Tonight’s sky of new research

Efficient numerical evolution of self-gravitating systems with dark-matter-baryon scattering

Marc Kamionkowski, Vera Gluscevic, Kris Sigurdson

• Astrophysics of Galaxies
• High Energy Physics - Phenomenology
• High Energy Physics - Theory

AstronomerThe authors present NSphere-IDM, a fast numerical code for spherically symmetric dark-matter–gas systems with dark-matter–baryon scattering. It extends NSphere’s reduction of collisionless phase space from six to three dimensions with one-dimensional Lagrangian gas shells, Monte Carlo scattering between dark-matter particles and gas shells, and radiative cooling valid in the weak-cooling regime. These additions increase runtime only incrementally, permitting laptop calculations at a small fraction of the computational cost of full 3D N-body/hydrodynamical simulations. Demonstrations include a roughly 10^13-solar-mass halo with a scattering cross section per dark-matter mass of 0.1 cm²/g and no cooling, followed by cooling examples in which dark-matter interactions modify gas cooling. These are simulation demonstrations, not observational findings. The code enables rapid parameter exploration under spherical symmetry; extensions to other physics and use as a calibration or benchmark for full 3D simulations are described as capabilities.

PublicThe researchers have developed NSphere-IDM, a computer program that simulates how dark matter and gas evolve together when they can scatter off one another. By assuming the system is spherically symmetric, the program greatly reduces the computing work, allowing calculations on a laptop rather than requiring the resources of a full three-dimensional simulation. In example simulations, interactions with dark matter change how gas cools. These are computer-model results, not observations of a galaxy. The cooling method applies only when cooling is weak, and the spherical assumption limits what the model can represent. The program offers a fast way to explore possible effects of dark-matter interactions on galaxy evolution and could help test more detailed simulations.

Young explorerScientists made a computer program to explore how gas and dark matter might change together in space. It treats everything as arranged in round layers, which makes the pretend space system simple enough to run on a laptop. In some computer examples, bumps between dark matter and gas changed how the gas cooled. This does not mean scientists saw those bumps in a real galaxy. The program works with a simplified round shape, and its cooling rule works only when cooling is gentle.

The unified Bound Dark Energy--Bound Dark Matter model: theory and constraints from DESI DR2

Jose Agustin Lozano Torres, Axel de la Macorra

AstronomerThe proposed unified Bound Dark Energy–Bound Dark Matter (BDE-BDM) model derives dark energy and all dark matter from a supersymmetric SU(3) gauge sector with six flavors. Gauge-coupling unification predicts a condensation scale of 34 eV, with a −11/+16 eV uncertainty, before cosmological fitting. Relative to ΛCDM, its dark-energy sector adds no parameters and its dark-matter sector adds one. Fits combine DESI DR2 BAO, Planck CMB, Planck+ACT DR6 CMB lensing, and three alternative supernova compilations. With Union3.1, the inferred condensation scale is 43.67 ± 0.13 eV, within the predicted range, and the present dark-energy equation of state is w₀ = −0.9262 ± 0.0005; the model never crosses w = −1. Relative to ΛCDM, BAO χ² decreases by 2.95–3.67 and supernova χ² by 2.53–4.07. BDE-BDM recovers 57%–71% of the total χ² improvement obtained by the two-parameter w₀wₐ dark-energy model, with lower BAO χ² than that model for two of the three supernova compilations. Reported ΔDIC values are −8.28 to −7.47 against ΛCDM, while ln B values are +4.09, +4.12, and +4.83. BDE-BDM has the highest Bayesian evidence among the six tested combinations of dark-energy and dark-matter prescriptions. These are model-dependent parameter estimates and comparisons, not a direct detection of the proposed dark sector.

PublicThis study tests a proposal that dark matter and dark energy come from a single underlying particle-physics theory. Before using observations of the universe, the theory predicts an energy scale at which its dark sector condenses. Fits to measurements of cosmic expansion, the cosmic microwave background, and gravitational lensing give a value within that predicted range. The model also describes dark energy as changing over time rather than remaining a cosmological constant. Across three alternative supernova datasets, the authors report better fits than the standard ΛCDM model. A statistical comparison that weighs fit quality against model complexity favors the proposal over ΛCDM, and it ranks highest among the six models tested. This is encouraging evidence within those comparisons, not proof that dark matter and dark energy share the proposed origin.

Young explorerScientists have a new idea about two mysterious things in space: dark matter and dark energy. Their idea says both could come from the same hidden source. They used measurements of the universe to test it. The idea matched those measurements better than the usual explanation in their comparisons, and one number agreed with what they had predicted beforehand. That is a promising clue, but it does not prove their idea is right.

Nonlocal Gravity, Restricted CPL Dynamics and DESI Constraints

Luca Amendola, Ismael Ayuso, Amlan Chakraborty+2 more

• General Relativity and Quantum Cosmology

AstronomerThe authors revisit the background dynamics and observational viability of the Maggiore–Mancarella nonlocal R □⁻² R gravity model, in which cosmic acceleration can arise dynamically without a fundamental cosmological constant. For fixed standard cosmological parameters, they explicitly map the nonlocal parameter to an effective (w₀, wₐ) pair, restricting the model to a trajectory in the Chevallier–Polarski–Linder plane rather than the full phenomenological parameter space. They implement the cosmological dynamics in a Boltzmann solver and perform a Markov chain Monte Carlo analysis using cosmic microwave background, supernova, and DESI baryon acoustic oscillation data. Within this analysis, current datasets constrain the nonlocal parameter close to the ΛCDM limit and show no statistically significant preference for nonlocal deviations.

PublicThis study tests a modified theory of gravity that could explain the universe’s accelerating expansion without introducing a fundamental cosmological constant. The theory makes a restricted set of predictions: once the standard cosmological parameters are fixed, each value of its additional parameter determines a particular pattern for how the acceleration-driving effect evolves. The researchers calculated these predictions and compared them with cosmic microwave background, supernova, and DESI measurements of baryon acoustic oscillations. Their analysis favors parameter values close to the standard ΛCDM model’s limit, with no statistically significant evidence that the proposed modification is preferred.

Young explorerThe universe is getting bigger, and its expansion is speeding up. Scientists tested an idea that changes the rules of gravity to explain this. They worked out what the idea predicts and compared it with clues from the universe. The clues keep the idea close to the usual explanation and do not clearly favor changing gravity.

Disentangling geometry & growth in cosmic neutrino mass constraints: a more physical split and diagnostic

Fei Ge, Frank J. Qu, Hanyue Wang+3 more

• High Energy Physics - Experiment

AstronomerThe authors investigate whether cosmological preferences for a neutrino mass sum below the oscillation-experiment minimum arise from geometry or structure growth. They split the mass-sum parameter at the Boltzmann-code level: one parameter controls H(z) for distances, the other H(z) for perturbation evolution, with both extended to negative values. Combining Planck primary CMB, Planck+ACT+SPT CMB lensing, and DESI BAO data yields a geometry parameter of -0.07 ± 0.10 eV and a growth parameter of -0.13 with +0.10/-0.12 eV uncertainties, all at 68% confidence. Both channels show similar sensitivity and a negative central value, not a detection of physically negative neutrino masses. Their difference supplies a ΛCDM null test, which current data pass at 0.4σ. Advanced SO CMB and DESI DR3 BAO forecasts predict that geometry alone could reject 0.058 eV at 3.0σ if its current negative mean persists. Further Fisher forecasts suggest a diagnostic distinction: an incorrect dark-energy model would shift the geometry parameter more strongly, whereas underestimated reionization optical depth would predominantly shift the growth parameter. These future sensitivities and diagnostic patterns are forecasts, not observed results.

PublicSome cosmological data favor a neutrino mass estimate below the minimum allowed by neutrino oscillation experiments, even giving a formally negative best-fit value. This is a tension in the interpretation of the data, not evidence that neutrinos really have negative mass. The researchers separate two effects of neutrinos: their influence on cosmic distances and on the growth of structure. Using cosmic microwave background and galaxy-distance data, they find that both channels favor negative central values, with uncertainties that include zero. The two estimates agree, so their comparison does not reveal a conflict with the standard cosmological model. Forecasts suggest that future observations could sharpen the tension if the current trend persists. They might also help distinguish an incorrect description of dark energy from an underestimated effect of cosmic reionization.

Young explorerScientists are trying to learn how much tiny particles called neutrinos weigh by studying space. They checked two clues: distances in space and how clumps of matter grow. Both clues gave surprisingly low answers, but the answers are uncertain and do not show that neutrinos really weigh less than nothing. Future measurements might help explain the puzzle.

Model-independent parameters from DESI DR1 LRG2 with an explicitly varying power-spectrum shape

Yong-Seon Song, M. Icaza-Lizaola, Minji Oh+1 more

AstronomerThe authors present a method for jointly constraining primordial shape parameters and model-independent distance and growth parameters, rather than fixing the shape to CMB-derived values. Their hybrid model supplements perturbation theory with templates measured from N-body simulations, incorporating nonlinear corrections beyond the perturbative truncation; small-scale accuracy is therefore set by the simulations. A Gaussian-process emulator, trained and validated across a range spanning 5σ of the Planck constraints, makes the joint analysis computationally feasible. Applied to DESI DR1 LRG2, the method measures α_perp, α_parallel, and fσ8. With the tight Planck prior adopted, the constraints differ from fixed-shape results by less than 0.05 times their own uncertainties. A post-fit projection onto flat ΛCDM finds mutual consistency among the three measurements, with χ² = 0.7 for two degrees of freedom and h = 0.724 ± 0.017. The analysis provides a methodological step toward distinguishing dark energy from modified gravity, not a determination of which causes accelerated expansion.

PublicTo investigate whether dark energy or a change in gravity explains the universe’s accelerating expansion, astronomers need measurements of cosmic distances and the growth of structure that do not assume the answer. This study introduces a way to fit those quantities while also allowing parameters describing the initial pattern of cosmic structure to vary. It combines theoretical calculations with computer-simulation templates and a fast statistical tool. Applied to one galaxy sample from DESI’s first data release, it yields distance-related and structure-growth measurements. Under the tight constraints from Planck used here, allowing the initial-pattern parameters to vary changes the results by much less than their measurement uncertainties. The measurements agree with one another when interpreted afterward within a flat ΛCDM model. The study does not establish whether dark energy or modified gravity causes the acceleration.

Young explorerThe universe is spreading out faster and faster, and scientists want to know why. These researchers made a new way to study how far away galaxies are and how groups of matter grow, using computer pretend-universes to help. They tried it on galaxy data. With tight limits from earlier information, the answers changed very little from the older method. This does not yet tell us why the universe is speeding up.

Minkowski Functionals of CII Line Intensity Maps: Probing Astrophysics and Primordial Features

Sandeep Kumar Acharya, Pravabati Chingangbam

• Astrophysics of Galaxies
• High Energy Physics - Phenomenology

AstronomerThis simulation and forecasting study investigates Minkowski functionals as morphological probes of CII line-intensity maps at z ≈ 6 and 7.6. The semi-numerical maps adopt a model relating CII luminosity to host dark matter halo mass. Under the noise characteristics expected for the upcoming CCAT survey, the analysis forecasts tight constraints on the astrophysical model parameters. A Fisher-matrix analysis further indicates that the effects of a bump superimposed on a standard single-power-law primordial power spectrum can be disentangled from astrophysical parameter effects. Combining smoothing scales and redshifts improves the forecast constraints and prospects for detecting such features; no observational detection is reported.

PublicRather than identifying individual galaxies, line intensity mapping measures their combined light at particular spectral lines. This study uses simulated maps of light from ionized carbon in the early universe and examines the maps’ shapes and patterns. With noise expected from the upcoming CCAT survey, the analysis suggests that these patterns could tightly constrain a model linking carbon-line brightness to the mass of a galaxy’s surrounding dark matter halo. The researchers also forecast that the method could distinguish a possible bump in the universe’s primordial pattern of fluctuations from changes in that galaxy-light model. Combining maps from different early epochs and examining them at several smoothing scales improves the prospects. These are forecasts based on simulations, not a detection of a primordial bump.

Young explorerImagine a picture made from the glow of lots of faraway galaxies, all mixed together. Scientists made pretend pictures like this on a computer and studied their shapes. Their tests suggest that a future sky survey could use those shapes to learn how galaxies glow and look for a possible extra bump in the pattern of tiny differences from the universe’s beginning. Looking at the pictures with different amounts of blur and at different early times could help. They have not found that bump in the real sky.

Hydrostatic Equilibrium Constraints on the Fuzzy Dark Matter Mass from Dwarf Spheroidals: Method, Systematics, and Robustness

Samrat Mitra, Koushik Dutta

AstronomerThe authors analyze a non-parametric estimator of the fuzzy dark matter boson mass that assumes local hydrostatic equilibrium, balancing classical gravitational acceleration against the quantum-potential gradient in the Schrödinger–Poisson–Madelung system. They apply it to pyGravSphere density and enclosed-mass posteriors for nine Milky Way dwarf spheroidal galaxies, without imposing a soliton or other parametric profile. Least-squares balancing over a fixed radial window yields a mass posterior for each galaxy. Median estimates span approximately (0.8–4.6) × 10^-20 eV, with Draco and Ursa Minor lowest and Carina and Sextans highest. The weighted estimate is (1.3 ± 3.5) × 10^-20 eV, dominated by Draco and Ursa Minor. These are model- and equilibrium-dependent inferences, not a direct particle detection; the abstract reports detailed characterization of systematics.

PublicThe study estimates the mass of a proposed dark matter particle whose behavior is described by waves. Using reconstructed matter distributions in nine small galaxies orbiting the Milky Way, the researchers ask which particle mass would allow a quantum effect to balance gravity. Their method does not require a preset shape for the dark matter distribution. The middle estimates for individual galaxies range from about 0.8 to 4.6 × 10^-20 electronvolts. A weighted estimate is (1.3 ± 3.5) × 10^-20 electronvolts, with Draco and Ursa Minor contributing most strongly. The large quoted uncertainty matters: this is an estimate conditional on the proposed model and balance assumption, not confirmation that such particles exist. The authors also examine systematic uncertainties.

Young explorerScientists are trying to understand invisible stuff in space called dark matter. One idea says it is made of tiny things that act like waves. The scientists studied nine small galaxies and asked how light those tiny things would need to be for a wave effect to balance gravity’s pull. Different galaxies gave different answers, and the combined answer was very uncertain. This does not prove the tiny things are real—it is a way to explore the idea.

Stimulated capture of axion dark matter around primordial black holes

Nuno P. Branco, João G. Rosa

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

AstronomerThis theoretical study examines stimulated capture of axions and axion-like particles by primordial black holes through quartic self-interactions. It identifies parameter regions where Bose-enhanced growth outpaces cosmological dilution and derives analytic criteria for efficient formation and long-term survival of hydrogenic ground-state clouds, assessed against current axion-photon coupling bounds. Two potential observational signatures are considered: resonant axion-to-photon conversion in neutron-star magnetospheres and finite-size microlensing distortions. For conversion, resonance selects a shell outside the neutron-star surface, and high cloud occupation numbers can offset low conversion probabilities. Predicted transient line flux densities can exceed nominal VLA and ALMA sensitivities in parameter regions with observationally relevant Galactic encounter rates. Clouds comparable to or larger than the Einstein radius can also alter point-lens microlensing light curves. These are conditional theoretical predictions, not reported detections.

PublicThe researchers explore theoretically whether primordial black holes could gather clouds of hypothetical particles called axions or axion-like particles. They identify conditions under which interactions among these particles could help clouds grow despite the dilution caused by cosmic expansion, and remain intact over long periods. They also compare those conditions with existing limits on how axions interact with light. The study predicts two possible clues to such clouds. During an encounter with a neutron star, some axions could turn into light in a resonant region outside the star. Although each particle would have a small conversion probability, a sufficiently populated cloud could produce a brief signal above the nominal sensitivity of the VLA or ALMA, under suitable conditions and encounter rates. A sufficiently extended cloud could also change the pattern of brightening caused by gravitational lensing. The abstract reports theoretical possibilities, not observations of these systems.

Young explorerScientists used math to ask whether tiny, mysterious particles could gather like a cloud around a black hole from the early universe. Their work suggests that, if the conditions are right, a cloud could grow and last a long time. If it met a neutron star, some particles might turn into light and make a brief glow. A big enough cloud might also change how the black hole makes light from something behind it look brighter. These are ideas about what we might see, not clouds the scientists have found.

The gravitational constant and the cosmic microwave background

Brahim Lamine, Sébastien Beauchamp, Alain Blanchard+3 more

AstronomerThis theoretical and numerical study makes explicit how G affects recombination and the CMB acoustic spectrum, rather than reporting a new observational constraint. Using modified CLASS calculations, the authors scan lambda_G = sqrt(G/G_N) from 0.25 to 2 at fixed physical densities and CMB temperature, recomputing helium for each model. They compare analytic rate arguments with numerical ionization histories, visibility functions, damping integrals and TT spectra. The equality and acoustic angular scales are nearly G-independent, whereas non-equilibrium recombination yields ell_damp proportional to lambda_G^(-0.304). This dependence occurs only above a critical G approximately G_N/49. Dark-ages optical depth changes by only 16% when G increases by a factor of 64, making it a negligible channel in this analysis. Within the model, G enters through the expansion rate, and the competition with atomic rates is governed by alpha_G = G m_e mu/(hbar c), where mu is the mean matter mass per photon. A late-time gravity change rescales all three angular scales alike. The authors therefore identify ell_damp/ell_A as a diagnostic of G at recombination relative to its laboratory value, subject to lensing and screening effects.

PublicThe cosmic microwave background, light left over from the early universe, already constrains gravity's strength at the time atoms formed to within a few percent of its laboratory value. This study uses calculations and computer models—not a new measurement—to explain how that sensitivity arises. Changing gravity changes how quickly the universe expands, affecting whether atom formation can keep pace. In the models, two characteristic pattern scales change very little, but the scale at which small features are smoothed out responds to gravity's strength. That response occurs only above a threshold about 49 times weaker than laboratory gravity. The authors identify a ratio of pattern scales that could distinguish gravity during atom formation from later changes in gravity. Gravitational lensing and screening effects still matter when interpreting that ratio. The study does not establish that gravity actually changed.

Young explorerThe universe has very old light with patterns in it. Scientists used computer models to ask what those patterns would look like if gravity had been stronger or weaker when atoms formed. They found that gravity could change how much the tiny patterns get blurred. Comparing that blur with another pattern size could help check gravity long ago. This does not mean gravity really changed.

Breaking de Sitter Symmetry with Cosmic Topology: Cosmological Role of Infrared Vacuum Freedom

Anna Negro, Kurt Hinterbichler, Glenn D. Starkman+5 more

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

AstronomerThis theoretical study examines vacuum selection for a scalar field in de Sitter spacetime with toroidal spatial sections. The local Hadamard conditions remain insensitive to compactification, but toroidal identifications break global de Sitter invariance and affect the infrared sector, removing the usual symmetry argument for discarding zero modes. Treating the remaining zero-mode freedom as an effective topology-induced source, the authors show within a semiclassical framework that a massless scalar can have a zero-mode stress-energy contribution with P = -ρ. This cosmological-constant-like contribution allows the source of an inflationary de Sitter expansion to depend on the quantum state's infrared structure, not solely on local action terms. Its possible relevance to present-day accelerated expansion is suggested, not established.

PublicCould the way space connects to itself affect what drives cosmic expansion? This theoretical study considers a model in which space wraps around in a toroidal shape. In that setting, the usual symmetry-based reasoning for choosing a quantum vacuum no longer fully applies. The authors find that, for a massless scalar field, a remaining freedom in the field's spatially uniform component can contribute energy and pressure like a cosmological constant. In their semiclassical model, this means that an early period of accelerated expansion could depend partly on the large-scale structure of the quantum state, rather than only on local physical terms. This is not observational evidence that space has this shape or that this mechanism drives expansion today; the latter is raised only as a possibility.

Young explorerImagine space wrapping around so that going far enough could bring you back around. Scientists used a mathematical model to ask whether space shaped this way could change how a tiny quantum field helps space grow. They found that one part of the field could act like an energy that makes space expand faster. This is a possibility in their model, not something they have seen in the sky. They also wonder whether it could help explain why space is expanding faster today.

The Forgetful Black Hole: Memory Burden and Hysteresis in Hawking Evaporation

Yen Chin Ong

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

AstronomerThis theoretical study revisits the proposal that retaining quantum information can dynamically suppress Hawking emission. It derives scaling conditions for incremental memory accumulation at fixed fractional mass loss and a conditional no-go result: entropy-suppressed, zero-mean deposits with subextensive integrated correlations cannot yield an order-one luminosity modification through unamplified accumulation and bounded feedback. A viable dynamical memory must be written, retained, and coupled back to subsequent evaporation. Illustrative toy models produce either prolonged but finite lifetimes or asymptotic approach to a finite-mass state, described as an effective remnant. The authors distinguish kinetic-, thermodynamic-, and spectral-memory mechanisms and demonstrate that an independently evolving memory variable can produce evaporation-accretion hysteresis: equal-mass black holes can have different retained memories and luminosities depending on their histories. Possible implications for primordial black holes and memory resetting or reorganization in mergers remain proposals, not observational findings.

PublicCould a black hole’s stored quantum information slow its loss of energy? This theoretical paper examines that proposal rather than reporting observations. It argues that information must be recorded, preserved, and able to affect later evaporation for such a slowdown to occur. Under specified assumptions, small memory contributions cannot accumulate into a substantial change in the energy emitted. Simplified mathematical models nevertheless illustrate ways memory could extend a black hole’s lifetime or make it approach a state with some mass remaining. The models also show how a black hole could emit differently after losing and regaining mass, because its retained memory has changed. Whether these ideas affect primordial black holes, or whether mergers could reset the memory, remains uncertain.

Young explorerScientists used math to ask whether a black hole could keep a kind of memory that makes it lose energy more slowly. In their simple models, that can happen only if the memory is saved and can change what happens next. Some models let the black hole last longer or approach a state with some mass left. This is an idea being studied, not something they saw happen.

Leptogenesis with a GeV-Scale Quasi-Dirac Neutrino

Stephen F. King, Soumen Kumar Manna, Rishav Roshan+1 more

• High Energy Physics - Phenomenology

AstronomerThis theoretical study presents Higgs-decay leptogenesis in a type-I seesaw model with spontaneously broken global lepton number and a discrete Z2 symmetry. Two nearly degenerate, predominantly sterile right-handed neutrinos approximately form a single GeV-scale Dirac neutrino; higher-dimensional lepton-number-violating operators generate the tiny mass splitting needed for resonant enhancement. Including finite-temperature effects, the authors find that thermal Higgs decays can reproduce the observed baryon asymmetry for quasi-Dirac masses of 0.1–10 GeV, with CP asymmetry arising from the interplay of vacuum and thermal contributions to the splitting. The successful parameter region is accessible to future searches at SHiP, MATHUSLA and FCC-ee. Unstable domain walls from the same symmetry-breaking sector could also produce a stochastic gravitational-wave background upon annihilation. These are model-based explanations and prospective probes, not reported detections.

PublicWhy the universe contains more matter than antimatter remains a puzzle. This theoretical study proposes an explanation involving Higgs particle decays and two nearly identical, mostly sterile neutrinos that behave approximately like one particle. The authors calculate that, when hot-universe effects are included, neutrinos with masses of 0.1–10 GeV could allow this process to account for the observed matter–antimatter imbalance. The explanation depends on a tiny difference between the two neutrino masses. Future searches at SHiP, MATHUSLA and FCC-ee could test the relevant neutrinos. The model also allows temporary structures called domain walls, whose disappearance could generate a background of gravitational waves and offer another test. Neither the proposed neutrinos nor this gravitational-wave signal is reported as detected.

Young explorerThe universe has more matter than antimatter, its opposite partner. Scientists studied an idea for how that could happen: in the hot, early universe, particles called Higgs particles might have broken apart in a way that helped leave extra matter. Their idea uses two almost-twin tiny particles called neutrinos. Their calculations suggest it could work, but they have not shown that nature really did this. Future experiments could look for these particles. The idea might also make tiny ripples in space that scientists could search for.

Testing the inelastic dark matter interpretation of the LZ event with heavy-element experiments

Peter W. Graham, Juan P. Luengas, Harikrishnan Ramani+1 more

• High Energy Physics - Phenomenology
• Astrophysics of Galaxies
• High Energy Physics - Experiment

AstronomerThe authors explore an inelastic-dark-matter interpretation of the 248 keV event observed by LZ, not an established dark matter detection. Using example velocity distributions motivated by the Large Magellanic Cloud (LMC), they show that model viability and complementary experimental sensitivity depend strongly on the high-velocity tail. A reduced tail flux relative to simulations improves the thermal Higgsino fit, while an extension to higher velocities at fluxes below current simulation resolution can evade solar-neutrino constraints; these possibilities motivate higher-resolution simulations rather than establish the required distribution. Even confirmation by xenon experiments would require complementary tests to identify inelastic scattering and resolve mass–splitting degeneracies. Proposed heavy-element paleodetectors could cover most relevant parameter space, constrain mass and splitting through different target elements, and probe an LMC origin through sensitivity to the distribution's history. Luminous detection in large neutrino detectors supplemented with heavy elements could test inelasticity and measure the splitting, with radiative-decay-rate sensitivity potentially providing strong evidence for a Higgsino interpretation.

PublicLZ observed an event with an energy of 248 keV. This paper explores whether it could come from inelastic dark matter, rather than claiming that dark matter has been found. The explanation depends strongly on how many dark matter particles move at very high speeds. The authors examine possible speed distributions influenced by the Large Magellanic Cloud. They describe conditions that could allow a candidate called the thermal Higgsino to remain compatible with solar-neutrino limits, but part of the required fast-moving population lies below the resolution of current simulations. Better simulations are therefore needed. Even if other xenon experiments confirm the event, additional tests would be needed to establish its cause and measure the proposed particles' properties. Suggested approaches include heavy-element paleodetectors, which could also probe the history of the dark matter population, and searches for light in large neutrino detectors supplemented with heavy elements. These are proposed tests, not reported detections.

Young explorerA detector called LZ spotted an event, and scientists are asking whether it might be a clue to invisible stuff called dark matter. They have not shown that it is. Their idea depends on how much dark matter moves very fast, perhaps because of another galaxy. Computer models cannot yet check all the fast-moving bits they need to understand. The scientists suggest other ways to look for clues. If those tests work, they could help tell whether this dark matter idea is right and what the tiny particles might be like.

From Cosmic Bounces to Primordial Black Holes: The Role of Primordial Magnetic Fields

Ajeet Singhal, Shreya Banerjee

• General Relativity and Quantum Cosmology

AstronomerThis theoretical analysis links primordial black hole (PBH) formation to magnetogenesis during a non-singular ekpyrotic bounce. A time-dependent electromagnetic coupling to a scalar background amplifies gauge fluctuations during contraction, producing magnetic fields whose anisotropic stress dominates during radiation domination in the model. Retaining finite-wavenumber cutoffs, the authors calculate an ultraviolet-dominated curvature spectrum, density-perturbation variance, and PBH abundances under monochromatic and critical-collapse prescriptions. For benchmark parameters, the critical-collapse mass spectrum peaks near 2.0 × 10^-3 solar masses, with a total dark matter fraction f_PBH ≈ 10^-5. Requiring f_PBH ≤ 1 yields H_end ≤ 1.6 × 10^3 GeV and q ≤ 0.247, consistent with the electromagnetic backreaction limit. Reaching asteroid masses or a larger dark matter fraction requires modifying the ultraviolet cutoff and contraction duration. These are model predictions, not detections, and the inferred abundance depends importantly on the cutoffs and collapse prescription.

PublicCould magnetic fields in a bouncing early universe have helped create black holes? This theoretical study explores a model in which the universe contracts and then bounces without a singularity. During contraction, a changing interaction strengthens electromagnetic fluctuations, generating magnetic fields that can seed the disturbances responsible for primordial black holes. For one benchmark set of assumptions, the predicted black hole mass distribution peaks at about two-thousandths of the Sun's mass, and the black holes together account for only about one hundred-thousandth of dark matter. Requiring that the model not produce more black hole dark matter than the total available places limits on its contraction parameters. The predictions depend strongly on the range of fluctuation scales included and on how collapse is modeled; producing asteroid-mass black holes or a larger dark matter share would require changes to the model. The study does not report observed black holes.

Young explorerImagine the very young universe getting smaller and then bouncing instead of squeezing into a single point. Scientists used math to explore whether magnetic fields in that story could help make black holes. In one example, their math predicts black holes much lighter than the Sun, making up only a tiny bit of the mysterious stuff called dark matter. They did not see these black holes. What their math predicts changes when they change some of the rules in their model.

From Non-Thermal to Thermal: Cosmological Imprints of Self-Interacting Secluded Dark Matter

Koushik Dutta, Deep Ghosh, Ahamadullah Khan

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

AstronomerThis theoretical study numerically solves the momentum-dependent Boltzmann equation for a real scalar dark matter field with quartic self-coupling, produced by perturbative inflaton decay during reheating. Elastic 2→2 self-scattering establishes internal thermalization without number-changing processes, leaving a nonzero chemical potential. In the modeled scenarios, an inflaton mass above or below the reheat temperature permits dark matter to be respectively hotter or colder than the Standard Model sector during Big Bang Nucleosynthesis, with negative or positive chemical potential, without violating cosmological constraints. Self-scattering tends to reduce the comoving free-streaming length relative to collisionless production, weakening the lower mass bound by approximately 40% for a suitable quartic coupling. The bounds depend strongly on production history and can lie well below those in warm dark matter scenarios. For an inflaton mass of 10^3 GeV, the reported thermalized dark matter mass limits are 2.2×10^-10 GeV at a reheat temperature of 5×10^6 GeV and 0.47 GeV at 5 MeV. These are model-dependent numerical results, not observational detections.

PublicCould dark matter reach its own temperature without exchanging heat with ordinary matter? This theoretical study explores that possibility for a particular hypothetical dark matter particle produced during reheating in the early universe. Numerical calculations show that collisions among these particles can redistribute their motion while preserving their total number. Depending on the assumed early-universe conditions, the dark matter can be hotter or colder than ordinary matter during the formation of the first atomic nuclei, while remaining compatible with cosmological constraints. The collisions also tend to shorten the distance dark matter travels freely. For a suitable interaction strength, this lowers the model’s minimum allowed particle mass by about 40% compared with the same production scenario without collisions. The conclusions depend on the particle model and production history; they are not a detection of dark matter.

Young explorerScientists used computer calculations to imagine tiny dark matter particles bumping into one another when the universe was very young. In their model, the bumps help the particles share their energy and can keep them from traveling as far. That could allow the particles to be lighter than in the version without bumps. This is an idea scientists tested with math, not something they have seen happen.

Modified hydrogen recombination rate due to non-Hubble redshift effects

I.V Krasnov, N.S. Nedelko

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

AstronomerThe authors revisit recombination calculations, investigating how interactions between Lyman-alpha photons and moving neutral hydrogen atoms can correct the photons’ escape rate from the resonance line. In an analysis of CMB data using the modified model, they find a preference for a non-Hubble redshift effect, slightly higher H_0, and lower Omega_m, S_8, and scalar spectral index n_s than in standard LambdaCDM. These are model-dependent preferences; the abstract does not quantify their statistical strength or establish that the modification resolves disagreements among cosmological measurements.

PublicDifferent methods of measuring the universe’s properties have produced significantly different answers. This study investigates a change to calculations of how light escaped interactions with hydrogen as the early universe recombined. The authors find that encounters with moving neutral hydrogen atoms can alter the escape rate of Lyman-alpha light. When they analyze cosmic microwave background data with this modified model, the data favor an additional redshifting effect beyond that caused by cosmic expansion and somewhat different estimates of several cosmic properties, including a slightly faster present-day expansion rate. The abstract does not establish that this change solves the measurement disagreements.

Young explorerScientists get different answers when they try to measure some things about the universe. This study looks at how moving hydrogen atoms could change the way light got free long ago. When the scientists used this idea to study old light from the universe, their model gave somewhat different answers, including a slightly faster expansion today. That is a clue to explore, not proof that they have solved the puzzle.

From Axion Detection to Dark Matter Astronomy

Jae Hyeok Chang, Stefano Profumo

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

AstronomerThe abstract proposes using a global haloscope network, following an axion discovery, to probe dark matter substructure and transients. The approach combines interferometric phase, spatial coherence, and spectroscopy to infer flow directions and velocity distributions. A four-site forecast for tidal streams shows how longitudinal and transverse velocity dispersions could be measured jointly; this is a forecast, not an observational detection. Interpreting such measurements with dynamical and population models could test axion production scenarios. Proposed extensions to miniclusters, axion stars, and emitted bursts would broaden the astrophysical scope of laboratory detection.

PublicIf axions are discovered, a worldwide network of detectors called haloscopes could help study how this dark matter forms structures and changes over time. The proposed approach would combine signals across locations to work out which way axion flows travel and how their speeds vary. A forecast using four detector sites explores how to measure speed variations both along and across a tidal stream; it does not report observed axion streams. With models of how these structures move and how common they are, future measurements could test ideas about how axions were produced. The authors also suggest extending the approach to axion clumps, axion stars, and bursts.

Young explorerScientists have an idea for studying tiny things called axions, which might make up dark matter. First, axions would have to be discovered. Then detectors around the world could work together to learn which way they move and how their speeds differ. The scientists explored what four detectors could learn about a stream of axions, but they have not seen such a stream. If the idea works, it could help scientists learn how axions came to be.

Axion String Source Modelling

Amelia Drew, Tomasz Kinowski, E. P. S. Shellard

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

AstronomerThis simulation study examines massive and massless scalar emission from collisions of Gaussian travelling waves on an axion global string, scanning wave amplitude A and standard deviation σ_d to investigate dependence on the string curvature radius R_Gaussian. The collisions produce isotropic massless bursts with emitted energy proportional to A^γ; γ depends on the regime of A/δ, where δ is the string width. Massive emission is exponentially suppressed as exp(−ζR_Gaussian) in the quasi-linear regime σ_d ≫ δ, but decays as R_Gaussian^(−γ′) in the nonlinear regime σ_d ≲ 2δ, with ζ and γ′ varying between curvature-radius regimes. In the nonlinear regime, massive particles can carry up to 50% of the total emitted energy. All configurations studied yield an axion spectral index q ≳ 1, approaching 1 as A increases and indicating a growing high-frequency contribution. By analogy between axion emission from global strings and gravitational emission from Abelian-Higgs strings, the authors suggest that massive-particle emission could compete significantly with gravitational emission in comparable nonlinear bursts; this is an interpretation, not a direct gravitational-radiation result.

PublicComputer simulations explore what happens when two travelling disturbances collide on an axion cosmic string. The simulated collisions send bursts of massless radiation in all directions. The energy in these bursts depends on the disturbances’ amplitude, while radiation in massive particles depends strongly on how sharply the string curves and how narrow the disturbances are relative to the string’s width. Massive-particle emission is strongly suppressed in one regime, but can account for up to half the emitted energy in the nonlinear regime studied. Larger-amplitude disturbances also put a greater share of axion radiation into high frequencies. An analogy with another type of cosmic string suggests that massive-particle emission might be important compared with gravitational radiation in similar bursts, but these simulations do not directly establish that conclusion.

Young explorerScientists used a computer to study two wiggles bumping into each other on a special kind of space string. In their model, the bump sent energy out in every direction. For some wiggles, tiny particles with mass carried away as much as half of that energy. These are computer results, not something the scientists saw happening in the sky.

Constraining Dark Acoustic Oscillations with the High-Redshift UV Luminosity Function

Jared Barron, David Curtin, Hongwan Liu+2 more

• High Energy Physics - Phenomenology

AstronomerThe authors constrain small-scale dark acoustic oscillations (DAOs) using high-redshift galaxy UV luminosity functions in a model-agnostic framework. They introduce a phenomenological transfer function that allows a subdominant DAO-participating dark matter component, and predict the UVLF with an Extended Press–Schechter formalism calibrated against N-body simulations initialized with DAOs. Using measurements from Hubble, JWST, Subaru, and the Canada–France–Hawaii Telescope, they constrain the first DAO peak to k ≳ 50 h/Mpc, unless the participating dark matter fraction is below 0.07. This is a constraint on possible DAO features, not a detection.

PublicSome theories of dark matter allow wave-like patterns to develop in its distribution, potentially affecting how many early galaxies form at different ultraviolet brightnesses. The researchers compared galaxy measurements from four telescopes with predictions calibrated using computer simulations. Their analysis limits these possible patterns: the first peak must occur at a wave number of roughly 50 h/Mpc or higher, corresponding to smaller spatial scales, unless less than 7% of dark matter participates. The study does not establish that these dark matter waves exist.

Young explorerScientists wonder whether invisible stuff called dark matter could have made ripples that helped shape galaxies. They used telescope pictures of faraway galaxies and computer models to check this idea. They did not find proof of ripples. Instead, their study says the ripples would have to be small enough, unless only a little of the dark matter was making them.

Mock Catalogs of Strongly Lensed Gravitational Waves via a Halo Model Approach with Space-borne Detectors

Mingqi Sun, Kai Liao, Youkai Li+6 more

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena

AstronomerThe authors develop a simulation framework and mock catalogs, GW-LMC-Space, for strongly lensed gravitational waves in future space-borne detectors, using astrophysical models of source populations and lens distributions. For four years of LISA observations, they predict 0–131 lensed massive black hole binary events, depending on the adopted binary formation model, with lensing probabilities reaching approximately 0.3%. For one year of DECIGO observations, they predict 0–44 lensed events from stellar-mass binary black holes, binary neutron stars, and neutron star–black hole binaries, with a lensing probability of approximately 0.15%. The simulations indicate that overlapping lensed signals are common and can significantly affect signal-to-noise estimates and event identification. These are model-dependent forecasts, not detections, and motivate explicitly accounting for overlap in future analyses.

PublicFuture space-based detectors such as LISA and DECIGO may detect gravitational waves that have been strongly bent by galaxies or galaxy clusters along their path. The researchers built simulated catalogs to estimate how often this could happen. Their models predict between 0 and 131 such events during four years of LISA observations, depending on how massive black hole pairs form, and between 0 and 44 during one year of DECIGO observations. The estimated chance of strong lensing reaches about 0.3% for LISA’s massive black hole pairs and is about 0.15% for the compact-object pairs considered for DECIGO. The simulations also indicate that lensed signals often overlap, potentially complicating estimates of signal strength and the identification of events. These predictions are not observations, and the event counts remain uncertain.

Young explorerWhen two black holes or other very compact stars circle each other, they can make ripples in space. A galaxy in the way can bend those ripples before they reach us. Scientists made pretend sets of signals on computers to explore what future space detectors might find. Their models say the detectors might find some bent signals, or perhaps none. The signals can also overlap, like two sounds playing at once, making them harder to tell apart. These are computer predictions, not things the detectors have already found.

Repulsive ultralight dark matter from Hosotani mechanism

Philippe Brax, Patrick Valageas

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

AstronomerThe authors construct an ultralight dark matter model with repulsive self-interactions from a five-dimensional action containing only a U(1) gauge field and massive charged free fermions. After compactification to four dimensions, the gauge field's fifth component becomes the dark matter scalar. A single fermion yields only attractive self-interactions, whereas two fermions can produce repulsion through a Scherk-Schwarz twist around the fifth dimension. Checks of observational and theoretical consistency from inflation to the present leave broad parameter ranges allowed; this is model viability, not a detection. For scalar masses below 10^-12 eV, self-interactions are negligible and the model behaves as fuzzy dark matter. At higher masses, repulsive self-interactions govern the formation of astrophysical-sized solitons. Larger soliton sizes require a large initial misalignment or small masses in the fuzzy dark matter regime.

PublicThis theoretical study proposes a model in which extremely light dark matter particles can repel one another. The model starts with a theory in five dimensions; when the extra dimension is compactified, part of a gauge field becomes the dark matter field. One fermion species produces only attraction, but two can allow repulsion through a twist around the extra dimension. The authors check the model against observational and theoretical constraints across cosmic history and find many allowed parameter choices, rather than evidence that this dark matter actually exists. Below a particle mass of 10^-12 electronvolts, the repulsion is negligible and the model behaves as fuzzy dark matter. At higher masses, repulsion controls the formation of localized structures called solitons on astronomical scales. Larger structures require either a large initial offset of the dark matter field or small particle masses in the fuzzy regime.

Young explorerScientists made a math model of dark matter, the mysterious stuff in space. In their model, tiny bits of dark matter can push away from each other. They use an extra dimension and a special twist to make that possible. If the bits are extremely light, the push hardly matters. If they are heavier, the push helps decide how big the dark matter clumps become. The scientists checked whether their idea could fit what we know about the universe, and many versions could. That does not mean they have found this kind of dark matter.

JWST lensed quasar dark matter survey V: Hints of self-interacting dark matter from 29 quadruply imaged quasars

D. Gilman, A. M. Nierenberg, J. Gurian+21 more

• Astrophysics of Galaxies

AstronomerUsing 29 quadruply imaged quasars, the authors infer the population abundance of core-collapsed halos and subhalos over 10^6–10^10.7 solar masses from the collective lensing signal of low-mass perturbers. Their structure formation model predicts collapsed fractions as a function of mass and redshift. The data favor lens models containing core-collapsed halos, as predicted by self-interacting dark matter (SIDM), with Bayes factors of 8:1–24:1 against cold dark matter (CDM), depending on assumed SIDM subhalo abundances and collapsed-halo internal structure. The analysis considers systematic uncertainties in globular-cluster and subhalo abundances and deeply collapsed density structures. Within the modeling explored, fitting the data without core collapse requires both globular-cluster abundances well above expectations and subhalo abundances exceeding N-body predictions. The authors interpret this as a challenge to CDM, not a definitive identification of SIDM; a particle-physics interpretation is deferred to a companion paper.

PublicDark matter that interacts with itself is predicted to form halos whose centers eventually collapse, making them especially effective at bending light through gravity. The researchers used 29 quasars, each appearing as four images because of gravitational lensing, to infer how common such collapsed dark matter structures might be. The combined lensing signal favors models with collapsed halos over the cold dark matter models considered, with statistical evidence ratios ranging from 8 to 24 to one. That preference depends on assumptions about the numbers of smaller dark matter structures and the internal makeup of collapsed halos. In the models explored, explaining the data without collapse requires unusually many globular star clusters and more dark matter substructures than simulations predict. The findings challenge the cold dark matter picture but do not establish that dark matter interacts with itself.

Young explorerGravity can bend light, making one faraway bright object look like four. Scientists studied 29 objects like this to learn about invisible material called dark matter. One idea says dark matter can interact with itself and squeeze tightly into the middle of invisible clumps, helping them bend light more strongly. Models with these squeezed clumps fit the light patterns better than the other models tested. But the answer depends on how many clumps and star clusters the scientists think are there, so this is a clue, not proof.

LazyTB: Extended LTB-solutions with Multiple Interacting Fluids

Kimmo Kainulainen, Enrico D. Schiappacasse, Linda Tenhu+1 more

• General Relativity and Quantum Cosmology

AstronomerThe authors present LazyTB, an accessible numerical code for solving the Einstein equations in the ADM formulation under spherical symmetry. It supports an arbitrary number of fluids with user-defined equations of state and optional interactions mediated by drag vectors. Carefully chosen dimensionless variables analytically cancel potentially divergent terms to avoid some numerical instabilities. Demonstrations include the standard LTB model, radiation plus dark matter, polytropic dark energy with nonzero sound speed, and interacting dark matter and dark energy. Diagnostic tools include ray tracing to extract simulated observables such as luminosity distances for observers at arbitrary locations. These are numerical demonstrations, not observational findings. The code is available and designed for extension beyond the late-universe examples presented.

PublicLazyTB is a new, publicly available computer tool for simulating gravity in models that are symmetric around a center. It can represent several cosmic components, such as radiation, dark matter and dark energy, with customizable properties and optional interactions. The authors rearrange the equations to avoid some sources of numerical instability and demonstrate the tool on several example models. It can also trace light through a simulation to calculate quantities such as distances inferred from brightness for observers in different locations. These examples demonstrate the software's capabilities; they do not establish that the modeled dark-energy properties or interactions occur in the real universe.

Young explorerScientists made a computer tool called LazyTB to try out ideas about space and gravity. It makes pretend universes that are the same in every direction around a center, using different kinds of stuff. It can follow pretend light to work out how far away things would seem from different places. The scientists tried several examples, but these computer worlds do not prove that the real universe works that way.

Self-Interacting Dark Matter: From Particle Physics Theories to Structure Formation Simulations

Martin Rosenlyst, Vinh Tran, Oliver Zier+7 more

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

AstronomerThis work presents a theory-to-simulation framework for self-interacting dark matter (SIDM), connecting representative elementary and composite dark-sector models to validated implementations in AREPO-2. The mapping translates microscopic properties into cosmological initial conditions, internal-state mass splittings and populations, reaction networks, velocity- and angle-dependent cross sections, dissipative losses, and decay rates and recoil kinematics. Building on infrastructure from companion work, the implementations support isotropic and anisotropic scattering, constant and velocity-dependent cross sections, multi-state and inelastic reactions, dissipative scattering, and dark-matter decay. Validation spans beam-lattice deflection, thermalization, uniform-box decay, isolated-halo gravothermal core collapse, and cosmological box and zoom-in simulations. The authors report agreement with analytical predictions and published inelastic and dissipative benchmarks, as well as consistency across numerical schemes. The contribution is a modeling and numerical framework for deriving nonlinear astrophysical predictions, not observational evidence for any particular dark-sector model.

PublicThe researchers have built and tested a computer framework that connects theories about dark matter particles to simulations of how cosmic structures form. It accommodates proposed dark matter interactions in which particles scatter in different directions, change internal states, lose energy, or decay. The framework translates the details of these theories into instructions for the AREPO-2 simulation code. Tests ranging from controlled particle experiments inside the computer to simulations of dark matter halos and larger cosmic regions reproduced mathematical predictions and previously published simulation benchmarks. This gives researchers a way to compare a wider range of dark matter theories. The reported success concerns the simulation tools; it does not establish that real dark matter behaves according to any of these models.

Young explorerScientists made computer tools to try out ideas about dark matter. In these ideas, tiny particles can bump into each other, change, or lose energy. The tools passed tests by matching what calculations said should happen. That helps scientists explore their ideas, but it does not show which idea describes real dark matter.

New Massless Spectra from Cosmic String Cusps

Amelia Drew, Ivan Rybak

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

AstronomerThis theoretical study extends the standard description of cusps on Nambu-Goto cosmic-string loops, where the string momentarily reaches light speed. Standard cusps have a sharp profile, y ∼ x^(2/3), and a gravitational-wave spectrum proportional to ω^(-4/3). The authors identify alternative cusp solutions, including smooth shapes, and calculate their massless gravitational-wave and axion spectra. They derive a general asymptotic form for Nambu-Goto cusp spectra, κ̃(ω) ∝ ω^[-n/(2n−1)] ω^[-m/(2m−1)], with n, m ≥ 2. They also calculate waveform corrections from backreaction and finite string width, which introduce a high-frequency cutoff. These are theoretical results, not reported detections; departures from the standard cusp picture occur under particular conditions.

PublicCosmic strings are theoretical objects whose loops can develop brief features called cusps, where the string momentarily reaches the speed of light. The usual model predicts sharply pointed cusps that emit strong bursts of gravitational waves, making them targets for searches. This study finds mathematical solutions with other cusp shapes, including smooth ones, under certain conditions. The researchers calculate how these alternatives would emit gravitational waves and axions, and derive a general formula describing how the predicted signals vary with frequency. They also calculate how effects omitted from the simplest string model, including finite string width and backreaction, introduce a high-frequency cutoff. The work concerns theoretical predictions, not observations of cosmic strings or their signals.

Young explorerImagine a tiny loop of string in space that scientists think might be possible. In their usual math picture, it can briefly make a very sharp tip and send out ripples in space. The researchers found that their math also allows other shapes, even smooth ones, in some cases. They worked out how the ripples would change, and how giving the string some thickness changes the highest-frequency part of the signal. This is a prediction from math, not something they saw in space.

Classical conformal invariance and superhorizon dynamics in de Sitter

Maria Cristina Fiore, Andrea F. Sanfilippo

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

AstronomerThis theoretical study tests Soft de Sitter Effective Theory as a late-time description of equal-time correlators in classically conformally invariant models. For conformally coupled φ⁴ theory, the authors show that tree-level trispectrum matching does not fit the standard effective theory’s expected power counting, and argue that the construction does not capture the nontrivial late-time dynamics generated by quantum effects. By contrast, tree-level bispectrum matching in conformally coupled φ³ theory is consistent. They propose a prescription for identifying the leading superhorizon degrees of freedom as a starting point for a revised late-time effective description, rather than presenting a completed construction. The interpretation of log(-kη) terms is also briefly discussed.

PublicThe paper examines whether a simplified mathematical framework can describe how quantum fields behave at late times in de Sitter space. Using a toy model, the authors find that a calculation involving correlations among four field values does not fit the framework’s usual rules. A related calculation involving three field values in a different model does fit. They argue that the standard framework therefore misses important quantum-driven behavior in the first model. They propose a way to identify which features on scales larger than the horizon should enter a revised description, but do not yet provide that complete description. These are theoretical findings, not astronomical observations.

Young explorerScientists use simpler math rules to study very complicated things. Here, they tested some rules in a pretend universe. One test did not fit the rules, although a different test did. They suggest a new way to choose which pieces the math should keep, but they have not finished building the new rules. This was a math study, not something they saw in the sky.

ACT stands for Awkward Cosmology Theories

Loris Del Grosso, Alfredo Urbano, Marcello Ziccolella

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

AstronomerACT observations combined with Planck favor a scalar spectral index in tension with Starobinsky inflation. This theoretical reassessment examines two proposed remedies: higher-curvature corrections and altered reheating. Allowing a second mass scale to suppress higher-dimensional operators yields a one-coupling, two-scale effective theory. The authors find that fitting ACT drives this class toward greater UV sensitivity, potentially requiring fine-tuning of inflationary observables. No-scale supergravity and metric-affine gravity illustrate different realizations of the same underlying f(R) theory. For reheating, requiring CMB modes to re-enter the horizon before recombination strongly constrains the equation of state; fitting ACT favors an exotic phase with ω_reh > 1/3, incompatible with inflaton oscillations around the standard Starobinsky potential minimum. A proposed alternative involving cosmological stasis sustained by a tower of decaying massive states accommodates the ACT-preferred spectral index only with negative-energy-density states in this setup. The authors interpret these results as challenges to motivating the required ingredients in UV-complete theories and to retaining Starobinsky inflation’s original minimality, rather than as an observational exclusion of all extensions.

PublicMeasurements from the Atacama Cosmology Telescope, combined with Planck data, favor a property of primordial fluctuations that is in tension with the Starobinsky model of inflation. The authors investigate proposed ways to bring the model into agreement with those measurements, rather than report a newly observed cosmic process. Adding terms to the gravity theory makes the fit more sensitive to very-high-energy physics and may require fine-tuning. Changing reheating, the period after inflation, instead favors an unusual phase that ordinary oscillations in the standard model’s potential cannot produce. Another proposed phase, sustained by many kinds of decaying massive particles, works in the setup studied only if some states have negative energy density. The authors conclude that reconciliation requires theoretically difficult additions, weakening the original model’s simplicity without ruling out every possible extension.

Young explorerScientists have a simple idea about how the universe grew very fast when it was young. New telescope clues do not fit that idea comfortably. The researchers checked whether changing the idea, or what happened just afterward, could help. The fixes they studied need unusual ingredients that are hard to explain. This does not mean the idea is definitely wrong, but making it fit may mean it is no longer so simple.

JWST Observations of RR Lyrae in Leo P

Catherine M. Slaughter, Alessandro Savino, Meredith Durbin+5 more

• Solar and Stellar Astrophysics

AstronomerThe study analyzes co-spatial HST/ACS and JWST/NIRCam time-series photometry of RR Lyrae in the low-metallicity dwarf galaxy Leo P, identifying 20 in the HST imaging and 15 in the JWST imaging and measuring their periods, amplitudes, and mean magnitudes. A Period-Wesenheit-Metallicity (PWZ) fit to the HST population yields a Gaia-consistent distance modulus of 26.04 ± 0.07, corresponding to 1.61 ± 0.06 Mpc, in agreement with existing distance measurements. A simultaneous JWST PWZ fit using Leo P and previous WLM observations reduces the mean fractional uncertainties on the slope and intercept by 31% and 11%, respectively, relative to the existing calibration. These observations strengthen the calibration for JWST studies of metal-poor RR Lyrae.

PublicResearchers studied regularly brightening and fading stars called RR Lyrae in Leo P, a dwarf galaxy with a low abundance of elements heavier than helium. They identified 20 of these stars in Hubble images and 15 in James Webb images, measuring how quickly and how much their brightness changes. Using the Hubble measurements and a relationship linking the stars’ pulsation periods, brightness, and chemical composition, they estimated Leo P’s distance at 1.61 ± 0.06 million parsecs, agreeing with earlier measurements. Combining the Webb observations with earlier Webb data from the galaxy WLM also made a similar distance-calibration relationship more precise: the fractional uncertainties in its slope and intercept decreased by 31% and 11%. These improvements concern the calibration, not equivalent percentage reductions in Leo P’s distance uncertainty.

Young explorerSome stars get brighter and dimmer over and over, like lights that slowly pulse. Scientists watched stars like these in a galaxy called Leo P using the Hubble and James Webb space telescopes. The Hubble pictures helped them work out how far away the galaxy is, and their answer agreed with earlier measurements. They also put Webb’s measurements together with ones from another galaxy to improve a rule for using these pulsing stars to measure distances.

The Impact of High-Mass Clusters on the Binary Black Hole Merger Rate over Cosmic Time

Aidan Mai, Kyle Kremer, Fulya Kıroğlu

• High Energy Astrophysical Phenomena

AstronomerThis cosmological calculation combines Cluster Monte Carlo simulations spanning observed cluster masses, metallicities, and virial radii with an analytic cluster formation model and simulated merger delay-time distributions. The grid now includes 10-million-particle models, including a new solar-metallicity model. The calculation predicts that the local cluster binary black hole merger rate is dominated by systems with primary masses ≲20 solar masses originating in recently formed, high-metallicity clusters. Massive clusters preferentially produce hierarchical mergers involving remnants of earlier mergers, but their overall contribution is suppressed by the exponential cutoff in the cluster initial mass function. The predicted hierarchical fraction is consequently sensitive to the Schechter cutoff mass, M_S. The formation model reproduces the observed present-day globular cluster number density without fine tuning; M_S = 10^7 solar masses best matches the observed Virgo globular cluster mass distribution and yields a hierarchical fraction of 27% among local dynamical mergers, versus 18% for the canonical M_S = 10^6.26 solar masses. These fractions are model predictions, not measured merger fractions. The authors suggest that gravitational-wave constraints on hierarchical mergers could independently constrain the high-mass end of the cluster initial mass function, and provide public merger weights for comparisons with LVK distributions and other formation models.

PublicThe researchers used computer simulations and a model of how dense star clusters form to estimate how often pairs of black holes merge in those clusters across cosmic history. Their calculation predicts that nearby cluster mergers are mostly systems whose larger black hole has no more than about 20 times the Sun’s mass, originating in relatively recently formed clusters rich in elements heavier than helium. The most massive clusters are especially important for repeated mergers, in which a black hole left by one merger merges again. But these clusters are rare, so the predicted share of repeated mergers depends strongly on how common very massive clusters are assumed to be. A model that best matches the observed masses of Virgo globular clusters predicts that 27% of local dynamically produced mergers involve an earlier merger remnant, compared with 18% under a standard alternative assumption. These percentages are predictions, not observed fractions. The study suggests that gravitational-wave measurements could help reveal how common the most massive clusters were.

Young explorerBlack holes can join together, and sometimes the black hole they make joins with another one later. Scientists used computers to imagine this happening in crowded groups of stars. Their model says the biggest star groups are especially good places for black holes to join more than once. But those big groups are rare, so the answer changes depending on how many there are. These are computer predictions, not a count of what scientists have seen. The scientists hope that studying ripples in space from joining black holes could help them learn about those big star groups.

CoRGI in MaNGA - II. NGC 5717: cold-gas accretion and disk growth in a BGG

Damir Gasymov, Ivan Yu. Katkov, Eva K. Grebel+6 more

AstronomerNGC 5717 is among the most massive known galaxies with a counter-rotating stellar disk and the first identified example in a brightest group galaxy. MaNGA integral-field spectroscopy, CFHT imaging, ancillary HI data, and group spectroscopy reveal a dynamically cold disk embedded in an old, dynamically hot elliptical component. The disk is young (~1.3 Gyr), metal-poor ([Fe/H] ~ -0.7 dex), extended (scale length ~2.4 kpc), and massive (log M_star/M_sun ~9.9). Ionized gas co-rotates with the disk; available HI data indicate no significant remaining neutral atomic gas reservoir, with log M_HI/M_sun ≲9. These findings support formation of the secondary stellar component in situ from externally accreted gas. A chemical evolution model favors a cosmic-filament gas source and highly efficient, burst-like star formation with substantial metal-enriched outflows; the surrounding cosmic-web geometry is consistent with this interpretation. The proposed history remains an interpretation: NGC 5717 may record rare disk growth through external cold-gas accretion during an earlier stage of group assembly.

PublicAstronomers have identified a disk of stars rotating opposite to the older stellar component of NGC 5717, a massive galaxy that is the brightest in its galaxy group. This is the first identified case of such a disk in a brightest group galaxy. The disk's stars are about 1.3 billion years old and relatively poor in heavy elements. Ionized gas rotates with them, while the available observations indicate little neutral atomic gas remains. These clues support the idea that gas arrived from outside the galaxy and formed new stars there. A model of its chemical history favors gas supplied by a filament of the cosmic web, followed by an efficient burst of star formation and outflows carrying heavy elements away. That origin is not established directly, but it suggests that even a massive central galaxy may grow a new disk when conditions permit.

Young explorerIn a big galaxy called NGC 5717, astronomers found a flat group of younger stars spinning the opposite way from the older stars around them. Some gas spins with the younger stars, too. The clues suggest that gas came from outside the galaxy and made these new stars. A model suggests the gas traveled along a giant strand in space, but scientists are not sure that is how it happened.

How Little Red Dots Turn Blue: Evolution of Kelvin-Helmholtz Contracting Black Hole Envelopes and Observational Diagnostics

Zihao Wang, Kohei Inayoshi

• High Energy Astrophysical Phenomena

AstronomerJWST observations have identified compact, red, broad-line emitters termed little red dots (LRDs), alongside a bluer population termed little blue dots (LBDs), but their physical relationship remains uncertain. The authors propose a rapidly growing black hole embedded in a geometrically thick gas envelope with concurrent nuclear star formation. The model reproduces the observed spectral energy distributions of both populations and links them through Kelvin–Helmholtz contraction of the envelope and exposure of the nuclear accretion disk as the gas supply declines. Predicted tracks in the UV–optical slope plane move from the LRD regime through a red excursion toward (β_UV, β_opt) ≈ (2, −1), then turn toward the LBD regime. This excursion is largely insensitive to variations in the envelope-structure parameters explored, making it a proposed signature of transitional systems rather than an observed evolutionary sequence. The modeled transition lasts approximately 5–50 Myr, primarily depending on black-hole feedback and envelope gas-retention efficiencies. Within this framework, the transitional-to-LRD abundance ratio could constrain those efficiencies.

PublicJames Webb Space Telescope observations have revealed compact sources called little red dots and a bluer population called little blue dots. Whether these are related stages or different populations is still unclear. This study proposes that a rapidly growing black hole, surrounded by a thick gas envelope and nearby star formation, could explain both. The model matches their observed distributions of light across wavelengths. In the proposed sequence, a dwindling gas supply causes the envelope to contract, exposing the disk feeding the black hole and turning a red-dot system into a blue-dot system. The model predicts a distinctive detour toward redder colors before the blue phase, with a transition lasting about 5 million to 50 million years. This sequence has not been established by observations. If such transitional systems are identified, their numbers relative to red dots could help test how black-hole activity affects surrounding gas and how effectively the envelope retains it.

Young explorerA space telescope has seen tiny-looking red dots and blue dots far away. Scientists do not yet know whether they are different kinds of things or the same kind at different times. This study suggests that a growing black hole wrapped in thick gas, with new stars forming nearby, might explain both. In their model, the gas wrapping shrinks and lets us see more of the bright disk around the black hole. A red dot could then become a blue dot, after first looking even redder. The model says this would take millions of years, but scientists have not yet shown that the dots really change this way.

The Pristine survey XXIX. Data Release 2: Photometric metallicities for 15 millions stars down to G∼20.5

Zhen Yuan, Anke Ardern-Arentsen, Nicolas F. Martin+15 more

AstronomerPristine DR2 extends the survey’s narrow-band CaHK catalogue to approximately 8,000 square degrees and G ~ 20.5, providing photometric metallicities for 15 million FGK stars. It incorporates observations from March 2015 through January 2025, adding about 1,500 square degrees relative to DR1 and removing DR1’s depth restriction from the availability of Gaia XP spectrophotometry at G ≲ 17.65. Calibration uses bright stars with Gaia synthetic CaHK magnitudes to train the PhotCalib neural network; metallicities follow the established Pristine CaHK and Gaia G, BP, RP model. The derived metallicities show good agreement with independent DESI metallicities. DR2 reports more than 200,000 very metal-poor and 6,500 extremely metal-poor candidates, not spectroscopically confirmed populations, and expands the volume accessible for studies of the faint metal-poor halo.

PublicThe Pristine survey’s second data release estimates the metal content of 15 million Milky Way stars from their measured brightness through selected filters. The catalogue covers about 8,000 square degrees of sky and reaches much fainter stars than the first release, helping researchers search farther into the Galaxy’s faint, metal-poor halo. The team calibrated the measurements using bright stars with Gaia data and a neural network. Their estimates agree well with independent measurements from the Dark Energy Spectroscopic Instrument. The catalogue identifies more than 200,000 candidates with very low metal content and 6,500 candidates with extremely low metal content; these are promising selections rather than individually confirmed discoveries.

Young explorerStars have different mixes of ingredients. Astronomers used special filters to look at starlight and estimate how much metal is in 15 million stars. Their new list includes fainter stars and covers more sky than before. They picked out many stars that might have very little metal, including some that might have extremely little. These are stars to check more carefully, not all sure discoveries yet.

HI rotation curves and mass-size relation for 568 galaxies from the Apertif Wide-area Extragalactic Survey

Konstantin Haubner, Federico Lelli, Enrico Di Teodoro+13 more

AstronomerThe first Apertif Wide-area Extragalactic Survey HI kinematic-model release contains 568 reliable models selected from 1,924 HI detections, forming the largest homogeneous HI rotation-curve sample reported to date. The models provide rotation curves, velocity-dispersion and surface-density profiles, and disk geometries. Modeled disks span three orders of magnitude in HI mass, outer rotation velocities of approximately 20–300 km/s, and extents from 2 to more than 60 kpc. Rotation curves contain 3–23 data points, with the distribution peaking at four points, an important limitation on their sampling. Inner rotation-curve shapes vary, while outer curves generally tend toward flatness. For a homogeneous subset of 213 galaxies, the HI mass–size relation has an observed mass-direction scatter of approximately 0.101 dex and an inferred intrinsic scatter of 0.067 ± 0.007 dex. Fitting mass as a function of size gives a slope of 1.96 ± 0.03, indicating constant average HI surface density. Although rotation curves can test dark matter and modified gravity models, the abstract reports no such model comparison.

PublicAstronomers have released models of how hydrogen gas moves in 568 galaxies, drawn from 1,924 galaxies detected by the Apertif Wide-area Extragalactic Survey. This is the largest consistently constructed collection of hydrogen-gas rotation curves reported so far. The curves describe how orbital speed changes with distance from a galaxy’s center: their inner shapes differ, but they generally level off farther out. Many curves are sparsely sampled, with four measured points being the most common count. In a subset of 213 galaxies, gas mass and disk size follow a very tight relationship, indicating nearly the same average amount of hydrogen gas per unit disk area. These data offer a resource for studying galaxies and testing gravity theories, rather than establishing which theory is correct.

Young explorerScientists studied how gas moves around in 568 galaxies. Near the middle, the speed changes in different ways. Farther out, it usually becomes steadier. For a smaller group, bigger gas disks held more gas in a very regular pattern: each patch of disk had about the same amount of gas on average. These clues can help scientists learn about galaxies.

Wandering intermediate-mass black holes and off-nuclear tidal disruption events from early star clusters

Claire E. Williams, Smadar Naoz, Yihao Zhou+9 more

• High Energy Astrophysical Phenomena

AstronomerOff-nuclear tidal disruption events (TDEs) provide evidence for massive black holes outside galactic centers, but their origins remain uncertain. This study models wandering intermediate-mass black holes formed by runaway stellar collisions in dense clusters at 7<z<20. A semi-analytic prescription, coupled to IllustrisTNG TNG50 merger trees, follows the assembly of 15 elliptical galaxies with stellar masses of 10^9–10^11 solar masses. It compares a maximal cluster-formation model drawn from a high-resolution simulation with a conservative model calibrated to local cluster relations. The mechanism predicts TDE bursts within 10–100 Myr of black-hole formation as the loss cone is depleted, with events typically 10–10^3 kpc from host centers. Predicted rates increase with galaxy mass; in the maximal model, progenitors of the most massive galaxies reach peak rates of approximately 5×10^-4–4×10^-2 events per year per galaxy at z≈7–13. These are model predictions, not measured rates, and provide a framework for constraining early IMBH-forming star clusters through high-redshift off-nuclear TDEs.

PublicWhen a black hole tears apart a star far from a galaxy’s center, the event offers evidence for a black hole living outside the center. How these wandering black holes formed is uncertain. This study explores one possibility: repeated stellar collisions in dense star clusters in the early universe could have built intermediate-mass black holes. Using a mathematical model and simulated galaxy histories, the researchers predict that these black holes would tear apart stars in bursts during the first 10 million to 100 million years after forming, as the supply of stars on vulnerable orbits is depleted. The predicted events usually occur far from galaxy centers, and more massive galaxies have higher predicted rates. The team compares two different assumptions about early cluster formation; the event rates are predictions rather than observations. The framework could help use such stellar disruptions to constrain the population of early star clusters that formed black holes.

Young explorerSometimes a black hole tears a star apart far from the middle of a galaxy. Scientists are not sure how those black holes got there. This team used a computer model to explore an idea: long ago, stars in crowded groups might have bumped together again and again and made black holes. Their model says these black holes would tear apart nearby stars mostly soon after they formed, until fewer stars were left on paths that came too close. This is a prediction from a model, not proof that the black holes really formed this way.

An Attenuation Bump at z=9.3: Probing Dust Diversity at Cosmic Dawn

Giulia Rodighiero, Santiago Álvarez-Córdoba, Michele Catone+46 more

AstronomerJWST/NIRSpec observations from ZENITH and EMBER reveal a UV attenuation bump in the Black Pearl at spectroscopic redshift 9.3335, the highest-redshift example reported to date, approximately 500 Myr after the Big Bang. A broad depression in the rest-frame UV continuum is fitted by a Drude profile centered at 2132 ± 17 Å, with FWHM 413 ± 54 Å and peak attenuation 0.21 ± 0.02 mag. Flexible joint spectrophotometric modeling recovers the bump without imposing it, across the adopted star-formation histories. Modeling implies log10(M*/M☉) = 8.35 (+0.09/−0.08), SFR = 2.36 (+0.54/−0.42) M☉/yr, and visual attenuation 0.34 (+0.12/−0.11) mag. Optical emission-line diagnostics indicate a hard ionizing spectrum and permit a moderate AGN contribution, but provide no evidence for a powerful AGN dominating the UV continuum. The bump center is blueshifted by 43 ± 17 Å relative to the canonical Milky Way feature, a roughly 2.5σ offset, and by 127 ± 17 Å relative to the few known examples at z ≈ 7. Its width remains consistent with the Milky Way sightline distribution. The authors interpret the displaced center as evidence for diverse early UV-bump carriers; both PAHs and small graphite grains remain plausible.

PublicAstronomers using JWST have detected a broad dip in ultraviolet light from the Black Pearl, a galaxy seen approximately 500 million years after the Big Bang. The dip is a signature of dust blocking particular ultraviolet wavelengths and is the most distant such feature reported so far. Modeling independently recovers the feature without requiring it in advance and suggests a relatively low-mass galaxy actively forming stars. Compared with the familiar dust feature in the Milky Way, this one is centered at a shorter wavelength, although the difference has only moderate statistical significance, about 2.5 sigma. Its width is consistent with the range found in our galaxy. The shifted position suggests that the particles responsible for these features varied in the early universe, but their identity is uncertain: PAH molecules and small graphite grains are both plausible. The observations allow some contribution from an active galactic nucleus but give no evidence that a powerful one dominates the ultraviolet light.

Young explorerAstronomers used the JWST telescope to look at a galaxy called the Black Pearl, seen when the universe was very young. Some of its ultraviolet light—a kind our eyes cannot see—is missing in a pattern that shows dust is blocking it. The pattern is a little different from the familiar one in our own galaxy. That hints that the dust particles could be different, but scientists do not yet know exactly which particles made the pattern.

A model for the ongoing subcluster interaction in Centaurus

Felipe S. Lohmann, Magda Arnaboldi, Michael Hilker+10 more

• Cosmology and Nongalactic Astrophysics

AstronomerDeep VLT/FORS V- and I-band imaging is used to select globular-cluster (GC) candidates in the Centaurus core by morphology and colour. Voronoi tessellation reveals significant spatial substructure: red GCs concentrate around the brightest galaxies, while blue GCs form a more extended distribution. The study confirms and quantifies the previously reported bridge between NGC 4696 and NGC 4709, finding twice the GC population expected from the projected GC systems of the two galaxies alone. Using GC specific frequency and colour distributions, the authors infer a faint-end galaxy luminosity-function slope of α = −1.87 ± 0.06 for the population that assembled the core, consistent with previous Hydra I results. They propose, rather than establish, a recent nearly head-on passage of Cen 45 through Cen 30, approximately along the line of sight. This interpretation accounts for the subclusters’ large line-of-sight velocity difference, intervening hot X-ray gas, GC bridge, and extended, puffed-up GC system of NGC 4709.

PublicImages of the nearby Centaurus galaxy cluster reveal an uneven distribution of likely globular clusters—compact groups of stars that can preserve clues to how galaxies assembled. Redder globular clusters gather around the brightest galaxies, while bluer ones spread farther out. The researchers confirm a previously reported bridge of globular clusters between NGC 4696 and NGC 4709, finding twice as many as expected from simply overlapping the two galaxies’ projected globular-cluster populations. They also use the globular clusters to infer the distribution of galaxy brightnesses in the population that built the cluster’s core. To explain the evidence, they propose that one subgroup of galaxies, Cen 45, recently passed almost head-on through another, Cen 30, roughly along our viewing direction. This is an interpretation, not a directly established collision history, but it accounts for the bridge, the subgroups’ differing motions, hot gas between them, and the unusually spread-out globular clusters around NGC 4709.

Young explorerAstronomers looked at a big gathering of galaxies and found what looks like a bridge made of little groups of stars between two galaxies. It has twice as many star groups as they would expect from just seeing the two galaxies’ star groups overlap. They think one gathering of galaxies may have passed right through another, leaving clues behind. That could explain the star bridge and some other things they see, but they have not proved that this is what happened.

The ALMA-QUARKS Survey. IV. Core Mass Function and Evolutionary Trends in Core Formation Efficiency and Chemistry

Wenyu Jiao, Tie Liu, Dongting Yang+43 more

AstronomerALMA-QUARKS observed 139 ATOMS-selected massive protoclusters at 1.3 mm with approximately 0.3-arcsecond resolution, corresponding to about 1,000 au at the sample’s median distance of 3.8 kpc. Using getsf, the authors identify 3,374 dense cores and classify them as starless, protostellar, hot core, or H ii region candidates using spectral-line diagnostics and CO outflow associations. Excluding H ii region candidates, the global core mass function has a high-mass slope of γ = 0.98 ± 0.03 in dN/dlogM ∝ M^−γ, but is biased by distance effects. Individual distance bins instead yield approximately Salpeter-like high-mass slopes, with fitted lower mass limits increasing with distance. Core formation efficiency correlates positively with parental-clump luminosity-to-mass ratio, consistent with, but not establishing, an evolutionary increase in the mass fraction concentrated in cores. Molecular-tracer detection rates vary systematically with evolutionary stage. Differences in deuterated-species detection rates relative to ASHES, even at matched evolutionary stages, suggest an environmental influence on core chemistry.

PublicThe ALMA-QUARKS survey examined 139 clusters where massive stars are forming and identified 3,374 dense pockets of gas, called cores. Spectral signatures and gas outflows helped researchers classify these as candidates for different stages of star formation. The combined sample appears to contain a relatively large share of high-mass cores, but that pattern is biased by the different distances of the targets. Grouping targets by distance gives a different picture, with fewer high-mass cores relative to lower-mass ones than the combined sample suggests. Clumps with higher luminosity relative to their mass also tend to have a larger fraction of their mass in dense cores. This is consistent with that fraction increasing as the clumps evolve, rather than proof that it does. Molecular detections change with evolutionary stage, and comparisons with the ASHES survey suggest that the surrounding environment also affects core chemistry.

Young explorerAstronomers used ALMA to look at 139 places where big stars are growing. They found 3,374 thick pockets of gas and used clues in the light and moving gas to sort them into possible stages of star-making. Faraway places made it harder to get a fair picture of how many small and big pockets there were. The team also found clues that more gas may gather into these pockets as their surroundings grow older. The chemicals they detected suggest that both a pocket’s stage of growth and where it lives can matter.

The optical colors of hidden spiral-like features in nine Virgo early--type dwarfs

Mauricio Gracia, Rory Smith, Anna Pasquali+5 more

AstronomerThis pilot study uses deep NGVS g- and i-band imaging and residual-based decomposition to examine embedded spiral-like features in nine Virgo dwarf early-type galaxies with clear arms. The excess spiral-like light contributes about 1.5–5.5% of the total in i and 1.7–3.7% in g. Arm–interarm g−i comparisons reveal redder arms in four galaxies, no robust color difference in four, and a distinctly bluer spiral-like component in one. The blue case is consistent with a recently quenched transition object; the redder and color-uniform features are consistent with older or more metal-rich stellar populations. These interpretations do not establish unique formation histories, but the observed photometric diversity suggests multiple evolutionary channels. The pilot also demonstrates readiness to extend the analysis to the larger NGVS sample of candidate systems.

PublicSome small galaxies in the Virgo cluster contain faint spiral-like arms, even though they are classified as early-type galaxies. Researchers studied nine such galaxies using deep optical images, separating the extra light associated with the arms from the diffuse galaxy around them. The spiral-like features provide only a few percent of each galaxy’s total light. In four galaxies the arms are redder than the regions between them; in four there is no clear color difference; and in one the spiral-like component is distinctly bluer. The blue example could be a galaxy that recently stopped forming stars, while the other features are compatible with older stars or stars richer in elements heavier than helium. Colors alone do not settle how these structures formed, but their variety suggests that more than one evolutionary pathway may be involved. This small study prepares the method for a larger sample.

Young explorerSome little galaxies have faint shapes inside them that look like spiral arms. Scientists looked at nine of these galaxies and compared the colors of the arms with the spaces between them. Four had redder arms, four had no clear color difference, and one had bluer arms. The arms made only a tiny part of each galaxy’s light. The blue arms might mean that galaxy stopped making new stars not long ago. The colors are clues, not proof, but they suggest these galaxies may have changed in different ways.

Self Calibrated Galaxy Groups from the DESI DR1 Bright Galaxy Survey

I. Williams, J. Tinker, K. Wang+45 more

• Cosmology and Nongalactic Astrophysics

AstronomerThis DESI Bright Galaxy Survey DR1 group catalog uses the Self Calibrated Group Finder, whose free parameters are calibrated with observed clustering rather than simulations. It includes 2,229,741 galaxies over approximately 2,680 square degrees with three-pass coverage and an r-band selection of r < 19.5, assigning central/satellite classifications and estimating host halo masses. The authors report satellite fractions, luminosity–halo mass and stellar–halo mass relations, and non-parametric halo occupation distributions (HODs). Standard HOD models fit these distributions, with satellite power-law indices near 0.75 for star-forming galaxies and 1.1 for quiescent galaxies. Above stellar masses of 10^10.3 M_sun h^-1 and halo masses of 10^12.2 M_sun h^-1, the inferred central quenched fraction depends mainly on halo mass and is nearly independent of central stellar mass. An appendix introduces Hybrid Nearest Neighbor redshift assignment to mitigate fiber incompleteness. Using photometric redshifts and multiple on-sky neighbors, the method recovers correct redshifts about 50% of the time and yields unbiased halo occupation statistics in calibration on DESI Survey Validation 3 data.

PublicResearchers have built a catalog that organizes more than 2.2 million DESI survey galaxies into groups, identifies their central and satellite members, and estimates the masses of their surrounding dark matter halos. The grouping method is tuned using patterns in the observed galaxy distribution rather than simulations. The catalog shows how galaxy numbers, brightness, and stellar mass relate to estimated halo mass. For central galaxies above specified galaxy and halo mass thresholds, the fraction no longer actively forming stars depends mostly on halo mass and very little on the galaxy’s own stellar mass. The authors also introduce a way to estimate distances for targets missing spectroscopic observations, using approximate distance information and nearby targets on the sky. In calibration tests, it assigns the correct redshift about half the time while recovering unbiased statistics of how galaxies occupy halos; that statistical success does not mean every individual distance is reliable.

Young explorerGalaxies are huge families of stars, and galaxies can belong to groups too. Scientists used a sky survey to make a list of more than two million galaxies and work out which ones belong together. They also estimated how much invisible dark matter surrounds each group. For some of the bigger galaxies at group centers, whether they have stopped making new stars seems more closely linked to the surrounding dark matter than to how much mass they have in stars. The scientists also tested a way to fill in some missing information. It got the right answer about half the time, but still helped them count galaxies in groups without pushing those counts too high or too low.

JWST reveals a highly ionized nebula powered by an ultraluminous X-ray source with a massive black hole in the metal-poor galaxy Holmberg II

F. A. Fogantini, P. Zeidler, L. M. Oskinova+9 more

• High Energy Astrophysical Phenomena

AstronomerJWST IFU spectroscopy resolves the nebula around the ULX Ho II X-1 in low-metallicity Holmberg II on approximately 15–25 pc scales and provides the first detections of [Ne V] and [Ne VI] in this source. The highest-ionization emission occupies compact regions offset from the ULX toward previously detected radio knots, while lower-ionization emission traces the wider nebula. Alignment with the radio axis suggests anisotropic escape of the ionizing continuum and a connection to jet-ejection activity, rather than establishing that interpretation uniquely. Nebular lines are narrow and consistent with the instrumental resolution, indicating kinematically quiescent gas and disfavoring shocks as the dominant ionization mechanism. The observations directly link an individual ULX to a highly ionized nebula and identify the accreting black hole as responsible for extreme ionization on approximately 100 pc scales.

PublicJames Webb Space Telescope observations directly connect the ultraluminous X-ray source Ho II X-1, an accreting black hole in the galaxy Holmberg II, to extreme ionization in its surrounding gas. Researchers detected emission from two highly ionized forms of neon for the first time in this source. Gas in the highest ionization states lies in compact patches displaced from the black hole toward previously observed radio-emitting knots, while less ionized gas fills a broader region. This pattern suggests that ionizing radiation escapes more readily in some directions and may be connected to episodes of jet ejection. The narrow emission lines indicate relatively calm gas, making shocks unlikely to be the main cause of the ionization. The black hole's influence extends across a nebula roughly 100 parsecs in scale.

Young explorerA black hole in another galaxy is taking in material, and the light from around it is knocking tiny pieces called electrons off atoms in a nearby gas cloud. The Webb telescope found new signs of atoms that have lost many electrons. These atoms are in small patches mostly off to one side, suggesting that more powerful light gets out in some directions than others. The gas looks fairly calm, so big crashes in the gas probably are not doing most of the work.

ACACIAS II: element abundances for 39 stars in the dwarf galaxy Sculptor

Anell Cornejo-Cárdenas, Sven Buder, Melissa K. Ness+1 more

AstronomerThe second stage of ACACIAS analyses MUSE spectra of 39 stars in the Sculptor dwarf spheroidal at R = 1800 and SNR approximately 25. Using The Cannon with APOGEE abundance labels and MUSE-like LAMOST spectra, the authors infer [Mg/Fe], [Mn/Fe], [C/Fe], [N/Fe], and [Al/Fe] on the APOGEE scale, reporting precisions of 0.09–0.37 dex. Configuration comparisons favour targeted spectral windows for [Mg/Fe], [Mn/Fe], and [C/Fe], while stellar parameters and [Al/Fe] benefit from full-spectrum modelling with telluric masking. Importantly, restricted-window models recover abundances from direct spectral features, whereas full-spectrum models can exploit correlations among labels when diagnostic features are weak or absent. The results demonstrate the potential of low-resolution, low-SNR spectroscopy for extragalactic abundance work; the broader goal of a homogeneous stellar-abundance dataset spanning dwarf galaxies of different masses remains a program objective.

PublicAstronomers studied the light from 39 individual stars in the Sculptor dwarf galaxy to estimate their chemical makeup. Their method combines relatively low-resolution, noisy spectra with a data-driven model informed by other stellar surveys. It estimates the amounts of magnesium, manganese, carbon, nitrogen, and aluminium relative to iron. Different ways of analysing the spectra work best for different elements: selected wavelength regions give better results for some, while using nearly the whole spectrum helps with others. A key caveat is that some estimates rely on learned relationships between stellar properties rather than clear signatures of the element itself. This study is a step toward comparing the chemical histories of dwarf galaxies and the Milky Way on a consistent scale.

Young explorerStarlight has clues about what stars are made of. Astronomers studied light from 39 stars in a small galaxy called Sculptor. A computer helped them estimate the stars’ ingredients, even though the light was hard to read. Some clues were clearer than others. They hope to use this method to learn how different galaxies got their ingredients.

ALMA observations towards M83 reveal N₂H+ tracing dense gas

Nanase Harada, Yuri Nishimura, Toshiki Saito+6 more

AstronomerALMA observations of N2H+(1–0), HCN(1–0), and 1-mm and 3-mm continuum, combined with archival CO(1–0), probe M83’s southwestern bar-end region at 48 pc resolution over 2.1 × 1.8 kpc. N2H+ and HCN intensities are approximately linearly correlated, supporting HCN luminosity as a reasonable dense-gas proxy alongside N2H+. At high column densities, however, N2H+ increases superlinearly with HCN, suggesting greater sensitivity to dense gas. Radiative-transfer modeling with parametric column-density probability distribution functions can explain the observed trends using log-normal distributions alone or with power-law tails; modeled N2H+ intensities are substantially more sensitive to the tails than HCN intensities. An analysis incorporating archival data also indicates that N2H+ is a less reliable dense-gas tracer in galactic centers, possibly because warmer temperatures promote its destruction.

PublicAstronomers used ALMA to compare two molecular signals, N2H+ and HCN, in a region of the nearby star-forming galaxy M83. Both signals generally brighten together, suggesting that the commonly used HCN signal remains a useful way to estimate how much dense gas is present. Where more gas is packed along the line of sight, N2H+ brightens disproportionately, suggesting that it is more sensitive to dense gas. Models of how the gas produces these signals can explain the patterns with different distributions of gas column density, and show that N2H+ responds more strongly to an extended high-density tail in those distributions. This advantage is not universal: analysis including archival observations indicates that N2H+ is less reliable in galactic centers, where warmer conditions may help destroy the molecule.

Young explorerStars grow in thick clouds of gas. Scientists looked at part of a galaxy called M83 and compared signals from two kinds of tiny particles in the gas. The signals usually got brighter together, but one grew brighter faster where more gas was piled up. That suggests it may be better at pointing out thick gas clouds. The scientists used computer models to help explain the pattern. But this signal does not work as well near galaxy centers, perhaps because warmer gas can break those particles apart.

An Energetic Consistency Test for Feedback-Driven Gas Loss in Milky Way Dwarf Satellites

Sena A. Matsui, Tsutomu T. Takeuchi, Suchetha Cooray+1 more

AstronomerAn order-of-magnitude energy-budget analysis of nine Milky Way dwarf spheroidal satellites uses published star formation histories, galaxy-level velocity dispersions, effective radii, and integrated V-band luminosities to compare cumulative effective core-collapse supernova energy with an adopted gas binding energy. The energy-equivalence time is the first threshold crossing, where one exists, and is an energetic diagnostic rather than a measured wind-launch time. With fiducial parameters and the K+B16 kinematic–size prescription, all nine systems cross the threshold, although star formation often persists long afterward. Proximity between the corresponding lookback time and the epoch when 90% of the total initial stellar mass had formed is descriptive, not independent evidence for feedback-driven quenching, because both derive from the same cumulative star formation history. Threshold crossing depends on assumed halo mass, radius, retained gas fraction, and supernova–gas coupling efficiency. The analysis separates cumulative energy availability from the mechanisms setting quenching times, without resolving the relative roles of feedback, reionization, and environment.

PublicDwarf spheroidal galaxies have little detectable cold gas, but why they lost it remains uncertain. This study uses published measurements and star formation histories for nine small galaxies orbiting the Milky Way to estimate when exploding stars could have supplied enough energy to overcome the gravity holding their gas. Under the main set of assumptions, all nine reach that estimated energy threshold, yet star formation often continues long afterward. Reaching the threshold does not show that gas actually escaped at that time. The answer also depends on assumptions about the galaxies and how efficiently explosion energy reaches their gas. Any apparent closeness between the threshold time and the time when most stars had formed is not independent evidence that explosions stopped star formation, because both times come from the same star formation history. The study therefore distinguishes having enough energy in principle from explaining when and why star formation ends.

Young explorerNine little galaxies near our Milky Way have very little cold gas left. Scientists used clues about their stars to estimate whether exploding stars could have given the gas enough of a push to escape. With their main set of guesses, the answer was yes for all nine. But the galaxies often kept making stars after that point. The calculation does not show that the gas really left then, and different guesses can change the answer. Having enough energy for a push is not the same as knowing what happened.

A machine-learning-driven dataset of 144,111 polycyclic aromatic hydrocarbon infrared spectra for interpreting aromatic infrared bands

Xinghong Mai, Zu-Jia Lu, Zhao Wang

• Instrumentation and Methods for Astrophysics
• Solar and Stellar Astrophysics

AstronomerThe authors present a computed infrared spectral library with more continuous coverage of small- to medium-sized PAHs, complementing existing references used to interpret interstellar aromatic infrared bands. Their machine-learning double-harmonic framework combines neural-network force fields with electronic dipole models and is reported to achieve quantum-chemical accuracy at reduced computational cost, validated against independent density functional theory calculations and benchmark spectral databases. The dataset contains 144,111 spectra for 48,037 closed-shell, even-carbon benzenoid PAH structures in neutral, cationic, and anionic states, with per-spectrum uncertainty estimates. Its coverage remains restricted to these molecular classes rather than the full PAH chemical space. The publicly available spectra, optimized geometries, and code are resources for modeling JWST and future infrared observations, not new astronomical detections.

PublicScientists use reference patterns of infrared light to help interpret signals from molecules in space, but existing collections cover only part of the possible molecular variety. This work adds a large collection of computer-calculated patterns for molecules called polycyclic aromatic hydrocarbons, or PAHs. A machine-learning method produced 144,111 spectra for 48,037 molecular structures in three electrical charge states. Tests against independent quantum calculations and reference databases support the method’s accuracy, and each spectrum includes an uncertainty estimate. The collection covers a restricted family of small- to medium-sized PAHs, not every possible kind. The data and software are freely available to help interpret observations from JWST and future infrared missions; the study does not report finding these molecules in space.

Young explorerMolecules can have special patterns in infrared light, a kind of light our eyes cannot see. Scientists used computers to make a big pattern book for many kinds of molecules that may be in space. They checked their computer method against other calculations and reference patterns, and included estimates of how uncertain the patterns are. The book does not include every kind of molecule, and making a pattern does not mean that molecule has been found in space. It can help scientists understand what space telescopes see.

Disk tilts in Milky Way-like galaxies and their link to mergers

Runsheng Cai, Ling Zhu, Jiang Chang+3 more

AstronomerUsing 93 Milky Way-mass galaxies in TNG50, the authors identify 117 disk-tilt events and distinguish smooth reorientation from rapid disruption and regrowth. Each event is associated with the most massive merger occurring nearby in time. The analysis focuses on smoothly evolving disks: their tilts typically proceed at less than 10 degrees per Gyr, last 2–9 Gyr, and are generally associated with minor mergers. Roughly 40% of these smooth events exceed 30 degrees. Such large tilts are most often triggered by satellites with masses comparable to or below the host’s total stellar mass, on tangential orbits whose angular momentum is retrograde or nearly perpendicular to the disk spin. In the simulations, satellites drive disk-spin alignment toward their orbital angular momentum; initially retrograde encounters can produce large reorientations and an intermediate, nearly orthogonal configuration between the stellar disk and satellite orbital plane. Slow reorientation allows disks to remain stable and grow, with strongly tilted systems retaining stellar disks as thin as those without significant reorientation. These are simulation findings, not direct observations.

PublicComputer simulations suggest that a galaxy’s disk can change its orientation substantially without becoming thicker or being destroyed. Researchers studied 93 simulated galaxies similar in mass to the Milky Way and identified 117 episodes of disk tilting. They focused on episodes in which the disk changed smoothly rather than being disrupted and rebuilt. These gradual tilts typically lasted 2–9 billion years and were generally linked to mergers with smaller galaxies. About 40% of the smooth episodes turned the disk by more than 30 degrees. Large turns were most often driven by incoming galaxies orbiting against, or nearly at right angles to, the disk’s rotation. Their orbital motion steered the disk toward a new orientation. Because the turning was slow, disks could remain stable and keep growing. In these simulations, even strongly reoriented disks could remain as thin as disks that had not turned substantially.

Young explorerScientists used computer-made galaxies to see how their flat disks of stars can turn. When a smaller galaxy joins a bigger one, it can slowly tip the bigger galaxy’s disk in a new direction. Some disks turned a lot without getting thicker or falling apart. The slow turning let them stay steady and keep growing. This happened in computer simulations, not in galaxies the scientists watched in the sky.

Are High-EW LAEs good analogs for the earliest galaxies? A study on the ionizing conditions and gas properties of LAEs at 2≲z≲7

Lena Pless, Themiya Nanayakkara, Karl Glazebrook+3 more

AstronomerThe study tests whether high Lyα equivalent width (EW) reliably selects chemically primitive galaxies using 88 MUSE-selected LAEs at 2 ≲ z ≲ 7 that were undetected in deep HST imaging and followed up with JWST/NIRSpec. Only 50 have secure NIRCam counterparts, despite typical 3σ depths of mAB ≈ 30.3, and only 16 yield both secure stellar masses and gas-phase metallicities. Masses come from photometric SED fitting, while metallicities are inferred by fitting optical emission lines with BPASS+cloudy photoionization models. These 16 sources occupy diagnostic-diagram regions consistent with low-metallicity star formation. Although R3 appears to decline with increasing EW, full emission-line fitting provides no compelling evidence for a strong monotonic EW–metallicity relation. Stronger Lyα emitters nevertheless tend to fall below the average mass–metallicity relation, suggesting less chemical evolution at fixed stellar mass. The authors interpret high-EW LAEs as useful but imperfect analogs of proposed reionization-driving galaxies and suggest combining EW with stellar mass to identify chemically primitive candidates.

PublicAstronomers tested whether galaxies with especially prominent Lyman-alpha emission are reliably poor in elements heavier than helium. Such galaxies are often used as stand-ins for the faint galaxies thought to have driven cosmic reionization, an early transformation of intergalactic gas. The team studied 88 very faint galaxies, but only 16 had sufficiently secure estimates of both stellar mass and gas composition for the final comparison. Their model-based analysis found no compelling evidence that more prominent Lyman-alpha emission consistently means lower heavy-element abundance. However, galaxies with stronger emission tended to have fewer heavy elements than typical galaxies of the same stellar mass. The findings suggest that these emitters are useful but imperfect stand-ins for reionization-era galaxies, and that considering stellar mass alongside the emission strength may help identify the least chemically evolved systems.

Young explorerScientists looked at very faint galaxies to see whether a special kind of light could help them find galaxies with fewer heavy ingredients. They started with 88 galaxies, but could make the full comparison for only 16. A stronger light signal did not always mean fewer heavy ingredients. Still, galaxies with stronger signals tended to have fewer of those ingredients than other galaxies with the same amount of stars. The scientists think checking both the light signal and how much star material a galaxy has may work better than checking the light alone.

A ¹³CO Detection in a Massive Molecular Gas Flow in Abell 1795's Central Galaxy

J. A. Gray, H. R. Russell, F. Combes+6 more

AstronomerNew ALMA 13CO(2–1) observations detect the northern molecular filament in the central galaxy of the cool-core cluster Abell 1795. The 5–7 kpc molecular filaments closely surround AGN-inflated radio bubbles, and their smooth velocity gradients are consistent with bubble-driven entrainment. The detected 13CO velocity structure agrees with that of 12CO(2–1). Using this lower-opacity tracer and a range of plausible excitation temperatures and covering fractions, the authors infer a northern filament molecular mass of (0.1–2) × 10^9 solar masses, with the low end an order of magnitude below previous estimates. The implied α_CO is 0.4–5 solar masses (K km s⁻¹ pc²)⁻¹, approximately 0.1–1 times the standard Milky Way value. These estimates make direct entrainment by the northern radio bubble energetically and buoyantly plausible; measured X-ray cooling rates also permit in-situ condensation of uplifted, low-entropy hot gas. Neither origin is established, and both require multiple bubble generations at the higher filament masses.

PublicNew ALMA observations help constrain how long strands of molecular gas formed around the central galaxy in the Abell 1795 galaxy cluster. These strands extend 5–7 kiloparsecs and closely surround large radio bubbles inflated by jets from the galaxy’s active nucleus. Their smoothly changing velocities are consistent with gas being carried upward by expanding bubbles. By detecting emission from carbon monoxide containing carbon-13 in the northern strand, the researchers estimate its molecular gas mass at 100 million to 2 billion times the Sun’s mass, depending on assumptions about the gas. The lower end is ten times below previous estimates. With these revised estimates, the northern bubble could plausibly lift and support the molecular gas. Another explanation also remains possible: the bubbles lifted hot gas that then cooled and formed molecular gas. The observations do not settle which process occurred, and at the higher mass estimates either explanation needs several generations of bubbles.

Young explorerAstronomers used ALMA to study a long strand of gas near a galaxy. Big bubbles made by jets from the galaxy’s center lie beside the gas. A special signal from the gas suggests the strand might contain less material than people thought, though the amount is still uncertain. That could mean a bubble was strong enough to lift it. Or a bubble might have lifted hot gas that later cooled to make the strand. The astronomers do not yet know which happened. If the strand is heavier, either idea would need more than one round of bubbles.

A clump population framework for star formation across galactic scales

J. W. Zhou, Sami Dib, Tie Liu+11 more

AstronomerThe study identifies molecular clouds with a dendrogram algorithm in 30 dwarf and disk galaxies and derives molecular gas masses and star formation rates from integrated CO and mid-infrared emission, respectively. It finds a consistent molecular gas mass–SFR relation with little sensitivity to galactic environment. Including Milky Way cloud substructures down to sub-parsec scales and 311 diverse nearby galaxies extends the relation across ten orders of magnitude in molecular gas mass and SFR. A theoretical model of star formation in dense clumps embedded within molecular clouds reproduces the observed relation. Weak environmental dependence at the clump scale is offered as a possible explanation for the relation’s near universality, rather than a demonstrated universal law.

PublicA study of molecular clouds in 30 dwarf and disk galaxies finds a similar relationship between the amount of molecular gas and the rate of star formation, with little variation between galactic environments. The researchers estimate these quantities using carbon monoxide and mid-infrared emission. Adding smaller structures within Milky Way clouds and a sample of 311 nearby galaxies shows that the relationship spans ten orders of magnitude in both gas mass and star formation rate. A theoretical model in which stars form in dense clumps inside molecular clouds reproduces the observed pattern. This suggests a possible link between star formation on small and large scales, but does not establish that one universal law governs every environment.

Young explorerStars grow inside clouds of gas. Researchers looked at clouds in many galaxies and found a similar pattern: clouds with more gas tend to make stars faster. They found this pattern in tiny parts of clouds in our Milky Way and in whole galaxies, too. A model where stars form in tightly packed lumps inside clouds matches the pattern. That might help explain why very different places make stars in similar ways, but it is not proof that every place follows exactly the same rule.

Thermal Sunyaev-Zel'dovich Effect in the circumgalactic medium - III: does richness matter?

Sanskriti Das, Yi-Kuan Chiang, Smita Mathur

• Cosmology and Nongalactic Astrophysics

AstronomerUsing ACT+Planck observations, the authors measure the thermal Sunyaev–Zel’dovich effect around 7 million DESI Legacy Survey galaxies/groups spanning M200c = 10^12–10^14 solar masses at z ≤ 1, examining thermal pressure as a function of both mass and richness. They detect the one-halo term down to 10^12.2 solar masses at 5.8σ. Several mass–richness bins fit a standard GNFW pressure profile, while others favor flatter and/or miscentered profiles, with richness-dependent mass trends. The authors interpret this diversity as evidence for regimes ranging from dominant thermal feedback to efficient or substantial cooling. In some mass bins, assuming baryon-sufficient halos, the data impose temperature floors of approximately 2–7 times T200c, suggesting significant heating. Dominant kinetic-mode feedback is not required in any bin, challenging a universal ejective-feedback-versus-gravity interpretation rather than excluding kinetic feedback. The thermal energy–mass slope is consistent with self-similarity in the intragroup medium but falls below it by 7.3σ in the circumgalactic medium. The authors infer that relatively low-mass, low-richness halos dominate the thermal energy budget at z ≤ 1 and argue that scaling-relation calibrations should incorporate intrinsic and environmental galaxy properties beyond mass.

PublicThe researchers studied hot gas around 7 million galaxies and galaxy groups by measuring its effect on the cosmic microwave background, using ACT and Planck observations. The gas pressure varies with both the mass of a galaxy’s surrounding halo and its richness, a measure of how many galaxies it contains. Some systems match a standard pressure pattern, while others favor flatter patterns or an offset pressure center. The authors interpret this variety as signs of differing balances between gas heating and cooling. For some mass ranges, the gas must be unusually hot if the halos contain their full expected supply of ordinary matter. The measurements do not require energy injection dominated by bulk motion, although they do not rule it out. Gas thermal energy also changes with halo mass differently around galaxies than in galaxy groups. The authors infer that relatively low-mass, low-richness systems dominate the universe’s thermal energy budget over the studied range, and argue that mass alone is insufficient to describe these systems.

Young explorerGalaxies have gas around them that we cannot easily see. Scientists studied millions of galaxies and groups by looking at how that gas changes light traveling through space. They found different patterns of gas pressure. They think these patterns show that some gas has been heated strongly, while other gas has cooled. How heavy a galaxy’s surroundings are does not tell the whole story; its neighbors matter too.

Mixed modified-gravity--modified-inertia MOND theories

Mordehai Milgrom

• Cosmology and Nongalactic Astrophysics
• General Relativity and Quantum Cosmology

AstronomerThis theoretical study explores families of nonrelativistic MOND actions that modify both the kinetic and gravitational sectors. Each family is parameterized by 0 ≤ η ≤ 1, the common scaling dimension of all action terms in the deep-MOND limit; η = 0 and η = 1 correspond to pure modified gravity and pure modified inertia, respectively. The action terms remain broadly specified, and the constructions lack a single unifying principle governing both modifications. In the combined-modification examples, neither modified sector alone yields MOND phenomenology. Their joint effect nevertheless reproduces primary MOND predictions, including asymptotically flat rotation curves, the mass–asymptotic-speed relation, and the deep-MOND virial mass–velocity-dispersion relation. Distinct interpolating functions arise in the kinetic equations of motion and gravitational field equations, apply in different circumstances, and individually lack the standard deep-MOND limit. These constructions illustrate theoretical diversity rather than provide observational tests or a fundamental theory; differences in secondary predictions are expected.

PublicMOND is an approach to changing the usual laws of motion and gravity. This paper explores theoretical models that change both gravity and inertia—the resistance to a change in motion—rather than changing just one. The author shows how the two changes together can reproduce key MOND predictions: rotation speeds that level off far from a galaxy’s center, a relationship between mass and those outer speeds, and a relationship between mass and the spread of internal velocities. In these combined models, neither change works on its own. The models also use different mathematical transition functions for motion and gravity. They are not new observations or a completed fundamental theory: their mathematical ingredients are left fairly general, and no single underlying idea explains both changes. Their value is to show that different theoretical structures can produce MOND’s main predictions while potentially differing in other predictions.

Young explorerScientists use rules to describe how stars move. This paper tries changing two rules together: how gravity pulls and how things respond when their motion changes. In these models, the two changes work as a team to make some predictions about stars moving in galaxies; either change alone does not work. These are ideas explored with math, not new things seen in the sky, and they are not yet one complete explanation.

From Scaling Relations to Physical Laws: Constraining the Physics of Star Formation Across Local Galaxies

Jakob den Brok, Cecilia Bacchini, Leindert A. Boogaard+21 more

AstronomerObserved gas–star formation scaling relations do not uniquely identify the regulating physics: gravity, turbulence, and stellar feedback can reproduce similar galaxy-scale trends. The abstract argues that distinguishing their roles requires measurements of molecular gas temperature, density, excitation, and chemistry alongside its mass and distribution. It proposes ALMA2040 as a flagship interferometer with greater line sensitivity and bandwidth, intended to deliver multi-transition, multi-isotopologue diagnostics at giant molecular cloud resolution across nearby galaxy samples. The envisioned survey capability would yield millions of independent measurements of gas conditions. These are prospective capabilities, not reported results; the stated goal is to help establish a predictive theory of gas conversion into stars in concert with optical and radio facilities of the 2040s.

PublicAstronomers have measured links between the gas in galaxies and the stars they form, but those links do not yet explain what controls star formation. Gravity, turbulent gas motions, and the effects of existing stars can produce similar overall patterns. This abstract makes the case for ALMA2040, a proposed observatory designed to measure many kinds of molecular emission and resolve individual giant gas clouds across nearby galaxies. Those observations would reveal more about the gas’s temperature, density, and chemistry, helping researchers distinguish competing explanations. The abstract describes an ambition for future observations, not new measurements or a solved theory of star formation.

Young explorerStars form from cold, thick clouds of gas, but scientists do not yet know exactly what controls how this happens. They want to build a new telescope called ALMA2040 to study many clouds in nearby galaxies. It would look for different signals from the gas to learn how warm it is, how tightly packed it is, and what it contains. Those clues could help explain how clouds make stars. This is a plan for future discoveries, not something the telescope has already done.

Disentangling Multi-epoch Single-lined Binary Star Spectra to Reveal Interstellar Medium Features via MCMC

Shao-Song Huang, Jian-Jun Chen, Xiao-Xiao Ma+1 more

AstronomerMCMC-RVSD is a template-independent Bayesian MCMC method for separating stellar absorption from diffuse interstellar bands (DIBs) in binary-star spectra. It jointly fits the components using orbital RV shifts of stellar lines while DIBs remain stationary in the rest frame. Validation on mock spectra simulating LAMOST medium-resolution observations recovered the parameters of DIB λ6614, with reliable performance reported over resolving powers R=3000–7500. The authors also applied the method to 434 real LAMOST binary sources and introduced the DIB-chain autocorrelation time as a fit-quality diagnostic. Their analysis identifies an RV span greater than 20 km/s as the primary requirement for successful separation; denser orbital sampling further improves performance. Robustness is reported for SNR greater than 50 and RV errors below 5 km/s. Smaller parameter uncertainties than template matching are reported under ideal conditions, not as an unconditional advantage. The authors state that model and prior adjustments can accommodate multiple stellar contaminants, non-Gaussian DIB profiles, and other DIBs. The method targets precise interstellar-feature measurements rather than identification of the still-unknown DIB carriers.

PublicInterstellar material leaves absorption features in starlight, but the substances responsible for these diffuse interstellar bands remain unidentified. In cool stars, overlapping stellar features make the bands difficult to measure. This study presents a method that uses repeated spectra of binary stars: orbital motion shifts the stars’ features, while the interstellar features stay fixed. The algorithm fits both together without relying on a reference stellar spectrum. Tests on simulated observations recovered the properties of one interstellar band, and the researchers also applied the method to 434 binary sources observed by LAMOST. Their analysis finds that a sufficiently large change in stellar velocity is the main factor enabling separation, with more observations across the orbit providing further improvement. The method tolerates noise and velocity errors within the reported limits. Under ideal conditions, it gives smaller measurement uncertainties than traditional reference-spectrum matching; it does not identify what causes the bands.

Young explorerLight from stars has little marks in it. Some come from the stars, and others come from stuff between the stars whose identity is still a mystery. When two stars orbit each other, their marks move while the between-star marks stay still. Scientists made a computer method to tell those marks apart. They tested it with pretend observations and used it on real star pairs. It works best when the star marks move far enough.

The Radius-Luminosity Relationship for Active Galactic Nuclei with Hierarchical Bayesian Reverberation Mapping

Hugh McDougall, Tamara M. Davis, Benjamin J. S. Pope+6 more

• Cosmology and Nongalactic Astrophysics
• Instrumentation and Methods for Astrophysics

AstronomerThe authors present a computationally tractable, end-to-end Bayesian framework that jointly fits AGN reverberation lags and population models, including the radius–luminosity relation. It addresses poor light curves, seasonal aliasing, and inconsistent statistical treatments by marginalising over data uncertainty and quality rather than relying on traditional stacking and quality cuts. Applied to OzDES, the method reportedly provides more than twice the constraining power on population properties and an order-of-magnitude increase in recovered lags and black-hole masses. The authors compare 24 traditional high-quality lag recoveries with a new effective sample size of approximately 297; the latter is not presented as 297 individual high-quality detections. They report numerical stability as survey size increases and robustness against chance false positives.

PublicChanges in the brightness of active galactic nuclei take time to travel through the system. Measuring these delays helps astronomers estimate its size and the central black hole’s mass, but noisy measurements and seasonal observing gaps can make delays difficult to identify. This study introduces a statistical method that analyses many targets together while accounting for uncertainty and data quality. Applied to the OzDES sample, it reportedly more than doubles the information available about population-wide relationships and increases recovered delays and mass estimates roughly tenfold. The authors describe an effective sample size of about 297, compared with 24 high-quality delay measurements from traditional methods—not 297 equally secure individual measurements.

Young explorerAstronomers watch brightness changes around black holes. How long those changes take to travel gives clues about how big the area is and how heavy the black hole is. But the measurements can be messy, and there are gaps in the watching. Researchers made a new way to study many sets of measurements together. When they tried it, they could learn more while still allowing for measurements that might be wrong.

A Comprehensive AGN Inventory for the Dwarf-Dominated RESOLVE and ECO Surveys: Mass-Dependent AGN Types and Occupation Fractions

Mugdha S. Polimera, Sheila J. Kannappan, Chris T. Richardson+7 more

AstronomerThe authors catalog AGN in the volume- and mass-limited RESOLVE and ECO surveys using standard and alternate BPT demarcations, combined BPT/VO classifications that identify mixed star-forming/AGN systems (SF-AGN), and WISE mid-IR colors. AGN occupation fractions are 2–5% in dwarfs, 16–27% in transitional galaxies, and 20–48% in giants, with a steep, approximately fivefold rise across baryonic mass ∼10^9.7 solar masses; stellar-mass divisions give similar results. These fractions use all galaxies in each mass bin, including those not searchable for AGN, and the ranges reflect large systematic differences between crossmatched SDSS emission-line catalogs. Adding incomplete archival X-ray and broad-line detections raises the dwarf fraction to 3–6%. Optimized WISE photometry selects AGN in less than 1% of galaxies at every mass, while standard WISE catalog photometry produces high false-positive and false-negative rates. AGN classes form a demographic continuum correlated with gas content, star formation, and group environment, from SF-AGN at high star formation through Bonus AGN and Composites to Conventional AGN at low star formation. Typical metal-poor, star-forming dwarfs most often host SF-AGN, while typical transitional galaxies most often host Bonus AGN and Composites. The release includes homogenized SDSS line measurements, reprocessed WISE data, and UV+mid-IR star formation rates.

PublicThis study catalogs active galactic nuclei in the RESOLVE and ECO galaxy surveys using several optical and infrared selection methods. The identified fractions rise from 2–5% in dwarf galaxies to 16–27% in intermediate-mass galaxies and 20–48% in the most massive group. These are not precise estimates of every galaxy’s activity: the totals include galaxies that could not be searched for active nuclei, and the ranges reflect substantial differences between optical measurement catalogs. Adding available, but incomplete, X-ray and broad-line detections raises the dwarf fraction to 3–6%. With improved infrared measurements, the infrared method identifies active nuclei in fewer than 1% of galaxies at every mass; the standard infrared catalog both incorrectly flags some galaxies and misses others. The kinds of active nuclei identified also change with galaxy properties. Typical star-forming dwarf galaxies most often show mixed signatures of star formation and nuclear activity, while other classes become more prominent toward lower star formation. The authors also release updated measurements for further research.

Young explorerThe researchers looked at lots of galaxies for signs of activity in their centers. They found these signs more often in heavier galaxies than in lighter ones. In many small galaxies, the signs of busy centers are mixed with signs of new stars being made. But the counting is tricky: some galaxies could not be checked, and different measurements gave different answers. The team also found that one set of infrared measurements could both miss real signs and give false alarms, so they made improved measurements.

The Mission Market: Flying NASA's Vetted, Unflown Science

Blakesley Burkhart

AstronomerThe abstract presents Mission Market, a proposed advance market commitment to support lower-cost missions in astrophysics, heliophysics, and planetary science that NASA judges selectable but cannot afford to fly. The proposed funding would come primarily from capital flowing into AI companies interested in frontier data for scientific foundation models, supplemented by philanthropy and patron-scientists, without competing for federal appropriations. The abstract describes a financing concept, not demonstrated funding or completed missions.

PublicNASA judges more science missions worthy of selection each year than it can afford to launch. Mission Market proposes another way to pay for some lower-cost missions: an advance commitment to purchase what they provide. The plan would draw mainly on money flowing into AI companies that value new scientific data for their models, with additional support from donors and individual science patrons. It aims to avoid competing for federal funding, but the abstract does not report that the plan has funded or launched any missions.

Young explorerNASA has more good ideas for space trips than it has money to send them. Mission Market is a plan to help pay for some less expensive trips. Companies making AI computer programs might help because they want new information from space, and people who support science might help too. This is a plan, not a story about trips that have already happened.

Stellar Mass Census of S⁴G Local Bars

Yasmin Cavalcante-Coelho, Karín Menéndez-Delmestre, Taehyun Kim+7 more

AstronomerThe study uses GALFITM two-dimensional, multi-band decompositions of 344 barred S4G galaxies at 3.6 and 4.5 micrometers to estimate stellar masses for disks, bulges, bars, and nuclear point sources. Final models contain two to four components, with disk-plus-bar models typically associated with low-mass galaxies. More massive galaxies with prominent bulges host more massive bars and higher median bar-to-total stellar mass ratios. These bulges generally have Sérsic indices below 2, consistent with, but not establishing, a photometric signature of nuclear stellar disks. At fixed galaxy mass, relative bar lengths show a bimodal distribution, with bulge-hosting galaxies having relatively longer bars than bulgeless systems. The authors interpret these correlations as possible evidence for distinct evolutionary pathways, potentially involving different disk formation epochs and bar growth times; the roles of secular evolution and environment remain interpretations rather than demonstrated causes.

PublicResearchers analyzed infrared images of 344 galaxies containing bars, elongated structures made of stars. By modeling each galaxy as a combination of parts, they estimated how much stellar mass lies in its bar, disk, central bulge, and any compact central source. More massive galaxies with prominent bulges tended to have more massive bars and a larger median fraction of their stellar mass in the bar. Among galaxies of the same mass, relative bar lengths formed two groups: galaxies with bulges tended to have relatively longer bars than those without. The central bulges also had light profiles consistent with small central stellar disks, though this does not establish their nature. The authors suggest that different formation histories could have given some bars more time to grow. These observations reveal patterns, but do not establish what caused them.

Young explorerSome galaxies have a long shape made of stars across their middle, called a bar. Scientists studied pictures of 344 galaxies with these bars. Bigger galaxies with a bulge in the middle tended to have bars with more star mass. When galaxies had the same mass, those with bulges tended to have bars that stretched farther compared with the galaxy's size. Maybe some bars had more time to grow, but the scientists have not shown that this is why they are different.

Dark Matter in the Galaxy: Insights from the Dynamics of Stellar Streams

Mohammad Ayaz, Priya Hasan

AstronomerThis review examines how the morphology and kinematics of stellar streams from tidally disrupted globular clusters and dwarf galaxies can constrain the Milky Way halo's structure, shape, and substructure. It discusses gaps, spurs, and other perturbations, focusing on Sagittarius, GD-1, Palomar 5, Orphan-Chenab, and Cetus Polar, and surveys analytical, statistical, and Bayesian inference methods. Key limitations include parameter degeneracies, incomplete observations, uncertain progenitors, and time-dependent perturbations, particularly from the Large Magellanic Cloud. Upcoming astrometric and photometric surveys and improved dynamical modelling may tighten constraints on the dark matter distribution and help distinguish cold, warm, and self-interacting dark matter scenarios; the abstract reports no new measurements or discrimination among these scenarios.

PublicDark matter makes up most of the Universe's matter, but its nature and distribution remain uncertain. This review explores how trails of stars, pulled from star clusters and small galaxies by gravitational forces, can help map the Milky Way's surrounding dark matter halo. The shapes and motions of these streams—including gaps and features jutting away from them—provide clues to the gravity acting on them. The review covers five prominent streams and methods for interpreting them, while emphasizing that missing observations, uncertain origins, and changing gravitational influences such as the Large Magellanic Cloud complicate the picture. Future surveys and better models may sharpen this map and help test different ideas about dark matter; those possibilities are not presented as established results.

Young explorerSometimes gravity pulls stars out of a group and stretches them into a long trail. Scientists study how these star trails bend and move to learn about dark matter, matter we cannot see that pulls on stars. This paper brings together ways scientists use those clues. It is tricky because they cannot see every star, and other things can tug on the trails too. Better pictures and measurements may help them learn more, but they do not yet know what dark matter is.

Multi-phase investigation of outflows in the circumgalactic and interstellar media of luminous quasars at z 5

Matilde Brazzini, Valentina D'Odorico, Manuela Bischetti+4 more

AstronomerThe study combines UV/optical spectroscopy from VLT/X-Shooter with ALMA data available for six objects to characterise outflows in 39 quasars at z = 5.0–5.7. Emission and absorption diagnostics reveal powerful ionised outflows, with velocities exceeding 48,000 km/s in some cases. MgII-based black hole masses span log(M_BH/M_sun) = 8.5–10, and bolometric luminosities span log(L_bol/[erg/s]) = 46.9–48. The quasars lie above the local black hole–host galaxy mass relation, resembling z ~ 6 quasars. The authors interpret these findings as evidence suggestive of efficient black hole feedback persisting from z ~ 6 to z ~ 5, with black hole growth outpacing host growth, rather than a direct measurement of that evolutionary history. Absorption outflow detections are more frequent at larger CIV–MgII velocity shifts, suggesting a connection between emission- and absorption-traced outflows even if their driving mechanisms differ.

PublicAstronomers studied 39 distant quasars using light emitted and absorbed by gas, with additional ALMA observations available for six objects. They detected powerful flows of ionised gas moving away from the quasars, sometimes faster than 48,000 kilometres per second. The quasars also have unusually massive black holes relative to their host galaxies when compared with the relationship seen nearby. The researchers interpret this as suggesting that black holes were growing faster than their galaxies and that their outflows could have been influencing galaxy growth across the period studied. This evolutionary picture is an interpretation, not a directly observed growth history. Two different ways of detecting the outflows appear connected, although the processes driving them may differ.

Young explorerScientists studied 39 very bright objects called quasars in faraway galaxies. They found gas rushing away from them very, very fast. Their black holes are also unusually big compared with their galaxies. The scientists think the black holes may have been growing faster than the galaxies, and that the rushing gas may help change how galaxies grow. They are still figuring out how the different gas flows fit together.

Barycenter kinematics in Local Group analogues

I. A. López-Paredes, J. E. Forero-Romero

AstronomerThe study tests an additional constraint for selecting Local Group analogues in cosmological simulations: matching the Local Group barycenter velocity, accurately measured from cosmic microwave background data. Relative to traditional selection methods, this constraint selects simulated pairs with M31-like radial approach speeds toward their Milky Way counterparts that are 2%–7% lower, depending on cosmology, with no robust change in tangential velocity. The radial difference is statistically significant in 86 of 93 tested cosmological models, but amounts to only a few km/s against analogue velocity dispersions of tens of km/s. The authors therefore regard the constraint as an optional refinement with a measurable but modest kinematic effect, not a necessary selection criterion.

PublicResearchers tested a way to find galaxy pairs in computer simulations that resemble our Local Group. Alongside traditional selection methods, they required the pairs to match the motion of the Local Group’s center of mass, which is accurately measured using cosmic microwave background data. The selected simulated pairs approached one another 2%–7% more slowly, depending on the cosmological model, while their sideways motion showed no robust change. The approach-speed difference was statistically significant in 86 of 93 models, but small compared with the usual variation among simulated pairs. The study concludes that this extra requirement can refine the selection, but is not essential; it does not establish a change in the measured motion of the real galaxies.

Young explorerScientists use computers to make pretend pairs of galaxies like our Milky Way and its neighbor Andromeda. They tried an extra rule: choose pairs whose shared middle moves like the middle of our real galaxy group. With this rule, the pretend galaxies moved toward each other a little more slowly on average. There was no clear change in how they moved sideways. The difference was small compared with how much the pretend pairs already differed, so the scientists say the extra rule can help but is not needed.

Dark matter dynamical friction on binary stars in the faintest dwarf galaxies: I. Analytical approach

Nicolas Esser

AstronomerThis theoretical study derives formulas and secular evolution timescales for wide and close binaries experiencing dynamical friction in a uniform dark matter background, including the centre-of-mass motion. For conditions typical of the faintest ultra-faint dwarf galaxies, the calculations predict significant eccentricity oscillations in some binaries as their semi-major axes gradually decrease over a Hubble time. At the population level, friction depletes wide binaries and raises the fraction of highly eccentric systems. The effect is not strongest at the highest dark matter densities because the associated higher velocity dispersion weakens friction. Binary stars are proposed as potential probes of these galaxies’ dark matter content, contingent on more detailed theory and improving observations.

PublicThe researchers calculated how pairs of stars could change as they move through an evenly distributed background of dark matter and experience a drag-like effect called dynamical friction. Under conditions typical of the faintest ultra-faint dwarf galaxies, their theory predicts that some pairs’ orbits repeatedly become more and less elongated while gradually shrinking over a time comparable to the age of the universe. Across many pairs, the calculations predict fewer widely separated binaries and a larger share with very elongated orbits. More dark matter does not necessarily mean a stronger effect: the greater spread of velocities associated with higher dark matter densities weakens the friction. These are theoretical predictions, not reported observations. With further theoretical work and better observations, star pairs might help reveal how much dark matter these faint galaxies contain.

Young explorerTwo stars can circle each other while traveling together through dark matter. Scientists used math to work out how a gentle slowing effect might change their dance. In their calculations, some stars’ paths become more stretched out and then rounder again, while the paths slowly get smaller over a very, very long time. Having more dark matter does not always make this effect stronger. The scientists have not reported seeing these changes; they hope that studying star pairs could one day help us learn about dark matter in very faint galaxies.

Dissecting the 3D chemo-dynamical structures of NGC 1381: A galaxy hosting an ancient slow bar with an accretion-related bulge and thick disc

Yunpeng Jin, Ling Zhu, Shude Mao+4 more

AstronomerThree-dimensional chemo-dynamical orbit-superposition models of the barred S0 galaxy NGC 1381 in Fornax separate six components: a warm nuclear disc (~5%), a rigidly rotating box/peanut- or X-shaped bar (~30%), a hot spheroidal bulge (~17%), a cold thin disc (~28%), a vertically extended thick disc (~16%), and a hot diffuse stellar halo (~5%). The nuclear disc, bar, and thin disc are metal-rich ([Z/H] ≳ 0), alpha-poor ([Mg/Fe] ≲ 0.2), and approximately 13 Gyr old, interpreted as early in situ populations. The bulge, thick disc, and halo are metal-poor, alpha-rich, and younger than or comparable in age to those components, suggesting accretion through minor mergers. Flat metallicity and [Mg/Fe] gradients support a similar, likely predominantly ex situ population in the thick disc and halo. The bulge’s negative metallicity gradient permits either predominantly ex situ stars or mixed origins; current data cannot quantify its ex situ fraction. The modelling yields a slow bar with R = 2.40 (+0.54/−0.27), pattern speed 34 (+4/−7) km s⁻¹ kpc⁻¹, length 2.24 (+0.43/−0.22) kpc, and corotation radius 5.38 (+1.59/−0.28) kpc. The authors interpret the slow bar as consistent with ancient formation.

PublicResearchers built a three-dimensional model of the stars’ motions and chemical properties in NGC 1381, a barred galaxy in the Fornax cluster. The model separates the galaxy into six structures, including a central disc, a bar, a bulge, thin and thick discs, and a diffuse outer halo. The central disc, bar, and thin disc contain stars estimated to be about 13 billion years old, with chemical properties interpreted as evidence that they formed within the galaxy early in its history. The other components have different chemical signatures, suggesting that many of their stars arrived through mergers with smaller galaxies. Similar chemical trends link the thick disc and halo, but the bulge’s origins remain less certain: the available data cannot establish what fraction of its stars came from elsewhere. The model also indicates a slowly rotating bar, which the authors regard as consistent with an ancient origin rather than proof of when it formed.

Young explorerScientists made a model of a galaxy to learn how its stars move and where they might have come from. The model sorts the stars into six groups, including a bar across the middle and a fluffy outer group. Some stars seem to have been born inside the galaxy long ago. Others may have come from smaller galaxies that joined it. The scientists still cannot tell where all the stars in its central bulge were born.

A Deep Look at the Ultra-Faint Milky Way Satellite Virgo III with Rubin Observatory Data Preview 2

Aashay Pai, Alex Drlica-Wagner, Peter S. Ferguson+9 more

AstronomerDeep Rubin DP2 imaging of Virgo III in the M49 First Look field provides 924 u,g,r,i visits totaling approximately 10.5 hours, with 5-sigma limits approaching the expected 10-year LSST depth. Maximum-likelihood analysis with ugali identifies 114 ± 11 candidate member stars, compared with 25 previously, substantially tightening morphological constraints. The fitted morphology and stellar population parameters broadly agree with earlier measurements and remain consistent with an ultra-faint dwarf galaxy, with M_V = -2.72 (+0.49/-0.70). The photometry also separates metal-poor and metal-rich stars in color-color space. Period estimates for three known RR Lyrae members, together with theoretical PLZ and PWZ relations, yield independent distance estimates broadly consistent with previous measurements. These findings demonstrate characterization capabilities and motivate future satellite searches; they do not report newly discovered satellites.

PublicDeep images from the Vera C. Rubin Observatory give a clearer view of Virgo III, a very faint companion of the Milky Way. Researchers identified 114 candidate member stars, more than four times the number in the discovery study, allowing a more precise estimate of its shape and size. Its measured properties broadly match earlier work and support its classification as an ultra-faint dwarf galaxy. The images can also distinguish stars with relatively low and high abundances of elements heavier than helium using their colors. For three known pulsating stars, researchers estimated pulsation periods and used theoretical relationships to infer distances that broadly agree with earlier estimates. The work shows how Rubin data can help study faint galaxies and supports future searches for more Milky Way companions.

Young explorerVirgo III is a very faint group of stars near our Milky Way. Scientists used deep telescope pictures to spot many more stars that might belong to it. That helped them work out its shape and size more clearly. What they found still fits the idea that Virgo III is a tiny, faint galaxy. They also watched three stars that get brighter and dimmer, and used a theory about those stars to estimate how far away they are. Their answers mostly agreed with earlier ones. Pictures like these could help scientists look for more faint galaxies.

ATLAS. III. Dust Around Little Red Dots: Hydrogen Line Ratios beyond Dust-free Non-Case B Models

Tomokazu Kiyota, Masami Ouchi, Hiroto Yanagisawa+7 more

AstronomerThe study measures broad hydrogen-line ratios in five high-redshift (z>2) little red dots (LRDs) with JWST/NIRSpec spectra and fifteen literature sources at z=0.1–0.9, all with broad Hβ detected above 5σ. Accounting for absorption and neighboring emission, the measured broad Hα/Hβ ratios span 6–30, well above Case B. Plane-parallel Cloudy models, including emission from both slab faces, jointly test Balmer and Paschen ratios for three sources. High density, log(nH/cm−3)≈10–11, reproduces one low-redshift source; the other two require E(B−V)≳0.2 in addition to non-Case B effects. Their narrow-line ratios do not indicate comparably strong extinction, supporting an association of the obscuring dust with the broad-line region. Ten of the twenty sources have Hα/Hβ>13, beyond these non-Case B models, suggesting dust obscuration in at least roughly half the population. A lower-column-density counterpart of an AGN dusty torus is proposed to reconcile this obscuration with weak hot-dust emission.

PublicAstronomers studied hydrogen light from twenty objects called little red dots. In their broad emission lines, one hydrogen line was 6–30 times stronger than another, far above a standard theoretical expectation. Computer models explored whether dense gas alone could explain the ratios. For three objects with additional hydrogen lines measured, dense gas could explain one, but the other two also needed substantial dust dimming. Comparing broad and narrow lines suggests that this dust is associated with the region producing the broad lines, rather than affecting both regions equally. Half the sample had ratios too large for the tested dust-free explanations, suggesting that dust obscuration may be common among little red dots. The researchers propose that this dust could be a thinner counterpart of the dusty structures around active galactic nuclei.

Young explorerScientists looked at light from twenty things in space called little red dots. Some kinds of hydrogen light were much stronger than others. They used computer models to ask why. Tightly packed gas could explain some clues, but others seemed to need dust that blocks light too. Dust may hide parts of many little red dots, though the scientists are still working out what it is like.

The impact of nonlinear Landau damping on cosmic ray streaming and the role of external turbulence

Rouven Lemmerz, Mohamad Shalaby, Ellen Zweibel+2 more

• Astrophysics of Galaxies
• Plasma Physics

AstronomerThis study tests whether nonlinear Landau damping (NLLD) intrinsically saturates the cosmic-ray streaming instability using fluid-PIC simulations with and without Landau closures for thermal ions and electrons. For self-generated waves driven by monoenergetic cosmic rays, the runs are indistinguishable: NLLD is inefficient, and cosmic rays isotropize in the wave frame. When high-amplitude Alfvén waves representing external turbulence are seeded, NLLD limits wave growth and equalizes forward- and backward-propagating waves. In this regime, the saturated cosmic-ray drift is sub-Alfvénic and can be predicted accurately from the wave spectra alone. Undersampling the cosmic-ray distribution produces a numerical instability that generates spurious backward waves and an inverse cascade, corrupting the largest resonant scales. Although power-law cosmic-ray distributions may allow stronger NLLD, the simulations suggest that its effectiveness depends on externally supplied modes rather than being an intrinsic saturation mechanism of the streaming instability.

PublicCosmic rays can generate magnetic waves as they stream through ionized interstellar gas. Those waves scatter the particles, helping determine how much energy and momentum they transfer to the gas. This study uses computer simulations to test a commonly assumed way of damping these waves, called nonlinear Landau damping. When cosmic rays all have the same energy and generate the waves themselves, this damping has little effect. When strong waves representing turbulence from outside the cosmic-ray stream are added, however, it limits wave growth and balances waves traveling in opposite directions. The researchers also identify a numerical error that creates artificial waves when too few simulated particles represent the cosmic rays. These are simulation findings, not direct observations. They suggest that this damping depends on waves from other sources, although a broader cosmic-ray energy distribution might make it stronger.

Young explorerTiny particles called cosmic rays travel through space and can make waves that change how the particles move. Scientists used a computer to ask whether one kind of wave-slowing process could keep those waves from growing. When the particles all had the same energy and made their own waves, the process barely helped. When the scientists added strong waves from elsewhere, it did help. The computer also made some pretend waves by mistake when it used too few particles. These computer tests give clues, but particles with different energies might behave differently.

Compact Dark Matter with Globular Cluster Pulsars

Soobeom Chung, Jeff A. Dror

• Cosmology and Nongalactic Astrophysics
• High Energy Physics - Phenomenology

AstronomerThe authors propose targeting inner-Galaxy globular clusters for compact-dark-matter searches using Shapiro delays in pulsar arrival times. Detectable transit counts depend on the dark-matter density integrated along each Earth–pulsar sightline. These clusters offer high crossing rates and many pulsars within a single telescope beam; a joint timing analysis could also remove much of the recently detected nanohertz gravitational-wave background because its contribution is nearly common to the cluster pulsars. Their ranking identifies Terzan 5, with 49 pulsars, as the most promising known cluster. They forecast that 40 years of weekly four-hour observations at the sensitivity envisioned for SKA phase two could probe compact objects of 0.02 solar masses constituting 6% of dark matter. This is a projected reach, not a detection. Their estimated stellar and stellar-remnant foreground is subdominant near the benchmark's most sensitive low-mass region but important over parts of the stellar-mass range.

PublicPulsars send out remarkably regular pulses. A compact dark-matter object passing near a pulse's path to Earth could delay its arrival through gravity, providing a possible way to find such objects. The researchers propose monitoring pulsars in globular clusters in the inner Milky Way, where they expect more dark-matter crossings and can observe many pulsars with one telescope beam. They identify Terzan 5, which contains 49 known pulsars, as the best target among the clusters they ranked. They estimate that a 40-year program of weekly four-hour observations, using the sensitivity envisioned for the second phase of the Square Kilometre Array, could test whether objects each weighing 2% of the Sun's mass account for 6% of dark matter. No compact dark matter is reported detected. Combining the pulsars' signals could reduce interference from the gravitational-wave background, while ordinary stars and stellar remnants could complicate the search in some mass ranges.

Young explorerPulsars are stars that send us very steady flashes, like ticking clocks. If a little clump of invisible dark matter passed near a flash's path, its gravity could make the flash arrive late. Scientists suggest watching a group of 49 pulsars in a star cluster called Terzan 5. Watching them together could help sort out some other things that change the ticks. The scientists think a very sensitive telescope watching for 40 years could look for certain dark-matter clumps this way. They have not found those clumps in this study, and ordinary stars could sometimes make the search harder.

mm-jets in the multi-messenger era

Karri I. I. Koljonen, Thomas D. Russell, Britton Jeter+16 more

• Instrumentation and Methods for Astrophysics

AstronomerThis science-case abstract describes the prospective jet and outflow capabilities of ALMA2040, rather than reporting new observations or simulations. It spans YSOs, XRBs, AGN, GRBs, and TDEs, targeting jet launching, acceleration, collimation, dissipation, particle acceleration, and environmental coupling. Millimeter/submillimeter diagnostics include evolving synchrotron turnovers for calorimetry and Lorentz-factor constraints, full-Stokes polarization and Faraday diagnostics near jet bases, and global VLBI imaging. The envisioned interferometer combines an order-of-magnitude sensitivity gain, rapid response, simultaneous multiband coverage, full-Stokes polarimetry, and global VLBI integration. These capabilities are projected to enable statistically controlled, trigger-driven samples in the 2040s and beyond; the abstract presents anticipated science opportunities, not demonstrated performance or resolved jet-physics questions.

PublicJets and outflows from forming stars, systems containing black holes, and powerful cosmic explosions raise questions about how matter is launched, focused, and energized, and how it affects its surroundings. This abstract outlines what a proposed next-generation observatory, ALMA2040, could contribute—not new discoveries. Observations at millimeter and submillimeter wavelengths can help estimate jet energies and speeds, investigate magnetic conditions near their origins, and produce detailed images by linking telescopes across the globe. The envisioned combination of roughly tenfold greater sensitivity, fast responses to transient events, and simultaneous observations in several wavelength bands is intended to support systematic studies of many kinds of jets in the 2040s and beyond.

Young explorerSome stars and places around black holes send streams of stuff into space. Scientists want to know how these streams start, speed up, and affect things nearby. They describe a future telescope called ALMA2040 that could catch faint light, look quickly when something changes, and work with telescopes around the world. It could help them learn more about these streams, but this is a plan for future studies, not a report of new discoveries.

Study of pulse jitter characteristics of PSR J1744-1134: Towards high precision pulsar timing with InPTA

Jibin Jose, Manoneeta Chakraborty, Neelam Dhanda Batra+15 more

• Instrumentation and Methods for Astrophysics

AstronomerThis work presents the first detailed characterization of jitter noise in PSR J1744-1134 at 300–500 MHz, using Indian Pulsar Timing Array observations with the upgraded Giant Metrewave Radio Telescope. Pulse-level analysis and Bayesian inference reveal clear signatures of jitter, the broadband arrival-time noise arising from pulse-shape variations beyond radiometer noise. Comparison with earlier higher-frequency measurements shows differences in jitter amplitude that suggest, but do not establish, frequency evolution. Although jitter limits timing precision relevant to nanohertz gravitational-wave searches, it is not the limiting factor for the dispersion-measure precision achieved for this pulsar on the observation timescale studied.

PublicPulsars send out repeated radio pulses that astronomers use as precise clocks to search for extremely low-frequency gravitational waves. Changes in the shapes of individual pulses create timing noise called jitter. Using the upgraded Giant Metrewave Radio Telescope, researchers found clear evidence of this noise in the pulsar PSR J1744-1134 at radio frequencies of 300–500 MHz. Differences from earlier measurements at higher frequencies suggest that the strength of the jitter may depend on radio frequency, but this is not yet established. The study also found that jitter did not set the limit on how precisely the researchers could measure the dispersion measure, which describes how material along the path delays the radio signals, over the observation timescale examined.

Young explorerA pulsar is a star that sends us radio flashes, a bit like a ticking clock. But its flashes can change shape, making their arrival times seem a little wobbly. Scientists used a radio telescope to find this wobble in one pulsar. The wobble may be different when they listen to different radio frequencies, but they are not sure yet. In these observations, the wobble was not what limited how well they could measure the way material in space delays the flashes.

FUGUE: A New GPU-accelerated General Relativistic Magnetohydrodynamics Code with Weak-Field Multipole Self-Gravity and Quasi-Stationary Kerr Black Hole Evolution

Piotr Plonka, Agnieszka Janiuk

AstronomerFUGUE is a new GPU-accelerated GRMHD code with optional quasi-stationary updates to Kerr black hole mass and spin, plus weak-field multipole self-gravity from a spherical harmonic Poisson solver. It uses shock-capturing methods and RK2 time integration, and is validated through hydrodynamic, MHD, relativistic, and self-gravity convergence tests. A demonstration simulates a one-solar-mass, magnetized, self-gravitating, Toomre-unstable accretion disk around a Kerr black hole. In this model, gravitational instabilities are associated with changes in the mass accretion rate and Blandford–Znajek luminosity; these are simulation findings, not observations. The abstract suggests possible relevance to gamma-ray bursts, but its sentence on that connection is incomplete. The authors report performance comparable to or exceeding current state-of-the-art GRMHD codes, including more than 470 million zone-cycles per second on one NVIDIA GH200 GPU with linear reconstruction.

PublicThe researchers introduce FUGUE, a computer program for simulating magnetized matter near black holes, including the gravity of the matter itself in an approximate form. They check the program with several tests and demonstrate it using a disk containing one Sun’s worth of matter around a spinning black hole. In that simulation, gravitational instabilities accompany changes in how quickly matter falls inward and in the power extracted from the spinning black hole. These are simulated effects, not telescope observations. A possible connection to gamma-ray bursts is suggested but not established. The authors also report computing speeds competitive with or better than leading comparable programs.

Young explorerScientists made a fast computer program to pretend how matter swirls around a black hole. In one pretend disk, changes caused by gravity went along with changes in how fast matter fell in and how much power came out. This happened in a computer, not in a picture of space.

A model for the image structure and spectral energy distribution of relativistic jets

Dominic W. Pesce, Ramesh Narayan, Yuh Tsunetoe

AstronomerThe authors present a Python implementation of the semi-analytic jet model of Tsunetoe et al. (2025), combining an axisymmetric force-free solution with prescriptions for nonthermal electron heating, synchrotron cooling, electron pitch-angle anisotropy, and straight-ray radiative transfer. Parameter exploration identifies approximately self-similar scalings of the predicted spectral energy distribution with black hole mass, accretion rate, and electron heating efficiency. For M87, one fiducial parameter set qualitatively reproduces multifrequency VLBI images, matches the observed longitudinal intensity profile, and produces a broadband spectrum quantitatively consistent with radio through X-ray measurements. For Sgr A*, fitting the quiescent spectrum shows that a collimated jet with nonthermal heating efficiency comparable to M87's is also quantitatively consistent with radio through X-ray data. That model predicts a compact jet with radio size inversely proportional to frequency, consistent with VLBI constraints; the fit does not establish that a jet is the source of the observed emission.

PublicThe researchers present Python software for modeling the light emitted by jets near black holes. It links the jet's structure to how energetic electrons are heated, lose energy, and produce radiation. Their calculations reveal approximate patterns in how the predicted spectrum changes with black hole mass, the rate of matter accretion, and electron heating efficiency. For M87, a single set of model settings broadly reproduces radio images at several frequencies, matches the brightness pattern along the jet, and agrees quantitatively with measurements from radio waves to X-rays. For Sgr A*, the model can also match the spectrum observed during its quiet state using a narrow jet with a similar electron heating efficiency. It predicts that this jet would appear smaller at higher radio frequencies, in agreement with existing observational limits. This makes a jet a possible explanation for Sgr A*'s emission, not a confirmed detection.

Young explorerScientists made a computer model of how a narrow stream of material near a black hole could shine. For a place called M87, the model looks roughly like the pictures of its jet and matches measurements of its light. For another place, called Sgr A*, a tiny jet in the model could also explain the light seen when it is quiet. The model says that jet would look smaller with higher-frequency radio waves. That agrees with what observations allow, but it does not prove the tiny jet is really there.

Detecting and Identifying Supernovae in AGN Accretion Disks

Zhi-Peng Ma, Kai Wang

• Astrophysics of Galaxies

AstronomerThis modeling study predicts emission from supernovae embedded in AGN accretion disks using analytic shock dynamics coupled to a one-zone radiation model. Across four progenitor types, lower black hole masses or lower Eddington ratios generally improve contrast against the AGN and allow detectability across a broader range of bands, from infrared to soft X-rays. However, substantial degeneracies with isolated supernovae, particularly those interacting with circumstellar material, complicate identification. Across the modeled progenitor types, characteristic emission shifts from EUV at black hole masses below roughly 10^7 solar masses to UV/optical at 10^8 solar masses, while visibility increases from less than a day to approximately 3–70 days; the latter models have peak temperatures of approximately 3–8 eV. The authors identify UV/optical searches around 10^8-solar-mass black holes as particularly promising, but report predictions rather than detections.

PublicStars may live and eventually explode inside the disks of material feeding active galactic black holes. This study models the light from such explosions; it does not report observing them. The calculations suggest that explosions around less massive black holes, or those feeding at lower Eddington ratios, are generally easier to see against the bright disk. Yet seeing an explosion would not by itself establish that it occurred inside the disk, because supernovae outside these disks can look similar, especially when they collide with surrounding material. The models also predict that explosions around black holes of about 100 million solar masses could remain visible for roughly 3–70 days, with characteristic emission in ultraviolet and visible light. This makes those wavelengths and systems promising targets for searches.

Young explorerSome stars might live inside the swirling disk around a giant black hole. If one explodes, could we spot its flash through the disk’s bright glow? Scientists used a model to work out what that might look like; they did not find an explosion in this study. Their model suggests that some flashes could last for days, giving us time to look. But other exploding stars can look similar, so a flash alone would not prove that the star lived inside the disk.

Neutrino production at the extreme vicinity of supermassive black hole in NGC 1068

Zhi-Peng Ma, Kai Wang

AstronomerUsing updated IceCube observations of NGC 1068 extending down to approximately 0.2 TeV, the authors infer neutrino-production conditions through a statistical analysis constrained by multi-messenger data. They calculate hadronuclear and photomeson neutrino production and accompanying cascade gamma rays, exploring parameter space with Latin hypercube sampling. Their inference excludes emission-region radii R ≳ 10 Schwarzschild radii at approximately 5σ and R ≳ 6 Schwarzschild radii at approximately 3σ. Reproducing at least roughly 80% of the observed neutrino flux requires R ≲ 3 Schwarzschild radii. These are inferred constraints, not direct measurements of the emission region. Among the acceleration mechanisms explored, stochastic acceleration naturally meets the constraints, while alternatives require extreme, finely tuned parameters; the authors therefore favor stochastic acceleration without establishing it as uniquely proven.

PublicHigh-energy neutrinos observed from the galaxy NGC 1068 offer clues to the extreme conditions near its supermassive black hole. The researchers compared calculations of neutrinos and accompanying gamma rays with observations to estimate where the neutrinos could be produced. Their analysis strongly disfavors a large production region. Accounting for at least about 80% of the observed neutrino signal requires a region with a radius no more than roughly three times the black hole’s Schwarzschild radius, a characteristic size scale. This location is inferred from the calculations rather than directly observed. The authors favor stochastic acceleration, in which particles gain energy through random interactions, because it meets their constraints more naturally than the alternatives they examined.

Young explorerScientists have spotted tiny particles called neutrinos coming from a galaxy with a huge black hole. They used observations and calculations to work out where those particles might be made. Their calculations suggest a very small place close to the black hole. They think particles getting lots of random little energy boosts is the best explanation they tested, but they have not proved that this is what happens.

Dark Matter Particle Explorer: Ten-Year On-Orbit Performance and Scientific Outcomes

Jian-Hua Guo, Chuan Yue, Yun-Long Zhang+2 more

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

AstronomerThis overview reviews the instrument, on-orbit status, and scientific highlights of the Dark Matter Particle Explorer (DAMPE, or Wukong), whose objectives include indirect dark-matter detection, cosmic-ray physics, and high-energy gamma-ray astronomy. Its large geometrical factor and thick imaging calorimeter enable detection of cosmic-ray electrons and positrons and gamma rays up to 10 TeV, and nuclei up to PeV energies. Launched into a Sun-synchronous orbit on 17 December 2015, DAMPE is reported to have operated smoothly for more than ten years. Highlighted work includes measurements of the combined electron–positron energy spectrum, proton and other nuclear spectra, and a high-energy gamma-ray line search. The abstract gives no specific spectral findings or line-search outcome and does not report a dark-matter detection.

PublicDAMPE, also called Wukong, is a space mission that studies energetic particles and gamma rays, with goals that include searching for indirect signs of dark matter. The abstract reports that it has operated smoothly for more than ten years since its launch on 17 December 2015. This overview describes the detector and its condition in orbit, and highlights measurements of how the energies of cosmic-ray electrons, positrons, protons, and other atomic nuclei are distributed. It also covers a search for a narrow feature in gamma-ray energies. The abstract does not state what that search found or claim that dark matter has been detected.

Young explorerWukong is a machine in space that catches tiny, speedy particles and very energetic light. It has been working for more than ten years. Scientists use it to measure the particles and look for clues about dark matter, something they hope to learn more about. This report describes the machine and some of its science work, but it does not say that Wukong has found dark matter.

Optical observations of supernova candidates with the ILMT

Monalisa Dubey, Bhavya Ailawadhi, Talat Akhunov+10 more

AstronomerThe 4-m International Liquid Mirror Telescope (ILMT), a zenith-pointing optical survey telescope with a 22.3 × 22.3 arcmin field of view, discovered six supernova candidates using the PyLMT pipeline: AT 2023yjc, AT 2024agkc, AT 2024aifv, AT 2024aiha, AT 2024fxn, and AT 2024zsm. It also detected ten additional supernova candidates discovered by other surveys. The study presents gri-band light curves for all 16 candidates and estimates their rise times, decline rates, and peak magnitudes. The abstract identifies these sources as candidates, not confirmed supernovae, and gives no numerical light-curve results.

PublicAstronomers using the International Liquid Mirror Telescope discovered six objects that may be exploding stars, known as supernovae. They also detected ten other possible supernovae first found by other surveys. The telescope points straight overhead, and its image-processing software helps identify faint objects that appear or change brightness. The study presents measurements of how these 16 candidates changed brightness in three optical bands and estimates how quickly they brightened, how quickly they faded, and how bright they became. The abstract does not report confirmation that they are supernovae.

Young explorerA telescope that looks straight up found six spots of light that might be exploding stars. It also saw ten more possible exploding stars that other searches had already found. The scientists tracked how bright the spots were over time to estimate how fast they brightened and faded. They are still called possible exploding stars, not sure ones.

Identification of ultra-high-energy neutrinos in vertical air showers with surface detectors

Jaime Alvarez-Muñiz, Ruben Conceição, Pedro J. Costa+2 more

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

AstronomerAir-shower and detector simulations support a neutrino-identification channel for surface arrays using vertical showers with zenith angles ≤60°, a region largely unexplored by current searches. The method exploits enhanced ground-level electromagnetic content associated with energetic leptons from neutrino interactions. Electromagnetic- and muon-sensitive observables discriminate simulated neutrino-induced showers from hadronic showers, both for idealized shower quantities and realistic water-Cherenkov and scintillator signals. Identification efficiencies yield effective mass and, primarily, effective area under background-rejection requirements appropriate to targeted multi-messenger searches. The approach is not competitive with inclined-shower searches under the stringent rejection needed for diffuse-flux analyses, but the simulations establish its feasibility as a complementary channel that could extend surface-array coverage for transient-source observations. No observed neutrino detections are reported.

PublicComputer simulations suggest that ground-based detector arrays could search for ultra-high-energy neutrinos using particle showers arriving from more nearly overhead, a direction range largely unexplored in current searches. In the simulations, neutrino-triggered showers have a stronger electromagnetic component at ground level, helping distinguish them from showers caused by other particles. The study tests this distinction with simulated signals from two detector types, rather than reporting actual neutrino detections. The approach could widen the sky coverage of surface arrays and complement searches linked to short-lived sources observed through multiple cosmic messengers. It is less competitive for diffuse neutrino searches, which require much stricter rejection of background events.

Young explorerScientists used computer models to test a new way to look for tiny particles called neutrinos. They studied showers of particles coming down from the sky and found clues that could help tell neutrino showers from other showers. They have not reported finding real neutrinos this way. It could help with some searches, but not all.

Polarization Properties of Thomson-Scattering Triaxial Ellipsoids

Naoki Hachisu, Tatsuya Matsumoto, Tomonori Totani

• Instrumentation and Methods for Astrophysics

AstronomerThis computational study calculates Thomson-scattering continuum polarization from spheroidal photospheres across a broader range of deformations and viewing angles than previously considered, and extends the calculation to triaxial ellipsoids. Strongly deformed spheroids show a non-monotonic dependence of polarization on viewing angle, a behavior the authors identify as overlooked in earlier studies. Triaxial ellipsoids produce more diverse signatures, whose qualitative behavior is interpreted through the area of surface elements seen nearly edge-on, where local polarization is strongest. These model results can help constrain transient photospheric geometry through polarimetry; the abstract reports no observational application. The computational results are planned for public release.

PublicThe polarization of light—its preferred orientation of vibration—can offer clues to the shapes of distant objects. This study calculates how scattering by electrons polarizes light from differently shaped light-emitting surfaces of short-lived astronomical events. In the calculations, strongly distorted spheroids show a more complicated pattern than a steady rise or fall in polarization as the viewing angle changes. Ellipsoids with three unequal axes show still more varied patterns. The authors explain these patterns in terms of how much of the surface is seen nearly edge-on, where local polarization is strongest. The work provides a way to interpret polarization observations, rather than reporting a measured shape for a particular event. The authors plan to make their calculations publicly available.

Young explorerLight can carry clues about the shape of something far away. The researchers used computer calculations to study those clues for stretched and squashed shapes. They found that, for very bent-out-of-shape ones, changing where you look from does not make the light's clue simply grow or shrink—it can change direction along the way. Parts of the surface seen almost sideways help explain the pattern. These calculations could help astronomers work out the shapes of bright events in space; they are not a picture or measurement of one real event.

A Shell Collision Scenario for EP251222b/GRB 251222A: Connecting Prompt Emission and Double-Peaked Afterglow

Run Shi, Di Xiao, Brajesh Kumar+23 more

AstronomerGRB 251222A, a long-duration burst at spectroscopic redshift z=3.171, was detected by EP as the soft X-ray transient EP251222b before and during its gamma-ray emission. A multi-wavelength investigation identifies prompt soft X-ray and gamma-ray features and two afterglow rebrightenings. The authors test a multiple-shell interpretation in which a faster, narrower shell overtakes a slower, wider shell, assuming selected pulse groups trace distinct ejecta and a late X-ray flare marks their collision. Modeling the post-collision outflow as an effective merged core plus an outer annular component, a joint multi-band afterglow fit yields Lorentz factors of approximately 293 and 228, respectively. Under this mapping, the inferred dissipated energy is (1.6 +2.1/-0.9) × 10^52 erg and the dynamical dissipation efficiency is (0.37 +0.07/-0.14)%. The event offers a test of a prompt–afterglow connection through shell collisions, but does not uniquely establish that interpretation.

PublicAstronomers studied the long-duration gamma-ray burst GRB 251222A using soft X-rays, gamma rays, optical light and near-infrared light. EP detected its soft X-ray signal before and during the gamma-ray emission, and the fading afterglow brightened again twice. The researchers explored whether these signals could be linked by a collision between a faster, narrower shell of ejected material and a slower, wider shell. Their model assumes that selected groups of early pulses came from different ejecta and that a later X-ray flare marked the collision. Fitting the afterglow under these assumptions gives estimates of the outflow’s motion and the energy released in the collision. The observations provide a way to test this explanation, but they do not show that a shell collision is the only possible cause.

Young explorerScientists watched a burst of light in space. They saw X-rays before and during its gamma-ray flash, and its afterglow got brighter again twice. They wondered if one fast layer of material caught up with a slower layer and bumped into it. They used a model to see how that idea could explain the light. It is an idea they can test, not something they know for sure happened.

Probing fundamental physics with ALMA2040 mm-wavelength observations of neutron stars

Kuo Liu, Marilyn Cruces, Gregory Desvignes+8 more

AstronomerThe abstract outlines prospective capabilities of ALMA2040 rather than reporting new observations. It argues that ALMA2040 would enable the first systematic exploration of millimeter-wavelength emission from pulsars and fast radio transients, potentially revealing new phenomena and constraining the still poorly understood physics of coherent radio emission. Additional opportunities include uncovering the Galactic Centre neutron-star population, testing fundamental physics near Sgr A*, probing the possible presence of dark matter, and investigating the region’s dense, dynamic interstellar and magnetic environment. These are anticipated scientific opportunities, not demonstrated results.

PublicThe physical process that produces powerful radio bursts or pulses from pulsars, magnetars, and fast radio transients is still poorly understood. This abstract describes how ALMA2040 could help by systematically studying pulsars and fast radio transients at millimeter wavelengths. It could reveal new kinds of signals and help explain how the emission is produced. It could also uncover neutron stars in the centre of our Galaxy, enable tests of fundamental physics near the supermassive black hole Sgr A*, investigate whether dark matter is present there, and study the surrounding material and magnetic environment. These are prospects for future research, not discoveries reported here.

Young explorerSome things in space send out strong radio flashes, but scientists do not yet know exactly how they make them. ALMA2040 could help scientists study those flashes in a new way. It could also help them find neutron stars near the middle of our galaxy and learn about the area around a huge black hole. These are things scientists hope to do, not things they have already found.

Extracting the Central Sound Speed of Neutron Stars through Intrinsic Stellar Structure Scaling with Reduced Equation-of-State Model Dependence

Jian-Hao Shi, Bao-Jun Cai, Yu-Gang Ma

• General Relativity and Quantum Cosmology
• Nuclear Theory

AstronomerThis theoretical study constructs six EOS families, each with 1,000 samples, using a nonlinear Walecka model with generalized omega-meson self-interactions and identical nuclear and astrophysical constraints. Despite meeting those constraints, the families yield substantially different high-density and core properties; higher-order omega interactions can produce interior sound-speed peaks in purely nucleonic matter. Using intrinsic and perturbative analysis of the dimensionless TOV equations, the authors derive an EOS-independent estimator Θ(X, Ψ) for central squared sound speed, where X is central pressure divided by central energy density and Ψ describes the mass response to central energy density. For 1.4-solar-mass stars, its linear correlations with central squared sound speed have R² ≈ 0.94–0.99. Minimizing dispersion among family-dependent relations gives central squared sound speed ≈ 0.523 ± 0.044 and X ≈ 0.173 (+0.020, −0.018); excluding the family without omega self-interaction gives 0.496 ± 0.092 and 0.167 (+0.030, −0.029). Corresponding radii are 11.73 (+1.08, −0.92) km and 11.92 (+1.76, −1.28) km, respectively, with 95% confidence intervals. A unified scaling fitted to all samples supports both extractions. These are model-based inferences, not direct core measurements, demonstrating reduced EOS-model dependence across the tested families even though existing observations cannot distinguish their EOS descriptions.

PublicThe properties of a neutron star’s core are difficult to infer because different descriptions of matter can fit the same available evidence. Researchers built six families of theoretical models that satisfy the same nuclear and astronomical constraints but predict different conditions deep inside these stars. They then developed a mathematical estimator linking stellar structure to how fast sound travels at the center. For modeled stars with 1.4 times the Sun’s mass, the different families approached similar estimates of central conditions, with corresponding radii near 12 kilometers. The estimates shift and their uncertainties widen when one model family is excluded. These are theoretical inferences rather than direct measurements: the method reduces dependence on the chosen description of matter across the models tested, while current observations still cannot distinguish those descriptions.

Young explorerA neutron star is a star packed very tightly. Scientists use math to guess what it is like deep inside, but different math recipes give different answers. This study found a way to make those guesses agree better about how fast sound moves in the middle. They have not measured that directly, so there is still uncertainty.

Secular Evolution of Quasiperiodic Eruptions: eRO-QPE2

Zirui Zhang, Cong Zhou, Zhen Pan

AstronomerAn analysis of quiescent and eruption emission from eRO-QPE2 in 11 XMM-Newton observations spanning 4.33 years finds approximately constant eruption peak count rates, while the quiescent count rate declines approximately linearly with a superposed large-amplitude oscillation. No secondary eruptions are detected between normal eruptions; any such events must be more than two orders of magnitude fainter. The recurrence time decreases at an average rate of approximately dT_rec/dt = -5 × 10^-6. These findings are consistent with, but do not establish, an extreme mass-ratio inspiral interacting with a precessing accretion disk and generating two normal eruptions per orbital period. Within this interpretation, Bayesian timing analyses constrain the orbital eccentricity to e < 0.033 at 95% confidence.

PublicResearchers studied recurring soft X-ray flares from the galactic nucleus eRO-QPE2 using 11 XMM-Newton observations over 4.33 years. The peak X-ray count rate during flares stayed roughly steady, while the count rate between flares generally declined with a large oscillation superimposed. The flares also came progressively closer together. No extra flares were detected between the usual ones; any that occurred would have to be more than 100 times fainter. The observations fit an explanation in which a much lighter object spirals toward a massive companion and interacts with a disk of surrounding material whose orientation changes, producing two flares per orbit. This explanation is not confirmed. Under that interpretation, the timing analysis indicates a nearly circular orbit, with eccentricity below 0.033 at 95% confidence.

Young explorerScientists watched a place in the middle of a galaxy that flashes in X-rays again and again. The tops of the flashes stayed about the same, but the glow between them got weaker overall while also going up and down. The flashes came closer together over time. Scientists did not see extra flashes in between, though very faint ones could have been missed. One possible explanation is a small object circling a much heavier one and meeting a disk of material, making two flashes each trip around. The scientists think this could fit what they saw, but they have not proved it.

Convective Oscillations of Cosmic Rays

Yiran Zhang, Siming Liu

AstronomerThis theoretical study derives cosmic-ray spatial-fluctuation power spectra produced by incompressible and acoustic turbulent convection, assuming an ensemble-averaged Gaussian cosmic-ray distribution of width Λ(t,p). At k ≪ 1/Λ, the incompressible contribution scales as P_s ∝ k^4 and the acoustic contribution as P_d ∝ k^2. At k ≫ 1/L_s and k ≫ 1/L_d, respectively, the spectra scale as P_s ∝ k^(γ_s−4) and P_d ∝ k^(γ_d−2), where γ_s and γ_d describe the corresponding turbulent velocity spectra below their outer scales. These theoretical asymptotic relations suggest a way to probe interstellar turbulence with future high-resolution images of pulsar gamma-ray halos; no observational test is reported.

PublicTurbulent motion in interstellar plasma can make cosmic rays unevenly distributed. This theoretical study calculates how those variations depend on spatial scale, assuming that the average cosmic-ray distribution has a bell-shaped profile. Swirling motion that does not compress the plasma and sound-wave motion produce different patterns, whose small-scale behavior depends on the turbulence itself. The results could help researchers study interstellar turbulence using future detailed images of gamma-ray halos around pulsars, but the abstract does not report an observational test.

Young explorerSpace has tiny, speedy particles called cosmic rays. Stirring the gas around them can make some places have more of these particles than others. Scientists used math to work out how two kinds of stirring could make different patterns. Future pictures of gamma-ray glows around stars called pulsars might help scientists learn about that stirring, but this study has not shown it in real pictures.

Are E>B regions essential for particle injection in relativistic magnetic reconnection?

Omar French, Fan Guo, Xiaocan Li+4 more

• Plasma Physics

AstronomerFully kinetic particle-in-cell simulations test whether electric-field-dominated X-point regions are essential for injection into the nonthermal population during relativistic magnetic reconnection. Across magnetizations σ = 12–800, the authors partition energy gains up to the injection threshold γ_inj = σ/4 into work inside E>B regions, during the first gyration after exit, and at all other times. This last, magnetized channel supplies the largest share of pre-injection energy gain for approximately 95% of injected tracers at σ = 12 and 65% at σ = 800. Most tracers in this magnetized majority never enter an E>B region before injection. The simulations therefore indicate that E>B regions are neither necessary for injection nor the dominant direct source of pre-injection work by injection share, within the studied regime of two-dimensional, nonradiative pair-plasma reconnection at vanishing guide field.

PublicWhen magnetic fields reconnect, they can accelerate particles to high energies. Some earlier studies proposed that particles need to pass through special regions where the electric field is stronger than the magnetic field to join a high-energy population. In computer simulations, the researchers tracked where particles gained energy before reaching a defined entry threshold. For most particles that reached it, the largest energy contribution came while their motion was governed by the magnetic field, rather than inside those special regions or just after leaving them. Most particles in that majority never entered an electric-field-dominated region before reaching the threshold. This challenges the claim that such regions are essential, but the conclusion is limited to the simulated conditions: a two-dimensional electron–positron plasma, without radiative effects and with no guide magnetic field.

Young explorerScientists used a computer to watch tiny particles speed up as magnetic fields changed their connections. They wanted to know if the particles had to visit special spots to get enough energy to join a speedy group. Most got their biggest boost before joining from other parts of the simulation, and many never visited the special spots at all. So those spots were not needed in this computer experiment, though things could work differently in other conditions.

X-ray point sources towards the giant radio lobes of Centaurus A

Karthik Balasubramaniam, Hsiang-Kuang Chang, Łukasz Stawarz+1 more

AstronomerFive Chandra/ACIS-I pointings toward the giant radio lobes of Centaurus A yield 185 point sources in the 0.5–7 keV band. Accounting for selection effects, foreground stars and the cosmic X-ray background, the authors find no excess attributable to the lobes. Hardness ratios are consistent with background AGN plus a few foreground stars. Above the flux threshold at which half the footprint is covered, the selected sample contains 83 sources, including 9 foreground stars, compared with 101 expected background sources: a 27% deficit after excluding stars, significant at only −1.5 sigma with a 15% background-normalisation uncertainty. The 90% upper limit on a lobe-associated population above 6.9 × 10^36 erg/s is fewer than 18 sources, relaxing to fewer than 38 with a conservative 30% normalisation uncertainty. The analysis indicates no need for an additional lobe-associated source correction to diffuse-emission or inverse-Compton measurements beyond standard resolved-source masking and background subtraction.

PublicAstronomers examined whether the giant radio-emitting lobes of the nearby galaxy Centaurus A contain an extra population of compact X-ray sources. They catalogued 185 sources in five Chandra observations, then accounted for how readily sources could be detected, foreground stars and the expected X-ray background. They found no excess: the sources appear consistent with mostly active galaxies farther away, plus a few foreground stars. In the sample used for the number comparison, excluding stars left fewer sources than expected, but the shortfall was not statistically compelling. This does not prove that the lobes contain no compact X-ray sources; the study places an upper limit on how many could be present above its stated brightness threshold. The findings indicate that standard removal of resolved sources and subtraction of background X-rays are sufficient for measurements of the lobes' diffuse X-ray emission, without an extra correction for a lobe-associated population.

Young explorerA galaxy called Centaurus A has two huge lobes that give off radio waves. Scientists looked toward them with an X-ray telescope to see whether extra tiny-looking X-ray lights belonged to the lobes. They found many lights, but most seem to be galaxies far behind the lobes, with a few stars in front. They did not find extra lights that they could link to the lobes. Some could still be there, so the scientists worked out a limit on how many might be hiding in their count.

Coherent states of neutrinos in rotating matter

Alexander Breev, Maxim Dvornikov

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

AstronomerThis theoretical study constructs generalized coherent states for neutrinos interacting electroweakly with rotating matter. Starting from the massive Dirac equation with a position-dependent matter potential, the authors take the massless limit and adopt a specific matter velocity profile that reduces the Hamiltonian to harmonic-oscillator form. They obtain exact solutions, construct creation and annihilation operators, and interpret the resulting coherent states classically. These states approach plane waves as matter rotation becomes slow. The study also defines an interaction-induced effective neutrino mass, examines a special class of coherent states and degenerate system parameters, and calculates effective masses at different neutrino energies using realistic parameters for a rapidly rotating neutron star. These are theoretical calculations, not observational measurements.

PublicThe researchers use mathematics to study how neutrinos—particles interacting through the weak force—travel through spinning matter. For a particular pattern of matter motion and treating the neutrinos as massless, they find exact wave solutions and combine them into organized states called coherent states. Their calculations show that these states approach plane waves when the matter rotates slowly. They also define an effective mass arising from the neutrinos’ interaction with rotating matter, rather than an intrinsic particle mass. Applying the theory to dense material in a rapidly rotating neutron star, they calculate this effective mass for different neutrino energies. The work presents theoretical results, not observations of neutrinos in a star.

Young explorerNeutrinos are tiny particles that can travel through a star. These scientists used math to explore how they might move through spinning star material and found special wave patterns. They also calculated how the material could make particles treated as having no mass behave as if they had some mass. This was a math study, not something they watched happen inside a star.

Numerical simulations of low-mass black hole-neutron star mergers with moderate eccentricities

Ivan Markin, Gonzalo Morrás, Tim Dietrich

• General Relativity and Quantum Cosmology

AstronomerThis numerical-relativity study tests eccentric black hole–neutron star waveform models and explores remnant disks, including magnetized cases. The simulated subset has orbital eccentricities roughly five times those inferred for GW200105_162426; these are simulation results, not a new observational detection of eccentricity. SEOBNRv5EHM agrees reasonably with the simulated gravitational waves unless tidal contributions become important, while the inspiral-only post-Newtonian models pyEFPE/pyEFPEHM show larger late-inspiral disagreement. In the equal-mass case, which has the largest effective tidal deformability, eccentric tidal corrections change the phase by about 0.1 rad. Eccentricity has almost negligible effects on remnant black hole properties but produces differences of up to a factor of two in remnant disk mass. Trapped disk g modes retain the same frequency across eccentricities, supporting their primary dependence on remnant black hole properties. Strongly magnetized disks become less dense and less structured, and the trapped modes identified in unmagnetized cases are efficiently damped. A confident observational detection of eccentricity would strongly indicate dynamical formation, but this study does not report such a detection.

PublicResearchers used computer simulations to study mergers between black holes and neutron stars whose orbits depart from circles. Such orbital shapes, if confidently detected in gravitational waves, would be a strong clue that the pairs formed through dynamical interactions. This study instead tests how well theoretical wave predictions match simulated mergers. One model generally agrees reasonably well, except when tidal effects become important; two others disagree more near the end of the inward spiral. In these simulations, orbital eccentricity barely changes the final black hole’s properties, but the mass of the surrounding disk can differ by as much as a factor of two. Certain disk oscillations keep the same frequency despite changes in orbital eccentricity, supporting the interpretation that they depend mainly on the final black hole. Strong magnetic fields make the simulated disks less dense and less clearly structured, while strongly damping those oscillations.

Young explorerScientists used computers to imagine a black hole and a neutron star going around each other on paths that are not quite circles, then joining together. They checked how well their predictions matched the computer’s ripples in space. Some predictions worked better than others. Changing the paths hardly changed the black hole left behind, but it could change how much material stayed around it. In the computer experiments, strong magnetic fields also made some wiggles in that material fade away. These are computer results, not something newly seen in space.

Breakdown of hydrodynamic universality in causal first-order viscous neutron star oscillations

Lennox S. Keeble, Alejandro Cárdenas-Avendaño

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study examines the breakdown of hydrodynamic universality in radial oscillations of viscous neutron stars across a broad range of causal hydrodynamic frames in Bemfica–Disconzi–Noronha–Kovtun (BDNK) theory. Causality and finite stellar size can prevent sufficiently viscous stars from accessing the long-wavelength regime in which different formulations share the same physical content. Increasing bulk viscosity drives the studied causal frames outside the BDNK validity regime, with all eventually outside it at viscosities of roughly 10^30–10^31 g/cm/s. The breakdown accompanies substantial changes in the calculated mode structure: non-hydrodynamic modes acquire damping times comparable to hydrodynamic modes, the first overtone can outlive the fundamental, and unphysical instabilities can appear on sub-millisecond timescales. Nevertheless, the gravitational-collapse threshold remains at its inviscid value within BDNK theory, even where universality fails. These modeling results provide evidence, rather than a definitive demonstration, that first-order relativistic hydrodynamic theories may be insufficient for sufficiently viscous neutron stars.

PublicDifferent mathematical descriptions of a neutron star’s fluid should agree when its motions vary over sufficiently large distances. This theoretical study finds that, for sufficiently viscous stars, the star’s finite size and the requirement that signals respect causality can prevent that agreement. Across a broad class of descriptions within a theory called BDNK, increasing viscosity eventually takes the calculations beyond the theory’s range of validity. The calculated vibrations then change: some persist for unexpectedly long times, and unphysical, rapidly growing disturbances can appear. These are findings about the models, not observed stellar behavior. Despite these problems, the calculated threshold for gravitational collapse remains the same as without viscosity. The results suggest that first-order fluid theories may not adequately describe sufficiently viscous neutron stars.

Young explorerScientists use math to study how neutron stars wiggle. Different math recipes should agree in some situations. But this study finds that, when the star’s fluid has enough internal friction, the recipes can stop agreeing and go beyond where they can be trusted. Some even make pretend wiggles grow in unphysical ways. This is a warning about the math, not something scientists saw a star do.

Jittering jets in stripped-envelope core-collapse supernovae

Nikki Yat Ning Wang, Dmitry Shishkin, Noam Soker

• Solar and Stellar Astrophysics

AstronomerUsing one-dimensional MESA stellar-evolution simulations, the authors compare expected core-collapse supernova explosion times in the jittering jets explosion mechanism (JJEM) and the delayed neutrino mechanism. They identify the JJEM onset time with accretion of the core’s inner convective layer onto the newborn neutron star. Across hydrogen-rich, hydrogen-stripped, and helium-plus-hydrogen-stripped progenitor models with initial masses of 12–40 solar masses, most—but not all—contain at least one strong convective zone within the approximately 2.65-solar-mass coordinate adopted as the maximum neutron-star baryonic mass, potentially facilitating the JJEM. The authors conclude that, for most models, JJEM activity would begin before neutrino heating fully revives the stalled shock, even where the neutrino mechanism might otherwise produce an explosion. These model-based timing estimates support JJEM viability rather than demonstrating jet-driven explosions observationally.

PublicThis study compares when two proposed ways of making a collapsing star explode could begin working: jittering jets and energy supplied by neutrinos. Using one-dimensional computer models of stars, the researchers estimate that the jets would start operating when an inner layer of churning material falls onto the newly formed neutron star. In most, but not all, of their models, this would happen before the neutrino mechanism could fully restart the stalled outward shock—even in cases where neutrinos might eventually cause an explosion. Most modeled stars, which began with 12–40 times the Sun’s mass, contain an inner churning region that could help the jet mechanism work. The findings support jets as a possible explosion mechanism, but are estimates from stellar models, not observations or direct demonstrations of explosions.

Young explorerWhen a big star’s middle falls inward, what makes the star explode? Scientists used computer models to compare two ideas: wiggling jets of material, or help from tiny particles called neutrinos. Their models suggest that jets could get started first in most of the stars they studied, but not all. This is a clue that jets might help stars explode, not proof that real stars explode this way.

The impact of gamma-ray propagation effects on indirect dark matter searches

Ignacio Martínez López, Rafael Alves Batista, Miguel A. Sánchez-Conde+1 more

• High Energy Physics - Phenomenology

AstronomerThis modeling study revisits gamma-ray predictions from WIMP annihilation by treating propagation beyond attenuation through pair production on the extragalactic background light. It includes inverse Compton scattering by the resulting electrons and positrons, which can regenerate high-energy gamma rays. For distant sources and channels such as τ+τ−, the fuller treatment can change the predicted flux reaching Earth by up to three orders of magnitude for heavy WIMPs. The implications for dark matter exclusion limits depend on WIMP mass and annihilation channel. These are propagation-model results, not a dark matter detection, and they underscore the need for detailed propagation calculations when predicting signals and deriving limits.

PublicResearchers studied how gamma rays from hypothetical dark matter particles could change while traveling to Earth. Many models account for gamma rays being absorbed and producing electrons and their antimatter partners, but overlook how those particles can generate gamma rays again. Including this process can change the predicted signal by as much as a factor of 1,000 in some cases involving heavy dark matter particles and distant sources. This is a calculation, not a detection of dark matter. It suggests that limits on dark matter based on gamma-ray searches may need revision, with the effect depending on the particles’ mass and how they annihilate.

Young explorerScientists are looking for a mysterious kind of stuff called dark matter. If some possible dark matter particles meet and disappear, they could make special light. On its way to us, that light could turn into tiny particles that make more light. Scientists calculated that this could change how much light we expect to see, sometimes by a lot. They did not find dark matter in this study.

A grid of fast-rotating, chemically-homogeneous, supernova and/or long-GRB progenitors

M. Renzo, O. Gottlieb, H. S. Chan+6 more

• Solar and Stellar Astrophysics

AstronomerThe authors present a MESA grid of 113 single-star evolutionary models with initial masses of 30–90 solar masses, rigid rotation at 0.5–0.99 of the critical rate, and metallicity Z = 0.001. A 128-isotope reaction network follows weak reactions responsible for core deleptonization during and after silicon core burning. Chemically homogeneous evolution driven by rotational mixing is built into the model selection. At the onset of collapse, the models retain substantial, structured angular momentum, potentially sufficient to form accretion disks around a proto-compact object. These are progenitor calculations, not demonstrated explosions or observations. The grid provides updated structures for investigating some stripped-envelope supernovae, including possible jetted, broad-lined, collapsar or magnetar-powered events, and long gamma-ray bursts; the proposed connections remain conditional.

PublicHow a massive star collapses—and whether it explodes—depends strongly on its internal structure. To help study this uncertainty, the researchers calculated 113 computer models of rapidly rotating stars initially weighing 30–90 times as much as the Sun. The models were constructed to undergo strong rotational mixing and were followed to the start of collapse. They retain large amounts of rotational motion, which might allow material to form a disk around the compact object developing at the center. The calculations provide starting points for investigating several kinds of stellar explosions and long gamma-ray bursts. They do not show that these stars actually produce those events.

Young explorerScientists used a computer to make pretend versions of big, fast-spinning stars and follow them until they started to fall inward. The model stars were still spinning a lot. That might help their material make a disk around the squashed center. These models could help scientists study star explosions, but they do not show that an explosion really happens.

A binary black hole merger rate comparison within the same metallicity-star formation rate framework

Lumen Boco, Michela Mapelli, Michele Bosi+2 more

• Cosmology and Nongalactic Astrophysics
• Astrophysics of Galaxies

AstronomerThis study tests the reported excess of predicted local binary black hole (BBH) merger rates by combining a broad set of binary population synthesis merger efficiencies with an observationally motivated, metallicity-dependent star formation rate density and 18 metallicity variations representing observational uncertainties. In 17 of the 18 variations, no model considered predicts a rate within or below the observed 90% credible interval; even in the most favorable variation, fewer than 10% are consistent with observational constraints. Full calculations incorporating self-consistent delay-time distributions for the lowest-rate models confirm overprediction for almost all metallicity variations. Including the low-metallicity tail from low-mass galaxies and starbursts, and treating iron rather than oxygen abundance, systematically raises predicted rates. The results indicate persistent tension across the explored assumptions, not a definitive exclusion of binary population synthesis models generally.

PublicModels of how pairs of black holes form and eventually merge appear to predict more mergers in the nearby universe than observations allow. This study explores whether that mismatch survives a broad range of assumptions about binary evolution and the history of star formation, including uncertainty in the chemical composition of newly formed stars. For 17 of 18 chemical-composition variations, every model tested predicts a merger rate above the observed 90% credible range. Even in the most favorable variation, fewer than one in ten models agree with the observational constraints. More complete calculations for the models predicting the fewest mergers largely preserve the mismatch. The authors find that accounting for stars with very low abundances of heavier elements, and tracking iron rather than oxygen, increases predicted rates. The tension remains unresolved within the assumptions explored.

Young explorerTwo black holes can come together and join into one. Scientists use computer models to work out how often this should happen. In this study, they tried many different ways of describing how stars are born and change. Most models still predicted more black hole pairs joining nearby than observations suggest. What stars are made of changed the predictions, but the mismatch mostly stayed. Scientists still have a puzzle to solve.

Fast X-ray Transient EP260321a: Shock Breakout through an Extended Circumstellar Matter

Maokai Hu, Yi Yang, Xiaofeng Wang

• Solar and Stellar Astrophysics

AstronomerEinstein Probe discovered the fast X-ray transient EP260321a, whose optical counterpart was subsequently classified as a broad-lined Type Ic supernova. Its observed rise time of about 690 seconds is inconsistent with theoretical predictions for shock breakout from a Wolf-Rayet star. The authors instead propose shock breakout within extended circumstellar matter (CSM), with initially trapped photons diffusing through unshocked CSM as the ejecta expand and the opacity decreases. They model photon diffusion with Monte Carlo simulations and temperature evolution with an analytical approach. Markov Chain Monte Carlo fitting yields best-fit values of log10(Mcsm/Msun) = -3.3, Rin = 160 Rsun, and Rout = 612 Rsun. Within this interpretation, the inferred dense CSM points to episodic mass loss just days before explosion, constraining the progenitor’s late-stage evolution.

PublicEinstein Probe detected a brief X-ray event called EP260321a, later linked through its optical counterpart to a broad-lined Type Ic supernova. The X-ray signal took about 690 seconds to rise, longer than theoretical predictions for a shock emerging from a Wolf-Rayet star, the type of star typically thought to produce such stripped-envelope explosions. The researchers propose that the shock instead emerged within surrounding material, where light was temporarily trapped before escaping as the explosion expanded and the material became more transparent. Simulations and analytical modeling support a best-fit surrounding shell with a mass of about 0.0005 times the Sun’s mass, extending from 160 to 612 times the Sun’s radius. If this interpretation is correct, the star shed material in episodes just days before exploding.

Young explorerA space telescope saw a quick flash of X-rays from an exploding star. But the flash brightened more slowly than scientists expected. The researchers think there may have been material around the star that held the light back, then let it escape as the explosion grew. They used computer models and math to test this idea. If they are right, the star threw off that material just a few days before it exploded.

Radio Continuum Study of One of the Brightest Large Magellanic Cloud Supernova Remnants N 132D

Rami Z. E. Alsaberi, Zachary J. Smeaton, Miroslav D. Filipovic+5 more

AstronomerATCA and MeerKAT radio-continuum observations of the Large Magellanic Cloud supernova remnant N 132D show spatial correspondence with X-ray emission in the central and left regions and the right shell, suggesting a close connection between thermal and non-thermal plasma. Polarisation measurements indicate predominantly radial magnetic fields, with mean fractional polarisations of 1.2%, 3.0%, and 4.0% at 2100, 5500, and 9000 MHz, respectively. A double-peaked Faraday-depth spectrum is interpreted as evidence for regions with differing magnetisation or magnetic-field geometry. ATCA rotation measures average approximately 2 rad m^-2 and reach approximately 338 rad m^-2. Under a constant-partition assumption relating electron and magnetic-field energy densities, the authors estimate a magnetic field of approximately 90 microgauss and a minimum energy of 3 × 10^50 erg. The integrated radio spectrum follows a power law with spectral index −0.74 ± 0.01. These findings constrain the remnant’s magnetic structure and energetics and inform studies of particle acceleration and shock evolution.

PublicAstronomers used the ATCA and MeerKAT radio telescopes to study N 132D, the remains of an exploded star in the Large Magellanic Cloud. In several regions, the radio emission closely matches the X-ray emission, suggesting a connection between hot gas and the particles producing non-thermal radiation. The polarisation of the radio waves indicates that the magnetic fields mostly point radially, outward or inward relative to the remnant’s centre. A double-peaked pattern in how the emission is affected by magnetised material suggests regions with different magnetic properties or field arrangements; it does not uniquely identify which explanation applies. Assuming a fixed relationship between the energy in electrons and in the magnetic field, the researchers estimate a field strength of about 90 microgauss. The observations help constrain how magnetic fields, energetic particles, and shocks behave in this supernova remnant.

Young explorerScientists used radio telescopes to look at what is left after a star exploded. In some places, the radio picture matches the X-ray picture. They also found clues that invisible magnetic fields mostly point toward or away from the middle. Other clues suggest the fields are not arranged the same way everywhere. These pictures help scientists learn about the star’s leftovers.

Radial Oscillations of Viscous Stars

Lennox S. Keeble, Jaime Redondo-Yuste

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study treats linear, purely radial perturbations of cold, polytropic, spherically symmetric neutron stars in both acausal Eckart and causal Bemfica–Disconzi–Noronha–Kovtun (BDNK) hydrodynamics. The calculations find viscous damping on millisecond timescales and fractional frequency shifts that grow with compactness and viscosity, reaching the percent level for the fundamental mode at bulk viscosities around 10^30 g/cm/s. At higher viscosities, the oscillation frequency decreases, reaching zero in an overdamped mode for bulk viscosities of roughly 10^31 g/cm/s or greater. At the linear collapse threshold, Eckart viscosity cannot stabilize an unstable inviscid star, consistent with recent analytic results in the zero-heat-conductivity limit. Numerical evidence suggests BDNK viscosity likewise cannot prevent collapse, although it slightly shifts the collapse threshold. These are model results, not observations, and inform viscous asteroseismology with next-generation gravitational-wave detectors.

PublicNeutron-star vibrations can carry information about the nuclear matter inside them. This study calculates how viscosity, a form of internal resistance to motion, affects idealized cold, spherical neutron stars as they expand and contract radially. Using two descriptions of fluid motion and a small-disturbance approximation, the researchers find that viscosity damps these vibrations on millisecond timescales and changes their frequencies. The frequency changes grow with the star’s compactness and viscosity, reaching about one percent for the lowest radial mode in some models. At sufficiently high viscosity, that mode no longer oscillates. The calculations also find that viscosity cannot rescue an otherwise unstable star from gravitational collapse in one fluid theory; numerical evidence points to the same conclusion in the other, though its collapse threshold shifts slightly. These theoretical findings, rather than detected stellar vibrations, help develop tools for studying neutron-star matter with future gravitational-wave detectors.

Young explorerThe researchers used math to imagine a neutron star gently puffing out and squeezing back in. They asked what happens when the stuff inside resists moving. In their models, this makes the shaking fade very quickly and changes how fast it shakes. With enough resistance, the shaking stops being a back-and-forth motion. They also studied stars that would collapse and found that this resistance did not seem able to save them. This was a study using math, not something they watched a real star do.

Linear causality and stability constraints on relativistic second-order magnetohydrodynamics

Yiwei Qiu, Duan She, Defu Hou

• Fluid Dynamics
• High Energy Physics - Phenomenology

AstronomerThis theoretical study constructs a second-order relativistic magnetohydrodynamic framework from entropy-current analysis, incorporating finite relaxation times for dissipative fluxes. Linearization about homogeneous equilibrium separates magnetosonic, Alfvén, and charge-diffusion sectors while retaining their couplings. Long- and short-wavelength asymptotic dispersion relations are checked against exact numerical roots. The numerical analysis supports these approximations but reveals angular dependence, particularly near special propagation directions where the ordinary momentum expansion becomes less reliable. Short-wavelength propagating branches and damping of non-hydrodynamic modes yield mode-dependent linear causality constraints controlled jointly by propagation direction, anisotropic transport coefficients, and relaxation times. These are theoretical and numerical results for linear perturbations, not observational findings or a demonstration of general nonlinear causality.

PublicThe researchers developed a mathematical description of how a magnetized fluid behaves when relativity matters, allowing dissipative processes to adjust over a finite time rather than instantly. They studied small disturbances around a uniform, steady state to investigate which model conditions allow stable behavior and respect the relativistic speed limit for signals. Their approximate formulas for long and short waves agree with numerical solutions, although a standard expansion becomes less reliable for waves traveling in certain directions. The resulting limits depend on the type of disturbance, its direction, the fluid's direction-dependent transport properties, and its adjustment times. This is a theoretical study supported by numerical calculations, not a report of astronomical observations; its conclusions concern small disturbances around equilibrium.

Young explorerImagine a fluid with a magnetic field running through it. Scientists made math rules to study how tiny ripples could move through that fluid when the rules of relativity matter. Their model lets the fluid take time to adjust instead of changing all at once. They checked their ripple formulas with computer calculations and found that the direction a ripple travels matters. Their rules help work out when tiny ripples behave steadily and do not send signals faster than light. This was a study using math and computers, not something they watched in space.

A Parsec-scale Circumstellar Shell Around VX Sgr: Mass Loss and RSG/TŻO Nature

Julian Shapiro

• Astrophysics of Galaxies

AstronomerA newly discovered thin, arc-shaped shell around VX Sgr has a characteristic radius of about 0.59 pc and is reported as the largest known circumstellar shell around a red supergiant. Its extinction-corrected Hα intensity is about 38 R, with an ionized mass of about 0.1 solar masses. VX Sgr’s low peculiar velocity of 12 km/s and the absence of far-infrared emission in the arc argue against a bow-shock origin; the favored interpretation is steady red-supergiant wind material or ejecta photoionized by a nearby O- or B-type star. The shell geometry and emission measure yield an estimated mass-loss rate of about 4 × 10^-5 solar masses per year. VX Sgr’s classification remains debated among red supergiant/hypergiant, super-AGB star, and Thorne–Żytkow object. The Sgr OB1 association’s kinematic age disfavors the super-AGB interpretation, while proposed arc spectroscopy could potentially distinguish a red supergiant from a Thorne–Żytkow object. An exploration of future supernova interaction using the shell-to-ejecta mass ratio suggests that the shell would likely not significantly affect the forward shock.

PublicAstronomers have discovered a thin, curved shell of gas around VX Sagittarii, reported as the largest known such shell around a red supergiant. The ionized gas contains roughly one-tenth of the Sun’s mass. The star’s slow motion and the lack of far-infrared emission from the arc argue against a shell formed by the star plowing through its surroundings. Instead, the researchers favor gas released by the star and made to glow by radiation from a nearby hot star. What kind of star VX Sagittarii actually is remains uncertain. The age inferred for its stellar association argues against one proposed classification, a super-AGB star. Studying the arc’s spectrum is proposed as a possible way to distinguish a red supergiant from the more exotic Thorne–Żytkow interpretation. The researchers also suggest that, in a future supernova, this shell would probably have little effect on the explosion’s outward-moving shock.

Young explorerAstronomers found a thin, curved cloud of gas around a star called VX Sagittarii. They think the star let this gas go and a nearby hot star makes it glow, but they are not sure. They also do not know exactly what kind of star VX Sagittarii is. Looking more closely at the cloud’s light might help them find out.

A Search for Dust in the Outflow of the HH₂₁₂ Class 0 Protostellar System

Adele L. Plunkett, Per Bjerkeli, Jon P. Ramsey+2 more

• Earth and Planetary Astrophysics
• Astrophysics of Galaxies

AstronomerRe-imaging archival, multi-frequency ALMA continuum observations of HH212 reveals extended dust emission. Using Bands 7 and 9, the authors estimate the dust spectral index and dust mass in the wind-launching region, finding a small but significant dust mass spatially coincident with the molecular outflow cavity. They assess this finding against the hypothesis that the outflow transports dust away from the protoplanetary disk; spatial coincidence alone does not establish such transport. Removal of enough dust could affect the material budget for planet formation, but that consequence is not demonstrated here.

PublicYoung stars eject material, and winds may also lift dust from the disks where planets can form. By reprocessing archived ALMA telescope observations of the young-star system HH212, researchers detected extended dust emission and estimated a small but significant amount of dust in the region associated with the molecular outflow cavity. The finding offers evidence relevant to the idea that an outflow can carry dust away from a disk, but it does not establish that this is happening. Whether enough dust is removed to affect future planet formation remains unresolved.

Young explorerA baby star called HH212 has a dusty disk around it and sends gas outward. Scientists looked again at telescope pictures and found a little dust glowing in a place near the escaping gas. They wonder if the gas can carry dust away from the disk, but this finding does not prove it. If enough dust leaves, there could be less left to make planets.

Beyond Mergers: the Role of Metallicity in Forming a Reservoir of Massive and Detached Binary Black Hole Systems

Siyuan Chen, Monica Gallegos-Garcia

AstronomerThe observed gravitational-wave population suggests isolated binary evolution may not explain all BBH mergers, particularly those with primary masses above roughly 30 solar masses. Using POSYDON, the authors simulate binaries at eight metallicities from 10^-4 to twice solar metallicity, classifying BH-forming systems as merging BBHs, detached BBHs, or binaries disrupted during BH formation. The simulations show metallicity-dependent differences, especially above roughly 25 solar masses. Across the range 0.01–0.45 times solar metallicity, massive BH formation persists even as massive merging BBHs become scarce and detached systems remain abundant; the detached-to-merging ratio for 25–35-solar-mass BHs increases by more than two orders of magnitude across this range. With cosmic star-formation weighting, the models place massive BHs predominantly in detached binaries with orbital periods of at least roughly 100 days. These results predict a substantial detached population from isolated evolution, not an observed census. Dynamical interactions in dense stellar environments are proposed as a possible route to subsequent mergers.

PublicPairs of stars evolving without outside encounters can produce pairs of black holes, but gravitational-wave observations suggest this pathway may not explain every black hole merger, especially those involving heavier black holes. The researchers simulated binary evolution with different abundances of elements heavier than helium. Their models show that massive black holes can still form under conditions where few massive pairs merge: many instead remain in detached binaries. After accounting for cosmic star formation, the simulations predict that massive black holes mostly occupy detached pairs taking roughly 100 days or longer to orbit each other. Encounters in crowded stellar environments might later push some pairs toward merging, but this is a possible next step, not a demonstrated outcome.

Young explorerTwo stars can become two black holes that circle each other. The researchers used computer models and found that many heavy black holes could stay in pairs without joining together. These are predictions, not pairs they found in the sky. In crowded groups of stars, a passing neighbor might help a pair move closer and someday join.

EPRV Asteroseismology of the K dwarfs GJ 570 A and GJ 783 A with ESPRESSO. Empirical mode-amplitude scaling in tension with 3D convection simulations

T. L. Campante, Y. Zhou, Y. Li+21 more

AstronomerHigh-cadence ESPRESSO radial velocities spanning five nights for GJ 570 A (K4 V) and six for GJ 783 A (K2.5 V) reveal 6 and 24 solar-like oscillation modes, respectively. Peak radial-mode amplitudes are 2.57 ± 0.52 and 4.90 ± 0.81 cm/s. The observations support a transition near the G/K-dwarf boundary from amplitude scaling approximately as (L/M)^0.7 to a steeper (L/M)^1.5 toward lower luminosity-to-mass ratios. By contrast, 3D radiative-hydrodynamical simulations incorporating excitation and damping calculations predict approximately (L/M)^0.9 for K dwarfs. These detections extend Doppler asteroseismology into the mid-K regime. The scaling discrepancy suggests missing physics in the implemented convection-pulsation coupling and/or limitations of the modeling assumptions, rather than establishing a specific physical cause.

PublicAstronomers used ESPRESSO to measure tiny back-and-forth motions caused by vibrations in two K-dwarf stars, GJ 570 A and GJ 783 A. They identified 6 vibration modes in the first star and 24 in the second. Such vibrations are difficult to detect through brightness measurements because their amplitudes are so small. The results support a sharper decline in vibration strength toward lower stellar luminosity-to-mass ratios than the researchers’ three-dimensional simulations predict. The observations therefore provide a test of how surface convection drives and damps stellar vibrations. The mismatch may reflect missing physics or limitations in the models; its precise cause remains unresolved.

Young explorerStars can gently wiggle. Scientists measured tiny wiggles in two stars, even though the wiggles were very hard to spot. Their computer models did not match how the wiggle sizes change from star to star. The scientists think their models may be missing something, but they do not yet know exactly what.

Finite-Element Asteroseismology I: Two-Dimensional Adiabatic Oscillations of Rapidly Rotating N=3 Polytropes

Zhao Guo, Adrian J. Barker

AstronomerThis computational study develops a finite-element formulation for linear adiabatic oscillations of axisymmetric, uniformly rotating, centrifugally distorted, self-gravitating N=3 polytropes. Self-consistent-field equilibria are remeshed onto a surface-fitted oblate domain, and FEniCSx solves the coupled displacement–gravitational-potential polynomial eigenvalue problem, including the exterior vacuum potential. Nonrotating axisymmetric modes closely match an independent one-dimensional calculation, while several clean axisymmetric p-mode branches at finite rotation reproduce frequencies tabulated by Reese (2006). The authors report rotation-induced relative frequency differences below 3 × 10^-4 for low-order branches up to approximately 60% of critical rotation. Eigenfunction tracking and angular decomposition reveal continuous evolution from nearly single-degree spherical-harmonic structures to strongly mixed states at rapid rotation. These are numerical results for idealized stellar models, presented as a step toward multidimensional asteroseismology of more realistic rotationally and tidally distorted stars.

PublicThe researchers developed a computer method to calculate how an idealized spinning star vibrates, including how rotation changes its shape and how its changing gravity affects the vibrations. They checked the method against an independent calculation for a nonspinning model and published frequencies for spinning models, finding close agreement in the tested cases. By following individual vibration patterns as rotation increased, they found that initially simple patterns gradually became mixtures of different angular patterns. This is a computational study, not a report of observations of real stars. The method is intended to help build future tools for studying more realistic stars distorted by rotation and tides.

Young explorerA spinning star can get squashed and wiggle in different ways. Scientists made a computer model of a pretend star to work out those wiggles. They checked some answers against other calculations and found close matches. In their model, faster spinning made simple wiggle patterns mix together into more complicated ones. They hope this will help them study more realistic stars later.

An HST survey of photometry and multiplicity of brown dwarfs and planetary-mass objects in the field of Taurus

Pengyu Liu, Beth A. Biller, Clémence Fontanive+11 more

• Earth and Planetary Astrophysics

AstronomerAn HST photometric and multiplicity survey targeted 26 young Taurus objects with estimated masses of 6–37 Jupiter masses and spectral types later than M8. Searches using multiband colours and point-spread-function fitting detected no companion candidates beyond 30 au. Updated membership and age assignments, combined with evolutionary models, yielded luminosities, temperatures, and masses. Artificial-star injection tests indicate sensitivity to companions of 1 Jupiter mass, or less for some targets. After completeness correction, the binary-frequency upper limit is 6.5% at 68% confidence for mass ratios of 0.1–1 and separations of 30–7,000 au. No significant binary-frequency difference was found among planetary-mass objects in Taurus, Upper Scorpius, and the field. The authors interpret these findings as supporting a binary frequency established early, probably before 1–10 Myr, with inefficient formation of wide planetary-mass binaries and likely very early disruption in a low-density environment; these formation and disruption scenarios are interpretations rather than direct observations.

PublicAstronomers used the Hubble Space Telescope to search for companions around 26 young objects in the Taurus star-forming region, with estimated masses between 6 and 37 times Jupiter’s mass. They found no companion candidates farther away than 30 times the Earth–Sun distance. Tests using artificial stars added to the images suggest that the observations could detect companions as light as Jupiter, or lighter around some targets. Accounting for missed detections, the study places a 68%-confidence upper limit of 6.5% on the fraction with companions in the tested range of distances and relative masses. Comparisons with planetary-mass objects elsewhere revealed no significant difference in how often they occur in pairs. The authors suggest that widely separated pairs rarely form and may break apart very early, but the survey did not directly observe those processes.

Young explorerAstronomers used a space telescope to look at 26 young objects that weigh several times as much as Jupiter. They looked for faraway buddies but did not spot any. That does not mean every object is alone: some buddies could be too close or too hard to see. The scientists think far-apart pairs may be hard to make or may split up very early, but they did not watch that happen.

Intermediate- and high-resolution optical spectroscopy on the nascent planetary nebula Vy 2-2: Evidence of binary-star evolution

Roldán A. Cala, Luis F. Miranda, José F. Gómez+2 more

• Astrophysics of Galaxies

AstronomerNew intermediate- and high-resolution échelle spectra of the nascent planetary nebula Vy 2-2 reveal previously unreported nebular recombination and forbidden lines, as well as stellar emission lines. Derived abundances are subsolar and consistent with earlier estimates. The revised ADF(O²⁺) of 13.6 ± 2.6 places Vy 2-2 among planetary nebulae with unusually large abundance discrepancies. Morphokinematical and ionization analysis identifies a relatively high-excitation central region and two low-excitation bipolar lobes, with no significant shock excitation detected in the main ionized shell. Combining published angular expansion with the H⁺ expansion velocity yields a distance of approximately 1.68 kpc and an inferred kinematical age of approximately 210 years. The stellar emission spectrum is wels-like, but the authors favor an origin in an irradiated close companion rather than the central star. The high ADF, nebular structures, fluorine detection, and other evidence suggest, rather than establish, a post-common-envelope binary. Chemical abundances and circumstellar mass estimates suggest a progenitor initial mass no greater than about 0.9 solar masses.

PublicNew spectra of Vy 2-2 offer a view of a planetary nebula in its earliest stages. The analysis reveals a more highly excited central region and two opposing, lower-excitation lobes. The main ionized shell shows no significant evidence of excitation by shocks. The researchers find chemical abundances below solar values, but different abundance diagnostics give an unusually large disagreement for doubly ionized oxygen. Using the nebula’s expansion, they estimate a distance of about 1.68 kiloparsecs and an expansion-based age of roughly 210 years. Several clues suggest that its central system may contain two close stars that previously shared a common envelope, although this is not confirmed. Emission lines may come from a companion illuminated by the central star rather than from the central star itself. The chemistry and surrounding mass also suggest that the original star began with no more than about 0.9 times the Sun’s mass.

Young explorerAstronomers studied light from a young cloud of gas around a star. They found a middle part and two parts sticking out in opposite directions. The cloud’s spreading motion suggests it is about 210 years old. Some clues hint that two stars, not just one, may be hiding inside. Scientists are not sure yet, but a nearby partner might help explain the cloud’s unusual features.

Influence of numerical domain design in simulations of solar coronal heating with the MAGEC code

Anamaría Navarro, E. Khomenko, T. Felipe+1 more

AstronomerA MAGEC parameter study examines how domain dimensions, upper boundary conditions, and vertical grid stretching affect the relaxed thermal structure, energy budget, and long-term stability of 2D solar-atmosphere simulations with a vertical magnetic field. Taller domains produce higher mean coronal temperatures and steeper transition-region gradients. Among the less artificial upper boundary conditions tested, non-reflecting characteristic conditions delay coronal cooling most effectively. The authors identify a threshold domain height at which a dynamic upper boundary can mimic fixed-temperature setups, and a maximum grid stretching that reduces computational cost while preserving physical accuracy; the abstract supplies no numerical thresholds. Height-dependent budgets of radiative losses, thermal conduction, pressure work, and internal energy flux show substantial boundary-condition dependence. These are simulation findings demonstrating sensitivity to numerical setup, not observational evidence for a particular coronal heating mechanism.

PublicThe Sun’s hot outer atmosphere is difficult to understand, and computer simulations are an important tool for studying it. This study tests how the size of a simulated region, the spacing of its calculation grid, and the rules imposed at its upper edge affect two-dimensional models of the solar atmosphere. Taller simulated regions develop hotter outer atmospheres on average and sharper temperature changes in the transition region below. Of the less artificial upper-edge rules tested, one designed to let disturbances leave without reflecting them back delays cooling most effectively. The researchers also identify limits on grid spacing and a region height at which a changing upper-edge rule can behave like one held at a fixed temperature, though the abstract gives no numerical values. The results show that modeling choices strongly affect simulated temperatures and energy flows; they do not establish what heats the real Sun’s outer atmosphere.

Young explorerScientists made computer models of the Sun’s air to help study why its outside is so hot. They tried making the model taller, changing how closely its calculation points were spaced, and changing the rules at its top edge. Taller models had hotter outer air on average. One top-edge rule that lets disturbances leave without bouncing back helped the model stay hot longer. These were computer tests, not measurements of the Sun. They show that how scientists build a model can change what it does.

Investigation of an X-class Flare and Quasi-Periodic Pulsations in NOAA AR 13842 using SDO, Aditya-L1 and Solar Orbiter

Pawan Kumara, Sanjay Kumara, Sushree S. Nayak+3 more

AstronomerThe study examines the X9.0 flare SOL2024-10-03T12:08 in NOAA AR 13842 using SDO, Aditya-L1 and Solar Orbiter observations, together with a sequence of non-force-free-field extrapolations. Observed QPP periods are approximately 2 and 6 minutes in EUV, 7 minutes in UV and 1 minute in X-rays. The extrapolations reconstruct a flux rope, a sheared arcade and an enveloping hyperbolic flux tube (HFT), with the rope gaining twist as it rises toward a torus-unstable region, making it a candidate for eruption. The authors interpret arcade footpoint motion as generating current associated with the initial sigmoidal brightening and bringing non-parallel field lines closer beneath the rope. They propose recurrent arcade reconnection to explain the rope's ascent, increasing twist and parallel ribbons, and HFT reconnection to explain remote and quasi-circular ribbons. Repeated reconnection in both locations is a speculative explanation for the QPPs, not an established causal result.

PublicObservations from three solar missions captured a powerful X9.0 solar flare on October 3, 2024, with complex bright patches and ribbons. Its brightness pulsed on different timescales: about 2 and 6 minutes in extreme ultraviolet light, 7 minutes in ultraviolet light and 1 minute in X-rays. To investigate the magnetic structure behind the flare, the researchers reconstructed the Sun's magnetic field. Those reconstructions indicate a twisted bundle of magnetic field rising and becoming more twisted, alongside an arch-shaped magnetic structure and a surrounding region with a distinctive magnetic geometry. The researchers propose that repeated rearrangements of magnetic connections in these structures could explain the bright ribbons, help the twisted bundle rise and produce the pulses. These explanations remain interpretations rather than directly demonstrated causes.

Young explorerScientists watched a very strong burst of light on the Sun. It got brighter again and again, with some flashes coming about a minute apart and others several minutes apart. They used a model to work out what the Sun's invisible magnetic lines might look like. The model showed a twisted bundle rising and getting more twisted. They think magnetic lines changing their connections again and again might explain the flashes and bright stripes, but they have not shown for sure that this is what made them.

The formation of merging black holes via stable mass transfer in massive binary stars

Xiao-Tian Xu, Norbert Langer, Jakub Klencki+2 more

• High Energy Astrophysical Phenomena
• General Relativity and Quantum Cosmology

AstronomerThis study models the stable mass transfer channel for isolated massive binaries using detailed evolution calculations from the zero-age main sequence to black hole formation, skipping only the rapid late burning stages. The models include internal differential rotation and interstellar transfer of mass and angular momentum. They find that the evolving mass and chemical structure of the accretor strongly affects subsequent reverse mass transfer. The resulting black hole spins and mass ratios fall within the observed regime for gravitational-wave sources with primary black hole masses of 10–25 solar masses. Given the many known progenitor binaries for this channel, the authors infer that it likely contributes to the observed gravitational-wave population; they do not establish its contribution quantitatively.

PublicMost pairs of massive stars are not expected to produce two black holes that eventually merge. This study uses detailed computer models to investigate one possible route, in which the stars exchange matter through stable mass transfer. The calculations track their evolution to black hole formation, apart from brief late stages of nuclear burning. They suggest that changes inside the star receiving matter are crucial when material later flows back toward its companion. The modeled black hole spins and relative masses match the range observed in gravitational-wave sources whose heavier black hole has 10–25 times the Sun’s mass. Because many potential stellar starting systems are known, the researchers conclude that this route likely produces some observed sources, though they do not determine how many.

Young explorerSome big stars live in pairs and can pass material to each other. Scientists used computer models to explore how some pairs could become two black holes that later crash together. The models suggest that changes inside the star getting material matter when it later gives material back. The black holes in the models spin and have sizes compared with each other that fit what scientists have found from ripples in space. The researchers think this could explain some black hole pairs, but not all of them.

Confidently Wrong: Why Ignoring Binaries Biases IMF Inference at Large Sample Sizes

Anna L. Rosen

• Astrophysics of Galaxies

AstronomerSynthetic tests quantify when unresolved binaries make single-star inference of the high-mass IMF slope α “confidently wrong”: the negative systematic bias remains constant with sample size N, while posterior credible intervals shrink as N^−1/2. Across four environments spanning α = 1.60–2.30, idealized mass addition, a formal upper bound on unresolved-system mass overestimation, produces bias magnitudes of 0.054–0.086, exceeding the full 95% credible-interval width at N ≈ 5,000–10,000. Idealized luminosity addition using the ZAMS mass–luminosity relation yields smaller biases of 0.011–0.021 and crossover at N ≈ 75,000–150,000. A binary-aware mixture likelihood marginalizing over the Moe & Di Stefano (2017) binary population model recovers the true slope in the synthetic tests presented. These are idealized tests, not measurements of biases in individual published studies; the authors infer that unmodeled binaries could plausibly cause slope errors of order 0.01–0.09 and argue for binary-aware inference in large stellar samples.

PublicTwo stars too close together to distinguish can be mistaken for one, distorting estimates of how common massive stars are at birth. This study uses synthetic star samples to show why collecting more data does not automatically solve that problem: statistical uncertainty shrinks, but the error from ignoring paired stars persists. Under two idealized ways of combining a pair’s apparent contribution, the inferred high-mass distribution becomes confidently incorrect at sample sizes ranging from roughly 5,000–10,000 to 75,000–150,000. Those thresholds depend on the modeling assumptions and are not universal survey limits. A method that explicitly accounts for paired stars recovers the correct distribution in the tests presented. The authors argue that such modeling will likely be necessary as surveys deliver larger samples; they do not establish the actual error in any particular published measurement.

Young explorerImagine two stars so close together that they look like one. If we count them as one star, we can get the wrong idea about how many big stars are born. Researchers tried this with pretend groups of stars. Counting more and more stars made their answers look more certain, but did not fix the mix-up. In their tests, a method that allowed for hidden star pairs found the right answer. Real stars may be more complicated than these pretend groups.

The Kick Velocities of Neutron Stars in Binary Systems

Paul Disberg, Ilya Mandel, Ryosuke Hirai

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena

AstronomerThe authors compare observed orbital periods, eccentricities, and systemic kick estimates for five classes of neutron-star binaries with COMPAS population-synthesis predictions under different natal-kick prescriptions. Kicks calibrated to young isolated pulsar velocities reproduce most properties of Gaia neutron-star binaries, low-mass X-ray binaries, and neutron-star–white-dwarf binaries, although matching Gaia eccentricities requires a small contribution from additional “rocket” kicks. High-mass X-ray binaries and double neutron stars instead favor substantially reduced natal kicks. The apparent eccentricity–systemic-kick correlation in double neutron stars can be explained by Blaauw kicks if natal kicks are approximately 10 km/s or less. The model fits low-metallicity Gaia systems, high-eccentricity Be X-ray binaries, and double-neutron-star mass estimates poorly; alternative explanations remain hypothetical. Reduced natal kicks for neutron stars formed with high-mass companions offer a relatively consistent, but incomplete, interpretation.

PublicNeutron stars receive a kick when they form in supernova explosions. This study compares the orbits and estimated kicks of neutron stars in several kinds of paired-star systems with computer simulations. Kick models based on the speeds of young, isolated pulsars reproduce most properties of three groups, though the Gaia systems require a small extra “rocket” kick contribution to explain their orbital shapes. High-mass X-ray binaries and pairs of neutron stars instead show evidence for much smaller birth kicks. The authors suggest that neutron stars born beside high-mass companions receive weaker kicks. This is a model-based interpretation, not a direct measurement of those birth kicks, and it does not explain all the observations well.

Young explorerWhen a neutron star is born in an exploding star, it gets a push. Scientists compared real pairs of stars with computer-made ones to learn how strong those pushes might be. Their comparisons suggest that neutron stars born beside very heavy partner stars get smaller pushes. But the computer models do not match everything scientists see, so this explanation is not the whole story.

Temperature effects on white dwarfs in modified gravity

Sofía Vidal, Aneta Wojnar, Laur Järv

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study numerically examines how a finite-temperature equation of state affects white-dwarf equilibrium structure in massive Brans–Dicke theory and in models with symmetron and dilaton screening mechanisms. The calculations yield mass–radius relations, effective gravitational constants, and radial profiles of the scalar field, pressure, and metric. Within the models studied, nonzero temperature increases the stellar radius while leaving the total mass essentially unchanged. The authors also discuss the interplay among effective gravitational strength, central density, and radius; these are numerical model findings, not reported observations.

PublicThe researchers used numerical models to explore how temperature changes the structure of white dwarfs under alternative descriptions of gravity. They calculated the stars’ masses and sizes, along with how gravity and conditions inside the stars vary. In the models studied, allowing a nonzero temperature makes a white dwarf larger while leaving its mass almost unchanged. The study also examines how the strength of gravity, the density at the star’s center, and its size are connected. These findings come from theoretical calculations rather than observations of stars.

Young explorerScientists used computer calculations to study stars called white dwarfs, trying different ideas about how gravity works. In their models, including warmth made a star bigger without changing how much matter it had by very much. This is what their calculations showed, not something they watched happen to a real star.

A Misaligned Debris Disk relative to the Host Star CPD-72 2713 from JWST/NIRCam Imaging

Jingwen Zhang, Maxwell A. Millar-Blanchaer, Kellen Lawson+17 more

• Solar and Stellar Astrophysics

AstronomerJWST/NIRCam provides the first scattered-light images of the debris disk around CPD-72 2713, a 24 Myr-old member of the β Pic moving group, revealing a nearly face-on disk. Forward modeling gives radii of 55.4 (+3.0/−3.2) AU in F210M and 39.1 (+4.6/−2.6) AU in F444W, significantly smaller than thermal-emission radii from ALMA and Herschel/PACS. The authors interpret this difference as scattered light tracing inner disk regions and thermal emission tracing outer regions. Combining the TESS rotation period with spectroscopic projected rotational velocity yields a stellar inclination of 47.2° (+11.1°/−7.7°, 1σ). The inferred minimum star–disk mutual inclinations are 27.6° (+11.5°/−8.2°) and 27.3° (+12.5°/−10.9°), respectively, at 1σ. Both exceed 10° at the 95% credible level, suggesting misalignment with the stellar equatorial plane, although variation among published disk inclinations and potential systematic uncertainties may affect that probability. Imaging excludes planets down to 0.3 Jupiter masses at separations of 0.5 arcseconds and beyond, disfavoring—but not eliminating—a planetary explanation for the misalignment.

PublicNew James Webb Space Telescope images show a nearly face-on ring of debris around the 24-million-year-old star CPD-72 2713. Models fitted to images in two filters place the disk’s characteristic radius at about 55 and 39 times the Earth–Sun distance. These are smaller than sizes measured from the disk’s heat emission, suggesting that reflected starlight and heat emission reveal different regions. By combining the star’s rotation measurements with the disk images, the researchers infer that the disk may be tilted relative to the star’s equator. Their analysis gives a 95% probability that the minimum tilt exceeds 10 degrees in both filters, but differences among published measurements and possible systematic errors could affect this estimate. The images also rule out planets down to about 0.3 Jupiter masses at angular distances of 0.5 arcseconds and farther from the star. This makes a planet a less favored explanation for the possible tilt, without ruling it out entirely.

Young explorerScientists used the James Webb Space Telescope to take pictures of a ring of dusty leftovers around a young star. We see the ring almost face-on, like looking down at a plate. The pictures and measurements suggest that the ring may be tipped compared with the star’s middle, but the scientists are not completely sure. They also looked for planets big enough and far enough from the star for their pictures to reveal. They did not find those planets, so a planet may be a less likely reason for the possible tip.

Orbital Stability of Apsidally Aligned Planetary Systems

Gabriel Teixeira Guimarães, Eiichiro Kokubo

AstronomerDirect N-body simulations separate eccentricity into a systematic component shared by all planets and a random component controlling apsidal alignment. The simulations find that random eccentricity drives neighboring pairs into mean-motion resonance overlap, producing chaotic evolution and destabilization. Systematic eccentricity, by contrast, has little effect on instability timescales over a wide range because apsidal alignment preserves nearly fixed relative orbital orientations; initially aligned systems are nearly as stable as initially circular ones. This protection fails above a critical systematic eccentricity, where coherent apsidal precession breaks down, differential precession develops, and instability timescales fall rapidly. The results motivate analytical stability criteria that account for coherent apsidal precession rather than eccentricities alone.

PublicComputer simulations suggest that the stability of closely packed planetary systems depends not just on how stretched their orbits are, but also on whether those orbits keep pointing in nearly the same direction relative to one another. In the simulations, a random component of orbital stretching pushes neighboring planets into overlapping orbital resonances, leading to chaotic motion and instability. A shared component of stretching has much less effect while the orbits remain aligned: systems that begin aligned are nearly as stable as systems that begin with circular orbits. That protection has a limit. Above a critical amount of shared stretching, the orbits stop turning together and instability develops much sooner. These simulation results point toward improved ways to assess planetary stability; they are not observations of actual planetary systems.

Young explorerScientists used a computer to study planets moving on oval paths close together. In their simulations, planets whose oval paths kept pointing the same way stayed almost as stable as planets on round paths. When the paths did not line up well, the planets could move in a mixed-up way and become unstable. But lining up did not always protect them: if the ovals became too stretched, they stopped turning together and became unstable much sooner.

Dust Activity Evolution and Constraints on Icy Grains in the Interstellar Comet 3I/ATLAS

Bin Liu, Xiaoping Zhang, Xiaodong Liu+1 more

• Astrophysics of Galaxies

AstronomerZwicky Transient Facility observations trace the dust evolution of interstellar comet 3I/ATLAS across perihelion. Before perihelion, the effective scattering cross section followed C_e ∝ r_H^−γ, with γ increasing from 1.63 ± 0.14 to 1.88 ± 0.34 with aperture size within the inner 20,000 km. After perihelion, γ decreased from 2.44 ± 0.09 at 5,000 km to 1.54 ± 0.09 at 80,000 km, indicating more rapid fading of the inner coma. Adopted grain-size and residence-time assumptions imply dust mass-loss rates of approximately 123–203 kg/s before and 596–1,412 kg/s after perihelion. Morphology-derived sunward and effective perpendicular velocity scales are (190 ± 3)a_μm^−1/2 and (79 ± 6)a_μm^−1/2 m/s, respectively. Post-perihelion surface-brightness slopes temporarily steepened to about −2.7 in late November and early December, coincident with an unusually blue outer coma; by January, slopes approached −1.5 and the blue anomaly had disappeared. The fading component has a projected destruction length of approximately 64,000–72,000 km. Thermophysical sublimation calculations find this scale and the approximate water production near the main imaging epoch consistent with initially 5–10 μm icy grains containing about 0.1% absorbing carbonaceous material. This supports, but does not establish, a short-lived, volatile-bearing icy-grain contribution to the early post-perihelion coma.

PublicObservations with the Zwicky Transient Facility followed how the dusty cloud around interstellar comet 3I/ATLAS changed before and after its closest approach to the Sun. After that passage, the inner cloud faded faster than the outer cloud. In late November and early December, the outer cloud was also unusually blue, and its brightness dropped more sharply with distance from the comet. By January, the blue feature had disappeared and the brightness profile had become less steep. Calculations suggest that small icy grains, about 5–10 micrometers in size and containing a tiny amount of carbon-rich material, could explain the fading component and be consistent with the approximate water production. The observations therefore suggest a temporary population of icy grains, rather than proving that such grains were present. Estimates of dust loss also depend on assumptions about grain sizes and how long dust remains in the measured regions.

Young explorerScientists watched a comet from beyond our solar system as it went around the Sun. Its dusty cloud changed: the outside looked extra blue for a while, but that blue look later went away. Their calculations suggest that tiny bits of ice mixed with dust may have helped make the changing cloud. That is a possible explanation, not something they know for sure.

Post-perihelion dust activity and a candidate icy-grain halo in long-period comet C/2023 A3 (Tsuchinshan--ATLAS)

Bin Liu, Xiaoping Zhang, Xiaodong Liu+1 more

AstronomerArchival Zwicky Transient Facility imaging of C/2023 A3 (Tsuchinshan–ATLAS) from 15 February to 26 May 2025 probes post-perihelion dust activity and a candidate icy-grain halo. Within a fixed projected aperture radius of 40,000 km, the comet faded from 12.86 to 14.77 mag as its heliocentric distance increased from 2.64 to 3.90 au, interrupted by two brief brightenings. The inferred effective dust cross section declined by a factor of 2.4, scaling as r_h^-3.1; the derived dust production rate scaled as r_h^-3.41, consistent with a contribution from water-ice-driven activity. Extrapolation to perihelion gives a model-dependent cumulative dust loss of 3.0 × 10^11 kg, equivalent to approximately 1.4 m of global erosion for an assumed 5.9 km nucleus radius. Shallower-than-steady-state coma profiles suggest radial changes in dust distribution or scattering, possibly from delayed aggregate fragmentation. A persistent central brightness excess and less-red inner-coma colors support, but do not establish, an icy-grain halo. Among the models explored, approximately 10-micrometer grains with approximately 0.1% carbon reproduce halo radii during enhanced activity on 21–25 February, with modeled lifetimes of 2.8–3.2 × 10^5 s. No fixed grain size and composition explains the full evolution; increasing carbon content is a possible explanation for the broad halo-radius trend, potentially reflecting near-surface refractory enrichment.

PublicImages taken from February to May 2025 show that comet C/2023 A3 (Tsuchinshan–ATLAS) generally faded as it moved farther from the Sun after its closest approach, although it briefly brightened twice. The researchers inferred that its dust output declined in a way consistent with some activity being powered by water ice turning into gas. They also found a persistent bright central region whose light was less red than that of the surrounding coma, the cloud around the comet. These features are consistent with a halo of icy grains, but do not prove that interpretation. Models using ice grains about 10 micrometers in radius with a small carbon fraction matched the halo's size during a February episode of enhanced activity. However, no single grain size and composition explained all of the halo's changes. An increasing carbon fraction could help explain the overall trend. Extrapolating the dust-production model back to closest approach gives an estimated total dust loss of 300 billion kilograms, but that estimate depends on the model.

Young explorerAfter this comet passed closest to the Sun, pictures showed it getting dimmer as it traveled away, with two quick brightenings along the way. It also had an extra-bright patch near its middle. Scientists think tiny icy specks might help make that patch, but they are not sure. They tried models of different specks, and some matched the patch at one time, but no single kind explained all its changes.

Thermodynamics of Viscously Heated Circumplanetary Disks

Zhuo Chen, Jing Yang, Xue-Ning Bai

AstronomerThis theoretical study develops an axisymmetric viscous radiation-hydrodynamic model of circumplanetary disks, incorporating α-viscosity, free-fall mass infall, and boundary-layer accretion. Simulations with Guangqi use flux-limited diffusion; eight of nine runs reach quasi-steady states with self-consistent energy conversion and transport. Simulated disks become thicker with increasing accretion rate and thinner with increasing planet mass. The boundary layer substantially affects inner-disk angular momentum transport and thermodynamics, producing high-entropy accreted gas with s_real > 11 k_B m_H^-1 and potentially causing dust sublimation. A supersonic, low-angular-momentum flow at high elevations carries 2–5% of the total accretion rate. For planets of roughly 3 Jupiter masses or more, the authors predict that its impact on the planetary surface could produce observable Hα emission if the shock accretion rate is at least approximately 5.5 × 10^-8 Jupiter masses per year; this is not an observational detection.

PublicDisks of gas around growing giant planets help shape both the planets and their moons, but they remain poorly understood. This study models these disks with computer simulations rather than observations. Eight of nine simulations settle into approximately steady conditions. The modeled disks are thicker when gas arrives faster and thinner around more massive planets. The region where the disk meets the planet strongly affects how gas moves and heats up, potentially making it hot enough to vaporize dust. The simulations also reveal a fast stream high above the disk that carries 2–5% of the incoming gas. The authors suggest that, for sufficiently massive planets and sufficiently strong impacts, this stream could produce detectable hydrogen light when it hits the planet. That light is a prediction, not a reported detection.

Young explorerA growing giant planet can have a spinning disk of gas around it. Scientists used a computer to pretend how that gas moves and gets hot. In their computer models, some gas rushed toward the planet from high above the disk. They think that gas might make a special kind of light when it hits a big enough planet, if enough gas hits it. They have not reported seeing that light in this study.

A first look at the protoplanet WISPIT 2 b with VLTI/GRAVITY+

GRAVITY+ Collaboration, K. Abd El Dayem, R. Abuter+97 more

AstronomerNew VLTI/GRAVITY+ observations independently confirm WISPIT 2 b, a roughly 5 Myr-old protoplanet, as a self-luminous, point-like companion within the gap of its host’s transitional disk, at about 60 au. The companion is detected at an angular separation of approximately 322 mas. An updated orbital fit incorporating high-precision GRAVITY+ astrometry favors moderate eccentricity. Analysis of the medium-resolution K-band spectrum together with new VLT/SPHERE and literature photometry indicates an effective temperature of 900–1300 K, with a slight preference for cloudy atmospheric models over pure blackbody emission. No circumplanetary disk is spatially resolved; the observations instead constrain its possible extent with an upper limit. Higher signal-to-noise or longer-wavelength observations are needed to characterize the atmosphere and assess the presence of circumplanetary dust through its thermal emission.

PublicNew observations confirm that WISPIT 2 b, a planet still forming at an age of about five million years, emits its own light and lies in a gap in the disk surrounding its star, about 60 times the Earth–Sun distance away. Measurements of its position favor a moderately elongated orbit, although this remains an orbital-fit result rather than a fully traced path. Its light suggests an effective temperature of 900–1300 kelvin and slightly favors models of a cloudy atmosphere over a simple idealized heat emitter. The observations do not resolve a disk around the planet itself, but they set an upper limit on how large such a disk could be. More sensitive observations or measurements at longer wavelengths are needed to better understand the atmosphere and look for heat emitted by dust around the planet.

Young explorerAstronomers studied a very young planet called WISPIT 2 b that is still forming. It gives off its own light and sits in a gap in a big disk around its star. Its light gives a small hint that its air may have clouds, and measurements suggest its path around the star may be a little stretched rather than round. The pictures show the planet as a tiny dot. They cannot show whether it has its own little disk of dust, so astronomers need better observations to learn more.

WALTzER: Wide-band Atmospheric Laboratory for Transiting Exoplanet Research

A. G. Sreejith, L. Fossati, M. Lendl+81 more

• Instrumentation and Methods for Astrophysics
• Solar and Stellar Astrophysics

AstronomerWALTzER is an ESA F3 mission candidate intended to investigate exoplanet atmospheric origins, evolution, and connections between lower and upper atmospheric layers while characterising stellar and planetary variability simultaneously. The concept uses a 35 cm Cassegrain telescope feeding co-aligned NUV (240–325 nm) and VIS (450–820 nm) spectrographs and a broadband NIR (900–1700 nm) photometer. A shared optical train is designed to minimise instrumental systematics and maximise observing efficiency. The authors describe the science drivers and instrument design, projecting atmospheric detection and characterisation for more than 30 gas-rich transiting exoplanets, with additional Solar System and Galactic applications. These are proposed capabilities, not reported atmospheric measurements.

PublicWALTzER is a proposed space mission to study the atmospheres of planets outside our Solar System as they pass in front of their stars. It would measure ultraviolet and visible spectra alongside near-infrared brightness, observing the planets and their changing stars at the same time. The aim is to understand how planetary atmospheres form and evolve, and how their lower and upper layers connect. Its planned 35-centimetre telescope could support atmospheric studies of more than 30 gas-rich planets. The paper presents a mission and instrument design, not results from an operating telescope.

Young explorerWALTzER is an idea for a space telescope that would watch planets move in front of their stars. It would look at different kinds of light at the same time to help scientists learn about the gases around those planets and how they change. It would also watch how the stars change. This paper describes the plan, not things the telescope has already found.

Time-reversible timestepping in many-body planetary systems

David M. Hernandez, Tenri Jinno, Junichiro Makino

• Instrumentation and Methods for Astrophysics
• Chaotic Dynamics

AstronomerThe authors develop MTR, an almost exactly time-reversible direct N-body integrator that assigns each planetary pair its own evolving timestep, adapting on the fly without a global timestep. This targets the inefficiency and possible under-resolution of fixed-step simulations during close encounters, scattering, and collisions. They provide a C implementation and report no energy-error drift in their tests. For systems with up to 975 particles, MTR agrees with the orbital distributions obtained using GPLUM in direct Hermite mode while running up to two orders of magnitude faster, although GPLUM is not optimized for that mode. In the default configuration, MTR matches or exceeds the speed of GPLUM's optimized tree mode, with speedups up to an order of magnitude despite using direct rather than approximate force calculations. These are simulation benchmarks; the abstract does not establish symplecticity or exact time reversibility.

PublicFollowing planets through close encounters in a computer simulation requires very small time steps, but using those small steps everywhere can waste computing time. The authors introduce MTR, a simulation method that lets each pair of planets use its own changing time step. It is designed to be almost exactly reversible in time, and its tests showed no persistent drift in energy error. In comparisons involving up to 975 simulated bodies, MTR produced orbital distributions consistent with those from another code, GPLUM, in its direct-calculation mode and ran up to 100 times faster. GPLUM is not optimized for that mode. Against GPLUM's optimized mode, which uses approximate forces, MTR's default setup was as fast or up to 10 times faster. These findings describe computer tests, not observations of real planetary systems.

Young explorerScientists made a new way for a computer to pretend that planets are moving around. When two planets need a closer look, the computer can follow them in tiny steps without making every pair take the same tiny steps. In their tests, this new way was sometimes much faster than another program. One comparison also gave similar patterns of planet paths. These were pretend planets inside a computer, not new planets found in space.

A Sample of Thick-Disk Stars Hosting Hot Jupiters

Victoria DiTomasso, Samuel W. Yee, Romy Rodriguez Martinez+6 more

• Astrophysics of Galaxies
• Solar and Stellar Astrophysics

AstronomerA homogeneous analysis of 268 confirmed and candidate transiting hot-Jupiter hosts with 4800 K < Teff < 6200 K combines TRES spectroscopy, Gaia/2MASS/WISE photometry, and Gaia astrometry to derive stellar properties and classify hosts into low-[alpha/Fe] thin-disk, high-[alpha/Fe] thick-disk, or chemically intermediate populations. Two confirmed hot Jupiters, WASP-81 b and TOI-5322 b, and three candidates, TOI-3118.01, TOI-2728.01, and TOI-5781.01, orbit newly recognized high-alpha thick-disk members. Among confirmed planets, both high-alpha planets and 8 of 11 intermediate-population planets have masses below the low-alpha population's median. No confirmed high-alpha or intermediate-population planet has a period below 2.7 days, compared with 22% of the low-alpha sample. These are tentative population differences, not established environmental effects; possible explanations include formation, evolution, and differing stellar properties. The authors present the catalog as the largest chemically identified sample of confirmed and candidate thick-disk hot-Jupiter hosts. These systems, older than 8 billion years, may help constrain environmental influences on formation and long-term orbital evolution.

PublicResearchers analyzed 268 stars hosting confirmed or possible hot Jupiters—giant planets that orbit close to their stars—and used the stars' chemical compositions to identify their Milky Way populations. They found that two confirmed planets and three planet candidates orbit previously unrecognized members of the chemically distinct thick disk. In their sample, confirmed planets around thick-disk stars and stars with intermediate chemistry show hints of lower masses and a lack of the shortest orbits compared with planets around thin-disk stars. Neither thick-disk planet, nor any confirmed planet in the intermediate group, takes less than 2.7 days to orbit, whereas 22% of the thin-disk planets do. With only two confirmed thick-disk planets, these patterns remain tentative. They could reflect differences in planet formation, changes over time, or differences between the stars themselves. The ancient systems, older than 8 billion years, offer a way to investigate how giant planets form and how their orbits change over long periods.

Young explorerSome giant planets travel very close to their stars. Scientists studied 268 stars with these planets or possible planets. By looking at what the stars are made of, they found that two known planets and three possible ones belong to a very old group in our galaxy. There are hints that planets in this group and a similar group may be less heavy and take longer to go around their stars than planets in another group. But there are too few known planets in the very old group to be sure. Studying them could help scientists learn how planets are made and how their paths change as they grow old.

A New Method for Constraining 3D Exoplanet Atmospheres: Application to WASP-94A b's Panchromatic Spectrum

Sagnick Mukherjee, Luis Welbanks, Guangwei Fu+2 more

• Instrumentation and Methods for Astrophysics

AstronomerThe authors introduce a limb-resolved atmospheric retrieval framework based on the wavelength-dependent apparent mid-transit time shift rather than separate leading- and trailing-limb transit depths. Conventional limb-depth estimates are strongly anti-correlated; ignoring these correlations can bias retrieved molecular abundances by 3σ. The time-shift spectrum can be extracted from existing light curves using a spherically symmetric transit model and is uncorrelated with the spherically averaged transit depth. Jointly fitting these two spectra with separate atmospheric columns for the two limbs, the authors demonstrate approximately 30–50-fold lower abundance mean squared error than the next-best alternative tested and approximately 3–6-fold better abundance precision. Applied to WASP-94A b using NIRISS/SOSS and NIRSpec/G395H observations spanning 0.8–5 μm, the framework finds an aerosol-obscured morning limb throughout that range and evening-limb constraints on H2O, CO2, CO, and H2S. The retrieved limb-to-limb temperature difference is 415 ± 58 K at 1 mbar. The analysis yields [M/H] = +0.32 ± 0.11 and C/O = 0.724 ± 0.013, consistent with the host star.

PublicThe two edges of a planet crossing in front of its star can reveal different atmospheric conditions, but separating their signals is difficult. This study presents a method that uses tiny, wavelength-dependent shifts in the apparent midpoint of the crossing, together with the amount of starlight blocked. The authors demonstrate that this approach reduces errors and improves precision in inferred gas abundances compared with alternative methods; conventional analyses can give biased answers if they ignore linked uncertainties. Applying the method to observations of WASP-94A b, they find that aerosols obscure its morning edge across the observed wavelength range, while its evening edge provides information about water, carbon dioxide, carbon monoxide, and hydrogen sulfide. Their analysis infers a temperature difference of 415 ± 58 kelvin between the edges at a specified atmospheric pressure. The inferred overall enrichment in heavier elements and carbon-to-oxygen ratio are consistent with those of the host star.

Young explorerWhen a planet passes in front of its star, some starlight travels through the air around its edges. Scientists tried a new way to read that light by looking at tiny changes in when the planet seems to be halfway across the star. For a planet called WASP-94A b, their study finds that one edge is hidden by haze, while the other lets them learn about gases, including water vapor. They also work out that the two edges have different temperatures. The new method helps them separate the clues from each edge more accurately.

Identifying deformed exoplanets with JWST and Ariel: A target selection metric for phase curve observations

Vanesa Ramirez, Yamila Miguel, Billy Edwards+2 more

• Instrumentation and Methods for Astrophysics

AstronomerThis study assesses the prospects for constraining hot-Jupiter fluid Love numbers through full-orbit phase curves with JWST and the future Ariel mission. The authors introduce a deformation metric, D, combining expected tidal deformation with anticipated photometric signal-to-noise, and apply it to the Ariel target list. WASP-33 b, WASP-76 b, and HAT-P-32 b rank as the most favourable targets currently lacking Love number measurements. End-to-end retrieval simulations for WASP-76 b forecast uncertainties in h₂f of approximately 0.09 from one continuous JWST phase curve and 0.18 from one Ariel visit. These are simulated precisions, not new measurements; the authors argue they would likely provide meaningful constraints on internal density distributions and help distinguish competing interior models.

PublicA giant planet orbiting close to its star can be pulled out of a round shape by the star’s gravity. How much it deforms offers clues to how matter is distributed inside it. This study explores whether brightness measurements taken throughout an orbit with JWST or the future Ariel mission could reveal that response. A new ranking method identifies WASP-33 b, WASP-76 b, and HAT-P-32 b as especially promising planets that do not yet have measurements of this response. Simulations using WASP-76 b suggest that one continuous JWST observation covering an orbit, or one Ariel visit, could measure it precisely enough to help test different models of the planet’s interior. These are forecasts, not actual measurements, and their usefulness for distinguishing interior models remains a likely prospect rather than an established result.

Young explorerA star’s gravity can stretch a nearby giant planet so it is not perfectly round. How much it stretches can give scientists clues about what is deep inside. The scientists used computer tests to explore whether the JWST telescope and a future telescope called Ariel could spot this by watching a planet’s light as it goes around its star. Their tests suggest this could work well for a planet called WASP-76 b, but they have not measured its stretching this way yet.

Singles in Disguise: Kepler's Low-SNR Single-Transiting Systems as Incompletely Detected Multis

Daniel A. Yahalomi, David Nesvorny, David Kipping+2 more

• Instrumentation and Methods for Astrophysics

AstronomerKepler systems with one detected transiting planet show an excess of low-signal-to-noise detections relative to systems with multiple detected transiting planets. Using ExoMOD population synthesis and the Kepler DR25 catalog, the authors show that a shared parent population can explain this difference: detected multis have shorter mean orbital periods and therefore higher mean detection SNR. Detecting several planets favors compact architectures, while longer-period, lower-SNR planets preferentially appear as singles. In this explanation, most singles are intrinsically multiplanet systems with undetected companions. The authors attribute the low-SNR excess to transit geometry and period-dependent detection sensitivity, without requiring false positives or a distinct population of intrinsically single or highly inclined systems. This does not establish that false positives or distinct populations are absent.

PublicKepler found many stars with just one detected planet passing in front of them, and these detections tended to have weaker signals than those in systems with several detected planets. A study combining simulated planetary populations with Kepler’s catalog offers an explanation that does not require two separate kinds of planetary systems. Finding several planets favors closely packed systems with shorter orbits and stronger detection signals. Planets on longer orbits are more likely to be the only ones detected around their stars. In this explanation, most apparent single-planet systems contain other planets that Kepler missed. False detections or a separate planetary population are not needed to explain the weak-signal excess, though the study does not rule them out.

Young explorerKepler watched for planets passing in front of stars. Sometimes it spotted just one planet, with a faint signal. Scientists used computer models and Kepler’s findings to explain why: other planets could be there but go unseen. One spotted planet does not always mean one planet all alone.

LSST and Keck characterization of outer Main Belt comet P/2026 N2

Bryce Bolin, Leo Alcorn, Max Brodheim+5 more

AstronomerOptical observations characterize P/2026 N2 on a low-inclination outer Main Belt orbit (a=3.07 au, e=0.21, i=2.25 degrees). LSST and Keck/LRIS imaging show active morphology over 102 days spanning perihelion. Keck colors within a projected radius of approximately 1,000 km are consistent with nearly neutral B/C-complex reflectance. Phase-corrected dust-brightness measures are comparable between Keck and LSST, and geometry-corrected aperture photometry is consistent between July and October, supporting sustained observable activity compatible with prolonged or recurrent dust production. Archival DECam imaging recovers the object in 2021 but does not establish its activity state. A 5,000-particle forward dynamical integration retains a concentrated outer Main Belt core over 50 Myr. Volatile sublimation, possibly involving water ice, is proposed as the driver of near-perihelion activity, not established by the observations.

PublicComet P/2026 N2 travels in the outer part of the main asteroid belt. Telescope images showed signs of activity over 102 days around its closest approach to the Sun. Its measured brightness, after corrections for viewing geometry, was consistent between July and October, supporting activity sustained by prolonged or repeated dust production. An older image shows the comet in 2021, but cannot establish whether it was active then. Separately, computer simulations retained a concentrated group of modeled orbits in the outer asteroid belt for 50 million years. The researchers suggest that ice turning into gas near the Sun could sustain the activity, possibly involving water ice, but this explanation remains unconfirmed.

Young explorerThis comet travels around the Sun in a place where many asteroids live. Telescope pictures showed it looking dusty over 102 days, including when it was closest to the Sun. It may have kept making dust or made dust again and again. Scientists think sunlight might warm ice so it turns into gas and helps release dust, but they do not know yet if that is what happened.

TEMPUS: Relativistic coordinate time scales for any solar-system body from arbitrary ephemerides

Yan Seyffert, Agnès Fienga

AstronomerTEMPUS numerically evaluates the IAU 2000 post-Newtonian transformation between body-centered coordinate time TCX and Barycentric Coordinate Time TCB using positions and velocities from a chosen ephemeris. It integrates dTCX/dTCB with an order-12 Adams–Moulton predictor-corrector and supports sampled tables or Chebyshev coefficients. The tested gravitational potential includes the Sun, eight planets, Pluto, up to 343 main-belt asteroids, and 30 trans-Neptunian objects. Computational comparisons with independent solutions show planetary rate agreement with the Klioner solutions at the 10^-21 s/s level over 200 years, and the same level of agreement with the released INPOP19a TCG–TCB solution. These are agreement tests, not direct observational measurements of absolute accuracy. Including main-belt asteroids and trans-Neptunian objects shifts planetary time-scale rates at approximately 10^-18 s/s; choices of planetary and lunar ephemerides also produce differences at that level. The tool supports arbitrary ephemerides, but transformations must remain consistent with the selected ephemeris.

PublicDeep-space science and navigation require consistent ways to translate between time systems tied to different solar-system bodies. These translations depend on gravity and motion. The researchers present TEMPUS, software that calculates them using a selected set of solar-system positions and velocities. Tests against independent calculations found extremely close agreement, including planetary time-rate differences at the 10^-21 second-per-second level over 200 years. This is a comparison of calculations, not a direct measurement of clocks in space. The tests also show that including asteroids and distant objects beyond Neptune, or changing the underlying solar-system position calculations, affects the predicted time rates at the larger 10^-18 second-per-second level. TEMPUS is designed to work with different sets of those position calculations.

Young explorerKeeping time around the solar system is tricky because gravity and movement affect it. Scientists made a computer tool called TEMPUS to help translate between different ways of keeping time. They checked its answers against other calculations and found very close matches. Even small space rocks can make tiny differences in the answers.

A Vision for Little Red Dots in the Low-Redshift Universe with ALMA2040

Fengwu Sun, Xiaojing Lin, Miguel Pereira-Santaella+1 more

• Astrophysics of Galaxies

AstronomerThis feasibility study explores ALMA2040 observations of local Little Red Dots using J1025+1402 (“The Egg,” z=0.1007) as a benchmark; it reports forecasts and mock observations, not new gas or black-hole mass measurements. For an assumed molecular gas mass of 10^9 solar masses, CO(2–1) detectability depends strongly on the CO-to-H2 conversion factor. At the large values considered for low-metallicity gas, α_CO ≈ 315–725 solar masses per K km s−1 pc², detection would be very challenging with current ALMA but likely robust with ALMA2040. Its best projected resolution at this frequency, 14.6 mas or 27 pc, may also resolve the emission. Under an optimistic, SMC-like conversion assumption, mock position–velocity diagrams for a 50-hour integration suggest that a steeper central velocity structure may distinguish a 10^7-solar-mass black hole from a no-black-hole model. The study identifies potential gas-mass, depletion-time, and excitation measurements, with dynamical black-hole constraints potentially achievable for the CO-bright subset.

PublicLittle Red Dots discovered with JWST offer a view of black-hole growth, but their black-hole masses and supplies of cold gas remain uncertain. This study asks what the future ALMA2040 could learn from nearby examples, focusing on one nicknamed “The Egg.” The authors predict that ALMA2040 could detect radiation from carbon monoxide and use it to estimate the molecular gas supply, although the prediction depends strongly on how much gas corresponds to a given carbon-monoxide signal. These are forecasts, not new measurements. In an optimistic simulation of a 50-hour observation, gas motions near the center might distinguish a black hole with ten million times the Sun’s mass from a model without one. The work suggests that ALMA2040 could help measure gas supplies and how quickly they are used up, while black-hole mass constraints may be possible for the brighter carbon-monoxide sources.

Young explorerAstronomers have found little red dots in space, but they still have questions about the black holes and cold gas inside them. They used pretend observations of one called “The Egg” to see what a future telescope called ALMA2040 might find. It may be able to spot the gas and watch how it moves, giving clues about the black hole. These are possibilities to test, not things the telescope has seen yet.

Tracing small-scale structure formation through cosmic time with strong gravitational lensing: A case for a next-generation sub-millimetre/millimetre interferometer

Hannah R. Stacey, John P. McKean, Mamta Pandey-Pommier+12 more

• Cosmology and Nongalactic Astrophysics
• Astrophysics of Galaxies

AstronomerRealistic simulations indicate that a 255-element submillimetre/millimetre interferometer could detect gravitational perturbations in strongly lensed dusty star-forming galaxies from objects with masses down to at least 10^5 solar masses. This would probe the largely unexplored regime below 10^7 solar masses relevant to dark matter haloes and wandering black holes. The abstract suggests that lensing data alone may partly or entirely distinguish these populations, rather than establishing that all perturbers can be classified unambiguously. Combined with ELT characterisation of lens galaxies and the large lens samples expected from Euclid and SKA, such a facility could enable a census of these populations across cosmic time. These are simulated capabilities and future prospects, not reported detections.

PublicSmall dark matter clumps and wandering massive black holes may be too difficult to see directly, but their gravity could distort the images of distant galaxies that are already magnified by gravitational lensing. In realistic simulations, a 255-element array observing at submillimetre and millimetre wavelengths could detect such distortions from objects as light as 100,000 Suns. The distortions might also help distinguish dark matter clumps from black holes, though not necessarily without ambiguity. With additional information about the lensing galaxies from the ELT and the large samples of lenses expected from Euclid and SKA, this approach could reveal how common these hidden objects are at different times in cosmic history. No actual detections are reported here.

Young explorerSome things in space are very hard to see, like dark matter clumps and black holes wandering around. Their gravity can bend light and change how a faraway galaxy looks. Scientists tried this idea in computer pretend experiments. Those tests suggest that a big group of telescopes could spot the changes and might help tell what caused them. This is a way scientists hope to find hidden things, not a report that they have found them yet.

Probing ordered magnetic fields in galaxies across cosmic time

Jianhang Chen, Melanie Kaasinen, Enrique Lopez-Rodriguez+16 more

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena

AstronomerThis white paper outlines prospects for early-Universe magnetism with the ALMA2040 concept. Existing ALMA detections of polarised dust emission indicate ordered magnetic fields extending up to kiloparsec scales in massive star-forming galaxies at redshifts as high as z~5.6, although evidence at cosmological distances remains scarce. The authors argue that nearly tenfold improvements in sensitivity and angular resolution, together with full-polarisation capability extended to higher-frequency bands, would enable constraints on galactic dynamos, early magnetic-field strengths, links between magnetism and galaxy evolution, and dust-grain properties through polarised spectral energy distributions. They summarise angular-resolution, spectral-coverage, and sensitivity requirements and discuss synergies with next-generation telescopes; these are proposed capabilities and science goals, not new observational results.

PublicAstronomers see organised magnetic fields throughout the nearby Universe, but know much less about when these fields formed or how they changed. Recent ALMA observations of polarised light from dust indicate that large, organised fields already existed in massive galaxies forming stars in the early Universe, reaching redshifts of about 5.6. This paper makes the case for ALMA2040, a proposed upgrade offering nearly tenfold improvements in sensitivity and image detail, with expanded ability to measure polarisation at higher frequencies. The authors argue that it could help reveal how galaxies generate magnetic fields, how strong early fields were, how they relate to galaxy evolution, and what dust grains are like. These are future research goals, not findings already delivered by the proposed upgrade.

Young explorerSpace has invisible magnetic fields. Astronomers have found clues in light from dust that some faraway galaxies already had big, neatly arranged magnetic fields long ago. But they still do not know much about how those fields began or changed. This paper describes an idea to make a telescope called ALMA much better at spotting faint light and seeing small details. The authors hope it could help them learn how these fields form, how strong they are, and how they are connected to galaxies and tiny dust grains. The better telescope is a plan, not something that has already made these discoveries.

Planet forming disk populations and their connection to the environment

Thomas J. Haworth, Giovanni Rosotti, Carlo Manara+35 more

• Earth and Planetary Astrophysics

AstronomerExisting submillimetre observations, including those from ALMA, provide statistics on planet-forming disk mass reservoirs in stellar clusters out to roughly 400 pc. The authors argue that this sample is strongly biased because many stars and planets form in more massive, more distant clusters, where UV radiation, ambient gas reservoirs, and stellar density differ. They identify measurements of the disk mass distribution out to roughly 3 kpc, including nearby parts of the Sagittarius arm, as necessary to sample multiple massive clusters. They anticipate that ALMA2040's sensitivity will enable robust measurements of the distribution's slope and median, rather than only a handful of disk detections. Combining these future disk mass measurements with existing and upcoming accretion-rate measurements would yield accretion timescales, helping distinguish disk evolutionary pathways and their dependence on cluster environment. These are anticipated capabilities and scientific applications, not reported results from a new distant-cluster survey.

PublicDisks around young stars hold the material from which planets can form. Current observatories such as ALMA have measured these material supplies across nearby stellar clusters, out to about 400 parsecs. But the authors argue that this nearby view is biased: many stars and planets form in more massive clusters farther away, where radiation, surrounding gas, and crowding can affect disks differently. They describe how ALMA2040 is expected to measure disk populations out to about 3,000 parsecs, reaching several massive clusters. Instead of detecting just a few disks, it could establish how disk masses are distributed. Combining those measurements with measurements of how quickly material falls onto stars would help researchers distinguish possible ways disks evolve in different environments. The abstract presents this as a future opportunity, not an already completed survey.

Young explorerYoung stars can have disks of material around them that can make planets. Astronomers have studied many disks nearby, but many stars are born in bigger groups farther away. Those groups can have different amounts of light, gas, and nearby stars, which may change the disks. The researchers expect ALMA2040 to help them study many more of these faraway disks and compare how much material they hold. They also want to learn how fast material moves from the disks onto the stars. Together, those clues could help explain how disks change. This is a plan for future studies, not something they have finished.

Has JWST Seen Everything? Hunting for "NIRCam-dark" Dusty Star-Forming Galaxies at z ≃6 - 9 with ALMA2040

Fengwu Sun, Belén Alcalde Pampliega, Hiddo Algera+21 more

• Astrophysics of Galaxies

AstronomerALMA has identified dusty star-forming galaxies at z>6 that remain extremely faint or undetected with JWST/NIRCam, but the small, heterogeneously selected sample cannot establish their abundance or evolutionary importance. This study presents sensitivity and survey-speed calculations for a proposed blind ALMA2040 1.3-mm survey spanning z≈6–9, rather than new survey detections. A 10σ detection of a source with a dust-obscured star-formation rate of 60 solar masses per year at z=8 requires an RMS of 21 μJy per beam; at a matched 7.5-GHz normalization, ALMA2040 is projected to reach this depth about 90 times faster than current ALMA. For 100 hours on-source over approximately 0.5 square degrees, the predicted mean yield is about 16 NIRCam-dark DSFGs at 7.5<z<9, conditional on a fiducial number density of 3×10^-6 per comoving cubic megaparsec. Independent fields with deep JWST coverage would reduce cosmic variance and facilitate characterization. The expected instantaneous bandwidth of at least 512 GHz would also enable [C II] detections across a wide redshift range for redshift confirmation. The survey would test, not establish, whether these galaxies represent a rapid-growth phase linking UV-luminous systems at z>10 to massive quiescent galaxies at z≳4.

PublicALMA has found dusty galaxies forming stars in the early universe that remain extremely faint or invisible even to JWST’s NIRCam camera. Too few have been found, using too varied a set of searches, to tell how common they are or how important they were in building massive galaxies. The researchers calculate what a future blind survey with ALMA2040 could achieve. Under their assumed abundance of these galaxies, 100 hours of observations covering about half a square degree could find roughly 16 at redshifts between 7.5 and 9. This is a forecast, not a reported discovery count. Spreading the survey across separate regions already observed deeply by JWST would help limit the effect of regional differences and support follow-up studies. The survey could test whether these dusty galaxies mark a hidden burst of growth between the earliest ultraviolet-bright galaxies and later massive galaxies that had largely stopped forming stars; that connection remains a hypothesis.

Young explorerSome faraway galaxies are making stars behind lots of dust. ALMA has found some that are very hard for one of the Webb telescope’s cameras to see. Scientists have worked out how a future version of ALMA could search for more of them. They think it might find about 16 in one planned search, but that depends on how many are really out there. Finding more could help us learn whether these dusty galaxies were a hidden growing-up stage for some big galaxies. We do not know yet.

ALMA2040: Understanding the Early Assembly of Galaxies - The Formation of Star-Forming Clumps and their Role in Shaping Galaxy Evolution

Anita Zanella, Andreas L. Faisst, Rodrigo Herrera-Camus+25 more

• Astrophysics of Galaxies

AstronomerThis prospective science case presents ALMA2040 as a next-generation submillimeter facility for spatially resolved studies of giant molecular clouds (GMCs) at z>1. HST and JWST observations reveal compact star-forming clumps from Cosmic Noon to the Epoch of Reionization, reaching z≈6, but their connection to molecular gas remains unclear. The proposed facility is intended to detect individual GMCs in representative lensed and unlensed galaxies. CO and [CII] observations, complemented by dust continuum and molecular-gas kinematics, would probe gas reservoirs, physical conditions, and dynamics. Combined with JWST and ELT observations, these measurements would address how GMC properties vary with redshift and environment, how gas, dust, and young stars are spatially related, and whether clumps originate in unstable disks or disturbed systems. These are anticipated capabilities and scientific goals, not reported ALMA2040 results.

PublicHubble and James Webb telescope observations show compact clumps of star formation in distant galaxies, but astronomers do not yet understand how these clumps connect to the cold gas that supplies new stars. This abstract outlines a science case for ALMA2040, a proposed next-generation telescope facility designed to distinguish individual giant molecular clouds in distant galaxies. Measurements of gas emission, dust, and gas motion, combined with observations from other telescopes, could reveal how star-forming clouds change with their surroundings and over cosmic history. They could also help explain how clouds and stellar clumps form and survive. The abstract describes expected capabilities and questions to investigate, rather than new measurements from ALMA2040.

Young explorerStars are born in huge clouds of cold gas. Telescopes have seen little bunches of stars forming in faraway galaxies, but scientists do not yet know how those bunches fit together with the gas clouds. They want a future telescope called ALMA2040 to look closely at the clouds. It could help them learn where the gas, dust, and baby stars are and how they move. This is a plan for what scientists hope to learn, not something the new telescope has already found.

The dawn of the first galaxies

Livia Vallini, Tanio Diaz Santos, Belen Alcalde Pampliega+55 more

• Astrophysics of Galaxies

AstronomerJWST has revealed unexpectedly UV-bright galaxies at z>10, whose emission suggests rapid stellar-mass growth that challenges current assembly models. Their cold-gas reservoirs remain poorly constrained: the abstract reports that current ALMA sensitivity limits routine detections to the brightest ionized-gas tracers, such as [OIII] 88 μm, while [CII] 158 μm remains undetected beyond z≈8. The authors argue that ALMA2040 could enable systematic [CII] surveys to constrain gas fractions, depletion times, ISM conditions, enrichment, and feedback. For a simulated galaxy at z=11.3, they predict detection and spatial resolution of merging [CII]-emitting cold gas on approximately 200 pc scales in 5 hours and below 100 pc in 10 hours. Simultaneous, spectrally resolved observations of multiple lines are proposed to help disentangle density, metallicity, and radiation-field effects and map the multiphase ISM. The authors also project [OIII] detectability to z≈20. These capabilities are forecasts for ALMA2040, not observations of the first galaxies' cold gas.

PublicJWST has found unexpectedly bright galaxies from very early in cosmic history. Their ultraviolet light suggests that they built up stars rapidly, challenging current models, but the cold gas supplying that growth remains largely hidden. The authors make the case for ALMA2040, a future submillimeter facility that could measure this gas and investigate how early galaxies formed stars, accumulated metals and dust, and regulated their growth. In a simulation of one early galaxy, the proposed facility could reveal merging cold-gas structures about 200 parsecs across in five hours, with finer detail in longer observations. Measuring several emission lines together could help distinguish the effects of gas density, chemical enrichment, and radiation. The authors also predict that emission from ionized oxygen could be detected as far back as a redshift of about 20. These are projected capabilities, not discoveries already made by ALMA2040.

Young explorerJWST has spotted very bright galaxies from when the universe was young. Their light suggests they were making lots of stars quickly, but the cold gas they need to make those stars is hard to see. Scientists want a future telescope called ALMA2040 to look for that gas. They tested the idea with a pretend galaxy in a computer, and the test suggests the telescope could show clumps of cold gas coming together. That could help us learn how the first galaxies grew. The new telescope has not made these pictures yet.

Understanding cosmic explosions

Karri I. I. Koljonen, Tomek Kamiński, Anna Y. Q. Ho+11 more

• High Energy Astrophysical Phenomena

AstronomerThis science and capability outlook argues for ALMA2040 follow-up of millimeter transients, including SNe, TDEs, novae, stellar mergers and electromagnetic counterparts to GW sources. It summarizes discoveries indicating that informative phases of shock interaction, particle acceleration and jet formation occur above traditional centimeter-wave frequencies, where synchrotron self-absorption weakens and thermal, nonthermal and dust components can be disentangled. Upcoming wide-field millimeter surveys are expected to reveal a new population of short-lived transients, but with coarse localization and limited spectral characterization. The authors identify improved sensitivity, wide instantaneous spectral coverage, rapid response, sub-arraying, polarimetry and extended baselines as capabilities needed to turn these discoveries into physical constraints. The abstract presents scientific priorities and future capability requirements, not new measurements or demonstrated ALMA2040 performance.

PublicMillimeter-wavelength light can reveal important stages of cosmic explosions and other short-lived events that are harder to study at longer radio wavelengths. The authors describe how past discoveries have highlighted its value for studying shocks, accelerated particles and the formation of jets, while separating different sources of emission. They expect upcoming wide-area surveys to find a new population of brief events, but those surveys will have limited ability to pinpoint their locations or characterize their light across frequencies. This paper makes the case for ALMA2040 capabilities that would enable more sensitive, detailed and rapid follow-up in the 2040s. It is an outline of scientific goals and future needs, rather than a report of new observations.

Young explorerBig bursts in space give off kinds of light our eyes cannot see. One kind, called millimeter light, can help astronomers learn what happens during these bursts. The authors expect future searches to find new, quick flashes, but those searches may not show exactly where the flashes are or enough about their light. They explain how they want ALMA2040 to take a closer look and react quickly. This is a plan for learning more, not a report that those future discoveries have already happened.

uGMRT Polarization Observations with Walsh Modulation

Salmoli Ghosh, Preeti Kharb, Sandeep Chaudhari+1 more

AstronomerTest observations assessed Walsh phase switching for uGMRT Band 4 (550–750 MHz) polarimetry, using polarized 3C138 as the target and unpolarized 3C147 for amplitude, phase, and leakage calibration. Walsh ON and OFF datasets underwent identical flagging, calibration, and imaging procedures. Walsh ON yielded smoother leakage solutions, lower residual scatter in Stokes I, Q, and U, and suppression of some anomalous data at the correlation stage, reducing subsequent flagging. Final self-calibrated images showed improved fidelity, lower r.m.s. noise, and reduced error in 3C138's fractional polarization. These tests support the scheme's potential to mitigate instrumental cross-talk, but possible spurious frequency-dependent structure introduced into Q and U remains unresolved and requires further investigation.

PublicTests with the upgraded Giant Metrewave Radio Telescope compared observations made with a signal-switching technique called Walsh phase switching turned on and off. Researchers observed the polarized radio source 3C138 and used another source, 3C147, to calibrate the measurements, processing both datasets in the same way. With switching on, they found less scatter in the measurements, fewer anomalous data needing later removal, and cleaner, less noisy images with smaller errors in the measured fraction of polarized emission. The results suggest the technique could reduce unwanted interference between the telescope's signal channels and improve polarization measurements. However, the switching might itself create false patterns that vary with frequency in the polarization signals, a possibility that still needs investigation.

Young explorerScientists tried turning a special signal switch on and off in a radio telescope. With the switch on, the pictures were clearer and less noisy, and measurements of how the radio waves were lined up had smaller errors. But the switch might also add pretend patterns to those measurements. The scientists still need to check that.

Multi-Method Machine Learning Classification of Astronomical Sources with Rubin Data Previews: a Spectroscopy-Free Approach with DP1 and DP2

Andrés Alejandro Plazas Malagón, Yasna Ordenes-Briceño, Dan S. Taranu+8 more

AstronomerThis study benchmarks six machine-learning methods for binary point-like versus extended-source classification using Rubin DP1 and DP2 photometry and supporting catalogs, without external spectroscopy. In the deepest DP1 field, ECDFS, balanced-training 10-fold cross-validation macro-F1 scores are 0.95–0.97, compared with 0.87–0.92 on the imbalanced held-out test set. Random Forest and the soft Voting ensemble tie at 0.918, but differences among leading methods are within statistical uncertainty. FWHM dominates permutation importance, and all six methods agree on 79.5% of the full catalog. Applied without retuning to two additional DP1 fields, the pipeline maintains headline macro-F1 above 0.87 across fields spanning approximately sevenfold variation in E(B-V) and tenfold variation in stellar density. Across four DP2 fields, the best test macro-F1 using colors and morphology is 0.83–0.88, with six-method agreement of 77–86%. Adding per-band photometric uncertainties as features raises the best reported macro-F1 to about 0.95 in ECDFS DP1, 0.97 in ECDFS DP2, and approximately 0.97–0.98 in the other fields.

PublicResearchers tested six machine-learning approaches to sort sources in Rubin Observatory preview data into those that look like points and those that look extended. The workflow uses brightness measurements in several color bands, information about apparent shape, and supporting catalogs, without relying on external spectroscopy. On a held-out test sample in the deepest field of the first preview, classification scores ranged from 0.87 to 0.92 on a scale where 1 is ideal. Two approaches tied for the highest score, but the leading methods were too close to distinguish within the statistical uncertainty. The pipeline also worked across other first-preview fields without adjusting its settings, despite substantial differences in dust reddening and the density of stars. Tests on four second-preview fields gave best scores of 0.83–0.88 using colors and shapes. Including the uncertainty in each brightness measurement improved the best reported scores to roughly 0.95–0.98. These scores measure classification performance, not the percentage of objects classified correctly; the six methods did not agree on every source.

Young explorerSome things in pictures of the sky look like tiny dots, and others look more spread out. Scientists tested six computer helpers to sort them into those two groups. The helpers used clues such as color, brightness, and how wide each thing looked. They did well in tests on several patches of sky, but they sometimes disagreed, and there was no clear winner among the best helpers. Giving them another clue—how uncertain each brightness measurement was—helped them sort things better.

What fuels the growth of stars and black holes in galaxies through cosmic time? The physics and chemistry of the interstellar medium in distant galaxies

Leindert A. Boogaard, Manuel Aravena, Matus Rybak+25 more

• Astrophysics of Galaxies

AstronomerThis abstract presents the science case for ALMA2040, a proposed flagship submillimetre interferometer with greatly increased instantaneous spectral-line sensitivity and broad spectral coverage. Despite major advances in mapping cold gas and dust beyond the local universe, limited line sensitivity has restricted 12CO measurements to a few tens of typical, massive main-sequence star-forming galaxies at z>1, with fainter gas tracers accessible only in the brightest galaxies. The proposed facility is envisioned to enable multi-transition, multi-species and multi-isotopologue studies of the atomic and molecular ISM in thousands of typical galaxies across populations and redshifts. These anticipated capabilities would support statistical studies of ISM evolution, detailed constraints on multiphase gas conditions and chemistry, and investigations of how cold gas regulates and responds to star formation and black-hole growth; they are prospective outcomes, not results reported here.

PublicCold gas and dust supply the material for new stars and growing black holes in galaxies. Observations at millimetre and submillimetre wavelengths can reveal this material, but current instruments struggle to detect the faint signals needed to study ordinary distant galaxies in detail. The abstract notes that, after more than a decade of surveys, molecular gas has been measured using carbon monoxide in only a few dozen typical, massive star-forming galaxies at redshifts above one. It makes the case for a proposed observatory called ALMA2040, designed to detect much fainter signals across a broad range of wavelengths. The authors expect it could examine gas conditions and chemistry in thousands of typical galaxies, helping explain how galaxies develop over cosmic time. These are goals for a future facility, not findings already obtained.

Young explorerGalaxies have cold gas and dust that help make new stars and feed growing black holes. Scientists can use special telescopes to study this material, but its signals are often too faint to see well in faraway galaxies. They propose a much more sensitive telescope called ALMA2040. They hope it could study the gas in thousands of galaxies and help us learn how galaxies grow. That is their plan, not something the new telescope has already done.

Modal estimation of high-order wavefront drifts on coronagraphic testbeds for high-contrast direct imaging of exoplanets

Saikrishna Manojkumar, Susan F. Redmond, Leonid Pogorelyuk+13 more

AstronomerSlow mechanical and thermal drifts can introduce high-order wavefront errors that degrade contrast for the planned Habitable Worlds Observatory. This study evaluates a modal Extended Kalman Filter on the HiCAT simulator, estimating drifting wavefront modes rather than independent dark-zone pixel electric fields. The parameter scan varies deformable-mirror drift, incident photon rate, and phase-diversity dither magnitude, and introduces a covariance-based method for selecting the probe magnitude. The simulated modal EKF results show a 15-fold contrast improvement relative to single-pixel dark zone maintenance experiments, bringing performance within a factor of 2–3 of model-based photon-noise theoretical bounds. These are simulator results, not an on-sky demonstration.

PublicThe planned Habitable Worlds Observatory aims to photograph Earth-like planets around other stars, but slow changes in its optics could make faint planets harder to see beside bright starlight. Researchers tested a correction method in the HiCAT computer simulator that tracks patterns in the distorted light wave rather than treating each camera pixel separately. They also introduced a way to choose the strength of small test adjustments used to guide the correction. The simulated method improved contrast by a factor of 15 compared with earlier pixel-by-pixel experiments, reaching within a factor of 2–3 of theoretical limits set by photon noise. The work is a simulation study, not a demonstration of planet imaging with the future observatory.

Young explorerA future space telescope will try to take pictures of planets next to very bright stars. Tiny, slow changes in the telescope could let extra starlight hide the planets. Scientists used a computer version of a telescope to test a new way to fix this problem. Instead of checking each little dot in the picture on its own, the method looks for patterns in how the light has changed. In the computer test, it kept the dark part of the picture darker than an older method did. It still needs testing beyond this simulation.

Correlated Radio Frequency Interference Monitor for Radio Telescopes

Lindsay Berkhout, Ian Hendricksen, Joshua Montgomery+8 more

AstronomerThe paper presents a prototype design for an auxiliary array of horizon-pointed antennas to help identify and mitigate radio frequency interference (RFI) at CHORD. The proposed array would be cross-correlated with the main telescope in real time at full cadence, providing fine-timescale flags and cross correlations rather than only the monitoring available from a traditional omnidirectional observatory monitor. The motivation includes residual RFI contamination in deep HI intensity-mapping datasets, which require hundreds to thousands of hours of integration, and false transient triggers that interfere with FRB detection. The abstract describes a proposed design, not demonstrated mitigation performance, and states that the general setup and techniques could apply to other radio telescopes.

PublicUnwanted radio signals can contaminate radio telescope data and trigger false alerts during searches for brief cosmic events such as fast radio bursts. This paper proposes an extra set of antennas aimed toward the horizon to help the CHORD radio telescope recognize this interference. The antennas would work in sync with the main telescope, allowing their signals to be compared in real time and suspect data to be marked on very short timescales. This could help protect both long observations used to study the universe and searches for brief signals. The paper presents a prototype design; the abstract does not report how well it performs in practice.

Young explorerA radio telescope listens for signals from space, but unwanted radio noise can get in the way or make a false alarm. Scientists have designed extra antennas that would point toward the horizon and listen at the same time as a telescope called CHORD. Comparing what they hear could help mark the unwanted noise. This is a plan for a helper system, not a report showing that it already works.

Unveiling the Baryon Cycle Through Cosmic Time

Manuel Aravena, Leindert A. Boogaard, Jorge González-López+28 more

• Astrophysics of Galaxies

AstronomerThis proposal outlines how ALMA2040 could expand molecular-gas surveys to trace the baryon cycle across cosmic time. The envisioned combination of roughly 10-fold better sensitivity and at least 512 GHz of simultaneous frequency coverage would provide about 100-fold faster mapping at fixed depth and a further bandwidth gain of at least 25-fold, increasing spectroscopic survey speed by orders of magnitude. Proposed survey tiers include an ultra-deep 4–5 arcmin² field, a roughly 0.25 deg² survey with molecular-line sensitivities comparable to current ultra-deep fields, and thousands of independent pointings to reduce cosmic variance. Simultaneous coverage of multiple CO transitions, [CI], H₂O, feedback tracers, far-infrared fine-structure lines, and dust continuum would constrain molecular reservoirs, ISM conditions, obscured star formation, and gas flows, including in serendipitously detected galaxies. Combined with future HI, optical, and near-infrared surveys, these capabilities could support population-resolved tests of galaxy formation models. These are projected capabilities and proposed strategies, not reported survey results.

PublicGalaxies grow and change as gas arrives, forms stars, and is pushed around or expelled by stars and active galactic nuclei. This abstract proposes using ALMA2040 to follow the molecular gas involved in that cycle far more efficiently than current surveys can. The envisioned improvements would make mapping about 100 times faster at the same sensitivity to faint signals, while observing a much wider range of frequencies at once. Suggested surveys would combine a very deep view of a small patch of sky, a larger-area survey, and thousands of separate views to reduce the risk of drawing conclusions from an unrepresentative region. The broad frequency coverage could reveal several gas signatures and dust emission together, helping researchers study hidden star formation and gas movement. Even observations aimed at individual targets could reveal additional galaxies. These are proposed capabilities, not new measurements; alongside other future surveys, they could help test explanations of how galaxies evolve.

Young explorerGalaxies use gas to make stars, and some of that gas gets moved around or pushed out. Scientists want a better way to find this gas and learn what happens to it. They propose improving a telescope called ALMA so it could look for faint gas much faster and catch more kinds of signals at once. They could look very carefully at a tiny piece of the sky and also look at many other places. They might even find galaxies they were not looking for! This is a plan for what the improved telescope could do, not something it has already done.

Optimization of multi-resolution observation strategies for cosmic microwave background experiments

Sara M. Simon, Jacques Delabrouille, Julien Carron+4 more

AstronomerThe authors present a general simulation framework for evaluating CMB observing strategies that combine small-aperture telescopes (SATs) and large-aperture telescopes (LATs), balancing site restrictions, instrument constraints, and science goals. Focusing primarily on inflationary science, they determine optimal LAT coverage for delensing SAT measurements. They also propose a deep-scan strategy for an experiment in Chile that, in their simulation-based assessment, improves observing efficiency by 26% within the deepest-observed 3% of the sky. These are strategy-design findings rather than results from new sky observations. The study also discusses ways future surveys could further improve observing efficiency.

PublicTelescopes with smaller and larger openings provide complementary views of the cosmic microwave background, the universe’s ancient background light. This study uses simulations to explore how to coordinate their observations while accounting for practical limits and scientific priorities. The main focus is planning measurements to investigate inflation, an early period of cosmic expansion. The researchers assess how large-telescope coverage can help remove gravitational-lensing effects from small-telescope measurements. They also propose an observing pattern for an experiment in Chile that their simulations indicate would improve observing efficiency by 26% in the most deeply observed 3% of the sky. This improvement is a simulation-based finding, not a demonstrated gain from actual observations.

Young explorerScientists want to use small and big telescopes together to study very old light from space. They tried different ways of pointing the telescopes in a computer. Their new plan for telescopes in Chile worked more efficiently in the small patch of sky they would watch most closely. The computer test looks promising, but it is not the same as trying the plan with real telescopes.

The energetic atmosphere of the Sun

Sven Wedemeyer, Mats Kirkaune, Miroslav Barta+16 more

• Solar and Stellar Astrophysics

AstronomerThis abstract presents a case for proposed ALMA2040 capabilities, not new observational heating constraints. Shocks, turbulence, magnetohydrodynamic waves, reconnection-driven jets, and nano-flares are thought to contribute to chromospheric and coronal heating, but their spatial, temporal, and spectral signatures remain difficult to constrain directly. Optically thick thermal millimeter emission offers a comparatively direct gas-temperature diagnostic. ALMA already provides temperature diagnostics and high-cadence imaging, but its current capabilities limit studies of rapidly evolving, small-scale phenomena. The authors argue that improved spatial resolution, enhanced uv-coverage, and simultaneous multi-band observations would probe dynamics across multiple heights and enable time-dependent three-dimensional thermal and magnetic tomography of the chromosphere. Complementary diagnostics and simulations would be needed to test the heating contributions of these processes.

PublicWhy the Sun's chromosphere and corona are much hotter than its visible surface remains an open question. Small, fast-changing processes may supply much of the heat, but observing their signatures directly is difficult. The ALMA telescope array already uses millimeter-wavelength emission to provide a comparatively direct measure of gas temperature. This abstract describes how proposed ALMA2040 upgrades could reveal finer details and follow changes at several heights in the chromosphere at once. Combined with other observations and simulations, these capabilities could help test possible heating mechanisms; the abstract does not report a new measurement establishing which mechanism supplies the heat.

Young explorerSome outer layers of the Sun are much hotter than the surface below, and scientists are still figuring out why. Tiny, quick events might help heat them. Scientists propose improving a telescope called ALMA to watch these events more closely and test their ideas. Those improvements have not yet shown what causes the heating.

CHARIZARD: A High-throughput Generic Pipeline for Present and Upcoming Interferometers

Arpan Pal, Ruta Kale

AstronomerCHARIZARD is a distributed radio-interferometric reduction pipeline taking raw measurement sets through flagging, cross-calibration, self-calibration and full-Stokes imaging. Sub-bands remain independent through cross-calibration; self-calibration work is divided by target field and sub-band, with stages operating on disjoint data run concurrently. A scheduler-agnostic layer manages PBS or SLURM jobs, and computations use a single rootless container. Benchmarks on MeerKAT measurements with full polarization calibration yield residual on-axis instrumental polarization of 0.13% linear and 0.06% circular. The deepest field reaches 4.11 microJy per beam across 787 MHz, with sigma_I/sigma_V = 1.010. Positions agree with RACS-low to better than 0.4 arcseconds, and the median flux-density ratio is 1.06. A 1.5 TB track completes 48.6 core-hours of work in 18.4 hours, including self-calibration and polarization calibration. These benchmarks demonstrate the implementation; the abstract does not quantify a speedup against another pipeline. The authors present work distribution as a useful approach to future processing demands.

PublicModern radio telescopes collect so much data that turning measurements into images can be difficult even with automated software. CHARIZARD is a new processing pipeline that tackles this by splitting data into frequency sections and target fields, allowing independent tasks to run at the same time on a computing cluster. It removes problematic data, calibrates the measurements and makes images that include the radio waves’ polarization. In tests using MeerKAT observations, the authors report low residual instrumental polarization and close agreement with a reference survey in source positions and brightness. One 1.5-terabyte observation took 18.4 hours to process, including calibration steps. The work suggests that organizing computing tasks efficiently can help handle growing radio-astronomy datasets, although the abstract gives no direct speed comparison with another pipeline.

Young explorerRadio telescopes collect lots of information from space. A new computer program called CHARIZARD divides that information into smaller jobs, so computers can work on different pieces at the same time. It helps clean up the information and turn it into pictures. The team tried it on real telescope data and checked how well it worked. They think sharing the jobs this way could help with even bigger piles of telescope information.

The Birth and Early Feedback of Massive Star Clusters Across the Local Universe

Jiayi Sun, Rebecca C. Levy, Cecilia Bacchini+11 more

• Astrophysics of Galaxies

AstronomerYoung massive clusters (YMCs; masses ≳10^4 solar masses) trace an extreme mode of star formation and provide present-day analogues of the environments that assembled globular clusters and Cosmic Noon stellar populations. Severe dust extinction makes (sub-)millimeter observations essential for probing their earliest assembly and feedback. Existing ALMA work is limited to individual regions and their most massive YMCs, leaving initial conditions, integrated star and cluster formation efficiencies, dominant pre-supernova feedback channels, and the prevalence and extent of cluster-driven outflows unresolved. The abstract forecasts that ALMA2040 will enable mass-complete, spatially resolved surveys in hundreds of host galaxies, shifting the field from case studies to statistical measurements across diverse galactic environments; it does not report results from such surveys.

PublicYoung massive star clusters contain at least roughly 10,000 times the Sun's mass and offer nearby examples of the kinds of environments where major stellar populations formed in the distant past. Dust hides their earliest stages, so astronomers need millimeter and submillimeter observations to study how they assemble and affect their surroundings. ALMA studies so far have examined individual regions and mainly their most massive clusters. Important questions remain about how efficiently stars and clusters form, how young clusters influence surrounding gas before supernova explosions, and how common and far-reaching cluster-driven outflows are. The abstract anticipates that ALMA2040 will allow detailed surveys in hundreds of galaxies, covering the full cluster mass range of interest rather than only the most massive examples. These are expected capabilities, not completed survey findings.

Young explorerSome stars are born together in huge groups, hidden behind thick dust. Astronomers use a telescope called ALMA to look through that dust with a kind of light our eyes cannot see. So far, they have studied only a limited set of places, mostly looking at the biggest groups there. They still have questions about how these groups grow and push nearby gas around. They expect a future version called ALMA2040 to help them study many more groups in hundreds of galaxies, but that big study has not happened yet.

Unveiling star formation at sub-solar metallicity with ALMA2040

Francesco Fontani, Frédérique Motte, Maria T. Beltrán+9 more

• Astrophysics of Galaxies

AstronomerThe abstract outlines a science case for ALMA2040 to test the environmental dependence of star formation. The Milky Way and Magellanic clouds span large variations in metallicity, gas surface density, pressure, dust abundance, radiation field, and cosmic-ray flux. The outer Milky Way and Magellanic clouds offer nearby low-metallicity laboratories, but resolving individual star-forming cores and disks requires substantial improvements in ALMA capabilities. Recent ALMA and other observations have begun characterizing these regions physically and chemically; the abstract reports no specific measurements. Proposed investigations address the universality of prestellar-core properties, metallicity-dependent fragmentation and the stellar initial mass function, dust evolution and protoplanetary-disk survival, and molecular formation and survival under reduced metal abundance and dust shielding. ALMA2040 is presented as a means to compare solar- and sub-solar-metallicity regions, not as having already resolved these questions.

PublicDo stars form in the same way everywhere, or does their galactic neighborhood change the process? This abstract describes how improved ALMA capabilities could help answer that question. The outer Milky Way and the nearby Magellanic clouds contain star-forming regions with fewer heavy elements than the Sun and different gas and dust conditions. Observations have begun revealing their properties, but studying individual star-forming cores and disks requires much greater capability. The proposed ALMA2040 studies would examine how these environments affect the breakup of gas clouds, the masses of stars that form, and the survival of planet-forming disks and molecules. These remain open questions, not established results.

Young explorerStars are born in clouds of gas and dust. Scientists want to know whether stars grow the same way in different places. They have started looking at nearby places with different ingredients, but need a better view. Planned improvements to a telescope called ALMA could help them find out.

Resolving the Assembly of Disk Galaxies from the Epoch of Reionisation to Cosmic Noon

Melanie Kaasinen, Mahsa Kohandel, Francesca Rizzo+45 more

• Cosmology and Nongalactic Astrophysics
• Astrophysics of Galaxies

AstronomerThe abstract makes the case for ALMA2040 to resolve the cold-gas assembly of representative disk-galaxy progenitors at z>1. Existing kpc-scale ALMA CO and [C II] observations reveal rotation-dominated disks even at z>2, with kinematic signatures consistent with spiral arms, bars, and tidal tails. These studies, however, are restricted to massive, highly star-forming galaxies, with M_star>10^10.5 solar masses and star-formation rates roughly 100 solar masses per year or higher. The proposed tenfold improvement in line sensitivity is expected to enable routine resolved observations of hundreds of galaxies with M_star>10^9 solar masses, including systems on and below the star-forming main sequence. Resolved CO, [C I], and [C II] observations across z=1–6 would provide sub-kpc constraints on cold-gas kinematics and morphology and access a larger fraction of the cold-gas reservoir. These are anticipated capabilities, not reported results; their goal is to address gas acquisition, baryon–dark matter coevolution, feedback, and radial gas transport in the progenitors of ordinary present-day spirals.

PublicHow did spiral galaxies like the Milky Way acquire their gas and build their disks? ALMA has already revealed rotating gas disks in the early universe, with motions that could indicate spiral arms, central bars, or tidal tails. But these detailed observations have mostly reached unusually massive galaxies forming stars rapidly, rather than the smaller ancestors of typical spirals. The abstract argues for ALMA2040, a next-generation facility with ten times better sensitivity to emission lines. It is expected to map cold gas in hundreds of less massive galaxies across a broad span of cosmic history, showing how that gas is distributed and moves. Such observations could help explain how galaxy disks formed and changed. They are a proposed future advance, not findings already obtained.

Young explorerGalaxies like our Milky Way have wide, spinning disks. Astronomers have seen gas spinning in some galaxies long ago, but they have mostly studied very big ones that were making lots of stars. They want a more sensitive telescope called ALMA2040 to look at smaller galaxies too. Watching where their cold gas is and how it moves could help explain how galaxies like ours grew. Those new observations have not happened yet.

Dust at cosmic dawn: unveiling the onset of dust and obscured star formation at z≳8

Hiddo Algera, Tom Bakx, Manuel Aravena+31 more

• Astrophysics of Galaxies

AstronomerThis abstract makes the science case for ALMA2040, a next-generation (sub)millimeter interferometer with a proposed tenfold sensitivity increase over ALMA, rather than reporting new observations. Dust constitutes less than 1% of a galaxy’s baryonic mass but strongly affects its multi-wavelength appearance; measuring dust reservoirs at z > 8 is largely beyond current facilities. The authors forecast routine dust-continuum detections and simultaneous multi-band constraints on dust masses, temperatures, and infrared luminosities. Combined with ancillary metallicity measurements, including those from far-infrared lines detected by ALMA2040, these data are intended to distinguish the relative contributions of supernovae and grain growth to early dust production. The facility would also quantify the dust-obscured star-formation fraction at cosmic dawn and assess how much early galaxy growth rest-UV and optical surveys miss. These are anticipated capabilities and scientific goals, not demonstrated results.

PublicCosmic dust makes up less than 1% of a galaxy’s ordinary matter, yet it can hide much of the galaxy’s activity from view. This abstract argues for ALMA2040, a future telescope array intended to be ten times more sensitive than ALMA. The authors predict that it could routinely detect dust in very early galaxies, at redshifts above 8, where such measurements are largely beyond today’s facilities. Observing at several wavelength bands would help measure how much dust these galaxies contain, how warm it is, and how much infrared light they emit. Together with measurements of their chemical enrichment, this could reveal the relative importance of supernovae and the growth of dust grains in building early dust supplies. It could also show how much early star formation is hidden from ultraviolet and optical surveys. The abstract describes expected benefits of a future facility, not findings already obtained.

Young explorerDust in faraway galaxies can hide places where stars are being made. The authors want a much more sensitive telescope called ALMA2040 to look for the faint glow of that dust. They hope it will help us learn how much dust was in some of the earliest galaxies, how it was made, and how many new stars it hides. This is a plan for what a future telescope could discover, not something it has already found.

Probing cold gas and dust in quiescent galaxies across cosmic time

Anita Zanella, Sirio Belli, Belen Alcalde Pampliega+35 more

• Astrophysics of Galaxies

AstronomerJWST discoveries of massive quiescent galaxies at high redshift indicate rapid early quenching, but its physical drivers remain unknown. This abstract advocates a next-generation ALMA2040 facility rather than reporting new gas or dust measurements. Current submillimeter facilities cannot routinely detect faint molecular gas and dust reservoirs or pinpoint molecular outflows in statistically representative quiescent samples. The envisioned capabilities include CO, [CI], and [CII] measurements at cosmic noon and beyond, constraints on cold-ISM conditions through CO spectral line energy distributions, dust inventories, and molecular-gas kinematics to identify outflows driven by supermassive black holes. Combined with JWST, ELT, and SKAO survey data, these proposed observations aim to distinguish quenching mechanisms and evolutionary pathways across cosmic time.

PublicJWST has discovered massive galaxies that stopped forming stars early in the Universe’s history, but astronomers do not yet know what made them stop. Their remaining cold gas and dust could provide important clues, yet today’s facilities cannot routinely measure these faint reservoirs in representative groups of such galaxies. The authors argue for a next-generation observatory called ALMA2040 to measure the gas and dust, study gas motions, and identify gas flowing out under the influence of supermassive black holes. Together with other surveys, these proposed observations could help explain when and why galaxies stop making stars. The abstract presents the case for these future capabilities, not new measurements demonstrating the cause.

Young explorerJWST has found big galaxies that stopped making new stars when the Universe was young. Scientists do not know why they stopped. They want a future telescope called ALMA2040 to look for the cold gas and dust left inside these galaxies and see how the gas moves. Those clues could help solve the mystery, but the telescope has not made these discoveries yet.

Direct measures of black hole masses through cosmic time

Roberto Decarli, Sabine Thater, Ivan Delvecchio+16 more

• Astrophysics of Galaxies

AstronomerThe abstract argues that a future facility such as ALMA2040 could enable black hole mass measurements through direct observations of cold-gas kinematics in galaxy cores, from the local Universe to very high redshift and irrespective of black hole activity. This is a prospective capability, not a report of new mass measurements. The motivation is that black hole masses remain difficult to determine, limiting constraints on their growth histories and interplay with host galaxies, including feedback that suppresses star formation.

PublicMeasuring the masses of supermassive black holes remains difficult, leaving important questions about how they grow and influence their galaxies unanswered. The authors argue that a future observatory such as ALMA2040 could measure these masses by tracking the motion of cold gas in galaxy centers, both nearby and at very high redshift. The proposed approach would work whether or not the black hole is active. The abstract describes a future opportunity, rather than reporting new measurements.

Young explorerGiant black holes are hard to weigh. The authors say a future telescope could help by watching how cold gas moves around the centers of galaxies. It could study black holes even when they are not active. This is an idea for what a future telescope could do, not something the authors have already measured.

Beyond the Beacon: State and Corporate Competition after an Information-Rich Technosignature Detection

Michael Garrett

• Popular Physics
• Physics and Society

AstronomerThis paper considers post-detection governance for hypothetical information-rich technosignatures, rather than reporting a detection. The 2026 SETI declaration calls for recording detected content and openly preserving and sharing underlying data, methods, and code. The author argues that recoverable data, imagery, or machine-readable content could shift much of the challenge from verification to information stewardship and encourage competitive decoding and use. Unlike geopolitical discussions focused mainly on states, the paper highlights large corporations with computing, AI, and sometimes receiving capabilities that could independently pursue a signal without an obligation to disclose findings. It proposes supplementary guidance and preliminary community questions about maintaining openness under these conditions, not a settled policy framework.

PublicWhat if a signal from extraterrestrial intelligence contained pictures or usable data, rather than simply announcing its presence? This paper explores that possibility; it does not report finding such a signal. The author argues that managing and sharing its contents could become a major challenge, especially if governments or companies competed to decode and use them. Some large companies already have the computing power, AI tools, and sometimes signal-receiving equipment to pursue a signal independently, without being obliged to share what they find. The paper calls for further guidance on how to uphold the SETI declaration’s commitment to openness and offers initial questions for discussion rather than final rules.

Young explorerImagine we someday hear a message from aliens that has pictures or information inside. This paper does not say we have found one. It asks what people should do if that happens. Some big companies might be able to study the message and keep what they learn to themselves. The writer wants people to think about how to share the message openly, but does not give a finished set of rules.

Tracking the flow of interstellar gas across scales: from galaxies to star clusters

Ana Duarte-Cabral, Maxime Valeille-Manet, Mathilde Bouvier+30 more

• Astrophysics of Galaxies

AstronomerThis paper outlines technical requirements for linking parsec-scale star-formation physics to galactic ecosystems spanning tens of kiloparsecs. The motivation is to trace matter and energy flows across diverse environments and clarify how the interstellar medium’s baryon cycle regulates star formation and galaxy evolution. The abstract identifies current facilities’ inability to map entire galactic ecosystems down to individual star-forming clumps as a key limitation. It presents requirements for a future capability, not observational results or an established answer to what regulates star formation across cosmic time.

PublicGalaxies form stars from gas, but understanding how matter cycles through a galaxy and controls star formation remains difficult. Today’s observing facilities cannot map a whole galactic ecosystem while also resolving its individual star-forming clumps. This paper outlines the technical requirements for observations that could connect those small regions to the much larger galaxy and track flows of matter and energy. The goal is to learn what regulates star formation throughout cosmic history; the abstract does not report that this goal has been achieved.

Young explorerA galaxy is a huge place where stars can be born in little clumps of gas. Scientists want to see both the little clumps and the whole galaxy to learn how the gas moves and why stars form. Today’s tools cannot show all of that together in enough detail. This paper describes what future tools would need to do, rather than saying the scientists have already solved the puzzle.

AGN Feeding and Feedback: Resolving the Torus

M. Pereira-Santaella, F. Combes, A. Alonso-Herrero+16 more

• Astrophysics of Galaxies

AstronomerThe abstract outlines the scientific case for a facility such as ALMA2040 to investigate SMBH fueling and AGN feedback. Existing constraints come mainly from very nearby active galaxies (z < 0.008; D < 35 Mpc), where high spatial resolution reveals randomly oriented dusty molecular tori that supply SMBHs. With substantially greater sensitivity and angular resolution than current ALMA, the proposed facility would aim to trace fueling dynamics down to the accretion disk in nearby galaxies and spatially resolve tori and circumnuclear regions in more energetic, cosmologically significant AGN, including local quasars at z ~ 0.1 with Lbol > 10^45 erg/s. The abstract presents these as prospective capabilities beyond existing and planned observatories, not as new observational results.

PublicActive galactic nuclei are bright central regions powered by supermassive black holes, and their effects on surrounding gas help regulate star formation. Most detailed information about how these black holes receive material comes from very nearby galaxies, where observations reveal dusty, molecular rings with varied orientations. The abstract argues that a facility such as ALMA2040, with sharper views and greater sensitivity than today's ALMA, could follow the motion of material feeding nearby black holes down to their accretion disks. It could also distinguish the dusty structures and surrounding regions of more powerful active galaxies, including local quasars. These are proposed future capabilities, not observations already achieved.

Young explorerA giant black hole lives in the middle of an active galaxy. Gas can feed it, and the active center can affect the gas where stars form. Astronomers have seen dusty rings that feed black holes in very nearby galaxies. They say a future telescope facility called ALMA2040 could help them watch how gas moves much closer to black holes and see dusty rings around more powerful galaxy centers. These are things they hope to study, not things the new telescope has already seen.

Molecular atlas of nearby galaxies through sensitive high-resolution multi-band molecular line surveys

Mathilde Bouvier, Erica Behrens, Laura Colzi+21 more

• Astrophysics of Galaxies

AstronomerThe abstract motivates astrochemical inventories as diagnostics of dense star-forming gas and of the reciprocal relationship between stellar feedback and the ISM. Large spectral surveys of a few individual galaxy centres have demonstrated the ability of molecular inventories to reveal detailed physical conditions. It presents a next-generation (sub)millimetre facility in the 2040s as a prospective means of extending this approach to the local star-forming galaxy population, with the aim of obtaining a comprehensive physical and chemical view of the local molecular ISM; that population-wide view is not reported as an existing result.

PublicThe molecules in gas clouds can help astronomers work out the conditions in which stars form and understand how stars change their surroundings. Large surveys of molecular signals have already demonstrated this approach in a few galaxy centres. The abstract looks ahead to a next-generation telescope facility operating at millimetre and submillimetre wavelengths in the 2040s, which could extend such studies across the nearby population of star-forming galaxies. This broader picture is a future prospect, not a completed survey.

Young explorerStars are born in clouds of gas, and stars can also change the gas around them. Different molecules in the clouds give astronomers clues about what the gas is like. Scientists have shown that this works in the middles of a few galaxies. A future telescope could help them study these clues in many nearby galaxies where stars are being born, but that bigger study has not happened yet.

From local chemistry to galactic evolution: unlocking the power of interstellar isotopes with ALMA2040

Laura Colzi, Hayley A. Bunn, Víctor M. Rivilla+29 more

• Astrophysics of Galaxies
• Solar and Stellar Astrophysics

AstronomerThis forward-looking abstract presents molecular isotopic inventories as probes of stellar nucleosynthesis, Galactic chemical evolution, and chemical inheritance into planetary systems. It emphasizes that molecular isotopic ratios need not reflect elemental abundances: chemical fractionation, isotope-selective photodissociation, grain chemistry, and radiative-transfer effects can modify observed ratios. Disentangling these contributions requires simultaneous observations of multiple transitions, isotope systems, and molecular families, including rare and multiply substituted isotopologues. The authors envision ALMA2040 providing an order-of-magnitude sensitivity improvement and at least 512 GHz of instantaneous bandwidth, enabling statistically significant Galactic and nearby extragalactic samples. These are anticipated capabilities and scientific outcomes, not reported observational results.

PublicThe proportions of different isotopic forms of molecules could help astronomers trace how matter moves from stars into clouds and eventually new planetary systems. But these proportions are not a simple record of which atoms are present: chemical reactions, light-driven destruction of molecules, processes on dust grains, and the way radiation travels can all affect what astronomers measure. The authors argue that comparing many kinds of molecules and many signals from each is needed to untangle those effects. They envision a future ALMA2040 observatory with ten times better sensitivity and at least 512 GHz of simultaneous frequency coverage, allowing broad surveys in the Milky Way and nearby galaxies. The abstract describes expected opportunities rather than results from such surveys.

Young explorerSpace has clouds of gas that can help make new stars and planets. Some molecules in those clouds have slightly heavier or lighter versions of the same atoms. These differences could give scientists clues about where the material came from, but things happening inside the clouds can muddle the clues. The authors say a future, more sensitive ALMA2040 telescope could look at many kinds of molecules to help sort the clues out. This is something they hope to do, not something they have already done.

ALMA2040: The High-Redshift Circumgalactic Medium. Imaging the fueling and feedback of galaxies in the early universe

Kirsty M. Butler, Justin Spilker, Seiji Fujimoto+23 more

• Astrophysics of Galaxies

AstronomerThis paper presents three science cases for a proposed ALMA2040 telescope targeting the cool circumgalactic medium (CGM), rather than reporting new detections. Atomic and molecular CGM gas provides a reservoir for star formation and dominates the mass budget of outflows, linking galaxies to accretion, mergers, and feedback. Existing submillimeter observations have detected extended cold-gas halos and flows at high redshift, but are limited to massive, extreme, or gravitationally lensed sources and a handful of strong lines. The authors argue that a 5–10-fold improvement in spectral-line sensitivity over current ALMA is needed to access new regimes. Their proposed goals are direct imaging of extended [CII] halos around Milky Way progenitors at z = 4–8, resolving cold, clumpy outflows on roughly 100 pc scales associated with individual star-forming clumps, and using multiple species and transitions in emission and absorption to jointly constrain cool-CGM density, chemistry, and radiation fields.

PublicGalaxies exchange gas with their surroundings through an extended gaseous atmosphere. Cold gas in this region can supply future star formation, while gas flowing outward carries material away. Observations have already revealed cold gas around distant galaxies, but mostly in unusually massive or extreme systems, or ones magnified by gravitational lensing. This paper proposes goals for a future ALMA2040 telescope, not new observational results. The authors argue that spectral-line sensitivity 5–10 times better than current ALMA would open new opportunities: mapping gas halos around early ancestors of galaxies like the Milky Way, resolving small clumps of escaping cold gas, and using several gas signatures to investigate its density, chemistry, and radiation environment.

Young explorerA galaxy is surrounded by a big cloud of gas. Some gas can move in and help make stars, and some can flow out. Astronomers have already seen cold gas around some faraway galaxies. Now they are proposing a better telescope to see more of it and learn what it is like. These are plans for future studies, not things the new telescope has already seen.

Evolved stars, multiplicity and planets: Shaping and Being Shaped by Stellar Evolution

Theo Khouri, Wouter Vlemmings, Elvire De Beck+21 more

• Earth and Planetary Astrophysics
• Solar and Stellar Astrophysics

AstronomerThis white paper outlines the prospective role of next-generation ALMA (ALMA2040) in studying the survival, interaction, and destruction of planetary and stellar companions around evolved stars. It anticipates detecting and characterising accreting companions and signatures of planetary engulfment in hundreds of systems, rather than reporting such detections. The stated motivation is to improve predictions for the long-term evolution of planetary systems like our own and understanding of stars’ contributions to galactic chemical evolution.

PublicAs stars age, planets and companion stars may survive, interact with their host, or be destroyed. This white paper describes how a future generation of ALMA, called ALMA2040, could investigate these processes by finding companions gathering material and signs that stars have swallowed planets. The authors anticipate studying hundreds of systems; these are expected capabilities, not reported discoveries. Such work could help explain the distant future of planetary systems like ours and how stars contribute to changes in galaxies’ chemical makeup.

Young explorerWhen stars grow old, nearby planets and other stars might stay around, interact with them, or be destroyed. The writers describe how a future telescope called ALMA2040 could look for little neighbors collecting material and clues that stars have swallowed planets. They hope to study hundreds of star families, but this paper does not say they have found those clues yet.

Frontiers of chemical complexity in the interstellar medium: unveiling the cosmic origins of life

Víctor M. Rivilla, Miguel Sanz-Novo, Maite Beltrán+33 more

• Astrophysics of Galaxies

AstronomerMore than 350 interstellar molecules are known, but the limits of chemical complexity, its evolution from clouds to planetary systems, and its contribution to prebiotic feedstocks remain poorly constrained. This abstract presents the proposed ALMA2040 facility, rather than new molecular detections. Its envisioned capabilities include at least a tenfold improvement in spectral-line sensitivity, high-fidelity imaging from sub-arcsecond to tens-of-arcsecond scales, and ultra-broad instantaneous coverage from 35 to 950 GHz at high spectral resolution. The authors argue that these capabilities would enable systematic detections at abundances relative to H2 below 10^-11 and identification through multiple weak rotational transitions. The intended outcome is comprehensive molecular inventories across evolutionary stages, including searches for complex organic and heavy-element-bearing species, to test whether precursors of prebiotic chemistry are widespread in the Galaxy; that prevalence is not established here.

PublicAstronomers already know of more than 350 molecules in the gas and dust between stars, but they do not yet know how complex this chemistry can become or how much it supplies the ingredients associated with the chemistry preceding life. The abstract describes ALMA2040, a proposed facility designed to detect much fainter molecular signals across a far broader range of frequencies than current facilities can cover at once. Its planned capabilities would help researchers identify molecules using several characteristic signals and compare chemical inventories in environments where stars and planets form. Amino acids, nucleobases, sugars and lipids are among the kinds of molecules motivating these searches, not discoveries reported here. The proposal aims to establish whether molecular precursors to prebiotic chemistry are common across the Galaxy; it does not report an answer.

Young explorerThe space between stars has tiny bits of stuff called molecules. Scientists already know more than 350 kinds are there. They want to learn which kinds are around while stars and planets are forming. They have a plan for a tool called ALMA2040 that could hear much fainter molecule signals, like listening for quiet whispers. If it is built with the planned abilities, it could help look for ingredients that might take part in the chemistry before life. This is a plan to search, not a report that those ingredients have been found everywhere.

Evolved stars: dust formation and mass loss

Luis Velilla-Prieto, Wouter Vlemmings, Guillermo Quintana-Lacaci+18 more

AstronomerThis forward-looking abstract argues that next-generation facilities, particularly ALMA2040, will enable systematic, spatially resolved studies of mass loss and dust formation in evolved stars. Empirical constraints on the interplay among pulsation, convection, magnetic fields, mass loss, and dust formation at milliarcsecond scales are currently limited to a handful of sources. The anticipated expansion of study samples from a few tens to hundreds of objects is presented as a route to understanding evolved stars’ roles in recycling baryonic matter and enriching the Universe with nucleosynthetic products and dust, not as an achieved observational result.

PublicAging stars produce chemical elements and cosmic dust, helping enrich the Universe. Understanding how they release this material requires studying how stellar pulsations, internal churning, magnetic fields, and dust formation work together. Detailed observations on the very small scales needed are currently available for only a handful of stars. The abstract looks ahead to future facilities, especially ALMA2040, which are expected to make detailed studies of hundreds of aging stars possible. This is an outlook for future research rather than a report of new measurements.

Young explorerOld stars make tiny bits of dust and materials that help fill the Universe. Scientists want to learn how these stars puff material out and how the dust forms. So far, they can look closely enough at only a few stars. They expect future tools, especially one called ALMA2040, to help them study many more. That is a plan for learning more, not something they have already done.

Planet formation on solar system scales

Francesco Zagaria, Andrés F. Izquierdo, Jaehan Bae+32 more

• Earth and Planetary Astrophysics

AstronomerThe authors argue that the proposed next-generation submillimetre/millimetre interferometer ALMA2040 could reveal forming Jupiter-like planets and their interactions with natal discs. Relative to ALMA, the envisaged capabilities are 25-fold better continuum sensitivity, 10-fold better line sensitivity, and threefold higher angular resolution. They predict sensitivity to emission around a forming Jupiter-like planet orbiting a Sun-like star within 150 pc, as well as kinematic characterisation of disc interactions involving Jovian and sub-Jovian planets. These are anticipated capabilities, not reported detections. The scientific goals include understanding gap carving, accretion, satellite formation, and the influence of gas giants on planetary-system architecture.

PublicGiant planets can help shape planetary systems as they form, but the abstract reports no new planet detection. Instead, the authors make the case for ALMA2040, a proposed successor to ALMA with greater sensitivity and sharper vision at millimetre and submillimetre wavelengths. They predict that it could detect emission around a growing Jupiter-like planet orbiting a Sun-like star within about 150 parsecs and study how planets disturb the motion of gas in their birth discs. Such observations could help explain how giant planets open gaps, gather material, form moons, and influence the layout of other planets.

Young explorerA growing giant planet can change the disc of gas and dust around its star. Scientists want a new telescope called ALMA2040 to look more closely at these young planets. They think it could spot light from material around a growing planet like Jupiter and watch how planets move the gas around them. That could help us learn how giant planets grow and get moons. This is a plan for what the telescope might do, not a new planet they have found.

Star Formation across the Galaxy

Alvaro Sanchez-Monge, Henrik Beuther, Maryvonne Gerin+41 more

• Astrophysics of Galaxies

AstronomerThe abstract makes the case for ALMA2040 as a next-generation (sub)millimeter facility to study star formation across Galactic environments, rather than reporting new observations or simulations. Gravity, turbulence, feedback, and magnetic fields couple scales spanning more than six orders of magnitude, from molecular clouds to protoplanetary disks. Resolving fragmentation, accretion, and feedback across these scales is presented as essential for developing a predictive account of star formation across stellar masses and environments. The authors state that current facilities provide detailed access to less than 5% of Galactic star-forming regions, with a strong bias toward nearby regions, and argue that ALMA2040 is needed to achieve the requisite sensitivity and resolution across the Galaxy.

PublicThis abstract argues for ALMA2040, a next-generation facility for observing at millimeter and submillimeter wavelengths, to help explain how stars form. Star formation links enormous gas clouds to much smaller disks around young stars, with gravity, turbulent motion, magnetic fields, and effects from stars all playing roles. According to the authors, current observatories can reveal the details in less than 5% of the Milky Way’s star-forming regions, mostly those nearby. They argue that studying how gas breaks apart, gathers onto forming stars, and is affected by stars across the Galaxy’s varied environments requires ALMA2040. This is a case for a future facility, not a report of new discoveries.

Young explorerStars grow from gas in space. To understand how that happens, scientists need to see both huge clouds and tiny disks around young stars. Right now, they can look closely at only a small part of the places where stars are forming in our galaxy, mostly places near us. The writers say a future observatory called ALMA2040 is needed to look closely at more of these places. They are explaining what scientists need, not announcing something they have already found.

Planetary system architectures in the final stages of planet formation

Patricia Luppe, Zoe Roumeliotis, Sebastian Marino+18 more

• Earth and Planetary Astrophysics

AstronomerDebris discs contain second-generation dust and gas produced by collisions among bodies remaining after protoplanetary disc dispersal. Resolved belt images can probe dynamical histories, including giant impacts and planet–belt interactions, during terrestrial planet formation at ages of 10 to a few hundred Myr. High-resolution millimetre and optical/near-infrared imaging has revealed diverse structures with plausible, but not established, planetary imprints, while ALMA has detected gas in a growing number of systems. Current samples strongly favour bright, mostly young belts around early-type stars; low surface brightness limits access to crucial structure even in these systems. The abstract argues that a future submillimetre/millimetre facility with roughly tenfold improvements in continuum and line sensitivity would enable statistically meaningful surveys of faint outer belts across all stellar spectral types, imaging of inner-system planetary collisions, and gas measurements tracing volatile delivery to terrestrial planets. These are proposed capabilities, not demonstrated results.

PublicCollisions among the bodies left over from planet formation make dusty, sometimes gas-rich belts around stars. Images of these belts reveal varied shapes that may carry signs of planets, and ALMA has found gas in an increasing number of systems. But present observations mostly reach unusually bright, young belts around certain types of stars, leaving the much larger faint population poorly explored. The authors argue that a future millimetre/submillimetre observatory with about ten times greater sensitivity to both dust emission and gas signals could change this. It could survey faint belts around a wider range of stars, image planetary collisions close to stars, and use gas to trace the delivery of volatile materials to rocky planets. These are goals for a future facility, not findings already achieved.

Young explorerWhen leftover pieces around a star crash together, they make dust and gas. Astronomers have seen rings of this dust, and some shapes might be clues to planets. But most rings are too faint to study well. The authors say a much more sensitive future telescope could help us see those faint rings and learn how planets finish growing. That is a plan for the future, not something already done.

Multi-wavelength Polarization as a Probe of Planet Formation

Ian Stephens, Sarah Sadavoy, Akimasa Kataoka+11 more

• Earth and Planetary Astrophysics
• Astrophysics of Galaxies
• Solar and Stellar Astrophysics

AstronomerThis abstract outlines prospective disk-polarimetry capabilities for an upgraded ALMA2040, rather than reporting new observations. Circumstellar-disk polarized emission is typically only 0.5% to a few percent of total emission, demanding high sensitivity. Current ALMA limitations include lengthy, separate multi-wavelength observations, prohibitive observing times for large samples, limited spectral-line polarization sensitivity and frequency coverage, and insufficient calibration across all Stokes parameters. The authors argue that greater collecting area, wider bandwidth with multi-band capabilities, and accurate polarization calibration would enable continuum and line polarimetry to test streaming instabilities, constrain grain shape, size, porosity and alignment, resolve polarized disk substructures on scales below 5 au in large samples, rapidly survey hundreds of disks, and measure disk magnetic-field strengths and morphologies. These are anticipated capabilities contingent on the proposed improvements, not demonstrated results.

PublicLight from disks around young stars can be polarized, meaning it has a preferred orientation. Measuring this polarization at several wavelengths can reveal clues about planet formation, dust grains and the magnetic fields that influence how material falls onto a star. But the polarized signal is usually only 0.5% to a few percent of the total emission, making it difficult to measure with ALMA's current capabilities. The authors describe how a proposed ALMA2040 upgrade—with more collecting area, broader wavelength capabilities and better calibration—could study fine disk structures, survey hundreds of disks, constrain dust properties and map magnetic fields. It could also test a proposed planet-formation process called streaming instability. These are goals for an upgraded observatory, not discoveries reported in this abstract.

Young explorerYoung stars can have disks of dust and gas around them where planets may grow. A tiny part of the light from these disks has a special pattern called polarization. That pattern can give scientists clues about the dust and magnetic fields. It is hard to measure because the signal is so faint. Scientists describe how improving a telescope called ALMA could help them study many more disks and see smaller details. These are things they hope the improved telescope could do, not things it has already done.

Missed Detections and False Alarms in a CNN Technosignature Detector on Breakthrough Listen Data

Omer Imran

• Machine Learning
• Popular Physics

AstronomerThis study stress-tested one standard competition detector, trained once and then frozen, using 15,000 injections spanning ten morphologies and five amplitudes in real Green Bank backgrounds. The tests examined injected technosignature-like signals beyond straight narrowband lines and interference resembling the training data. Recall did not follow the predicted ordering and decreased with increasing amplitude, even for a training-like needle morphology, from 0.590 to 0.090. One interference morphology produced a false-positive rate of 0.627, compared with baseline genuine-signal recall of 0.5525. Grad-CAM indicated attention along the injected path for one missed family under a pre-specified test, with visual evidence for a second; this did not ensure detection. A pre-specified, time-averaged ON-OFF filter removed false alarms and genuine detections at the same rate. The author interprets the false alarms as a consequence of the detector reading only ON panels: it discards the OFF-panel evidence needed to distinguish target-star origin from terrestrial interference and instead recognizes resemblance to training data. The missed signals reflect learned recognition limitations that adding OFF panels alone would not resolve. These are injection-test findings for a single frozen detector, not detections of extraterrestrial technology.

PublicA machine-learning system used to screen radio searches for possible extraterrestrial technology struggled when tested beyond familiar examples. The researcher added 15,000 artificial signals and interference examples to real Green Bank radio backgrounds, then tested a detector whose training had already been completed. Brighter signals were sometimes missed more often, even when their shape resembled the detector's training examples. One type of interference was frequently mistaken for a signal. An additional comparison filter rejected real signal injections and false alarms at the same rate, rather than separating them. The author argues that a central limitation is the detector's input: it ignores comparison panels containing the evidence needed to tell whether a candidate comes from the target star. Recognizing familiar patterns is therefore not the same as establishing a signal's origin. The results concern one tested detector and artificial injections, not a discovery of alien transmissions.

Young explorerA scientist tested a computer that helps look for possible radio messages from space. They put pretend signals into real radio recordings. The computer missed some signals, even brighter ones, and sometimes picked noise instead. It also ignored comparison pictures needed to check where a signal came from. This test did not find aliens; it showed ways this computer could make mistakes.

Chemistry on solar system scales

Catherine Walsh, Maria Drozdovskaya, Dmitry Semenov+33 more

• Earth and Planetary Astrophysics

AstronomerThis abstract makes the science case for ALMA2040 rather than reporting new observations. Key C-, O-, and N-bearing molecules, along with rarer S- and P-bearing species, remain difficult to observe in the inner ≲10 au of protoplanetary disks. The authors call for roughly tenfold or greater improvement in line sensitivity over current ALMA, at spatial resolution of about 5 au or finer at 140 pc, corresponding to a factor of 3–4 improvement in resolution for low-surface-brightness emission. Regions at this distance include Taurus and Lupus, with populations of Sun-like stars. The proposed capability is intended to map chemistry on terrestrial-planet-forming scales within the water snowline and detect molecular feedstock for potentially habitable worlds, helping establish how disk processes set planetary compositions.

PublicThe chemical ingredients of planets come from the disks of gas and dust around young stars, but many important molecules are still very difficult to observe where planets form close to those stars. The authors argue for a more powerful facility called ALMA2040, with roughly ten times or more the sensitivity to molecular signals of today's ALMA and the ability to distinguish finer detail in faint emission. Their goal is to map the chemistry in regions where rocky planets form, including inside the boundary where water freezes into ice. This is a proposal for future observing capabilities, not a report of newly detected molecules or habitable planets.

Young explorerYoung stars have disks of gas and dust where planets can grow. Scientists want to find out which tiny chemical pieces are there, but many are too hard to spot with the tools they have now. They want a better telescope system called ALMA2040 to look more closely at the places where rocky planets could grow. This is a plan for what scientists hope to see, not something the new telescope has already found.

Properties and limitations of linear models for mutual coupling in 21 cm arrays

Vincent MacKay, Robert Pascua, Eleanor Rath+7 more

• Cosmology and Nongalactic Astrophysics

AstronomerMutual coupling in low-frequency arrays can leak bright foregrounds into otherwise clean regions of the 21 cm power spectrum. The authors decompose coupling into an antenna mode constructed from translated isolated responses and a residual structural mode. Full-wave simulations of a 37-element hexagonal array with HERA-like feeds and dishes show that the antenna mode contributes only about 1% of beam-perturbation power. Its importance changes in sky-weighted beam correlations, however: correcting this mode removes more than half of the coupling power in simulated visibilities. Relaxing the coefficient relationships imposed by re-radiation models also permits linear corrections to suppress structural-mode coupling. Beam-derived corrections reduce coupling power by more than an order of magnitude in noiseless, perfectly redundant simulations. Fitting known isolated visibilities improves residuals further on the fitted field, but those targets are generally unavailable observationally. Practical mitigation still requires constraints that separate coupling from the unknown sky while preserving the cosmological signal. An extension of holographic back-projection provides an aperture-plane view of the perturbations.

PublicAntennas in low-frequency radio arrays can affect one another, mixing bright foreground radio emission into measurements intended to reveal the universe’s 21 cm signal. The researchers used computer simulations of 37 antennas to test how this interference might be corrected. A component that standard models are expected to remove accounts for only about 1% of the simulated changes in individual antenna responses, yet correcting it removes more than half of the interference power in the simulated combined measurements. More flexible corrections perform better still, reducing interference power by more than a factor of ten under idealized conditions with no noise and perfectly repeating antenna arrangements. These are simulation results, not a demonstrated correction of telescope observations. Applying the method to real measurements will require additional information to distinguish antenna interference from the unknown sky without erasing the desired cosmic signal.

Young explorerRadio antennas listen to signals from space, but they can also disturb their neighbors. That makes a faint space signal harder to hear. Scientists made a computer model of a group of antennas and tried ways to clean up the mix-up. Their methods helped a lot in the model, where there was no extra noise and the antennas were arranged perfectly. They still need to work out how to do this with real observations without accidentally removing the space signal they want.

ALMA2040: Mapping the Spatially Resolved Dust and Star Formation Physics Driving High-z Galaxy Assembly

Daizhong Liu, Gergö Popping, Pierre Cox+19 more

• Astrophysics of Galaxies

AstronomerSingle-frequency continuum imaging cannot disentangle dust column density from local heating, limiting resolved dust-mass and star-formation estimates. Published spatially resolved multi-band dust temperatures at z>1 cover only about 10 extreme systems, leaving typical main-sequence disks largely unexplored. This paper presents the scientific rationale and technical requirements for a future ALMA2040 survey of more than 100 representative main-sequence galaxies. The proposed capability relies on an anticipated roughly 30-fold continuum-sensitivity improvement over current ALMA, simultaneous multi-band receivers, and kiloparsec or finer resolution. Visibility simulations indicate radial temperature-gradient precision of about 0.5–4 K for a galaxy with infrared luminosity around 10^12 solar luminosities at z≈2 in two hours on source. These are simulated capabilities, not new observations; intended applications include separating intrinsic compactness from temperature gradients and establishing temperature-calibrated, extinction-free resolved star-formation relations.

PublicDust absorbs and re-emits about half the starlight produced across cosmic history. Knowing its temperature helps astronomers estimate how much dust and molecular gas galaxies contain and how rapidly they form stars. Yet detailed temperature maps of distant galaxies remain rare and mostly concern unusual systems. The authors outline a future survey of more than 100 representative star-forming disk galaxies using ALMA2040, an anticipated upgrade with much greater sensitivity and simultaneous measurements in multiple wavelength bands. Simulations suggest it could map temperature changes within distant galaxies. These are forecasts, not new observations: the goal is to distinguish genuinely concentrated dust from strongly heated dust and improve maps of star formation.

Young explorerDust in faraway galaxies catches starlight and warms up. Scientists want to map where that dust is warmer or cooler to learn where stars are being born. They propose using a future, improved telescope system. Computer tests suggest it could work, but these new maps have not been made yet.

ALMA2040: Submillimeter-wave Limb Sounding of Venus and Mars

Hideo Sagawa, Arianna Piccialli, Miriam Rengel+5 more

• Earth and Planetary Astrophysics

AstronomerThe abstract presents a prospective role for ALMA2040 in complementing spacecraft observations of Venus and Mars with long-term atmospheric monitoring. High-resolution submillimeter heterodyne spectroscopy and limb sounding would enable vertically resolved measurements of winds, temperature, and trace species. A proposed angular resolution of approximately 0.01 arcseconds would resolve scales comparable to the atmospheric scale heights of Venus and Mars, around 5 and 11 km, respectively. Potential applications include three-dimensional studies of Venusian upper-atmospheric circulation and Martian global dust storms, CO2 photochemistry, water loss traced by HDO/H2O fractionation, and Venusian sulfur chemistry and cloud formation. Repeated coverage across local times, seasons, and solar activity would add temporal context to spacecraft measurements. These are anticipated capabilities and science opportunities, not reported observational results.

PublicVenus and Mars are rocky planets, but their atmospheres, climates, and surfaces have developed very differently. This abstract describes how a proposed ALMA2040 capability could help explain those differences by complementing close-up spacecraft observations expected by the 2040s. Detailed observations from the ground could measure atmospheric winds, temperatures, and small amounts of different gases at different heights. Repeating those measurements over time could reveal changes in circulation, dust storms, chemistry, water loss, and cloud formation that spacecraft snapshots alone cannot fully capture. Such studies could also help scientists interpret rocky planets beyond our Solar System and their potential habitability. The abstract outlines future possibilities rather than presenting new measurements.

Young explorerVenus and Mars are both rocky worlds, but their air and weather are very different. Scientists want to understand why. They propose using ALMA2040, a telescope facility on Earth, to watch the planets again and again while spacecraft look up close. It could help them study winds, warm and cold air, clouds on Venus, and dust storms on Mars. Watching for a long time could show changes that a quick visit might miss. This is a plan for what scientists could learn, not something they have measured yet.

High-frequency water megamasers as precision probes of black holes, galaxies and cosmology: A case for a next-generation sub-mm/mm interferometer

Ingyin Zaw, C.M. Violette Impellizzeri, Dominic W. Pesce+8 more

• Cosmology and Nongalactic Astrophysics
• Astrophysics of Galaxies

AstronomerThe abstract makes the case for ALMA2040, a proposed next-generation sub-mm/mm interferometer for circumnuclear water-maser studies. Existing 22 GHz VLBI observations provide geometric distances, black hole masses, and sub-parsec disk geometry; ALMA accesses transitions probing different physical conditions and disk regions, but detections remain limited to a few bright extragalactic sources in nearby galaxies. The authors argue that tenfold better line sensitivity and threefold longer baselines than ALMA would enable population-level studies and black hole masses and geometric distances from sub-mm masers alone, independently of and complementary to 22 GHz measurements. As part of a VLBI array, the proposed facility is projected to resolve maser disks beyond 160 Mpc, extend mass measurements into the largely untested intermediate-mass black hole regime, probe disk magnetic fields through polarization, and test systematics in H0 measurements. These are projected capabilities, not reported observational achievements.

PublicWater molecules in disks around active galaxies’ central black holes can produce intense microwave emission called masers. Astronomers already use one such signal to measure black hole masses and galaxy distances, helping constrain how fast the universe expands. ALMA detects other water-maser signals that probe different conditions, but current detections are limited to a few bright sources in nearby galaxies. This paper advocates a proposed observatory called ALMA2040. The authors argue that much greater sensitivity and longer separations between antennas would make these studies possible across a larger population. Linked into a wider telescope network, it could also map more distant disks and investigate their magnetic fields. These are anticipated benefits of the proposal, not discoveries already made.

Young explorerWater near some black holes makes bright signals that telescopes can catch. Those signals help scientists work out how heavy the black holes are and how far away their galaxies are. Scientists are suggesting a more powerful telescope called ALMA2040 to study more of these signals. They think it could show things today’s telescopes cannot, but it is still a proposal, not something they have already done.

Bridging the gap between stars and planets

Aina Palau, Dimitris Stamatellos, Matthew Bate+58 more

AstronomerThis abstract sets proposed observational requirements for a next-generation millimeter interferometer such as ALMA2040, rather than reporting detections. Brown dwarf (BD) and free-floating planet (FFP) formation remains poorly constrained: competing scenarios invoke gravitational fragmentation of molecular clouds or formation in circumstellar disks followed by dynamical ejection. Discriminating between them requires observations from cloud scales (~10 pc) to disk scales (~10 au). Proposed capabilities include detecting an embedded ~1-Jupiter-mass FFP at ~10 kpc in 1 hour, or within roughly 400 pc in tens of seconds, enabling cloud-wide censuses for comparison with scenario predictions. Other targets include CO outflows from substellar first hydrostatic cores and possible molecular outflows from ~1-Jupiter-mass FFPs, as predicted in the star-like scenario. Detecting ~2-Earth-mass disks around young BDs would test the larger disk-to-star mass ratios predicted by the planet-like scenario. Detecting complex organic molecule emission predicted for star-like proto-BDs at 400 pc would require tenfold greater line sensitivity at 5–10 au resolution. Detecting Earth-like protoplanets around young BDs at 400 pc is a further proposed goal for constraining radial drift and planet formation in the substellar regime.

PublicHow brown dwarfs and planets that wander without a host star form is still uncertain. They might form directly from collapsing gas clouds, much as stars do, or form in disks around stars and later be thrown out by gravitational encounters. This paper describes what a future millimeter-wave telescope array, such as ALMA2040, would need to do to help distinguish these possibilities; it does not report new discoveries. The proposed observations would survey whole clouds for very low-mass objects and examine their disks, gas outflows and molecular emission. These features could test differences predicted by the two formation routes, including whether brown dwarfs have relatively more massive disks when they form through the planet-like route. The authors also call for the ability to detect Earth-like planets still forming around young brown dwarfs, to investigate how planets grow in these environments.

Young explorerSome planets travel through space without a star, and brown dwarfs are objects less massive than stars. Scientists are not sure how they are born. Maybe they form from a cloud of gas squeezing together, or maybe they grow near a star and later get tossed away. This paper describes a future telescope scientists would need to help find out. They want it to look for these objects, the gas flowing away from them, and the disks where planets might grow. These are plans for what to look for, not things the paper says have already been found.

Millimetre/Sub-Millimetre SETI: Expanding the Radio Technosignature Parameter Space with ALMA2040

Louisa A. Mason, Michael A. Garrett, Sofia Z. Sheikh+5 more

AstronomerBuilding on the first ALMA technosignature survey, the authors propose four ALMA2040 searches in the largely unexplored millimetre/submillimetre SETI regime: phased-array narrowband searches accommodating large frequency drift rates; broadband aggregate leakage from hypothetical Kardashev Type I civilisations; cold computational waste heat in proposed Slysh haloes around M dwarfs; and visibility-function ringing caused by occulting megastructures, using phased ALMA within a mm/sub-mm VLBI array. For the leakage search, they project a roughly 60 pc horizon with 128–512 GHz of instantaneous bandwidth and one hour on source. Their motivation includes effectively transparent, non-dispersive interstellar and interplanetary propagation above 35 GHz, sparse terrestrial interference, and frequency-dependent gains in antenna gain and usable fractional bandwidth. They identify bandwidth, beamforming, commensal access, spectral resolution and sub-second time resolution as requirements. These are proposed capabilities and conditional detectability estimates, not reported technosignature detections.

PublicMost searches for extraterrestrial intelligence have used longer radio wavelengths, leaving millimetre and submillimetre wavelengths largely unexplored. The authors argue that these higher frequencies offer advantages for directed, high-data-rate communication and propose four searches for ALMA2040: concentrated signals in narrow frequency channels, the combined leakage of many transmissions, cold waste heat from hypothetical computing structures, and patterns produced when artificial structures block a background source. For the combined-leakage search, they estimate a reach of about 60 parsecs in a one-hour observation, assuming the proposed very broad frequency coverage. Carrying out these searches would require specific improvements in bandwidth, signal processing, observing access and time resolution. The paper presents a search programme and estimates of what it might detect, not evidence that alien technology has been found.

Young explorerCould someone far away in space be sending messages? This paper suggests new ways a telescope called ALMA2040 could look for clues using kinds of radio waves that people have hardly searched. It might look for messages, signals escaping from lots of machines, heat from giant computers, or shapes blocking light. These are ideas for what to look for, not things the scientists have found. The telescope would need special abilities to try these searches.

Chemical Demographics of Star-forming Regions

Maria N. Drozdovskaya, Timea Csengeri, Maria Teresa Beltrán+35 more

• Earth and Planetary Astrophysics
• Astrophysics of Galaxies
• Solar and Stellar Astrophysics

AstronomerThe abstract argues that current knowledge of complex organic molecules (COMs) in star formation is biased toward a few sources with bright molecular lines, limiting demographic tests of chemical inventories and physicochemical models. It advocates a next-generation ALMA2040 with a tenfold improvement in line sensitivity to enable wideband (>100 GHz) surveys of samples exceeding 1,000–10,000 prestellar and protostellar sources, routinely reaching COM abundances of 0.01% relative to methanol. These are proposed capabilities and survey goals, not reported results. Such samples would test how chemical complexity depends on stellar mass regime, cloud and Galactic environment, metallicity, cluster feedback, and variable accretion, and assess the ubiquity and uniformity of COM chemistry. The motivation is to constrain the chemical reservoir available for planet formation and its eventual influence on planetary atmospheres.

PublicHow widespread is complex organic chemistry in the material that forms stars and planets? The abstract argues that existing observations cannot yet answer this reliably because they favor a small number of sources with especially bright molecular signals. It calls for a future ALMA2040 telescope upgrade with ten times better sensitivity to molecular lines, enabling broad surveys of thousands of star-forming objects. These proposed surveys—not results already obtained—would investigate whether chemical inventories vary with environment, the masses of forming stars, and changes in how they gather material. The goal is to understand which complex molecules are available for planet formation and may ultimately help shape planetary atmospheres.

Young explorerStars and planets form from clouds of material. Scientists want to know whether those clouds have the same kinds of complicated molecules, or different ones. So far, they have mostly studied a few places where molecules are easier to spot. The authors want a better telescope system to look at many more places, including ones with much fainter signals. That could help us learn what ingredients are around when planets form. They have not done this big survey yet.

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 integrate optimal frequentist statistics for gravitational-wave memory searches into enterprise and compare a noise-marginalized statistic with a simpler maximum-posterior method. Tests use simulated pulsar timing arrays containing red and white noise, as well as the NANOGrav 15-year data set. 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 estimates suffice to identify potentially detectable signals in realistic PTAs, while noise marginalization could help assign false-alarm probabilities to Bayesian results. The abstract reports a search-method comparison, not a gravitational-wave memory detection; such a detection could provide a unique test of general relativity.

PublicPulsar timing arrays could detect gravitational-wave memory and thereby provide a distinctive test of Einstein’s general relativity. This study compares two ways of handling noise when searching for that signal, adding the search statistics to a software suite called enterprise. The researchers tested the methods on both simulated data and the NANOGrav 15-year data set. The methods produced no significant differences in the simulations and only small differences in the real-data comparison. The authors conclude that the simpler method is sufficient for finding potentially detectable signals, while the more involved method could help assess how often noise might produce a false alarm in Bayesian analyses. This is a comparison of search techniques, not a reported detection.

Young explorerScientists are looking for something called gravitational-wave memory by checking the timing of pulses from stars. They compared two ways to deal with noise that can make a signal hard to spot. They tried made-up data and real telescope data, and the two ways gave very similar answers. They think the simpler way is enough to find possible signals, while the other way might help check whether noise is fooling them. They did not report finding gravitational-wave memory.

Displacement-noise-free gravitational-wave detector using quantum tomography of photon orbital angular momentum states

Haorong Wu, Xilong Fan, Lixiang Chen

• General Relativity and Quantum Cosmology
• Instrumentation and Detectors
• Optics
• Quantum Physics

AstronomerThe authors propose a gravitational-wave detection framework based on GW-induced transitions between photon orbital-angular-momentum (OAM) states, rather than differential arm-length measurements. Parametrized quantum state tomography of the induced OAM sidebands is proposed to recover seven wave parameters with one V-shaped detector: frequency, propagation direction, two polarization amplitudes, and their initial phases. Direct sideband detection is estimated to yield approximately 10^-15 W; adding a stronger reference state with r = 0.01 enhances the predicted signal. For 4 m arms, 160 round trips, paraxial parameter 0.1, 10 kW incident power, 1064 nm wavelength, and GW amplitude 10^-18, the authors estimate transition amplitudes near 10^-10 and signal powers of order 1 nW. They give a shot-noise-limited sensitivity floor of 1.6 × 10^-20 Hz^-1/2. The proposed OAM readout is described as intrinsically displacement-noise-free and broadband, targeting the 0.1–10 Hz gap. These are framework predictions and sensitivity estimates, not reported detections or demonstrated instrument performance.

PublicThe authors propose a new way to detect gravitational waves by reading changes in light’s orbital angular momentum, a property associated with its spatial structure, instead of measuring differences in detector arm lengths. Their calculations suggest that one V-shaped detector could recover a wave’s frequency, direction, and polarization properties. Because the direct signal would be extremely faint, they propose adding stronger reference light to enhance it. For a specified design with 4-metre arms and 10 kilowatts of incident light, they estimate a signal of about one nanowatt. The scheme is intended to avoid displacement noise and cover frequencies from 0.1 to 10 hertz. Its sensitivity is a prediction limited by light’s shot noise, not demonstrated performance.

Young explorerScientists have an idea for finding tiny ripples in space by watching how they change the twist of light. They would add brighter reference light to help reveal the tiny signal. Their calculations suggest it could work, but this is a proposed detector, not a report of catching a ripple.

Using 23 Years of ACS/SBC Data to Understand Backgrounds: Significant Reductions in Expected Background Levels

Christopher. J. R. Clark, Roberto J. Avila, Alyssa M. Guzman+1 more

AstronomerAn analysis of 23 years of Hubble ACS/SBC data finds more than an order-of-magnitude variation in backgrounds for F115LP, F122M, F125LP, PR110L, and PR130L, apparently driven by airglow variability. Dark-rate-dominated F150LP and F165LP backgrounds vary much less. For airglow-dominated filters, measured backgrounds are substantially below Exposure Time Calculator (ETC) v33.2 predictions: its average-airglow estimates exceed measured medians by factors of 2.51, 2.64, 105, and 3.64 for F115LP, F122M, F125LP, and F140LP, respectively. Preliminary analysis suggests that some OI airglow lines are usually fainter than assumed by the ETC; this explanation is not established. The lower backgrounds imply substantially shorter exposure times for background-limited observations with shorter-wavelength SBC filters than previously expected. The abstract announces an option for ETC v34.1 to estimate SBC exposure times using empirical background percentiles.

PublicResearchers examined 23 years of observations from a Hubble instrument and found that unwanted background light varies greatly between observations. Settings affected by airglow showed much larger changes than settings dominated by the detector’s own background. The measured backgrounds were also generally lower than predicted by the exposure-planning software for airglow-dominated filters. In one filter, the software’s average-airglow prediction was 105 times the measured median. A preliminary explanation is that certain oxygen emissions producing airglow are usually weaker than the software assumes. Lower backgrounds mean some observations can reach their goals much faster than previously expected, though conditions vary. A planned software option will use measured background distributions to help estimate exposure times.

Young explorerHubble takes pictures of space, but extra glow can make faint things harder to see. Scientists checked 23 years of its observations. They found that this glow changes a lot and is often weaker than their planning tool expected. That means some observations can take less time, though not every time.

Using 23 Years of ACS/SBC Data to Understand Backgrounds: Explaining & Predicting Background Variations

Christopher J. R. Clark, Roberto J. Avila, Alyssa M. Guzman+1 more

AstronomerAnalysis of 23 years of Hubble ACS/SBC data found background variations exceeding an order of magnitude in most filters. Airglow is understood to dominate the shorter-wavelength backgrounds, but the drivers of variability remain poorly constrained across filters. Using more than 8,000 archival SBC observations and 23 observational parameters, the authors developed a machine-learning model reported to predict observation backgrounds accurately. The model identifies Solar elevation, Solar separation angle, Earth limb angle, SBC temperature, and target Galactic latitude as the main predictors, with their importance depending on the filter. These model-based findings identify influential parameters without establishing the physical causes of the variations.

PublicThe unwanted background light in Hubble’s ACS/SBC images can change greatly: a review spanning 23 years found more than tenfold variation in most filters. Glow from Earth’s atmosphere is understood to supply most of this background at shorter wavelengths, but exactly what drives its changes is still uncertain. Researchers trained a machine-learning model on more than 8,000 archived observations, using 23 details about each observation, and report that it predicts background levels accurately. Depending on the filter, the model points mainly to the Sun’s position relative to the observation, the angle from Earth’s edge, the detector’s temperature, and where the target lies relative to the Milky Way’s plane. These are model-identified predictors, not proof of what physically causes the changes.

Young explorerHubble takes pictures of space, but extra light can make the background brighter. Scientists found that this extra light changes a lot between pictures. They taught a computer using more than 8,000 old observations, and say it can predict how bright the background will be. The computer found clues in where the Sun and Earth are compared with where Hubble looks, how warm part of the camera is, and where Hubble points in our galaxy. These clues help, but scientists still do not know exactly why the extra light changes.

Co-design of ground-based gravitational wave detector networks

Daniel Lanchares, Lysiane Mornas, Luigi Toffolatti+1 more

• General Relativity and Quantum Cosmology

AstronomerThe authors propose IfoScout, a machine-learning methodology for co-designing next-generation ground-based gravitational-wave detectors. Their demonstration is a two-stage simulation of a network of fictional L-shaped interferometers under physical and geographical constraints. Using publicly available data for two illustrative locations, reinforcement learning sets detector lengths and orientations; differential programming then optimizes internal parameters related to cavity stability for sensitivity. The optimization is described as indirectly reducing costs. This is a simulated proof of concept, not a realized detector design or an observational result. The authors argue that such pipelines could inform projects including the Einstein Telescope and Cosmic Explorer, provided precise data and detailed, realistic interferometer simulations are available.

PublicIfoScout is a proposed machine-learning approach to help design future ground-based detectors of gravitational waves. In a computer demonstration using fictional L-shaped detectors and public data for two example locations, one stage chooses the detectors' lengths and directions within physical and geographical limits. A second stage adjusts internal settings to improve sensitivity. The authors describe lower costs as an indirect benefit of this optimization, rather than reporting a completed detector or measured savings. They suggest the approach could help future projects such as the Einstein Telescope and Cosmic Explorer, but that would require precise data and detailed, realistic simulations.

Young explorerScientists want to build big machines that listen for tiny wiggles in space. They have suggested a computer helper called IfoScout to help plan them. In a pretend computer test, it chose how long some L-shaped machines should be and which way they should point, then adjusted parts inside to help them listen better. These were not real machines being tested. The scientists think this helper might be useful for future machines, but it would need very good information and more lifelike computer tests.

Beyond the BLUE I: the advantage ceiling - how much can any estimator beat the matched filter in mm/submm survey data?

Kaustuv Basu

• Cosmology and Nongalactic Astrophysics

AstronomerThis methodological study introduces an advantage ceiling, eta: the Fisher information for source amplitude relative to that of the matched filter, bounding potential variance reduction for estimators unbiased at every true amplitude. It can be assessed using noise-only simulations before training a network. Because the matched filter is the best linear unbiased estimator at fixed noise covariance and the minimum-variance unbiased estimator for Gaussian noise, an advantage requires image-dependent covariance or non-Gaussian noise. For simulated millimeter/submillimeter survey noise with an instrumental white-noise floor, Gaussian cases yield eta = 0.94–1.06 with uncertainty ±0.04, consistent with unity. Covariance mixtures have exact ceilings reaching 10.2 for spectral tilt with an extended template; residual artifacts give eta ≤ 1.09. Source confusion provides substantial headroom, with lower bounds eta ≥ 3.8 for extended sources and ≥ 2.4 for compact sources. These ceilings are not demonstrated network gains: a tested ResNet realizes a factor 1.8 of the available 10.2 and is 6–15% less efficient than the matched filter under Gaussian noise after prior shrinkage is removed. A zeroed DC mode, missing white-noise floor, or floating-point rounding can manufacture apparent advantages of up to two orders of magnitude.

PublicCan a neural network really measure an astronomical source’s strength more precisely than a standard matched filter? This study develops a way to assess the possible improvement from simulated noise before training a network. For estimates without systematic bias at any source strength, an improvement requires noise whose statistical pattern changes between images or departs from a Gaussian distribution. In simulated millimeter/submillimeter survey conditions, ordinary Gaussian noise leaves essentially no room for improvement. Some changing noise patterns and confusion from overlapping sources allow substantially more room, but that does not mean a network achieves it. In one test, a network achieved a factor of 1.8 improvement where the theoretical ceiling was 10.2; with Gaussian noise it performed worse than the matched filter after accounting for an effect of its prior assumptions. The study also identifies numerical and noise-modeling problems that can create misleadingly large apparent gains.

Young explorerMeasuring how bright something is in a space picture can be tricky when the picture is noisy. The researchers used pretend noisy pictures to check how much a computer could improve on a standard measuring tool. Some kinds of noise leave room to do better, but others do not. Having room to improve does not mean the computer will manage it. Computer mistakes can also make it look better than it really is.

The optical high-resolution spectral archive of the HERMES spectrograph mounted on the 1.2m Mercator telescope

Hans Van Winckel, Saskia Prins, Gert Raskin+13 more

• Solar and Stellar Astrophysics

AstronomerThis archive-release and instrument-reference paper reviews more than 16 years of operations of HERMES, the high-resolution, fibre-fed optical spectrograph on the 1.2 m Mercator telescope at Roque de los Muchachos, Spain. Scientific operations began in June 2009, with regular upgrades supporting continued spectral quality. The authors release about 150,000 high-resolution spectra, describe the instrument’s overall performance, major upgrades and global release properties, and document a standard one-year proprietary period with exceptions. Built using GAVO DaCHS, the archive supports a dedicated web interface and Virtual Observatory tools, including PyVO, TOPCAT and Aladin. Worked examples demonstrate searching for and downloading fully wavelength-calibrated, cosmic-cleaned, barycentric-corrected 1D spectra. The contribution provides archive documentation and a reference for users rather than reporting a new astrophysical finding.

PublicAstronomers are opening an archive of about 150,000 high-resolution spectra from HERMES, an instrument on the 1.2-metre Mercator telescope in Spain. Spectra separate light by wavelength so researchers can study it in detail. The paper reviews more than 16 years of operations since June 2009 and describes upgrades that have helped maintain the instrument’s data quality. Researchers can search and download processed spectra through a website or compatible astronomy software. The data normally have a one-year period reserved for their original users, though there are exceptions. This paper introduces the archive and explains how to use its data; it does not announce a new discovery about the universe.

Young explorerA telescope in Spain has a tool called HERMES that spreads light into tiny steps of color. Astronomers are sharing about 150,000 of these light records in a big online collection. This paper explains the tool, how it has been improved, and how people can find and use the records. Most records are kept for the people who first collected them for one year before being shared, but there are some exceptions. The paper shares a collection to explore, not a new discovery in space.

XuYi Interferometer Observation Simulator

M. Hadjara, T. Xu, Y. Sun+21 more

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

PublicResearchers have developed XIOS, a software tool to help plan observations with the XuYi Interferometer, a Chinese telescope system still under development. The tool lets users explore when targets can be observed, how the telescope arrangement affects observations, and whether proposed setups fit the system's operating limits. It also estimates the interference signals produced by combining the telescopes' light. The paper describes the software and presents example simulations for a three-telescope setup using near-infrared light. These examples predict possible observing performance; they are not measurements from completed observations.

Young explorerScientists are building a system that will combine light from telescopes to study the sky. They made a computer program to help plan how to use it. The program checks when something in the sky could be watched and predicts how the telescopes could work together. The scientists show computer examples using three telescopes and a kind of light our eyes cannot see. These are practice plans, not things the telescopes have already seen.