Tonight’s sky of new research

DarkMatterFM-Registry: A Machine-Readable Registry of Dark-Matter Models Extracted from the arXiv Literature

Ioana A. Zelko, Jo Bovy, Nolan Koblischke

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

AstronomerDarkMatterFM-Registry organizes dark-matter models extracted from arXiv full texts using a staged large-language-model pipeline. It contains 6,145 structured model cards, ranked by expected value for observational follow-up; roughly 2,000 are enriched with observables, constraints, and theory-to-observable routes. Schema checks pass 97.8% of cards. In an LLM-judged assessment of a stratified sample, 81% of section verdicts were rated correct, 18% partially correct, and none hallucinated; these sample-based ratings do not establish universal accuracy. The authors classify computational steps in the enriched routes as available, partial, or missing and aggregate gaps using model-priority weights to propose 25 community projects. Their analysis identifies shared infrastructure, rather than missing theory, as the main bottleneck for the highest-priority models: model files for existing relic-abundance solvers, a general non-cold Boltzmann-code framework, reusable indirect-detection likelihoods, and a non-cold-dark-matter Lyman-alpha forest likelihood. The latter is the largest identified gap for structure-formation probes. This is a registry and infrastructure roadmap, not a new observational constraint on dark matter. Cards, schemas, rankings, and the roadmap are released.

PublicResearchers have built a searchable, computer-readable catalog to help scientists compare dark-matter ideas and work out how to test them. An AI-assisted pipeline extracted 6,145 model summaries from research papers, with more detailed testing information added to about 2,000. Automated format checks passed 97.8% of summaries, but format compliance is not the same as scientific accuracy. A separate AI-judged sample assessment rated 81% of section verdicts correct and 18% partly correct, with none judged hallucinated in that sample. Using the catalog, the authors propose 25 projects to improve dark-matter research tools. Their analysis suggests that many high-priority models are held back more by missing shared software and tools for comparing predictions with data than by missing theory. The released catalog and roadmap support future tests; they do not report a discovery of dark matter.

Young explorerScientists have many ideas about dark matter, but the information is spread across lots of papers. A computer helper helped make a big set of cards to organize those ideas. Some checks found mistakes or partly right information, so the cards still need care. The researchers also made a list of shared computer tools scientists could build to help test the ideas. They did not discover dark matter.

Primordial or Post-Inflationary: Distinguishing the Origin of Scale-Dependent Features in the CMB

Matteo Braglia, Wenzer Qin, Xingang Chen+1 more

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

AstronomerThis initial modeling study tests degeneracies between sharp and resonant primordial features and two post-inflationary scenarios: exotic energy injection, which alters the plasma’s thermodynamic history, and early dark energy, which changes background expansion and gravitational perturbations. In representative examples, primordial features generate oscillations in the CMB power spectrum with essentially arbitrary frequency and running, whereas the post-inflationary models generally cannot reproduce their characteristic running. Analysis using the most significant principal components finds no significant degeneracies among the feature classes considered. A full likelihood analysis likewise finds no significant changes in posterior distributions when fitting the classes separately or jointly. These are conclusions about distinguishability within the tested models, not a detection of new physics. Both post-inflationary scenarios use simplified phenomenological implementations; the methods could be extended to more realistic or other signals.

PublicDifferent kinds of new physics could leave patterns in the cosmic microwave background, the ancient light from the early universe. This study asks whether patterns originating in primordial physics could be mistaken for effects arising after inflation. The researchers compare selected primordial models with two later scenarios: unusual energy release into the early plasma and early dark energy. In the examples studied, the primordial models can produce oscillating patterns whose spacing changes in ways the later models generally cannot imitate. Two statistical analyses support the conclusion that these particular signals are distinguishable, with little evidence that fitting them together changes the inferred model parameters. The study does not report a discovery of new physics, and its conclusions are limited to the examples tested, including simplified descriptions of the two later scenarios.

Young explorerVery old light from space can carry patterns that help us learn about the early universe. Scientists used models to ask whether patterns made at different early times could look alike. In the examples they checked, some wiggly patterns were hard for the other models to copy. That could help scientists tell possible explanations apart. It does not mean they found something new in space, and they still need to check more kinds of patterns.

Anisotropic three-point statistics of the peculiar velocity and galaxy density fields: modelling in Fourier and configuration space

M. Guidi, A. Farina, A. Nusser+1 more

AstronomerThis theoretical study develops a tree-level model for the anisotropic redshift-space three-point correlation of one line-of-sight peculiar velocity and two galaxy densities, including quadratic and tidal galaxy bias. Starting from the velocity-divergence bispectrum, the authors derive Fourier- and configuration-space predictions using spherical harmonics. They check the Fourier calculation against a closed-form expression and assess numerical convergence in configuration space. In a fiducial model, triangle-orientation dependence is predominantly dipolar, with smaller multipoles distinguishing growth and galaxy-bias responses. The configuration-space BAO feature depends on which triangle side crosses the acoustic scale and on the velocity projection. The authors also connect the model to the density-weighted statistic measured by peculiar-velocity catalogues and formulate observable-multipole estimators. These are model predictions and methodological developments, not new observational detections; future measurements and covariance analyses are needed to establish the additional cosmological information available.

PublicGalaxies have motions beyond the overall expansion of the universe. These motions can probe how matter is distributed without relying solely on where galaxies are found. This study develops a theoretical model linking one galaxy-motion measurement to the galaxy density at two locations, to investigate how cosmic flows and their surroundings interact. The predicted pattern depends on the orientation of the three locations relative to our view. A feature associated with ancient sound waves also changes with the triangle’s geometry and the measured component of motion. The researchers check their calculations and propose ways to measure the patterns in velocity catalogues. Future observations and uncertainty studies must establish how much extra information this approach provides about the universe.

Young explorerGalaxies move around while the universe grows. Scientists made a math model that connects a galaxy’s motion with where other galaxies gather. It predicts patterns that change depending on how we look at them. Scientists still need to measure these patterns to learn how much they can tell us about the universe.

VENUS: Strong Lens Mass Models and Einstein Radii of 60 Galaxy Clusters

Masamune Oguri, Vasily Kokorev, Shun Nishida+25 more

AstronomerThe study presents refined strong-lensing mass models for 60 galaxy clusters targeted by the JWST VENUS program. Using glafic, the authors fit approximately 4,500 multiple-image positions, including about 1,150 newly identified images aided by multiband JWST imaging, and validate the models with jackknife tests. The sample was selected for high lensing strength. For sources at redshift 9, the inferred Einstein radii have a median of approximately 30 arcseconds and extend to approximately 60 arcseconds, placing these clusters among the strongest known lenses. MACS J0717.5+3745, MACS J0600.1−2008, and PLCK G287.0+32.9 have the largest Einstein radii and the largest areas with absolute magnification above 10. The authors find the observed Einstein radii fully compatible with the standard cold dark matter model.

PublicGalaxy clusters bend light from objects behind them, sometimes producing several images of the same object. Researchers used about 4,500 such images, including roughly 1,150 newly identified with help from James Webb Space Telescope images, to refine maps of how mass is distributed in 60 clusters in the VENUS program. They checked the models using a statistical method called jackknife testing. These clusters were deliberately chosen for their strong lensing, and the results place them among the strongest known cosmic lenses. For background sources at redshift 9, three clusters stand out for both their lensing size and the area where they magnify light by more than ten times. The measured lensing sizes are consistent with the standard cold dark matter model, rather than evidence against it.

Young explorerBig groups of galaxies can bend light like giant magnifying glasses in space. They can even make one faraway object look like several copies. Scientists used these copies, with help from pictures from the James Webb Space Telescope, to make better maps of where the mass is in 60 galaxy groups. They chose groups that are especially good at bending light, and their maps show that these really are very strong space magnifying glasses. What they found also fits with a scientific idea about invisible matter called cold dark matter.

Short-term optical monitoring of quadruply imaged quasars

L. J. Goicoechea, V. N. Shalyapin, A. Esteban-Gutiérrez+2 more

AstronomerTwo observational case studies demonstrate the utility of short-term optical monitoring of quadruply imaged quasars. Liverpool Telescope and TTT3 gr-band monitoring from July 2025 to January 2026 detected microlensing variability on a roughly 150-day timescale in QSO 2237+0305. Its A–B g-band difference light curve constrained the g-band source half-light radius to 3.5–16 light-days at 1σ confidence. For PS J0147+4630, r-band light curves of the arc-like ABC images yielded new AB and AC time-delay constraints with approximately 2-day uncertainties at 2σ, informing the lensing mass distribution. These cases support suitably designed campaigns with ground-based 2m-class telescopes lacking sophisticated atmospheric-distortion correction, rather than establishing that all quads are suitable targets. The authors outline target properties and monitoring strategies and report the first validation of TTT3 for precision photometric monitoring of lensed quasars.

PublicBy tracking two quasars that each appear as four images because of gravitational lensing, astronomers showed how months-long observing campaigns can probe both the light-emitting regions and the mass responsible for the lensing. Observations with the Liverpool Telescope and TTT3 between July 2025 and January 2026 revealed microlensing-related brightness changes over about 150 days in QSO 2237+0305. Those changes constrained the radius enclosing half of its g-band light to 3.5–16 light-days, at the stated 1σ confidence level. For PS J0147+4630, the team constrained differences in the arrival times of brightness variations among three images, with uncertainties of about two days at the stated 2σ level; these constraints helped investigate the distribution of lensing mass. The two case studies support carefully chosen targets and observing strategies using ground-based telescopes in the two-metre class, even without sophisticated correction for atmospheric distortion. They also provide the first validation of TTT3 for this type of precision brightness monitoring.

Young explorerSpace can bend light so that one faraway bright object looks like four copies. Astronomers watched two objects like this for several months. For one, changes in brightness helped them work out how big its glowing part might be. For the other, they studied how much later a change appeared in one copy than another, helping them learn about the matter bending the light. Their answers still have some uncertainty. These two examples show that carefully planned watching with telescopes on the ground can teach us a lot.

Nonstandard Dark Matter at Nonlinear Scales

Rafael C. Nunes

• High Energy Physics - Phenomenology

AstronomerUsing N-body simulations, the study examines matter density and velocity-divergence fields from linear to deeply nonlinear scales in two extensions of standard ΛCDM: interacting dark matter and dark energy, and dark matter with a nonzero equation-of-state parameter. In the coupled scenario, simulated matter power spectra differ from ΛCDM by roughly 50–100%, with scale-dependent deviations persisting into the nonlinear regime; velocity-divergence spectra offer complementary, partially independent sensitivity. For nonzero dark-matter equation of state, deviations remain within 5% across all scales probed. The simulations identify scales with greater discriminatory power, but robust observational constraints from current and forthcoming large-scale-structure surveys require deeper theoretical understanding and accurate nonlinear modelling. These are simulation findings, not observational detections of either scenario.

PublicComputer simulations explore how cosmic matter would gather and move if dark matter behaved differently from the standard cosmological model. The researchers test two possibilities: dark matter interacting with dark energy, and dark matter departing from its usual pressureless description. In the interacting scenario, the simulated measure of matter clustering differs from the standard model by about 50–100%, depending on scale, while patterns in matter's motion provide additional information. In the second scenario, differences stay within 5% over the scales tested. These findings do not show that either possibility occurs in nature. The study indicates which scales could help distinguish the models, but interpreting galaxy-survey data reliably will require better theoretical understanding and accurate modelling of complex matter clustering.

Young explorerScientists used computers to imagine how the stuff in space might bunch up and move if invisible dark matter behaved in two different ways. In one version, dark matter interacts with dark energy, and the computer makes very different bunches. In the other, dark matter is not quite pressureless, and the changes are small. These are computer experiments, not discoveries that dark matter really acts this way. Scientists need to understand their models better before they can use maps of space to test these ideas reliably.

Modified Newtonian Dynamics and galaxy clusters

Francoise Combes

AstronomerThis study uses X-ray data for 106 galaxy clusters to reconstruct the residual missing-mass distribution in Modified Newtonian Dynamics (MOND). Newtonian total masses are first inferred assuming hydrostatic equilibrium and spherical symmetry, followed by reconstruction with the modified Poisson equation. MOND reduces the required dynamical mass by a factor of 4–10 but does not eliminate the mass discrepancy. Relaxed cool-core clusters show the highest missing-mass density peaks, with pronounced central concentrations and steep truncations just beyond core radii of 20–30 kpc, consistent with previous studies. The residual missing mass scales with total gas mass and is approximately half as large. The paper investigates non-radiating baryonic matter as its possible source; the reconstruction does not establish the missing component’s composition.

PublicA study of 106 galaxy clusters asks whether ordinary matter that does not shine could account for the mass still missing under Modified Newtonian Dynamics (MOND), an alternative to the standard dark-matter framework. Using X-rays from hot cluster gas, the researchers estimate masses under assumptions that the clusters are spherical and their gas is in hydrostatic balance, then calculate the missing matter required by MOND. MOND lowers the required dynamical mass by a factor of 4–10, but some unseen mass remains—approximately half the total gas mass. In relaxed clusters with cooling gas at their centers, the inferred unseen matter is especially concentrated near the center. Stellar remnants, diffuse gas and dense clouds of cold gas are proposed possibilities, not identified discoveries.

Young explorerGalaxies gather in huge groups called clusters. Scientists studied X-ray light from hot gas in 106 of these groups to work out how much stuff they need to stay together. They tried a different rule for gravity called MOND. With that rule, their calculations needed less stuff, but still more than they could see. They wonder whether the hidden stuff could be ordinary matter that does not shine. They have not shown what it is, and their answer depends on assumptions about the clusters’ shapes and how their gas is balanced.

Primordial non-Gaussianity as a large-scale cosmic-web bias

Kilian Peraza Vera, Francisco-Shu Kitaura, Francesco Sinigaglia

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

AstronomerThe authors reformulate the large-scale tracer-bias response to local-type primordial non-Gaussianity (PNG) as an anisotropic, nonlocal environmental-bias effect. They define H_ij = ∂_i∂_j∇^−4δ, whose trace is ∇^−2δ and thus carries the k^−2 enhancement of the conventional scale-dependent-bias term. Its eigenvalues define four environments analogous to knots, filaments, sheets, and voids, but on scales much larger than the conventional nonlinear cosmic web. Tests with AbacusPNG N-body simulations at f_NL = −100, −30, 30, and 100 show that one weight per environment reproduces the large-scale k^−2 bias rise. The authors also demonstrate post-processing of halo catalogs without PNG to imprint an effective f_NL signature. They propose, rather than observationally establish, a complementary statistic measuring changes in tracer occupation across these environments relative to a matched Gaussian reference. The motivation is to probe inflation despite the cosmic-variance limitations of the largest-scale modes.

PublicPatterns left over from the very early universe could reveal how inflation worked, but their effects on the largest cosmic structures are difficult to measure because those scales offer limited independent information. This study presents a different way to describe one such signal, called local primordial non-Gaussianity. The authors sort the simulated matter distribution into four enormous environments resembling knots, filaments, sheets, and voids, much larger than the familiar cosmic web. Giving each environment a weight reproduces the characteristic large-scale clustering effect in their simulations. They also show how to add an effective version of that signal to existing simulated halo catalogs that lack it. The work motivates a proposed observational test: compare how tracers of matter populate these environments against a matched reference without primordial non-Gaussianity. It does not report a detection in the real universe.

Young explorerScientists want to learn how the universe began by studying the huge patterns that matter makes in space. In computer-made universes, they sorted places into four kinds, a bit like clumps, strings, pancakes, and empty spaces. By giving each kind a different importance, they could copy a pattern linked to a possible clue from the universe’s beginning. They suggest looking for that clue in the real universe by comparing where things gather with a matching pretend universe that has no such clue. They have not found it in the real sky in this study.

Through Ups and Downs: the Transient Lensing Behaviour of SIDM halos undergoing Core Collapse

Frank C. van den Bosch, Yarone M. Tokayer

• Astrophysics of Galaxies

AstronomerUsing an emulator calibrated on gravothermal fluid calculations, this study models lensing by initially NFW self-interacting dark matter haloes through core formation and collapse into the short-mean-free-path regime. The calculations assume isolated spherical haloes with elastic, velocity-independent interactions, with external shear included in selected cases. Lensing strength evolves non-monotonically: it falls during core formation, rises during early collapse, and generally declines later despite increasing central density. The late decline accompanies a shrinking, increasingly low-mass dense inner core embedded in a more extended, lower-density core. Optimal lensing typically occurs during early collapse, when the characteristic core surface density is near critical. Time-averaged enhancement over NFW depends on the lensing statistic, concentration, and interaction cross section. In these calculations, equal-mass generalized NFW profiles with cusp slopes gamma >= 2 always lens more effectively than core-collapsed SIDM haloes and poorly represent their arc and Einstein-ring sizes and radial thicknesses. These are modeling results, not observational detections: the evolving mass distribution, rather than central density alone, determines SIDM lensing efficacy.

PublicA denser dark matter center does not necessarily make a stronger gravitational lens. Using a model calibrated against calculations of how self-interacting dark matter evolves, researchers followed haloes as their centers first formed cores and then collapsed. Their modeled ability to magnify background sources initially weakened, strengthened during early collapse, and generally weakened again later—even while the central density kept rising. In the later stages, the very dense inner core became smaller and contained less mass, surrounded by a larger, less dense core. The strongest lensing typically occurred early in collapse. The study also finds that certain steeply peaked profiles used to represent these haloes overestimate their lensing strength. These findings concern idealized modeled haloes, not observed lenses, and show why the full distribution of dark matter matters more than central density alone.

Young explorerDark matter can bend light like a lens. Researchers used a computer model to see what happens when a dark matter cloud squeezes its middle tighter. The lens did not just keep getting stronger: it became weaker, then stronger, then usually weaker again. Even a very tightly packed middle can be tiny and hold little matter. The whole cloud matters, not just its middle.

Does DESI point towards transient cosmic acceleration?

Muhammad Ahmad, Saddam Hussain, Ayodeji Ibitoye+3 more

• General Relativity and Quantum Cosmology

AstronomerThe study tests a dark-energy equation of state oscillating around w_de = -1, with a source term proportional to the cube of the number of e-folds. This term shifts the oscillations toward w_de < -1 at higher redshift and toward w_de > -1 in the future. In this model, future dark-energy dilution makes H approach zero asymptotically: acceleration is transient, expansion becomes decelerated, and the Universe approaches a static state as the scale factor tends to infinity, without contraction. These are model predictions, not observed future behavior. Fits combine Planck and DESI BAO with Pantheon+, Union3, or DES-Dovekie supernova data, comparing the sourced model, BellDE, CPL, and flat LambdaCDM. Across the dynamical models and dataset combinations, H0 ranges from 66.0 (+0.80/-0.79) to 67.84 (+0.69/-0.74) km/s/Mpc, and Omega_m from 0.3067 (+0.0073/-0.0072) to 0.3271 (+0.0083/-0.0080). These are consistent with the baseline, except for a mild upward Omega_m shift with Union3. Relative to LambdaCDM, BellDE has the strongest comparative Bayesian evidence: weak with Pantheon+ and moderate with Union3 and DES-Dovekie. Evidence for the sourced oscillatory model is inconclusive with Pantheon+ and Union3, and weak with DES-Dovekie.

PublicThe researchers investigate a model in which dark energy changes in an oscillating pattern rather than behaving as a cosmological constant. The model predicts that today's accelerating expansion would eventually give way to slowing expansion. The expansion rate would approach zero indefinitely, without the Universe ever contracting; this is a theoretical prediction, not an observed outcome. The team tests the model against combinations of Planck, DESI BAO, and supernova data, alongside other dark-energy models. Its estimates of the current expansion rate and matter content are broadly consistent with the standard model. Statistical evidence for this particular oscillating model is inconclusive for two supernova compilations and weak for the third. A different model, BellDE, receives stronger support, though only weak to moderate depending on the compilation.

Young explorerThe Universe is getting bigger, and scientists are testing an idea about how that might change. In their idea, something called dark energy changes back and forth. Much later, the Universe would grow more and more slowly, without shrinking. That is a prediction, not something scientists have seen happen. The measurements they checked do not clearly show that this idea is the right one.

Odd Loops: What Structures Can Produce a Parity-Violating Inflationary Trispectrum?

William Ortolá Leonard, Zachary Slepian

AstronomerThis model-independent theoretical study examines which Wick contractions of Gaussian fields allow perturbative kernels for inflationary non-Gaussianity to generate parity-violating contributions to the trispectrum. Evaluating all contraction configurations arising from third- and second-order density perturbations, the authors find that only one third-order configuration can support parity violation, because it retains three independent wave-vectors. None of the four second-order configurations can contribute under statistical isotropy. These are conditions for possible contributions, not a detection or a demonstration that a particular inflationary model generates them. The results are a first step toward deriving suitable inflationary kernels for future parity-violation searches in galaxy surveys and provide guidance for CMB analyses.

PublicThe researchers explore whether mathematical descriptions of fluctuations produced during the universe’s inflationary era could allow a statistical pattern that distinguishes the universe from its mirror image. Their theoretical calculations examine a four-point correlation called the trispectrum. Of the configurations considered at third order in their expansion, only one can support this mirror asymmetry; none of the four second-order configurations can do so if the statistics have no preferred direction. The study does not detect such an asymmetry. Instead, it identifies a possible mathematical route toward models and searches using galaxy surveys and maps of the cosmic microwave background.

Young explorerImagine comparing a picture of the universe with its reflection in a mirror. Scientists used math to ask whether patterns from the very early universe could tell the two apart. Among the possibilities they checked, one kind could allow a difference, while several others could not if no direction is special. They have not found this difference in the sky. Their work could help scientists plan how to look for it.

Lessons from double-plane lenses for galaxy profiles, the Hubble tension, and the mass-sheet degeneracy

Daniel P. Johnson, Martin Millon, Pierre Fleury+7 more

AstronomerDouble-plane lenses retain a mass-sheet degeneracy, but their images constrain a particular combination of the mass-sheet components in the two lens planes when a prior on the relative expansion history is supplied. This does not require time delays, velocity dispersions, or an H0 prior. The authors derive system-specific constraints using published cosmological scaling factors for J0946 and AGEL0353, a measurement from the point-source images of J1721, and a reference value of Ωm. Their analysis indicates that images of a second source can improve individual time-delay-lens H0 measurements by up to approximately 50%, depending on key assumptions. Forecasts for Euclid and LSST double-plane lens samples indicate strong population-level mass-sheet constraints, with potential implications for H0, dark energy, and galaxy dark matter profiles.

PublicGravitational lenses bend light into multiple images, but different distributions of matter can produce images that are difficult to tell apart. This study shows that lenses involving two lensing planes can partly reduce this ambiguity if researchers assume how the universe’s expansion changes over time. The authors use information from three known lens systems to constrain the ambiguous mass contribution. Their analysis also indicates that adding images of a second background source could improve measurements of the universe’s current expansion rate by up to about 50%, depending on important assumptions. Forecasts—not results from completed surveys—suggest that future Euclid and LSST samples could help establish how common these mass contributions are, benefiting studies of cosmic expansion and dark matter.

Young explorerSpace can bend light like a funny magnifying glass. Different amounts of hidden matter can sometimes make the same-looking pictures, so scientists cannot easily tell which answer is right. This study shows that pictures made by two layers of space magnifiers can help, if scientists make an assumption about how the universe grows. They used clues from three real examples. They also predict that many more examples could help us learn about hidden matter and how fast the universe is growing.

Challenges for minimal warm inflation in the Standard Model and beyond

Anish Ghoshal, Alessandro Strumia

• High Energy Physics - Phenomenology

AstronomerThis theoretical analysis identifies tensions in minimal warm-inflation models with an effective inflaton coupling φ G̃G, including Standard Model realizations. Each sphaleron transition releases energy much greater than the plasma temperature, placing the Standard Model solutions in tension with the plasma calculation. The effective-operator description is also challenged: embedding φ as the Goldstone boson of a renormalizable Peccei–Quinn theory requires an anomaly coefficient ≳100, implying a QCD Landau pole. More strongly coupled dark gauge sectors relax these tensions, but the abstract does not claim to eliminate them.

PublicThe paper examines a theoretical model called warm inflation, in which the universe’s early rapid expansion involves a hot plasma. The authors identify problems with a minimal version built using the Standard Model of particle physics: individual particle-field transitions release far more energy than the plasma’s temperature scale, challenging the calculation. Giving the model’s assumed interaction a more fundamental theoretical basis also leads to problematic behavior in the strong force. The authors find that models using more strongly interacting dark sectors ease these difficulties. These are theoretical findings, not observational evidence for warm inflation or a dark sector.

Young explorerScientists studied an idea about how the very young universe might have grown quickly while staying warm. They found problems in the math: some changes would release much more energy than the warm mixture’s temperature suggests, and another part of the idea also becomes troublesome. Adding a hidden set of things that interact more strongly could make the problems smaller. That does not mean scientists have seen those hidden things or proved the idea is right.

Galaxy and Halo Root Systems: Fingerprints of Mass Assembly

Mark Neyrinck, Miguel Aragón-Calvo, István Szapudi

• Astrophysics of Galaxies

AstronomerThe authors define halo or galaxy root systems as collections of particle pathlines tracing infall from an initially uniform matter distribution into a collapsed structure. Clumping during infall produces filamentary density enhancements when projected through time, providing a local, physical and geometric analogue of a merger tree at a cosmic-web node. In their dark-matter analysis, the largest cluster haloes have more roots and branches on average than small haloes, indicating more complex assembly even without gas physics. Higher spin is associated with curvier roots, and many systems receive mass contributions originating far from compact central protohalo cores. Root systems are also sensitive to anisotropic infall, although the reported simulation evidence for this is tentative and comes from a relatively small simulation box.

PublicThe study describes a way to picture how matter gathers into galaxies or dark-matter haloes: trace the paths of incoming particles, and the resulting pattern resembles branching tree roots. These patterns connect a single growing structure to the larger cosmic web. In the dark-matter analysis, the largest cluster haloes have more roots and branches on average than smaller haloes, suggesting more complicated growth even without gas. Faster-spinning haloes have more curved roots, and many systems gather some matter from far beyond their compact starting cores. A simulation also offers tentative evidence that the patterns reveal matter arriving preferentially from particular directions, but its relatively small size limits that finding.

Young explorerIn computer simulations, scientists can follow how tiny bits of matter come together to make big clumps in space. The paths look like tree roots, but they are not real roots! The biggest clumps tend to have more branches, and clumps that spin faster have bendier paths. Some bits come from far away. There are also hints that matter comes more from some directions than others, but the scientists are not sure about that part yet.

How Significant are Cosmological Collider Signals in the Planck Data?

Petar Suman, Dong-Gang Wang, Wuhyun Sohn+2 more

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

AstronomerThe authors introduce simplified cosmological-collider bispectrum templates spanning a broader range of particle masses, sound speeds, and interactions. They propose orthogonalizing these templates against tightly constrained single-field predictions and report enhanced signals for all four templates studied after removing that contribution. A systematic parameter scan using the Modal pipeline and Planck CMB data yields a maximum spin-0 significance of 2.4σ after accounting for the look-elsewhere effect; indicative spin-1 and spin-2 results peak around 2σ. These are not established detections of primordial non-Gaussianity or massive particles during inflation. The authors argue that refined templates and analysis strategies offer credible prospects for both with forthcoming observations.

PublicHeavy particles present during the universe’s early period of inflation could have left distinctive patterns in the cosmic microwave background. This study develops a broader set of mathematical patterns to search for those traces and proposes separating them from patterns already tightly constrained by observations. Applying the method to Planck data, the researchers find tentative hints, with the strongest reaching 2.4σ after allowing for the many possibilities searched. That is not enough to establish a discovery. The authors suggest that better search patterns and analysis methods, combined with forthcoming observations, could help reveal both departures from the simplest statistical patterns in the early universe and evidence of massive particles during inflation.

Young explorerScientists looked at light left over from when the universe was very young. They made new pattern guides to look for tiny clues that heavy particles might have left long ago. They found a few possible hints, but those hints could just be chance. They hope better searches and new observations will help them find out.

An information-theoretic framework for quantifying coherence in the cosmic density field

Biswajit Pandey, Anindita Nandi

AstronomerThe authors introduce a mutual-information framework for measuring statistical coherence between cosmic density fields at different redshifts in cosmological N-body simulations. Subtracting a reference baseline isolates excess statistical dependence generated by gravitational evolution, including nonlinear and higher-order correlations. The shared information rises with coarse-graining, peaks, and then declines; tests indicate that the peak location is primarily an estimator finite-sampling effect, not a fundamental physical coherence scale, and empirically indicates the estimator’s robust measurement range. In the simulations, mutual information is sensitive to cosmic evolution and cosmological parameters, and filamentary environments retain more statistically accessible shared information across epochs than sheets or clusters. Shared information between the initial and present-day fields is positive but extremely small, interpreted as reflecting information redistribution during nonlinear structure formation.

PublicUsing computer simulations, the researchers developed a way to measure how much statistical information the Universe’s matter distribution shares with its earlier states. Their method, called mutual information, captures complex relationships that conventional clustering measurements do not. The amount of shared information changes as the simulated matter is grouped into progressively larger regions, first rising and then falling. Crucially, tests show that the peak mainly comes from limited sampling in the measurement method, rather than revealing a special physical size in the Universe. In the simulations, threadlike structures retain more accessible shared information about earlier times than sheets or clusters do. The initial and present-day matter patterns share a positive but extremely small amount of information. The method also responds to cosmic evolution and cosmological parameters, suggesting its usefulness for studying how cosmic structure retains traces of its past.

Young explorerScientists used computer-made universes to ask how much a later pattern of matter still has in common with an earlier one. They made a new way to compare the patterns. In these pretend universes, long threads of matter kept more clues about earlier times than flat sheets or bunches did. The very first pattern and today’s pattern had only a tiny bit of information in common. One size seemed to give the most clues, but the scientists checked and found that this mostly came from how their counting method works—not from a special size in the real Universe.

An efficient model of cosmology dependence in the covariance matrix of the matter power spectrum

Theodore Steele, Robert Smith

AstronomerThe authors develop a fast model for the parameter dependence of the matter-power-spectrum covariance, rather than assuming a fixed covariance in cosmological likelihood analyses. Their approach Taylor-expands the true covariance around a fiducial cosmology, projected onto a theoretically known precision matrix. If the known model approaches the true matrix, the expansion truncates at its first term; less accurate models require additional terms. Using linear power spectra from the Quijote simulation suite, they construct model covariances with and without super-sample covariance for variations in Omega_m, Omega_b, n_s, sigma_8, h, and w_0. Three interpolation variants reproduce the input cosmologies well in these tests, although different approximations perform best in different regimes. This is a simulation-based validation against constructed model covariances, not an observational test. The method enables rapid calculation of parameter-dependent covariance and precision matrices for likelihood modelling.

PublicWhen scientists compare models of the Universe with data, they need to describe both uncertainties and how those uncertainties are linked. These relationships can change as the model’s cosmological settings change, but calculating them repeatedly can be expensive. This paper develops a faster way to estimate those changes for a measure of how matter is distributed across different scales. The researchers tested three versions of the method against model uncertainty matrices built using information from cosmological simulations, including cases with and without the influence of fluctuations larger than the sampled region. All three reproduced the test inputs well, but different versions worked best in different situations. The results support a computational tool for analysing cosmological models, rather than a new observational finding about the Universe.

Young explorerScientists use computers to study how matter is spread around the Universe. Their calculations need to keep track of uncertainty, and that uncertainty can change when they change the model. The researchers made three quicker ways to work this out. They tried them on examples made using computer simulations, and the answers matched the examples well. Different ways worked best in different cases. This could help scientists do their calculations faster.

Universal Dark-matter Density Profiles of Cosmic Filaments

Peng Xu, Fangzhou Jiang, Farhanul Hasan+4 more

• Astrophysics of Galaxies

AstronomerAn analysis of radial dark-matter density profiles in TNG50 examines filaments extracted with DisPerSE at z = 0, 0.5, 1, 2 and 3. The authors find that the directly extracted spines miss the density ridges; their shrinking-cylinder re-centering algorithm raises inferred central densities and restores inner power-law behavior. Scaling radius by the virial radii of terminal nodes yields a nearly universal profile with only weak dependence on redshift, node mass and filament length, suggesting structural self-similarity. Separating smoothly distributed, unbound dark matter from the full particle population shows that embedded low-mass halos primarily produce the central cusp, whereas the smooth component has a flat core within R/Rvir ≲ 0.1. Its evolution suggests, rather than establishes, a shift from predominantly smooth accretion at high redshift toward clumpier accretion at late times. A generalized triple-power-law model accurately describes the universal profile. These findings concern simulated filaments, not observational measurements.

PublicUsing the TNG50 computer simulation, researchers studied how dark matter is distributed around the threadlike structures of the cosmic web. They found that the method used to trace these threads did not precisely locate their densest centers. A new centering method revealed higher central densities. When distances were adjusted using the characteristic sizes of the structures at each thread’s ends, the density patterns became nearly alike across different cosmic times, endpoint masses and thread lengths. The simulation also showed that small dark-matter halos embedded along the threads account for most of the sharp central density rise; the smoothly distributed, unbound dark matter instead levels off near the center. Changes in this smooth component suggest that material fed into filaments more smoothly early in cosmic history and in more clumps later. These are simulation results and interpretations, not direct observations of the universe.

Young explorerIn a computer-made universe, scientists studied long threads of dark matter, a kind of matter we cannot see directly. They found a better way to locate the middle of each thread. After adjusting for size, the threads had nearly the same pattern: how packed the dark matter was changed in a similar way from the middle outward. Little bunches of dark matter made the middle look especially packed, while the matter outside those bunches was more evenly spread near the center. The computer results also hint that the threads gathered matter more smoothly long ago and in more bunches later. Scientists have not shown this by watching real threads in space.

TDCOSMO XXVI: Uniform lens modeling of eight doubly imaged quasars

Ryan Brady, Xiang-Yu Huang, Simon Birrer+7 more

• Astrophysics of Galaxies

AstronomerThis study presents the first uniform lens-modeling analysis of eight doubly imaged quasars using multi-band Hubble Space Telescope observations and a Lenstronomy pipeline tailored to doubles. Modeled Einstein radii agree with literature values at an average of 1.5 sigma, while image separations differ from Gaia DR2 measurements by an rms of 3.6 milliarcseconds. The authors find a strong correlation between Fermat-potential precision and the surface brightness of extended host-galaxy arcs, identifying arc surface brightness as the primary driver of mass-model precision in this sample. Fits constrained only by quasar image positions yield substantially broader posteriors than full-image modeling, supporting the importance of the arcs. No H0 inference is reported here: a hierarchical analysis incorporating time delays and stellar kinematics is deferred to a subsequent publication. The authors expect the pipeline and brightness trends to aid future time-delay cosmography samples from LSST, Roman, and Euclid.

PublicGravity can bend a distant quasar’s light so that it appears as two images, with its host galaxy stretched into arcs. Researchers used Hubble Space Telescope observations to model eight such systems consistently. These two-image lenses are more abundant than four-image lenses but provide fewer geometric clues, making them harder to model. In this sample, the surface brightness of the host-galaxy arcs was the main factor determining how precisely the lensing mass could be modeled. Using only the quasar image positions gave much less precise results than modeling the full images. The work prepares the way for measuring the universe’s expansion rate, but does not report that measurement; an analysis combining these models with time delays and stellar motions is planned for a later paper.

Young explorerGravity can bend light and make one faraway bright object look like two. Scientists studied eight of these pairs in Hubble telescope pictures. They also looked at stretched-out light from the galaxies around those objects. When those stretched shapes were brighter, the scientists could work out more precisely how the gravity was bending the light. They hope this will help them learn how fast the universe is growing, but they have not worked out that answer in this study.

Cancellation of one-loop time dependence in superhorizon curvature perturbations from all scales

Keisuke Inomata

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

AstronomerThis theoretical calculation demonstrates conservation of superhorizon curvature perturbations at one-loop order in spatially-flat gauge in the decoupling limit ε ≡ −Ḣ/H² → 0. Unlike treatments assuming loop wavenumber k ≫ external wavenumber q, it includes all loop scales, explicitly covering k ≲ q. Using the nonlinear inflaton-to-curvature relation in the δN formalism, the authors show that the apparent time dependence of the one-loop curvature power spectrum cancels when all contributions, including boundary terms, are consistently combined.

PublicThis theoretical study examines whether extremely large-scale ripples in the early universe change in strength over time. The calculation includes a correction called a loop and accounts for ripple scales omitted by an assumption used in earlier work. Once all mathematical contributions are included, the apparent change cancels. The result applies in a particular limiting case where the expansion rate changes negligibly; it is a mathematical finding, not an observational measurement.

Young explorerImagine tiny ripples spread across the early universe, with some stretched over enormous distances. Scientists used math to ask whether the strength of those huge ripples changes with time. Some pieces of the math made it look as though it did, but when they put all the pieces together, the change disappeared. This answer comes from a calculation with special rules, not from watching the ripples.

Effects of Solar Wind Plasma Noise on Stochastic Gravitational Wave Background Searches with a Space Based Interferometer Network

Mengfei Sun, Borui Wang, Jie Wu+2 more

• General Relativity and Quantum Cosmology

AstronomerThis study estimates solar-wind plasma-induced bias in LISA-Taiji stochastic gravitational-wave background (SGWB) cross-correlation searches, using high-time-resolution Wind/SWE electron-density data and Lomb-Scargle fluctuation spectra. The calculation propagates plasma noise into the TDI A/E channels, incorporating finite-arm propagation, Taylor frozen-flow spatial correlations, and the network overlap reduction response. Although the single-detector plasma residual lies below the reference noise, its interdetector-correlated component directly biases the cross-correlation estimator. Under dual-detector-scale coverage, calculated parameter biases reach 12.73% of the corresponding Fisher uncertainty for a power-law SGWB and 19.26% for ln Gμ in M2/M3 cosmic-string spectra. These are modeled biases, not observed SGWB measurements, and apply to the network configurations, observing times, and frequency bands considered. Single-detector residual noise alone is therefore insufficient to assess this systematic.

PublicComparing signals from LISA and Taiji can improve sensitivity to a background of gravitational waves, but solar-wind disturbances shared by both detectors could skew the inferred properties of that background. Researchers used measured electron-density fluctuations from Wind/SWE to calculate how this plasma noise would affect the network. Their calculations show that noise too small to stand out in either detector alone can still matter when the two signals are compared. For the cases studied, the resulting shifts in inferred parameters can reach 12.73% of the estimated statistical uncertainty for one background model and 19.26% for a cosmic-string model. These percentages describe shifts relative to uncertainty, not percentage errors in the parameters themselves. The results are calculations for particular network arrangements, observing durations, and frequency ranges, rather than a detection of gravitational waves or a measured bias in LISA-Taiji data.

Young explorerScientists want to compare two space detectors to look for tiny ripples in space. But particles blowing from the Sun could disturb both detectors in a similar way and confuse the comparison. Using measurements of those particles, researchers calculated how much confusion they might cause. They found that a disturbance can matter when the detectors are compared, even if it is very small in each one alone. This is a calculation of what could happen, not something already seen in the two detectors.

Alcock-Paczynski Blinding Scheme for the Ly-α Forest Analysis

G. Perez-Sanchez, S. F. Beltran, G. Niz+45 more

AstronomerThe authors present and validate a catalog-level blinding method for Lyα forest cosmology based on a modified Alcock–Paczynski test. After continuum fitting and fluctuation-field extraction, the method geometrically shifts each forest in wavelength space and consistently changes QSO redshifts to conceal the background expansion history. Tests progress from idealized low-noise mocks through realistic DESI year-one synthetic datasets to DESI DR1 data, using both Lyα auto-correlations and Lyα–QSO cross-correlations. The method shifts the BAO peak in the 3D correlation functions to the expected position for changes of around 5% in the matter content, without changing the shapes of model-parameter posteriors. Mixed metal and Lyβ contamination limits the blinding, primarily in the 1D correlation function, where other strategies can mitigate the effect. The authors conclude that the approach is viable, particularly for joint analyses with other tracers blinded in the same way.

PublicThe researchers tested a way to hide information about the universe’s expansion from scientists while they analyze absorption patterns in quasar light. This kind of blinding helps keep expectations from influencing an analysis. Their method shifts the wavelengths assigned to the absorption patterns and consistently adjusts the quasars’ redshift positions. In both simulated datasets and real data from DESI’s first data release, it moved a characteristic large-scale clustering feature to the intended position, corresponding to a change of about 5% in the assumed matter content, while preserving the shapes of the statistical uncertainty distributions. This is a deliberate alteration for blinding, not a measured change in the universe’s matter content. Absorption from metals and another hydrogen transition makes the hiding imperfect, especially in one-dimensional correlations; complementary blinding methods can help. The authors find the approach promising for cosmological analyses, especially when other cosmic tracers are blinded consistently.

Young explorerScientists look at patterns in light from faraway quasars to learn how the universe grows. But knowing what answer to expect can influence their work. These researchers tested a way to move the patterns a little, like hiding the answer until a puzzle is finished. It worked in pretend data and real observations: an important pattern moved where they wanted it to. The universe itself did not change—only the information used for the test did. Some mixed-in light patterns made the hiding imperfect, so extra tricks may help.

Primordial tensor mode from the neutrino sector

Shohei Saga, Shuichiro Yokoyama

AstronomerThis theoretical study identifies a regular primordial tensor solution sourced by higher-order multipoles of the collisionless neutrino distribution after decoupling. For the leading tensor-octupole mode, the authors derive Einstein–Boltzmann initial conditions and calculate CMB angular power spectra. Relative to the standard gravitational-wave mode, this mode produces a weaker large-scale metric response, a suppressed reionization bump, and a shifted oscillation phase in the tensor CMB spectra. These calculated signatures offer a way to distinguish the modes; the abstract reports no observational detection.

PublicThe researchers calculate how a particular pattern in the distribution of neutrinos after they stopped colliding could produce primordial ripples in spacetime. Their theoretical model predicts a different imprint on the cosmic microwave background, the light left over from the early universe, than the standard gravitational-wave pattern. In particular, one feature associated with the universe’s reionization would be weaker, and the peaks and troughs of the predicted pattern would be shifted. These differences could help distinguish the two possibilities, but the study does not report finding this neutrino-related pattern in observations.

Young explorerScientists used math to study how tiny particles called neutrinos might make ripples in space long ago. They worked out how those ripples could leave a different pattern in the universe’s oldest light. Part of the pattern would be weaker, and its wiggles would line up differently from another kind of ripple. This is a prediction from their math, not something they have spotted in the sky.

A low value of H₀ in tension with the distance ladder from Megamasers using peculiar velocity reconstruction

Richard Watkins, Hume A. Feldman

AstronomerThis reanalysis of megamaser distances and redshifts estimates H0 independently of the traditional distance ladder. Its principal change is a peculiar-velocity correction based on a new velocity-field reconstruction combining constrained cosmological simulations with redshift-survey data to capture coherent flows and non-Gaussian individual galaxy motions. The authors argue that earlier megamaser estimates were susceptible to peculiar-velocity bias. Their revised H0 is closer to the CMB-inferred value than to the distance-ladder value, while remaining consistent with both; earlier megamaser results agreed with the distance ladder but showed greater than 2σ tension with the CMB. The authors interpret this shift as suggesting an unidentified distance-ladder systematic rather than new physics, not as establishing that explanation.

PublicMegamasers provide a way to measure cosmic distances without the usual chain of distance measurements known as the distance ladder. Researchers reanalyzed these distances and galaxy redshifts to estimate how fast the nearby universe is expanding. They used a reconstruction combining galaxy-survey data with cosmological simulations to better account for galaxies’ own motions, which can complicate the expansion measurement. The revised estimate is closer to the value inferred from the cosmic microwave background than to the distance-ladder estimate, but remains compatible with both. The authors suggest that an unidentified problem in the distance ladder might explain the disagreement between expansion estimates, rather than new physics; this analysis does not prove that explanation.

Young explorerScientists want to know how fast the universe is growing. They looked again at measurements from special bright sources in space. Galaxies also move around on their own, so the team used observations and computer simulations to better account for that motion. Their new answer is closer to one earlier answer, but could still fit another. They think a hidden problem in one measuring method might explain the difference, but they have not proved it.

Average soft X-ray surface brightness profile of massive galaxy clusters in Magneticum simulations

A. Kruglov, N. Lyskova, I. Khabibullin+2 more

• High Energy Astrophysical Phenomena

AstronomerThe study compares stacked SRG/eROSITA 0.3–2.3 keV surface-brightness profiles of several dozen massive, low-redshift galaxy clusters with equivalently derived population averages from the Magneticum cosmological hydrodynamical simulations. Self-similar rescaling motivates stacking to reduce object-to-object stochasticity and improve sensitivity in faint outskirts. The observed and simulated profiles show very good out-of-the-box agreement overall, but differ significantly in the innermost region. The authors interpret this discrepancy as likely excessive core gas redistribution by the simulated AGN feedback. Beyond several virial radii, the simulations predict a highly noisy profile whose mean signal lies orders of magnitude below a radially flat but strongly fluctuating local emission background. Detecting this predicted component would therefore be very challenging even with larger future samples.

PublicResearchers combined X-ray observations of several dozen massive, relatively nearby galaxy clusters and compared their average brightness profiles with computer simulations. Combining clusters reduces the influence of individual differences and helps reveal faint emission in their outskirts. The observations from SRG/eROSITA and predictions from the Magneticum simulations agree very well overall without additional adjustment. They differ significantly at the centers, possibly because feedback from active galactic nuclei moves too much gas around in the simulations. Far beyond the clusters’ usual boundaries, the simulations predict extremely faint, irregular X-ray emission overwhelmed by a fluctuating background. This outer emission is a prediction, not a reported detection, and finding it would remain difficult even with more clusters.

Young explorerScientists put together X-ray views of many big groups of galaxies to see their faint edges better. They compared the views with computer models, and most of the brightness matched very well. The middles did not match as well, perhaps because the models moved too much gas around there. The computers also predict a very faint X-ray glow far outside the groups, but it would be very hard to spot against other X-ray light.

PIFFLE: Characterizing Foreground Dispersion Measure Contributions Across 4 Decades in Halo Mass in the FRB20230907D Field

Qi Guo, Khee-Gan Lee, Sunil Simha+14 more

AstronomerFRB20230907D, localized to a galaxy at z=0.464, has DM_obs=1031 pc cm^-3 and lies above the Macquart relation. Foreground spectroscopy, group catalogs, imaging, and X-ray data identify a massive system at z≈0.09 with M_vir≈7.7×10^14 solar masses and another group at z≈0.02565. Assuming modified-NFW halo gas profiles, their estimated observer-frame DM contributions are 205 (+30/-25) and 80 (+60/-40) pc cm^-3, respectively. Accounting for other foreground and host contributions yields DM_UGC7596=58 (+53/-40) pc cm^-3 for a closely intersected dwarf with stellar mass ≈10^8 solar masses at projected separation ≈0.03 R_vir. The authors report this as the first such dwarf-galaxy DM constraint; it is model-dependent and consistent with hydrodynamical predictions for low-mass halos. The work highlights the value of dense foreground spectroscopy and multi-wavelength data for interpreting FRB dispersion measures.

PublicThe radio burst FRB20230907D shows more dispersion than expected for its galaxy’s redshift. Researchers investigated galaxies and galaxy groups between us and the burst to assess what might explain this excess. They identified a massive foreground system and another galaxy group, then used an assumed gas-density model to estimate their contributions. After accounting for these and other contributions, they also constrained the dispersion associated with the dwarf galaxy UGC7596, which lies very close to the burst’s line of sight. The authors describe this as the first such constraint for a closely intersected dwarf galaxy. Its substantial uncertainty and dependence on the foreground accounting matter, but the estimate agrees with predictions from simulations of low-mass galaxy halos.

Young explorerA quick flash of radio waves came from a faraway galaxy. Its signal was more spread out than expected. Scientists looked at groups of galaxies in front of it and estimated how much their gas could explain. They also estimated a part linked to a small galaxy near the flash’s path. Their answer fits what computer models predicted, but it is still uncertain and depends on how they think the gas is arranged.

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

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

AstronomerUsing synthetic galaxy-clustering data designed to reproduce Stage-IV survey signals, the authors investigate Bayesian prior-volume effects in analyses with models including EFT and VDG∞. They find that these effects are largely driven by priors on parameters expressed in Mpc/h, which introduce a spurious correlation with the Hubble parameter h. A physically motivated formulation in Mpc strongly mitigates marginalisation-induced shifts across ΛCDM, KCDM, wCDM and w0waCDM tests, reducing discrepancies from fiducial values 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 strategy, replacing σ8 with σ12 improves performance even at high redshift, where dark-energy equation-of-state constraints are weaker. The conclusions persist with additional BAO constraints and reduced statistical power. These are synthetic-data validation results relevant to future Stage-IV analyses, not new observational cosmological measurements.

PublicHow researchers express distances can affect what they infer from the pattern of galaxies. In Bayesian analyses, the assumed ranges and weighting of model parameters can unintentionally link those parameters to h, a measure of the Universe’s expansion rate, when distances are expressed in Mpc/h. The authors tested an alternative formulation using Mpc on synthetic galaxy data resembling signals expected from a Stage-IV survey. Across several cosmological models, this substantially reduced shifts away from the values used to generate the data: discrepancies of several statistical standard deviations fell to well within one. The approach performed about as well as other proposed remedies, and its benefits persisted when extra distance information was included or the data were less statistically powerful. The study also found an improvement to one alternative method by changing how it describes the strength of density fluctuations. These tests support a way to make future galaxy-survey analyses more reliable; they do not report a new measurement of the real Universe.

Young explorerThe researchers made pretend maps of galaxies with answers they already knew. Then they checked whether their math could find those answers. They found that one way of writing distances could mix up the math’s starting guesses with how fast the Universe grows. Using a different way of writing distances helped the math get much closer to the known answers. It worked in several kinds of pretend universes, but this was a test—not a new discovery from real galaxy maps.

Gravitational waves from strong first-order phase transitions in an expanding Universe

Jintao Zou, Zizhuo Zhao, Yongtao Jia+1 more

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

AstronomerThree-dimensional lattice simulations of a coupled scalar field–fluid model examine slow, strong first-order phase transitions in an expanding Universe. In these simulations, sound waves dominate gravitational-wave production over bubble collisions, with two spectral peaks associated with the mean bubble separation and sound-shell width. Bubble collisions generate rotational fluid modes whose magnitude increases with transition strength α. The effective sound-wave source lifetime increases for slower transitions and smaller α, and decreases for faster transitions with larger β/H. The normalized gravitational-wave amplitude is of order 10^-2, consistent with Minkowski-spacetime results, but the spectra differ markedly. These are numerical findings, not observational detections.

PublicComputer simulations explore how a strong change of state, proceeding through growing and colliding bubbles in an expanding Universe, could generate gravitational waves. In the simulated slow transitions, sound waves in the surrounding fluid produce a much stronger gravitational-wave signal than the bubble collisions themselves. The sound-wave spectra have two peaks, linked to the typical spacing between bubbles and the thickness of the sound shells. Collisions also create swirling fluid motions, which grow stronger for stronger transitions. The sound-wave source lasts longer for slower or weaker transitions. Although the normalized gravitational-wave strength resembles results from simulations without cosmic expansion, the pattern across frequencies differs substantially. The study reports simulation results, not waves detected in the Universe.

Young explorerScientists used a computer to study bubbles growing and bumping together while the Universe expands. In their model, the bubbles form as material changes from one state to another. The sounds moving through the material made much bigger ripples in gravity than the bubble bumps did. The bumps also made the material swirl. This happened in a computer experiment; it was not something scientists watched happening in space.

FOMO-Z. Optimal galaxy classification, photometric redshifts, and reconstruction of population distributions

G. F. Lesci

• Astrophysics of Galaxies

AstronomerFOMO-Z is a publicly available Python framework for galaxy selection and probabilistic inference from photometry using a reference sample with known properties. Its explicit, physically interpretable criteria impose no assumed functional form on color distributions. Binary selections use linear color cuts or flexible color–color grids to maximize completeness subject to a purity threshold. Probabilistic inference matches reference galaxies with compatible colors within photometric uncertainties to estimate criterion-membership probabilities, continuous-property PDFs such as redshift, and property distributions for selected populations. The framework accommodates prior weights and reference redshift PDFs and includes informative-color selection. Demonstrated applications include background-galaxy selection, population classification, tomographic redshift calibration, and photometric redshift estimation. The authors report results consistent with machine-learning approaches such as self-organizing maps, with computational efficiency supporting prospective use in large surveys and Stage IV cosmological analyses.

PublicThe researchers present FOMO-Z, publicly available Python software that uses galaxy colors to classify galaxies and estimate properties such as redshift. It compares galaxies with a reference sample whose properties are already known, accounting for uncertainty in the measured colors. Rather than always giving a single answer, it can assign probabilities to possible properties. Users can also tune selections to recover more of their desired galaxies while setting a minimum requirement for how free the sample is from unwanted galaxies. In the demonstrated applications, the authors report results consistent with machine-learning methods while using explicit, physically interpretable rules. They describe the software as computationally efficient and suitable for future large galaxy surveys; this is a proposed use, not a reported analysis of those future surveys.

Young explorerScientists made a computer tool called FOMO-Z to help sort galaxies by their colors. It compares them with galaxies that scientists already know about. Because colors are not measured perfectly, the tool can say how likely different answers are instead of pretending it knows for sure. The scientists tried it on several galaxy tasks and say its answers agree with those from other computer methods. They think it could help study very big collections of galaxies in the future.

Targeting the future of spectroscopic galaxy surveys -- A cosmological study case with the Wide-field Spectroscopic Telescope

Constantin Payerne, Antoine Rocher, Aurélien Verdier+21 more

AstronomerThis work develops target-selection strategies for the proposed 12-metre Wide-field Spectroscopic Telescope (WST), expected to operate in the 2040s, explicitly linking survey depth, multiplexing and observing time to cosmological constraining power. Using deep multi-band photometry, including CLAUDS and HSC COSMOS-field data, it revisits established galaxy and quasar selections at z ≲ 1.6, introduces the magnitude-limited MagMax sample with three-dimensional color-color star-galaxy separation, and develops Lyman-break dropout selections reaching z ≳ 2. Fisher-matrix forecasts assess constraints on BAO distance parameters, the growth rate, evolving dark energy, local-type primordial non-Gaussianity and the summed neutrino mass. These are forecasts for a WST-like survey, not measurements from WST; the abstract reports no numerical constraint values. The principal contribution is an optimisation framework intended to guide WST and other future Stage-V spectroscopic surveys.

PublicHow should a future telescope choose which galaxies and quasars to study? This work develops selection strategies for the proposed Wide-field Spectroscopic Telescope, a 12-metre facility expected to operate in the 2040s. Using existing images taken in several wavelength bands, the researchers adapt established methods and introduce additional ways to select targets, including more distant galaxies. They then forecast how a WST-like survey could investigate cosmic expansion, the growth of structure, dark energy, conditions in the early universe and neutrino masses. These are projections, not new measurements of those properties. The main contribution is a planning framework that connects telescope capabilities and observing time to the scientific information a survey could deliver.

Young explorerScientists are planning how a future telescope could choose galaxies to study. They use pictures of the sky to work out which ones to pick, then estimate what the telescope might teach us about how the universe grows and changes. The telescope is still proposed, so these are plans and predictions, not discoveries made with it.

Asymmetric Dark Matter from Low-Scale Spontaneous Leptogenesis

Hiroki Takahashi, Juntaro Wada

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

AstronomerThe authors propose an asymmetric dark matter framework in which the dark matter and baryon asymmetries arise together through low-scale spontaneous leptogenesis, with right-handed neutrino masses well below the Davidson–Ibarra bound of 10^9 GeV. Both asymmetries are predominantly sourced by the majoron, a dynamical CP phase whose kinetic misalignment supplies a sufficiently large, time-dependent effective CP phase. The correlated CP-violation sources yield a conditional prediction for the dark matter mass: typically of order 0.1–100 GeV if the dark matter asymmetry reaches equilibrium before freeze-out, broadening to roughly 0.1 GeV–10 TeV if weak coupling prevents equilibration. The authors place the equilibrium-case range within direct-detection sensitivity. These are theoretical model predictions, not reported detections.

PublicThis theoretical study proposes a shared origin for the universe’s excess of ordinary matter over antimatter and a corresponding imbalance in dark matter. In the model, a changing field called the majoron drives both imbalances, allowing the mechanism to work with right-handed neutrinos much lighter than a commonly used theoretical bound. Linking the two imbalances lets the authors predict a range of dark matter particle masses, but that range depends on how the dark matter develops. If its imbalance reaches equilibrium before the relevant reactions cease to be effective, the predicted mass is typically about 0.1–100 GeV, a range the authors describe as accessible to direct-detection experiments. If weak interactions prevent that equilibrium, the allowed range expands to about 0.1 GeV–10 TeV. The study does not report a dark matter detection.

Young explorerScientists have an idea for how the universe could have made more matter than antimatter, while also making an imbalance in invisible dark matter. In their idea, one changing field helps make both imbalances together. That connection gives them clues about how heavy a dark matter particle might be. The answer depends on whether the dark matter had time to settle into a balance before some reactions stopped working. This is an idea to test, not a discovery of dark matter.

Graviton Floor

Himeka Matsuo, Asuka Ito, Kazunori Kohri+2 more

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

AstronomerThe study investigates conversion of the observed cosmic photon background, spanning radio to gamma-ray frequencies, into gravitons in magnetic fields in the Milky Way and blazar jets. The authors find that blazar jets dominate the resulting predicted graviton background. They interpret this background as a graviton floor for high-frequency gravitational-wave searches for new physics, analogous to the neutrino floor. The abstract does not report a detection of this graviton background.

PublicSpace is filled with background light, from radio waves to gamma rays. This study examines how some of that light could turn into gravitons, the particles associated with gravitational waves, in magnetic fields in our galaxy and in jets from objects called blazars. The authors predict that blazar jets would provide most of the resulting graviton background. They argue that this background would act as a source of interference for high-frequency gravitational-wave detectors looking for new physics. This is a predicted background, not a reported detection.

Young explorerSpace is full of light that our eyes cannot all see. Scientists studied how magnetic fields might turn some of that light into tiny bits of gravity called gravitons. Their work suggests that most of these gravitons would come from powerful streams in space called blazar jets, rather than from our own galaxy. This could make it harder for special gravity detectors to spot something new, like trying to hear a quiet sound over background noise. The scientists have not reported finding these gravitons.

A combined PRIMER+MINERVA study of the evolution of [OIII]+Hβ equivalent width from z=3 to z=8.5

Isaac J. B. Holst, Ross J. McLure, Ryan Begley+15 more

AstronomerCombining JWST/NIRCam PRIMER and MINERVA imaging in the UDS field, this study measures the evolution of [O III]+Hβ equivalent width over z=3–8.5. The medium- plus broad-band data reduce the photometric-redshift outlier rate to 4.7% at m_F444W≤28, a 42% reduction relative to PRIMER alone, and enable equivalent-width recovery in five bins centred near z=3.2, 4.0, 5.0, 7.2 and 8.3. The final sample contains 1,964 galaxies with M_UV≤−19.25 and provides new bright-end constraints on the z=7–8 [O III]+Hβ luminosity function. SED modelling with non-parametric continuity star-formation histories yields a monotonically increasing median log10(Wλ), from 2.54±0.01 at z≈3 to 3.05±0.03 at z≈8. The log-equivalent-width distribution also becomes increasingly asymmetric; the fraction of extreme emission-line galaxies, defined by Wλ>1,000 Å, reaches 0.50±0.10 at z=8.3. The modelling attributes this evolution to increasingly bursty star formation and associates extreme emitters with particularly high specific star-formation rates during the preceding 10 Myr. That physical explanation is a model-based interpretation rather than a direct observation of individual star-formation histories.

PublicAstronomers combined two sets of James Webb Space Telescope images to study light emitted by oxygen and hydrogen in 1,964 galaxies. The combined images improved estimates of galaxy redshifts, reducing the rate of large redshift errors by 42% compared with one imaging set alone. Across redshifts from about 3 to 8, the oxygen-and-hydrogen emission becomes stronger relative to the galaxies’ underlying light. At redshift 8.3, an estimated 50% of the selected galaxies qualify as extreme emitters, with an uncertainty of 10 percentage points. The researchers also placed new limits on how common the brightest line-emitting galaxies are at redshifts 7–8. Models of the galaxies’ light suggest that increasingly bursty star formation drives the trend, with extreme emitters forming stars especially rapidly relative to their existing stellar mass during the previous 10 million years. This explanation depends on the modelling; the images do not directly reveal those past histories.

Young explorerScientists used pictures from the Webb telescope to study faraway galaxies. They found that a special kind of light from oxygen and hydrogen was stronger compared with other galaxy light when the universe was younger. Their computer models suggest that these galaxies made new stars in big bursts. That is an explanation the models suggest, not something the scientists watched happen.

Constraining Dust Attenuation Curves in Star-Forming Galaxies at Cosmic Noon Using Multiple Emission Line Ratios

Owen Zafuta, Joseph Havens, Bren E. Backhaus+3 more

AstronomerUsing JWST/NIRSpec spectroscopy from JADES, the authors constrain effective dust attenuation curves for 386 star-forming galaxies at 0.5 ≤ z ≤ 7. They combine Hα, Hβ, and one additional hydrogen recombination line per galaxy to fit the normalization τ_V and slope n of an assumed power-law attenuation curve, rather than fixing the slope as required by Balmer-decrement-only corrections. Both parameters span broad ranges even at similar redshifts. Combinations including Paschen transitions constrain the slope substantially better than Balmer-only combinations. The authors report more consistent star formation rates with less scatter than obtained using SMC-like or Calzetti-like corrections. The method offers improved dust corrections for studies of peak cosmic star formation and the early universe, while retaining the assumption of a power-law effective attenuation curve.

PublicDust dims the light from galaxies, making it harder to estimate how quickly they are forming stars. Common corrections assume how strongly dust dims different wavelengths, even though this varies between galaxies. Using JWST observations from the JADES survey, researchers studied hydrogen emission lines in 386 star-forming galaxies. They fitted a simple mathematical model of dust dimming separately for each galaxy and found a wide range of dust effects, even among galaxies at similar redshifts. Including hydrogen lines from the Paschen series gave tighter constraints than using only Balmer lines. Compared with two commonly used dust corrections, their method yielded more consistent star formation estimates with less scatter. This could improve studies of star formation across cosmic history, though the estimates still depend on the chosen model of dust dimming.

Young explorerDust can hide some of a galaxy’s light, making it tricky to tell how quickly new stars are being born. Scientists used the JWST space telescope to study light from 386 galaxies where stars are forming. They found that dust dims the light differently in different galaxies. Using several kinds of light from hydrogen helped them work out the dust’s effect more clearly. Their way of correcting for dust gave more consistent guesses about how quickly stars are being born, but those guesses still depend on a simple rule they use to describe the dust.

FORGE'd In The Early Universe II: Constraining The Pop III Initial Mass Function

Yasmine J. Meziani, Philip F. Hopkins, Pratik J. Gandhi+4 more

• Solar and Stellar Astrophysics

AstronomerThis cosmological radiation-magnetohydrodynamic zoom-in simulation using FORGE'd in FIRE follows 56 Population III stars across five minihalos for just over 500 Myr, from z ≈ 16 to z ≈ 7. The initial conditions target an isolated ultra-faint galaxy with a z = 0 halo mass of approximately 10^9 solar masses; maximum mass and spatial resolutions reach approximately 0.01 solar masses and 0.001 pc. The emergent stellar IMF has dN/dM proportional to M^−α, with α = 1.9 above approximately 2.2 solar masses. The simulated population includes single stars, binaries, higher-order multiples, and stars below one solar mass. Initially, the high-mass IMF is more top-heavy, with α ≈ 1.4–1.5, and steepens with continued star formation. The authors suggest that their much longer evolutionary coverage may partly explain differences from earlier simulations. The first star-forming minihalo hosts the most massive stars and has α ≈ 1; later minihalos have lower maximum stellar masses and lower-density parent clouds. These are findings from this simulated population, not observational measurements or a demonstrated universal Pop III IMF.

PublicA computer simulation follows the formation of 56 stars from the universe’s first stellar population across five small dark-matter halos. It tracks star formation for more than 500 million years, substantially longer than earlier studies. Early in the simulation, the balance of stellar masses favors massive stars more strongly; as star formation continues, the mass distribution becomes less weighted toward massive stars. The simulation also produces stars lighter than the Sun, along with pairs and larger groups of stars. The first star-forming halo produces the most massive stars, while later halos form stars with lower maximum masses in less-dense clouds. The researchers suggest that following star formation for longer may partly explain why their results differ from earlier simulations. These results describe a simulated population, not stars directly observed.

Young explorerScientists used a computer to explore how some of the very first stars might have formed. Their model made 56 stars, including stars smaller in mass than our Sun and stars in pairs or bigger groups. At first, big stars were more common compared with smaller ones than they were later. This is a computer experiment, not something scientists watched happen in the sky.

Magnetically Arrested Accretion and Black Hole Spin in a Semi-Analytic Model of Galaxy Formation

Antonio J. Porras-Valverde, Angelo Ricarte, Priyamvada Natarajan+4 more

AstronomerMad Sage extends the Dark Sage semi-analytic galaxy-formation model by coupling black hole mass and spin evolution to accretion and AGN feedback under magnetically arrested disk conditions. It incorporates GRMHD-calibrated spin evolution and jet power, spin-dependent radiative efficiencies, and merger-remnant spins. Model comparisons show that incoherent accretion combined with Blandford-Znajek spin-down drives massive black holes toward low spins, reducing jet efficiencies and weakening massive-galaxy quenching. Within the tested models, reproducing the high-mass end of the stellar mass function requires either exclusively coherent accretion or additional mechanical feedback from ADAF outflows. The models broadly reproduce observed black hole–galaxy scaling relations, disk surface density profiles, and the AGN luminosity function at redshifts approximately 2–6, but the spin models underpredict faint AGN number densities at low redshift. Predicted spins decrease with black hole mass at redshifts below approximately 3; this mass dependence weakens at higher redshifts. Predicted spin distributions peak at an absolute value of the dimensionless spin parameter of approximately 0.5–0.7, below current X-ray reflection spectroscopy measurements. They become bimodal for massive, quiescent black holes accessible to the next generation Event Horizon Telescope and the Black Hole EXplorer. Predicted LISA event rates are nearly independent of the adopted accretion and spin models.

PublicThe researchers present Mad Sage, a model that explores how growing, spinning black holes influence galaxy formation through radiation, jets, and other outflows. In the model, gas arriving without a consistent rotational direction, together with energy extraction by jets, slows massive black holes and weakens their ability to suppress star formation. Matching the observed abundance of the most massive galaxies requires either consistently aligned accretion or extra feedback from outflows associated with an advection-dominated accretion flow. The models broadly match several observed galaxy and black hole properties, including active black hole brightness distributions at redshifts approximately 2–6, but predict too few faint active black holes at low redshift. At redshifts below approximately 3, the models predict that more massive black holes generally spin more slowly; this trend weakens at higher redshifts. The predicted spin distributions peak at spin magnitudes of approximately 0.5–0.7, lower than current X-ray-based measurements. For massive, relatively inactive black holes, the models predict two spin groups that future Event Horizon Telescope and Black Hole EXplorer observations could probe. Forecast LISA event rates change little between the accretion and spin models tested.

Young explorerScientists made a model to explore how black holes grow and spin, and how their jets affect galaxies. In their model, gas coming in without a steady direction can help slow big black holes, making their jets less powerful. To match how many very big galaxies we see, the model needs either gas arriving in a steady direction or extra outflows. It matches some things astronomers see, but not everything: it predicts too few faint, active black holes and spins lower than current measurements suggest. It also predicts two spin groups among big, quiet black holes. Those are predictions for future telescopes to check, not things this study has already seen.

FORGE'd in Fragments: Pop III star formation in a Milky Way-like progenitor halo

Vasilii Pustovoit, Shivan Khullar, Norman Murray+5 more

• Solar and Stellar Astrophysics

AstronomerThis radiation-magnetohydrodynamic cosmological zoom-in simulation follows Population III star formation in a Milky Way-like progenitor halo at z ≈ 21. Primordial gas collapses across 10 orders of magnitude, forming a disk that becomes gravitationally unstable about 3 kyr before the first protostar forms. Spiral-arm fragmentation produces approximately 60 sink formation events during the first 8 kyr of post-collapse evolution; total stellar mass exceeds 150 solar masses by the simulation endpoint at 15 kyr. The disk remains magnetically supercritical and magnetic energy remains subdominant, despite increasing by about 3.5 orders of magnitude after the first star forms. The mass-to-flux ratio declines from roughly 100–1,000 to 15 as inflow supplies magnetic flux. Initially sub-virial, the disk reaches virial equilibrium within about 2 kyr. Stellar mass grows as t², consistent with predicted accelerating accretion in self-gravitating turbulent collapse, with rates around 0.001–0.01 solar masses per year. Star formation efficiency reaches approximately 90% within the disk after about 11 kyr, versus roughly 50% within a 0.1 pc sphere. The simulated IMF is top-heavy, with high-mass slope α ≈ 1. Envelope feeding sets the disk's boundary conditions, while disk spreading shifts fragmentation sites outward from about 500 to 1,350 AU before depletion. These are simulation outcomes, not observations or a determination of the population's later evolution.

PublicA computer simulation explores how the universe's first generation of stars could form from primordial gas. The gas collapses into a disk whose spiral arms break into many star-forming fragments. By the calculation's end, 15,000 years after the first star forms, the simulated stars together contain more than 150 times the Sun's mass. Their combined mass grows increasingly quickly, consistent with a theoretical prediction for collapsing, turbulent gas. The simulated population favors massive stars. Magnetic energy rises substantially but remains a secondary part of the disk's energy throughout. Gas arriving from the surroundings feeds the disk, which spreads as its fragmentation sites move outward. About 90% of the mass within the disk becomes stellar mass, compared with roughly 50% within a larger surrounding region. These findings describe one simulated early star-forming system, not direct observations or its ultimate fate.

Young explorerScientists used a computer to imagine how some of the very first stars might have formed. In their model, gas made a spinning disk with curly arms. The arms broke into pieces where stars could grow. Gas kept coming in, and the stars grew faster over time. This was a computer experiment, not stars that scientists watched being born.

Jeans Dynamical Constraints on the IMF in Massive Quiescent Galaxies at z∼0.7 from JWST/NIRSpec

Martje Slob, Mariska Kriek, Chloe M. Cheng+19 more

AstronomerThe JWST-IMFERNO study derives dynamical masses for nine massive quiescent galaxies at z~0.7 using approximately 32-hour spatially resolved NIRSpec/MSA spectroscopy and NIRCam imaging. Jeans Anisotropic Modelling is incorporated into a forward model accounting for instrumental optics, source morphology, and geometric effects. The authors test whether stellar masses inferred from previously measured, dwarf-sensitive IMF constraints agree with the dynamical masses. A Milky Way IMF gives physically plausible dynamical-to-stellar mass ratios, but requires a dark matter fraction within one effective radius of 0.54 ± 0.06, approximately twice that in local early-type galaxies and simulations. Applying the absorption-feature-derived IMF uniformly gives a mean dark matter fraction of 0.02 ± 0.18; stellar masses exceed dynamical masses at 2σ significance in two of the seven galaxies in that comparison. Applying the measured IMF only within one effective radius and a Milky Way IMF outside yields consistent dynamical masses and a dark matter fraction of 0.28 ± 0.12. These model-dependent comparisons support, rather than uniquely establish, bottom-heavy cores in the most massive quiescent galaxies at z~0.7. They are consistent with subsequent inside-out growth through minor mergers after quenching, largely preserving those cores.

PublicResearchers used deep James Webb Space Telescope observations to estimate the masses of nine massive galaxies at redshift about 0.7 that are no longer actively forming stars. They compared masses inferred from stellar motions with estimates based on the galaxies’ stars. Earlier measurements suggested that the most massive galaxies formed an unusually large proportion of low-mass stars. Assuming that this mix applies throughout each galaxy creates tension: in two of seven galaxies tested, the estimated stellar mass exceeds the total mass inferred from motions at a significance of two standard deviations. Assuming a Milky Way-like mix instead requires about twice the central dark matter fraction found in nearby early-type galaxies and simulations. A model with more low-mass stars in the centers and a Milky Way-like mix farther out gives a more consistent mass balance. The findings support, but do not prove, a picture in which these galaxies later grew mainly around their edges by merging with smaller galaxies while largely preserving their centers.

Young explorerScientists watched how stars move in nine big galaxies to help work out how heavy the galaxies are. They compared this with estimates from the stars themselves. Their models fit better when the biggest galaxies have extra small stars in their middles, but a different mix farther out. This supports an idea that the galaxies grew by adding smaller galaxies around their edges while keeping their middles mostly unchanged. It does not prove that story.

Digging into the Interior of Hot Cores with ALMA (DIHCA). VIII. Feeding a high-mass binary system in the making

Fernando A. Olguin, Yoko Oya, Patricio Sanhueza+9 more

• Solar and Stellar Astrophysics

AstronomerALMA observations at 1.33 mm resolve gas kinematics in the likely proto-binary NGC 6334I(N) ALMAe9–ALMAe14 at 66 mas (about 90 au); the sources are separated by 740 au. Lower-excitation CH3OH lines reveal ordered circumbinary gas motion within roughly 1000 au and rotation around both sources, with approximately aligned rotation axes. The estimated secondary mass is 2 solar masses, uncorrected for inclination; a primary mass of 5 solar masses comes from previous work. Higher-excitation CH3OH lines trace circumstellar rotation around ALMAe9 consistent with the lower-excitation tracers. Vibrationally excited SO also traces rotation around ALMAe9 and may trace an accretion shock associated with a flow feeding ALMAe14's disk. CH3OH emission identifies two candidate inflows from the circumbinary gas toward the circumstellar disks, with estimated rates of about 10^-6–10^-4 solar masses per year. A third apparent inflow may feed the primary from larger scales.

PublicALMA observations reveal organized gas motion around two young stellar sources that likely form a binary system, including at least one growing high-mass star. The sources are about 740 times the Earth–Sun distance apart. Gas moves around the pair and rotates around each source, with the rotation axes pointing roughly in the same direction. Different molecular emissions provide consistent evidence for rotation around one source. The researchers also identify two possible streams carrying gas from the surrounding reservoir toward the individual disks, and a possible third stream feeding the primary from farther away. One emission feature may mark a shock where incoming gas meets a disk, but that interpretation remains uncertain.

Young explorerAstronomers looked at two young stars that probably make a pair. They saw gas swirling around each star and moving around the pair. They also found what might be streams bringing more gas to the stars' disks. That gas could help the stars grow, but the scientists are still checking what the streams are doing.

TRGB Distances to the Andromeda Dwarf Satellites from the INT Monitoring Survey

Hedieh Abdollahi

AstronomerThe authors measure TRGB distances for 17 M31 dwarf satellites using Sloan i-band photometry from the INT monitoring survey, supplementing these with earlier survey distances for And I, And VII and And IX. A Sobel filter identifies the TRGB in luminosity functions within two half-light radii. Distance moduli span 23.38 ± 0.06 mag for And XVI (474 kpc) to 25.35 ± 0.06 mag for And XVIII (1177 kpc); 15 of the 20 systems lie at 650–850 kpc. Most distances agree with at least one published estimate. Relative to Conn et al. (2012), the measured tips are brighter for 12 of 18 shared galaxies, by up to 0.39 mag, possibly owing to central crowding. And XII's distance of 844 (+40/−38) kpc places it about 60 kpc behind M31, consistent with first infall into the Local Group. And XXII is at 753 (+28/−27) kpc, closer than all earlier estimates; its approximately 59 kpc three-dimensional separation from M33, assuming an M33 distance of 794 kpc, is consistent with an association. And XVIII lies about 400 kpc behind M31, precluding a secure M31 association.

PublicResearchers measured distances to 17 small galaxies considered satellites of the Andromeda galaxy, M31, and combined them with three earlier measurements. They used a brightness feature in red giant stars as a distance marker. The 20 galaxies range from 474 to 1177 kiloparsecs away, with 15 between 650 and 850 kiloparsecs. Most measurements agree with at least one earlier study, although differences from one comparison study may reflect stars being crowded together near galaxy centers. The new distances also help assess which galaxies may belong together. And XII lies about 60 kiloparsecs behind Andromeda, consistent with entering the Local Group for the first time, though this is not established by the distance alone. And XXII is closer than previously estimated and may be associated with M33: its calculated separation from M33 is about 59 kiloparsecs, assuming M33 is 794 kiloparsecs away. And XVIII lies about 400 kiloparsecs behind Andromeda, too far away for a secure association.

Young explorerAstronomers looked at red giant stars to work out how far away some small galaxies are. They measured 17 galaxies and added earlier measurements for three more. Most were at similar distances from us, but some were much closer or farther away. These measurements help astronomers check which galaxies might be neighbors. One small galaxy might belong with a galaxy called M33. Another is so far behind the big Andromeda galaxy that astronomers cannot be sure they belong together.

KCWI Observations of Type 2 Quasar-driven Ionized Outflows at z 0.1

Alison L. Coil, Saloni Agrawal, David S. N. Rupke+5 more

AstronomerKCWI integral field spectroscopy of seven z<0.1 quasars—six Type 2 AGN and one narrow-line Type 1 AGN—reveals more extended warm ionized outflows than previously known in these sources and additional high-velocity kinematic components. The study reports a 50–70% incidence of multiple outflows on 4–10 kpc scales. Trends among extent, kinematics, and ionized mass and energy outflow rates imply that faster, often smaller outflows carry higher mass and energy outflow rates than slower, larger outflows. The ionized outflows reach the known extent of narrow-line ionized emission, which depends weakly on AGN luminosity. These observations characterize the warm ionized phase rather than the full multiphase outflow.

PublicObservations of seven nearby quasars—galaxies with exceptionally bright active centers—reveal outflowing ionized gas extending farther than previously recognized in these objects, along with additional fast-moving components. Using the Keck Cosmic Web Imager, the researchers report multiple outflows in 50–70% of the sample, on scales of 4–10 kiloparsecs. Their analysis indicates that faster outflows, often smaller in extent, carry gas and energy outward at higher rates than slower, larger ones. The outflows reach as far as the known region of narrow-line emission from ionized gas. The study examines one phase of these complex flows; it does not establish their full impact on star formation.

Young explorerSome galaxies have very bright centers that push gas outward. Scientists looked at seven of them with a telescope instrument and found moving gas farther out than people had seen there before. They also spotted extra fast-moving streams. Their study suggests that faster streams, even when they do not reach as far, carry more gas and energy outward each moment than slower streams. They looked at just one kind of gas, so this is only part of the story.

Predicting Continuum Emission in Massive Star-Forming Regions with Embedded HII Regions - Dust, Free-Free, and Anomalous Microwave Emission with POLARIS

Stefan Reissl, Alessio Traficante, Paolo Suin+3 more

• Solar and Stellar Astrophysics

AstronomerThis simulation study follows continuum emission as an HII region expands in a 10^4-solar-mass cloud, using RAMSES radiation-magnetohydrodynamical simulations post-processed with POLARIS. Six snapshots spanning 1–10^4 GHz include thermal dust, free-free emission, and anomalous microwave emission (AME), with grain charging, rotational processes, radiative torques, and rotational disruption modeled. The simulated ionized region evolves from compact and optically thick to extended and optically thin; around 15 GHz, the free-free spectrum changes from a ν² to a ν^−0.1 regime and increasingly traces electron column density. The thermal dust peak shifts from mid- to far-infrared as colder material contributes, while dust emission remains strongly correlated with total gas column density. Modeled AME peaks at 26–37 GHz, with correlations with gas and electron distributions that depend on spatial scale. Rotational disruption is the dominant modeled dust-destruction mechanism affecting mid-infrared emission and the high-frequency AME tail. These simulation results support complementary, scale-dependent continuum diagnostics of stellar feedback and emphasize self-consistent multi-frequency interpretation; they are not reported observational measurements.

PublicThe researchers used computer simulations to explore how radiation from massive stars changes a surrounding cloud and its emitted light as a region of ionized gas expands. They modeled emission from dust, ionized gas, and tiny grains across a wide range of frequencies. In the simulations, the ionized region grows from a compact structure that strongly absorbs its own radio emission into a more extended, transparent one. Its radio emission then more closely traces the amount of electrons along the line of sight. Cooler dust contributes increasingly, shifting the dust-emission peak to longer infrared wavelengths. An additional microwave component peaks at 26–37 GHz, but how closely it follows the gas depends on the size of the structures examined. The model identifies grains breaking apart through rapid rotation as the main dust-destruction process affecting some infrared and microwave emission. These are modeled findings, not observations, and suggest that several kinds of emission must be interpreted together to understand how massive stars reshape their surroundings.

Young explorerBig stars shine on the clouds around them and change them. Scientists made a computer model to see how a growing bubble of gas and its dusty cloud might glow. In the model, the bubble spreads out, and cooler dust adds more of its glow. Tiny dust grains can also spin so fast that they break apart. Different kinds of light tell different parts of the cloud’s story. These are things that happened in the computer model, not things the scientists watched happen in a real cloud.

Identifying Chemically Coherent Stellar Families in the Galactic High-α Disk with Low-Resolution Spectroscopy

Tianmin Wu, Maosheng Xiang, Jianrong Shi+2 more

• Solar and Stellar Astrophysics

AstronomerThe study applies DBSCAN to 18 elemental abundances derived from LAMOST low-resolution spectra (R~1800) for 87,275 red giants in the Galactic high-alpha disk. Comparisons with clustering of high-resolution survey abundances and mock catalogs suggest that coherence across elements can support chemical-family identification despite substantial uncertainties in individual low-resolution abundances. Scanning DBSCAN parameters and merging the resulting groups yields 133 candidate chemical families comprising 4,642 unique stars, or 5.3% of the sample. Their multi-element patterns differ, particularly in neutron-capture elements at nearly identical [Fe/H]. These candidate families may trace similar enrichment histories, not necessarily common birth environments, and offer constraints on chemical-enrichment diversity and high-alpha disk assembly.

PublicResearchers searched for groups of chemically similar stars among 87,275 red giants in a chemically defined part of the Milky Way’s disk called the high-alpha disk. They used measurements of 18 elements from low-resolution spectra, which separate starlight into relatively coarse detail. Although individual element measurements have sizable uncertainties, comparisons with higher-resolution survey measurements and simulated catalogs suggest that the combined chemical patterns can still reveal meaningful groups. The analysis identified 133 candidate chemical families containing 4,642 stars, about 5.3% of the sample. Some families have nearly the same iron abundance but notably different amounts of elements associated with neutron capture. These patterns could help researchers understand the disk’s chemical and assembly history, but chemically similar stars did not necessarily form together.

Young explorerScientists looked at the chemical ingredients in lots of stars in part of our Milky Way. They found 133 possible groups whose stars have similar mixes of ingredients. Some groups had almost the same amount of iron but different amounts of other ingredients. The measurements were not perfect, so the scientists checked their method against more detailed measurements and make-believe star catalogs. The groups might help tell the story of how that part of our galaxy came together. But having similar ingredients does not mean the stars were born in the same place.

Phosphorus-rich star formation in giant molecular clouds hosting primordial globular clusters

Kenji Bekki, Takuji Tsujimoto

• Solar and Stellar Astrophysics

AstronomerObservations have identified P-rich stars ([P/Fe] > 1.0) in the Galactic field and in globular clusters, including three confirmed cluster cases. This study uses analytical globular-cluster formation models to explore whether oxygen-neon nova ejecta polluting otherwise pristine gas in cluster-forming giant molecular clouds could produce these stars. Across varied nova yields and dilution factors, defined as pristine gas mass divided by total nova ejecta mass, most models show positive correlations among [P/Fe], [N/Fe], [O/Fe], [Al/Fe], [Si/Fe], [S/Fe], and [Si/S]. Additional pollution by interacting low-mass asymptotic giant branch stars can raise [Ce/Fe] to 1. The scenario makes P-rich star formation highly unlikely where cloud–nova interactions are infrequent and predicts anomalously low 14N/15N, 16O/17O, and 16O/18O ratios as observational tests. The discussion of field-star abundances assumes a globular-cluster origin. The authors interpret P-rich stars as evidence of pollution by pre-existing stellar populations; that interpretation remains distinct from the observed abundance anomaly.

PublicAstronomers have found stars unusually rich in phosphorus both inside globular star clusters and elsewhere in our Galaxy. This study explores a possible explanation using analytical models: material expelled by oxygen-neon novae could have mixed into gas clouds before those clouds formed clusters and their stars. Most models link phosphorus enrichment with increases in several other chemical abundance ratios. Explaining elevated cerium requires an additional contribution from certain aging stars. The models also predict unusual proportions of nitrogen and oxygen isotopes, which future observations could use to test the idea. The proposed explanation is not established by these calculations, and the discussion of stars outside clusters assumes they originally formed in clusters.

Young explorerSome stars have much more phosphorus than usual. Scientists used math models to explore how that might happen. Their idea is that blasts called novae sprinkled material into big gas clouds before new stars formed there. The models suggest those stars should have a special mix of different kinds of nitrogen and oxygen atoms. Looking for that mix could help scientists check whether the idea is right.

SEDust: A DUSTY-Based SED-Fitting Pipeline for Dust and Mass-Loss from AGB and LPV Stars

Hamidreza Mahani, Narges Rostami, Atefeh Javadi+4 more

AstronomerThe authors present SEDust, an automated pipeline for spectral energy distribution fitting and estimation of stellar mass-loss and dust-production rates, and apply it to NGC 6822, focusing on long-period variables and pulsating asymptotic giant branch (AGB) stars. They infer a total stellar mass-loss rate of (3.70 ± 1.16) × 10^-3 solar masses per year. An LPV-based method gives a total about 2.3 times lower, while DESK gives one about 2.4 times higher; the authors adopt these differences as an estimate of method-dependent systematic uncertainty. They report a positive correlation among luminosity, intrinsic reddening from circumstellar dust self-extinction, and mass-loss rate. The inferred AGB specific mass-return rate is (7.40 ± 2.30) × 10^-11 per year. The authors conclude that AGB mass return alone cannot sustain the galaxy’s current star formation rate, implying a need for external gas accretion or additional mass-return mechanisms.

PublicThe researchers developed SEDust, an automated tool that uses stars’ light across different wavelengths to estimate how much material and dust they shed. Applied to the dwarf galaxy NGC 6822, it estimates that stars lose a total of about 0.0037 solar masses each year, with a quoted uncertainty of about 0.0012. The choice of method matters substantially: two alternatives give totals about 2.3 times lower and 2.4 times higher. The study also finds that brighter stars, stronger reddening by dust around the stars, and greater material loss are positively linked. The estimated material returned by aging stars called AGB stars is not enough on its own to maintain the galaxy’s current pace of star formation. The authors interpret this as a need for gas arriving from outside the galaxy or other sources of returned material.

Young explorerSome old stars shed material and make dust around themselves. Scientists made a computer tool to estimate how much they shed in a galaxy called NGC 6822. Different tools gave different answers, so the amount is uncertain. The scientists found that one kind of old star does not give back enough material to keep making new stars as fast as the galaxy does now. They think more gas must come from outside the galaxy, or more material must come from other sources.

The N/O-O/H relation across large-scale environments

Yllari K. González-Koda, Almudena Zurita, Laura Sánchez-Menguiano+7 more

AstronomerUsing central SDSS emission-line spectra from a local galaxy sample curated within CAVITY, the study compares the gas-phase N/O–O/H relation across clusters, voids, and non-cluster/non-void (NCNV) environments. Residuals about the main relation are best predicted by stellar-mass-related variables, with little influence from recent star formation history. Void and NCNV galaxies show no significant differences, whereas cluster galaxies have a systematically lower relation, with N/O residuals of approximately −0.02. Cluster galaxies also differ in their mass–metallicity and N/O–stellar-mass relations. The authors interpret these combined offsets as evidence favoring processes associated with the dense intracluster medium, including strangulation or re-accretion of metal-enriched gas; the observations do not establish which mechanism is responsible.

PublicThis study asks whether a galaxy’s place in the Universe’s large-scale web affects the chemistry of its gas. Using spectra from the central regions of nearby galaxies, the researchers compared nitrogen relative to oxygen at a given oxygen abundance. Galaxies in sparsely populated voids showed no significant difference from those outside both voids and clusters. Cluster galaxies, however, had a slightly lower nitrogen-to-oxygen relation and also differed in how their chemical abundances relate to stellar mass. Across the sample, stellar-mass-related properties were better predictors of deviations from the main chemical relation than recent star formation history. The authors suggest that the dense cluster surroundings alter galaxies’ gas supply or allow enriched gas to return, but these mechanisms remain interpretations rather than demonstrated causes.

Young explorerGalaxies have stars and gas, and their gas contains ingredients called nitrogen and oxygen. Scientists looked at light from the middles of galaxies to compare those ingredients. Galaxies in crowded clusters had a slightly different mix from the others. Galaxies in very empty places looked much like galaxies in places that were neither empty nor crowded into clusters. The scientists think crowded surroundings might change the gas a galaxy gets, but they have not shown exactly why the mix is different.

Where the red rise stops: JWST/MIRI reveals a near-infrared turnover in the Little Red Dot Abell2744-QSO1

E. Iani, P. Rinaldi, A. Torralba+9 more

AstronomerJWST/MIRI F770W and F1000W imaging probes rest-frame 0.96 and 1.24 micrometres in the triply lensed Little Red Dot Abell2744-QSO1 at z=7.04. The source is unresolved, and its steep optical continuum turns over near 1 micrometre. Through 1.24 micrometres, the continuum is consistent with a roughly 4450 K blackbody or a hotter, dust-reddened one, with no sign of the hot dust typical of most type-1 quasars. Statistically preferred stellar SED fits require (3–4) × 10^9 solar masses, exceeding the dynamical host-mass limit by more than a factor of 100 and thus disfavouring that interpretation. A dense-gas-cocoon accretion-disc model respects the mass limit but overpredicts the 1.24-micrometre flux by 5 sigma. Super-Eddington models with a thermalising envelope reproduce the turnover only with a black hole about 2.5 dex less massive than the dynamical estimate. For a dust-reddened disc with A_V about 2 magnitudes, roughly 1200 K dust can reradiate at most about 2% of the absorbed luminosity; most must emerge from dust at roughly 70–600 K unless the covering fraction is small. Dynamics favour accretion power, but the observations do not distinguish dust reddening from dense-gas processing. MIRI imaging beyond 18 micrometres could discriminate between these scenarios.

PublicNew James Webb Space Telescope infrared images examine Abell2744-QSO1, a distant compact source in the class known as Little Red Dots. Gravitational lensing produces three images of this source. Its light rises steeply toward redder optical wavelengths, but the new observations show that this rise stops near a rest-frame wavelength of 1 micrometre. The measurements show no sign of the hot dust found in most unobscured quasars. Several explanations remain problematic: the best statistical fits using stars require far more stellar mass than the source's dynamics allow, while tested models involving a black hole surrounded by dense gas either predict too much infrared light or require a much smaller black hole than the dynamical estimate. A dust-reddened black-hole model would generally need most absorbed light to be released by cooler dust, unless the dust surrounds only a small part of the source. The dynamics favour light powered by matter falling toward a black hole, but the data cannot tell whether dust or dense gas shapes its red appearance. Observations at longer infrared wavelengths could help resolve that uncertainty.

Young explorerAstronomers used the James Webb Space Telescope to study a tiny-looking red dot far away. They found that its light stops getting stronger as they look farther past red into invisible infrared light. They think the dot is probably powered by stuff falling toward a black hole, rather than just by stars. But they still do not know whether dust or thick gas changes the light to make it look red. The ideas they tested do not explain all the clues comfortably. Looking at another kind of infrared light could help solve the puzzle.

Violent relaxation redux

Michael L. Nastac, Yonadav Barry Ginat, Robert J. Ewart+2 more

• Cosmology and Nongalactic Astrophysics
• Statistical Mechanics
• Chaotic Dynamics
• Plasma Physics

AstronomerThe authors propose that gravitational turbulence reconciles collisionless violent relaxation with Lynden-Bell maximum-entropy equilibria. They derive universal sub-Jeans turbulence spectra and find that turbulent phase-space mixing breaks phase-space-volume conservation on a timescale only logarithmically longer in particle number N than the dynamical time. This separation allows an approximately adiabatic sequence of Lynden-Bell equilibria constrained by evolving Casimir invariants. Their theory predicts a long-time state near a ground-state distribution, whose adjusted Casimirs make the system’s energy its minimum possible energy: a minimum-energy, maximum-entropy state. One-dimensional N-body simulations corroborate this picture, but its ability to explain universal equilibria of galaxies and dark-matter halos remains a hypothesis.

PublicThis study proposes an explanation for how systems such as merging galaxies settle into stable arrangements under their own gravity. Large-scale changes in gravity could stir particles into complicated motions, producing what the authors call gravitational turbulence. Their calculations suggest that constraints on how the particles can be rearranged gradually change, allowing the system to pass through a succession of maximum-entropy states. Eventually, it should approach a state that combines maximum entropy with the lowest energy allowed by its adjusted constraints. Simulations with particles moving in one dimension support this picture. Whether it explains the common final arrangements of galaxies and dark-matter halos remains a hypothesis, not an observational finding.

Young explorerHow does a galaxy settle down after being stirred up? The scientists suggest that changing gravity mixes its moving pieces around. As the rules limiting that mixing slowly change, the pieces may settle into a special resting pattern, even though they keep moving. A simple computer model supports their idea, but they have not shown that it explains real galaxies.

The AIDA-TNG project: Galactic bar pattern speeds in self-interacting dark matter

Asiyeh Habibi, Mahmood Roshan, Giulia Despali+3 more

AstronomerThe study tests whether dark matter self-interactions alleviate the fast-bar tension: CDM simulations predict larger corotation-to-bar-radius ratios, R = Rcr/Rbar, than inferred for local galaxies. Using the 51.7 Mpc AIDA-TNG volume, the authors compare CDM with constant-cross-section SIDM1 and velocity-dependent vSIDM for barred disks with stellar masses above 10^10 solar masses at z = 0.2, 1.0, 1.5, and 2.0. Both SIDM models generally yield lower bar pattern speeds than CDM at nearly all sampled redshifts and roughly 10% more effective subsequent slowdown. The authors suggest velocity anisotropy as the likely explanation for the enhanced slowdown. At low redshift, both SIDM models have significantly larger mean R, exacerbating rather than alleviating the tension in these scenarios.

PublicElongated structures of stars called bars rotate within some galaxies. Standard dark matter simulations predict bars that are too slow by a commonly used measure compared with observations of nearby galaxies. This study asks whether allowing dark matter particles to interact with one another could improve the agreement. In cosmological simulations comparing two such models with standard cold dark matter, the bars generally rotated more slowly and experienced roughly 10% more effective slowdown. At low redshift, the simulated mismatch with observations became larger, not smaller. The authors suggest that differences in how dark matter moves in different directions may explain the extra slowdown, but this mechanism remains an interpretation. The conclusion applies to the two self-interacting dark matter models tested.

Young explorerSome galaxies have a long bar of stars that turns around. Scientists made computer versions of galaxies to see whether letting dark matter particles interact with each other would make the bars turn more like the ones astronomers see. In the two kinds they tried, the bars usually turned more slowly instead. That made the computer galaxies match the real ones less well by the measure the scientists used. This happened in their simulations; it does not mean every kind of interacting dark matter would do the same thing.

Multi-phase Carbon Structure and Dynamics in NGC 6334: Insights from CO, [C I], and [C II]

S. Neupane, F. Wyrowski, N. Schneider+9 more

• Solar and Stellar Astrophysics

AstronomerHigh-angular- and velocity-resolution observations of [CII] 158 micron, [CI] 609 micron, and 12CO and 13CO J=3–2 map carbon phases in the central region of NGC 6334. [CII] is the most extended and kinematically complex tracer, whereas 13CO is compact and relatively quiescent; [CI] and 12CO occupy intermediate regimes. The authors interpret bright [CII] near H II bubbles along the central filament as photodissociation-region (PDR) emission, with extended [CII] tracing diffuse warm gas potentially involved in cloud formation or dispersal. Systematically high [CII]/[CI] and [CII]/CO ratios indicate widespread diffuse emission and localized UV-illuminated surfaces. Line-ratio analysis and K-means clustering using [CI]/13CO and 870- and 70-micron dust emission reveal chemical stratification and suggest deep UV penetration into the clumpy ridge, to Av approximately 18, consistent with a porous PDR. The overall interpretation is a clumpy, feedback-dominated PDR ridge with coexisting carbon phases. Multiple velocity components in [CI] and [CII] are interpreted as signatures of dynamical processing, potentially involving colliding flows or cloud-cloud collisions, rather than establishing a unique dynamical origin.

PublicObservations of the star-forming region NGC 6334 show that carbon in different forms traces different parts of its gas clouds. Electrically charged carbon produces the most widespread emission and reveals complex gas motions. Emission from one form of carbon monoxide is more concentrated and shows quieter motions, while neutral carbon and another form of carbon monoxide fall between these extremes. The researchers interpret the pattern as a clumpy ridge whose surfaces and deeper layers are exposed to ultraviolet light. Their analysis suggests that gaps in the ridge allow this light to penetrate deeply. Some gas motions may reflect colliding clouds or converging flows, while the widespread warm gas could be involved in either cloud formation or dispersal; these explanations are interpretations, not uniquely established causes.

Young explorerAstronomers looked at a place where stars are forming. They watched light from carbon, a kind of building block in the gas. Some gas spreads far out and moves in complicated ways; other gas stays in smaller, calmer patches. Starlight may shine through gaps in the clouds, and some clouds might be bumping together.

SN 2026ahvu in NGC 1433 May Be a Prompt Type Ia Supernova with a Delay Time Under 100 Myr

Sumit K. Sarbadhicary, Kiana Henny, Adam Leroy+30 more

• Solar and Stellar Astrophysics

AstronomerArchival PHANGS HST and JWST imaging places the Type Ia SN 2026ahvu in NGC 1433 at angular separations of 0.19 and 0.26 arcsec from two UV-bright clusters. These correspond to projected separations of 8 and 11 pc at 9.1 Mpc, or 17 and 24 pc at 18.9 Mpc. The estimated chance-alignment probability for an unrelated Type Ia SN near a cataloged cluster is approximately 0.4%, supporting—but not establishing—a physical association. HST+JWST SED fits yield cluster ages of 37 (+3/−5) and 95 (+15/−13) Myr; HST-only fits give 57 (+14/−9) and 88 (+14/−12) Myr. If either association is real, the cluster age would constrain a prompt SN Ia delay time. Association with the younger cluster would imply an explosion almost immediately after white dwarf formation; the older-cluster interpretation also has a central delay-time estimate below 100 Myr, although its age uncertainty extends above that threshold. The authors interpret this as likely the first Type Ia SN associated with relatively young clusters in a nearby galaxy.

PublicA Type Ia supernova called SN 2026ahvu exploded very close on the sky to two young star clusters in the nearby galaxy NGC 1433. Archival Hubble and James Webb images reveal this proximity, and the researchers estimate that an unrelated Type Ia supernova would have only about a 0.4% chance of appearing so close to a cataloged cluster. That makes a connection likely, but not certain. Depending on the images used to estimate their ages, the younger cluster is about 37–57 million years old and the older one about 88–95 million years old, with uncertainties. If the exploding star belonged to either cluster, its age would provide unusually direct evidence for how quickly some Type Ia supernovae occur. A connection to the younger cluster would suggest an explosion almost immediately after the star became a white dwarf. The key uncertainty is whether the supernova truly belonged to either cluster.

Young explorerAstronomers found a star explosion that looks very close to two groups of young stars. It might have come from one of those groups, but they are not sure. If it did, the group's age could help tell them how quickly this kind of star explosion can happen. If it came from the younger group, it would mean the star exploded very soon after becoming a small star called a white dwarf.

Correcting for the effects of the point spread function in intra-halo light measurements and application to deep Hyper Suprime-Cam data

L. P. Garate-Nuñez, A. S. G. Robotham, S. Bellstedt+1 more

AstronomerThe authors present a correction for telescope PSF scattering to improve measurements of diffuse intra-halo light (IHL), fitting an exponential IHL component with an MCMC optimiser. They test the method on 5,440 mock observations of GAMA groups constructed using HSC-SSP PDR3 data, with input IHL flux fractions of 0.01–0.5. In these tests, uncorrected PSF scattering overestimates IHL effective radii and biases fluxes, especially at low IHL fractions; flux corrections are needed for fractions below 0.4. The correction brings recovered fluxes and radii closer to their input values, rather than establishing perfect recovery. Applied to real HSC-PDR3 UD observations of the GAMA group G400138, the method yields median IHL fractions of approximately 0.19 (+0.09/−0.01), 0.08 (+0.06/−0.02), and 0.06 (+0.04/−0.02) in g, r, and i, respectively.

PublicA faint glow of stars surrounds galaxies and galaxy groups, potentially revealing how these systems assembled. Measuring this intra-halo light is difficult because telescopes also scatter light into a diffuse glow. The researchers developed a correction and tested it on 5,440 simulated observations with known amounts of intra-halo light. Without correction, the glow appeared too extended and, especially when its contribution was small, too bright. The correction brought the measurements closer to the simulated inputs. The team also applied the method to real images of one galaxy group, G400138. They estimated that intra-halo light contributes about 19% of the light in the g filter, 8% in r, and 6% in i, with reported uncertainties of +9/−1, +6/−2, and +4/−2 percentage points, respectively.

Young explorerSome stars make a very faint glow around groups of galaxies. But a telescope can spread light around too, making that glow look bigger and brighter than it really is. The scientists made a way to correct for this. They tried it on pretend pictures where they already knew how much glow there should be, and it helped them get closer to the right answer. Then they used it to estimate the faint glow in real pictures of one galaxy group. Those estimates still have some uncertainty.

The Baryon Budget of Galaxies across the First Billion Years

Umberto Maio, Céline Péroux

• Cosmology and Nongalactic Astrophysics
• Solar and Stellar Astrophysics
• Space Physics

AstronomerUsing ColdSIM hydrodynamical simulations with time-dependent non-equilibrium chemistry, the authors inventory baryons in cold, warm, hot, and stellar phases within galaxies and their circumgalactic gas, and in the diffuse intergalactic medium. The simulations predict predominantly cold cosmic gas before reionisation, followed by warm-phase dominance attributed to increased star formation and ultraviolet reionising radiation. Stellar return fractions are approximately 0.15–0.20, about half the commonly adopted values. Gas-phase masses, including explicitly computed HI and H2, increase with host mass and star formation rate; depletion times decrease to 0.01–0.1 Gyr and depend only weakly on metallicity. Star formation efficiencies remain a few per cent, while gas-to-star fractions decline with mass, influenced by feedback and environment. The authors report consistency with later-epoch gas surveys; this is not a direct observational census of early galaxies. They discuss implications for stellar mass functions, Population III star formation, and IMF changes, and provide fitting functions for the simulated trends.

PublicThis study uses computer simulations, rather than a direct observational inventory, to track ordinary matter in early galaxies and the gas around and between them. In the simulations, most cosmic gas is cold before reionisation, when radiation changes the electrical state of intergalactic gas. Later, warm gas dominates, which the authors attribute to increased star formation and stronger ultraviolet radiation. More massive galaxies and those forming stars faster contain more gas. The simulated gas depletion times reach 10–100 million years, while star formation efficiencies remain only a few per cent. The simulations also indicate that stars return about 15–20% of their mass to gas, roughly half the fraction commonly assumed. The authors report agreement with gas surveys of later cosmic times, offering a comparison rather than direct confirmation of the early-universe predictions.

Young explorerThe researchers used a computer to make pretend young galaxies and follow their gas and stars. In their model, most gas starts out cold. Later, more of it becomes warm as stars form and bright ultraviolet light grows stronger. Bigger galaxies tend to hold more gas, but only a small share becomes stars. Some gas comes back out of stars, too. These are computer-model findings, and the researchers say they agree with some measurements from later in the universe’s life.

Estimation of the magnetic field strength from ALMA dust polarization in the protocluster G327.29

A. Koley, P. Sanhueza, A. M. Stutz+6 more

AstronomerHigh-resolution ALMA 12-metre observations of the high-mass star-forming region G327.29 reveal a complex plane-of-sky magnetic-field morphology, with orientations uniformly distributed from −90 to +90 degrees. The observed filament and central dense clump both contain multiple dense cores. For the filament and clump, respectively, DCF–ADF estimates of total field strength are 1.7 ± 0.8 and 3.6 ± 1.5 mG, at number densities of (1.5 ± 0.3) × 10^6 and (2.3 ± 0.7) × 10^6 cm^-3. The ST method gives approximately threefold lower strengths: 0.6 ± 0.3 and 1.1 ± 0.5 mG. Virial parameters of 2.8 ± 1.9 and 0.5 ± 0.4 leave gravitational binding uncertain when errors are considered. Inferred turbulent-to-magnetic energy ratios of approximately 0.17–0.34 indicate greater dynamical importance for magnetic fields than turbulence. Their relative influence on core dynamics nevertheless appears to depend on the field-strength–density scaling in the densest gas.

PublicALMA observations have mapped a complicated magnetic-field pattern in G327.29, a region where massive stars form. The observed area contains a filament and a dense central clump, each holding several dense cores. The researchers estimate that magnetic fields are more important dynamically than turbulent gas motions, although two methods give field strengths differing by about a factor of three. Uncertainties also leave open whether gravity binds the regions. The study suggests that the balance between magnetic fields and turbulence in the dense cores depends on how field strength changes as gas becomes denser; their exact roles in star formation remain uncertain.

Young explorerAstronomers looked at a big cloud of gas where stars are forming. They found a tangled pattern of invisible magnetic fields. Their study suggests these fields matter more than the gas’s swirling motions for how the cloud moves. But the measurements are uncertain, and scientists are still learning how magnetism, swirling gas, and gravity work together to help stars form.

Spatially resolved optical and mid-infrared spectroscopy of SDSS1335+0728: implications for the origin of the Ansky event

P. Sánchez-Sáez, M. Masterson, L. Hernández-García+25 more

AstronomerSpatially resolved VLT/MUSE and JWST MIRI/MRS spectroscopy constrains the accretion history of SDSS1335+0728, host of the December 2019 Ansky brightening and extreme X-ray quasi-periodic eruptions (QPEs). Two counter-rotating stellar components and cold gas with velocity dispersion ≲60 km/s are consistent with a past minor merger. An old stellar population dominates, with ongoing star formation confined to an intermediate-radius ring. Ionisation diagnostics distinguish an accretion-powered nucleus containing most of the high-ionisation coronal emission, the star-forming ring, and a LINER-like outer region. Balmer-line light echoes imply a minimum ionising luminosity of log10(Lion,min/[erg/s]) ≈40.5 at projected distances beyond the reach of radiation from Ansky, suggesting pre-2019 nuclear activity. Strong 9.7 and 18 micrometre silicate emission indicates directly illuminated dust with low effective mid-infrared optical depth; the 9.7 micrometre strength is at the high end for AGN and closer to MIR-selected tidal disruption events. The data allow either a pre-existing low-luminosity AGN or a long-lived tidal-disruption remnant disc. Both interpretations place the slow, faint Ansky transient around an approximately million-solar-mass black hole already accreting before 2019, offering an alternative to a faded-AGN interpretation without settling the QPE origin.

PublicThe galaxy SDSS1335+0728 suddenly brightened in December 2019 in an event called Ansky and hosts extreme, roughly repeating X-ray eruptions whose cause remains debated. Observations with the VLT and JWST suggest that material was already feeding its central black hole before the brightening. The key clue is glowing gas too far from the centre for radiation from Ansky to have reached it, pointing to earlier activity. The galaxy also contains two groups of stars rotating in opposite directions, consistent with a past merger with a smaller galaxy, and a ring where stars are forming. Strong infrared emission reveals directly illuminated dust. The earlier black-hole feeding could have come from a persistently weak active nucleus or a long-lived disc left by a tidal disruption event. Neither explanation is established, but both imply that Ansky occurred in a system already feeding its black hole, rather than beginning all its activity in 2019.

Young explorerA galaxy suddenly got brighter, and it also gives off big flashes of X-rays. Scientists found glowing gas that suggests its black hole was already eating nearby material before the brightening. They have two possible stories about where that food came from, but do not yet know which is right. They also still do not know what makes the X-ray flashes.

Set them free: extending RAMCOAL to model massive black hole triplets in hydrodynamical simulations of galaxies

Kunyang Li, Ricarda S. Beckmann, Yohan Dubois+1 more

AstronomerThis simulation-method study extends RAMCOAL from massive black hole binaries to triplets, modelling evolution below the resolution of hydrodynamical galaxy simulations. The binary prescription includes dynamical friction, stellar scattering, gas torques, circumbinary-disc coupling, and gravitational-wave emission. When a hierarchical triplet becomes chaotic, the model samples outcomes from direct N-body experiments, tracking mergers, exchanges, and ejections alongside accretion and spin evolution. Isolated-galaxy tests show that changing the orbital configuration alone can alter which pair merges and its coalescence time. The authors report the first evolution of a massive black hole triplet to coalescence within a hydrodynamical simulation of gas-rich galaxies. Subgrid integration takes less than 1 ms of single-core time per black hole system per time step, independently of particle resolution. These are simulation results, not observations; unresolved interactions are represented by prescriptions and sampled outcomes. The framework is a step towards merger catalogues connecting gravitational-wave signatures with host galaxies, with coalescence properties reflecting the environment experienced during subgrid evolution.

PublicRepeated galaxy mergers can bring three massive black holes together, but galaxy simulations cannot directly resolve all the small-scale interactions that determine their fate. The researchers extended a model called RAMCOAL to represent those interactions, using a library of detailed gravitational simulations when the three-body motion becomes chaotic. In simulated tests, changing the black holes’ orbital arrangement alone changed which two merged and how long they took to do so. The authors also report following a triplet to a merger within a simulation of gas-rich galaxies, while accounting for changes in the black holes and their galactic surroundings. These are computer-simulation findings, not observations of a real triplet. The model is a step towards predicting connections between gravitational waves from black hole mergers and the galaxies where those mergers occur.

Young explorerScientists made a computer model of three huge black holes moving around each other inside galaxies. In their pretend galaxies, changing how the black holes moved could change which two joined together and how long that took. This was a computer experiment, not something they watched happen in the sky. The model may help scientists understand black hole mergers better.

Gas-Phase Metallicity and Nitrogen Abundances in Low-Mass Galaxies Down to M(⋆)≃10(6.6)M(☉) at z≃4.5--9.8 from JWST Lensing Cluster Surveys

Hiroya Umeda, Masami Ouchi, Kimihiko Nakajima+7 more

AstronomerThe study analyzes 405 deep JWST/NIRSpec spectra of star-forming galaxies at z=4.5–9.8 from lensing-cluster surveys, probing stellar masses down to approximately 10^5.7 solar masses. Individual spectra and mass-binned stacks provide gas-phase metallicities and nitrogen and carbon abundances. New empirical strong-line calibrations, anchored to direct-method measurements in the stacks, extend the z≈6 mass–metallicity relation to approximately 10^6.6 solar masses, where 12+log(O/H)≈7.2. A two-parameter linear fit yields a slope of 0.318±0.037, slightly steeper than the local low-mass slope and broadly consistent with hydrodynamical simulations. In the approximately 10^7.7-solar-mass stack, N/O inferred from N IV] exceeds that inferred from [N II] by approximately 1.4 dex. This discrepancy could reflect a localized, highly ionized, nitrogen-rich component whose high N/O and subsolar C/O resemble nitrogen-rich globular-cluster populations. Together with He II λ4686/Hβ≈0.03, well above BPASS predictions, the abundance patterns suggest a possible contribution from Wolf–Rayet stars to both prompt CNO-cycle enrichment and hard ionizing radiation. The inferred Wolf–Rayet population could potentially supply the nitrogen excess on globular-cluster scales; this remains an interpretation rather than a demonstrated origin.

PublicUsing 405 JWST spectra, researchers studied the chemical makeup of distant star-forming galaxies, including very faint, low-mass systems. They developed new ways to estimate gas enrichment from spectral lines and traced how oxygen abundance increases with galaxy stellar mass around redshift 6. The measured trend is broadly consistent with computer simulations. One combined spectrum revealed a puzzle: ultraviolet and optical nitrogen lines implied markedly different nitrogen-to-oxygen ratios. The researchers suggest that the ultraviolet signal may come from a small, highly ionized region enriched in nitrogen, with chemical proportions resembling nitrogen-rich populations in globular star clusters. These abundance patterns and a helium-line signal stronger than model predictions point to Wolf–Rayet stars as possible sources of both nitrogen enrichment and energetic radiation. Their role is suggested by the evidence, not established.

Young explorerScientists used the James Webb Space Telescope to study light from faraway groups of stars called galaxies. The light gave clues about ingredients in their gas, like oxygen and nitrogen. Bigger galaxies tended to have more oxygen compared with hydrogen. When the scientists combined light from some galaxies, two kinds of nitrogen clues did not match. They think special stars might have added extra nitrogen to a small part of the gas, but they are not sure yet.

ASKAP discovery of a pair of large radio bubbles: on the origin of odd radio circles

Renzhi Su, Minfeng Gu, Hengxiao Guo+9 more

AstronomerASKAP EMU 944 MHz imaging reveals a serendipitously discovered, low-surface-brightness radio bubble centred on the elliptical galaxy LEDA 217397 at z=0.040. Its projected diameter is approximately 399 kpc, with two partly overlapping shells of approximately 114 kpc radius each. The integrated 944 MHz flux density is 56.8±2.9 mJy, implying a rest-frame 1.4 GHz luminosity of approximately 1.4×10^23 W Hz−1. Combined EMU and MWA GLEAM-X measurements yield a steep integrated spectral index of −1.04±0.04; a two-frequency map suggests, but does not establish, exterior flattening. SED fitting indicates a massive, quiescent host, with no mid-infrared AGN signature; no overdense environment is identified. Comparison with ORCs and large radio shells motivates several origin scenarios. A starburst wind is energetically disfavoured, while halo-scale merger shocks and spherical nuclear blast waves do not explain the regular double-shell geometry. The authors favour relic bubbles inflated by a bipolar AGN jet episode, possibly triggered by a supermassive-black-hole merger, with potential later shock re-energisation. This interpretation requires confirmation through deeper broad-band radio, polarimetric, spectroscopic and X-ray observations.

PublicAstronomers have discovered a large, faint radio-emitting bubble centred on the elliptical galaxy LEDA 217397. Radio images show two partly overlapping shells spanning about 399 kiloparsecs in projected diameter. The galaxy is massive but forms very few new stars, and it shows no mid-infrared signature of an active galactic nucleus. The bubble’s origin remains uncertain. The researchers argue that a wind powered by intense star formation would struggle to supply the required energy, while some shock scenarios cannot explain the unusually regular double-shell shape. Their preferred explanation is an old episode of jets from the galaxy’s central black hole. A merger of supermassive black holes is suggested as a possible trigger, not an observed event. Further observations are needed to test this explanation.

Young explorerAstronomers found a huge, faint shape around a galaxy using radio waves. It looks like two bubble shells overlapping. They think old jets from the galaxy’s central black hole may have blown the bubbles, but they do not know for sure. They need more observations to find out what happened.

Rapid Growth of Intermediate-Mass Black Holes through Disk-induced Stellar Disruptions

Mengye Wang, Yiqiu Ma, Qingwen Wu+3 more

• High Energy Astrophysical Phenomena

AstronomerDirect N-body simulations with analytic prescriptions for star–disk interactions examine disk-induced tidal disruption events (dTDEs) around intermediate-mass black holes in dense stellar clusters. The calculations follow cusp formation, capture through repeated disk crossings, orbital damping, inward migration, and stellar consumption, accounting for the coupled effects of relaxation, depletion, replenishment, and stellar mergers rather than relying on single-orbit migration estimates. The simulations find sustained stellar mass supply rates of approximately 10^-3 solar masses per year, exceeding the Eddington-limited gas accretion rate for black holes below 10^5 solar masses. This is a simulated stellar supply rate, not an observational measurement or a demonstration of equivalent black-hole mass growth. The authors identify dTDEs as an efficient feeding channel in gas-rich dense clusters and suggest that it could help approximately 10^3-solar-mass black holes become more massive seeds, provided compact clusters and accretion disks persist for more than 30 million years.

PublicComputer simulations explore how a gas disk around an intermediate-mass black hole could help supply it with stars. Stars repeatedly crossing the disk can lose orbital motion, become captured, and move inward until the black hole tears them apart. The study follows how this process changes the surrounding star cluster, including the loss and replacement of stars and collisions between them. In the simulations, disrupted stars can supply about 0.001 times the Sun’s mass each year—more than the Eddington-limited gas accretion rate for black holes lighter than 100,000 Suns. That supply does not by itself establish how quickly the black hole actually gains mass. The authors suggest this mechanism might help smaller black holes grow into more massive seeds, but only if the compact cluster and gas disk survive for more than 30 million years. These are simulation findings, not observations.

Young explorerScientists used computers to imagine stars moving around a black hole inside a crowded group of stars. A disk of gas can slow some stars down and guide them inward, where the black hole tears them apart. In the computer model, this keeps bringing in star material. It might help the black hole grow bigger, but the star group and gas disk would need to last a very long time.

ALMA Chemical Evolution (ACE) survey: the dust content of subsolar metallicity galaxies at cosmic noon

M. Solimano, I. Shivaei, G. Popping+11 more

AstronomerThe ACE survey probes dust in 25 star-forming galaxies at z≈2.3, with strong-line metallicities extending to ≈0.3 times solar. Dust masses inferred from 873 μm or 1.3 mm continuum assume an optically thin, single-temperature modified blackbody. Detected galaxies have a median dust mass of 6.4×10^7 solar masses: 4–9 times that of local galaxies matched in metallicity and stellar mass, but more than ten times below infrared-selected galaxies at z≈2. Dust mass correlates positively with stellar mass, metallicity, and SFR. Dust-to-stellar mass ratios scatter around 0.01, with no clear metallicity trend unless a metallicity-dependent dust-temperature prescription is adopted. The positive dust-mass-to-SFR correlation with metallicity suggests more efficient dust buildup at higher metallicity, potentially through ISM grain growth or enhanced survival. The dust-to-stellar mass relation with specific SFR shows no evidence of a high-specific-SFR turnover indicating inefficient dust buildup. Among CO(3–2)-detected galaxies, molecular-to-stellar mass ratios are ≳1; these large gas reservoirs may explain the elevated specific SFR and dust-to-stellar mass ratios relative to local galaxies.

PublicResearchers studied dust in 25 star-forming galaxies at redshift about 2.3, extending measurements to galaxies less massive and less rich in heavy elements than those usually studied at this epoch. Their dust estimates depend on assumptions about how the dust emits radiation and its temperature. Among detected galaxies, the typical dust mass was 64 million times the Sun’s mass—4–9 times that of present-day galaxies with comparable stellar masses and heavy-element abundances. Galaxies with more stars, more heavy elements, or faster star formation generally contained more dust. One trend suggests that dust accumulates more efficiently where heavy elements are more abundant, perhaps because grains grow or survive better, but this explanation is not established. Large molecular-gas reservoirs in the subset detected through carbon monoxide emission may help explain their elevated star formation and dust content relative to nearby galaxies.

Young explorerGalaxies contain stars, gas, and tiny bits of dust. Scientists studied dust in 25 faraway galaxies. Using a model to estimate how much dust was there, they found that some had more dust than similar galaxies nearby. Galaxies with more stars usually had more dust, too. The scientists think dust might grow more easily or last longer in some galaxies, but they are not sure yet.

How bursty star formation shapes spectral diversity at high redshifts: breaking degeneracies in early galaxy formation

Viola Gelli, Charlotte A. Mason, Daniel P. Stark+4 more

AstronomerMotivated by JWST observations of abundant z>10 galaxies and diverse spectra, this study models bursty star formation histories as an explanation for the UV luminosity function (UVLF) excess and spectral diversity. Matching the z~6 UVLF and observed recent-upturn and downturn fractions requires strong burstiness, with UV scatter of about 0.9 mag at halo mass 10^10 solar masses, increasing toward lower halo masses. The model reproduces UVLFs and upturn/downturn fractions over z~6–11. It predicts increasing bright-end dominance by recent upturns at higher redshift, accompanied at fixed UV magnitude by higher median emission-line equivalent widths, bluer UV slopes, weaker Balmer breaks, and broader property distributions. Downturn fractions are especially sensitive to stochasticity. However, the baseline model underpredicts the z~14 UVLF. Two alternatives match it: increased burstiness or increased star formation efficiency. From z=10 to 14, the former predicts approximately doubled downturn fractions and 1.5-fold higher weak-emitter fractions (Hβ EW<50 Å) at fixed UV magnitude; the latter predicts constant downturn fractions and declining weak-emitter fractions. These are model predictions, not observed trends. Spectroscopy across a broad UV-magnitude range is proposed to distinguish the explanations.

PublicJWST has found unexpectedly many galaxies at redshifts above 10, with a wide variety of spectral features. This study tests whether galaxies forming stars in bursts, rather than steadily, could help explain those observations. Models with strong fluctuations, especially in smaller dark matter halos, reproduce galaxy UV brightness distributions and the observed proportions with recently rising or falling star formation over redshifts of roughly 6–11. But the main model still predicts too few galaxies at redshift 14. The authors therefore explore two possible fixes: stronger bursts or more efficient star formation. Both can reproduce the UV brightness distribution there, but they predict different proportions of galaxies with declining star formation and weak emission lines. Future spectroscopic samples covering a wide range of UV brightness could test these alternatives; the study does not establish which explanation is correct.

Young explorerJWST has spotted surprisingly many galaxies from very early in the universe. Scientists used computer models to ask whether those galaxies made stars in big spurts, with quieter times between. That idea explains some observations, but not all. Stronger spurts or better star-making could each help the models fit. Studying the galaxies’ light more closely could help scientists tell which idea works better.

Rotational Excitation of HC₅NH⁺ by He: Collision Dynamics and Astrophysical Applications

Ziyu Xiang, Liman Tian, Tong Sun+2 more

AstronomerThe authors compute a two-dimensional HC5NH+–He potential energy surface at the CCSD(T)-F12B/cc-pVTZ-F12 level, then use quantum close-coupling calculations and Maxwell–Boltzmann averaging to derive rotationally inelastic collisional rate coefficients. Incorporating these data into a non-LTE radiative transfer model for TMC-1, they fit seven observed transitions by global chi-squared minimization. The model-dependent best fits are n(H2) = 1.63 × 10^5 cm^-3 and N(HC5NH+) = 5.09 × 10^11 cm^-2, with a minimum reduced chi-squared of 0.87. Modelled intensities agree well with observations. The calculated collision data concern helium, while the fitted cloud density is expressed in terms of H2.

PublicResearchers calculated how collisions with helium change the rotation of HC5NH+, a charged molecule found in interstellar space. They used those calculations in a model of the molecule’s emission from the cold dark cloud TMC-1 and compared the predictions with seven observed signals. The model reproduced the signals well and yielded estimates of the cloud’s hydrogen density and the amount of HC5NH+ along the line of sight. These estimates come from fitting a model to observations, rather than from direct measurements of those quantities.

Young explorerA tiny charged molecule in a cold cloud in space sends out signals as it spins. Scientists calculated how bumps with helium could change its spinning. Then they made a computer model and compared it with seven signals seen from the cloud. The model matched well, helping them estimate how crowded the cloud is and how much of the molecule is there.

A Sub-Parsec Origin for Rapid Accretion-State Transitions in Radio-Loud AGN

David Garofalo

AstronomerWithin the Garofalo, Evans & Sambruna (2010) framework, the author proposes a physical explanation for FRII HERG-to-LERG evolution. The required transition timescale of about 4 million years is attributed to viscous regulation of fueling at 0.1–0.3 pc, approximately 1,000–10,000 gravitational radii for black holes of 100 million to 1 billion solar masses. These scales overlap the broad-line region and inner dusty torus, where multiphase gas dynamics could regulate inward mass flux. The proposed mechanism is that FRII jet feedback heats and perturbs surrounding gas, suppressing the supply to the inner disk; below a critical accretion rate of about 0.01, the inner flow rapidly becomes an advection-dominated accretion flow. Observed molecular gas reservoirs are compatible with reduced inward fueling rather than wholesale cold-gas removal, but this compatibility does not establish the proposed mechanism.

PublicThe paper proposes an explanation for how some radio-emitting active galaxies change the way gas flows into their central black holes. Powerful jets may heat and disturb nearby gas, slowing the supply reaching the black hole without removing all the galaxy’s cold gas. The author argues that regulating this supply a fraction of a parsec from the black hole could account for a transition lasting about 4 million years. Once the supply drops below a critical level, the innermost gas flow would change rapidly to a different state. Observations showing that radio galaxies retain molecular gas fit this explanation, but do not prove it.

Young explorerA giant black hole in a galaxy can have gas swirling toward it and powerful jets shooting outward. This paper suggests that the jets stir and heat nearby gas, so less gas reaches the black hole. Over millions of years, that could change how the gas swirls close to it, even while plenty of cold gas stays farther away. Astronomers see gas that could fit this idea, but that does not mean they know the idea is right.

Hydrodynamic Natal Kicks and Formation of Black Hole Binaries

Edwin Santiago-Leandro, Clarissa Avilés-Niebla, Aldo Batta

AstronomerThe abstract reports more than 300 LIGO-Virgo-KAGRA gravitational-wave events and examines whether effective spin can distinguish compact-binary formation channels. Dynamically assembled binaries are expected to have randomly distributed effective spins between -1 and 1, whereas isolated binary evolution is expected to yield positive effective spins unless natal kicks substantially alter spin-orbit orientations. The authors use three-dimensional smoothed particle hydrodynamics simulations of asymmetric mild explosions in 13, 21, 28, and 34 solar-mass pre-supernova models to investigate large kicks during massive black-hole formation. They find that even kicks of roughly 1000 km/s do not consistently reorient the orbit. Reorientation requires a suitably directed kick and quite high supernova explosion energy, limiting how reliably natal kicks can produce this outcome in the modeled systems.

PublicGravitational waves from merging compact objects carry clues about how the pairs formed, including how their spins line up with their orbit. Pairs brought together by encounters in crowded stellar environments are expected to have random spin arrangements, while stars that evolve together in isolation are expected to produce more aligned systems—unless a strong shove at a compact object's birth changes the alignment. The researchers tested this possibility with three-dimensional simulations of uneven stellar explosions that form massive black holes. In their models, even birth kicks of about 1000 kilometers per second did not reliably turn the orbit. Such a change required both a kick in the right direction and a very energetic explosion. These are simulation findings, not direct observations of black-hole birth kicks.

Young explorerWhen two black holes circle each other, the way they spin may give clues about how they became a pair. Scientists used computer models to ask whether a shove when a black hole is born could turn the pair's orbit. Even a very fast shove did not always do that. In the models, the shove had to point the right way, and the star's explosion also had to be very powerful.

Testing influence of tides on gravitational wave emission with SPH code PHANTOM

Marat Sh. Potashov, Sergei I. Blinnikov, Aleksandra V. Mishakina

• General Relativity and Quantum Cosmology

AstronomerThe authors demonstrate a simulation-based method for estimating tidal contributions to gravitational-wave waveforms with the Newtonian SPH code PHANTOM. For a 1.5 + 1.5 solar-mass neutron-star binary, comparison with waveforms calibrated against full numerical GR simulations indicates that about 10^4 SPH particles can reliably recover the tidal contribution, provided the Newtonian–GR compactness difference is accounted for. Beyond 100 km separation, the relative tidal contribution falls below SPH numerical noise, although point-source waveforms are sufficient for detection at those separations. A 0.6 solar-mass white dwarf paired with a 1.5 solar-mass neutron star requires far more particles and separations of tens of thousands of kilometers because tidal mass transfer and disruption begin rapidly. The authors conclude that, despite surmountable computational challenges, the richness of Newtonian effects prevents useful results from this approach for that system. Hydrostatic/hydrodynamic relaxation of the initial models is essential in all cases; without it, numerical noise obscures the entire GW signal.

PublicThis study tests a computer-simulation method, rather than reporting an astronomical observation. The authors use Newtonian gravity to estimate how the stretching of two neutron stars changes their gravitational-wave signal. In an example with two stars each weighing 1.5 times the Sun, roughly 10,000 simulated particles were enough to recover this tidal effect when checked against waveforms calibrated using full general-relativity simulations. The method must account for differences in how compact the stars are under the two descriptions of gravity. Beyond 100 kilometers apart, the tidal effect is smaller than the simulation’s numerical noise, but waveforms treating the stars as points are adequate for detection there. The method does not yield useful results for the white dwarf–neutron star example studied: rapid mass transfer and disruption require much larger simulations, and the complexity of Newtonian effects remains a limitation. Carefully settling the initial simulated stars is essential to avoid burying the whole signal in numerical noise.

Young explorerThe researchers made pretend stars in a computer to study the tiny stretching that changes ripples in space. For two neutron stars, their method could find that stretching effect when compared with a more complete kind of calculation, but they had to allow for differences between the two ways of describing gravity. When the stars were farther apart, the effect was too small for their computer method to pick out. Their method did not give useful answers for a different pair with a white dwarf, which quickly starts losing material and breaking apart. They also had to let the pretend stars settle down first, or unwanted computer wiggles hid the ripple signal.

Neutrino pair annihilation in curved spacetime: a fast moment method and the geometry of flavour conversion

Rafael C. R. de Lima, Luciano de Oliveira Junior, Pedro Martins Bailer

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

AstronomerThis computational study examines whether relativistic transport and neutrino flavour conversion can be treated separately when calculating neutrino–antineutrino annihilation above black-hole accretion discs. It combines backward ray tracing in Schwarzschild and Kerr spacetimes with an exact angular-moment annihilation kernel, validated against an analytic spherical solution and published disc calculations. Conversion corrections are geometry-independent for uniform conversion with negligible initial heavy-lepton emission. Approximate separability persists for uniform conversion when flavour-dependent emitting regions overlap: relative to flat-space discs with the same local velocities, gravity enhances energy deposition by factors of 1.4–5 but changes the relative conversion effect by at most 6% for most temperature profiles considered. Spatially varying conversion raises that difference to 22% around a rapidly spinning hole. When heavy-lepton neutrinos instead emerge from an inner ring separated from electron-flavour emission, relativistic bending and energy shifts preferentially enhance annihilations involving inner-ring neutrinos; relativistic conversion factors reach 2.4 times their flat-space counterparts. In one configuration, flavour equipartition decreases deposition by 54% in flat space but increases it by 11% in Kerr spacetime. These model results, rather than observations, identify the spatial arrangement of flavour-dependent neutrinospheres as crucial to the validity of treating conversion and relativistic transport independently.

PublicCalculations in this study explore how gravity and changes between neutrino types jointly affect the energy released when neutrinos and antineutrinos annihilate above a disc around a black hole. The researchers find that the two effects can sometimes be calculated separately. This works exactly under restrictive assumptions, including uniform conversion and negligible initial emission of certain neutrino types, and approximately in several models where the emitting regions overlap. But it can fail when different neutrino types come from separate regions. If some originate in an inner ring, gravity can give their annihilations greater weight, substantially changing the effect of neutrino conversion. In one model, equalizing the flavour populations reduced energy deposition by 54% without gravity but increased it by 11% around a spinning black hole. These are computational findings, not observations: the answer depends strongly on where each neutrino type is emitted.

Young explorerScientists used calculations to study tiny particles called neutrinos near a black hole. These particles can change type, and meeting their opposite partners can release energy. The calculations suggest that gravity and changing type sometimes act like separate effects. But when different types start in different places, gravity can change the answer a lot—even turning less energy into more in one model. This was a calculation, not something scientists watched happen.

Bicoherence States from QPO-Accretion Flow Coupling in Black Hole X-ray Binaries

Seth Rowan Larner

AstronomerThe authors analytically calculate the bispectrum of a black hole X-ray binary light-curve model in which lognormal inner-flow fluctuations are multiplicatively modulated by a QPO and its harmonic. The model reproduces all canonical bispectral states, which characterize nonlinear coupling between QPOs and broadband noise. In the model, changes in dilution by additional incoherent variability, together with changes in QPO amplitude, drive transitions between these states. Larger QPO amplitudes in high-inclination sources favor the cross state, while weaker QPOs in low-inclination sources favor the hypotenuse state, offering an explanation for the observed inclination correlation. Dilution by equatorial winds, if present, would further favor the cross state at high inclination. These are analytical model results and interpretations of observed patterns, rather than new observational measurements.

PublicBlack hole X-ray binaries show both roughly repeating pulses and irregular fluctuations in their X-ray brightness. Observations reveal nonlinear links between these variations, with characteristic patterns that change as the X-ray spectrum changes. The authors calculate a model in which the repeating signal modulates irregular fluctuations from the inner flow. It reproduces all the standard patterns of frequency coupling. In the model, transitions between patterns arise from changes in pulse strength and in the contribution of additional, unrelated variability. The results could also explain why different patterns are associated with different viewing angles: stronger pulses in systems viewed at high inclination favor one pattern, while weaker pulses at low inclination favor another. Equatorial winds, if they dilute the signal, could strengthen this tendency at high inclination.

Young explorerX-rays from a black hole and its companion star flicker, with a beat that almost repeats mixed into a jumble of changes. Astronomers have seen different ways that the beat and the jumble are linked. The researchers made a math model that can copy all those familiar patterns. In the model, changing how strong the beat is and adding other flickers can change the pattern. This might help explain why the patterns differ when we look at these systems from different directions.

Unlocking Pandora's Secrets: Probing the Thermodynamics of Abell 2744

Randall Rojas Bolivar, Akos Bogdan, Daniel Wik+1 more

• Cosmology and Nongalactic Astrophysics
• Astrophysics of Galaxies

AstronomerNuSTAR observations of the merging cluster Abell 2744 map its ICM temperature structure and identify a prominent shock front aligned with the southeastern boundary of the radio halo, with Mach number 1.58 (+0.42, −0.30). Global spectra were tested with single- and two-temperature thermal models and thermal-plus-power-law models. Purely thermal emission adequately describes the spectra, with an average kT of approximately 11 keV; no significant non-thermal hard X-ray component is detected. The authors derive a 90% confidence upper limit of 2.31 × 10^-12 erg s^-1 cm^-2 on the 20–80 keV inverse Compton flux. Combining this constraint with VLA diffuse radio measurements at 1.5 GHz yields an estimated lower limit on the average magnetic field of B > 0.2 μG.

PublicAbell 2744, also called Pandora's Cluster, is a massive collection of galaxies undergoing several collisions. Using NuSTAR X-ray observations, researchers mapped its hot gas and identified a shock wave along the southeastern edge of its diffuse radio glow. The X-ray spectra are adequately explained by hot gas alone, with an average temperature expressed as an energy of about 11 keV. The team found no significant evidence for an additional high-energy X-ray signal from inverse Compton scattering by relativistic electrons, so they set an upper limit rather than reporting a detection. Combining that limit with radio observations, they estimated that the cluster's average magnetic field is stronger than 0.2 microgauss.

Young explorerPandora's Cluster is a huge group of galaxies crashing together. Scientists looked at its very hot gas and found a shock wave. They also searched for an extra kind of X-ray light, but did not clearly find it. That limit, together with radio observations, helped them estimate how weak the cluster's magnetic field could be.

Modeling of the X-ray Flux and Polarization Energy Spectra of Black Hole X-Ray Binaries with the KerrC Code

Kun Hu, Henric Krawczynski

AstronomerThis chapter introduces kerrC, a framework for joint modeling of X-ray spectra and polarization from black hole systems, based on Monte Carlo ray-tracing simulations in Kerr spacetime. The simulations include thermal seed emission from a geometrically thin, optically thick disk, Comptonization in a hot corona with variable geometry and physical properties, and self-consistent reflection of disk and Comptonized photons using xillver tables. Photons are propagated forward in time through multiple corona and disk scatterings, with their polarization 4-vectors transported throughout. The chapter describes the simulation mechanics and fitting models and discusses how X-ray polarization observations could constrain black hole spin and coronal geometry; the abstract reports no observational constraints.

PublicThe chapter presents kerrC, a computer model designed to interpret both the energy spectrum and polarization—the orientation information carried by light—of X-rays from black hole systems. Its simulations follow photons from a thin disk of hot material through a hot surrounding region called the corona, accounting for scattering, reflection from the disk, and the strongly curved spacetime near the black hole. The model keeps track of polarization throughout these interactions. The authors discuss using it with X-ray polarization observations to help determine how fast a black hole spins and the shape of its corona, but the abstract does not report measurements of those properties.

Young explorerScientists made a computer model to follow X-ray light near a black hole. In the model, light starts in a thin disk of hot material and can bounce off the disk or scatter through hot gas nearby. The computer also keeps track of which way the light waves wiggle. Scientists hope this will help them learn how a black hole spins and what shape the hot gas has. This chapter explains the model, rather than announcing that those answers have been found.

Probing Dark Matter via the Migdal Effect in LUX-ZEPLIN Data

Yang Yu, Lei Feng

AstronomerUsing new LUX-ZEPLIN results with a 4.2 tonne-year exposure, the authors evaluate sensitivity to spin-independent DM–nucleon scattering through Migdal ionization accompanying atomic recoil. This electronic signal offers a way to probe low-mass DM that deposits little energy in conventional searches. For DM masses of 350 MeV–10 GeV, the projected 90% upper limits on the scattering cross section range from 6.5×10⁻³⁷ to 9.6×10⁻⁴² cm². The authors use these projected limits to constrain minimal scalar- and vector-mediator models. In the light-mediator model, the coupling constraint reaches α≈10⁻¹², reported as stronger than or comparable to constraints from kaon decays, stellar cooling, and SN1987A. These are sensitivity projections and model constraints, not a reported DM detection.

PublicLight dark matter particles would leave very little energy in conventional detectors, making them difficult to find. This study examines an additional possible clue: an atom struck by dark matter could also release an electron, producing a signal known as the Migdal effect. Using new results from the LUX-ZEPLIN experiment, the authors estimate how tightly this method could limit the strength of dark matter’s interactions with ordinary matter. They apply the projected limits to models in which a scalar or vector particle carries the interaction. For a model with a light carrier, the estimated restriction on its coupling is stronger than or comparable to limits from certain particle decays and stellar observations. The study reports projected limits, not a discovery of dark matter.

Young explorerDark matter is something scientists are trying to learn about. A very light dark matter particle might give an atom such a tiny bump that it is hard to notice. But the bump could also knock out an electron, leaving another clue. Scientists used results from an experiment called LUX-ZEPLIN to work out how this clue could help test ideas about dark matter. They estimated how strong its bumps could be; they did not report finding dark matter.

Quasi-spherical fallback in binary neutron-star mergers: fuel and obstacle for extended emission

Zhiwei Chen, Marie Cassing, Paramvir Singh+1 more

AstronomerSome short gamma-ray bursts show extended emission lasting hundreds of seconds with both thermal and nonthermal components. Motivated by approximately quasi-spherical late-time fallback in binary-neutron-star merger simulations, and possible shortcomings in radioactive-heating power, the authors propose a fallback-fed secondary jet. Material circularizing around the black hole feeds the jet, while polar fallback resists its propagation. A semi-analytic toy model identifies jet-dominated, cocoon-dominated, and choked regimes, controlled mainly by the circularization fraction, jet opening angle, and polar refilling, with approximate scaling L̃ ∝ f_circ/(ξ_pol θ_j²). Post-processing merger simulations yields a bound fallback fraction avoiding prompt capture of f_npc ≈ 0.52, an upper bound on the circularizable supply rather than a measured circularization fraction. With suitable prescriptions for nonthermal jet emission and thermal jet-head emission, estimated isotropic-equivalent 0.3–10 keV energies reproduce the observed extended-emission distribution in the jet-dominated branch and its low-energy end in the cocoon-dominated branch. These model-dependent results support feasibility and energetic consistency, not confirmation of the mechanism.

PublicSome short gamma-ray bursts are followed by emission lasting hundreds of seconds. The authors propose that, after two neutron stars merge, some returning matter settles around the resulting black hole and powers a second jet, while other returning matter obstructs it. Their simplified model allows the jet to push through, produce emission dominated by a surrounding cocoon, or become trapped. Analysis of merger simulations suggests that about 52% of the bound returning matter avoids immediate capture, setting an upper limit on the supply that could settle into orbit. With suitable assumptions about how radiation is produced, the model matches the observed extended-emission energy distribution for jet-dominated cases and its lower-energy end for cocoon-dominated cases. This makes the proposal plausible, but does not establish it as the actual cause.

Young explorerSometimes a short flash in space keeps shining for hundreds of seconds. Scientists have an idea: after two neutron stars crash together, falling-back material might feed a black hole and help launch another narrow blast. Other falling material could block it. Their simplified calculations suggest this could explain the extra light, but they have not shown that it really happens.

GW230729_082317 and GW231118_005626: A Candidate of Hierarchical Triple Mergers

Bo Gao, Shao-Peng Tang, Yi-Zhong Fan+1 more

AstronomerThe study tests whether GW230729_082317 and GW231118_005626 represent a hierarchical triple merger, in which the remnant of one binary black hole merger subsequently merges with a third black hole. Their sky localizations and luminosity distances are consistent, and the Bayes factor for association is 110. However, incorporating prior odds reduces the odds ratio to 0.1, so the current evidence does not favor this scenario over non-association. The abstract also reports no detectable orbital eccentricity or line-of-sight acceleration for an event labeled GW230720_0823. The inferred properties are interpreted as favoring dynamical formation, such as few-body scattering or gas-assisted mergers, over a primordial triple origin; an active galactic nucleus accretion disk is proposed as the most plausible environment. Rate constraints are derived under both null and candidate scenarios. Assuming no detected hierarchical triple mergers, the strongest reported 90% confidence upper limit from GWTC-4 is 4.2 Gpc^-3 yr^-1 for t_max = 10 years.

PublicResearchers investigated whether two gravitational-wave events could be successive steps in one black hole merger sequence: two black holes merge, and their remnant later merges with a third. The events, GW230729_082317 and GW231118_005626, have compatible inferred sky positions and distances. Although this agreement supports a possible connection, accounting for the prior odds leaves the overall evidence insufficient to favor a linked sequence over unrelated events. The researchers interpret the inferred properties as suggesting encounters among black holes, possibly aided by gas, rather than a system born as a triple. They propose the gas disk around an active galactic nucleus as the most plausible setting, but this is not an established location. They also estimate limits on how frequently such sequences occur, including an upper limit that assumes none has been detected.

Young explorerTwo black holes can join to make one bigger black hole. That bigger one might later join with a third. Scientists looked at two signals from black hole collisions to see if this happened. The signals could come from the same place at a matching distance, but that is not enough to show they are connected. The scientists suggest that, if they are connected, the black holes may have met in a disk of gas near the center of a galaxy. That is an idea, not something they have proved.

Activity of the ejected galactic nuclei and cosmic rays

Yu. N. Eroshenko

AstronomerThe study considers cosmic-ray acceleration following the possible ejection of a supermassive black hole during double or triple encounters in hierarchical galaxy formation. An ejected black hole may retain an accretion disk and some stars, and renewed nuclear activity could drive an ultrafast outflow and shock. The authors argue that lower ambient gas density and higher shock-front velocity make acceleration more effective than in a stationary galactic nucleus. In this scenario, protons could reach approximately 10^19 eV, about an order of magnitude above the energies attainable in an ordinary central nucleus. This is a theoretical scenario, not a reported observational detection.

PublicEncounters between supermassive black holes can potentially kick one out of a galaxy's center, carrying some surrounding gas and stars with it. This study explores how renewed activity around that displaced black hole could launch an extremely fast gas outflow and a shock wave. The authors argue that thinner surrounding gas and a faster shock could boost cosmic-ray particles more effectively than near a black hole that remains at the center. They estimate that protons could reach about 10^19 electron volts—roughly ten times the energy possible in an ordinary galactic nucleus. The abstract describes a theoretical explanation rather than an observed example.

Young explorerWhen giant black holes meet, one might get kicked away from the middle of its galaxy. It could take some gas and stars along. Scientists suggest that gas around the black hole could then make a powerful wave that gives tiny particles an extra-big energy boost. This study explores how that might happen, rather than reporting that someone has seen it.

Constraints on Cosmic-Rays and the MeV Emission from Jupiter's Atmosphere

Dimitris Tsatsis, Thomas Siegert, Volodymyr Savchenko+8 more

AstronomerThe authors investigate Jupiter’s atmospheric albedo as an indirect probe of isotropic soft-X-ray to gamma-ray emission, using 22 years of serendipitous INTEGRAL/SPI observations over 30 keV–8 MeV. Monte Carlo simulations model photon and cosmic-ray interactions in a 1000 km-deep spherical atmosphere based on Galileo probe measurements. No statistically significant Jovian emission is detected. The analysis yields 2σ upper limits, compared with cutoff power-law, reflected cosmic gamma-ray background, cosmic-ray-induced, and long-lived-mediator dark matter models. Jupiter’s MeV bremsstrahlung luminosity is constrained to 10^18 erg/s, close to the value inferred from Juno/JEDI in situ measurements. Expected background-reflection and cosmic-ray signals are respectively factors of 10^4 and 100 below the upper limits, so the proposed use of planetary atmospheres to probe diffuse gamma-ray backgrounds remains a prospect for future MeV missions.

PublicCould Jupiter help reveal a poorly understood background of high-energy light spread across the sky? Researchers searched 22 years of observations from the SPI instrument aboard INTEGRAL for radiation scattered or produced in Jupiter’s atmosphere. They also simulated how incoming light and energetic particles interact with the atmosphere. They found no statistically significant gamma-ray signal from Jupiter and instead set upper limits on its brightness. The predicted signals from the cosmic gamma-ray background and cosmic rays are about 10,000 and 100 times fainter than those limits, respectively. The study therefore does not detect this background through Jupiter, but presents the planet’s atmosphere as a possible tool for future, more sensitive missions.

Young explorerJupiter has a thick blanket of gas around it. Scientists think this blanket could bounce back some invisible, very energetic light from space. They searched many years of telescope observations and used computer models to work out what might happen. They did not find a clear signal from Jupiter. The signals they expect are much too faint for this search, but future space telescopes might use Jupiter to learn about this light.

XMM-Newton observations of the highest field polar AR UMa: An extreme case of soft-blobby accretion

Kala G. Pradeep, Axel D. Schwope

• Solar and Stellar Astrophysics

AstronomerThe first high-state XMM-Newton observation of AR UMa, the highest-field polar (B ≈ 230 MG), combined with UV and optical spectral-timing analysis, showed accretion onto one active southern pole. Its spectrum was dominated by a blackbody-like soft component with kT ≈ 35 eV, with no evidence for the optically thin hard X-ray component expected from a cooling post-shock column. Faint, approximately constant, optically thin emission at ≈ 1 keV persisted throughout the orbit without correlation with the soft component; the authors attribute it to shock-heated material in the stagnation region. Absorption dips associated with puffed-up material in that region probed the density structure and evolution of the clumpy flow. The UV spectrum provides evidence for a southern-pole cyclotron harmonic near 2300 angstroms, corresponding to 160 MG. Minute-long quasi-periodic oscillations were detected in optical, UV, and X-ray light curves. The authors interpret AR UMa as an extreme soft, blobby accretor with an effectively infinite soft excess because the usual hard component is undetected, and as a rare detection of X-rays from stream–magnetosphere interaction.

PublicObservations of AR UMa, a binary system with an exceptionally strong magnetic field, revealed material falling onto just one magnetic pole during the observation. Most of that pole’s X-ray emission was soft, or relatively low-energy; the researchers found no evidence for the usual higher-energy X-rays from a hot accretion column. A separate, faint X-ray component remained nearly constant, which they interpret as gas heated where the incoming stream interacts with the magnetic field. Dips in brightness helped trace clumps of absorbing material, while optical, ultraviolet, and X-ray brightness varied in roughly minute-long, not perfectly regular cycles. There was also evidence for ultraviolet emission associated with electrons moving in the magnetic field. The findings support an extreme form of clumpy accretion dominated by soft X-rays, rather than the usual hot-column emission.

Young explorerAR UMa is a pair of stars where gas falls toward a very strong magnet. During this look, one magnetic end glowed mostly in a lower-energy kind of X-ray light. Clumps of gas sometimes blocked the glow, and the light wobbled on about a minute’s timescale. The scientists think a separate, faint X-ray glow comes from gas getting heated as it meets the magnetic field.

Fundamental Noise Processes in Pulsar Timing

James M. Cordes, Stella Koch Ocker, Shami Chatterjee+4 more

AstronomerThis work reviews pulsar timing fundamentals and precision limits, develops timing-quality metrics, and applies them to sources in current pulsar timing arrays to help characterize future discoveries. It considers spin noise, magnetospheric beam variability, interstellar multipath propagation, pulsar–observatory geometry uncertainties, and instrumental effects. The authors identify sources of non-Gaussian timing residuals, distinguishing chromatic from achromatic contributions and variability on seconds-to-minutes versus days-to-months timescales. They predict that interstellar propagation will increasingly limit timing precision as telescope sensitivity improves. Simultaneous arrival-time measurements across wide receiver bandwidths enable mitigation of chromatic interstellar effects and identification of non-Gaussian events amid random fluctuations. The authors recommend timing-procedure changes to exploit these capabilities; the abstract does not quantify the resulting precision gains.

PublicPulsars are spinning neutron stars whose radio pulses act as remarkably steady cosmic clocks. Their timing has supported planet discoveries and tests of gravity, and has helped open the study of gravitational waves at extremely low frequencies. But these clocks are imperfect: changes in the star’s spin and radio beam, the pulses’ journey through turbulent material between stars, and measurement uncertainties can all shift their apparent arrival times. This study develops ways to rate pulsars’ timing quality and applies them to stars already used in pulsar timing arrays. The authors expect interference from interstellar material to become an increasingly important limit as telescopes grow more sensitive. Measuring pulses at many radio frequencies at once helps distinguish and reduce some of these effects. The paper recommends changes in timing methods, but does not report a numerical improvement from adopting them.

Young explorerSome stars spin and send out radio flashes that we can use like the ticks of a clock. But the ticks do not always arrive exactly when we expect. The star can change a little, and material between the stars can make the radio signals take different paths. These scientists made ways to judge how good these star clocks are and used them on some already being watched. They explain how listening at many radio frequencies at once can help spot and reduce some problems. They also suggest better ways to measure the ticks, but do not say exactly how much better those changes will make the clocks.

A possible connection between the ridge and hypotenuse in the bispectrum of black hole X-ray binaries through quasi-periodic modulation

Pei Jin, Mariano Méndez, Federico Garc\'ıa+4 more

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

AstronomerThe authors develop a mathematical model in which a QPO-phase-locked modulator multiplicatively couples to broadband variability in black-hole X-ray binaries. Frequency mixing produces the fundamental QPO’s ridge and hypotenuse as parts of one bispectral structure, extends to the second harmonic, and predicts opposite-sign biphases for each ridge–hypotenuse pair. NICER observations of Swift J1727.8−1613 and MAXI J1820+070 show structures broadly consistent with these predictions, including qualitatively opposite-sign biphases. Biphase maps also reveal weak coupling structures that are difficult to identify in bicoherence alone. Predictions for the bispectral modulus of isolated ridges and hypotenuses broadly reproduce the observed frequency dependence, but localized deviations persist near the fundamental and second harmonic, where structures overlap. The model offers a possible mathematical explanation for the web-like pattern, rather than establishing its physical origin.

PublicBlack-hole X-ray binaries show roughly repeating changes in X-ray brightness mixed with less regular fluctuations. Statistical maps reveal ridge-like and web-like patterns linking these variations, but their origin remains unclear. The researchers propose a mathematical model in which a process synchronized with the repeating signal multiplies the underlying fluctuations, mixing their frequencies. The model predicts linked patterns with opposite signs in a measure of their phase relationships. NICER observations of two systems, Swift J1727.8−1613 and MAXI J1820+070, broadly match these predictions. The phase maps also help reveal weak connections that another statistical measure struggles to show. Some differences remain where patterns overlap, so the model is a possible explanation, not a confirmed account of the physical cause.

Young explorerX-rays from systems with black holes get brighter and dimmer, sometimes with a beat and sometimes more messily. Scientists made a math model in which something following the beat changes how strong the messy flickering is. This could make connected patterns in special charts. When they looked at two real systems, the patterns mostly fit the model, but not everywhere. It is a promising idea, not yet a sure explanation.

Forecasting Fundamental-Plane Tests of Intermediate-mass Black Holes in Radio-selected Dwarf Galaxies

Ramananda Santra, Samik Mitra, Shahram Abbassi

• Astrophysics of Galaxies

AstronomerUsing published VLA, VLBA, Chandra, and HST observations of radio-selected dwarf galaxies, the authors assess whether radio/X-ray Fundamental Plane tests can constrain intermediate-mass black holes. Such tests require the compact radio emission, intrinsic hard X-rays, accretion state, and host association to describe the same accretor. The VLBA follow-up shows that radio compactness alone does not establish association with the target dwarf; for the best nuclear candidates, the FP-relevant radio component remains unisolated on scales between the VLA and VLBA measurements. The authors instead calculate detection probability as a function of assumed black-hole mass, incorporating intrinsic FP scatter, X-ray uncertainties, radio spectral index, accretion state, and source size relative to the beam. Under these assumptions, existing VLBA nondetections have low completeness across the adopted intermediate-mass range and yield no useful mass upper limits. Stronger tests require deeper, resolution-matched radio imaging, recovery of intermediate-scale emission, and contemporaneous intrinsic hard-X-ray measurements. The resulting source-specific detection functions could also support completeness and selection-function estimates for larger samples.

PublicCan a missing radio signal tell us how massive a black hole is? This study examines that question using published radio, X-ray, and optical observations of dwarf galaxies. A relationship between black-hole mass and radio and X-ray emission is useful only if the signals really come from the same black hole in the required feeding state. The observations show that a compact radio source is not enough to prove it belongs to the target galaxy, and even the best candidates still lack a clearly isolated radio component needed for the test. The researchers calculate how likely each radio observation would be to detect a black hole of an assumed mass, accounting for several uncertainties. They find that the existing radio nondetections do not set useful upper limits on black-hole mass. They recommend deeper radio observations that capture the relevant emission scales, alongside X-ray measurements taken at the same time. Their method could also help assess which black holes larger surveys are likely to miss.

Young explorerScientists looked at observations of small galaxies to learn about black holes. They wanted to use radio and X-ray signals as clues, but first they must check that both clues come from the same black hole. A tiny-looking radio spot is not enough to be sure. They worked out how likely the radio observations were to notice a black hole of a certain size. They found that not seeing a radio signal does not yet tell them a useful biggest possible size for these black holes. They say better radio pictures and X-ray checks taken at the same time are needed.

Superorbital period evolution of Hercules X-1

Abhisek Tamang, Hemanth Manikantan, Kinjal Roy+2 more

AstronomerTiming analyses of Her X-1 using five X-ray monitors over 1995–2025, supplemented by literature data spanning about 50 years, reveal a long-term decrease in the superorbital period at approximately −5 × 10⁻⁵ s s⁻¹. This contrasts with earlier reports from 1970–1990 of stochastic fluctuations without a long-term trend. Shorter-timescale structure in the observed-minus-calculated (O−C) timing residuals prevents a simple quadratic description. The mean count rate correlates positively with the superorbital period across different linear segments of the O−C curve. Variations over a few to a few tens of superorbital cycles suggest, but do not establish, a restoring mechanism. The origin of the modulation remains debated between a counter-precessing twisted, tilted accretion disc and free precession of the neutron star; the abstract does not identify either as the established explanation.

PublicHercules X-1 is an X-ray binary whose X-ray brightness follows a repeating cycle. Researchers examining continuous observations from 1995 to 2025 found that this cycle is gradually getting shorter, unlike earlier observations that showed irregular changes but no long-term trend. Faster fluctuations are layered on top of the overall shortening, so a simple steady-change model does not fully describe the timing. Across different stretches of the data, longer cycles also tend to coincide with higher average X-ray count rates. The fluctuations suggest that something may act to restore the cycle after changes, but this is an interpretation rather than a confirmed mechanism. Scientists still debate whether the cycle comes from a changing orientation of the surrounding disc of material or a wobble of the neutron star itself.

Young explorerHercules X-1 is a pair of stars that sends out X-rays, a kind of light our eyes cannot see. Its X-ray light gets brighter and dimmer in a repeating pattern. Scientists watched it for 30 years and found that the pattern is slowly repeating sooner, with little changes along the way. They still do not know exactly why. A wobbling star or a turning disc of material around it might explain the pattern.

Entanglement in Collective Neutrino Oscillations on a Quantum Computer

Katarina Bleau, Nikolina Ilic, Joachim Kopp+2 more

• High Energy Physics - Phenomenology
• Quantum Physics

AstronomerThe authors investigate whether entanglement makes full multiparticle treatments necessary for neutrino flavour evolution in dense environments. They simulate entangled ensembles with varying particle number N on classical and quantum hardware and compare them with conventional mean-field treatments based on Boltzmann-type kinetic equations. For simple toy systems, analytical and numerical results show agreement between full multiparticle and mean-field predictions in the large-N limit. They also develop algorithms for efficient simulation on both types of hardware and discuss physical situations in which mean-field dynamics alone cannot describe an entangled neutrino system. Possible conditions for realizing these situations in supernova cores or neutron star mergers are discussed, rather than established observationally. The work does not demonstrate a quantum computational advantage.

PublicNeutrinos can change between different types, or flavours, as they travel. In dense settings such as supernovae and merging neutron stars, quantum links called entanglement might affect how groups of neutrinos change together. The researchers used classical and quantum computers to simulate these groups and compared the results with a simpler, average-based approach. For the simplified systems they tested, they showed mathematically and numerically that the two approaches agree when the number of particles becomes very large. They also developed simulation algorithms and discussed circumstances where the simpler approach would not be enough. Whether those circumstances occur in supernova cores or neutron star mergers remains a question of physical conditions; these are simulation and theoretical findings, not observations of those events or proof that quantum computers outperform classical ones.

Young explorerNeutrinos are tiny particles that can change from one kind to another. The scientists used computers to pretend to follow groups of them, including special quantum links between the particles. In simple pretend groups, they found that a simpler way of doing the sums gives the same answer when the group gets very, very big. They also talked about times when the special links could make that simpler way miss something important. They have not shown that those times really happen inside exploding stars or when two neutron stars crash together.

Phentax: A JAX implementation of the IMRPhenomTHM waveform model

Alessandro Santini, Diganta Bandopadhyay, Jonathan Gair

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

AstronomerThe authors present Phentax, a JAX re-implementation of IMRPhenomTHM, a time-domain phenomenological waveform model for comparable-mass binary black holes that includes higher-order modes. The implementation is designed to be fast, batchable, and differentiable, supporting development of LISA global-fit algorithms that jointly infer parameters across overlapping sources and require hundreds of thousands of waveform-template evaluations. IMRPhenomTHM is already used to simulate and analyze massive black hole binary signals for LISA, whose expected sources include binaries with masses of 10^4–10^7 solar masses. This is a waveform-software contribution for a future mission, not an observational detection; the abstract provides no quantitative performance benchmarks or demonstration of a complete global fit.

PublicThe future LISA space observatory is expected to measure gravitational waves from many systems at once. Separating their overlapping signals will require researchers to estimate the properties of all the sources together, using large numbers of predicted waveforms. The authors introduce Phentax, a new implementation of an existing model for waves from pairs of black holes of comparable mass. It is designed to calculate waveforms quickly, process many at once, and provide mathematical derivatives useful in analysis. The aim is to help develop LISA’s joint-analysis methods; the abstract reports no new observations or numerical speed comparisons.

Young explorerLISA is a future space observatory that is expected to pick up tiny ripples in space from many things at once, including pairs of black holes. Scientists will need to tell those mixed-up ripples apart. The authors made a computer tool called Phentax that is designed to quickly make lots of examples of the ripples black hole pairs could create. Those examples could help scientists sort out LISA’s signals. This is a new tool, not a report of black holes LISA has already found.

A pipeline for identifying astrophysical signals and instrumental glitches in LISA data

Aryamann Rao, Jess McIver, Rhiannon Udall+2 more

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

AstronomerThe authors introduce a two-stage pipeline for simulated LISA data: a search for candidate transients followed by machine-learning classification into gravitational-wave signals or instrumental glitches. This distinction is particularly relevant for massive black hole binaries around 10^6 solar masses, whose transient signals could resemble glitches. Initial simulation results show classification accuracy close to 98% and processing of one month of data in under two minutes on a laptop. These results suggest potential use in rapid, low-latency alerts and in supporting model selection for global-fit analyses through initial estimates of signal locations and types; neither application is established here with flight data. The paper also discusses training challenges and limitations of the current framework. LISA, scheduled for launch in the 2030s, is expected to encounter non-astrophysical transients.

PublicLISA, a space-based gravitational-wave detector scheduled to launch in the 2030s, is expected to record both signals from astronomical sources and unwanted bursts caused by its instruments. The researchers tested a two-step method on simulated LISA data: first finding brief events, then using machine learning to classify them as gravitational waves or instrumental glitches. Very massive black hole binaries are an important case because their signals could look similar to glitches. Initial tests achieved close to 98% classification accuracy and processed a month of simulated data in under two minutes on a laptop. The method could eventually help issue rapid alerts and guide more detailed analysis, but these are potential uses, not demonstrated results from the future detector. Training challenges and limitations remain.

Young explorerScientists are getting ready for LISA, a future space detector that will look for tiny ripples in space. Some things it records may be real signals, and others may be little hiccups in the machine. The team made a computer helper that first finds short events and then tries to tell the two kinds apart. In early tests with pretend LISA data, it picked the right kind about 98 times out of 100 and checked a month's worth of data in less than two minutes on a laptop. It might someday help scientists send quick notices about interesting signals, but it has not been tested on real LISA data, and it still has limitations.

Baryon Number Susceptibilities of Hot and Dense Nuclear Matter in Relativistic Mean-Field Models

Deepak Kumar, Biswarup Das, Sandeep Chatterjee+1 more

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

AstronomerThe authors develop a fully analytical framework for baryon-number susceptibilities in relativistic mean-field (RMF) models of hot, dense nuclear matter at finite temperature and baryon chemical potential. Applying it to representative nonlinear RMF parameterizations, they examine the model dependence of baryon-number fluctuations. All parameterizations considered reproduce the overall qualitative beam-energy dependence of cumulant ratios. The calculated skewness and kurtosis are reported to agree with experimental values, with FSU-family parameterizations showing relatively small deviations from measured heavy-ion cumulant ratios. The abstract does not quantify those deviations or the uncertainties, so the reported agreement does not establish a uniquely preferred parameterization.

PublicThis study develops an analytical way to calculate fluctuations in baryon number in models of hot, dense nuclear matter. The researchers compare several versions of these models with measurements from heavy-ion experiments. All the versions tested reproduce the broad pattern of how statistical measures of the fluctuations change with collision energy. The authors report agreement with measured skewness and kurtosis, which describe the asymmetry and shape of the fluctuation distribution. Models in the FSU family show relatively small differences from the measured ratios. These are theoretical calculations compared with existing measurements, not new experimental findings; the abstract does not give the sizes or uncertainties of the differences.

Young explorerScientists made a new math recipe to study very hot, tightly packed matter. They used it with several models to work out how the number of particles called baryons can vary. The models followed the broad pattern seen in experiments that smash heavy particles together. One family of models had fairly small differences from the measurements. This is a comparison using math, not a new experiment, and it does not prove that one model is the only right one.

Probing flavor-dependent neutrino-dark matter interactions with the flavor composition of high-energy cosmic neutrinos

Ki-Young Choi, Ankhbayar Tugssaikhan

• High Energy Physics - Phenomenology

AstronomerThe authors model flavor-dependent neutrino–dark matter interactions for neutrinos produced within a dense dark matter spike around the supermassive black hole in TXS 0506+056. Coherent forward scattering induces a flavor-diagonal potential V_alpha = A_alpha rho_chi(r), while scattering attenuates the flux. Their calculation finds adiabatic propagation through the spike and halo. For A much smaller than 10^-38 cm^3, mixing is unaffected, and IceCube three-flavor composition constraints imply sigma_nu_chi/m_chi less than approximately 10^-28 cm^2/GeV. At larger A, the interacting flavor becomes isolated in one source matter eigenstate; the other two eigenstates escape unattenuated, yielding a survival plateau that can weaken the limits by up to four orders of magnitude. A potential with opposite signs for neutrinos and antineutrinos can produce distinct flavor signatures even without attenuation. Requiring the local dark matter potential not to alter the observed PMNS mixing gives A less than approximately 10^-30 cm^3. The combined constraints are compared with a vector-mediator benchmark; these are model-dependent calculations and constraints, not a detection of neutrino–dark matter interactions.

PublicThis study asks how hypothetical interactions with dark matter could change high-energy neutrinos traveling from the blazar TXS 0506+056 to Earth. The authors assume the neutrinos originate inside a dense concentration of dark matter around its central supermassive black hole. Their calculations include both changes in how neutrinos mix among their three types, or flavors, and losses caused by scattering. When the dark matter effect on mixing is very weak, IceCube measurements of the flavor mixture tightly constrain scattering. With a stronger effect on mixing, however, two of the three propagation states can escape without being scattered away, allowing the inferred scattering limits to be as much as 10,000 times weaker. The model also predicts that neutrinos and antineutrinos could arrive with different flavor mixtures even without scattering losses. Measurements of neutrino mixing near Earth provide an additional constraint. The study does not establish that these dark matter interactions occur.

Young explorerNeutrinos are tiny particles that can come to us from far away in space. They come in three kinds and can change kinds as they travel. Scientists used calculations to ask what might happen if these particles met dark matter near a giant black hole. In their model, dark matter could change the mix of kinds and scatter some particles away, while letting others pass through. They compared the model with measurements to see what might be allowed. They have not shown that neutrinos really interact with dark matter this way.

Mathematical foundations and numerical simulations of BDNK hydrodynamics: from heavy-ion collisions to astrophysics

Teerthal Patel, Henry V. Hirvonen, Fábio S. Bemfica+3 more

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

AstronomerThis theoretical and numerical study develops two flux-conservative algorithms for causal, stable first-order BDNK relativistic viscous hydrodynamics on arbitrary 3+1-dimensional spacetime metrics. Both are hyperbolic, causal, and well-posed, pass convergence tests, and reproduce known results. One uses a first-order reduction with mathematically preserved constraints and optional cleaning fields for numerical violations; the coupled cleaning system is proven hyperbolic and well-posed. The other uses a mixed-order formulation proven strictly equivalent to the original BDNK system, without cleaning fields. A new theorem supplies sufficient conditions for converting mixed-order systems into strictly hyperbolic systems. The authors also provide a practical prescription for admissible hydrodynamic frames across a broad class of equations of state, including nonconformal cases. Simulations capture viscous shock broadening and suppression of Kelvin–Helmholtz vortices, reproduce Bjorken and Gubser flows, and examine departures from stationary ideal-fluid configurations in Michel accretion and rotating tori on fixed Schwarzschild and Kerr backgrounds. Boost-invariant heavy-ion simulations using a lattice-QCD-based equation of state and fluctuating TRENTo initial conditions agree with minimal Israel–Stewart theory at small shear viscosity but can differ substantially at larger viscosities, especially with early initialization and rapid longitudinal expansion. These are mathematical and simulation results, not observational findings.

PublicThe researchers develop and test two computer methods for modeling viscous fluids under relativity, including in curved spacetime. Their mathematical analysis establishes that the methods have well-posed equations and respect causality, so influences do not travel faster than light. They also give a practical way to choose valid mathematical descriptions of the fluid for a broad range of relationships between pressure, density, and other properties. In simulations, viscosity spreads out shocks and suppresses swirling instabilities. The team also studies gas falling toward a black hole and rotating rings of fluid, keeping the black-hole spacetime fixed rather than evolving it with the fluid. In simulations relevant to heavy-ion collisions, their approach and another fluid theory agree when shear viscosity is small but can differ substantially at larger viscosity, especially during rapid early expansion. The work presents mathematical proofs and numerical tests, not new observations.

Young explorerScientists made two new computer methods to study how sticky fluids move when gravity and very fast motion matter. In their computer tests, stickiness spread out sudden changes and reduced some swirls. Two ways of describing the fluid mostly matched when it was less sticky, but could disagree when it was stickier. These were computer experiments, not things seen in the sky.

Extragalactic photon-ALP conversion at CTA energies

A. Kartavtsev, G. Raffelt, H. Vogel

• High Energy Physics - Phenomenology

AstronomerThis theoretical study examines photon–axion-like particle (ALP) conversion in extragalactic magnetic fields between galaxy clusters, which could reduce gamma-ray absorption by the extragalactic background light. For TeV photons, refraction on background photons makes the photon–ALP oscillation length comparable to the magnetic-field coherence and transition lengths. The authors derive exact statistical evolution equations for the means and variances of photon and ALP transfer functions in the non-adiabatic regime, where the oscillation and coherence lengths are comparable and much larger than the transition length. They also give analytical predictions for the quasi-adiabatic regime, where the oscillation length is much smaller than both field scales. These are theoretical results, not an observational detection of ALPs; they are relevant to the upcoming Cherenkov Telescope Array and may also apply to models with nonzero ALP masses.

PublicVery energetic gamma rays traveling between galaxies can be absorbed by background light. This paper explores a possible way for them to avoid some of that absorption: magnetic fields might convert light particles into hypothetical axion-like particles and back again. The authors develop mathematical equations describing the average transmission and its variability when the conversion length is comparable to the distance over which the magnetic field remains coherent, but much longer than the distance over which it changes significantly. They also make predictions for a different regime, where conversion occurs over much shorter distances than either magnetic-field scale. The work is theoretical rather than evidence that these particles exist. It could help interpret future observations from the Cherenkov Telescope Array and may apply to models in which axion-like particles have nonzero mass.

Young explorerVery energetic light traveling across space can get swallowed by other light. Scientists wonder whether magnets in space could help it change into a different kind of tiny particle and then change back, letting more light get through. Nobody has shown that happening in this study. The researchers used math to work out how it might happen when the magnets change in different ways. Their math could help scientists understand what a future telescope sees.

Early X-ray emission of short Gamma-Ray Bursts: insights into physics and multi-messenger prospects

Annarita Ierardi, Gor Oganesyan, Stefano Ascenzi+3 more

AstronomerThe study analyzes early X-ray emission (t < 1,000 s) from 16 Swift merger-driven GRB candidates using time-resolved spectroscopy over 0.3–150 keV. Spectra are fitted with a physical synchrotron model and an empirical smoothly broken power law, tracking spectral peak energy and bolometric flux. For the 10 bursts with measured redshifts, the authors find tight rest-frame spectral-energy–isotropic-equivalent-luminosity correlations: νc,z ∝ Liso^(0.64 ± 0.03) for the synchrotron fits and Ep,z ∝ Liso^(0.58 ± 0.04) for the smoothly broken power-law fits. Extrapolating these relations to typical prompt-emission energies reproduces the properties of short GRBs detected at MeV energies; this is an extrapolation, not a direct measurement across that entire energy range. The authors interpret the results as evidence for a common origin of prompt and steep-decay emission and conclude that high-latitude emission does not dominate the early X-ray tails. They also assess detectability with Einstein Probe’s Wide-field X-ray Telescope, without reporting detections by that instrument in this abstract.

PublicResearchers studied the fading early X-ray light from 16 gamma-ray bursts thought to be caused by mergers. Using Swift observations, they compared two models of how the X-ray emission changes during the first 1,000 seconds. For the 10 bursts whose redshifts were known, they found a tight relationship: greater luminosity went with higher characteristic X-ray energy. The precise relationship depended on the model used. Extending these relationships to higher energies also matched the properties of short gamma-ray bursts. The authors interpret this as evidence that the initial flash and the rapidly fading X-rays share an origin, and argue against high-latitude emission as the main explanation for the X-ray tails. They also evaluated whether Einstein Probe’s X-ray telescope could detect such sources; the abstract does not report new detections with it.

Young explorerScientists watched X-ray light fade after 16 huge flashes in space that may have come from things merging together. For 10 flashes, they found that brighter light went with more energetic X-rays. Their results suggest that the first flash and its fading light come from the same kind of process, but they do not prove exactly how it works.

New Constraints on Cosmic-ray boosted Sub-GeV Dark Matter via Light Mediators

Yang Yu, Guan-Sen Wang, Bo Zhang+3 more

• High Energy Physics - Phenomenology

AstronomerThis study investigates cosmic-ray upscattering as a mechanism for making sub-GeV dark matter accessible to underground detectors, where conventional nuclear recoils are otherwise too low in energy. Using LZ, XENON, and Borexino data, the authors derive coupling constraints for scalar, vector, pseudoscalar, and axial-vector mediators with masses from 10^-6 to 1 GeV. The constraints turn over around mediator masses of 10^-3–10^-2 GeV as the relative importance of momentum transfer and mediator mass changes. These model-dependent limits extend direct-detection sensitivity into the sub-GeV regime and highlight the importance of momentum dependence for light mediators; they are not a reported dark matter detection.

PublicVery light dark matter could give atomic nuclei kicks too weak for traditional searches to detect. This study examines whether collisions with cosmic rays could speed up dark matter enough to make it detectable underground. Using data from LZ, XENON, and Borexino, the researchers place limits on the interaction strengths allowed in four theoretical models, rather than report a dark matter discovery. The limits depend on the mass of the proposed particle carrying the interaction and on the momentum exchanged in collisions. Accounting for these effects lets the analysis test lighter dark matter than conventional searches can readily probe.

Young explorerDark matter is something scientists are trying to find. If its tiny bits are very light, they might give a detector a nudge too small to notice. The scientists studied whether fast particles from space could bump those bits and make them move faster. They used clues from three experiments to work out which possible kinds of bumps are still allowed. They did not report finding dark matter.

Global Magnetohydrodynamic Simulations of Monster Shocks in Neutron Star Magnetospheres

Michael P. Grehan, Bart Ripperda, Andrei M. Beloborodov+2 more

• Plasma Physics

AstronomerGlobal relativistic magnetohydrodynamic simulations investigate ultra-relativistic, magnetized “monster shocks” in smooth and perturbed (“wrinkled”) magnetospheres with a global dipolar geometry. The mechanism involves initially small waves from the neutron-star surface or inner magnetosphere growing relative to the background magnetic field and steepening into shocks in magnetically dominated plasma. The simulations confirm analytical predictions for equatorial shocks and provide new insight into oblique shocks away from the equator. Runs in which Alfvén-to-fast-mode conversion forms the shock further support the mechanism’s generic nature. Additional magnetospheric modes of comparable amplitude can fragment the shock front, substantially reduce magnetization, create localized Lorentz-factor enhancements relative to an unperturbed dipole background, and intermittently produce additional shocks along a line of sight. Such shocks could power high-energy emission around isolated magnetars, merging binaries, or collapsing neutron stars; the findings reported here are simulation results, not observational detections.

PublicComputer simulations explore how small waves near a neutron star can grow relative to its surrounding magnetic field and steepen into extremely fast “monster shocks.” These shocks could power high-energy emission. The researchers modeled both smooth magnetic surroundings and surroundings disturbed by other waves. Their simulations agree with earlier mathematical predictions for shocks near the magnetic equator and reveal more about shocks traveling at an angle away from it. They also show that converting one type of wave into another can form these shocks. When other waves have comparable strength, they can break up the shock front, reduce the magnetic dominance of the surrounding material, create localized boosts in speed, and sometimes generate extra shocks along a viewing direction. These are findings from simulations, not observations of actual neutron stars.

Young explorerScientists used computers to study waves around a neutron star. Their models show how small waves can grow into very fast crashes called “monster shocks.” Other waves can break up a crash and sometimes make extra ones. These crashes might help make powerful light, but this study modeled them on computers rather than watching them happen in space.

Kinetic magnetohydrodynamics and Landau fluid closure in relativity

Abhishek Hegade K. R., James M. Stone

• General Relativity and Quantum Cosmology
• Plasma Physics

AstronomerThis theoretical work develops a general-relativistic framework for weakly collisional plasmas, motivated by low-luminosity black hole accretion flows in which ion and electron distributions can depart substantially from thermal equilibrium. The authors derive relativistic drift kinetic equations from the Vlasov-Maxwell equations, formulate moment evolution equations for the gyroaveraged distribution function, and introduce an analytic Landau fluid closure for anisotropic relativistic heat flow. Unlike standard collisional general-relativistic magnetohydrodynamics or extended magnetohydrodynamics, the model does not require strong collisions to maintain thermal equilibrium and consistently incorporates Landau damping through its closure. It offers a complementary approach to fully kinetic simulations; its potential relevance to interpreting horizon-scale black hole images is a motivation, not an observational result reported here.

PublicIn the thin plasma flowing toward some supermassive black holes, particles collide too rarely to keep their energies in thermal balance. Their individual motions can therefore affect how the whole flow moves and carries heat, potentially complicating interpretations of black hole images. This paper presents a theoretical mathematical framework that accounts for these effects within general relativity. It includes a new way to describe heat flowing differently in different directions and incorporates Landau damping, a process involving interactions between particles and plasma waves. The framework complements simulations that follow particle behavior in detail. The abstract reports a theoretical development, not new observations or a demonstrated improvement in black hole image interpretation.

Young explorerNear a giant black hole, tiny bits of matter can swirl around without bumping into each other very often. How those bits move can change how the whole swirl moves and spreads heat. The scientists made a new set of math rules to help describe this. The rules might help scientists understand pictures of black holes, but this paper does not show that they have done that yet.

Identifiability of g mode Resonances in Eccentric Binary Neutron Stars with Multidetector Observations

Mengfei Sun, Jie Wu, Qianning Hu+6 more

• Astrophysics of Galaxies

AstronomerThis simulation study tests whether deep learning can identify weak g-mode resonant phase signatures in eccentric binary neutron star strain signals. Such signatures could probe internal stratification, superfluidity, composition gradients, and the equation of state beyond bulk adiabatic tidal deformability, but are unlikely to be resolved at current detector sensitivities. The authors construct four classes: point-particle, adiabatic-tide, resonant g-mode, and pure-noise samples. For simulated Einstein Telescope, Cosmic Explorer, and joint ET+CE data, neural-network classification accuracies are 0.650, 0.809, and 0.875, versus 0.534, 0.703, and 0.718 for matched filtering on the same samples. The authors attribute the advantage to learning local phase and morphology differences superimposed on the adiabatic tidal background. These four-class simulation results suggest improved identifiability with joint third-generation observations; they are not observational detections of g-mode resonances.

PublicSubtle vibrations inside neutron stars could leave faint timing patterns in gravitational waves from pairs moving on elongated orbits. Those patterns might reveal properties of the stars’ interiors, but current detectors are unlikely to resolve them. Using simulated signals and noise for the proposed Einstein Telescope and Cosmic Explorer, researchers trained neural networks to distinguish four categories, including signals with and without resonant vibrations and noise alone. The networks classified these samples more accurately than the matched-filtering method tested, with the best performance when both detectors were combined. The authors suggest that the networks learn small, local differences in the wave patterns. This is a promising simulation result, not a detection of neutron-star vibrations in real observations.

Young explorerTwo neutron stars moving around each other can make ripples in space. Tiny wiggles inside the stars might leave little clues in those ripples. Scientists made pretend signals and taught a computer to sort them, even with extra noise mixed in. It did best using information from two planned detectors together. Scientists have not found these tiny clues in real signals yet.

Formation of rotating supergiants via stellar mergers in dense clusters: Implications for black hole natal spins

Ishaan Satish, Kyle Kremer, Fulya Kıroğlu+2 more

• Astrophysics of Galaxies

AstronomerThis modeling study investigates stellar mergers as a source of black hole natal spin in young star clusters. The authors analyze roughly 150 Cluster Monte Carlo (CMC) N-body models, prioritizing mergers with mass ratio q > 0.1, and use MESA models to explore angular momentum injection and post-merger evolution for selected candidates. In their current dataset, representative of Milky Way-like globular clusters, up to roughly half of black holes form from stellar mergers, with roughly 10% forming from the significant-merger subset. Angular momentum estimates indicate substantial merger-driven spin-up, while trends with mass ratio and stellar properties suggest correlations with final black hole spin. Dimensionless spins a ≃ 0.5 or higher are expected in some cases, not observationally measured. The proposed pathway includes collapsar-like merger products retaining thick accretion disks that enable efficient spin-up, contrasting with the usual expectation of low natal spins after angular momentum loss. The authors discuss implications for the dynamical formation and retention of gravitational wave sources in clusters.

PublicCould collisions between massive stars help create rapidly spinning black holes? This study explores that possibility using computer models of star clusters and stellar evolution, rather than observations. In the simulated cluster sample, up to about half of black holes come from merged stars; about 10% come from mergers in which the smaller star has more than one-tenth the mass of the larger. The calculations suggest that mergers can add substantial rotation, potentially producing black holes with dimensionless spin values around 0.5 or higher in some cases. A proposed explanation is that some merged stars retain thick disks of material that help spin up the resulting black holes. Whether this rotation survives until black hole formation is central to the study. The process could affect how clusters produce and retain sources of gravitational waves.

Young explorerWhen two big stars join together, they might make a star that spins faster. Scientists used computer models to explore whether that spinning could help make a fast-spinning black hole later. Their models suggest it could happen sometimes, especially if material stays around the black hole and helps it spin up. This is a possibility from models, not something they watched happen.

The Extended Ultrahigh-energy Gamma-Ray Emission in the Vicinity of PSR J2238+5903

Zhen Cao, F. Aharonian, Y.X. Bai+97 more

AstronomerAnalysis of LHAASO data suggests that the TeV gamma-ray source LHAASO J2238+5900 is significantly extended, with a fitted angular extension of 0.54° ± 0.01°, and spatially coincident with PSR J2238+5903. Its spectrum is described by a power law with a cutoff at 41.0 ± 3.5 TeV. A 7.9σ signal above 100 TeV supports its classification as a PeVatron candidate, rather than a confirmed PeVatron. The emission is consistent with a pulsar wind nebula, but the large angular extent also permits a halo interpretation involving electron–positron pairs escaping from the nebula.

PublicLHAASO observations show that the gamma-ray source LHAASO J2238+5900 appears spread out across the sky and overlaps the position of a pulsar. The fitted angular extent is 0.54° ± 0.01°. Its gamma-ray spectrum follows a power-law pattern with a cutoff at 41.0 ± 3.5 TeV, and emission above 100 TeV is detected with a statistical significance of 7.9 sigma. This makes it a candidate for a PeVatron, an accelerator of extremely energetic particles, but does not confirm that classification. The radiation could come from a nebula powered by the pulsar; alternatively, its broad extent could reflect a halo formed by electrons and positrons escaping from that nebula.

Young explorerScientists found a spread-out patch of very energetic light in space, in the same direction as a spinning star called a pulsar. The light may come from a cloud powered by that star. Another possibility is that tiny particles escape the cloud and make a bigger glowing patch around it. The light gives scientists a clue that something there might boost particles to enormous energies, but they are not sure yet.

Residual Galactic binary foreground in LISA stochastic gravitational-wave background inference: source power concentration and spectral degeneracy

Ruo-Yu Guan, Yan Wang

• General Relativity and Quantum Cosmology

AstronomerUsing LISA Data Challenge 2A injections and the Erebor injection-recovery match, the authors construct a catalog residual spectrum over 0.4–6.0 mHz, rather than analyze LISA observations. They separate finite-source non-Gaussianity, quantified by excess kurtosis for independent random phases, from spectral degeneracy between residual power and a stochastic gravitational-wave background (SGWB). Instrumental noise and fiducial SGWB power strongly suppress the excess kurtosis in most bins, but the spectral degeneracy remains. A local Fisher analysis jointly constrains SGWB amplitude Ω₀ and residual-power factor β. For a frequency-independent SGWB with Ω₀ = 10⁻¹¹ and residual power uniform across Fourier frequencies within each bin, marginalizing over β increases the Ω₀ uncertainty by 13.6% with Gaussian Fourier-amplitude covariance and 13.8% with finite-source diagonal random-phase covariance. Under the Gaussian covariance, keeping that increase within 10% requires a prior standard deviation on β no larger than 0.0073. Recomputing this covariance at each fiducial amplitude gives uncertainty increases of 12.7–20.7% across Ω₀ = 10⁻¹³–10⁻¹⁰. The degeneracy persists for alternative within-bin residual-power distributions and diagonal covariances; omitting the residual biases the fitted SGWB amplitude.

PublicPairs of compact objects in our galaxy are expected to produce a strong gravitational-wave foreground for LISA. Signals left over after recovering these sources could obscure a broader gravitational-wave background. Using simulated LISA challenge signals and their recovery results, the researchers studied two different problems: departures from a Gaussian statistical pattern and similarity between the leftover signal’s spectrum and the background spectrum. Noise and the assumed background largely suppress the first effect in most frequency bins, but not the second. In one specified scenario, allowing for uncertain leftover power increased the uncertainty in the background’s strength by about 14%. Ignoring that power biased the fitted background strength. These are findings from simulated data and an uncertainty calculation, not LISA observations; their numerical size depends on the assumed background and residual model.

Young explorerImagine trying to hear a quiet hum while lots of other sounds play. LISA will look for tiny ripples called gravitational waves, but signals from pairs of objects in our galaxy could get in the way. Using pretend LISA data, scientists found that leftover signals can make the hum harder to measure. Ignoring those leftovers can give the wrong answer.

3D Hydrodynamic Simulations of Micro-Tidal Disruption Events Favor a Narrow, Ultra-relativistic Jet for GRB250702B

Fulya Kıroğlu, Taeho Ryu, Alexander Tchekhovskoy+3 more

AstronomerGRB250702B, the longest detected gamma-ray burst, showed seven hours of prompt gamma-ray emission, a day-long X-ray precursor, and a fading X-ray tail lasting weeks. The authors propose a jetted micro-tidal disruption event as an explanation. Their 3D AREPO hydrodynamic simulations of a 1-solar-mass star disrupted by a 10-solar-mass black hole produce a quasi-steady debris envelope within several hours, including a low-density polar funnel with density proportional to r^-2 and a half-opening angle of approximately 15 degrees. Applying an analytic jet-stability model to this simulated environment suggests that luminous ultra-long gamma-ray bursts operate near the stability threshold. Jets with power above a few times 10^47 erg/s, Lorentz factor around 100, and opening angle near 1 degree can survive current-driven kink instability, escape the envelope, and reproduce the observed isotropic-equivalent luminosity of approximately 10^51 erg/s. In the model, post-breakout widening combined with wind-suppressed accretion yields an early isotropic-equivalent X-ray decline proportional to t^-4; after the opening angle saturates near 10 degrees, the decline becomes t^-2. These simulation-based and analytic results favor, but do not establish, narrow relativistic jets as the engines of luminous ultra-long bursts. They also predict a low-luminosity population powered by failed jets and early jet breaks, motivating early multi-wavelength follow-up.

PublicGRB250702B emitted gamma rays for seven hours, making it the longest gamma-ray burst detected. It also had a day-long X-ray signal beforehand and a fading X-ray tail lasting weeks. The researchers propose that a black hole tearing apart a star could explain this unusual sequence. In their computer simulations, the stellar debris forms an envelope around the black hole, with a relatively clear funnel through which a jet might escape. An additional mathematical model suggests that only sufficiently powerful, fast, narrow jets can avoid a twisting instability and emerge brightly. In this explanation, the escaping jet spreads out while its power decreases, producing a rapid X-ray fade that later slows. This is a proposed explanation supported by simulations and modeling, not confirmation of what powered this particular burst. The work also predicts dimmer ultra-long bursts whose jets fail to escape, and early changes in fading behavior that future observations could test.

Young explorerAstronomers saw a space burst shine in gamma rays for seven hours, with X-rays before it and for weeks afterward. Scientists think a black hole pulling a star apart might explain it. In their computer model, the torn-up star makes a blanket of gas. A strong, skinny stream can get through that blanket, then spread out and fade. We do not yet know if this is what really happened. The scientists also predict weaker streams that get stuck inside.

An Optically Motivated Gamma-ray Study of Fermi-LAT Novae

Owen K. Henry, Timothy A.D. Paglione, David Zurek+1 more

AstronomerThe study investigates the proposed shock-powered connection between optical and GeV gamma-ray emission in novae by varying Fermi-LAT analysis time bins and comparing the significance-maximizing duration, t_gamma*, with optical eruption properties. Across the sample, t3—the time for the V-band brightness to fade by three magnitudes—appears to be the favored integration duration for maximizing gamma-ray detection significance, but with substantial scatter. V679 Car, previously considered a marginal gamma-ray nova, is reported at greater than 5 sigma significance. The authors also perform optical–gamma-ray cross-correlation analysis, without reporting its outcome in the abstract. These findings explore, rather than establish, the interpretation that collisionless, non-relativistic shocks generate the gamma rays and supply reprocessed optical emission.

PublicNova eruptions can produce both visible light and high-energy gamma rays. One proposed explanation is that shocks generate the gamma rays and that some shock energy is converted into visible light. To investigate this connection, researchers compared gamma-ray measurements collected over different time intervals with the eruptions’ visible-light fading. The interval that gave the strongest gamma-ray detection tended to match the time needed for the visible brightness to fade by three magnitudes, although the pattern varied substantially between novae. The study also reports a greater-than-five-sigma gamma-ray detection of V679 Car, previously considered only marginally detected. The results do not establish the proposed shock explanation.

Young explorerWhen a star has an eruption called a nova, it can shine with light we see and gamma rays we cannot see. The researchers tried collecting the gamma rays over different lengths of time. They found a rough pattern: the time that made the gamma rays easiest to spot often matched how long the star took to fade by a certain amount. But the eruptions did not all follow the same pattern. The team also found stronger evidence for gamma rays from an eruption called V679 Car. They are exploring whether shocks help make both kinds of light; this study does not show that idea is definitely right.

Finding and using interpretable latents in a neutrino foundation model with sparse autoencoders

Raphaël Bonnet-Guerrini, Johann Ioannou-Nikolaides, Inar Timiryasov+1 more

• Artificial Intelligence
• Machine Learning
• High Energy Physics - Experiment

AstronomerThe authors present a first application of sparse-autoencoder-based mechanistic interpretability to particle physics, examining a neutrino foundation model pretrained on IceCube data and fine-tuned for direction reconstruction. They identify an atlas of physical concepts in its internal representation, validated through held-out tests, matched nuisance controls, and replication across independent dictionary trainings. Causal interventions indicate that the direction-reconstruction head makes little use of this atlas. A newly trained uncertainty head, which predicts angular reconstruction error from the same event-level representation, instead depends causally on atlas features associated with quality and brightness. These model-level findings suggest that interpretability can expose encoded physical information and guide downstream task design; the abstract does not establish improved direction reconstruction.

PublicResearchers examined how an AI model trained on IceCube neutrino data represents information internally. They identified features linked to physical concepts and checked them using separate test data, controls for potentially confounding influences, and repeated analyses. Interventions on the model showed that the component estimating a neutrino's direction barely used these features. The team then trained another component to predict how far the model's direction estimate would be from the correct direction. This component did rely on identified features related to quality and brightness. The results suggest that inspecting an AI's inner workings can help researchers use information it has learned, but they do not demonstrate better direction estimates.

Young explorerScientists looked inside a computer program that learns from data about tiny particles called neutrinos. They found clues it had learned and checked that those clues were not just a fluke. The part that guesses which way a particle came from hardly used these clues. So they taught another part to guess how wrong that direction guess might be. This new part used clues about brightness and quality. That suggests looking inside a program can help scientists find uses for what it has learned, even if it does not make the direction guess better.

Resolving the Galactic Center Region's Gamma-Ray Emission and Searching for its Neutrino Counterpart with HAWC and IceCube

S. Yun-Carcamo, R. Babu, HAWC+1 more

AstronomerUsing approximately 2,860 days of HAWC data with improved machine-learning gamma/hadron separation, the authors present the first spatially resolved model of the Galactic Center at the highest gamma-ray energies. They separate point source HAWC J1745-2857 from Galactic diffuse emission not significant in earlier HAWC analyses. After accounting for the diffuse component, the point-source spectrum extends beyond 100 TeV without evidence of a cutoff, supporting a PeVatron interpretation that is not an artifact of unresolved diffuse emission. Assuming a hadronic origin, they derive a neutrino template and search 12 years of IceCube muon-track data. No significant excess is detected. The first high-energy neutrino upper limit associated with this HAWC-derived multi-component model is approximately 12 times the nominal hadronic prediction. It does not yet test the optically thin hadronic scenario, but establishes the sensitivity needed for future neutrino tests.

PublicThe center of our Galaxy may accelerate cosmic-ray particles to extremely high energies. Using about 2,860 days of HAWC observations, researchers separated its gamma-ray glow into a point source and a diffuse component. Even after accounting for the diffuse glow, the point source emits gamma rays above 100 TeV, with no evidence of a high-energy cutoff. This supports—but does not prove—the interpretation that the Galactic Center accelerates particles to petaelectronvolt energies. If the gamma rays come from interactions involving high-energy protons or other atomic nuclei, neutrinos should accompany them. A search through 12 years of IceCube data found no significant neutrino excess. The resulting upper limit is about 12 times the predicted neutrino signal, so it is not yet sensitive enough to test the scenario in which the gamma rays escape without substantial absorption.

Young explorerScientists looked at very powerful light from the middle of our Galaxy. They separated a bright spot from a spread-out glow. The bright spot still makes extremely powerful light, suggesting that something there may give tiny particles huge boosts. They also looked for tiny particles called neutrinos that could help explain the light, but found no clear extra signal. They need a more sensitive search to check that idea.

Tidal Deformability of Neutron Stars in Scalar-Tensor Theories of Gravity

Stephanie M. Brown

• General Relativity and Quantum Cosmology

AstronomerThe authors calculate fully relativistic neutron-star tidal Love numbers for multipoles l ≥ 2 in scalar-tensor gravity, using several realistic equations of state to examine mass, radius, and tidal-deformability relations relative to general relativity. In certain regimes, their calculations yield electric tidal-deformability differences of approximately 200% and magnetic tidal-deformability differences of approximately 300%. These deviations arise at high compactness, C = M/r ≳ 0.2, and vary slightly with the equation of state. These are theoretical results, not observed departures from general relativity. They suggest that adopting general-relativistic Love numbers could introduce significant errors in gravity tests using binary-neutron-star and neutron-star–black-hole gravitational-wave signals, highlighting the need to distinguish gravity effects from equation-of-state uncertainty.

PublicNeutron stars can be distorted by a companion’s gravity, and those distortions affect the gravitational waves produced as the objects spiral together. Such signals have already helped constrain how matter behaves at extreme densities. This study calculates how neutron stars would respond to tides in scalar-tensor theories, alternatives to Einstein’s general relativity. For especially compact stars, the calculated electric and magnetic tidal responses can differ from general-relativity predictions by about 200% and 300%, respectively, with some dependence on the assumed properties of dense matter. These are theoretical predictions, not detections of a failure of Einstein’s theory. They suggest that using only general-relativity tidal responses could lead to substantial errors when testing gravity with mergers involving neutron stars.

Young explorerA neutron star is a very tightly packed ball in space. When another heavy object is nearby, its gravity can stretch and squeeze the star a little. Scientists used math to work out how this happens under different rules for gravity. For some very tightly packed stars, the answers were very different from what Einstein’s rules predict. They did not see these differences in real stars in this study. Their work suggests that choosing the wrong rules for how stars stretch could make tests of gravity give misleading answers.

Challenging the Weak Cosmic Censorship with Phantom Fields

Giovanni Caridi, Fabrizio Corelli, Paolo Pani

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

AstronomerHigh-accuracy numerical relativity simulations examine spherical collapse of a negative-energy phantom scalar field, deliberately violating the dominant energy condition to test the robustness of weak cosmic censorship outside that assumption. The simulations use fourth-order finite differences to evolve smooth, asymptotically flat initial wave packets with fully coupled matter and geometry. Whereas an ordinary positive-energy scalar field exhibits standard Choptuik critical behavior at the black-hole threshold, the phantom field disperses at every amplitude studied, with no evidence of trapped surfaces, naked singularities, or alternative stationary end states. Although a negative-mass Schwarzschild geometry without an event horizon is possible in principle, the simulations do not dynamically produce such an outcome. No dynamical violation of cosmic censorship is found within the explored parameter space; this is not a general proof.

PublicCould gravitational collapse create a singularity exposed to the wider universe rather than hidden behind a black hole’s event horizon? Researchers tested this possibility in computer simulations of a hypothetical field with negative energy density, removing an important assumption behind the cosmic censorship conjecture. Although such a field could in principle produce a negative-mass geometry without an event horizon, every simulated wave packet spread out instead. The researchers found no evidence of exposed singularities or trapped surfaces. These are simulation results, not astronomical observations, and they show no violation of cosmic censorship only for the configurations tested.

Young explorerScientists used a computer to ask whether a pretend kind of stuff with negative energy could squeeze into a place where the usual rules of space and time break down, without a black hole hiding it. In every case they tried, the stuff spread out instead. They did not find an uncovered trouble spot, but they have not tested every possibility.

Relativistic mode sums for neutron-star tidal response

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

• General Relativity and Quantum Cosmology
• Nuclear Theory

AstronomerThis theoretical study develops a relativistic mode-sum tidal response for non-rotating neutron stars in Regge-Wheeler gauge, using near-zone boundary conditions to define the interior tidal field, overlap integrals, and mode amplitudes. The dominant f-mode contribution agrees with direct matching calculations to within approximately 3% across the equations of state considered. However, the mode-inner-product operator is not positive definite on the full gauge function space, so the mode sum truncated at order ω² is not expected to converge strictly to the direct matching solution. The interior tidal field is also nonunique, although the extensions studied have only a limited effect on the dominant f-mode response. The method’s demonstrated utility therefore rests on a controlled low-mode approximation, not a formally convergent strong-field expansion.

PublicAs two neutron stars spiral toward each other, their gravity raises changing tides that can carry information about the stars’ internal structure. This theoretical work develops a way to calculate those tides within general relativity by combining patterns of stellar vibration. For the models examined, the dominant vibration pattern reproduces a more direct calculation to within about 3%. Important limitations remain: the mathematical structure does not guarantee that the approximation approaches the direct answer as more vibration patterns are included, and the internal tidal field can be defined in different ways. The choices studied have only a limited effect on the dominant pattern. These are findings about a calculation method, not measurements of neutron stars.

Young explorerWhen two neutron stars circle close together, each star’s gravity can stretch and shake the other. Scientists made a new math recipe for working out that shaking. In the star models they tried, using the biggest kind of shake gave an answer very close to a more direct calculation. But adding more kinds of shakes is not guaranteed to make the recipe better, and some choices in the math are still tricky. They tested the recipe with calculations, not by watching real stars shake.

New Universal Relations for Magnetized Neutron Stars

Byon N. Jayawiguna, Siddarth Ajith, Takuya Katagiri+2 more

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study identifies universal relations for magnetized neutron stars assuming a purely poloidal dipolar field and treating magnetic effects perturbatively through second order in field strength. With suitable normalization by stellar mass and polar magnetic-field strength, the authors find an exact relation between magnetic dipole moment and compactness within this framework. They also obtain approximate relations among magnetic dipole moment, magnetically induced quadrupole moment, and ellipticity, with equation-of-state-dependent fractional variations of order 10%. Analytic estimates for Newtonian polytropes reproduce the numerical behavior. The dipole–quadrupole relation is proposed as potentially useful for analyzing gravitational-wave signals from binaries containing magnetized neutron stars; no observational application is reported.

PublicHow a neutron star’s mass relates to its radius depends strongly on the behavior of the dense matter inside it. This theoretical study finds that some relationships involving the star’s magnetism and magnetic distortion depend much less on that uncertain physics. For a particular dipole-shaped magnetic field, and using an approximation that keeps magnetic effects through second order, the researchers find one exact mathematical relationship between suitably scaled magnetic dipole strength and stellar compactness. Other scaled relationships linking magnetism and stellar shape vary by roughly 10% with the assumed properties of the interior. Simplified mathematical models support the numerical findings. One relationship could help scientists analyze gravitational waves from pairs of stars containing a magnetized neutron star, but that use has not been demonstrated here.

Young explorerScientists used math to study very dense stars with magnetic fields. In their models, they found rules linking a star’s magnetism to how squeezed together it is and how its shape changes. Some rules stayed almost the same when they changed their ideas about the stuff inside the star. The rules work for the special kind of magnetic field they studied, so they may not fit every star. One rule might someday help scientists understand tiny ripples in space from pairs of stars.

On the nature of oscillating modes of proto-neutron stars

Dimitra Tseneklidou, Alejandro Torres-Forne, Pablo Cerda-Duran+2 more

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study introduces an automatic classification of oscillation modes in newborn proto-neutron stars (PNSs) surrounded by stalled accretion shocks, using the energy of the modes’ restoring forces. Applied to 28 non-rotating 1D, 2D and 3D core-collapse supernova simulations spanning two numerical codes, different progenitors and different equations of state, the method consistently distinguishes mode families associated with different regions. The authors identify f- and p-mode families associated with the PNS and the shock, and two g-mode families arising in convectively stable regions in the PNS core and near its surface. In these simulations, the dominant high-frequency emission mode is identified as the PNS f-mode, associated with the strong surface density gradient. These are simulation-based findings, not detected gravitational-wave modes. The scheme provides a basis for systematic studies linking mode frequencies to PNS properties and, ultimately, parameter estimation from future gravitational-wave observations.

PublicA newborn neutron star can vibrate, potentially revealing its internal structure through gravitational waves. Researchers have disagreed about how to label these vibrations. This study proposes an automatic sorting method based on the forces that restore the vibrating material toward equilibrium. Tested on 28 computer simulations of stellar explosions without rotation, the method consistently separates vibration families associated with the newborn star, the stalled shock surrounding it, and different regions inside the star. In the simulations, the strongest high-frequency emission mode is linked to the sharp change in density at the star’s surface. These findings are not observations of gravitational waves from newborn neutron-star vibrations. The method could help researchers interpret future detections and infer the stars’ properties.

Young explorerA baby neutron star can wiggle in different ways. Scientists used computer models of exploding stars to sort those wiggles by what pushes the star’s material back into place. They found different kinds of wiggles in different places. This was a computer study, not wiggles spotted in space. The sorting tool could help scientists understand signals they hope to catch someday.

Constraining the Quadratic-mode Amplitude Coupling in GW250114

Yuxin Yang, Changfu Shi, Yi-Ming Hu

• General Relativity and Quantum Cosmology

AstronomerUsing Bayesian inference on the GW250114 ringdown with a model containing the 220, 221, and 220×220 modes, the authors infer the amplitude-coupling coefficient of the quadratic 220×220 mode. Second-order perturbation theory predicts that a quadratic mode’s amplitude scales with the product of its parent-mode amplitudes, with a remnant-spin-dependent coupling coefficient. The inferred coefficient agrees with numerical-relativity fits and second-order perturbation-theory predictions, with no discrepancy exceeding 1.3 sigma. The current data cannot distinguish among these spin-dependent predictions; the measurement provides a basis for tighter tests of nonlinear ringdown dynamics.

PublicAs a black hole settles down, its gravitational waves can contain patterns that interact in ways predicted by Einstein’s theory of general relativity. Researchers analyzed the fading waves of GW250114 to estimate how strongly one predicted pattern is linked to the pattern that produces it. Their estimate agrees with predictions from both computer simulations and mathematical calculations, with no difference larger than 1.3 sigma. However, the data are not precise enough to tell those predictions apart. The analysis opens a path toward more demanding tests of how gravity behaves in black-hole ringdowns.

Young explorerA black hole settling down is a little like a bell after it is tapped, but it sends out ripples in space instead of sound. Scientists studied ripples from an event called GW250114 to see how one ripple pattern might make another. Their estimate fits what their gravity rules predict, but the ripples are not clear enough to choose between the different predictions yet.

Rotation slows the instability of Ellis-Bronnikov wormholes

Nikita M. Shirokov, Ilya Nachevsky

• General Relativity and Quantum Cosmology

AstronomerNonlinear numerical evolutions of stationary rotating Ellis–Bronnikov drainholes supported by a phantom scalar field extend earlier slow-rotation perturbative work. Backgrounds constructed with an independent spectral solver reproduce published symmetric solutions; a misprint identified in a published field equation did not affect the original numerical results. Evolutions seeded only by discretization error show slower collapse with rotation. Some intermediate-spin throats expand instead, with the direction of departure depending on the effective perturbation. At the fastest evolved spin, no growing departure of the throat’s areal radius is detected through t=150 code units, approximately 28 static-instability e-folding times, at three resolutions. Two other rapidly rotating models show no growth during their reliable evolution intervals. Collapsing rotating throats produce axisymmetric quadrupolar gravitational-wave bursts, with greater energy at the higher of the two spins compared. Second-order initial data seed the instability through background truncation error. These results demonstrate delayed collapse and prolonged nondetection of radial growth for the sampled asymmetric backgrounds, not indefinite stability or stability against general nonaxisymmetric perturbations.

PublicComputer simulations suggest that rotation can delay the collapse of theoretical wormholes supported by a phantom scalar field. These are mathematical models, not observed objects. Small numerical errors trigger changes in the simulated wormholes: rotation slows collapse, while some moderately rotating throats expand instead, depending on the disturbance. The fastest-spinning model shows no growing change in throat size throughout a run lasting about 28 times the static instability’s characteristic growth time; two other rapidly rotating models also show no growth during the intervals the researchers consider reliable. This does not prove that spinning wormholes remain stable forever, especially because the simulations start from axisymmetric conditions. Collapsing models also emit simulated gravitational-wave bursts, with more energy in the faster-spinning of the two cases compared.

Young explorerScientists used computers to study pretend space tunnels called wormholes. In their models, spinning made the tunnels close more slowly. Some tunnels grew wider instead. The fastest-spinning tunnel did not start getting steadily bigger or smaller while the scientists watched it on the computer. But watching for a while does not mean it will stay that way forever, and this does not show that real space tunnels exist.

Expanding the Volatile Abundance Inventory for High-Priority K-Dwarf JWST Exoplanet Systems

David R. Coria, Neda Hejazi, Ian J. M. Crossfield+7 more

• Earth and Planetary Astrophysics
• Astrophysics of Galaxies

AstronomerThe study derives [C/H] and [O/H] for six K dwarf exoplanet hosts—K2-141, NGTS-10, WASP-43, WASP-69, WASP-80, and HATS-72—using near-infrared IGRINS spectra, MARCS atmospheres, and TurboSpectrum synthesis. These measurements address the difficulty of traditional optical abundance analyses in cool, molecular-line-rich spectra, especially below 4700 K. Analysis of CO lines near 2.3 microns yields sub-solar carbon-12/carbon-13 ratios for five of the six stars, but the observed spectra are too noisy to measure oxygen-16/oxygen-18 ratios. Uniform gyrochronological ages are also derived for comparison with Galactic chemical evolution models and investigation of abundance-age trends; the abstract reports no specific trend. All six systems host planets targeted for JWST characterization, making the stellar abundances useful chemical baselines rather than direct measurements of planetary composition.

PublicResearchers used near-infrared spectra to measure carbon and oxygen abundances in six cool stars that host planets targeted for study with JWST. Such measurements are scarce because these stars’ crowded visible-light spectra are difficult to analyze with traditional methods. The team also examined isotopes, forms of the same element with different masses: five of the six stars had lower carbon-12 to carbon-13 ratios than the Sun, while the spectra were too noisy to measure oxygen-16 to oxygen-18 ratios. They estimated the stars’ ages from their rotation to investigate possible links between age and chemistry, but the abstract reports no particular age-related pattern. The stellar measurements provide reference points for understanding the planets’ chemistry, origins, and evolution; they do not directly establish the planets’ compositions.

Young explorerScientists studied light from six cool stars that have planets going around them. They worked out how much carbon and oxygen the stars have. Carbon comes in different kinds, and five stars had a smaller balance of the lighter kind compared with the heavier kind than our Sun does. The light measurements were too fuzzy to compare two kinds of oxygen. Learning what is in these stars can help scientists understand their planets, but it does not tell them exactly what is in the planets.

Constraining the Merger Fraction and the Upper Mass Limit of Ultramassive White Dwarfs

Gracyn Jewett, Mukremin Kilic, Pierre Bergeron+7 more

AstronomerThe survey targeted 293 Gaia DR3-selected white dwarf candidates with inferred masses of at least 1.3 solar masses and effective temperatures of at least 11,000 K. Follow-up spectroscopy reached 97% completeness, and model-atmosphere analysis constrained composition and mass; offset dipole models were also applied to selected magnetic objects. Using magnetism, unusual composition, kinematics, and rapid rotation as merger indicators, the authors infer a merger fraction of 53% with uncertainties of −6 and +7 percentage points for white dwarfs above 1.3 solar masses. This supports, rather than directly demonstrates, a binary-merger origin for roughly half of these objects. The sample provides an empirical upper-mass constraint in the solar neighborhood: including general relativistic effects, its most massive member, J0318+7923, has a mass of 1.33–1.35 solar masses, depending on its unknown core composition. Newly identified ultramassive pulsator candidates could probe crystallized CO or ONe interiors if confirmed.

PublicA spectroscopic survey examined a sample of very massive, hot white dwarfs. From clues including magnetic fields, unusual atmospheric chemistry, motions, and rapid rotation, the researchers estimate that about 53% of white dwarfs above 1.3 times the Sun’s mass formed when two stars merged, with an uncertainty of roughly six to seven percentage points. These clues support a merger interpretation rather than directly recording the mergers. The heaviest white dwarf in the sample, J0318+7923, is estimated to have 1.33–1.35 times the Sun’s mass; the exact value depends on its unknown core composition. The survey also identified possible pulsating white dwarfs that, if confirmed, could help reveal their crystallized interiors.

Young explorerScientists studied very heavy stars called white dwarfs. They found clues suggesting that about half of the heaviest ones may have formed when two stars joined together. They also found some that might pulse. If those pulses are confirmed, they could help scientists learn what is inside these stars.

The Complex Magnetic Anatomy of a White Dwarf Chromosphere

Leyla Iskandarli, Jay Farihi, Stefano Bagnulo+6 more

AstronomerPhase-resolved spectroscopy and spectropolarimetry of the DAHe white dwarf LP 705-64 reveal two apparently discrete chromospheric regions that alternate in visibility and magnetic polarity as the star rotates. Hα Zeeman splitting gives field strengths of 9.5 and 22 MG. The 9.5 MG component remains nearly constant and is visible for 60% of the rotation; the 22 MG component increases modestly during the remaining phases. Emission-line equivalent widths vary in antiphase with the broadband light curve, as in GD 356. Abrupt, transit-like transitions require at least one magnetic region to be highly localised and substantially smaller than the inferred dark spots. Intensity and Stokes V/I spectra indicate a configuration significantly more complex than an offset dipole, although higher-cadence observations are needed to distinguish a global field from localised magnetic regions. The data are consistent with co-located magnetic, chromospheric, and dark surface regions. They support intrinsic, localised chromospheric emission consistent with predicted heating by dynamo-driven electrical currents near magnetic poles, rather than establishing that mechanism directly.

PublicObservations of the white dwarf LP 705-64 show two apparently separate regions in its upper atmosphere taking turns in view as the star rotates. Their magnetic fields have opposite polarities and strengths of 9.5 and 22 million gauss. The emission lines become stronger relative to the surrounding spectrum when the star is dimmer overall. Abrupt switches between the magnetic regions imply that at least one is much smaller than the dark surface spots inferred for the star. The magnetic pattern is more complicated than a simple displaced two-pole field, but more closely spaced observations are needed to determine its structure. The measurements are consistent with the magnetic regions, atmospheric emission, and dark spots occupying the same locations. They support—but do not prove—an explanation in which electrical currents generated by a dynamo heat small areas of the upper atmosphere near magnetic poles.

Young explorerAstronomers watched a small star called a white dwarf as it turned. They found signs of two magnetic patches taking turns facing us. The switch between them was very sudden, so at least one patch must be tiny compared with the star’s dark spots. The patches may sit in the same places as those dark spots and glowing gas above them. Scientists think electric currents might heat that gas and make it glow, but they need more observations to understand the star’s magnets better.

Interferometric survey of stellar parameters. Reliable methodology for a direct measurement of the angular diameter in exoplanet host stars

H. Nowacki, D. Mourard, N. Ebrahimkutty+22 more

• Earth and Planetary Astrophysics
• Instrumentation and Methods for Astrophysics

AstronomerThe study addresses calibration bias in evolutionary-model estimates of stellar properties, on which many inferred exoplanet parameters and compositions depend. Using their sample, the authors demonstrate a currently achievable stellar-radius precision of approximately 2% with the CHARA Array. The error budget is dominated by angular-diameter uncertainty, while their methodology yields systematic uncertainties of order 1%. The achieved precision is consistent with the literature. The authors report that their methods improve the accuracy of inferred planetary parameters and improve precision by approximately 50% for planetary radius and 30% for planetary mass.

PublicHow well we know a planet’s size and mass often depends on how well we know its star. The authors note that estimates of stellar properties based on models of stellar evolution suffer from calibration bias. Using their sample and the CHARA Array, they demonstrate that stellar radii can currently be determined with about 2% precision. Most of the uncertainty comes from measuring how wide a star appears in the sky; systematic uncertainties are about 1% with their method. The authors report that this approach also makes inferred planet properties more accurate, improving precision by about 50% for planet size and 30% for planet mass.

Young explorerTo work out how big a faraway planet is, scientists often need to know how big its star is. In this study, scientists used the CHARA Array to measure stars’ sizes very precisely, though the measurements still have some uncertainty. They report that their method also helps them work out planets’ sizes and how much matter they contain more accurately. It does not mean they can look inside the planets.

Tidal Braking Does Not Dominate Open-Cluster Slow Rotators

Zixun Zhan, Chenyu He, Weijia Sun+1 more

• Astrophysics of Galaxies

AstronomerExtended main-sequence turn-offs in open clusters younger than 2 Gyr are commonly attributed to a spread in stellar rotation rates. This study tests the proposed origin of slow rotators through tidal synchronization in close binaries. The authors measured radial-velocity dispersions for eMSTO-associated slow-rotator samples in eight open clusters using VLT/GIRAFFE and SALT/RSS spectroscopy, and extended the analysis to 40 clusters with Gaia DR3 radial velocities. Observed dispersions are generally substantially below predictions for binary populations dominated by close systems in the period range where tidal synchronization should be effective; all 40 Gaia clusters lie below the prediction of the P = 10 d binary-population model. The findings disfavor close, tidally synchronized binaries as the dominant source of slow rotators, but do not exclude contributions from undetected or wider binaries.

PublicStars in open clusters younger than two billion years show a spread in a feature of their brightness-and-color patterns that is commonly linked to different spin rates. One proposed explanation for the slow-spinning stars is that a close companion changes their spin through tidal forces. Researchers tested this idea by measuring the spread in stars' speeds toward or away from us, using spectroscopy for eight clusters and extending the analysis to 40 clusters with Gaia data. The observed speed spreads were generally much smaller than predicted for populations dominated by close pairs. All 40 Gaia clusters fell below the prediction of a model with 10-day binary orbits. This suggests that close companions whose tides synchronize stellar spin with orbital motion are unlikely to explain most slow-spinning stars in these clusters. Undetected companions or more widely separated pairs could still contribute.

Young explorerSome stars in groups spin slowly. Scientists wondered if a nearby partner star could slow their spinning through a tug called a tide. They checked how fast stars were moving toward or away from us. The speeds were less spread out than a model predicted if most slow-spinning stars had very close partners. So very close partners probably are not the main reason these stars spin slowly. But some stars could still have partners that were missed or are farther away.

Dynamical formation of Gaia neutron star binaries in star clusters as a phase-dependent process

Ryutaro Iwakura, Long Wang, Ataru Tanikawa+3 more

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena

AstronomerGaia has discovered detached compact-object binaries with no observable interaction between the compact object and its luminous companion, but their formation pathways remain unclear. Previous N-body studies efficiently produced Gaia BH-like systems in clusters but not Gaia NS-like systems, attributing the difference to a black-hole subsystem dominating the core. This study uses direct N-body simulations of 10^4 solar-mass clusters in a Galactic tidal field to investigate neutron-star–main-sequence binaries during the late, black-hole-depleted phase. In these simulations, systems meeting Gaia-sensitive criteria form only after black-hole depletion. Neutron stars remain in the core throughout, but the black-hole subsystem monopolizes strong encounters until it is depleted. The results support delayed, rather than prevented, dynamical formation of Gaia-sensitive neutron-star–main-sequence binaries relative to Gaia BH-like systems; they do not establish the formation histories of individual observed systems.

PublicGaia has discovered binaries in which a black hole or neutron star has a visible stellar companion but shows no observable interaction with it. How these pairs form remains uncertain. Researchers simulated star clusters containing 10,000 times the Sun’s mass to explore why earlier cluster simulations produced black-hole pairs resembling Gaia’s discoveries more readily than neutron-star pairs. In the new simulations, neutron-star pairs meeting criteria relevant to Gaia’s sensitivity formed only after the cluster’s black-hole population had been depleted. Neutron stars were in the cluster’s center all along, but black holes dominated the strong encounters there until that later stage. The simulations suggest that star clusters can make such neutron-star pairs, but later than similar black-hole pairs; this is not direct evidence of how any particular observed pair formed.

Young explorerGaia has found stars paired with black holes or neutron stars, with no visible signs that they are interacting. Scientists used computer models of groups of stars to explore how some of these pairs might form. In the models, black holes took over the close meetings near the middle of the group. Only after the black holes became scarce did neutron stars form pairs with ordinary stars that met the researchers’ rules for what Gaia could detect. This suggests those neutron-star pairs may need more time to form, but the models do not tell us for sure how the real pairs were made.

Chromospherically Active Stars in the MeerKAT Galactic Plane Survey

Okwudili D. Egbo, David A. H. Buckley, Paul J. Groot+4 more

AstronomerOptical spectroscopic follow-up of 99 radio- and X-ray-active G-, K-, and M-type stars associated with SARAO MeerKAT Galactic plane survey point sources identified chromospheric activity in 46 stars. Ca II H&K emission appears in 39 stars and Ca II infrared-triplet emission in 18, with 11 showing both. Of the 39 H&K emitters, 37 have activity levels exceeding the solar-minimum level. Optical photometry indicates short rotation periods, with activity decreasing as rotation period increases. In a subset with analysed optical light curves, flares coincide with enhanced chromospheric activity; the authors interpret this association as evidence that both trace the same underlying magnetic activity process.

PublicAstronomers examined the visible-light spectra of 99 stars already identified as active at radio and X-ray wavelengths. They found signs of activity in a layer of the stellar atmosphere called the chromosphere in 46 stars. Among 39 stars showing one particular set of calcium emission lines, 37 were more active than the Sun at its quietest. Measurements of changing brightness indicated short rotation periods, with slower-spinning stars tending to show weaker activity. For a subset of the stars, flares occurred at the same time as stronger atmospheric activity. The researchers interpret this timing as evidence that the flares and atmospheric emission arise from the same magnetic process.

Young explorerStars can have busy times when their magnetic fields help make their outer layers glow and flare. Scientists looked at light from 99 stars and found signs of this activity in 46 of them. Stars that took longer to spin around tended to be less active. On some stars, bursts of light happened when their outer layers were more active too. The scientists think the same magnetic activity helps cause both.

Successive Decimetric Bursts Associated with Breakout Magnetic Reconnection during the Decay Phase of an M-Class Flare

Suli Ma, Yihua Yan, Wei Wang+11 more

• Space Physics

AstronomerMUSER imaging spectroscopy at 0.4–2 GHz and SDO observations trace a twisted coronal structure through internal eruption, rise and expansion, and breakout eruption during the M1.1 flare of 17 December 2014. The flare peaked at 01:50 UT during the internal eruption, whereas successive type III-like decimetric bursts occurred during the decay phase, associated with breakout. The radio source coincides with a high-Q region in nonlinear force-free field extrapolations, indicating a quasi-separatrix layer. The authors interpret the bursts as plasma emission from nonthermal electrons accelerated by breakout reconnection between the erupting structure’s outer envelope and the surrounding corona. They attribute sustained acceleration to the larger, higher-altitude twisted structure, extended high-Q region, favorable geometry, and repeated sub-eruptions. The absence of a soft X-ray enhancement suggests upward electron escape or energy loss before reaching the chromosphere. Concentrated burst positions suggest, rather than establish, that pseudostreamers can accelerate, trap, and channel electrons.

PublicResearchers used radio and solar observations to study an eruption accompanying a solar flare on 17 December 2014. A twisted magnetic structure erupted in three stages. The flare reached its brightest point during the first stage, but a series of radio bursts appeared later, as the flare faded and the eruption broke outward. Magnetic-field modeling placed the radio source at a layer where the arrangement of magnetic connections changes sharply. The researchers interpret the bursts as evidence of electrons accelerated when magnetic fields reconnect there. They propose that repeated smaller eruptions helped sustain this acceleration. No accompanying soft X-ray increase was seen, suggesting that most accelerated electrons escaped upward or lost energy before reaching the Sun’s lower atmosphere. The tightly grouped radio sources also suggest that magnetic structures called pseudostreamers may accelerate and guide electrons, but this remains an interpretation.

Young explorerScientists watched an eruption on the Sun using radio signals and pictures. They saw several radio bursts after the solar flare was already fading. They think the Sun’s magnetic fields were changing their connections and giving tiny particles called electrons a push. The bursts came from nearly the same place, suggesting the magnetic fields might guide the electrons along a narrow path. That is an explanation of the clues, not something they watched directly.

Existence of Distinct Strong and Weak Shear Regimes of Self-Generated Turbulent Magnetic Reconnection

Qihui Ming, Alexander J. B. Russell

• Plasma Physics

AstronomerUsing 3D resistive-MHD simulations at S_L = 10^5, the authors test the role of magnetic shear by varying the guide field while holding the initial reconnecting field strength and rate normalization fixed. Compared with the weaker-shear guide-field configuration, the anti-parallel, strong-shear limit develops short-wavelength current-layer corrugations and substantial broadening rather than retaining a narrow layer with locally coherent flux ropes. Fluctuation EMF sustains the reconnection-layer electric field, and V_rec/V_A rises from approximately 0.01 to 0.03. The simulations indicate that magnetic shear can select between a guide-field regime consistent with flux-rope mediation and a faster, turbulence-broadened regime. The proposed connection to the sudden onset of fast reconnection in eruptive solar flares is an interpretation, not an observational demonstration.

PublicMagnetic reconnection rearranges magnetic fields, but what controls its rapid, turbulent form remains uncertain. In three-dimensional computer simulations, the researchers changed the magnetic-field geometry while keeping the initial strength of the reconnecting field fixed. When the opposing fields were anti-parallel, representing stronger magnetic shear, the reconnection region developed small-scale ripples and became much broader. This differed from the narrower region containing coherent, rope-like magnetic structures in the weaker-shear case. The simulated reconnection rate was about three times higher in the strong-shear case. The authors suggest that this change of mechanism could explain why fast reconnection suddenly begins in eruptive solar flares, but the study does not establish that explanation through observations of flares.

Young explorerThe scientists used a computer to study how magnetic fields change the way they connect. In one setup, the magnetic pattern had little rope-like shapes. When the fields pointed straight against each other, the place where they changed became wiggly and wider, and the change happened about three times as fast. The scientists think this might help explain why magnetic changes can suddenly speed up during big flares on the Sun, but the computer study does not prove that happens on the Sun.

The OpenMULTI3D stellar analysis package. A 3D non-LTE spectrum synthesis code for AFGKM-type stars within the DISPATCH framework

Richard Hoppe, Maria Bergemann, Philipp Eitner+4 more

AstronomerThe authors present OpenMULTI3D, an open-access 3D non-LTE radiative-transfer and spectrum-synthesis code based on the unreleased MULTI3D. Intended to support large grids of AFGKM stellar spectra for upcoming surveys including WEAVE, 4MOST, and SDSS-V, the paper describes its input physics and numerical implementation. Selected tests compare outputs with literature results for 1D and 3D NLTE departure coefficients, 3D NLTE abundance corrections, synthetic spectral energy distributions for three stellar types, and 3D NLTE Balmer-line profiles of a metal-poor red giant. The abstract does not quantify agreement or computational performance. The authors also demonstrate time-dependent spectral synthesis, suggesting possible applications in precision stellar physics and exoplanet spectral analysis. These are code calculations and tests, not new observational findings.

PublicThe paper introduces OpenMULTI3D, openly available software for calculating how light travels through a three-dimensional model of a star’s atmosphere and what spectrum it produces. It accounts for departures from local thermodynamic equilibrium, rather than assuming that atomic states are set by local conditions alone. The aim is to help scientists interpret the millions of stellar spectra expected from upcoming surveys. The authors describe the software and compare selected calculations with published results, though the abstract gives no numerical measure of accuracy or speed. They also demonstrate calculations of spectra that change with time, which could be useful for precise studies of stars and for analyzing exoplanet spectra. The work presents a modeling tool, not a new discovery from telescope observations.

Young explorerStarlight can be spread out into a pattern of colors that helps scientists learn about stars. The authors made a computer tool called OpenMULTI3D that makes pretend starlight from a model star, including how light moves through its outer layers. They compared some of its calculations with results other scientists have published. They also showed how it can make light patterns that change with time. The tool could help scientists understand real starlight, but this paper is about computer models, not finding a new star or planet.

A joint astrometric, eclipse timing and radial velocity orbit for the hierarchical triple V819 Herculis

Furkan Akar, Özgür Baştürk

AstronomerA joint Bayesian Keplerian analysis of ground-based astrometry, radial velocities and eclipse timing variations yields a self-consistent three-dimensional outer orbit for the hierarchical triple V819 Herculis. The fitted period is 2016.97 ± 0.27 d and eccentricity is 0.6800 ± 0.0016; the same geometry reproduces the sky-plane astrometry, eclipse-timing light-travel-time signal and tertiary radial velocities. Dynamical masses inferred from these data alone are 2.721 ± 0.055 solar masses for the inner binary combined and 1.954 ± 0.070 solar masses for the tertiary. The fit gives a light-travel-time amplitude of 0.0104 d, a tertiary RV semi-amplitude of 18.46 km/s and an orbital parallax of 14.08 ± 0.13 mas, consistent with Gaia DR3, Gaia DR2 and the HIPPARCOS New Reduction. The tertiary mass exceeds expectations for a standard G8 main-sequence star, suggesting, but not establishing, an advanced evolutionary stage. The outer period is about 900 times the inner period. Predicted tertiary positions cover five years beyond 2026.5 to support future observations.

PublicV819 Herculis contains a close pair of stars and a third star on a much wider orbit. Researchers combined measurements of positions on the sky, motion toward or away from us, and shifts in eclipse times to infer the system’s orbit and masses. Their model finds that the wide orbit is distinctly elongated and takes 2016.97 ± 0.27 days, about 900 times as long as the close pair’s orbit. The close pair together has 2.721 ± 0.055 times the Sun’s mass, while the third star has 1.954 ± 0.070 times the Sun’s mass. The distance inferred from the orbit agrees with Gaia and HIPPARCOS results. The third star is more massive than expected for its G8 classification if it were a standard main-sequence star, which may mean it has reached a later stage of its life; this is an interpretation, not a confirmed evolutionary state. The researchers also predict its positions for five years beyond 2026.5 to help plan future measurements.

Young explorerV819 Herculis is a family of three stars. Two circle close together, while the third follows a much bigger, stretched-out path around them. Scientists studied where the stars appear, how they move, and when one star hides another. They used these clues to work out the stars’ paths and how heavy they are. The third star seems heavier than expected for its kind, so it might be at a later stage of its life, but scientists are not sure. They also worked out where it should appear over five future years, so new observations can check their predictions.

SQUALO II: Probing Accretion Through CO Molecular Outflows in Massive Star-forming Clumps

S. Mercimek, G. A. Fuller, A. Traficante+6 more

• Astrophysics of Galaxies

AstronomerAn ALMA CO (J=2–1) study of 13 SQUALO massive clumps with clump-scale infall identifies 51 high-velocity lobes belonging to 31 outflow systems. Physical and dynamical properties are derived assuming local thermodynamic equilibrium; outflow-inferred accretion rates are typically 10^-5–10^-3 solar masses per year. Maximum outflow velocity depends little on candidate driving-core mass, making it an unreliable protostellar-mass tracer in clustered environments. Outflow momentum flux correlates positively with clump surface density, while the apparent decrease in accretion rate with increasing virial parameter is statistically nonsignificant. Total outflow-inferred accretion rates show a tentative positive relation with clump infall rates but are systematically lower, suggesting that detected outflows account for only part of the large-scale mass flux. Clump luminosity-to-mass ratio moderately anticorrelates with projected outflow length, but projection, observational limitations, and the embedded source population preclude a unique evolutionary interpretation. Together with continuum-derived fragmentation properties, the observations indicate that compact cores within infalling clumps drive the outflows. A connection between clump infall and protostellar accretion remains tentative; mass transfer from filaments to individual protostars is not directly traced.

PublicAstronomers used ALMA to study fast-moving molecular gas expelled by forming stars in 13 massive gas clumps where material is also falling inward. They identified 31 outflow systems, comprising 51 lobes of high-speed gas. From these outflows, they indirectly estimated that the forming stars typically gather between one hundred-thousandth and one thousandth of the Sun’s mass each year. The fastest outflow speeds were only weakly related to the masses of the candidate source cores, so speed alone is not a reliable guide to a young star’s mass in these crowded regions. Outflows carried momentum away at higher rates in clumps with greater mass per unit area. There was also a tentative indication that faster inward flow across a clump accompanies faster growth of its forming stars, but the inferred stellar growth rates were consistently lower than the clump’s inward-flow rate. This suggests that the detected outflows reveal only part of the overall movement of material. The observations indicate that compact cores inside the clumps drive the outflows, but they do not directly follow gas all the way from filaments to individual forming stars.

Young explorerBaby stars grow inside big clouds of gas. As they grow, they also send some gas rushing outward. Astronomers looked at 13 big gas clouds and found 31 sets of these outward flows. They used the escaping gas to estimate how quickly the baby stars were growing. Clouds with more gas falling inward might have faster-growing stars, but the scientists are not sure yet. They also could not watch the gas travel all the way from long strands of cloud into each baby star.

Ensemble Individual Mode Frequency Modeling of Kepler Giants - Extending the IACgrid towards the red-giant branch

D. H. Grossmann, S. Mathur, P. G. Beck+7 more

AstronomerThe authors fit individual oscillation-mode frequencies using a grid of stellar evolutionary models to improve parameter estimates for red-giant branch stars beyond global asteroseismic modeling. Validation against published individual-frequency analyses yields closely agreeing masses, radii, and ages. Applied to around 100 Kepler red-giant branch stars with near-solar masses and metallicities, the method gives average random uncertainties of 3.4% in mass, 1.3% in radius, and 13.2% in age. In this sample, inferred ages are on average 14% larger than those from global seismic mass-constrained modeling. Modeled luminosities agree within 1.0% with luminosities derived from Gaia parallaxes. The authors conclude that individual-frequency modeling improves age precision by a factor of two, strengthening constraints for galactic archaeology. These are model-dependent parameter estimates; the reported random uncertainties should not be read as a complete accounting of systematic errors, and the application is restricted to the stated stellar sample.

PublicEstimating stellar ages helps reconstruct the Milky Way’s history, but the answers depend on how stars are modeled. This study uses individual vibration frequencies of red-giant stars, rather than only broad summaries of their vibrations, to compare observations with models of stellar evolution. After checking the method against earlier detailed studies, the researchers applied it to around 100 stars observed by Kepler, with masses and chemical compositions near the Sun’s. Their average random age uncertainty was about 13%, and their inferred ages were on average 14% older than estimates from the comparison method. The authors report roughly twice the age precision, while their modeled brightnesses closely match estimates based on Gaia distances. Better precision does not eliminate possible systematic errors in the models.

Young explorerStars wiggle, a little like bells ringing. Scientists used the separate wiggles of about 100 big stars to help work out how old they are. They compared the wiggles with computer models of how stars grow older. Their age estimates were less uncertain than before and usually older than estimates from another method. They still do not know the exact ages. This could help us learn our galaxy’s story.

Cosmic Ray Inter-Station Fluctuations as Precursors of Geomagnetic Storms: Causal Baseline Analysis and Forecasting Limitations

Haoyang Li, Zongyuan Ge, Zhaoming Wang

AstronomerThe study analyzes 25 years of hourly neutron-monitor data from seven stations (1995–2019), using a strictly causal baseline fitted only to past geomagnetically quiet days to avoid solar-cycle bias associated with non-causal baselines. Two direction-free indices, inter-station dispersion and mean-removed variance, show average enhancements before storm sudden commencements relative to a quiet random control, with larger window-mean amplitudes for stronger storms. These broad ensemble enhancements do not establish event-specific lead times. In a Molchan-diagram evaluation, single-threshold alerts from either index fail to exceed the random-alert baseline at the 95th-percentile threshold. The storm-intensity correlation is moderate (ρ = −0.28), with AUC = 0.66 for severe versus moderate storms. The authors interpret these fluctuations as diagnostics of heliospheric disturbance, not standalone operational predictors, and conclude that reliable warnings require combination with solar-wind and interplanetary-magnetic-field information.

PublicCan changes in cosmic rays help warn of geomagnetic storms? Researchers examined 25 years of hourly measurements from seven neutron-monitor stations, comparing each period only with earlier geomagnetically quiet days. Two measures of differences and fluctuations across stations were higher, on average, in the days before storms, and stronger storms tended to have larger signals. But this broad average pattern does not tell us how far ahead any particular storm can be predicted. When tested as simple alerts, neither measure performed better than random alerts at the study’s 95th-percentile threshold. The authors conclude that these cosmic-ray fluctuations can reveal disturbed conditions in space, but cannot provide reliable storm warnings on their own; they would need to be combined with solar-wind and magnetic-field information.

Young explorerScientists used seven stations to watch tiny particles from space for 25 years. They found that the stations’ readings tended to differ more before magnetic storms around Earth, especially stronger ones. But that pattern did not reliably tell them when a storm was coming: simple warnings based on it did no better than random warnings in their test. The scientists say these readings offer clues about unsettled space weather, but need other clues too before they can give reliable warnings.

Late Epoch Infrared Spectroscopy and Two-Component 3D Photoionization Modeling of Classical Nova V5668 Sgr

Sarah H. Taft, Charles E. Woodward, Bruno C. Santos+2 more

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena

AstronomerInfrared spectroscopy probes the ejecta of the Fe II classical nova V5668 Sgr, which erupted on 15 March 2015. Mt. Abu near-infrared spectra show emission from H, He, N, S, Ti, and Si. SOFIA/FORCAST spectra reveal forbidden [Ne II] and [O IV] lines at 12.8 and 25.9 micrometres, respectively, plus features at 6.2 and 11.3 micrometres attributed to polycyclic aromatic hydrocarbons. One-dimensional Cloudy photoionization models require two components, suggesting morphologically complex ejecta, and infer He, N, Ne, S, Ti, Si, and O abundances above fiducial solar values. Three-dimensional pyCloudy emission profiles provide visualizations of the ejecta and their complex composition. The structural and abundance conclusions are model-based interpretations, rather than direct measurements of a unique three-dimensional configuration.

PublicAstronomers studied infrared light from gas expelled by V5668 Sgr, a nova that erupted in March 2015. Its spectrum contains signatures of several elements, including hydrogen, helium, neon, and oxygen. Two additional features are attributed to polycyclic aromatic hydrocarbons, a family of carbon-based molecules. Computer models needed two gas components to reproduce the system, suggesting that the expelled material has a complicated structure. The models also indicate that several elements are more abundant than in a standard solar comparison. Three-dimensional visualizations help illustrate the ejecta, but their structure and chemical enrichment are inferred through modeling rather than directly mapped by these observations.

Young explorerA star called V5668 Sgr had a big outburst and threw gas into space. Astronomers studied the gas’s light to find clues about what it contains. They found signs of different elements and possible carbon-based molecules. Computer models suggest the gas is not one simple cloud and may be richer in some elements than the Sun. Those ideas come from matching models to the light.

Dynamical plausibility of triple-assisted interaction in Be-star multiple systems

C. A. Guerrero, O. V. Maryeva, M. Kraus

AstronomerThe study tests whether observed classical Be-star multiple systems permit triple-assisted interaction, with a tertiary inducing Kozai–Lidov eccentricity excitation in an unresolved inner binary. Speckle detections, reported inner periods, and proper-motion anomalies (PMa) are compared with synthetic hierarchical triples subject to stability, secular-timescale, inner-periastron interaction, and observational constraints. Mass-aware simulations identify HD 35079 and HD 55606 as the clearest period-plus-speckle matches. HD 205329 is plausible but depends on an approximate PMa constraint; HD 37330, HD 41600, and HD 71510 are also PMa-dependent candidates. For HD 41335, period-plus-speckle and PMa-plus-speckle constraints are separately compatible, but no configurations satisfy all three at the adopted tolerance. A separate angular-momentum estimate gives a median required accreted mass fraction of about 4.8%, conditional on the adopted assumptions. The results establish dynamical plausibility for stable, KL-active architectures, not a confirmed evolutionary origin for Be-star rotation.

PublicClassical Be stars spin rapidly and have disks of gas around them, but the source of their spin remains uncertain. This study tests one possible explanation: in a three-star system, an outer companion could stretch the orbit of an inner pair, bringing those stars close enough to interact. The researchers compared observations with simulated triple-star systems. HD 35079 and HD 55606 provided the clearest matches using measured inner orbital periods and speckle observations. Several other systems remained possible candidates, although their compatibility depended on constraints from apparent motion. For HD 41335, some combinations of observations could be matched, but all three constraints could not be satisfied together within the chosen tolerance. A separate estimate suggests that the median mass needed to be gained to supply the spin is about 4.8%, under the study's assumptions. These findings show that the proposed mechanism is dynamically possible in several systems; they do not show that it actually produced the stars' rapid rotation. Further observations are needed.

Young explorerSome stars spin very fast and have gas around them like a disk. Scientists wonder whether other stars helped them spin so fast. They used observations and computer models to test an idea: a third star might change how two nearby stars move, making them come close enough to interact. The models showed that this could work for some of the star systems they studied, but not every system fit all the clues. That means the idea is possible, not that scientists have proved it happened. They need to keep watching the stars.

TitanMPAS - a new global and regional Titan atmospheric circulation model. Part I: Global model results

Yuan Lian, Mark I. Richardson, Claire E. Newman+1 more

• Atmospheric and Oceanic Physics

AstronomerTitanMPAS is a new global and regional Titan climate model coupling the non-hydrostatic MPAS dynamical core with TitanWRF physics, corrections to thin-atmosphere approximations in gravity and curvature terms, an improved moist-convection parameterization, and observed surface properties. Simulations spanning more than 100 Titan years at 1° resolution with realistic topography produce stratospheric superrotation, with typical equatorial winds above 120 m/s and maximum zonal winds exceeding 170 m/s. Modeled temperature profiles agree well with Cassini CIRS observations, and tropospheric winds, temperatures, and methane abundances agree well with Huygens measurements. The simulations also reproduce major seasonal methane-precipitation patterns inferred from cloud activity and methane-abundance variations derived from Cassini VIMS reanalysis. Resolution tests yield faster stratospheric superrotation and stronger near-surface winds at higher resolution, the latter attributed to better-resolved terrain. The model exhibits diurnal variations in near-surface temperature, pressure, wind magnitude, and methane abundance despite weak insolation. Potential topographic effects on methane transport and eddy momentum flux remain topics for future investigation.

PublicResearchers developed TitanMPAS, a new computer model of Titan’s climate that simulates atmospheric motion and the methane cycle. In simulations lasting more than 100 Titan years, the model produces fast winds in the upper atmosphere and agrees well with several measurements from Cassini and the Huygens probe. It also captures broad seasonal patterns of methane rainfall inferred from observed clouds, along with variations in atmospheric methane derived from Cassini data. More detailed simulations produce faster upper-atmosphere winds and stronger winds near the surface, where finer detail better represents the terrain. The model predicts daily changes in conditions near the surface, including temperature, pressure, wind speed, and methane abundance, even under weak sunlight. The simulations also suggest that terrain may affect methane transport and the movement of momentum through the atmosphere, but those possible effects need further study.

Young explorerScientists made a new computer model to explore Titan’s weather. It follows winds and methane, which can fall as rain there. Some of the model’s weather matches measurements taken by spacecraft, and it makes very fast winds high above the ground. It also shows weather changing during the day, even though the sunlight is weak. The shape of the ground may change how the air and methane move, but scientists still need to study that more.

Coherent radio emission at 45 MHz from the nearby planet-hosting star GJ 725A

H. W. Edler, J. R. Callingham, I. Davis+7 more

• Solar and Stellar Astrophysics

AstronomerAn untargeted circular-polarization survey with LOFAR LBA detected transient emission coincident with the quiescent, planet-hosting M dwarf GJ 725A at 3.5 pc during a one-hour observation. The signal has 74±16% circular polarization and a peak brightness of 135±17 mJy/beam at 42–50 MHz. A 3σ upper limit of 48 mJy/beam at 50–66 MHz implies a drop of at least a factor of three across 12 MHz, indicating a strong spectral feature or cutoff near 50 MHz. The authors report this as the lowest-frequency confirmed detection of a stellar system. The estimated brightness temperature of approximately 10^14 K, transient character, and polarization favor electron cyclotron maser emission, but do not establish its astrophysical origin. Proposed explanations are auroral emission from an undetected wide-orbit giant planet with a magnetic field of at least 18 G, interaction between the star and its known 11-day terrestrial planet GJ 725Ab, or stellar magnetic activity. Further ultra-low-frequency monitoring, preferably simultaneous X-ray, UV, and Hα observations, and a search for a giant planet on a thousands-of-days orbit are proposed to distinguish these scenarios.

PublicA radio survey detected a brief, very-low-frequency signal at the position of GJ 725A, a nearby star known to host a planet. The authors report that it is the lowest-frequency confirmed radio detection of a stellar system. The signal appeared between 42 and 50 MHz but was not detected in the higher 50–66 MHz band, suggesting a sharp feature or cutoff near 50 MHz. Its strong circular polarization and estimated intensity favor a mechanism called an electron cyclotron maser, which produces radio waves in a magnetic environment. However, the observations cannot tell where within the system the signal originated. It could come from auroras on a still-undiscovered giant planet, a magnetic interaction involving the known planet, or the star's own magnetic activity. More radio monitoring, observations at other wavelengths, and a search for an additional planet are needed to test these possibilities.

Young explorerAstronomers found a short burst of radio waves coming from the direction of a nearby star that has a planet. The burst had clues that suggest magnets in space helped make it. But they do not yet know exactly where it came from. It might be from the star itself, from the star and its known planet affecting each other, or from glowing auroras on a big planet nobody has found yet. They want to look again in different ways to find out.

Estimations for strong and weak hot Jupiter magnetism: A Python package with interpolators and scaling laws

Albert Elias-López, Aline Vidotto, Daniele Viganò+3 more

• Instrumentation and Methods for Astrophysics

AstronomerThe study models how the depth of energy deposition responsible for hot-Jupiter inflation affects predicted dynamo fields. It combines one-dimensional evolutionary interior models with magnetic-field scaling laws in the fast-rotating regime (Rossby number ≲0.1), considering deep and shallow heating as limiting cases. Deep heating maximizes convective flux through the dynamo region and predicts fields up to about 100 G; shallow heating suppresses convection and predicts fields of order 1 G. The authors argue that shallow deposition is more realistic for most proposed heating mechanisms. Strong-field predictions are compatible with indirect star–planet interaction estimates, while weak-field predictions agree with recent atmospheric constraints. Neither constitutes an unambiguous direct radio detection, which remains lacking. Observable-based scaling relations are derived to support future tests using atmospheric winds, star–planet interactions, and radio observations, potentially distinguishing competing interior-heating scenarios.

PublicHow strong are the magnetic fields of hot Jupiters, giant planets orbiting close to their stars? This study predicts that the answer depends strongly on where energy is deposited inside these inflated planets. In the models, deep heating drives stronger internal convection and can produce magnetic fields up to about 100 gauss. Heating closer to the surface instead produces fields around 1 gauss; the authors consider this shallower heating more plausible for most proposed mechanisms. These are model predictions, not direct measurements. Existing indirect evidence is compatible with different scenarios, and no unambiguous direct radio detection has yet been achieved. Future observations could help reveal both the planets’ magnetic fields and how their interiors are heated.

Young explorerSome giant planets live very close to their stars. Scientists used computer models to ask how strong these planets’ invisible magnetic fields might be. Heating deep inside could make a strong field, while heating nearer the outside could make a much weaker one. Scientists have clues, but they have not clearly detected these fields through radio signals yet. Future observations may help them find out.

New optimisations for exact, scalable 2D Gaussian process inference, with applications to astronomical time-series

Mark Fortune, Neale P. Gibson, Benjamin Pope

• Instrumentation and Methods for Astrophysics
• Computation

AstronomerThe authors present exact Gaussian-process optimisations in the JAX-based package luas that use Kronecker product algebra to extend 1D methods to multidimensional gridded data. They report flexible, efficient analysis of 2D datasets with millions of points, with computational costs often below those of transit light-curve modelling. The motivating application is JWST transmission spectroscopy: treating spectroscopic light curves as statistically independent can neglect wavelength-correlated noise from sources such as detector readout and stellar granulation, potentially biasing atmospheric retrievals. The abstract does not report a measured retrieval bias or a new atmospheric result. The authors argue that these methods will help spectroscopy of smaller targets around bright stars as noise floors become limiting. They also propose applications to ground-based high-resolution spectroscopic time-series, extreme-precision radial velocities and high-contrast imaging, noting that certain 2D GP models probabilistically generalise PCA. Novel optimisations for the Linear Mixing Model and Linear Model of Coregionalisation may also have uses in machine learning and geostatistics.

PublicAstronomical measurements often contain patterns of unwanted variation shared across time, wavelength or image position. The authors introduce software called luas that makes a statistical tool known as a Gaussian process more practical for large, multidimensional datasets. They report that it can efficiently handle two-dimensional datasets containing millions of measurements. One motivation is JWST observations of planets passing in front of their stars: analyses commonly treat measurements at different wavelengths as independent, even though stellar activity and detector noise can link them. Ignoring those links could bias estimates of a planet’s atmosphere, but the abstract does not establish that such a bias has been measured. The authors argue that their approach could help studies of smaller planets around bright stars and suggest other uses in astronomy and beyond; these are potential applications, not reported discoveries.

Young explorerWhen astronomers study a planet crossing in front of a star, they measure the light in different colors. Unwanted wiggles in one color can be linked to wiggles in another. If scientists ignore those links, they might get the wrong idea about the planet’s air. The researchers made a computer tool called luas to help handle linked wiggles in very large sets of measurements. They say it can work efficiently with millions of measurements. They hope it will help scientists study smaller planets, but they do not report discovering a planet or finding out what its air contains.

CO gaps in cold transition disks around low-mass stars

A.A. Rota, N. van der Marel, E.F. van Dishoeck+1 more

AstronomerHigh-resolution ALMA Band 6 observations probe three cold, inclined transition disks around K and M stars with no evidence for inner dusty disks. The 230 GHz continuum resolves dust cavities with radii of 30–40 au, while CO emission extends into these cavities; more abundant CO isotopologues have smaller apparent cavity radii. No inner continuum component is detected, consistent with the absence of near-infrared excess. Using the accretion rates, the authors estimate inner-disk gas-to-dust ratios at 1 au as high as 10^5. The 13CO brightness-temperature profiles resemble those of other transition and full disks, and neither brightness temperatures nor gas-to-dust ratios differ significantly from transition disks around more luminous stars, contrary to expectations. Target-specific thermochemical modeling or multi-transition analyses are needed to constrain cavity structures. Companions more massive than Jupiter on eccentric orbits could explain the observed structures, but this interpretation requires further modeling.

PublicALMA observations of three planet-forming disks around K- and M-type stars reveal large central gaps in the dust, each extending 30–40 times the Earth–Sun distance from its star. Gas traced by carbon monoxide reaches farther inward than the detected dust. No inner dust disk was detected, in agreement with the lack of extra near-infrared light that such dust could produce. Taking into account how quickly material falls onto the stars, the researchers estimate that gas could outweigh dust by as much as 100,000 to one at the Earth–Sun distance. Despite expectations, the measured gas brightness temperatures and estimated gas-to-dust ratios do not differ significantly from those in transition disks around brighter stars. Planets more massive than Jupiter traveling on stretched-out orbits might explain these structures, but the observations do not establish that explanation; further modeling is needed.

Young explorerAstronomers looked at three stars with big rings of dust around them. They found wide gaps in the dust near the stars, but gas still reaches into those gaps. They could not see a little dust ring close to any of the stars. Very big planets moving along stretched-out paths might help explain the gaps, but the astronomers need to do more work to find out if that idea is right.

Validation of Habitable Zone Limits with a New Radiative-Convective Equilibrium Climate Model

Jacob Haqq-Misra, Eric T. Wolf, Ravi K. Kopparapu

• Solar and Stellar Astrophysics

AstronomerExoColumn provides an independent one-dimensional radiative-convective equilibrium comparison with the widely used Clima habitable-zone boundaries. It combines independently developed atmospheric column physics with the ExoRT correlated-k radiation core shared by ExoCAM. After calibration to present-day conditions, its tropospheric temperatures agree with other RCE models within a few kelvin. Against line-by-line benchmarks, both ExoRT and Clima reproduce outgoing longwave flux within a few percent; their differences are attributed to their spectral line databases. Using the same inverse climate approach as previous studies, ExoColumn yields moist- and runaway-greenhouse inner limits of 0.970 and 0.966 au, respectively, and a maximum-greenhouse outer limit of 1.611 au at 8.7 bar CO2 partial pressure. Calculations extend to 12 host stars spanning 2000–7200 K and planets of 0.1, 1, and 5 Earth masses, with updated boundary coefficients provided. ExoColumn places the boundaries systematically closer to the star than Clima does, but agreement within a few percent in orbital distance supports the robustness of Clima’s estimates. This is model-based validation, not observational confirmation of planetary habitability.

PublicAstronomers use a star’s habitable zone as a guide when choosing planets to study. Its estimated boundaries depend on climate calculations, and a widely used set had not previously been independently checked with a comparable model. The new ExoColumn model supplies that check. Its simulated boundaries lie slightly closer to the host star than those from the established Clima model, but the two agree within a few percent in orbital distance. The researchers also calculate updated boundaries across a range of star temperatures and planet masses. These results support the reliability of the earlier climate estimates; they do not establish that any particular planet is habitable.

Young explorerScientists use computer models to work out where a planet might be neither too hot nor too cold for liquid water. They made a new model and compared its answers with an older one. The answers were close, though the new model put the edges a little nearer the star. That helps scientists trust their maps, but it does not mean they found a planet with water or life.

Advances in High-Precision Astrometry for Exoplanet Detection for Astrometric Missions

Fabien Malbet, Jerôme Amiaux, Florence Ardellier-Desages+13 more

• Instrumentation and Methods for Astrophysics
• Solar and Stellar Astrophysics

AstronomerThis review discusses detector characterization, reference-star optical-distortion calibration, and differential astrometry toward sub-microarcsecond accuracy for Earth-mass exoplanet detection and studies of galactic dark matter. It highlights RETINA, which aims to raise the technology readiness of Pyxalis GIGAPYX 220 MP CMOS detectors for future missions such as Theia and HWO. Calibration methods include Young’s fringe projection to monitor pixel geometry and intra-pixel response across gigapixel-scale focal planes. The target is astrometric precision of a few tens of micropixels on the focal plane. Technical strategies, laboratory validations, and system integration are discussed, but the abstract provides no quantitative validation results establishing that this target has been achieved.

PublicFinding Earth-mass planets around nearby Sun-like stars requires measuring extremely small changes in stellar positions. This review describes efforts to make those measurements more reliable by carefully mapping camera pixels, correcting distortions in telescope optics, and improving comparisons between stars’ positions. It focuses on RETINA, a project developing and calibrating detectors for possible use in future space missions, including Theia and the Habitable Worlds Observatory. One method projects interference fringes onto detectors to study how their pixels are shaped and respond to light. These advances are intended to support planet searches and studies of dark matter, but the abstract does not report a planet discovery or demonstrate that the intended measurement precision has been reached.

Young explorerA planet can make its star move just a tiny bit. Scientists want to measure those little movements to help find planets as light as Earth. This paper explains work on making space cameras very carefully checked, so tiny mistakes in their pictures do not fool us. A project called RETINA is working toward that goal, but the paper’s summary does not say the cameras are ready or that they have found a planet.

VLT and Keck recovery and characterisation of 2025 SC₇₉: linking 'Ayló'chaxnim and Atira asteroids

Bryce T. Bolin, Leo Y. Alcorn, Davide Farnocchia+9 more

AstronomerRecovery astrometry from Keck/LRIS and four-filter VLT/FORS2 photometry of 2025 SC79 support an investigation of its taxonomy, source region and transitions between the Atira and 'Ayló'chaxnim populations. Its SDSS-equivalent colours most closely match the Bus-DeMeo V-type class mean. Adopting the V-type median albedo of 0.362, rather than a measured albedo, gives a diameter of 0.379 km with lower and upper uncertainties of 0.025 and 0.027 km. Published source-model probabilities assign 95.4% combined probability to inner-Main-Belt delivery channels, favouring that origin alongside the V-like colours. Integrations of 10,000 covariance-sampled clones extend 5 Myr backward and forward; these are modelled histories and futures, not observed trajectories. Mean 'Ayló'chaxnim/Atira residence fractions are 30.2%/69.8% over the preceding 100 kyr and 3.6%/96.0% over the following 100 kyr, with the remaining 0.4% of future ensemble time following collision removal. Mean 'Ayló'chaxnim residence totals 231 kyr in the preceding 500 kyr and 120 kyr in the following 500 kyr. Forward 5-Myr collision fractions are 14.56% for Venus, 3.77% for Mercury and 0.22% for Earth. The simulations show transitions between both populations, without establishing a unique history or future for the asteroid.

PublicAstronomers recovered asteroid 2025 SC79, whose small apparent separation from the Sun makes it difficult to observe, and measured its colours. Those colours most closely resemble the V-type asteroid group, but this is a colour-based comparison. Assuming the typical reflectivity used for that group, the asteroid would be about 380 metres across; its reflectivity was not measured. Its colours and a source model favour an origin in the inner part of the main asteroid belt. Researchers also simulated 10,000 possible orbital paths, extending five million years into both the past and future. These simulations show movement between the Atira and 'Ayló'chaxnim groups. Some simulated paths end in planetary collisions, but they do not establish what will happen to the real asteroid.

Young explorerScientists found an asteroid again and measured its colours. It is hard to see because it looks close to the Sun in our sky. Its colours give clues about where it may have come from. A computer tried many possible journeys and showed it switching between two asteroid groups. Those journeys are possibilities, not things scientists watched happen.

Predicting next-week VIIRS fire detections in Bolivia: a reproducible benchmark with temporal and geographic evaluation

Victor Hugo Cuellar Flores

• Physics and Society
• Instrumentation and Methods for Astrophysics

AstronomerThis study evaluates weekly forecasts of at least one VIIRS fire detection from the Suomi National Polar-orbiting Partnership satellite in each 0.05-degree cell across Bolivia over the next seven days. Primary models were fixed before test scoring. Calibrated LightGBM achieved average precision (AP) of 0.323 on the 2023–2025 temporal test, with a 95% block-bootstrap interval of 0.222–0.383, versus 0.167 for climatology and 0.143 for persistence. Its paired AP improvement over climatology was 0.1567 (0.0998–0.2179). A separately selected geographic model achieved AP 0.384 in regions excluded from fitting, versus 0.181 for persistence. In the temporal test, the highest-ranked 5% and 10% of eligible area contained 38.4% and 55.8% of cell-weeks with detections. However, the highest-probability group remained overconfident. Retrospective rainfall offered no clear AP improvement; primary validation comparisons for vegetation, land cover, and their combination were inconclusive, despite positive secondary or exploratory intervals. Evaluation required complete target and recent-history observations and concerned satellite detections, not individual fires, causes, or burned area. Prospective evaluation, including archived weekly inputs and assessment of ranking, calibration, and monitoring utility, remains necessary.

PublicA study tested whether weekly forecasts could help focus fire monitoring in Bolivia. The model estimates where a satellite will detect at least one fire during the following seven days. In tests using 2023–2025 data, it ranked locations better than forecasts based on typical patterns or persistence of recent conditions. The highest-ranked 5% of eligible area contained 38.4% of location-weeks with satellite detections; the highest-ranked 10% contained 55.8%. These are retrospective test findings, not proof that the forecasts improve real-world monitoring. The model also overstated detection chances in its highest-probability group. Rainfall data showed no clear improvement, and tests of vegetation and land-cover information were inconclusive. The evaluation required complete observations and measured satellite detections—not the number of individual fires, their causes, or the area burned. Future weekly trials should assess both forecast accuracy and usefulness for monitoring decisions.

Young explorerResearchers tested a computer helper that picks places in Bolivia where a satellite might spot fire next week. When checked against past records, it picked promising places better than simpler guesses. But it sometimes sounded too sure. Satellite sightings do not tell us exactly how many fires there were or how much land burned. The helper still needs testing during real weekly monitoring.

Effects of a Nuclear Detonation in Low Earth Orbit

Zachary Petersen, Hong Qin, Sarah Thiele+1 more

• Physics and Society
• Instrumentation and Methods for Astrophysics

AstronomerThis modeling study couples prompt nuclear radiation, electron trapping and artificial radiation-belt evolution to satellite failures, collisions and atmospheric drag in low Earth orbit. For a hypothetical 1-megaton detonation at 500 km over the South Atlantic, repeated belt exposure disables approximately 98% of modeled satellites within one week in the central case. Tripling the assumed radiation tolerance delays widespread failure by only days, with approximately 97% disabled within two weeks. Loss of maneuverability raises the modeled collision risk to approximately 20 expected collisions within two years. Atmospheric drag removes many disabled spacecraft at lower altitudes, but replacement satellites could face radiation and debris hazards for years. These are scenario-dependent model predictions, not observed outcomes, and the authors present them as support for preventing nuclear weapons deployment and use in space.

PublicA modeling study explores how a nuclear explosion in space could damage the satellites operating close to Earth. Beyond the initial burst of X-rays, electrons released by radioactive material could become trapped in Earth's magnetic field, repeatedly exposing satellites to harmful radiation. In the study's central scenario—a hypothetical 1-megaton explosion 500 km above the South Atlantic—about 98% of modeled satellites stop working within a week. Even when satellites are assumed to tolerate three times as much radiation, about 97% fail within two weeks. The model also predicts about 20 collisions within two years as disabled satellites lose the ability to maneuver. Atmospheric drag would remove many lower-orbit spacecraft, but replacement satellites could still encounter radiation and debris for years. These predictions depend on the modeled scenario and assumptions; they are not reports of an actual explosion.

Young explorerScientists used a computer model to ask what might happen if a nuclear bomb exploded in space near Earth. They found that Earth's magnetic field could trap tiny particles from the explosion, making a dangerous region that satellites would pass through again and again. In their main pretend situation, almost all the satellites in the model stopped working within a week. Satellites that cannot steer could also crash into each other, and new satellites might face danger for years. This did not really happen—it is a prediction from the model.

Exoplanetary radio emission predictions and detectability in the SKA era

Mahdiyar Mousavi-Sadr, Fatemeh S. Tabatabaei, Alexander Wolszczan+1 more

AstronomerThe study applies radiometric Bode’s law to 1,027 confirmed exoplanets orbiting F–M main-sequence dwarfs to estimate auroral radio emission, rather than reporting detections. Permutation Importance and SHAP analyses identify planetary radius, orbital semi-major axis, stellar age, and distance from Earth as sufficient predictors of modeled radio flux density. After accounting for observational constraints, 15 planets are predicted to be detectable with the SKA, including nine accessible during the intermediate AA* deployment. Highlighted targets are WASP-14 Ab for SKA-Low, with a predicted 40.064 mJy at 57.5 MHz, and HD 141937 b for SKA-Mid, with a predicted 0.084 mJy peaking at 733.1 MHz. The authors project SNR >245 and >19, respectively, within feasible integration times. These detectability estimates remain model-based; TOI-4515 b is identified as likely affected by radio quenching, emphasizing a caveat for target selection.

PublicResearchers used a model to estimate radio signals associated with auroras on 1,027 known planets outside our Solar System. Their analysis points to planet size, distance from the host star, stellar age, and distance from Earth as useful predictors of signal strength. They predict that the Square Kilometre Array could detect signals from 15 planets, nine of them during an intermediate stage of its deployment. WASP-14 Ab and HD 141937 b stand out as promising targets for different parts of the telescope. These are forecasts, not reported radio detections. The study also flags TOI-4515 b as likely subject to radio quenching, which could suppress its emission and complicate target selection.

Young explorerPlanets far away might send out radio signals from glowing lights called auroras. Scientists used a math model to guess which planets a big radio telescope could hear. They picked 15 possible targets, but these are guesses to test—not signals they have already heard. One planet’s signal might also be quieted.

Origin and evolution of NiI and FeI in the coma of the interstellar comet 3I/ATLAS throughout its trajectory

Damien Hutsemékers, Jean Manfroid, Cyrielle Opitom+8 more

• Astrophysics of Galaxies

AstronomerHigh-resolution UVES+VLT observations detected strong neutral Ni and Fe emission in the coma of interstellar comet 3I/ATLAS after perihelion, persisting to large heliocentric distances. Near 2 au, the total metal production rate was at least an order of magnitude above that of typical Solar System comets. Production rates were higher and declined more gradually with heliocentric distance after perihelion than before it, particularly for FeI. The initially anomalously high pre-perihelion NiI/FeI ratio approached Solar System comet values near 2 au and showed weaker distance dependence after perihelion. To interpret these findings, the authors extended the hypothesis that rapid photodissociation of sublimated Fe(CO)5 and Ni(CO)4 supplies the neutral atoms. Direct carbonyl-sublimation models reproduce the production rates and high NiI/FeI ratio, but require temperature profiles shallower than the equilibrium relation T ∝ r_h^−1/2. A nucleus thermal model could reproduce the full dataset only after substantial empirical modifications, including reduced active areas through perihelion and an additional transient heat source at approximately 120 K. This proposed heat source, possibly associated with the amorphous-to-crystalline ice transition, could explain the early nickel excess. Subsurface carbonyl sublimation is inferred within this modified model, not established directly by the observations.

PublicObservations with UVES on the VLT found strong signals from nickel and iron atoms in the gas surrounding interstellar comet 3I/ATLAS after its closest approach to the Sun. These signals persisted as the comet moved farther away. At roughly twice Earth’s distance from the Sun, its total metal production rate was at least ten times that of typical Solar System comets. Metal production was higher and faded more slowly after closest approach than before, especially for iron. An unusually high nickel-to-iron ratio seen earlier moved toward values typical of Solar System comets. The researchers explored whether sunlight breaking apart vaporized nickel- and iron-bearing carbonyl molecules could explain the atoms. Their models can match the observations, but require particular temperature patterns. A more detailed thermal model needed substantial adjustments, including smaller active areas around closest approach and an extra, temporary heat source. A change in the structure of ice might supply that heat and explain the early nickel excess, but this remains an interpretation rather than a confirmed mechanism.

Young explorerA comet visiting from another star has tiny bits of nickel and iron in the cloud around it. Astronomers saw strong signs of these metals after the comet passed closest to the Sun, and still saw them as it traveled farther away. The comet released more metal after that close pass than before. Scientists think sunlight might break apart special molecules to free the metal atoms. Their models can explain what they saw, but need changes in how the comet warms up. An extra little burst of warmth might help explain it, but they do not yet know for sure.

The Science Potential of Characterizing Gas Giant Exoplanets with HWO

Beck Dacus, Jean-Baptiste Ruffio, Quinn Konopacky+19 more

• Instrumentation and Methods for Astrophysics

AstronomerEXOSIMS simulations predict that the planned Habitable Worlds Observatory (HWO) could characterize Jupiter-radius planets receiving Earth-like or Jupiter-like irradiation around the 164 ExEP target stars; these are modeled capabilities, not observed detections. Broadband visible-light detections at S/N ≥ 5 are predicted within 5 minutes, while 10 hours of near-infrared spectroscopy at R=1000 should reveal water, methane, and ammonia absorption in Jupiter-like atmospheres. Hourly photometry is predicted to achieve better than 1% flux precision for Earth-instellation giants across the target list and Jupiter-like giants within 7 parsecs, potentially revealing Jupiter-like rotational variability over tens of hours. High-cadence light curves may reveal eclipses involving Mars-sized exomoons around habitable-zone giants within 10 parsecs. For hypothetical Earth-like moons with oxygen-rich atmospheres within 7 parsecs, approximately 400 hours of R=1000 spectroscopy might detect molecular oxygen against the parent planet's photon noise. These moon-detection and atmospheric prospects remain conditional on such moons existing.

PublicThe planned Habitable Worlds Observatory could study giant planets as well as search for Earth-like worlds. In simulated observations, Jupiter-sized planets receiving amounts of starlight similar to Earth or Jupiter could be detected within five minutes. Ten-hour observations that split light into its component wavelengths should reveal water, methane, and ammonia in Jupiter-like atmospheres. Repeated brightness measurements could also reveal changes as planets rotate and might uncover eclipses involving moons as small as Mars around some nearby giant planets. A more demanding possibility is detecting oxygen in the atmosphere of a hypothetical Earth-like moon within 7 parsecs: this might require about 400 hours of observations, with the planet's light making the measurement difficult. These are predictions from simulations, not discoveries of planets, moons, or signs of life.

Young explorerScientists used a computer to imagine what a future space telescope might see. It could spot big planets and look for clues about what is in their air. By watching their light change, it might also find moons going around some of them. If a nearby moon like Earth exists and has lots of oxygen in its air, the telescope might find a clue to that oxygen—but it would need to watch for a very long time. The scientists have not found those moons; they are working out what the telescope might be able to do.

Tracking the evolution of sub-Neptunes. II. The radius valley on gyrochronological ages

Nino Greco, Alessandro C. Lanzafame, Isabella Pagano+3 more

• Solar and Stellar Astrophysics

AstronomerUsing gyrochronological ages, the study examines 746 planets around 510 FGK hosts spanning 0.1–4 Gyr, with a completeness-characterised reference sample of 581 planets around 404 hosts. A selection-conditioned mixture model incorporating stellar-age uncertainties infers that the intrinsic super-Earth fraction rises mainly during the first approximately 2 Gyr, with no significant evolution thereafter. An exponential approach-to-plateau model places 90% of the increase within 1.9 Gyr at 90% credibility. The radius valley is consistently resolved from approximately 1.5 Gyr onward, without significant evolution in depth or width. A shift in its minimum from approximately 1.5 Earth radii before 2 Gyr to approximately 1.8 Earth radii at older ages, together with a changing super-Earth radius distribution, is only suggestive. These findings are consistent with atmospheric loss continuing for some planets until approximately 1–2 Gyr. Later envelope loss by more massive cores is a possible interpretation of the tentative shift, but the data do not uniquely distinguish atmospheric-loss mechanisms.

PublicPlanets tend to fall on either side of a gap in size between super-Earths and sub-Neptunes, a pattern understood as a sign that some planets lose their atmospheres. This study investigates when that pattern develops, using 746 planets whose host-star ages were estimated from stellar rotation. After accounting for how readily planets are detected and confirmed, and for age uncertainties, the researchers infer that the proportion of super-Earths grows mainly during the first roughly 2 billion years, with no significant change afterward. The size gap is consistently distinguishable from about 1.5 billion years onward, with no significant change in its depth or width. There are tentative hints that the gap moves toward larger planet sizes at older ages. The findings are consistent with some planets continuing to lose atmosphere for 1–2 billion years, but they do not establish which atmospheric-loss mechanism is responsible.

Young explorerSome planets have thick blankets of gas, and others have much less gas. There are fewer planets of the sizes in between. Astronomers looked at planets around stars of different ages to learn how this happens. Their study suggests that the share of smaller planets grows mostly during the first two billion years—a very, very long time. This could mean that some planets slowly lose their gas blankets. But the astronomers still cannot tell exactly what makes the gas go away.

Sensitivity of the IceCube atmospheric muon rate to decadal trends in the effective atmospheric temperature

Tanvi Krishnan, Gabriela Barenboim, Carlos A. Argüelles

• High Energy Physics - Phenomenology
• High Energy Astrophysical Phenomena
• Atmospheric and Oceanic Physics

AstronomerThis study assesses IceCube atmospheric muon rates as a potential independent probe of decadal changes in effective atmospheric temperature, a vertically weighted quantity most sensitive to the stratosphere. Using atmospheric reanalysis and records of cosmic-ray, solar, and geomagnetic variability, the authors reproduce the measured seasonal muon-rate response and test its applicability to long-term changes with a different vertical temperature profile. Detector stability, rather than counting statistics, is the limiting requirement: an unmodeled rate drift of 1% per decade would mimic 2.8 K per decade, requiring approximately 0.3% per decade stability. Snow-accumulation contributions can be constrained within this budget. Atmospheric variability yields a one-sided 95% confidence-level statistical sensitivity of 1.6 K per decade for a 14-year record. The authors project that the approximately 0.9 K per decade cooling indicated by 2011–2025 atmospheric records could be constrained at 95% confidence after about 22 years of measurement; this is not an IceCube detection of that cooling.

PublicCould IceCube’s particle counts help track long-term temperature changes high above Antarctica? This study evaluates that possibility, which could provide an independent check where long-term atmospheric measurements are scarce. The researchers reproduce the observed seasonal changes in IceCube’s muon counts using existing atmospheric data and records of other relevant variability. But tracking changes over decades requires exceptionally steady detector performance: an unnoticed drift in the counts could look like atmospheric warming or cooling. The count rate would need to remain stable to about 0.3% per decade, with effects such as accumulating snow constrained. For 14 years of data, natural atmospheric variability limits the statistical sensitivity to 1.6 degrees Celsius of temperature change per decade. The authors estimate that about 22 years of measurements could constrain the roughly 0.9-degree-per-decade cooling suggested by atmospheric records from 2011–2025 at 95% confidence. They do not report that IceCube has already measured this cooling.

Young explorerScientists want to know whether counting tiny particles with IceCube could help tell if the air high above Antarctica is getting colder over many years. They can explain how the particle counts change with the seasons, but measuring slow changes is harder. The counting machine must stay very steady, or changes in the machine could look like changes in the air. The scientists think about 22 years of measurements could help check the slow cooling suggested by other air records. IceCube has not yet shown that cooling in this study.

System noise temperature measurements of a 19-element phased array feed

Shenghua Yu, Dejian Ding, Hongwei Xi+25 more

AstronomerMulti-epoch measurements characterize a 19-element hexagonal, room-temperature phased array feed using a modified Y-factor method and a Python pipeline with iterative channel calibration and maximum-SNR beamforming. Observations from March–June 2026 show receiver-noise drift attributed mainly to LNA temperature variations. The measured beam-equivalent system noise temperature is approximately 73–89 K across 1.37–1.47 GHz. The authors propose a covariance-based decomposition to extract mutual-coupling noise temperature, Tmc, and report a baseline of about 2–8 K, with a resonant peak exceeding 20 K under thermal loading. The baseline is consistent with S-parameter measurements indicating full-array Tmc below 10.7 K. Its fluctuations are interpreted as most likely reflecting superposed thermal and non-thermal spatial electromagnetic-field components. Comparative tests with a detachable stainless-steel shield indicate that unshielded environmental interference adds over 60 K to receiver noise temperature. The framework is offered as a practical reference for characterizing ground-based radio-telescope PAF prototypes.

PublicThe study measures unwanted radio noise in a room-temperature, 19-element antenna array designed for radio telescopes. Measurements from March to June 2026 show noise changing over time, mainly attributed to temperature changes in the receiver’s low-noise amplifiers. Across the tested frequency band, overall system noise was equivalent to about 73–89 kelvin; this is a measure of noise strength, not the equipment’s physical temperature. The researchers also propose a method for separating noise caused by interactions among antenna elements. They report that this contribution is usually about 2–8 kelvin but can peak above 20 kelvin under thermal loading. Tests using a removable steel shield show that environmental interference without shielding increases receiver noise by more than 60 kelvin. The work offers a way to assess prototype radio-telescope antenna arrays.

Young explorerA radio telescope uses antennas to listen for signals from space, but unwanted radio noise can get in the way. Researchers tested a group of 19 antennas. They found that the noise changed as parts of the receiver warmed or cooled. The antennas also affected one another. In tests with a removable steel shield, outside interference made much more noise when the shield was off. These tests can help researchers check how noisy new antenna groups are.

Suppression of water-ice UV photodesorption on cosmic dust analogs

Ph. Parent, C. Laffon

• Astrophysics of Galaxies

AstronomerLaboratory experiments tested morphology-dependent UV photodesorption from 2–6-monolayer H2O films on planar gold and olivine, soot nanoparticles, and olivine microparticles at 12 and 60 K. On gold, yields rose approximately linearly from about 5 × 10^-4 to 2 × 10^-3 molecule per photon between 2 and 6 monolayers, consistent with increased absorption in optically thin ice; planar olivine gave comparable yields. Particulate olivine suppressed photodesorption, with stronger suppression on soot, where yields were up to about 40 times lower than on gold at 12 K. X-ray photoelectron spectroscopy and reflection-absorption infrared spectroscopy both confirmed strongly reduced ice depletion on soot. Heterogeneous ice growth and altered energy redistribution within nanoscale ice domains are proposed explanations, not established mechanisms. The results suggest that planar-substrate yields may substantially overestimate photodesorption from thin ice mantles on cosmic dust.

PublicUltraviolet light can release water molecules from ice into gas, but laboratory measurements suggest that the surface beneath the ice strongly affects how readily this happens. Researchers exposed very thin water-ice films on flat gold and olivine surfaces, olivine particles, and tiny soot particles to ultraviolet light at two very low temperatures. Thicker films on flat gold released more water per incoming photon, and flat olivine behaved similarly. Ice on particles released less water, especially on soot: at 12 kelvin, its release rate per photon was up to about 40 times lower than on gold. Two measurement methods confirmed the strongly reduced ice loss on soot. The researchers suggest that uneven ice growth and differences in how energy spreads through tiny ice regions could explain the effect, but the mechanism remains uncertain. Measurements on flat surfaces may therefore substantially overestimate how much water ultraviolet light releases from thin ice coatings on cosmic dust.

Young explorerUltraviolet light can knock water molecules out of ice. Scientists shone this light on very thin ice layers sitting on different surfaces in a very cold laboratory. Ice on tiny soot particles lost much less water than ice on flat gold. Two ways of checking showed that the soot kept more of its ice. The scientists are not sure exactly why. This means tests using flat surfaces might make it seem easier for light to knock water off icy space dust than it really is.

Rapid and robust simulation-based inference for kilonovae

Stephanie M. Brown, Mattia Bulla, Hiranya V. Peiris+6 more

• High Energy Astrophysical Phenomena
• High Energy Physics - Phenomenology

AstronomerThe authors develop a simulation-based inference (SBI) framework for kilonova parameter estimation using density-estimation likelihood-free inference and a Gaussian process emulator trained on approximately 1,300 POSSIS simulations. In simulation tests, SBI recovers injected parameters, whereas MCMC with a standard Gaussian likelihood exhibits systematic bias because that likelihood does not capture the non-Gaussian, correlated emulator uncertainty. SBI instead learns this uncertainty structure from forward simulations. Applied to AT2017gfo, some MCMC posteriors accumulate at prior boundaries, while the SBI posteriors do not. Within this framework, SBI infers a total ejecta mass of approximately 0.087 solar masses, dominated by lanthanide-poor ejecta, and excludes toroidal and peanut ejecta geometries at the 99th percentile for both components. These are model-based inferences, not direct measurements of mass or geometry. The framework produces approximately 20,000 posterior samples in seconds; its demonstrated advantage concerns the likelihood misspecification examined here, not every possible source of modeling error.

PublicResearchers have developed a fast way to estimate the properties of material expelled in a kilonova. Their method learns from computer simulations rather than relying on a simplified mathematical description of uncertainty. In simulated tests, it recovered the input properties accurately, while the comparison method produced biased estimates because its uncertainty assumptions were inadequate. Applied to the kilonova AT2017gfo, the new method inferred expelled material totaling about 0.087 times the Sun’s mass, mostly poor in elements called lanthanides. Its analysis also disfavored doughnut-shaped and peanut-shaped material distributions at the reported 99th percentile. These conclusions depend on the modeling framework rather than being direct observations of the material’s mass or shape. The method can generate about 20,000 samples describing plausible parameter values in seconds.

Young explorerScientists want to understand a space event called a kilonova. They taught a computer using lots of pretend examples. In tests, their new method was quick and found the answers put into those examples more accurately than the method they compared it with. They also used it on a real kilonova to estimate how much material came out and what shapes it might have. Those answers are estimates, not things they measured directly.

WindsoCC: reconstructing the wind-driven halo in MagAO-X images using wavefront sensor telemetry

Jay K. Kueny, Jared R. Males, Alycia J. Weinberger+16 more

AstronomerUsing archival MagAO-X wavefront-sensor telemetry, the authors demonstrate a workflow to reconstruct and remove the wind-driven halo from individual coronagraphic science images. This low-spatial-frequency artifact arises from adaptive-optics servo lag and varies in intensity and position angle, making its subtraction particularly challenging when preserving extended emission. Their windsoCC pipeline cross-correlates recorded closed-loop residual wavefronts to measure wind vectors for several atmospheric turbulent layers above Las Campanas Observatory. These wind parameters feed a parametric model of the halo footprint. Applied to on-sky visible-light MagAO-X images of the disk around HR 4796A, the workflow demonstrates a dramatic improvement in object recovery; the abstract gives no quantitative recovery metric.

PublicAdaptive optics corrects atmospheric distortions in telescope images, but delays in those corrections leave a changing pattern of unwanted light called the wind-driven halo. Removing it can also erase light from extended objects, such as disks around stars. The researchers used archived measurements from MagAO-X, an instrument on the 6.5-meter Magellan-Clay telescope, to track winds in several turbulent layers of the atmosphere. They then used those wind measurements in a mathematical model to reconstruct and remove the unwanted pattern. Tests on real visible-light images of the disk around HR 4796A showed a dramatic improvement in recovering the disk, although the abstract does not quantify the improvement.

Young explorerMoving air makes it hard for a telescope to take clear pictures. A tool helps fix the picture, but it is a little late and leaves an unwanted glow. The scientists used saved records from the tool to work out how the air was moving. Then they made a model of the glow so they could remove it. They tried this on real pictures of a disk around a star, and the disk became much easier to see.

Towards Genuine Coexistence: Per-Satellite Emission and Radiation Limits to Protect Radio Astronomy and Geodetic VLBI at 1-14 GHz from Satellite Constellations

Balthasar Indermuehle, Lucia McCallum, Emma van der Wateren+7 more

AstronomerGeodetic VLBI links celestial and terrestrial reference frames and uniquely determines UT1-UTC. VGOS achieves millimetre accuracy using group delays synthesised across 3–14 GHz, with most channels outside primary radio astronomy allocations. Using SNIFFLES-I measurements of satellite emissions over 1–26 GHz, the authors model equivalent power flux density (EPFD) for current and future non-geostationary constellations against ITU-R RA.769 protection criteria, including frequencies without radio astronomy allocations. Monte Carlo modelling at AuScope VGOS stations scales the aggregate from approximately 12,000 catalogued satellites to the hundreds of thousands on file. The analysis finds present-day exceedances of single-dish protection criteria in two primary radio astronomy bands. For geodetic VLBI, it identifies the 5240 MHz second harmonic of the 2620 MHz direct-to-device downlink as the dominant threat, estimating at least 59% data loss under current conditions. This loss estimate comes from modelling informed by measured emissions, rather than a reported direct measurement of VLBI data loss. Inverting the EPFD analysis yields tolerable per-satellite spurious-emission and unintended-radiation field-strength limits for standards bodies. Proposed Sun-synchronous orbital data centres are treated separately as an unintended-radiation-dominated case.

PublicSatellite radio emissions could seriously disrupt a technique that connects sky and Earth coordinate systems and uniquely determines UT1-UTC, a measure related to Earth's rotation. The authors use measured satellite emissions to model interference from today's satellite fleet and much larger future fleets. Their analysis finds that current emissions already exceed single-telescope protection criteria in two frequency bands reserved primarily for radio astronomy. For the next-generation geodetic telescope network, the main modelled threat is an unwanted signal at twice the frequency of a satellite downlink designed to communicate directly with devices. The model estimates that this interference already causes at least 59% data loss under current conditions; the abstract does not report a direct observation of that loss. The study also derives satellite emission limits to inform standards and considers proposed orbital data centres as a separate potential source of unintended radio emissions.

Young explorerSome radio telescopes help scientists keep track of how Earth turns. Satellites can make extra radio noise that gets in the way. Scientists used measurements of satellite noise in a computer model. The model suggests that one kind of unwanted signal could already spoil more than half of some telescope data. They also worked out limits on satellite noise that could help protect the telescopes.

Amortized Opacity Marginalization Improves C/O Interval Calibration for Brown-Dwarf Retrievals

Kellen Heraty

• Earth and Planetary Astrophysics
• Solar and Stellar Astrophysics

AstronomerDisagreement among molecular line lists measurably shifts retrieved C/O, leaving a dominant systematic unaccounted for in fixed-opacity retrieval uncertainties. The authors marginalize over opacity uncertainty during neural posterior estimator training, using smooth multiplicative Fourier fields in log frequency and a discrete line-list mixture under a deliberately broad prior informed by measured inter-list differences. On 2,048 perturbed held-out simulated spectra, nominal 90% C/O intervals achieve 43.3% coverage for a standard estimator versus 82.4% for a compute-matched marginalized network. Three-seed control ensembles achieve 61.4% under perturbation versus 89.4% for the marginalized ensemble; ablations attribute most of the improvement to the continuous opacity field. In simulations using real JWST bad-pixel masks and median filling, marginalized-ensemble coverage falls from 0.894 to 0.683, while mask-augmented retraining yields 0.918 under full deployment preprocessing on 1,024 cases. Applied to one pipeline-combined JWST/NIRSpec G395H spectrum for each of 14 late-T and Y dwarfs, the recommended ensemble gives C/O medians of 0.24–0.62. Its interval for 2MASS J0415-0935 contains the Hood et al. (2024) value of 0.53, excluded by every fixed-opacity control network. With 90% intervals spanning about 43% of the prior width, this agreement is a consistency check, not validation.

PublicEstimating the ratio of carbon to oxygen from a dwarf's spectrum depends on molecular absorption reference lists, and different lists can shift the answer. This study trains an artificial-intelligence method on simulated spectra with deliberately varied absorption properties, so its uncertainty estimates account for those differences without repeating a full analysis for each possibility. In tests on altered simulations, its uncertainty ranges included the true carbon-to-oxygen ratio much more often than those from a standard method, although performance depended on the test conditions. Simulated tests also showed that filling bad detector pixels could undermine the method unless that processing was included in training. The researchers then analyzed JWST spectra of 14 late-T and Y dwarfs. For one benchmark object, the recommended method's uncertainty range included a previously published ratio that all fixed-opacity controls excluded. The ranges remain broad, so this agreement is a consistency check rather than proof that the method gives correct answers for real objects.

Young explorerScientists look at patterns in light to work out how much carbon there is compared with oxygen in space objects. But their reference lists do not quite agree. They taught a computer using pretend light patterns with different possible lists and changes. In pretend tests, this helped the computer give better ranges of possible answers. They also tried it on real light from 14 objects. One answer range agreed with an earlier study, but that does not prove the computer is right.

Grid Optimization for Wide Field Modulation Collimators

Steven E. Boggs

• High Energy Astrophysical Phenomena

AstronomerThis analytical study examines slat cross-sectional shape as a way to reduce self-vignetting in wide-field bigrid modulation collimators for transient localization. A general transmission framework based on geometry-dependent effective slit width compares rectangular, idealized diamond, etched hexagonal, and circular-wire profiles. At fixed bigrid pitch and thickness, the diamond profile widens the field of view and eliminates clipping through most of it; a hexagonal profile achievable with standard tungsten etching factors retains many of these benefits. In the four-phase demodulation analysis, diamond slats eliminate phase-space blind spots across a target field where rectangular slats do not. Finite-opacity leakage leaves the geometric blind-spot boundaries unchanged. These are analytical design results, not reported instrument measurements, and identify slat shape as a route to greater throughput and a wider blind-spot-free field.

PublicInstruments used to locate brief cosmic flashes, such as gamma-ray bursts, can use pairs of slatted grids to control incoming radiation. But thick slats also block rays arriving at an angle, limiting how much sky the instrument can usefully cover. This study uses mathematical analysis, rather than reported observations or hardware tests, to compare four slat shapes. With the same grid spacing and thickness, diamond-shaped slats allow a wider view than rectangular ones and avoid clipping incoming rays over most of that view. A hexagonal shape compatible with standard tungsten etching offers many of the same advantages. The analysis also finds that diamond slats remove certain blind spots in the position-decoding method across the target field studied. Radiation leaking through the slats does not change those blind-spot boundaries. The results suggest a way to improve future grid designs.

Young explorerImagine looking through two little fences to find a quick flash in the sky. Thick fence bars can get in the way when the flash is off to one side. Researchers used math to ask whether differently shaped bars would help. Their calculations show that bars shaped like diamonds could let the instrument look farther to the sides than ordinary box-shaped bars. They could also remove some places where the instrument has trouble working out where a flash came from. A six-sided shape that can be made by etching metal could help too. This is a design worked out with math, not a report of a new instrument being tested.

Optimal Strategies for Gravitational-Wave Memory Detection with Noise Marginalization in Pulsar Timing Arrays

Rand Burnette, Xavier Siemens

• General Relativity and Quantum Cosmology

AstronomerThe authors implement optimal frequentist statistics for gravitational-wave memory searches in the enterprise suite and compare a noise-marginalized statistic with a simpler maximum-posterior approach. Tests use simulated pulsar timing arrays containing red and white noise and the NANOGrav 15-year dataset. The detection statistics show no significant differences between methods in the simulations and only small differences in the NANOGrav comparisons. The authors conclude that maximum-posterior treatment is sufficient to identify potentially detectable signals in realistic arrays, while noise marginalization could help assign false-alarm probabilities to Bayesian results. The abstract presents a search-method comparison, not a gravitational-wave memory detection; such a detection could provide a distinctive test of general relativity.

PublicPulsar timing arrays could detect gravitational-wave memory, offering a distinctive test of general relativity. This study improves software for those searches and compares two ways of handling noise, using both simulated data and the NANOGrav 15-year dataset. The methods produced detection statistics with no significant differences in the simulations and only small differences in the real-data comparison. The authors conclude that the simpler method is adequate for finding potentially detectable signals, while the more involved method could help assess the chance of a false alarm in Bayesian analyses. They do not report a detection of gravitational-wave memory.

Young explorerScientists are looking for a special signal from gravity by watching the timing of flashes from stars called pulsars. They tried two ways to look for it among other changes in the timing, using both pretend data and real observations. The two ways gave very similar answers. The scientists think the simpler way is good enough to find possible signals, while the other way might help check whether an apparent signal is a false alarm. They did not say they found the special gravity signal.