see. They predict that these interactions occur in more than half of hydrogen-poor supernova binaries that stay together after the explosion, but rarely in systems producing hydrogen-rich supernovae. Predicted repeating cycles have a broad range of lengths, most commonly around 20–50 days, and the interactions could last 0.5–10 years. Some models match the observed timing of brightness variations in three supernovae, but matching the timing does not prove the explanation. Overall, up to 27% of hydrogen-poor supernovae could show repeating brightness changes, although only a few examples have been identified so far. The models also predict that swollen companions become brighter and easier to detect.

Young explorerMany big stars have a star buddy. When one star explodes, the stuff it throws out can hit its buddy and make it puff up. That buddy may then interact with the tiny object left by the exploded star, making the light get brighter and dimmer again and again. Scientists used computer models to explore this idea. A few real exploding stars have repeating light changes, but scientists are still checking whether this is why.

A Data-Driven Model for r-Process Production Patterns

Chen-Qi Li, Yong-Zhong Qian, Axel Gross+1 more

• High Energy Physics - Phenomenology
• Nuclear Theory

AstronomerA data-driven model based on elemental abundances in 68 metal-poor stars represents r-process patterns from Sr to U as mixtures of two components, Patterns 1 and 2. These mixtures adequately explain essentially all patterns in the sample and additional test stars, offering insights into the empirical limited-r, r-I, and r-II categories. A survey of yield templates from parametric r-process calculations motivates the proposal that Pattern 2 is dominated by a single template associated with a subset of neutron star mergers, whereas Pattern 1 averages multiple templates from other mergers and possibly magneto-rotational supernovae. These source assignments are interpretations, not established results. Potential systematic errors in abundance ratios involving different ionization states warrant attention. In particular, Os, Ir, and Pt measurements in HD 122563 need examination: the model assigns this star mainly to Pattern 1, with a prominent Pt peak. Confirmation would require a drastic revision of the limited-r category. Broader elemental coverage in a larger metal-poor stellar sample is needed to test and refine the model.

PublicThe researchers used measurements of elements in 68 metal-poor stars to build a model of how r-process elements, from strontium to uranium, appear together. Essentially all the patterns in these stars and additional test stars can be described by mixing two basic patterns. Comparing the model with computer calculations, the team proposes that one pattern may come from a subset of neutron star mergers, while the other may combine contributions from other mergers and possibly a type of supernova. Those origins remain interpretations rather than proven findings. The researchers also flag possible measurement biases. One star, HD 122563, has a pronounced platinum peak in their model that needs checking against measurements of platinum, osmium, and iridium. If confirmed, it would force a major rethink of the limited-r stellar category. Measurements of more elements in more stars are needed to test the model.

Young explorerScientists looked at the elements in 68 stars and made a model using two basic recipes. Mixing those recipes could explain almost all the element patterns they checked. They have ideas about which space events made the recipes, but those ideas are not proven. One star may have a surprising amount of platinum compared with other elements. Scientists need to check the measurements and study more stars to see whether their model is right.

The long period radio transient ASKAP J1448-68 is a cataclysmic variable

Geoffrey Mo, Akash Anumarlapudi, Iris de Ruiter+8 more

AstronomerThe authors identify the long-period radio transient ASKAP J1448-68 as a cataclysmic variable: a white dwarf accreting from a low-mass companion. Its spectroscopic orbital period is consistent with the radio pulse period, and the system may be a polar, although that classification remains tentative. Unlike the other known LPT cataclysmic variable, it lacks He II emission, a hallmark of magnetic CVs in high accretion states. New optical time-series observations show approximately 10% flickering, while the optical and infrared observations suggest, but do not establish, a period-bouncer origin. The identification extends the small sample of characterised LPT counterparts and supports a range of accretion states among LPT-producing white-dwarf binaries. The origins of the broader LPT population remain uncertain, with slowly spinning magnetars and magnetically interacting white-dwarf binaries both proposed.

PublicAstronomers have identified the source of repeating radio pulses called ASKAP J1448-68 as a white dwarf drawing material from a low-mass companion star. Measurements from its light spectrum indicate that the stars’ orbital period is consistent with the time between radio pulses. The system could belong to a magnetic class called polars, but this is not confirmed. It lacks a helium emission feature commonly seen in magnetic systems when they are strongly accreting. New observations also reveal visible-light flickering of about 10%. This discovery shows that white-dwarf pairs producing long-period radio pulses can have different accretion states, but it does not settle what causes all such radio sources.

Young explorerScientists studied something in space that sends out repeating radio flashes. They found a white dwarf star taking material from a lighter partner star. The time the stars take to go around each other seems to match the time between flashes. The light flickers, too. Scientists still do not know exactly how this pair makes its radio flashes.

From the Milky Way to the Early Universe: How Metallicity Shapes the Formation of Double Neutron Stars

Abhishek Chattaraj, Jeff J. Andrews, Monica Gallegos-Garcia+9 more

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena

AstronomerUsing POSYDON binary population synthesis across a cosmological metallicity range, the authors model double neutron star (DNS) formation and mergers. Their simulations favor common-envelope formation, with metallicity-dependent radial expansion and wind mass loss separating this route into subchannels that yield systematically different merging populations. Their best representative Galactic models predict local merger rates broadly consistent with GWTC-5 constraints, suggesting that radio-pulsar and gravitational-wave populations need not be in tension. Contrary to previous studies, modeled intrinsic merger efficiency rises toward lower metallicity across varied binary-evolution assumptions, although the enhancement's magnitude and physical drivers depend on metallicity regime. After convolution with cosmic star formation history, most modeled mergers originate from progenitors at approximately 0.1–1 times solar metallicity, with significant supersolar contributions. Weaker winds at low metallicity yield more nearly equal component masses, with q ≳ 0.9. The study also assesses detectability for proposed third-generation gravitational-wave observatory configurations; these population trends are model predictions, not direct observational measurements.

PublicPairs of neutron stars can merge and produce gravitational waves. Although astronomers know examples of these pairs in the Milky Way, understanding their population across the universe remains difficult. This study uses computer simulations to investigate how their formation depends on the abundance of elements heavier than helium in their parent stars. In the models, most pairs form through a stage in which two stars share a surrounding envelope of gas. Stars with fewer heavy elements produce merging neutron-star pairs more efficiently and tend to leave pairs with more equal masses. However, accounting for the universe's star formation history, most predicted mergers come from parent stars with roughly one-tenth to one times the Sun's heavy-element abundance, with a significant contribution from higher abundances. Predicted nearby merger rates broadly agree with gravitational-wave constraints. The trends remain dependent on modeling assumptions, and the study also considers detection with proposed future observatories.

Young explorerTwo tiny, very dense stars can circle each other and crash together, making ripples in space. Scientists used a computer to explore how these star pairs might form. In their pretend star universe, the ingredients inside the parent stars change how often pairs form and how similar their weights are. Some predictions fit what astronomers have learned from space ripples, but the computer model is not the same as watching all these stars form.

First Direct Identification of a Multi-Star Microlens System Hosting a Planet

Sean K. Terry, David P. Bennett, Jean-Philippe Beaulieu+11 more

• Astrophysics of Galaxies

AstronomerHigh-angular-resolution Keck adaptive-optics and HST imaging obtained more than 15 years after the OGLE-2006-BLG-284 microlensing event directly detects the lens system and measures its motion across epochs. The measured lens-source relative proper motion is 5.80 ± 0.15 mas yr−1. Combining microlensing light-curve parameters with host-star brightnesses in V, I, and K yields inferred stellar masses of 0.43 ± 0.05 and 0.12 ± 0.02 solar masses, and a planetary companion mass of 165 Earth masses, with uncertainties of +40 and −33 Earth masses. The analysis cannot establish whether the planet orbits one star or both; next-generation high-precision radial-velocity measurements are proposed to distinguish these configurations. The authors report the first direct detection of flux from a planet-hosting, two-star microlensing system.

PublicAstronomers have directly detected light from a two-star system with a planet that was studied through gravitational microlensing. Images from Keck and the Hubble Space Telescope, taken more than 15 years after the lensing event, let them identify the system as it moved away on the sky from the background source. Combining the stars’ brightnesses with the earlier lensing data, they estimate that the stars have about 43% and 12% of the Sun’s mass, while the planet has about 165 times Earth’s mass, with an uncertainty of +40 or −33 Earth masses. They still cannot tell whether the planet orbits one star or both. They propose future high-precision measurements of the stars’ motion toward and away from us to resolve that question. The authors describe this as the first direct detection of light from a two-star microlensing system known to host a planet.

Young explorerScientists found light coming from two stars that have a planet. Long ago, the stars’ gravity helped them study the planet by changing the light from a star behind them. More than 15 years later, new pictures let the scientists see light from the two-star system itself. They used that light and the earlier clues to work out how heavy the stars and planet probably are. They do not yet know whether the planet goes around just one star or both stars. They hope future measurements will help them find out.

Detecting multiple planets in Gaia data using Bayesian model selection

Emmanuel J. Greenfield, James E. Owen

• Instrumentation and Methods for Astrophysics

AstronomerThis investigation assesses Gaia's detection capabilities for one- and two-planet systems, particularly near the 2:1 mean-motion resonance, where stellar reflex motions are superimposed. The analysis finds that recovering the lower-S/N companion requires a higher detection threshold, especially with a more massive outer planet near 2:1 commensurability. Fitting a single-planet model to a circular, resonant two-planet system can yield spurious eccentricities up to 0.8, mass biases up to 100%, and inclination biases up to 50 degrees. Biases peak when the two astrometric signatures are similar. Bayesian model selection can identify many two-planet systems, but a sufficiently weak second signal can remain undetectable and bias the inferred outer-planet parameters. For outer planets roughly more than three times as massive as their inner companions, orbital approximations recover the astrometric resoeccentric degeneracy from these biases. In dynamically resonant systems with short orbital periods, apsidal precession measured over a sufficiently long baseline, such as DR5, could help break the degeneracy. These modeling findings, rather than reported planet discoveries, suggest potential systematic effects on formation, migration, and evolution constraints inferred from Gaia demographics.

PublicGaia is expected to provide a census of cold giant planets by measuring the tiny motions they induce in their stars. This study investigates how two planets can complicate those measurements, especially when one takes about twice as long as the other to orbit. Their combined pull can resemble the signal of a single planet, causing a one-planet fit to infer an orbit that is too elongated or to misestimate the planet's mass and orbital tilt. Statistical comparisons can reveal many of these two-planet systems, but a weaker planet may remain hidden. The analysis suggests that tracking gradual changes in orbital orientation over a long enough time could help resolve some ambiguous cases. These are findings about detection and modeling capabilities, not newly observed planets, and the resulting biases could affect what astronomers infer about how planets form and change.

Young explorerA planet makes its star wobble a little. Gaia measures those wobbles to help find planets. This study looks at what happens when two planets make a star wobble together. Sometimes their wobbles can look like just one planet, and astronomers could get that planet's size of pull or path wrong. Comparing different explanations can help, but a tiny wobble may still be hidden. Watching for longer might help with some of these puzzles. The study is about how to spot planets, not about finding new ones.

Discovery of a second-generation planet candidate accreting onto a white dwarf

Jamie T. Williams, Boris T. Gänsicke, Nicholas C. Stone+10 more

• Solar and Stellar Astrophysics

AstronomerHS 0209+0832 is a white dwarf accreting material with an abundance pattern unlike that of any Solar System object: its atmosphere is strongly enriched in trans-iron elements, including zinc, copper, and niobium, but depleted in silicon and iron. The authors interpret the high s-process-element enrichment as consistent with a candidate second-generation planet formed from material expelled during the host star’s giant phase, rather than a first-generation planet. Photospheric helium and the lack of terrestrial rock-forming elements suggest accretion from the escaping atmosphere of a photo-evaporating giant planet candidate. A sinusoidal photometric signal has a period of 4.399 ± 0.026 days and an amplitude of 0.120 ± 0.018%. The authors attribute this variability to either thermal emission associated with a planetary day-night cycle or a transiting cometary tail from an evaporating gas giant; neither interpretation establishes the planet’s existence or origin conclusively.

PublicAstronomers have found a white dwarf taking in material whose chemical makeup differs from that of any object in our Solar System. Its atmosphere contains unusually large amounts of elements such as zinc, copper, and niobium, but little silicon or iron, which are normally important ingredients of rocky bodies. The researchers suggest that the material may come from a giant planet formed from matter the star shed during its earlier giant phase. The chemical pattern, together with helium in the white dwarf’s atmosphere, points to a possible planet losing its gaseous atmosphere. The system also shows a small, repeating brightness change about every 4.4 days. This could reflect different temperatures on the planet’s day and night sides, or a trailing cloud of escaping material passing in front of the star. The planet and its proposed formation history remain interpretations, not confirmed findings.

Young explorerA white dwarf is a star’s leftover core. Astronomers found one taking in stuff with an unusual mix of ingredients, different from anything in our Solar System. They think the stuff might come from a big, gassy planet that is slowly losing its air. That planet may have formed from material the star threw out earlier. The light also gets a tiny bit brighter and dimmer in a repeating pattern. Maybe we are seeing a hotter side and a cooler side of the planet, or maybe a tail of escaping stuff is passing in front of the star. The astronomers have clues, but they are not yet sure there is a planet.

Enhancing the Interpretability of Radial Velocity Analysis Using Leave-one-out Cross-validation

Matthew C. Nixon, Ritvik Basant, Rafael Luque+2 more

• Instrumentation and Methods for Astrophysics

AstronomerThis study demonstrates leave-one-out cross-validation (LOO-CV) as a tool for model criticism and selection in precision radial-velocity analyses through three case studies. For HD 119130 b, two individual CARMENES measurements strongly drive the anomalously high inferred mass; removing them significantly reduces the tension with follow-up data from other instruments, which had revised the mass downward. For GJ 4276, LOO-CV favors an eccentric single-planet model over a two-planet model and identifies orbital phases where future observations could best distinguish them. For GJ 357, the method is extended to correlated-noise models using a Gaussian process. LOO-CV finds no predictive support for a fourth planetary signal, despite moderate support from Bayesian evidence, strengthening—but not proving—the previously reported three-planet interpretation. The authors also provide implementation guidance and an online tutorial.

PublicVery precise measurements of a star’s motion can reveal planets, but the conclusions can depend on a few measurements and on how the data are modeled. This study tests a method that leaves out one measurement at a time to assess a model’s predictions. In HD 119130, two measurements strongly influenced an unusually high estimate of one planet’s mass; removing them brings the original analysis closer to later observations that suggested a much lower mass. In GJ 4276, the method favors one planet on an elongated orbit over two planets and suggests when further observations could best tell these explanations apart. In GJ 357, it finds no predictive support for a proposed fourth planet, even though another statistical method moderately favors that signal. This supports the existing three-planet interpretation without establishing it conclusively.

Young explorerAstronomers watch how stars move to look for planets. In this study, they checked their ideas by setting aside one measurement at a time and seeing how well each idea could predict it. For one star, just two measurements helped make a planet seem much heavier than later measurements suggested. For another star, the check liked the idea of one planet moving on a stretched-out path better than the idea of two planets. More watching could help tell which idea is right. For a third star, adding a fourth planet did not help the predictions. That makes the three-planet idea look stronger, but it does not mean astronomers know for sure.

Exploring the ultrahot Neptune LTT 9779 b with CRIRES+. Non-detection of helium transmission spectra and detection of H₂O on the dayside

S. Liu, F. Yan, L. Nortmann+15 more

AstronomerHigh-resolution CRIRES+ transit and dayside thermal-emission spectroscopy of the ultrahot Neptune LTT 9779 b probes atmospheric escape and molecular features. No significant metastable He I 1083 nm transit absorption is detected; the 3σ upper limit on excess absorption depth is 0.45%, supporting earlier non-detections suggestive of weak ongoing escape. K-band cross-correlation reveals H2O absorption and a tentative CO feature, with a combined significance of 4.8σ. CRIRES+ and previous JWST data favor a non-inverted dayside temperature structure, with no evidence for a thermal inversion. A joint retrieval of CRIRES+ spectra and JWST/NIRISS SOSS secondary-eclipse observations yields low H2O abundance but weak constraints on CO abundance. The inferred equatorial rotation velocity of 4.9 (+4.4/−3.0) km/s is consistent within 1σ with the approximately 2.8 km/s expected for synchronous rotation, but its large uncertainty precludes strong constraints on the rotation state. Future higher-signal-to-noise CRIRES+ observations spanning more orbital phases are proposed to improve abundance constraints and probe atmospheric dynamics.

PublicResearchers studied the atmosphere of LTT 9779 b, an extremely hot Neptune-like planet whose faint light is difficult to separate from its star's. Using CRIRES+, they found no significant helium absorption as the planet passed in front of the star. This supports earlier indications that atmospheric gas may currently be escaping only weakly; it does not establish that escape is absent. In light coming from the planet's hot dayside, they identified a water absorption signal and a possible carbon monoxide feature. Both these observations and earlier JWST data favor a dayside atmosphere without a temperature inversion, meaning there is no evidence for an upper layer that becomes hotter with altitude. Combining the two sets of observations suggests a low water abundance, while the amount of carbon monoxide remains poorly constrained. The estimated rotation speed is compatible with the planet always keeping the same side toward its star, but the uncertainty is too large to establish this. More precise observations across more of the orbit could clarify the atmosphere's composition and motion.

Young explorerScientists studied a very hot planet called LTT 9779 b. Its light is hard to see next to its bright star. They found a sign of water in the planet's air and a possible sign of a gas called carbon monoxide. They looked for a helium signal that could help show air escaping, but did not find it. That suggests the planet may be losing air only slowly, though it does not prove that no air escapes. Their clues suggest there is only a little water in the air. The planet might always keep the same side facing its star, but scientists are not sure yet. More observations could help them learn what its air is like and how it moves.

Tracing the main belt origins of S-complex near-Earth objects: From space mission targets to meteorite sources

P. N. Simon, P. Vernazza, M. Marsset+5 more

AstronomerThe study infers ordinary-chondrite analogues and main-belt source families for six S-complex NEO mission targets by fitting near-infrared spectra with space-weathered OC analogues through reduced chi-squared minimisation, then cross-validating against probabilistic dynamical maps. The inferred associations are LL6–7 and Flora for Eros, Itokawa, Apophis, and Torifune; LL3 and Nysa for Toutatis; and L and Massalia for Didymos–Dimorphos. Classifications agree with available in situ observations of Itokawa and Eros. Across the broader MITHNEOS S-complex sample, spectral classifications and orbital distributions are broadly consistent with dynamical models. After accounting for observational biases, objects at diameters of 100 m or less show increasing H- and L-type fractions relative to LL6–7 types. Their low-inclination orbits are consistent with Koronis and Massalia origins, respectively. The authors interpret the approach toward meteorite-fall compositions below roughly 100 m as spectroscopic observational evidence for the emergence of ordinary-chondrite meteorite source regions; the individual family assignments remain model-supported inferences.

PublicResearchers combined near-infrared measurements of near-Earth asteroids with meteorite comparisons and models of asteroid motion to infer where several spacecraft targets originated. Their analysis links Eros, Itokawa, Apophis, and Torifune to the Flora asteroid family, Toutatis to Nysa, and Didymos–Dimorphos to Massalia. These are inferred origins, not directly observed journeys. The rock classifications agree with on-site observations where those exist, for Itokawa and Eros. In a larger asteroid dataset, the researchers also found that objects 100 metres across or smaller contain greater proportions of two meteorite-like categories, H and L, and a smaller proportion of the LL6–7 category, after accounting for observational biases. Their orbits are consistent with sources in the Koronis and Massalia families. The authors interpret this growing similarity to meteorites that fall to Earth as evidence revealing the asteroid regions that supply ordinary-chondrite meteorites.

Young explorerScientists studied light from space rocks near Earth to find clues about what they are made of and which rock families they came from. They compared those clues with meteorites and models of how space rocks move. This gave them likely family matches, but they did not watch the rocks travel from those families. They also found that the smaller rocks had a mix of rock types more like the meteorites that fall to Earth.

Discovery of 2 km ultra-fast rotating asteroid in Rubin DP2 catalog via varying Fourier order method

Dmitrii E. Vavilov, Siegfried Eggl, Sarah Greenstreet

• Instrumentation and Methods for Astrophysics

AstronomerThe authors present an improved asteroid rotation-period estimator using a Fourier series with object-specific order and automated reliability assessment to address false periodogram minima caused by sparse, irregular photometry. When a unique spin period cannot be reliably identified, the method returns alternative periods with probability estimates. Applied to the NSF-DOE Vera C. Rubin Observatory Data Preview 2 solar-system catalog, it yields reliable periods for a large asteroid sample, including 66 super-fast rotators with periods shorter than the classical 2.2-hour spin barrier. Asteroids 491384 and 566130 are both larger than 2 km and have reported rotation periods of about five minutes. The authors infer that significant internal cohesion is required for them to survive these spins. With a diameter of about 2.5 km, 491384 is reported as the largest ultra-fast rotator known so far.

PublicAsteroids’ changing brightness can reveal how quickly they rotate, but observations taken at uneven intervals can suggest misleading rotation periods. The researchers developed an improved method that adapts its mathematical model to each asteroid. If the data do not reliably identify one period, it lists possible alternatives and estimates their probabilities. Using the Vera C. Rubin Observatory’s Data Preview 2 catalog, the team identified 66 asteroids rotating faster than the classical 2.2-hour spin limit. Two, numbered 491384 and 566130, are each more than 2 km across yet turn once in about five minutes. The researchers infer that substantial strength holding their interiors together is needed to keep them intact. At about 2.5 km across, 491384 is reported to be the largest ultra-fast-spinning asteroid known so far.

Young explorerAsteroids are rocks in space that spin. Scientists watched how their brightness changes to work out how fast they turn. Their new way of checking the clues can give several possible answers when the clues are not clear enough. They found 66 asteroids spinning faster than a usual speed limit for asteroids. Two rocks, each more than two kilometers wide, turn all the way around in about five minutes! The scientists say these rocks must hold together strongly inside so they do not fly apart. One is the biggest asteroid known so far to spin this extremely fast.

Hubble Space Telescope Observations of Active Asteroid (101955) Bennu

David jewitt, Max Mutchler, Yoonyoung Kim

AstronomerOSIRIS-REx measurements established Bennu as an active asteroid. Deep, high-resolution Hubble observations at the 2023 orbit-plane crossing detected neither ejected material near Bennu nor a particle trail. Model-dependent mass-loss upper limits are 0.12 kg/s from near-nucleus surface-brightness profiles and 0.006 kg/s from the trail nondetection. These limits are one to two orders of magnitude below remotely measured mass-loss rates in other active asteroids, suggesting that weak activity could escape remote detection in many or most asteroids. Using a still lower mass-loss estimate from OSIRIS-REx, the authors calculate a specific rate of 1e-7 kg/km²/s and extrapolate it to the main-belt population. The estimated cumulative dust production is 850/sqrt(r_min) kg/s, with the minimum asteroid radius r_min in meters. For r_min > 1 m, the estimated contribution ranges from less than 1% to 10% of the rate required to maintain the Zodiacal cloud in steady state; this is an extrapolation, not a measurement of main-belt dust production.

PublicNASA’s OSIRIS-REx spacecraft revealed that asteroid Bennu sometimes releases particles. Researchers used Hubble in 2023 to look for escaping material when the viewing geometry favored spotting a particle trail, but found none. This does not establish that Bennu was completely inactive: the observations instead set model-dependent upper limits on how quickly it could have been losing material. Those limits are much lower than loss rates measured from afar for other active asteroids, raising the possibility that many asteroids shed material too slowly for remote observations to detect. The researchers also extrapolated a lower rate estimated from spacecraft data to the main asteroid belt. Depending on the smallest asteroid size included, their estimate for minimum radii above one meter amounts to less than 1% to 10% of the dust supply needed to maintain the Zodiacal cloud. That population-wide contribution is an estimate, not a directly observed result.

Young explorerBennu is a space rock that sometimes lets tiny bits float away. A spacecraft found this happening, but when scientists later looked with the Hubble telescope, they did not see any loose bits or a trail. There might have been too little material to see. Scientists also used Bennu to estimate how much dust lots of space rocks might make. Their estimate suggests those rocks could supply a small part of a big dust cloud in our solar system, but they did not measure all those rocks.

HD 715 b, a Warm Jupiter Orbiting a Massive Subgiant Discovered from a Single TESS Transit

Alexander Venner, Robert A. Wittenmyer, Andrew Vanderburg+23 more

AstronomerThe authors report the discovery and confirmation of HD 715 b (TOI-6893 b), a transiting Warm Jupiter around a bright subgiant (V = 8.70). A single transit in TESS Sector 70 prompted two seasons of radial-velocity follow-up with PFS, TRES, and MINERVA-Australis, which clearly detected the planetary orbit. The host mass of 1.60 ± 0.04 solar masses places HD 715 among the most massive stars known to host a transiting Warm Jupiter. A joint transit and radial-velocity fit yields an orbital period of 56.40 days (+0.19/−0.23), a planet mass of 0.635 ± 0.056 Jupiter masses, a radius of 1.07 ± 0.04 Jupiter radii, and an eccentricity of 0.21 (+0.07/−0.08). Its mass and radius are relatively typical for Warm Jupiters. The authors interpret its moderate eccentricity, compared with higher values for similar planets around evolved stars, as evidence of greater orbital diversity than previously known. Separately, the absence of transits in TESS Sectors 42 and 43 restricts possible periods to 56.01–56.35 days. Transit timing remains substantially uncertain; future photometry may recover another transit.

PublicAstronomers have confirmed a giant planet, HD 715 b, orbiting a bright star that has evolved into a subgiant. TESS first spotted one passage of the planet across the star. Two seasons of follow-up measurements detected the star’s motion caused by the orbiting planet, confirming the discovery. This Warm Jupiter takes about 56 days to orbit, has roughly two-thirds of Jupiter’s mass, and is slightly larger than Jupiter. Its orbit is moderately elongated, rather than circular. Compared with similar planets around evolved stars, whose orbits are more elongated, this finding suggests a wider variety of orbital shapes than previously recognized. Earlier TESS observations without a transit help narrow the possible orbital period, but the timing of the next passage remains substantially uncertain. Future observations may catch it again.

Young explorerAstronomers found a big planet going around a bright star. They saw it pass in front of the star once, and then watched the star wobble because the planet was pulling on it. The planet is a little bigger than Jupiter and goes around its star about every 56 days. Scientists are not yet sure exactly when they can see it cross the star again.

Ariel Tier 3 Observations: An Opportunity to Explore both Stellar and Planetary Variability through Broad Wavelength Time-domain Spectroscopy

Alexandra H. Thompson, Quentin Changeat, Theresa Luftinger+1 more

• Instrumentation and Methods for Astrophysics
• Solar and Stellar Astrophysics

AstronomerThis simulation study examines how host-star variability affects atmospheric retrievals from repeated Ariel Tier 3 observations. For a favourable system with different spot and facula configurations, the authors compare unmodified stacking, progressive exclusion of contaminated optical wavelengths, and visit-by-visit correction using combined star–planet retrievals. Under strong stellar variability, stacking inconsistent visits can substantially bias retrieved planetary properties, although a single activity correction can still recover parameters reasonably well. Removing progressively more optical data improves retrieval accuracy up to a point, with modest precision loss and no in-retrieval correction. Correcting individual visits before stacking yields more consistent spectra and generally smaller uncertainties, at greater computational cost. These findings come from simulated observations, not observed Ariel data, and their scope is limited by the favourable system tested. The authors advocate target-dependent mitigation supported by preparatory and contemporaneous stellar monitoring; stellar activity need not prevent atmospheric characterisation.

PublicA star that changes over time can make it harder to study a planet’s atmosphere by combining observations taken on different dates. The researchers tested this problem using simulated repeated Ariel observations of one favourable system, with different patterns of stellar spots and bright regions. Simply combining strongly mismatched observations could give misleading estimates of the planet’s properties. Leaving out the most affected visible-light wavelengths improved accuracy, up to a point, while slightly reducing precision. Correcting each observation before combining them generally reduced uncertainty but required more computing. These are simulation results, not findings from actual Ariel observations. The authors recommend choosing a correction strategy for each target and monitoring its star to help interpret the planet’s atmosphere.

Young explorerTo learn about a planet’s air, scientists study light. But spots and bright patches on its star can change the light and confuse the answer. Scientists tested pretend observations on a computer. They found that leaving out some confusing light, or fixing each observation before putting them together, could help. They suggest watching the star too, so its changes are easier to spot.

Blinding Lights: Simulation-Based Evidence for Terrestrial Giant Impacts as Astronomically Observable Events

Lucy Taylor, Simon J. Lock, Philip J. Carter+1 more

• Instrumentation and Methods for Astrophysics

AstronomerThe authors present a post-processing pipeline for smoothed particle hydrodynamics (SPH) simulations of giant impacts, designed to emulate realistic physical properties in multi-phase, multi-material collisions and better characterize low-density outer regions. These regions are difficult to resolve, particularly when SPH codes impose density floors for computational efficiency. Applied to one example terrestrial giant impact simulated at different resolutions and with different code parameters, the pipeline yields consistent photic surface geometries and estimates direct thermal emission and potential observational signatures. The modeled hot, unbound ejecta can have a temperature and luminosity comparable to an M-dwarf star during the first days after impact, suggesting possible astronomical detectability rather than reporting an observed event. The method could help high-cadence, large-sky surveys, including the planned Vera C. Rubin Observatory survey, constrain the frequency and properties of nearby giant impacts.

PublicCollisions between planet-sized bodies can dramatically reshape planets and planetary systems, but connecting a possible sighting to the collision that caused it is difficult. Computer simulations struggle to represent the extremely thin material at the outer edges of these events. The researchers developed a way to process simulation output to better estimate this material’s properties and the heat-generated light it could emit. For one simulated collision involving terrestrial planet-sized bodies, they obtained consistent emitting-surface shapes across different simulation settings. Their model suggests that, during the first few days, hot debris escaping the collision could rival an M-dwarf star in temperature and brightness. This is a simulation-based prediction, not a reported detection. The approach could help future wide-sky surveys, such as the planned Vera C. Rubin Observatory survey, investigate how often nearby giant impacts occur and what they are like.

Young explorerWhen two planet-sized things crash, they can throw out very hot bits. Scientists used computers to imagine one of these crashes and made a new way to work out how the thin cloud of bits might glow. In their computer model, some bits flying away could be as hot and bright as a small star for the first few days. They have not reported seeing this crash in the sky. Their work might help telescopes look for real crashes like it.

Reflex instabilities I: Boundaries makes grid-based disc simulations frame-dependent

Nathan Magnan, Michel Tagger, Clément Baruteau+3 more

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena
• Instrumentation and Methods for Astrophysics
• Fluid Dynamics

AstronomerThis analytical study examines feedback between an asymmetric accretion disc and the reflex motion of its central object. The authors provide the first analytical description and a physical explanation of the modes identified by Sanchez et al. (2025, Appendix A.3), proposing the name 'bracket modes' because they arise from the boundary term in integration by parts. They show that the same disc can be stable in a stellocentric frame but unstable in a barycentric frame because the simulation-domain boundaries are frame-dependent. Avoiding this problem requires modeling the entire disc from its central cavity to its outer edge, which the authors describe as prohibitively expensive; some discs also lack a central cavity. These are analytical findings, not astronomical observations. They motivate caution in interpreting asymmetric-disc simulations and suggest that adequate tools for modeling central-object reflex motion may not yet be available.

PublicAn uneven disc of matter can tug its central object away from the center, changing how that object pulls back on the disc. This paper investigates that feedback using mathematics rather than observations. The authors find that equations describing the same disc can predict stability or instability depending on whether the reference frame is centered on the central object or on the system's center of mass. They trace the difference to the frame-dependent boundaries of the modeled region. Modeling the whole disc could avoid this problem, but the authors say it is prohibitively costly, and some discs lack an inner cavity. They warn that simulations of uneven discs need careful interpretation and that suitable modeling tools may still be lacking.

Young explorerImagine a big object with a spinning disc of stuff around it. If more stuff is on one side, it can tug the big object, which pulls back. Scientists used math to study this. They found that changing where a model is centered can change whether it says wobbles grow, because the model's edges change too. They warn that computer models need care; this was not something they watched in space.

Reflex instabilities II: The reflex motion of the central object drives at least seven instabilities in accretion discs

Nathan Magnan, Michel Tagger, Clément Baruteau+3 more

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena
• Instrumentation and Methods for Astrophysics
• Fluid Dynamics

AstronomerUsing linear analysis, this second paper identifies or reproduces seven instabilities associated with the central object's reflex motion under the disc's gravity and proposes a classification. Three of the four previously known instabilities are judged artificial: one disappears with modern surface-density profiles such as power laws, one arises from domain-boundary placement, and one from boundary damping layers. Only the previously known SLING instability and three newly identified cavity instabilities appear capable of affecting accretion discs; all four are described with high precision by WKB methods. Their possible consequences include eccentricity growth, altered planet migration, planet-free spiral and crescent substructures, and enhanced central accretion. These are potential effects, not reported observations. Because the artificial instabilities are extremely difficult to avoid in simulations and could bias the same observables, the authors question whether current modelling tools can reliably handle central-object reflex motion.

PublicA disc of material can gravitationally tug on the object at its centre, making it move in response. This theoretical study examines how that motion might destabilize the disc. Mathematical analysis finds seven distinct instabilities, but the authors judge three to be artificial effects of modelling choices rather than realistic disc behaviour. The remaining four—one previously known and three newly identified—appear potentially relevant to real discs. They might change the disc's shape, influence how planets move, produce spirals or crescent-shaped features without planets, or increase the flow of material onto the central object. The study does not report observations of these effects. Its central warning is that artificial instabilities are very hard to avoid in simulations and could mimic the same signatures, raising doubts about the reliability of current modelling tools.

Young explorerImagine a ring of space stuff around a heavy object. The ring can tug on the object and make it wobble. Scientists used maths to find seven ways this might upset the ring. They think three come from how the models are set up, while four might happen in real space. Those four could change the ring's shape or help stuff fall inward. But computer models can be fooled, so scientists need to be careful.

SOPHIE and TESS characterization of fourteen TESS Objects of Interest: nine planetary systems and five low-mass stellar companions

N. Heidari, G. Hébrard, S. Sousa+61 more

AstronomerThe SOPHIE-TESS follow-up program classifies 14 TOIs using TESS and ground-based photometry, SOPHIE radial velocities, and high-resolution imaging: nine systems host planets, while five are eclipsing binaries with companion masses and radii of 0.1–0.6 solar units. Three transiting hot Jupiters have periods of 4.4–6.0 days, radii of 1.3–1.6 Jupiter radii, and masses of 0.3–1.3 Jupiter masses. Five transiting warm Jupiters have periods of 40.4–67.0 days, radii of 0.8–1.2 Jupiter radii, and masses of 0.5–1.0 Jupiter masses; the previously reported warm Jupiter TOI-6883A b is further characterized with new photometry and SOPHIE and TRES RVs. TOI-5217A also has an outer companion with a period of about 1761 days, a minimum mass of about 13 Jupiter masses, and eccentricity 0.53 ± 0.02. TOI-6842A b has a density of 0.08 ± 0.01 g/cm³, placing it among the nine lowest-density known planets; its transmission spectroscopy metric of about 250 motivates future atmospheric characterization, rather than constituting an atmospheric measurement. The six warm Jupiters have equilibrium temperatures of 377–846 K and are presented as low-irradiation benchmarks for hot-Jupiter inflation models. TOI-7025 b has eccentricity 0.82 ± 0.02, among the largest known for a planet orbiting a single star. Gaia astrometric excess noise provides a detection of TOI-5906 B, which the authors identify as the first object detected through transit, RV, and astrometry.

PublicAstronomers checked 14 possible planet-hosting systems found by TESS, combining measurements of starlight, stellar motion, and detailed images. Nine systems contain planets; the other five are pairs of stars that eclipse one another. The planets include three hot Jupiter-sized worlds and six warm Jupiters, one of which had already been reported and is now better characterized. One especially light planet, TOI-6842A b, has a density of just 0.08 ± 0.01 grams per cubic centimetre, making it one of the nine least-dense planets known. It is a promising target for future studies of its atmosphere, but this work does not report such atmospheric observations. Another planet, TOI-7025 b, follows an unusually stretched orbit. The six warm Jupiters could help test models explaining why some hotter giant planets are inflated. The researchers also find a distant companion in the TOI-5217A system whose minimum mass is about 13 times Jupiter’s mass; its true mass is not given. For the stellar companion TOI-5906 B, they combine evidence from eclipses, stellar velocities, and Gaia measurements of motion across the sky, reporting it as the first object identified using all three methods.

Young explorerScientists checked 14 places where they thought planets might be hiding. Nine had planets. In the other five, two stars were moving around each other and taking turns blocking some light. One planet is very big but very light for its size, like a puffy ball. Scientists think it would be a good planet to study its air around it, but they have not done that here. Another planet goes around its star on a very stretched-out path instead of a nearly round one.

Decoy and disclosure radii of invariant shape descriptors

Tanush Shaska, Lubjana Beshaj

• Computer Vision and Pattern Recognition
• Cryptography and Security
• Algebraic Geometry

AstronomerThis mathematical study quantifies the ambiguity of rotation-invariant surface descriptors: large descriptor fibers permit geometrically distant matching decoys, whereas small fibers can reveal the enrolled shape from the stored descriptor. For star-shaped surfaces represented by spherical harmonics through degree L, a descriptor of generic rank r has generic fiber dimension n−3−r modulo rotations. The standard pool of band powers, even bispectra, and three degree-three invariants leaves decoy families of dimensions 5, 13, and 20 at L=4, 6, and 8; its rank first reaches n−3 at L=16, but a mirror decoy persists at every L. Odd bispectra generically remove the mirror ambiguity for L≥4. At fixed mean radius, the standard pool determines enclosed volume exactly but does not determine clearance compliance. Exact and interval arithmetic certify an L=6 decoy matching all 32 invariants to relative precision 2×10⁻¹⁸ while remaining at orbit distance at least 0.87 times the enrolled tuple’s norm. Applied to the radar shape model of Bennu, the pool recovers the modeled volume but misses handedness and leaves the keep-out radius uncertain by more than 7 m. These are mathematical and model-based findings, not new asteroid measurements.

PublicA compact shape signature can recognize an object regardless of how it is turned, but different shapes may share that signature. This study mathematically examines that ambiguity: a signature that allows very different matching shapes can admit impostors, while one that tightly identifies a shape can expose it to anyone who obtains the stored signature. The authors certify an example in which a substantially different shape matches 32 signature values with extremely high precision. They also show that the studied signature can determine enclosed volume exactly when the mean radius is fixed, without determining whether the shape satisfies a clearance requirement. For the radar shape model of asteroid Bennu, it recovers the model’s volume but cannot distinguish its handedness and leaves the required keep-out radius uncertain by more than 7 metres. These findings concern mathematical representations and an existing asteroid model, not new observations.

Young explorerImagine giving a shape a special name made of numbers. Turning the shape around does not change its name. But the researchers showed that very different shapes can have the same name! For a model of the asteroid Bennu, these numbers tell how much space is inside, but they cannot tell it apart from its mirror twin or say exactly how far away to stay.

Exploring the Impact of Tilted Magnetic Dipoles on the Atmospheric Dynamics of Hot Jupiters: Towards an Improved Magnetohydrodynamic Framework

James Fecanin, Hayley Beltz, John Allen+1 more

AstronomerThis modeling study extends a commonly used aligned-dipole magnetic prescription in three-dimensional hot-Jupiter general circulation models to include an internal dipole tilted relative to the rotation axis. Strong dayside irradiation can thermally ionize atmospheric species, allowing atmospheric flows to interact with the planetary magnetic field. In the simulations, dipole tilt produces pronounced north–south temperature asymmetries, latitudinal shifts of hot spots, and deflections of otherwise axially symmetric winds. Simulated JWST/NIRSpec phase curves respond most strongly to magnetic-field strength: stronger fields increase phase-curve amplitude and reduce the hot-spot offset. These are simulation results, not reported observations. The framework offers qualitative insight into magnetic influences on circulation, with outcomes dependent on local atmospheric properties and the assumptions of the magnetic prescription.

PublicHot Jupiters are giant planets whose strongly heated daysides can become hot enough to electrically charge some atmospheric particles, allowing winds to interact with the planet’s magnetic field. Researchers used three-dimensional computer models to explore what happens when that field is tilted relative to the planet’s rotation axis. In their simulations, the tilt made temperatures differ between the northern and southern hemispheres, shifted hot regions in latitude, and redirected winds. They also simulated how the planets’ infrared brightness would change over an orbit as measured with JWST/NIRSpec. Magnetic-field strength had the largest effect on these simulated brightness patterns: stronger fields produced larger brightness variations and a smaller hot-spot offset. The study provides qualitative predictions rather than observational confirmation, and its findings depend on the models’ assumptions.

Young explorerSome giant planets get so hot that their winds can feel the pull of a magnetic field. Scientists made computer pretend-worlds to see what might happen if a planet’s magnet were tilted. In those pretend-worlds, the winds turned and the hottest places moved toward the top or bottom of the planet. Stronger magnets also made bigger changes in how bright the planet looked as it went around its star. These are clues from computers, not things the scientists watched happen on real planets.

Companion architectures of sub-Saturns: Distinct migration pathways across the Neptunian landscape

Luis Thomas, Louise D. Nielsen, Alex J. Cridland+2 more

AstronomerThis study compares companion architectures of close-in sub-Saturns (4.0–8.5 Earth radii) across the sparsely populated Neptunian desert, the ridge at orbital periods of 3.2–5.7 days, and the longer-period savanna. Using 86 systems with transit and radial-velocity data, the authors combine detection-completeness maps with a joint Poisson model to infer companion occurrence. Nearby companions (periods under 200 days) occur around 91.1% (+3.2/−4.3 percentage points) of savanna sub-Saturns, versus 36% (+16/−14) of desert and ridge sub-Saturns. Small companions, below 20 Earth masses, drive almost all of this contrast: their corresponding occurrence rates are 88.2% (+4.2/−5.5) and 29% (+17/−14). Medium-mass and giant companions within 200 days are rare everywhere, at approximately 13% or less. Savanna systems are typically compact multiplanet systems, and the contrasts persist across cuts in planet radius, density, eccentricity, and host-star properties. The authors interpret the desert/ridge architectures as dynamically depleted, with nearby companion rates resembling those of hot Jupiters, while savanna architectures resemble warm-Jupiter systems. These findings support, rather than establish, high-eccentricity migration into the desert and ridge and quieter disk migration or in-situ formation in the savanna.

PublicPlanets measuring 4–8.5 times Earth's radius show a striking difference in their planetary neighbors depending on their orbital periods. From 86 systems studied using both transits and stellar-wobble measurements, the researchers estimate that about 91% of planets in the longer-period region called the savanna have companions orbiting within 200 days, compared with about 36% in the shorter-period desert and ridge regions. These estimates have uncertainties, especially for the desert and ridge. The difference comes mainly from small companions; more massive companions are uncommon in all three regions. The pattern supports the idea that desert and ridge planets arrived through migration involving highly elongated orbits, leaving systems depleted of nearby planets. Savanna planets may instead have migrated gently or formed where they are. The companion evidence does not directly establish those histories.

Young explorerSome planets have lots of nearby planet neighbors, while others have fewer. Scientists studied 86 planet families and found that planets going around their stars more slowly usually had more nearby neighbors than those going around faster. They think some faster planets may have taken a rough journey toward their stars, leaving fewer neighbors nearby. Others may have moved gently or stayed where they formed. These are clues, not proof of what happened.

The ALMA View of the Edge-on Gomez's Hamburger System: A Highly-Dynamic, Asymmetric Protoplanetary Disk Reveals the Earliest Phases of Giant Planet Formation

Charles J. Law, Jensen Lawrence, Richard Teague+18 more

• Solar and Stellar Astrophysics

AstronomerALMA observations at approximately 0.2-arcsecond resolution map 12CO J=3–2, 13CO J=3–2, CS J=7–6, and SO J_N=8_8–7_7 in the large, edge-on Gomez’s Hamburger disk (IRAS 18059-3211). A detected narrow, one-sided SO arc peaks near a previously identified gas overdensity. Because sulfur-bearing molecules are predicted to be enhanced by shock heating, ice sublimation, and gravitational instability, the authors interpret the arc as evidence suggestive of localized heating around an early-stage giant protoplanet or disk fragment, not a confirmed planet detection. The edge-on view allows mapping of molecular gas vertically relative to millimeter- and (sub)-micron-sized dust. The observations also reveal a pronounced north–south continuum asymmetry and non-Keplerian CO emission indicative of a disk wind. The derived dynamical stellar mass is 2.2 ± 0.5 solar masses; a revised dust-extinction-map distance of 139 ± 24 pc places the system on the outskirts of Scorpius-Centaurus. Localized sulfur chemistry may therefore trace an early observable stage of wide-separation giant planet formation.

PublicAstronomers used ALMA to study Gomez’s Hamburger, a large disk of gas and dust viewed edge-on. They detected a narrow arc of sulfur monoxide on just one side of the disk, with its brightest emission near a previously known concentration of gas. Sulfur-bearing molecules are expected to become more abundant under conditions such as shock heating or the release of material from ice, so the arc may mark heating near a giant planet beginning to form—or near a fragment of the disk. It does not confirm that a planet is present. The team also mapped gas and dust at different heights, found uneven brightness between the disk’s northern and southern sides, and detected gas motions that suggest a wind flowing from the disk. They estimate the central star’s mass at 2.2 ± 0.5 times the Sun’s mass and revise the distance to 139 ± 24 parsecs. Together, the findings suggest that this dynamic disk could offer a glimpse of a very early stage of giant planet formation far from its star.

Young explorerA star has a big disk of gas and dust around it, and we see the disk from the side. Astronomers found a thin, curved patch of gas containing sulfur on one side, near a place where extra gas is gathered. That patch might be a clue that something nearby is warming it, perhaps a giant planet just starting to form or a clump in the disk. We do not know yet whether there is a planet there. The disk is also brighter on one side, and some gas moves as if a wind is carrying it away. These clues help astronomers learn how planets might begin.

Just a Phase? Weakening Vertical Shear Instability Explains Class II Disk Morphologies: Simulations with dust coagulation, sedimentation, thermal relaxation, and backreaction

Thomas Pfeil, Alexandros Ziampras, Shangjia Zhang+2 more

AstronomerThe simulations show that the Vertical Shear Instability (VSI) can coexist with thin millimeter-emitting dust layers and bowl-shaped micrometer scattered-light morphologies, consistent with observed disk geometries. This contrasts with simulations in which sufficiently rapid thermal relaxation allows VSI to loft dust to heights inconsistent with most observed class II disks. Including dust coagulation, sedimentation, and dust-gas thermal accommodation changes the outcome: sedimentation-driven coagulation depletes atmospheric dust and slows dust-driven gas cooling, while a dense midplane layer of millimeter-sized grains exerts aerodynamic drag on the gas. The VSI corrugation mode terminates, leaving only weak activity in the upper and lower hemispheres. Strong VSI-induced turbulence is suppressed within a few hundred thousand years, on the typical dust-growth timescale. The authors therefore suggest that strong VSI activity may generally be restricted to class I stages; this evolutionary implication is not an observational demonstration.

PublicYoung stars are surrounded by disks of gas and dust. A process called the Vertical Shear Instability can stir these disks and lift dust, but simulations with strong stirring can make disks look thicker at millimeter wavelengths than most observed class II disks. The new simulations account for dust growing, settling, and exchanging heat with gas. Growing and settling dust removes grains from the disk atmosphere, slowing gas cooling, while larger grains collect near the middle and drag on the gas. Together, these effects suppress strong stirring within a few hundred thousand years. The simulated disks retain both a thin appearance at millimeter wavelengths and the bowl-shaped appearance commonly seen in scattered light. The authors suggest that strong stirring of this kind may mainly occur during an earlier stage of disk evolution.

Young explorerA young star can have a disk of gas and dust around it. Gas motions can stir the dust upward. In computer models, dust grains grow and settle toward the middle, making the strong stirring fade. The model disks then look thin in one kind of light and bowl-shaped in another, like disks astronomers see. This suggests the strongest stirring may happen mostly when disks are very young.

Improved Constraints on the Surface of LHS 3844 b from its Mid-Infrared Spectrum

Kimberly Paragas, Heather A. Knutson, Renyu Hu+4 more

AstronomerAn updated JWST MIRI/LRS dayside emission spectrum of the ultra-short-period super-Earth LHS 3844 b combines eight new and three archival eclipse observations over 5–12 micrometers. The authors report the highest-SNR emission spectrum yet obtained for a rocky exoplanet, with a median SNR of 29 across 12 wavelength bins. The data are sensitive to predicted Si–O stretching signatures for many common materials and to a transparency feature that probes surface grain size and porosity. The spectrum is approximately blackbody-like shortward of 10 micrometers, disfavoring a transparency feature, while a tentative feature appears at 10–12 micrometers with a significance of 1.9–3.5 sigma. If astrophysical, this feature can be matched by fayalite, the iron end-member of olivine, but may also be consistent with spinel or silicon carbide. Composition is therefore not established: a wavelength-dependent instrumental ramp could bias the spectrum. The authors outline mitigation strategies for future observations.

PublicAstronomers used the James Webb Space Telescope to study heat emitted by LHS 3844 b, a rocky planet orbiting very close to a nearby small star. Combining eleven observations produced what the authors describe as the clearest heat-emission spectrum yet measured for a rocky planet outside our solar system. Most of the spectrum resembles that of an ideal heat emitter, but a tentative signal at longer infrared wavelengths might reveal something about the surface material. If the signal comes from the planet, it could fit an iron-rich mineral called fayalite, although spinel or silicon carbide might also explain it. The signal could instead arise from the instrument, so the observations do not yet identify the planet’s surface composition. The researchers propose ways to reduce this instrumental uncertainty in future observations.

Young explorerScientists used a space telescope to look at the heat shining from a rocky planet far away. They found a small hint that might help tell them what its rocks are made of. But different kinds of rocks could make that hint, and the telescope itself might have caused it. They need to look again more carefully before they can be sure.

Irradiated Atmospheres VII. Effect of Mixing Energy Flux on Atmosphere-Interior Coupling

Wei Zhong, Zhen-Tai Zhang, Mei Ting Mak+5 more

AstronomerThis theoretical study quantifies how energy transport associated with vertical mixing affects the coupled atmospheres and magma oceans of highly irradiated, underdense rocky planets termed puffy Venuses. The calculations indicate an additional greenhouse-like heating pathway that warms the deep atmosphere and raises pressure and temperature at the magma-ocean surface. These thermal changes alter atmospheric composition, particularly CO and H2O abundances, and the partitioning of C-, H-, and O-bearing volatiles between atmosphere and magma. The mid-infrared planet-to-star flux ratio is also modified, especially at low equilibrium temperatures and for higher-mass planets. At high C/O, the flux increases slightly near 3.5–4.0 micrometers, but atmospheric transparency and flux decrease more broadly. Atmospheric circulation and gravity-wave breaking are possible transport sources, not established mechanisms here. The resulting changes may affect radius estimates over a limited temperature range; these are theoretical findings rather than reported observations.

PublicSome strongly heated rocky planets may have thick atmospheres above oceans of molten rock, making them unusually low-density. This study calculates how moving energy vertically through their atmospheres could change those worlds. The calculations suggest that this transport warms the deeper atmosphere, increasing heat and pressure at the molten surface. It also changes the amounts of gases such as carbon monoxide and water vapor, and how carbon-, hydrogen-, and oxygen-containing substances are shared between the air and molten rock. These changes affect the planet's infrared brightness relative to its star, particularly for planets with lower equilibrium temperatures or greater mass. When carbon is abundant relative to oxygen, a narrow infrared wavelength range becomes slightly brighter, while the atmosphere more broadly becomes less transparent and its infrared output decreases. Such changes might alter estimates of planet size within a limited temperature range. The study offers theoretical results, not observations confirming that these effects occur.

Young explorerSome rocky planets might have thick blankets of air above seas of melted rock. Scientists used calculations to explore what happens when energy moves up and down through that air. They found that this could make the air near the melted rock hotter, change the gases, and change the invisible heat-light the planet gives off. That might change how big scientists think the planet is, but they have not shown these changes happening on a real planet.

An Assessment of the Triangulation Capabilities of a Multi-Site All-Sky Infrared Camera Array

Abraham Loeb, Alex Delacroix, Ezra Kelderman+2 more

AstronomerThe authors report commissioning three autonomous observing arrays near Las Vegas, with 2 and 10 km baselines. Each array contains eight long-wave infrared cameras covering 360 degrees in azimuth. Their triangulation pipeline estimates instantaneous 3D positions without assuming a trajectory, minimizing weighted squared distances to simultaneous sightlines; weights account for camera pointing uncertainty and object range. ADS-B aircraft provide calibration references where stars and fixed landmarks are unavailable, and a track-association scheme links detections across sensors. Validation against ADS-B records uses one week of observations comprising 1,650 camera-hours, 210 million detections and 5.3 million tracks. For aircraft reconstructed from three sites, 99% of distances and 78% of speeds were recovered within 5%; corresponding fractions for a single site pair were 83% and 63%. Identification completeness depends on apparent size, reaching 50% at a wingspan of 1.8 pixels. Characterizing known sky-object populations to isolate events outside those populations is the project's goal; the abstract reports commissioning and aircraft validation, not the discovery of such an event.

PublicThree automated observing stations near Las Vegas use infrared cameras to watch objects crossing the sky. By combining views from different locations, the team reconstructs an object's position at each moment without assuming how it should move. Aircraft broadcasts supply reference positions for calibrating the cameras and checking the results. In a week of observations, distances were accurate to within 5% for 99% of aircraft measured using all three stations, compared with 83% using two stations. Speeds met that accuracy level for 78% and 63%, respectively. Identification also depends on how large an object looks in the images: half were identified at an apparent wingspan of 1.8 pixels. The long-term aim is to distinguish familiar natural and human-made objects from events that do not fit those categories; this report does not announce such an unusual event.

Young explorerThree groups of special cameras watch things moving across the sky. Seeing the same airplane from different places helps the team work out where it is and how fast it goes. They checked their answers using messages sent by airplanes. Using all three places worked better than using two. Tiny-looking things were harder to identify. The team hopes to spot things that do not fit familiar groups, but this report does not say they found one.

BRICS Southern Observatory (BRICS-SO) Project: Invitation to African countries to invest in Chile

Massinissa Hadjara, Amokrane Berdja, Swagat R. Das+6 more

AstronomerThis abstract advocates coordinated investment in ambitious astronomical infrastructure by the expanded BRICS+ community, rather than reporting observational or simulation results. It describes a BRICS astronomy consortium and the inclusion of Egypt and Ethiopia among countries joining the expanded grouping. Citing northern Chile’s favorable climate, China’s establishment of astronomical facilities there, and increasing competition for access to existing facilities, it argues for prompt international collaboration. The proposed BRICS-SO astronomy hub is intended to expand research opportunities, attract skilled personnel, train new generations, and foster exchanges. The expectation that cooperation will rapidly close technological gaps is an aspiration, not a demonstrated outcome; the abstract provides no detailed facility design, implementation schedule, or performance assessment.

PublicThe abstract calls for countries in the expanded BRICS+ group to work together on major astronomy projects. It highlights northern Chile as a favorable place for astronomy and points to China’s facilities there as a possible opening for wider collaboration. The authors argue that existing facilities are increasingly difficult to access and propose a new astronomy hub, called BRICS-SO, to give researchers more opportunities and help train future astronomers. These are goals and arguments for cooperation, not evidence that the proposed hub has been built or that its promised benefits have been achieved.

Young explorerPeople from several countries want to work together to study space. They suggest making a new place where scientists can use tools to look at the sky and help new scientists learn. They think working as a team could help more people explore space. This is an idea they want to make happen, not something they have already finished.

XuYi Interferometer Observation Simulator

M. Hadjara, T. Xu, Y. Sun+15 more

AstronomerThe authors present XIOS, a lightweight MATLAB-based observation-planning simulator for the XuYi Interferometer, described as China’s first long-baseline optical interferometer and currently under development at NIAOT. A single graphical interface integrates target observability, baseline geometry, delay-line constraints, predicted (u,v) coverage, and visibility estimates. XIOS incorporates astronomical routines from MAAT and visualization concepts inspired by ASPRO2. The paper describes its architecture and principal modules and presents representative simulations for the current three-telescope configuration in the near-infrared H band. These are planning simulations for future scientific operations, not observational measurements or demonstrations of achieved on-sky performance.

PublicResearchers have developed software to help plan observations with the XuYi Interferometer, a Chinese telescope system still under development. An interferometer combines light from separate telescopes. The new simulator, called XIOS, helps users check when a target can be observed, how the telescope arrangement affects the observation, and whether the planned setup fits the system’s light-path adjustment limits. It also predicts aspects of the combined-light signal. The paper presents the software and example simulations for a three-telescope arrangement using near-infrared light. These examples forecast possible observations rather than report measurements of the sky.

Young explorerScientists are building a system that brings together light from three telescopes. Before using it to study the sky, they made a computer program to help plan what to look at and when. The program also helps them check how the telescopes could work together. The paper shows examples made by the computer, not new things the telescopes have seen in the sky.

A Technosignature Survey Of The Anti-Solar Point: The SETI Institute's Largest-Ever Campaign With The Allen Telescope Array

Isabel Gerrard, Sofia Z. Sheikh

AstronomerThe ATA-ASP campaign searches for radio technosignatures at the Anti-Solar Point (ASP), proposed as a Schelling point where observers on Earth and extraterrestrial agents might independently choose to search or transmit. The rationale is that an agent in the opposite-Sun direction could observe Earth transiting within the habitable zone. Using the Allen Telescope Array at 2356–3700 MHz, the survey targets Earth's ecliptic for narrowband, Doppler-drifting signals localized to the ASP through beam comparisons. The ATSAT pipeline combines bliss and NBeamAnalysis with radio-frequency interference removal; spectrograms are visually inspected and classified into six morphologies. So far, 126 observations cover approximately 12% of the projected coordinates. Analysis of 67% of observing sessions has yielded more than 11,000 plots, all inspected and 75% labeled. Among the labeled spectrograms, 25 contain narrowband drifting signals localized to the ASP, corresponding to 10 coordinates scheduled for re-observation. These are signals of interest, not established extraterrestrial detections. The authors describe this as the first observational coverage of a long-proposed ASP beacon search and anticipate a multi-year survey producing over 11 petabytes of data, the ATA's largest survey.

PublicA radio survey is testing an idea about where another civilization might choose to send a signal: the point in the sky opposite the Sun. Researchers propose this as a natural meeting place for a search because an observer in that direction could see Earth pass in front of the Sun within its habitable zone. The Allen Telescope Array searches there for signals concentrated in a narrow range of radio frequencies that shift over time, while checking whether they come from the target direction rather than radio interference. The campaign has completed 126 observations covering about 12% of its planned positions. Researchers have analyzed 67% of observing sessions and inspected more than 11,000 signal plots, with 75% labeled by signal shape. Of the labeled plots, 25 show narrow-frequency, drifting signals localized to the target direction. The 10 corresponding sky positions will be observed again; these findings do not establish that the signals come from extraterrestrial technology. The full survey is expected to take several years and generate more than 11 petabytes of data.

Young explorerScientists are using radio telescopes to listen for possible messages from far away. They are looking toward a spot in the sky opposite the Sun. They think someone out there might choose that same spot to send a message, because from that direction they could see Earth pass in front of the Sun. The scientists have found some radio signals they want to check again. Those signals are not proof of aliens, and unwanted radio noise can make the search tricky. There is still lots of sky to check, so the search will take several years.

Armillary: A Label-Free Coordinate System for Stellar Spectra

Yuan-Sen Ting, Serat Saad

• Astrophysics of Galaxies
• Solar and Stellar Astrophysics

AstronomerArmillary generalises the Sequencer from a one-dimensional ordering to multidimensional coordinates inferred from stellar spectra alone. It uses Wasserstein distances between signed absorption profiles and shortest paths on a nearest-neighbour graph to estimate distances along the low-dimensional spectral manifold; the same graph propagates stellar-parameter labels from a small training set. The resulting coordinates are more nearly linear in effective temperature and log surface gravity than those from principal components, t-SNE, UMAP or an autoencoder. Label transfer, without deep learning, is more precise than the first three methods and comparable to the autoencoder. For 202,932 APOGEE DR17 stars, an illustrative draw of 32 training stars recovers ASPCAP labels for held-out dwarfs and giants with 1-sigma errors of 100 K in effective temperature, 0.18 dex in log surface gravity and 0.083 dex in [M/H]. Resolving the disc's two [alpha/M] sequences among giants requires 128 training stars; with 2,048, errors in effective temperature, log surface gravity, [M/H] and [alpha/M] are respectively 33 K, 0.06 dex, 0.026 dex and 0.022 dex. For 104,799 DESI stars, 32 APOGEE training labels yield errors of 129 K, 0.25 dex and 0.203 dex in the first three parameters, even for spectra degraded to signal-to-noise about 20. At signal-to-noise about 100, 2,048 training labels resolve both alpha sequences in DESI giants, with respective errors against APOGEE of 51 K, 0.07 dex, 0.047 dex and 0.026 dex. These reported errors measure agreement with reference labels rather than independent absolute accuracy. The code is public.

PublicA star's spectrum—the pattern of its light across wavelengths—contains clues to its temperature, surface gravity and chemical composition. The researchers introduce Armillary, a method that builds a multidimensional map of stars using only their spectra. A network connecting similar spectra then lets it estimate properties of many stars from known values for relatively few examples, without deep learning. Tests used more than 200,000 APOGEE stars and more than 100,000 DESI stars. In one illustrative APOGEE test, just 32 labelled stars gave temperature estimates with a reported error of 100 kelvin relative to the survey's reference values. More training examples improved agreement and allowed the method to distinguish two chemical groups of giant stars in the Galactic disc. It also worked on DESI spectra with reduced signal quality. The reported accuracy describes agreement with existing survey estimates, not a separate measurement of the stars' true properties.

Young explorerStarlight has patterns that help us learn about stars. The researchers made a new way to put stars with similar light patterns near each other on a map. When they give the map information about a few stars, it can estimate things like how hot the other stars are. They tested it on lots of stars and compared its guesses with information already available. More examples helped it make better guesses, but the guesses are not perfect.

Optimal Photon Counting with Fast, Low Noise Astronomical Imagers

Jack T. Dinsmore, Christopher Layden, Roger W. Romani+9 more

• High Energy Astrophysical Phenomena

AstronomerShort-exposure observations of rapid variability accumulate repeated read noise, limiting sensitivity to faint sources. The authors present a photon-counting analysis method for sub-electron read-noise detectors that delivers optimal statistical uncertainties by exploiting individually resolvable electrons. They demonstrate it on optical CMOS data from proto-Lightspeed, recently commissioned at the Magellan Clay telescope at Las Campanas Observatory. They report signal-to-noise improvements of up to approximately 130%, equivalent to obtaining 5.3 times more observing time with conventional analysis. As an observational example, they detect four normal rotation-powered pulsars with confirmed optical pulses in under two hours of total exposure. The method is also applicable to non-CMOS detectors, including skipper CCDs and linear-mode avalanche photodiodes, although the demonstration described here uses CMOS data. The released lightspeedpy pipeline supports both photon-counting and standard reductions of proto-Lightspeed observations.

PublicTo study objects that change quickly, astronomers take many short exposures. Each exposure adds electronic noise when the detector is read, making faint objects harder to measure. The researchers developed a photon-counting analysis that takes advantage of detectors quiet enough to distinguish individual electrons produced by light. They tested it on telescope observations made with the proto-Lightspeed camera in Chile, reporting improvements in signal-to-noise ratio of up to about 130%. Achieving that improvement through additional observations alone would require 5.3 times as much observing time. They also detected four spinning stars called pulsars with confirmed visible-light pulses using less than two hours of total exposure. They provide software for analyzing the camera’s data with either the new method or standard techniques.

Young explorerScientists take lots of quick pictures to watch faint things in space blink. But the camera adds a little electronic fuzz each time. The scientists made a new way to count tiny signals from light in very quiet cameras. It helped them see faint objects more clearly. With a telescope camera, they detected the light flashes of four spinning stars in less than two hours of picture-taking.

A Classifier Framework for ALMA Bandpass Calibration Anomalies

Ci Xue, Brian S. Mason, Gazi A. Rakib+8 more

AstronomerThe authors present a supervised XGBoost framework for identifying anomalies in ALMA bandpass-calibration amplitude solutions. It combines multiple features, including kernel-based scan statistics that characterize deviating spectral intervals, to learn nonlinear decision boundaries rather than rely on the pipeline’s individual scalar thresholds. Trained on an extensive, quality-controlled ALMA dataset, the framework is reported to substantially reduce misclassifications relative to current pipeline heuristics, although the abstract gives no numerical performance measures. The authors position it as a scalable supplement to observatory operations, extensible to additional features and generalizable to next-generation radio facilities; the abstract does not report testing at those facilities.

PublicRadio telescopes need calibration to correct how their instruments respond at different observing frequencies. Unrecognized abnormalities in that calibration can compromise the resulting scientific data. The researchers trained a machine-learning system on quality-controlled ALMA data to recognize unusual patterns in calibration amplitudes. Unlike existing rules that assess individual numerical indicators against simple thresholds, the system combines several indicators and learns more complex distinctions. The authors report substantially fewer classification mistakes than the current pipeline rules, but provide no numerical comparison in the abstract. They present the method as a supplement to observatory operations and suggest it could also be useful for future radio facilities.

Young explorerA radio telescope needs checks to make sure it measures signals properly. Sometimes those checks have odd patterns that could spoil what scientists learn. The researchers taught a computer to look for these patterns in checks from a telescope called ALMA. They say it made fewer mistakes than the rules used now, but they do not say exactly how many fewer. They think it could help other radio telescopes in the future, too.

SPECULATE: A synthetic spectral library, emulator and fitting package for accretion disc winds -- Infrastructure and application to CVs

Austen G. W. Wallis, Christian Knigge, James H. Matthews+6 more

• High Energy Astrophysical Phenomena
• Solar and Stellar Astrophysics

AstronomerSpeculate is an open-source framework for emulating and fitting synthetic accretion-disc wind spectra from the Monte Carlo radiative-transfer code Sirocco. Its release includes 88,680 sparsely gridded ultraviolet and optical spectra for cataclysmic variables, pre-trained emulators, and an interactive Marimo interface. After principal component compression, regular-grid, neural-network, or Gaussian-process interpolation produces emulated spectra in 1–40 ms. The first two approaches support rapid chi-squared optimisation; the Gaussian process supports Bayesian inference with a covariance-aware, flexible likelihood adapted and accelerated from Starfish to accommodate correlated simulation–data discrepancies. Tests on unseen Sirocco spectra show broadly comparable accuracy across architectures and recovery of the simulated physical parameters. Applications to five representative nova-like cataclysmic-variable spectra reproduce several observed line features but also reveal mismatches attributed to relevant physics absent from the current grid. Fast emulation therefore facilitates inference without eliminating parameter degeneracies or limitations of the underlying simulations.

PublicGas flowing away from an accretion disc can leave many different patterns in its spectrum, making the wind’s properties difficult to infer. The researchers introduce Speculate, an open-source tool that quickly approximates spectra from expensive computer simulations. Trained on 88,680 simulated spectra, its three methods produce approximations in 1–40 milliseconds. Tests show that all three can reproduce previously unseen simulated spectra and recover the physical settings used to generate them. When applied to five observed spectra of nova-like cataclysmic variables, the tool reproduces several spectral features but not all of them. The researchers attribute these mismatches to physics missing from the current simulation grid. The tool speeds up comparisons with observations, but does not remove the simulations’ limitations or the ambiguity in interpreting spectra.

Young explorerGas can blow away from a swirling disc in space and leave patterns in its light. Scientists made a fast computer helper to copy patterns from their pretend space winds. It worked well on new pretend examples. It also matched some patterns in real space light, but not all: the pretend winds still leave out some important things.

The First Decade of Breakthrough Listen

David H.E. MacMahon, Daniel J Czech

AstronomerThis review traces Breakthrough Listen’s first decade through its instrumentation, processing pipelines, archive, and observatory partnerships, rather than presenting a technosignature detection. It identifies three architectural eras: packetized raw-voltage wideband recording at Green Bank and Parkes in 2016–2019, enabling surveys of thousands of nearby stars over approximately 0.7–8 GHz; network expansion in 2020–2023, including Sardinia and international LOFAR stations, alongside verification frameworks that became essential for prominent signal candidates; and fully commensal operations since 2023, using Ethernet-based commodity-GPU backends during routine observatory observations. Current systems include COSMIC at the VLA, real-time deep-learning pipelines at the revived Allen Telescope Array, and MeerKAT’s autonomous multi-beam BLUSE survey, with more than 1.2 million pointings since mid-2022. By March 2026, storage capacity reached approximately 42 PB, with approximately 31 PB used, across seven systems on four continents. The authors emphasize commodity hardware, open data, commensal science as backend validation, and early development of verification frameworks, and discuss prospects for SKA-era searches; the abstract does not establish any candidate as extraterrestrial technology.

PublicBreakthrough Listen searches for signs of technology beyond Earth. This paper reviews the equipment and infrastructure built during the program’s first decade, not a discovery of alien technology. Its early systems recorded wide bands of radio signals from thousands of nearby stars using the Green Bank and Parkes telescopes. The program then expanded to more observatories and developed ways to check intriguing signal candidates. Its latest systems collect and process data alongside telescopes’ routine observations, including at the VLA, Allen Telescope Array, and MeerKAT. MeerKAT’s survey has recorded more than 1.2 million telescope pointings since mid-2022. By March 2026, the program had about 42 petabytes of storage capacity, with about 31 petabytes in use. The review draws engineering lessons about readily available hardware, open data, and preparing candidate-checking methods in advance, and looks ahead to searches associated with the SKA. It does not report a confirmed signal from extraterrestrial technology.

Young explorerBreakthrough Listen uses big radio telescopes to look for signals that might come from technology far away in space. This paper tells how the team built better tools and computers over ten years to collect, check, and save those signals. Some tools now work while the telescopes are doing their usual jobs. Interesting signals need careful checking: this paper does not say the team found alien technology. It also talks about how to make future searches better.

Very Long Baseline Interferometry with the SKA Observatory

J. F. Radcliffe, J. Yang, Z. Paragi+97 more

AstronomerThis summary chapter describes prospective science and the current operational understanding for SKAO participation in VLBI arrays, rather than reporting observational results. SKAO is expected to add sensitive elements to existing arrays, enabling deep VLBI observations and the first low-frequency VLBI capability in the Southern Hemisphere. Science areas outlined include AGN physics, explosive transient localisation, Galactic structure, and gravitational waves. Because SKA-VLBI depends on partnerships with other instruments, the chapter also identifies outstanding issues and community considerations needed to maximise its scientific return.

PublicVery Long Baseline Interferometry (VLBI) combines signals from telescopes thousands of kilometres apart to make exceptionally detailed astronomical images. This chapter outlines how the Square Kilometre Array Observatory is expected to strengthen these telescope networks, allowing observations of fainter sources and providing the Southern Hemisphere’s first low-frequency VLBI capability. Planned science includes studying active galactic nuclei, locating explosive cosmic events, investigating our Galaxy’s structure, and addressing gravitational-wave science. These are future capabilities and science goals, not newly reported discoveries. The chapter also discusses how the networks may operate and unresolved matters requiring cooperation with other instruments.

Young explorerTelescopes very far apart can work together to make pictures of space with tiny details. This chapter explains how a new observatory called SKAO is expected to help that team notice fainter things. Scientists hope to use the team to study galaxies, find where big space explosions happen, and learn about our own galaxy. These are plans, not discoveries already made, and the telescope teams still have things to work out together.

Optimizing Laguerre-Gaussian Mode Interferometry in Gravitational-Wave Detectors through Modal Degeneracy Breaking

Liu Tao, Eleonora Capocasa, Matteo Barsuglia

• Optics

AstronomerThe study develops an axisymmetric corrective mirror profile to lift degeneracy within the sixth-order Laguerre-Gaussian subspace while preserving an injected donut-shaped LG_0,6 mode. A Fourier-Bessel expansion is optimized to maximize separation from the nearest unwanted resonance while minimizing target-mode loss. In a modeled Virgo-like Fabry-Perot arm cavity, the optimized profile separates LG_0,6 from LG_1,4 by 2.04% of the free spectral range, lowers unwanted-mode gains below unity at the target resonance, and introduces negligible target-mode loss. The modeling also indicates improved robustness against astigmatism and realistic surface distortions. Monte Carlo simulations yield mean contrast defect and reflected optical loss of 368 ppm and 979 ppm, respectively; the latter corresponds to approximately 3.5 ppm round-trip loss for this modeled cavity. The results outperform the central anti-reflective mask approach, with reflected loss within a factor of two of the fundamental Gaussian mode under identical simulation conditions. This is a simulated design route toward practical higher-order modes for reducing test-mass thermal noise, not an experimental demonstration.

PublicDonut-shaped laser beams could help gravitational-wave detectors reduce noise caused by thermal motion in their mirrors. However, imperfect mirrors can mix the desired beam with unwanted light patterns, causing losses. This study designs a rotationally symmetric adjustment to the mirror surface so that the desired pattern and competing patterns resonate at different frequencies. In simulations of a cavity similar to a Virgo detector arm, the design suppresses unwanted resonances while adding negligible loss to the desired beam and making it more tolerant of mirror imperfections. Simulations with realistic imperfections show substantially better performance than an earlier approach using a central anti-reflective mirror mask. The reflected light loss comes within a factor of two of that for a conventional Gaussian beam under the same simulated conditions. The work suggests a promising design for future precision detectors, but does not report a test in an operating instrument.

Young explorerScientists use laser light and mirrors to look for tiny ripples in space. Light shaped like a donut might help, but imperfect mirrors can mix it with light shapes they do not want. The researchers designed a tiny change to a mirror’s shape to help keep the donut light separate. In computer tests, their design kept more of the wanted light and reduced problems from imperfect mirrors. It looks promising, but they have not shown it working in a real detector in this study.

Rapid Sequence Cost Evaluation for Multi-Spacecraft Rendezvous: A Permutation-Invariant Set Transformer

An-yi Huang

AstronomerThis paper proposes a fast learned evaluator for multi-spacecraft, multi-rendezvous mission design, replacing repeated sequence optimization or accumulated leg-by-leg estimates with direct prediction of total cost for an unordered target set within a specified time window. Pairwise transfer-cost surfaces are compressed into latent features, and a permutation-invariant transformer uses these features and the window parameters without target-order information. Trained on about 0.85 million labeled sequences, the model reportedly achieves a mean relative error near 5% and sub-millisecond evaluations, about five orders of magnitude faster than precise optimization. In computational applications to GTOC9, an evolutionary search incorporating the evaluator yields the best known solutions for each tested fleet size, seven through ten spacecraft. The authors report inexpensive near-optimal solutions directly and further improvements over published solutions after differential-evolution refinement. These are mission-design results, not demonstrations of flown missions. Broader applicability is argued for low-Earth-orbit satellite servicing and deep-space multi-target visits, conditional on having a pairwise transfer-cost function and a sequence-level metric monotone in leg costs.

PublicPlanning missions in which several spacecraft visit many targets requires comparing enormous numbers of possible trips. This paper proposes an AI model that estimates a mission's total cost from its targets and allowed time window, without being given their visiting order. In the reported tests, its average relative error was about 5%, and each estimate took less than a millisecond—roughly 100,000 times faster than precise optimization. Used within a search algorithm for the GTOC9 mission-design problem, it produced the best known plans for every fleet size tested, from seven to ten spacecraft. Further optimization improved the plans beyond previously published solutions. These results concern computer-generated mission plans, not actual spacecraft operations, and the estimates are not exact. The authors argue that the approach could also help plan satellite servicing and visits to multiple targets in deep space, when the required cost functions satisfy its assumptions.

Young explorerImagine helping several spaceships plan trips to visit lots of places. Checking every possible trip can take a long time. Researchers made a computer helper that quickly guesses the cost of a trip from the places to visit and the time allowed. Its guesses were not perfect, but they helped another computer program find better plans in a planning challenge. The spaceships did not actually fly these trips; the researchers tested the plans on computers.

Nancy Grace Roman Space Telescope Wide Field Instrument: Grism Saturation Response to Bright Sources during Thermal-Vacuum Testing

Lipika Chatur, Dana R. Louie, Joshua E. Schlieder+3 more

AstronomerThis study uses Thermal Vacuum Test 2 bright-source grism data to investigate saturation and stray light in Roman’s Wide Field Instrument. The authors find that faint, diffuse combined grism orders produce significant structured stray light. Pixels neighboring saturated pixels retain linear signal growth until they reach their own saturation limits, contrasting with reported non-linearity around non-dispersed bright point sources. These are detector-test findings intended to assess potential impacts on scientific analysis, not results from Roman’s science survey.

PublicRoman will observe bright objects as well as faint, distant ones, and bright light can overwhelm its detector pixels. Using thermal-vacuum test data, researchers studied what happens when a grism spreads bright-source light into a spectrum. They found that faint, spread-out components of this light create substantial stray-light patterns. Pixels beside overwhelmed pixels continued to build up signal evenly until they too reached their limits, unlike behavior previously reported for bright sources whose light was not spread into a spectrum. The work investigates detector behavior that could matter when scientists analyze Roman’s observations.

Young explorerResearchers tested what happens when bright light is spread out in Roman’s space camera. Some of the light made extra patterns in the picture. When one tiny picture square got too much light, the squares beside it still collected light steadily until they became full too. This happened in a camera test, and it can help scientists understand pictures Roman will take.

Space-based Cosmic Neutrino Measurements

John F. Krizmanic

AstronomerThis review chapter examines Earth-target cosmic-neutrino detection from suborbital and low-Earth-orbit platforms. Neutrino-induced extensive air showers generate optical and radio signals, while showers in radio-transparent ice can produce Askaryan radiation that refracts out through the surface. The techniques differ in neutrino-flavor sensitivity and duty cycle. Optical observations require conditions close to astronomical night and are affected by moonlight and clouds; radio operation can be nearly continuous if anthropogenic and other backgrounds are minimal. At these viewing distances, current detection thresholds are above approximately 1 PeV for optical Cherenkov detection and 100 PeV for radio detection. The chapter discusses interactions, shower development, signal generation, and experiments that have set limits on very-high- and ultra-high-energy cosmic-neutrino fluxes. Its treatment of next-generation experiments concerns designs and simulated performance, not demonstrated capabilities.

PublicThis chapter reviews ways to search for extremely energetic cosmic neutrinos using Earth as a target. A neutrino interaction can create a shower of charged particles whose light or radio signals may be seen from an orbiting spacecraft or, for Earth observations, a balloon. Radio signals can also come from showers inside ice and escape through the surface. Light-based searches need dark conditions and are affected by moonlight and clouds. Radio searches can operate almost continuously, provided interfering signals are minimal. Current methods require very high neutrino energies: above roughly 1 PeV for optical detection and 100 PeV for radio detection. The chapter discusses experiments that have constrained how many such neutrinos arrive, rather than reporting a new detection. It also reviews future experiment designs and computer simulations of their performance.

Young explorerTiny particles from space called neutrinos can hit Earth and make a shower of other particles. That shower can make light or radio signals that machines high above Earth might spot. Looking for the light needs a dark sky, and clouds can get in the way. Scientists have used searches to limit how many neutrinos could be arriving. They are also using computer models to study future machines; those models are not real detections.

Time-Frequency Analysis for LISA: Galactic Foreground Modulation

Sudhi Mathur, Neil J. Cornish

• General Relativity and Quantum Cosmology

AstronomerThe authors present a fast forward model for LISA’s expected annually modulated, cyclostationary Galactic confusion foreground across the full set of time-delay interferometry channels. A line-of-sight integral of parameterized gravitational-wave luminosity density is evaluated on a HEALPix grid and expanded in spherical harmonics, while an analytic detector-response decomposition is independent of the Galaxy model. Each new Galactic model therefore requires one map evaluation, harmonic transformation, and contraction. The covariance calculation extends beyond the standard low-frequency limit, retaining second-order finite-armlength and first-order unequal-arm corrections. In the model, finite-armlength corrections alter normalized modulation curves by up to approximately 0.23% at 3 mHz and 0.64% at 5 mHz; unequal-arm corrections produce changes of approximately 0.074% in self channels and 0.71% in cross channels. A Fisher forecast using a notional disk-and-bulge Galaxy predicts that one year of observations could constrain disk scale width and scale height, each relative to the Galactic-center distance, at the 8% and 12% levels. The strongly correlated bulge fraction and bulge radius remain individually unconstrained. These are model calculations and forecasts, not measurements from LISA.

PublicLISA’s future gravitational-wave observations are expected to include a blended background of unresolved signals from our Galaxy. That background should vary over the year, and its changing pattern could reveal information about the Galaxy’s structure. The researchers developed a fast model connecting an assumed distribution of gravitational-wave emission in the Galaxy to the background expected in LISA’s measurement channels. They also calculated small changes caused by accounting more precisely for the detector’s arm lengths. Using an illustrative Galaxy with a disk and a central bulge, they forecast that one year of observations could constrain the disk’s width and height, measured relative to the distance to the Galactic center, to about 8% and 12%, respectively. In that forecast, the bulge’s contribution and size are too strongly linked to constrain separately. These are predictions based on a model, not results from actual LISA observations.

Young explorerLISA will look for tiny ripples in space. Many ripples from our Galaxy are expected to blend together, like lots of voices talking at once. Scientists made a fast computer model of how that mixed signal should change during the year. Their model suggests that watching for a year could help them learn how wide and thick the Galaxy’s disk is. But it could not separately tell them the size of the middle bulge and how much signal it makes. This is what their model predicts, not something LISA has measured yet.

LISA Sensitivity and SNR Calculations

Stanislav Babak, Martin Hewitson, Antoine Petiteau

• General Relativity and Quantum Cosmology

AstronomerThis technical note describes the computation of LISA’s noise power spectral density, sensitivity curve, and signal-to-noise ratio. Identified as LISA-LCST-SGS-TN-001 v1.1, it is an applicable document for ESA and the reference for the LISA Science Requirement Document. The abstract describes calculation methods, not observational findings or numerical performance results.

PublicThis note explains how to calculate LISA’s background noise, its sensitivity to signals, and how strongly a signal stands out above the noise. It serves as an official reference for the European Space Agency’s LISA science requirements. The abstract does not report detections or give numerical results.

Young explorerImagine trying to hear a quiet sound when there is noise around you. This note explains calculations that help scientists work out how well an instrument called LISA can pick out a signal from noise. It is a guide for doing the calculations, not a report of something LISA has found.

Superluminous supernova search with PineForest

T. Majumder, M. V. Pruzhinskaya, E. E. O. Ishida+3 more

• High Energy Astrophysical Phenomena

AstronomerThis study presents the first application of the PineForest active-learning algorithm to a targeted search for rare astronomical transients, specifically superluminous supernovae (SLSNe). Using eight previously confirmed SLSN light curves as priors, the authors searched approximately 14 million objects in Zwicky Transient Facility data releases and identified seven SLSN candidates, not confirmed SLSNe. They reported three previously unreported transients to the Transient Name Server: AT 2018moa and AT 2018mob as SLSN candidates, and AT 2018mpg as a possible supernova. They also detected a re-brightening of the SLSN-I SN 2018fcg approximately 1300 days after its main burst; its origin remains an open question.

PublicResearchers used a machine-learning method called PineForest to search a large astronomical data set for unusually luminous stellar explosions known as superluminous supernovae. Guided by brightness records from eight confirmed examples, the method helped identify seven candidates among about 14 million objects observed by the Zwicky Transient Facility. These candidates have not been established as superluminous supernovae. During the search, the team reported three previously unreported transient sources: two superluminous-supernova candidates and one possible supernova. They also found that the known superluminous supernova SN 2018fcg brightened again about 1300 days after its main outburst, with the cause still unresolved. This was PineForest's first use in a targeted search for rare astronomical transients.

Young explorerScientists taught a computer to help look for very bright exploding stars. They showed it how eight known explosions changed in brightness, then searched about 14 million things in space. They found seven that might be this special kind of explosion, but they are not sure yet. They also noticed that one known exploding star got brighter again about three and a half years after its big burst. They do not yet know why.

Fast and accurate bandpass integration of complex SEDs with neural networks

L. A. Bianchi

AstronomerThe paper introduces a neural-network method for approximating bandpass integrals of spectral energy distributions, released in the Python package pyfine (Fast Function Interpolation via NEural NEtworks). The authors motivate the approach by the smoothness associated with the non-local integral operator. In computational tests with 3 and 9 free parameters, the reported maximum relative residuals were as low as 0.002% and 0.08%, respectively, within the sampled parameter regions, with fast evaluation and little memory overhead. For the first test, using a simple modified blackbody SED, measured neural-network runtimes were about two orders of magnitude faster than an optimized multithreaded direct integral calculation. The authors identify expensive SED evaluations as an especially favorable use case; the reported accuracy applies to the sampled test regions, not arbitrary SEDs or parameter values.

PublicThe researchers developed a machine-learning shortcut for calculating how much of a modeled spectrum falls within a selected range of wavelengths. Their Python package, pyfine, uses a neural network to approximate this calculation rather than repeatedly performing the full integration. In two computational tests, with 3 and 9 adjustable model parameters, the largest relative errors were as low as 0.002% and 0.08%, respectively, within the tested ranges. In the simpler test, the shortcut ran about 100 times faster than an optimized direct calculation and used little extra memory. These are computational test results, not new astronomical observations, and they do not establish the same accuracy for every possible spectrum or parameter choice.

Young explorerThe researchers made a computer shortcut for adding up how much light in a model is inside a chosen range of colors. In two computer tests, its answers were very close to the full calculation, and in one test it was about 100 times faster. It worked well for the examples they tried, but that does not mean it will work just as well for every example.

Vector field dark matter search with Sagnac interferometer

Yuki Inoue, Quynh Lan Nguyen, Ippei Obata

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

AstronomerThis calculation forecasts improved quantum-noise-limited sensitivity to composition-dependent B-L vector-dark-matter forces using a material-asymmetric, dual-ring Sagnac speed meter rather than a Fabry–Perot Michelson position meter. The comparison holds incident power, input-mirror transmissivity, and cavity round-trip length fixed. For sapphire mirrors and a one-week benchmark, the quantum-noise-only median expected 95% confidence upper limit reaches 1.2×10⁻²⁷ at m_A = 4.1×10⁻¹⁴ eV/c² (10 Hz), a factor-57 improvement. The predicted material-induced displacement is essentially unchanged; the gain comes from reduced low-frequency quantum backaction. This is a forecast, not a dark-matter detection or demonstrated instrument sensitivity: it assumes negligible classical noise, and performance at 10 Hz remains unestablished for a realizable suspension and isolation system.

PublicThe researchers calculated how a different light-based measuring device could improve searches for a proposed kind of dark matter that would push differently on different materials. Their design measures mirror motion with a Sagnac speed meter instead of a Fabry–Perot Michelson position meter. In a one-week benchmark at 10 Hz, the predicted sensitivity improves by a factor of 57 because the new design reduces quantum disturbances from the measurement, not because dark matter would move the mirrors more. This is an idealized forecast, not a detection or an experimental demonstration. It leaves out non-quantum noise, and the researchers have not established whether a practical system could achieve that low-frequency performance.

Young explorerScientists worked out a new way to use light to watch tiny mirror movements. They hope it could help look for a kind of invisible matter that might push different materials differently. Their calculation says the new design could make the search much better by reducing some of the tiny disturbances caused by measuring. But they have not found this matter or shown that a real machine can work this well. Other shaking and noise could still get in the way.