Tonight’s sky of new research

Constraining Primordial Magnetic Fields with Weak Lensing

Anna D'Ambrosio, Matteo Viel

AstronomerThis simulation-based study investigates how primordial magnetic fields (PMFs) modify nonlinear matter clustering and the weak-lensing convergence power spectrum in ΛCDM. Dark-matter-only N-body simulations start from linear matter spectra with PMF-induced small-scale enhancements and yield enhanced convergence power at high multipoles. The authors construct a convergence-spectrum emulator that also includes intrinsic alignment and baryon feedback, then perform MCMC inference on mock data. For zero-field ΛCDM mocks, approximate 95% upper limits on the field amplitude smoothed at 1 Mpc are B_1Mpc < 1.6, 1.0, and 0.8 nG for maximum multipoles of 5000, 10000, and 20000, respectively; these are mock-data constraints, not observational limits. Recovery of nonzero B_1Mpc and the magnetic spectral index n_B depends strongly on the input model and multipole cutoff. Models with n_B = −2.1 are more readily constrained than those with n_B = −2.7 because their convergence-spectrum enhancement is stronger. No clear degeneracy is found with intrinsic-alignment or baryon-feedback parameters, but B_1Mpc and n_B can be degenerate; selected two-dimensional posteriors are characterized with linear fits.

PublicThe researchers used computer simulations to explore whether magnetic fields from the early universe could leave a detectable imprint on how matter clusters and bends light. In their models, these fields strengthen clustering on small scales and increase the predicted weak-lensing signal at fine angular scales. They then tested a fast prediction tool against artificial data, accounting for galaxy alignments and the effects of ordinary matter on clustering. When the artificial universe contained no primordial magnetic field, including finer-scale information produced tighter upper limits on the possible field strength. These limits are from simulated data, not measurements of the real universe. For artificial universes with magnetic fields, how well the fields could be recovered depended on their strength, their distribution across scales, and the range of angular scales analyzed. Different combinations of magnetic-field properties could produce similar signals, making them difficult to distinguish.

Young explorerScientists used computers to make pretend universes and ask what very old magnetic fields might do. In their computer models, the fields made matter bunch up more in small places and changed how that matter would bend light. Looking at smaller details sometimes helped them learn more about the pretend fields, but different kinds of fields could look alike. This was a test with pretend data, not a discovery of those fields in the real universe.

ROBIN-PIP: Robust Bayesian Field-Level Inference with Physics-Informed Priors

Ludvig Doeser, Simon Ding, Guilhem Lavaux+1 more

• Instrumentation and Methods for Astrophysics

AstronomerROBIN-PIP introduces simulation-derived, physics-informed priors for flexible galaxy bias models in Bayesian field-level inference. The framework allows high-fidelity simulations that cannot be incorporated directly into gradient-based inference to inform the allowed parameter space indirectly. In a simulated-universe proof of concept, the authors integrate ROBIN-PIP into Bayesian Origin Reconstruction from Galaxies and jointly infer cosmic initial conditions and truncated power-law bias parameters. Relative to inference without the simulation-based prior, posterior standard deviations of bias parameters decrease by up to 20%, and autocorrelation lengths fall from 730–870 to 440–550, increasing effective sample sizes. The authors find no bias in the recovered initial conditions and interpret the test as evidence that the priors guide inference toward physically consistent solutions without compromising the data likelihood. The demonstration is simulation-based, not an application to observed galaxy surveys, and suggests potential for using overparameterized bias models.

PublicGalaxy surveys show where galaxies are, but reconstructing the underlying matter distribution requires a model linking matter to galaxies. Flexible versions of these models can have many parameters that are difficult to constrain or interpret physically. The researchers introduce ROBIN-PIP, a method that uses detailed simulations to guide those parameters toward physically plausible values. They test it in a simulated universe while reconstructing both the universe's initial conditions and the parameters linking matter to galaxies. Compared with a version without this simulation-based guidance, uncertainties in the model parameters shrink by up to 20%, and the statistical sampling becomes more efficient. The authors find no bias in the reconstructed initial conditions. This is a promising demonstration using simulated data, rather than a result from real galaxy observations.

Young explorerImagine trying to work out how the universe began by looking at where its galaxies are now. Scientists need a rule for how galaxies match up with matter, but that rule can be tricky to figure out. They made a new helper that learns from detailed pretend universes on a computer. When they tested it on a pretend universe, it helped narrow down the rule and made the guessing process work better. They found no sign that it pushed their picture of the universe's beginning in the wrong direction. They have shown this in a computer test, not yet with real galaxy observations.

Emulation of the Halo Mass Function with Neural Networks

Olive Ross, Nicholas Battaglia

AstronomerThe authors present a neural-network emulator for the halo mass function, whose dependence on cosmological parameters makes it useful for inference. Given cosmological and astrophysical parameters, halo mass, and redshift, the network predicts the cumulative halo count above the specified mass directly, avoiding binning and functional or PCA-based data reduction. It also predicts its own error in units of Poisson shot noise. Leave-one-out validation uses the N-body MassiveNus suite and the hydrodynamical CAMELS IllustrisTNG and SIMBA suites, covering different box sizes, redshifts, sub-grid physics, and software. Across 1.2 million held-out predictions, 88% have model bias no greater than shot noise, and 99.9% are within three times shot noise. The only significant high-error tail occurs in MassiveNus: the predicted bias flags 76% of predictions exceeding three times shot noise, while the remaining high-error count is comparable to that expected from shot noise alone. These are simulation-validation results, not observational measurements. The publicly available emulator can be trained on other simulation suites and is intended for cosmological and astrophysical inference.

PublicThe number of galaxy clusters of different masses depends strongly on the properties of the universe, but the simulations used to calculate these numbers are costly. This study presents a neural network that learns from simulations to predict how many halos lie above a chosen mass for a given set of cosmic and astrophysical conditions. Each prediction includes an estimated error, measured against the random fluctuations expected when counting objects. Tests on three simulation collections—not observations of real clusters—checked 1.2 million predictions withheld from training. In 88% of cases, the prediction bias was no larger than those counting fluctuations; 99.9% were within three times that level. The most substantial large-error tail appeared in one simulation collection, and the network's error estimate flagged 76% of those cases, so its warnings are useful but not complete. The tool is publicly available and can be trained on other simulations.

Young explorerScientists make computer versions of the universe, but these can take lots of work to run. They taught a computer helper to guess how many big clumps would be heavier than a chosen amount. It also gives a warning about how wrong its guess might be. Most guesses were close when checked against the computer universes, but the helper did not catch every big mistake.

Effects of Poisson Isocurvature Perturbations on Induced Gravitational Waves

Zi-An Zhou, Cheng-Jun Fang, Zong-Kuan Guo

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study evaluates gravitational waves induced by Poisson isocurvature perturbations from discrete primordial black hole (PBH) number-density fluctuations during a sudden PBH-evaporation transition from early matter domination to radiation domination. It examines how the source’s hierarchy of intrinsic non-Gaussian statistics enters the induced tensor statistics. The calculation finds that the tensor power spectrum retains only scalar-source two-point correlations, whereas higher-order source correlations first appear in the tensor bispectrum. The relative amplitudes of different bispectrum configurations exhibit nontrivial scale dependence, which may help distinguish this discrete-PBH scenario from other induced-GW mechanisms. These are theoretical findings under the sudden-transition assumption, not observational detections.

PublicThe researchers calculate how gravitational waves could be generated in a proposed early-universe scenario involving the evaporation of primordial black holes. In this scenario, a sudden change from a universe dominated by matter to one dominated by radiation can strengthen the waves. Because the black holes are separate objects, their numbers naturally fluctuate from place to place in a particular statistical pattern. The calculation finds that the gravitational-wave power spectrum carries only information about correlations between pairs of source fluctuations, while the bispectrum, which describes correlations among three wave components, also carries higher-order information. How different bispectrum patterns compare changes with scale and might help distinguish this scenario from other ways of generating gravitational waves. The study does not report an observed signal.

Young explorerScientists used math to explore what might happen if tiny black holes in the very young universe evaporated suddenly. There could have been more black holes in some places than in others, and those differences could help make ripples in space. The scientists found that one way of studying the ripples keeps simple information about those differences, while another keeps more complicated clues. Those clues might someday help tell how the ripples were made. This is a calculation of what could happen, not ripples that the scientists have seen.

Weak-Lensing Shear Response for Photometric Redshift-Based Tomographic Binning

Xiangchong Li, Tianqing Zhang, Rachel Mandelbaum+1 more

AstronomerThe study extends analytical shear self-calibration, AnaCal, to account for photometric-redshift selection biases in tomographic weak lensing by propagating shear responses through the selection process. Correlations between photo-z estimates and shear can otherwise bias the amplitude and redshift evolution of the lensing signal and the inferred growth of cosmic structure. The correction does not require external image simulations for calibration, although simulations are used for validation. As an initial real-data sanity check, photo-z estimates from AnaCal fluxes in Rubin Observatory Data Preview 1 have quality comparable to standard LSST estimates and slightly better quality at high redshift. In LSST-like image simulations including blending at the expected LSST Y10 depth, the multiplicative shear bias induced by photo-z selection satisfies the ten-year requirement, absolute value of m less than 3 × 10^-3, in all five tomographic bins for both a template-fitting and a machine-learning photo-z algorithm. These simulation results support AnaCal as a self-consistent pipeline for upcoming LSST tomographic analyses; they are not a real-data demonstration of ten-year shear-calibration performance.

PublicWeak gravitational lensing uses small distortions in galaxy images to study how cosmic structure grows and to investigate dark energy. Researchers group galaxies by estimated redshift, which helps separate different periods of cosmic history. But correlations between these estimates and the measured distortions can bias the results. This study extends a method called AnaCal to correct that selection bias without needing external image simulations to calculate the correction. An initial check using real Rubin Observatory Data Preview 1 data found that AnaCal-based redshift estimates were comparable to standard LSST estimates and slightly better at high redshift. The researchers separately tested the shear correction in simulated images with overlapping galaxies and the expected depth of the ten-year LSST survey. For two representative redshift-estimation methods, the remaining multiplicative bias from redshift selection met the requirement that the absolute value of m be less than 3 × 10^-3 in all five redshift groups. The tests support the method's use in upcoming analyses, but the ten-year calibration performance was demonstrated in simulations, not observed survey data.

Young explorerGravity can make faraway galaxies look a little stretched. Scientists study those tiny stretches to learn how groups of galaxies grow. They sort galaxies into groups using estimates of how much their light has changed on its journey to us, but that sorting can make the stretching measurements unfair. The scientists improved a tool called AnaCal to fix this. In a first check with real telescope data, its estimates were about as good as the usual ones, and a little better for galaxies with more-redshifted light. They also tested the fix with pretend telescope pictures, including galaxies whose pictures overlap, made to resemble the expected ten-year survey. With two ways of estimating redshift, the leftover sorting error met their small-error rule in all five groups: the absolute value of m was less than 3 × 10^-3. That is encouraging, but this check of the stretching correction used pretend pictures, not the finished ten-year survey.

Cosmological inference from a joint DESI DR1 full-shape power spectrum and bispectrum analysis

Caroline Guandalin, Prakhar Bansal, Pedro Carrilho+9 more

AstronomerThis DESI DR1 joint full-shape analysis uses three luminous red galaxy (LRG) redshift bins and the quasar sample, modelling the redshift-space power spectrum at one loop and the tree-level bispectrum within the Effective Field Theory of large-scale structure. A Tripolar Spherical Harmonics decomposition expresses survey-window convolution as a direct linear transformation of theoretical bispectrum multipoles. Power-spectrum constraints agree well with the official DESI DR1 full-modelling results. Adding the bispectrum monopole reduces marginalised uncertainties in cold dark matter density and matter-fluctuation amplitude by 9–18% and 8–20%, respectively, for individual tracers; the reductions are 15% and 10% for the combined LRG sample, and 6% and 4% for all tracers combined. A restricted quadrupole test in the first LRG bin changes uncertainties by only a few percent, so it does not establish the quadrupole's impact across the full sample. In the extended w0waCDM analysis, cosmological posteriors broaden substantially; the bispectrum only mildly changes the allowed dark-energy parameter region, which remains sensitive to prior ranges. These data-analysis results support the potential of higher-order clustering statistics, rather than establishing strong new dark-energy constraints.

PublicResearchers analysed how galaxies and quasars are distributed in the first DESI data release. Alongside the power spectrum, which describes clustering through pairs, they used the bispectrum, which captures patterns involving triples and probes how gravity develops cosmic structure. Adding this information tightened estimates of the density of cold dark matter and the strength of matter fluctuations. For all samples combined, the uncertainties fell by 6% and 4%, respectively; improvements were larger for some individual samples. A more detailed bispectrum component made only a small difference in a limited test on one galaxy sample. When the researchers allowed a broader model of dark energy, the range of possible cosmological parameters widened substantially. The bispectrum then made only a mild difference to the allowed dark-energy parameters, and those limits still depended on the assumed parameter ranges. The study demonstrates a useful analysis method, not a decisive new finding about dark energy.

Young explorerScientists looked at patterns in where galaxies are found. Looking at groups of three, as well as pairs, helped them narrow down their guesses about how much dark matter there is and how unevenly matter is spread out. But it helped only a little with questions about dark energy. The answers still depend on which possibilities the scientists let their model consider.

Non-Gaussian Parameter Bias: Formalism and Validation

Nikolina Šarčević, Matthijs van der Wild, Elena Sellentin

AstronomerThe authors develop a DALI-based framework for propagating systematic data mismatches into parameter biases and posterior deformations beyond the Gaussian Fisher approximation. They derive analytic MAP and posterior-mean expressions, including a semi-analytic expansion in systematic amplitude, and validate them against direct numerical calculations and MCMC in a controlled nonlinear two-parameter benchmark up to a covariance-weighted mismatch of d_data = 5. At that mismatch, Fisher predicts the wrong shift direction for one parameter and has a Fisher-metric discrepancy of 23.1; the analytic DALI MAP prediction remains within 0.091, with componentwise errors of 0.04% and 0.46%. The response expansion gives posterior-mean errors of 0.02% and 0.18%, while the DALI posterior closely reproduces the sampled posterior’s displacement and deformation. Equal-significance mismatches with different directions yield markedly different responses, and additive mismatches can induce nonadditive parameter shifts through nonlinear inference. These are benchmark validation results, not observational measurements or a demonstration of equivalent accuracy for arbitrary applications.

PublicSmall, systematic differences between data and a model can change both the values researchers infer and the range of values they consider plausible. This study develops a mathematical method for tracking those changes when a commonly used Gaussian approximation is inadequate. In a controlled test with two unknown parameters, the standard approximation predicted a shift in the wrong direction for one parameter at the largest mismatch tested, while the new method closely matched detailed numerical calculations. The tests also show that equally significant mismatches can have very different effects depending on their direction, and that combining mismatches need not simply add their separate effects. The reported accuracy comes from this controlled benchmark, not from observations or tests of every possible application.

Young explorerScientists use clues to work out answers, but a small problem in the clues can move their best guess and change how sure they are. The researchers made a new way to follow those changes. In a special math test, it worked much better than an older shortcut. They also found that two problems together can change a guess in a surprising way.

Strongly mixed cosmological collider at unequal sound speeds

Javier Huenupi, Gonzalo A. Palma, Spyros Sypsas

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

AstronomerThis theoretical study derives canonically normalized modes for a two-field inflationary system with arbitrary constant quadratic mixing and unequal curvature and isocurvature sound speeds. A Laplace representation reduces the coupled dynamics to a second-order Heun equation, yielding the exact late-time curvature power spectrum for arbitrary mixing and entropy mass. With r_c = c_sigma/c_varphi, fixed nonzero mixing and r_c much smaller than one produce power-law enhancement, squared-logarithmic growth, or bounded oscillations in log r_c, depending on mass and mixing. For r_c much larger than one, the correction to the unmixed spectrum vanishes as log(r_c)/r_c² at fixed mass and mixing. The authors also compute tree-level bispectra for three representative cubic interactions, treating mixing exactly. For heavy entropy fields, unequal speeds change the collider amplitude and phase but preserve the strict squeezed-limit frequency determined by the final entropy mass. The power-normalized amplitude can depend nonmonotonically on r_c, and a sound-speed hierarchy can delay convergence to that asymptotic regime. These are analytical model results, not observational findings.

PublicThe researchers study a mathematical model of inflation, an early period of cosmic expansion, with two interacting types of fluctuations that travel at different speeds. They calculate exactly how the interaction affects the strength of curvature fluctuations within this model. When the second type travels much more slowly, the strength can grow or oscillate as the speed ratio changes, depending on the mass and interaction strength. When it travels much faster, the effect of the interaction fades at fixed mass and mixing. The researchers also calculate correlations among three fluctuations for three example interactions. For a heavy second field, different speeds alter the strength and phase of an oscillatory signature, but not its limiting frequency, which is set by that field’s final mass. Reaching this limiting behavior can require a more extreme configuration when the speeds differ greatly. These calculations describe theoretical behavior rather than a signal detected in the universe.

Young explorerScientists used math to study two kinds of tiny ripples in a model of the very early universe. The ripples can affect each other and move at different speeds. The math says that changing their speeds can make some ripple patterns stronger or change how they wiggle, depending on other parts of the model. This is something the scientists worked out with math, not something they saw in the sky.

From the Old to the New Starobinsky Inflation

Shinji Hirano

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

AstronomerThis theoretical study builds on the known background connection between Starobinsky’s original trace-anomaly-driven inflation and its R+R² scalaron formulation: an Euler-anomaly-supported early de Sitter phase evolves into the scalaron regime, where observable modes exit the horizon. Computing scalar and tensor spectra on the exact background, the authors find anomaly corrections controlled by aN*/(18b), with a the Euler-anomaly coefficient, b the R² coefficient, and N* the number of e-folds after pivot horizon exit. Scalaron inflation is recovered as this parameter vanishes. Matching the observed scalar tilt at N*=60 requires b/a≈35, rather than the b/a≳10⁹ of early realizations. At this benchmark, the predicted scalar spectrum is redder at fixed N*, while the tensor-to-scalar ratio is about 17% lower at fixed tilt than in scalaron inflation. With minimal gravitational reheating and N*≈53, the predicted tilt remains within 1σ of the Planck value for b/a≳35. Separately, the de Sitter analysis identifies a finite range of Weyl coupling that excludes an extra real spin-two pole and maintains a decaying causal response. These are theoretical predictions and consistency conditions, not an observational detection of the anomaly; a companion paper provides the full analysis.

PublicThe paper examines how two often separately treated versions of Starobinsky’s model of the universe’s early rapid expansion connect. The researchers calculate the patterns of density fluctuations and gravitational waves predicted by the connected model, including an effect called the trace anomaly. Their calculation can match the observed pattern of density fluctuations with a much smaller ratio of two model coefficients than early versions required: about 35 rather than at least a billion, assuming 60 e-folds of expansion after a reference fluctuation left the horizon. At that benchmark, the model predicts about 17% less gravitational-wave power relative to density-fluctuation power than the usual scalaron model when both have the same spectral tilt. A different assumption about reheating also gives a tilt within the stated Planck uncertainty for sufficiently large coefficient ratios. These are model predictions and comparisons with observations, not evidence that the anomaly’s distinctive signal has been detected.

Young explorerScientists made calculations about how the universe might have stretched very fast when it was young. They connected two versions of a model and included an extra effect called an anomaly. That effect changes the tiny patterns the model predicts, and some choices agree with what astronomers see. The model also predicts weaker ripples in gravity compared with its other tiny patterns. Scientists have not shown that this extra effect really happened.

Primordial Black Hole and Gravitational Wave by Peaked Cosmic Perturbations from Axion Curvaton

Keisuke Harigaya, Lian-Tao Wang, Jiangyi Yi

• High Energy Physics - Phenomenology

AstronomerThis theoretical study demonstrates that an axion field's inflationary dynamics can produce perturbations peaked at an intermediate wavenumber, and computes the resulting gravitational-wave spectrum and primordial-black-hole abundance through the curvaton mechanism. The predicted GW spectrum is triangular, with UV and IR slopes set by the axion's inflationary evolution and treated as free parameters. The PBH calculation accounts for both the nonlinear curvature-to-density relation and curvaton-generated primordial non-Gaussianity. Within the model, PBHs can constitute all dark matter, accompanied by blue-tilted isocurvature perturbations on small scales. An anti-correlation between the GW spectrum's IR slope and the magnitude of dark-matter isocurvature perturbations provides a proposed multi-messenger test, rather than an observational confirmation.

PublicThe researchers calculate how a hypothetical axion field during the universe's early inflationary expansion could create disturbances strongest at a particular scale. Through a process called the curvaton mechanism, these disturbances could generate gravitational waves and primordial black holes. The predicted gravitational-wave spectrum has a triangular shape, whose slopes depend on how the axion evolves. The black-hole calculation includes nonlinear effects and deviations from a Gaussian pattern in the initial disturbances. In this model, primordial black holes could make up all dark matter, with additional variations in dark matter's relative abundance that become stronger toward smaller scales. The model links the strength of these variations to the low-frequency slope of the gravitational-wave spectrum, suggesting a way to test it using both signatures. These are theoretical predictions, not reported detections.

Young explorerScientists did calculations about what might have happened when the universe was very young and growing very fast. A possible field called an axion could have made uneven patches that later produced black holes and ripples in space. In their idea, those black holes could make up all the mysterious stuff called dark matter. The calculations also connect the pattern of the ripples with how uneven the dark matter would be. Looking for both patterns could help test the idea, but this study does not show that it really happened.

QCD axion misalignment during reheating

Disha Bandyopadhyay, Debasish Borah, Nayan Das

• High Energy Physics - Phenomenology

AstronomerThis theoretical study examines QCD axion dark-matter production through vacuum and kinetic misalignment during extended reheating after slow-roll inflation. It assumes pre-inflationary Peccei–Quinn symmetry breaking and a monomial inflaton potential during reheating. Three perturbative decay scenarios are considered: inflaton decay into SM-like boson pairs, SM-like fermion pairs, or exclusively heavy right-handed neutrino pairs. In the third scenario, the neutrinos temporarily dominate the cosmic energy density before decaying into Standard Model final states. For each reheating scenario and misalignment mechanism, the authors identify parameter regions compatible with the observed dark-matter relic density and other cosmological and laboratory constraints. They also assess prospects for probing allowed regions with axion-detection and gravitational-wave experiments; the abstract does not specify detection forecasts or report a detection.

PublicThe researchers explore whether hypothetical particles called QCD axions could account for dark matter under different models of the early Universe. Their calculations focus on an extended reheating period after inflation, when energy from the field driving inflation was transferred into particles. They consider three possible decay routes, including one in which heavy neutrinos briefly dominate the Universe’s energy density before decaying into ordinary particles. They also compare two mechanisms for producing axion dark matter. Some combinations of model parameters match the observed amount of dark matter while meeting other cosmological and laboratory limits. The study considers whether axion searches or gravitational-wave experiments could test these possibilities, but it does not report evidence that axions exist or that any of these early-Universe histories actually occurred.

Young explorerScientists are trying to understand dark matter, something in space that we cannot see directly. They used math to explore whether tiny, still-undiscovered particles called axions could make it up. They tried different ideas about how the very young Universe made particles after growing very quickly. Some of their ideas could give the right amount of dark matter without breaking other rules from experiments. They also thought about how future searches might test these ideas. They have not found the axions in this study.

Graceful Exit to Radiation Domination in the Starobinsky Model: A Dynamical Realization

Bhargabi Saha, Malay K. Nandy

• General Relativity and Quantum Cosmology

AstronomerThis study numerically investigates inflation and reheating in the Starobinsky model using coupled scalaron-radiation equations that conserve energy exactly in an expanding background. Both components enter the Friedmann equation, including the backreaction of radiation produced by scalaron decay. For initially vanishing radiation and slow-roll initial conditions, the numerical evolution yields approximately 60 e-folds of scalaron-dominated inflation, with radiation remaining subdominant and slow-roll conditions persisting. After inflation, damped scalaron oscillations accompany rapid radiation growth. Continued scalaron depletion eventually leaves the radiation energy density substantially above the residual scalaron energy density, indicating a hot, radiation-dominated phase that satisfies the Kofman-Yi reheating criterion. These are numerical results for the stated model and initial conditions, supporting a self-consistent graceful exit and transition to radiation domination rather than constituting direct observations.

PublicThe researchers used a computer model to study how the early Universe could move from inflation, a period of rapid expansion, into a hot phase dominated by radiation. In the Starobinsky model, an ingredient called the scalaron drives inflation and produces radiation as it decays. The calculation conserves energy and includes the effect of both ingredients on cosmic expansion. Starting without radiation, the model keeps radiation secondary during inflation. After inflation ends, the scalaron oscillates and loses energy while radiation grows, eventually becoming dominant. The results support a smooth transition into reheating within this model and its chosen starting conditions; they are not direct observations of the early Universe.

Young explorerScientists used a computer to explore how the very young Universe might have changed. In their model, something called a scalaron makes space grow very quickly while making radiation. Later, the scalaron wobbles and loses energy, and radiation takes over. This shows how the model can lead to a hot Universe, not something scientists watched happen.

Analytical weak-lensing shear response of galaxy model fitting

Xiangchong Li

AstronomerThis study investigates the response of model-fitted galaxy flux, size, and shape to weak-lensing shear within AnaCal. It introduces quintuple numbers, an algebraic system inspired by dual numbers used in automatic differentiation, to propagate analytical pixel-level shear responses through the fitting process to the fitted parameters. The authors integrate this approach into AnaCal to derive shear responses for model-fitted shapes. Validation with image simulations that include realistic blending yields multiplicative shear bias below 0.003 for ground-based, oversampled images. This performance is demonstrated in simulations, not observational data.

PublicWeak gravitational lensing subtly distorts galaxy images, and measuring those distortions accurately requires understanding how galaxy-fitting software responds to them. The researchers introduce a mathematical tool called quintuple numbers into the AnaCal analysis framework to track how shear affects fitted galaxy brightness, size, and shape. They test the method on simulated images that include realistically overlapping galaxies. For ground-based images sampled more finely than usual, the simulations show a multiplicative bias—a proportional error in the shear estimate—below 0.003. The abstract does not establish the same performance on real observations.

Young explorerGravity can gently stretch the way galaxies look in pictures. Scientists use computer models to measure those pictures, but they need to check that the models do not give the wrong amount of stretching. This team made a new math tool to follow how stretching changes the measurements. They tested it on pretend galaxy pictures, including galaxies whose pictures overlap, and found a very small error in those tests. They have not shown here that it works just as well on real pictures.

Clustering of Primordial Black Holes in Excursion Set Theory

Hamed Kameli, Encieh Erfani

• High Energy Physics - Phenomenology

AstronomerThis theoretical study extends Excursion Set Theory to calculate the joint probability of primordial black hole (PBH) pair formation within a clustering distance, using two stochastic trajectories with a shared history. The calculations indicate that an enhanced power spectrum increases both PBH formation in particular mass ranges and clustering probability. The authors find a one-to-one correspondence between the blue-tilted spectral index and the mass ranges of PBH formation and clustering. Clustering probability decreases asymptotically as the clustering distance increases, while raising the critical density threshold suppresses clustering abundance. These are results within the theoretical framework, not observational detections.

PublicThe researchers use a mathematical model to study when primordial black holes might form near one another. Their calculations suggest that strengthening the fluctuations described by the model increases both the formation of black holes in certain mass ranges and their tendency to cluster. A parameter describing how the strength of those fluctuations varies is linked one-to-one with the mass ranges in which black holes form and cluster. The calculated clustering probability declines as the distance increases, and making the density requirement for formation stricter reduces the abundance of clustered black holes. The study presents theoretical findings rather than observations of black hole groups.

Young explorerThe scientists used math to explore whether black holes could form close together. In their model, stronger bumps can help more black holes form and make close-together groups more likely. The math also says that groups become less likely as the distance gets bigger, and that a stricter rule for making black holes means fewer of them form in groups. These are ideas worked out with math, not groups the scientists saw in space.

Recovering Subtle Cosmological Information with the Zel'dovich-inspired Transform

Yun Wang, Hao-Ran Yu, Yu Yu+1 more

AstronomerThe authors introduce the Zel’dovich-inspired (ZI) transform, a local nonlinear density transformation whose single parameter, η, controls the weighting of higher-order information. For η ≥ 3, it can substantially suppress gravitational non-Gaussianity. Using real-space matter density fields from the Quijote simulation suite, their Fisher analysis finds that a joint vector of transformed-field power spectra at η = ∞, 6, and 3 reduces marginalized uncertainties for every cosmological parameter considered. Forecast improvements range from several-fold for some ΛCDM parameters to factors of 290 for local primordial non-Gaussianity and 107 for the summed neutrino mass. Tests on independent fiducial simulations yield nearly unbiased parameter estimates. In the reported comparison, this statistic provides tighter constraints than other state-of-the-art summary statistics; these findings are simulation-based rather than measurements from observational data.

PublicThe way matter is clustered across the universe contains clues about cosmology, but gravity makes those patterns complicated to interpret. The authors propose a mathematical transformation that changes how different kinds of information in the matter distribution are weighted. Applied to simulated universes, it can reduce some of the statistical complexity produced by gravity. Their analysis predicts that combining three versions of the transformed clustering measurement would improve estimates of all the cosmological parameters they tested. The largest forecast gains are factors of 290 for a parameter describing departures from Gaussian patterns in the early universe and 107 for the total neutrino mass. Separate simulation tests produced estimates with little bias, and the method outperformed other advanced statistical summaries in the reported comparison. These are promising results from simulations, not demonstrated improvements using observations of the real universe.

Young explorerScientists want to learn about the universe by studying where its matter gathers. Those patterns can be hard to understand. This team made a new math trick to help read them. They tried it on pretend universes made by computers, and their tests suggest it could help scientists learn more clearly. They still have not shown here that it works on measurements of the real universe.

Testing ΛCDM with ANN-Reconstructed Expansion History from Cosmic Chronometers

Yuki Hashimoto, Kazuharu Bamba, Sanjay Mandal

AstronomerThe authors propose an artificial neural network framework for non-parametric reconstruction of the late-time cosmic expansion history, intended to avoid imposing a specific cosmological model. The framework undergoes a three-stage training and validation screening pipeline before application to observational data. Using the latest cosmic chronometer measurements, they reconstruct H(z) and find agreement with ΛCDM predictions within observational uncertainties. They interpret this consistency as supporting the approach’s robustness and reliability; it does not establish ΛCDM uniquely or demonstrate performance beyond the application presented.

PublicThe researchers propose a computer-learning method to trace how the Universe has been expanding in its more recent history without prescribing a particular mathematical form for that history. They train and check the method through three stages, then apply it to observations called cosmic chronometer measurements. The resulting expansion history agrees, within the measurements’ uncertainties, with the standard cosmological model known as ΛCDM. This agreement is an encouraging check of the method, rather than proof that the standard model is the only possible explanation.

Young explorerThe Universe is getting bigger. Scientists made a computer-learning tool to help work out how its growing speed has changed. They checked the tool in three stages and then used real measurements. Its answer fits what a usual model of the Universe predicts, but the measurements are not exact. That is a helpful sign that the tool works, not proof that we know the whole story.

Reionization, UV Luminosity and 21cm Sensitivity to Primordial Magnetic Fields: Impact of Energy Losses

Gaétan Facchinetti, Alexander Korochkin, Laura Lopez-Honorez+1 more

AstronomerThis study revisits primordial magnetic field (PMF) constraints by self-consistently evolving magnetic energy losses through ambipolar diffusion and decaying turbulence from recombination through reionization. The authors implement these processes in HyRec and exo21cmFAST to model their interplay with astrophysical processes, then use the NNERO neural-network emulator for an MCMC analysis combining late-time reionization probes and galaxy UV luminosity functions. Accounting for energy losses significantly relaxes previous bounds: declining field strengths weaken the PMF imprint on observables. A separate Fisher-matrix forecast suggests that HERA measurements of the 21 cm signal could substantially tighten current constraints through sensitivity to PMF-induced intergalactic-medium perturbations, but the projected improvement depends on astrophysical assumptions. These are model-based constraints and forecasts, not a detection of PMFs; a primordial origin for intergalactic magnetic fields remains uncertain.

PublicMagnetic fields are expected to exist in the space between galaxies, but their origin is unknown. If they formed in the early universe, they could have affected how intergalactic gas warmed and became ionized, as well as how small matter clumps grew. This study models how such fields would weaken as they lose energy over cosmic time, and compares the models with evidence about galaxies and the ionization history of intergalactic gas. Allowing the fields to weaken makes previous limits on their strength less restrictive, because weaker fields leave smaller observable effects. The researchers also predict that HERA's measurements of the 21 cm signal could improve these limits, depending on assumptions about astrophysical processes. The study does not establish that these fields have a primordial origin.

Young explorerSpace between galaxies may have magnetic fields that began when the universe was very young. Scientists used computer models to see what happens if those fields grow weaker over time. Weaker fields leave smaller clues, so the clues we have allow more room for how strong the fields could once have been. Future measurements might help, but scientists still do not know where the fields came from.

Secondary Dependence of Baryonic Effects on the Density Profile of Dark Matter Halos

Yikun Wang, Idit Zehavi, Sergio Contreras+3 more

AstronomerUsing the MillenniumTNG hydrodynamical simulation and its dark matter-only counterpart, this study compares density-profile ratios for matched halos to test how baryonic effects depend on secondary halo properties at fixed mass. At z = 0, concentration has a strong influence, especially for 12.5 < log(M_h/[h^-1 M_sun]) < 13.0: more concentrated halos show weaker inner enhancement and stronger intermediate-radius suppression. Concentration-dependent variations reach approximately 15% on small scales and decline toward larger scales; the trend weakens and reverses at higher halo mass. Environmental dependence is weaker, approximately 2%, and largely scale-independent, with denser environments associated with slightly weaker intermediate-radius suppression. Separating internal profile redistribution from total mass suppression indicates that concentration affects both, whereas environment mainly contributes an overall mass shift. These secondary dependencies persist at z = 0.5 and correlate with internal baryonic properties. Halo spin and velocity dispersion also show significant secondary dependence. These are simulation findings, not direct observational measurements, and suggest that modeling baryonic effects for cosmological surveys may require accounting for halo properties beyond mass alone.

PublicOrdinary matter can change how matter is distributed within the dark matter halos studied in cosmology, potentially complicating efforts to interpret large surveys. The researchers explored this using two versions of a simulation: one including ordinary-matter physics and one containing only dark matter. Among halos of the same mass, the changes depended strongly on how concentrated the halos were. In a lower-mass group, more concentrated halos had less central enhancement and more depletion at intermediate distances, with differences reaching about 15% on small scales. This pattern weakened and reversed for higher-mass halos. The surrounding environment had a smaller effect, about 2%, mainly associated with a change in total halo mass rather than its internal distribution. Related patterns also appeared at an earlier simulated epoch, and other halo properties mattered too. These simulation results suggest that future models may need to consider more than halo mass; they are not direct measurements of real halos.

Young explorerScientists made two computer versions of big clumps of matter in space: one with ordinary matter included and one with only dark matter. They found that ordinary matter changed the clumps differently depending on how tightly packed they were, even when the clumps had the same mass. Nearby surroundings mattered less. Bigger clumps sometimes showed the opposite pattern. These are clues from a computer model, not things the scientists directly saw in space.

Cosmology with Intensity Mapping via Statistics Beyond the Power Spectrum in the SKAO Era

Suman Majumdar, Debanjan Sarkar, Leon Noble+38 more

AstronomerThis chapter reviews the potential of higher-order statistics for extracting non-Gaussian information from post-reionization HI 21-cm intensity maps. The non-Gaussian distribution reflects nonlinear structure formation, complex galaxy biasing, and potentially primordial non-Gaussianity. Methods discussed include voxel intensity distributions, emission-line stacking, probability density functions, the ℓ1-norm, bispectra, and marked statistics. Morphological descriptors, including the Largest Cluster Statistic, local dimensions, and Minkowski functionals, may characterize cosmic-web geometry. The chapter presents detectability forecasts for future SKAO observations, rather than observational detections. These analyses include instrumental noise and observational effects, with foreground removal treated in some cases. More precise measurements could help break degeneracies between astrophysical and cosmological parameters, but this benefit remains prospective.

PublicMaps of neutral hydrogen made using its 21-centimeter radio emission could reveal more about the universe if researchers examine not just correlations between pairs of locations, but also richer patterns in brightness and shape. This chapter reviews several ways to do that, including methods for describing the geometry of the cosmic web. It forecasts how well future SKAO observations might measure these patterns, accounting for instrument noise and observational effects; some analyses also consider removing foreground signals. These are forecasts, not reported detections. The future measurements could help researchers distinguish the effects of galaxy physics from those of cosmology.

Young explorerScientists want to make radio maps of hydrogen gas in space. They can study the maps’ bright spots and shapes to learn about how the universe is arranged. This chapter explores ways a future telescope project called SKAO might do that. It predicts what scientists could measure, but does not report that they have measured it yet.

Disentangling modified gravity and galaxy bias with field-level inference

Sophie Hoyland, Daniela Saadeh, Kazuya Koyama+1 more

• General Relativity and Quantum Cosmology

AstronomerThe authors present a Bayesian field-level framework that jointly constrains modified gravity and galaxy bias from three-dimensional galaxy number counts, retaining non-Gaussian and Fourier-phase information discarded by power-spectrum analyses. They demonstrate it on real-space mock catalogues for f(R) gravity, using COLA to model nonlinear structure formation at different f_R0 values and a nonlinear galaxy-bias prescription designed to mimic the 2M++ BORG analysis. With the initial phases assumed known, field-level inference tightens constraints on f_R0 and the primary bias parameter beta, which corresponds to linear galaxy bias on large scales, and breaks the modified-gravity–bias degeneracy present in two-point statistics. Cosmic-web classification identifies underdense regions as the main contributors to distinguishing gravity models. Tests also support pipeline robustness to variations in initial conditions, Poisson noise, and galaxy-field thresholding. These are mock-data demonstrations, not observational constraints on gravity.

PublicThe way galaxies are spread through space can help test gravity, but it also depends on how galaxies trace the underlying dark matter. This can make different gravity models hard to tell apart. The researchers developed a method that examines the full three-dimensional galaxy pattern rather than reducing it to a power spectrum, a summary of clustering. In simulated galaxy catalogues, their method better separated the effects of an alternative gravity model called f(R) gravity from those of galaxy bias—the relationship between galaxies and dark matter. It also narrowed the allowed model parameters compared with using the power spectrum alone. An important assumption was that the initial phases, which help specify the starting spatial pattern, were known. Relatively empty regions supplied most of the information distinguishing the gravity models. The method passed several robustness checks in the simulations, but the study does not establish that gravity differs from the standard theory in the real Universe.

Young explorerGalaxies make a huge pattern in space, with crowded places and nearly empty places. Scientists made pretend galaxy maps on a computer to try a new way of studying gravity. Looking at more of the pattern helped them tell apart different kinds of gravity and different ways galaxies follow dark matter. The emptier places gave the biggest clues. For this test, the scientists already knew part of the starting pattern. The test worked better than looking at just a summary of the map, but it does not show that gravity really works differently in space.

Revisiting 2D and 3D Dainotti Correlations for GRBs Using Bayesian Neural Networks

Nilanjana Bagchi Aurpa, Abha Dev Habib, Nisha Rani

AstronomerThis study revisits the 2D Dainotti relation and 3D fundamental plane using Bayesian Neural Networks trained on updated Observational Hubble Data (OHD) and the Pantheon+ Type Ia supernova sample. Reconstructed luminosity distances provide model-independent calibration of the Platinum and Narendra et al. GRB samples, addressing the circularity problem that limits GRBs as standard candles. The analysis constrains correlation parameters and examines sensitivity to calibration data and GRB sample selection. Pantheon+ calibration gives tighter constraints than OHD, and the 3D relation has lower intrinsic scatter than the 2D relation. The authors interpret these results as supporting BNNs for calibration with reliable uncertainty propagation, while emphasizing that the underlying distance probe determines both the usable GRB sample size and constraint precision.

PublicGamma-ray bursts could help astronomers measure cosmic distances, but calibrating their brightness can involve circular reasoning: assuming a cosmological model to establish a distance tool that is then used to test cosmology. This study uses Bayesian neural networks trained on measurements of cosmic expansion and on Type Ia supernova data to reconstruct distances and calibrate relationships among gamma-ray burst properties without assuming a cosmological model. Calibration with the Pantheon+ supernova sample gives more precise constraints than calibration with the expansion data. A relationship involving three quantities also shows less intrinsic scatter than one involving two. The authors conclude that the approach handles calibration uncertainties reliably, but stress that the choice of reference data affects both how many bursts can be calibrated and how precise the results are.

Young explorerAstronomers want to use very bright flashes in space to help tell how far away things are. But first they need to check how well those flashes work as distance clues. In this study, they used a computer method that learns from other space measurements and keeps track of how uncertain its answers are. Measurements from exploding stars gave more precise answers than measurements of how fast the universe is expanding. A rule using three clues from the flashes also gave more consistent results than a rule using two. The flashes may be useful, but the answers still depend on which measurements the computer learns from.

The Role of Big Bang Nucleosynthesis in Joint Cosmological Analyses

Mehmet Akharman, Nicholas DePorzio, Cara Giovanetti+1 more

• High Energy Physics - Phenomenology

AstronomerThe authors jointly analyze DESI DR2 BAO data with BBN, with and without Planck CMB data, explicitly marginalizing over BBN nuisance parameters for the first time for these data combinations. Their fiducial ΛCDM constraints are h = 0.6833 (+0.0048, −0.0053) for BAO+BBN and h = 0.6823 (+0.0027, −0.0026) when CMB data are included. Allowing the effective number of relativistic species, N_eff, to vary gives h = 0.6791 (+0.0069, −0.0075) and N_eff = 2.974 (+0.098, −0.099) for BAO+BBN, versus h = 0.6838 (+0.0052, −0.0054) and N_eff = 3.065 (+0.078, −0.076) for BAO+BBN+CMB. These are model-dependent parameter inferences, not direct measurements of h or N_eff. The authors demonstrate sensitivity to investigator choices in the treatment of BBN, offer recommendations, and present a pipeline that accounts for BBN prediction uncertainties.

PublicThe researchers combine DESI DR2 measurements of patterns in the distribution of matter with calculations of how light elements formed in the early universe. They also repeat the analysis using Planck measurements of the cosmic microwave background. Their estimates of the universe’s expansion parameter cluster around h = 0.68, with uncertainties that depend on the model and the data included. In models that allow the effective number of relativistic species to vary, they infer values near three. These estimates come from fitting models to data rather than directly measuring those quantities. A central point is that choices about how to handle uncertainties in early-element calculations can affect the answers. The authors recommend ways to treat those uncertainties and demonstrate an analysis pipeline that accounts for them.

Young explorerScientists used clues from patterns in space and old light, together with calculations about how the universe made its first light elements, to work out how fast the universe is growing. Their answers were close to one another, but they are still estimates, not exact answers. The team also showed that how scientists handle uncertain parts of their calculations can change the answer. They demonstrated a way to keep track of those uncertainties.

Probing submillimeter number counts below the confusion limit: extreme-value statistics of the P(D) distribution and its modulation by gravitational lensing

Kaustuv Basu, Andrea Guerrero, Frank Bertoldi

• Instrumentation and Methods for Astrophysics

AstronomerThe authors introduce a peaks-over-threshold analysis of the confusion P(D) tail, modeling exceedances with a generalized Pareto distribution. They derive relations linking the threshold-dependent shape parameter xi(u) to the local logarithmic slope of galaxy number counts and its lensing modulation, Delta xi(u), to count curvature, and validate these relations with end-to-end simulations. Applied to Planck 857 GHz maps, the tail at 5-arcminute resolution traces the bright, clustered sky rather than faint counts, although the background alone excludes a single-power-law count model. In the Herschel/SPIRE 350-micrometer GAMA-09 map, xi increases markedly with threshold, consistent with a strongly lensed bright population; the authors describe this as the first detection of lensing in a P(D) tail. The bright-masked map favors Schechter counts. Cluster sightlines yield calibrated upper limits, not a detection, on Delta xi(u). Forecasts suggest CCAT/FYST should distinguish count models directly, but detecting cluster lensing would require more 10^15-solar-mass clusters than exist in the sky. The statistic is presented as normalization-free, invariant to map mean and gain, and robust to clustering, probing counts at fluxes comparable to the threshold below the detection limit.

PublicMany distant galaxies are too faint or crowded together to identify separately in submillimeter maps. Their combined glow nevertheless contains clues to how galaxy numbers vary with brightness, an important record of cosmic star formation. This study develops a way to read those clues from the unusually bright portions of a map and tests it using simulations and observations. Planck’s maps mainly reveal bright, clustered sources rather than the faint population, but their background rules out one simple model of galaxy counts. Higher-resolution Herschel observations show a brightness-dependent pattern consistent with bright galaxies magnified by gravitational lensing; masking bright sources favors a different count model. Looking behind galaxy clusters produced upper limits on the lensing signal, not a detection. The authors predict that CCAT/FYST could distinguish count models, while measuring cluster lensing remains much harder and awaits deep, high-resolution surveys.

Young explorerSome faraway galaxies look so faint and crowded that their light blends together. Scientists tried a new way to study the brighter patches in that blended light, testing it with computer-made skies and real sky maps. One map showed clues that gravity had made some galaxies look brighter. But when they looked behind groups of galaxies, they could only say how big that effect might be, not clearly find it.

Limits on Primordial Black Hole Evaporation from LUX-ZEPLIN

Jitumani Kalita

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

AstronomerLUX-ZEPLIN reported one anomalous nuclear recoil at 248 ± 23 keV, but no unexplained excess in its primary 5.4–50 keV search window. The authors argue that standard halo cold dark matter cannot kinematically produce the high-energy event and test a relativistic dark-matter flux from Hawking evaporation of primordial black holes with masses of 10^11–10^13 g. Using heavy non-relativistic effective field theory scattering operators and endothermic inelastic mass transitions, they find that the thermal emission spectrum and relativistic incident kinematics necessarily overproduce low-energy recoils if this mechanism accounts for the anomaly, violating LZ background bounds. Within the modeled framework, the low-energy null result excludes primordial-black-hole abundance fractions f_PBH ≳ 10^-6 at M_PBH ≈ 2 × 10^11 g at 90% confidence. This is a theoretical exclusion of the proposed explanation, not a detection of primordial black holes or dark matter.

PublicThe LUX-ZEPLIN experiment recorded one unusual, high-energy hit on an atomic nucleus, but found no unexplained extra hits in its lower-energy search range. This study asks whether fast dark-matter particles emitted by evaporating primordial black holes could explain that event. The authors’ calculations show that, under the scattering models they considered, producing the unusual hit would also produce too many lower-energy hits, conflicting with the observations. They therefore reject this proposed explanation within their framework and use the absence of lower-energy excesses to place strong limits on the abundance of those black holes. The study does not establish what caused the unusual event.

Young explorerA detector saw one unusual big bump, but no extra little bumps in the range scientists checked. The scientists tested an idea: maybe tiny black holes sent out very fast invisible particles that made the big bump. Their math said this idea would also make too many little bumps. Since those extra bumps were not seen, the idea does not work in the models they tested. They still do not know what made the big bump.

Testing Offsets Between Cluster-Scale Halos and BCGs in Strong Lensing Models Using the Jackknife Method

Sangjun Cha, Marceau Limousin, M. James Jee

• Astrophysics of Galaxies

AstronomerThe study tests whether allowing cluster-scale halo centers to be offset from BCGs improves strong-lensing predictive accuracy in Abell 370, RX J1347.5-1145, and MACS J0416.1-2403. MrMARTIAN models combine analytic mass profiles with a regularized grid representing additional mass structure. Fixed- and free-halo-position models are compared across regularization weights using jackknife predictions for source systems excluded from reconstruction. Mean RMS values agree within bootstrap uncertainties, and median paired differences remain close to zero, indicating comparable predictive performance. Total mass distributions are broadly similar, but fitted offset magnitudes depend on regularization, demonstrating a nonunique decomposition between grid mass and cluster-scale halos. For these clusters within this framework, offsets are not required to improve predictive accuracy; this does not establish that physical offsets are absent. Fitted halo positions alone therefore provide limited grounds for physical interpretation. Model dependence in magnification and time-delay estimates can also affect inferred high-redshift source properties or the Hubble constant.

PublicResearchers examined whether models of three galaxy clusters need to place the centers of their large dark matter halos away from their brightest galaxies. They tested this using strong gravitational lensing, in which a cluster bends light from objects behind it. Rather than judging only how well models fit the data used to build them, they checked predictions for source systems left out of the modeling. Allowing the halo centers to move did not improve predictive accuracy beyond the estimated uncertainties. The models gave broadly similar overall mass distributions, but the fitted offsets changed with how the models divided mass between different components. For these three clusters and this modeling method, the lensing data do not require offsets to improve predictions. That does not prove the actual centers coincide, but it cautions against treating fitted offsets alone as evidence about dark matter or cluster dynamics. Model choices can also affect estimates of light amplification and arrival-time delays, with consequences for studies of distant sources and the universe’s expansion rate.

Young explorerA big group of galaxies can bend light from things behind it. Scientists used that bent light to test maps of three galaxy groups, including invisible stuff called dark matter. They asked whether moving the middle of the dark matter away from the brightest galaxy made the maps predict better. In these tests, it did not make a clear improvement. Different ways of making the maps also put the dark matter’s middle in different places. So a map’s middle is not enough to tell us where the real middle is. The maps can also change how bright faraway things seem and when their light is expected to arrive.

Twin-peaked gravitational wave signals from a Z₂ phase transition

Rishav Roshan, Indrajit Saha

• High Energy Physics - Phenomenology

AstronomerThe authors calculate the gravitational-wave spectrum associated with spontaneous breaking of a Z₂ symmetry when an odd scalar singlet acquires a nonzero vacuum expectation value. For a second-order transition, the sole gravitational-wave source is annihilation of the resulting domain walls, with a bias attributed to quantum gravity. A first-order transition instead predicts a twin-peaked spectrum sourced by both the transition and biased domain-wall annihilation. An additional scalar doublet, odd under a separate Z₂ symmetry, strengthens the transition by maintaining thermal equilibrium between the singlet and the early Standard Model plasma. The same doublet produces fermionic dark matter through freeze-in, yielding a relic density consistent with observations. These are theoretical calculations and predictions, not reported gravitational-wave detections.

PublicThis theoretical study calculates possible ripples in spacetime from a change in the state of the early universe. The change creates boundaries called domain walls, whose eventual destruction produces gravitational waves. If the change is second-order, those disappearing walls are the only wave source. If it is first-order, the change itself also produces waves, giving the predicted signal two peaks. The model attributes the imbalance that causes the walls to disappear to quantum gravity. An additional particle field strengthens the change and also produces dark matter gradually through a process called freeze-in. The calculated amount of dark matter matches the observed abundance, but the abstract reports no detection of the predicted waves.

Young explorerThe scientists used math to imagine a change in the universe when it was very young. That change could make walls between different regions of space. When the walls disappear, they could make tiny ripples in space. In one version of the story, only the walls make ripples. In another, the change itself makes ripples too. Their model also makes dark matter, a kind of matter we cannot see, in an amount that matches observations. These are ideas worked out with math, not ripples the scientists have found.

Cosmology with a Non-minimally Coupled Dark Matter Fluid II. Cosmological Perturbations

Samuele Silveravalle, Andrea Lapi, Francesco Benetti+1 more

• General Relativity and Quantum Cosmology

AstronomerThe authors analyse linear perturbations in a cosmological model with a non-minimal dark matter–gravity coupling at the fluid level. Earlier work showed that this coupling can drive early accelerated expansion, addressing the horizon and flatness problems, and can permit a bounce with negative spatial curvature. Here they derive scalar, vector and tensor perturbation equations and analytic solutions in relevant regimes. Perturbations generated during accelerated expansion yield a strongly blue scalar power spectrum, incompatible with observations. Fluctuations generated during contraction in a bouncing solution instead yield an approximately scale-invariant scalar spectrum and a tensor-to-scalar ratio compatible with current bounds. Within the simplifying approximations used, the results indicate that a viable primordial spectrum requires a bounce and non-singular early evolution; those approximations need further refinement.

PublicThis theoretical study explores a model in which dark matter interacts with gravity in a nonstandard way. The researchers calculate how small disturbances evolve in two possible early histories of the universe. If the disturbances arise during an early period of accelerated expansion, the model predicts too much relative power on small scales to agree with observations. If they arise while the universe contracts before bouncing into expansion, the predicted pattern is approximately scale-invariant, with similar strength across scales, and the relative strength of gravitational-wave disturbances stays within current limits. The calculations therefore favour a bounce rather than accelerated expansion alone as the source of the initial fluctuations in this model. This is not observational evidence for a bounce: the conclusions depend on simplifying approximations that need to be improved.

Young explorerScientists used math to study a possible story about the very young universe, where dark matter and gravity work together in an unusual way. They asked how tiny uneven spots could grow. In their math, spots made while the universe was growing faster and faster did not match what we see. Spots made while it was shrinking, before turning around and growing again, could match better. That turn-around is called a bounce. This is a possible story, not a bounce scientists have seen, and they still need to check their math more carefully.

Analytic backreaction of a scalar wig on a Schwarzschild black hole

Marco de Cesare, Manuel Del Piano, Carlos A. R. Herdeiro

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

AstronomerThis theoretical study derives the leading gravitational backreaction of a spherically symmetric, massive complex scalar quasi-bound state on a Schwarzschild black hole in the small-coupling regime r₀μ ≪ 1. The authors evaluate the fundamental scalar s-wave stress-energy tensor and solve the Einstein equations to quadratic order in the field amplitude in ingoing Eddington-Finkelstein coordinates, retaining the state's exponential decay rather than assuming a steady state. They also derive its small-mass quasi-resonant frequency by matched asymptotic expansions and validate that frequency numerically with Leaver's method. Explicit metric perturbations and the Misner-Sharp mass yield the evolution of the future outer trapping horizon. At the perturbative order considered, the black-hole mass increases monotonically as the horizon flux decays, then saturates after absorption of the finite cloud; the cloud's mass loss exactly balances the horizon growth. The authors identify the domain in which both the scalar small-coupling approximation and the gravitational perturbative expansion remain valid.

PublicThis theoretical calculation examines how a cloud of a massive scalar field changes a nonrotating black hole as the cloud is absorbed. Rather than treating the cloud as a permanent, steady presence, the researchers include its gradual exponential fading and calculate the resulting changes to the black hole's geometry and horizon. Within their approximation, the black hole gains mass continuously, but the rate of growth slows as the cloud fades, and growth stops once the finite cloud has been absorbed. The mass lost by the cloud exactly matches the black hole's gain at the level of accuracy used. The researchers also calculate the cloud's oscillation-and-decay frequency and check it numerically. These are mathematical results, not observations, and apply only where both the weak-coupling and small-gravitational-disturbance approximations are valid.

Young explorerScientists used math to study a black hole with a special kind of cloud around it. In their calculation, the black hole slowly takes in the cloud and gets heavier. As less cloud is left, the black hole grows more slowly. When all the cloud has gone in, it stops growing. The cloud loses just as much mass as the black hole gains, as closely as their math can tell. They did not watch a real black hole do this, and their math works only for certain kinds of clouds.

Seeding baryonic dark matter

Domenec Espriu

• High Energy Physics - Phenomenology

AstronomerThe paper develops a proposed formation mechanism for primordial quark pellets (PQPs), ultra-dense quark-matter mini-stars that might account for cosmological dark matter. In this scenario, PQPs form at a temperature of about 1 GeV; the proposed population has a maximum mass of 10^-2 solar masses and radii of approximately 100 m, while smaller objects would be much more numerous and contain most of the dark matter. The mechanism enhances local baryon density through initially super-horizon Peccei–Quinn domain walls that sweep up quarks and gluons before entering the horizon. Assuming efficient baryon concentration by contracting walls, the authors derive a PQP mass spectrum, minimum mass, and cosmological abundance. These are conditional theoretical results, not observational evidence that PQPs exist or constitute dark matter.

PublicThe authors explore whether dark matter could consist of extremely dense, compact objects made of quark matter, called primordial quark pellets. In the proposed picture, these objects formed in the very early universe. Their maximum mass would be about one hundredth of the Sun's mass, with radii of roughly 100 metres, but smaller pellets would be far more common and account for most of the dark matter. The suggested formation process involves early-universe structures called Peccei–Quinn domain walls gathering quarks and gluons as they move and contract. Assuming this gathering process is efficient, the authors calculate the pellets' range of masses, smallest mass, and abundance. The abstract presents a theoretical possibility, not a discovery of these objects.

Young explorerScientists wonder if the universe's hidden matter could be made of tiny, super-packed balls. They suggest that, long ago, moving walls in space might have gathered tiny bits of matter to make these balls. They worked out how heavy the balls could be and how many there might be, but only if the walls were good at gathering the bits. This is an idea about what might have happened, not something they have seen.

Extreme Kerr Newman Black Holes: Differential Geometry, Symmetry, and the Golden Ratio

Remo Ruffini, Giorgio Sonnino

AstronomerThis theoretical study investigates how horizon geometry selects distinct extreme Kerr-Newman configurations. Beyond the Smarr extreme family, the authors identify a special family whose mass, charge, angular momentum, and irreducible mass are constrained by one irrational number, selected by a discrete symmetry in scaled charge and angular-momentum variables in the Christodoulou diagram. A further criterion based on local horizon differential geometry selects a unique extreme configuration, modulo charge and angular-momentum sign reversals, with the greatest local spherical symmetry compatible with rotating Kerr-Newman geometry. For this configuration, the relevant physical and geometrical quantities are related through the golden ratio. The study also examines reversible and irreversible transformations and extractable energy. These are mathematical findings, not observational detections.

PublicA mathematical study explores whether the shape of a rotating, electrically charged black hole's boundary can single out special black hole states. Within the extreme Kerr-Newman class, the researchers find that symmetry conditions select a special family and that a further condition on the boundary's local shape picks out one configuration, apart from reversals of charge or rotation. This configuration has the greatest local spherical symmetry allowed by the rotating geometry; it is not claimed to be a perfect sphere. Its energy, charge, rotation, and other properties are linked through the golden ratio. The authors also examine transformations and the energy that could be extracted. The work concerns theoretical black holes, not observed objects.

Young explorerThe researchers used math to study special black holes that spin and have electric charge. They asked whether the shape of a black hole's edge could help pick out a special kind. Their math found one whose edge is as sphere-like nearby as this spinning kind allows. Its properties are connected by a number called the golden ratio. This is a result from math, not a black hole they saw in the sky.

Water enhances the formation of refractory sulfur in interstellar ices

Carlos del Burgo Olivares, Hector Carrascosa, Guillermo M. Muñoz Caro+3 more

• Earth and Planetary Astrophysics
• Instrumentation and Methods for Astrophysics

AstronomerLaboratory UV-irradiation and warm-up experiments on H2S-containing interstellar-ice analogues, with and without water, produced refractory sulfur residues analysed ex situ. The detected products included sulfur allotropes S6–S8 and polythionic species; water enhanced allotrope formation by two orders of magnitude. The authors propose that ionic intermediates stabilised in the water-ice matrix facilitate sulfur-chain growth and cyclisation, predominantly yielding S8. This mechanism is proposed rather than established by the reported product detections. The occurrence of these species in the experimental residues, together with their reported presence in meteorites and asteroid-return samples, supports an interpretation involving formation in pre-cometary ice mantles. Their capacity to bind multiple sulfur atoms makes them a potential solid-phase reservoir for sulfur depleted from dense-cloud gas. The authors consequently suggest refractory sulfur as a tracer of water-ice environments; the abstract reports laboratory findings, not a direct detection of this reservoir in dense clouds.

PublicSulfur is abundant in space, but much of it appears to be missing from the gas in dense interstellar clouds. Researchers tested whether it could instead be stored in solids by exposing laboratory ices containing hydrogen sulfide to ultraviolet light and then warming them. They found sulfur-rich material left behind, including molecules made entirely of six to eight sulfur atoms. Adding water increased the formation of these sulfur molecules by about 100 times. The team proposes that water helps stabilise electrically charged intermediates that allow sulfur chains and rings to form. Similar substances have been reported in meteorites and asteroid samples. These laboratory results support the idea that icy dust grains could store some of the missing sulfur, but do not directly demonstrate that reservoir in space.

Young explorerScientists made ice like the ice that can cover tiny dust grains in space. They shone ultraviolet light on it and warmed it up. Some sulfur stayed behind in solid material. Ice with water made much more of it than ice without water. The scientists think this could help explain where some sulfur is hiding in space, but their experiment does not prove it is hiding there.

Which Milky Way Streams Make the Best Dark Matter Detectors?

Vedant Chandra, Charlie Conroy, Risa Wechsler+7 more

AstronomerThe study uses the semi-analytic model galacticus, including disk-driven tidal stripping, to forecast dark matter subhalo encounters for 24 Milky Way globular cluster streams whose initial conditions are chosen to best match present-day observations. The 10 most perturbed streams are predicted to undergo approximately 2–12 significant encounters each over their lifetimes, with velocity kicks above 0.1 km/s. Jet, AAU, GD-1, and Palomar 5 rank highest; Jet is predicted to encounter twice as many subhalos as any other stream. In the model, encountering subhalos retain 1–20% of their peak mass and are twice as compact as assumed in previous work. Stream spectroscopy with sub-km/s precision could reveal the influence of subhalos below the galaxy-formation threshold. These are forecasts, not detections; uncertainty in the abundance and scatter of low-mass subhalos reaching the inner galaxy remains a dominant limitation in connecting stream structure to dark matter models.

PublicLong trails of stars around the Milky Way could help test what dark matter is like: encounters with small dark matter clumps can change how stars are distributed and how they move. Using simulations matched to current observations of 24 star trails, the researchers predict that the 10 most disturbed trails each experience about 2–12 significant encounters over their lifetimes. Jet, AAU, GD-1, and Palomar 5 are the leading candidates, with Jet predicted to encounter twice as many clumps as any other trail. The simulated clumps have lost most of their original mass through the galaxy’s gravitational pull and are more compact than earlier studies assumed. Very precise measurements of stellar motions could reveal the influence of clumps too small to form galaxies. The study does not report such detections, and the uncertain number and variation of small clumps reaching the inner galaxy remain a major obstacle.

Young explorerSome stars make long trails around our galaxy. Invisible clumps of dark matter might give those stars little nudges. Scientists used a computer model to guess which trails would get nudged the most. A trail called Jet came first in their predictions. Carefully measuring how the stars move might help scientists find signs of these invisible clumps. They have not found the clumps this way in this study, and they are still unsure how many small clumps reach the galaxy’s inner parts.

LIGHTS. Limitations of Far-Infrared Tracers for Galactic Cirrus Mitigation in the Era of Ultra-Deep Imaging

Ouldouz Kaboud, Ignacio Trujillo, Ignacio Ruiz Cejudo+18 more

• Cosmology and Nongalactic Astrophysics

AstronomerThe study compares Galactic cirrus optical surface brightness in Sloan g and r with Herschel 250 μm emission. For cirrus with μ_g ≳ 27 mag/arcsec², the data are consistent with a linear optical–far-infrared relation under an optically thin dust assumption, with optical emission amounting to approximately 0.1% of the far-infrared flux. Herschel data identify cirrus over wide areas, but their coarser spatial resolution introduces source confusion. When cirrus is modeled with these data, the authors find an effective limiting surface brightness of μ_V ≈ 28 mag/arcsec², compared with nominal depths of μ_V ≈ 30.5 mag/arcsec² for LIGHTS or the 10-year LSST coadd. The limitation concerns cirrus mitigation using currently available far-infrared data, rather than optical sensitivity alone, and motivates higher-resolution cirrus tracers.

PublicVery deep images can reveal faint structures beyond our galaxy, but faint light from dust in the Milky Way can get in the way. The researchers compared this foreground light with far-infrared emission measured by Herschel. For sufficiently faint cirrus, the measurements fit a simple proportional relationship, assuming the dust is thin enough for light to pass through readily; the optical emission is about 0.1% of the far-infrared flux. Herschel maps help locate the dust across large areas, but their lower detail makes different sources hard to separate. Modeling the foreground with these maps limits reliable optical studies to about 28 magnitudes per square arcsecond, rather than the nominal 30.5 reached or targeted by the cited deep surveys; larger numbers mean fainter light. More detailed maps of the foreground dust are therefore needed to make full use of those surveys.

Young explorerScientists want to see very faint things far beyond our galaxy. But dust in our own galaxy makes a faint glow that gets in the way. They compared that glow with a special picture from Herschel that shows the dust in far-infrared light. The two kinds of light seem to follow a simple pattern if the dust is thin enough. The Herschel pictures help scientists find the dust, but they do not show enough small details to tell everything apart. That makes some very faint things harder to study, even when the ordinary pictures are very deep. Sharper pictures of the dust would help.

The impact of relativistic AGN jets on realistic galaxy cluster environments

K. Hervella-Seoane, M. Perucho, S. Planelles+2 more

• High Energy Astrophysical Phenomena

AstronomerSix three-dimensional relativistic-hydrodynamic simulations examine intermediate-power FRI-like jets with powers of 10^44–10^45 erg/s in realistic central ICM environments extracted from cosmological GADGET-3 runs. Each follows 20 Myr of continuous activity with radiative cooling. The initially mildly relativistic jets rapidly decelerate to trans-sonic velocities, with average Mach numbers of about 2.3, and produce weak bow shocks that dominate energy transfer. Approximately 80% of the injected kinetic power becomes internal energy of the ambient ICM, while bremsstrahlung cooling noticeably lowers the temperatures of expanding shocked shells. These simulation results support efficient heating through weak shocks. Their implications for low-power jets as a solution to cooling flows and as regulators of star formation are suggested interpretations, not observationally established outcomes.

PublicJets from active galactic nuclei may help keep the hot gas in galaxy clusters from cooling, but how efficiently they do this remains debated. Researchers ran six computer simulations of intermediate-power jets moving through realistic cluster environments, following 20 million years of activity and including gas cooling. In the simulations, the jets slowed rapidly and created weak shock waves that provided most of the energy transfer to the surrounding gas. About 80% of the jets’ injected kinetic power became internal energy in that gas, although radiation also cooled the expanding shocked layers. The findings suggest that even weak shocks can heat cluster gas efficiently. The authors propose that low-power jets could help address excessive gas cooling and regulate star formation, but these broader implications are not demonstrated observations.

Young explorerSpace jets can push on the hot gas around groups of galaxies. Scientists used computers to pretend how these jets move and how the gas cools. In their computer worlds, the jets slowed down and made weak shock waves that gave lots of energy to the gas. The gas also lost some heat by giving off light. The scientists think jets like these could help stop the gas from cooling too much and affect how many new stars form, but this study used computer models rather than watching it happen in space.

The star formation history of Orion is structured and episodic

Alena Rottensteiner, João Alves, Stefan Meingast+6 more

• Solar and Stellar Astrophysics

AstronomerThe study reconstructs Orion’s star formation history from the highest-resolution age map currently available, comprising 47 spatially and kinematically associated groups identified with SigMA and assigned homogeneous ages and memberships. Four enhancements appear at roughly 5 Myr intervals. The strongest, at ages of 6.4 and 11.3 Myr, together contain about 59% of the sampled stars, are statistically localized, and remain robust under resampling and changes to age fitting. Smaller enhancements at 16.2 and 21.4 Myr are identifiable but not yet demonstrated to be robust. The authors find no methodological bias capable of producing the structure and identify spatially and temporally connected structures, including three candidate cluster chains. Orion appears to share Sco-Cen’s approximately 5 Myr episode spacing but exhibits a different star formation pattern. The origin of this spacing remains unexplained and requires further investigation.

PublicResearchers used the ages, positions, and motions of 47 groups of stars to reconstruct how star formation unfolded in the Orion complex. They found signs of four periods of increased star formation, spaced about five million years apart. The two strongest periods, represented by stars about 6.4 and 11.3 million years old, account for roughly 59% of the stars studied and remain clear when the researchers vary their analysis. Evidence for two older, smaller increases is less secure. The study also identifies connected structures, including three possible chains of star clusters. A similar five-million-year spacing has been found in the nearby Scorpius-Centaurus region, although the pattern of star formation differs. The researchers found no analysis bias that could explain the spacing, but its physical cause is still a mystery.

Young explorerScientists looked at groups of stars in a place called Orion to learn when the stars were born. They found clues that more stars were born during four different busy times, about five million years apart. Two of those busy times have strong evidence, but the other two are less certain. Another star-making place seems to have busy times spaced about the same way. Scientists still do not know why this happens.

Star Formation Mitosis: The Effects of Particle Splitting on the Star Formation Outcome

Shivan Khullar, Michael Y. Grudić, Christopher D. Matzner+3 more

• Solar and Stellar Astrophysics

AstronomerThis numerical study tests particle splitting in star-formation simulations using approximately 220 GIZMO MFM-MHD runs of a collapsing, initially uniform-density turbulent gas sphere. The authors vary cloud mass and radius, feedback physics, initial resolution, splitting pace and cadence, and accreting sink versus non-accreting single-age stellar population particle prescriptions, comparing against uniformly high-resolution controls without splitting. They find no evidence of splitting-induced artificial fragmentation, but splitting produces smoother density fields and minor differences in density and turbulence statistics. Total stellar masses are approximately unchanged, while stellar mass spectra differ slightly and evolutionary histories change, especially with feedback. These differences remain within the intrinsic scatter estimated by varying the initial turbulent velocity field. The results support particle splitting for star-formation applications in the tested setups, while identifying systematic differences in the detailed outcomes.

PublicComputer simulations can follow collapsing gas in greater detail by splitting the particles that represent it into smaller pieces. But this shortcut can introduce numerical errors that alter how simulated stars form. In about 220 simulations, the researchers compared this approach with simulations that used fine resolution from the start. They found no evidence that splitting created artificial fragments. It did make the simulated gas smoother and slightly change its density and turbulent motions. The simulations formed about the same total mass in stars, but distributed that mass somewhat differently and followed different histories, especially when stars affected the surrounding gas. Those changes fell within the variation produced by changing the initial turbulent motions. The study therefore supports the method's usefulness for simulating star formation, though its detailed effects should not be ignored.

Young explorerThe scientists used computers to pretend that a big cloud of gas was squeezing together and making stars. They tested a trick: cutting the tiny pieces that stand for gas into even tinier pieces to see more detail. They compared this with starting with tiny pieces everywhere. The trick made the pretend gas smoother, but they found no sign that it made extra clumps by mistake. Both ways made about the same amount of star material, though the stars and the story of how they formed were a little different. Changing the cloud's starting swirls also changed the results by a similar amount. So the trick seems useful in these tests, but it does not give exactly the same story.

The Impact of Simulation Resolution on Dwarf Galaxy Stellar Stream Populations in FIRE

Yasmine J. Meziani, Nondh Panithanpaisal, Robyn E. Sanderson+4 more

AstronomerThe study tests whether numerical resolution contributes to the larger pericenters of present-day dwarf-galaxy streams in FIRE compared with observed Milky Way streams. It compares two FIRE-2 m12i cosmological zoom-in simulations with identical initial conditions and particle mass resolutions of 7070 and 880 solar masses. With the same 100-star-particle selection threshold, the higher-resolution run produces 22 streams versus 14, primarily by resolving lower-mass streams down to approximately 100,000 solar masses. Both runs form streams within 50 kpc of the galactic center, but the higher-resolution Triple Latte run produces more streams there, and its dwarf galaxies begin disrupting at smaller pericenters. Approximately 89% of lower-resolution candidates have identified higher-resolution counterparts; among matched systems on similar orbits, the higher-resolution counterparts remain intact longer. Higher-resolution stream orbital properties are broadly consistent with the observed Milky Way dwarf-galaxy stream population, unlike those in the lower-resolution run. These simulation results support resolution-dependent disruption as a possible explanation for the earlier discrepancy.

PublicSmall galaxies can be pulled apart by a larger galaxy’s tidal forces, leaving streams of stars. Earlier FIRE simulations produced streams whose closest approaches to the galactic center were farther out than those observed in the Milky Way. To investigate whether limited simulation detail could explain this difference, researchers compared two versions of the same simulated galaxy, one with finer resolution. The finer simulation produced 22 streams rather than 14, mostly because it could resolve lower-mass streams; the shared selection rule required at least 100 star particles, which represent less stellar mass in the finer simulation. It also produced more streams within 50 kiloparsecs of the center. For corresponding dwarf galaxies that followed similar orbits, those in the finer simulation stayed intact longer, and dwarf galaxies generally began breaking apart on closer approaches to the center. The finer simulation’s stream orbits broadly resemble the observed Milky Way population. This supports, but does not prove, the idea that insufficient resolution can make simulated dwarf galaxies break apart too readily.

Young explorerA big galaxy can pull a little galaxy apart and leave a long trail of stars. Scientists made two computer versions of the same galaxy: one with bigger pieces and one with smaller pieces that showed more detail. In the more detailed version, they could see more star trails. When they compared little galaxies traveling on similar paths, the ones in the more detailed version stayed together longer. Little galaxies also started coming apart closer to the big galaxy’s middle. The paths of those trails looked more like the ones seen in our Milky Way. This suggests that a computer picture without enough detail may make little galaxies fall apart too easily.

Do Submillimeter Galaxies Trace Megaparsec Large-scale Structures? -- An Overdensity Analysis of 449 Submillimeter Galaxies in COSMOS

Canze Deng, Daizhong Liu, Helmut Dannerbauer+19 more

• Cosmology and Nongalactic Astrophysics

AstronomerThe authors apply the Poisson Probability Method to assess megaparsec-scale overdensities around 449 A3COSMOS submillimeter galaxies (SMGs), including 168 with spectroscopic redshifts and 52 with CO or [CII] detections, and compare them with over 5000 main-sequence star-forming galaxies from COSMOS2025. The analysis recovers 15 known clusters and protoclusters and identifies 26 new robust candidates with overdensity δ ≥ 5 and significance σ ≥ 5; these remain PPM-based candidates rather than confirmed structures. Depending on the selection criteria, the overdensity fraction is 11.5–71.2% for the 52 line-detected SMGs and 1.3–61.0% for the full SMG sample. The comparison supports SMGs as overdensity signposts, but not all SMGs are associated with overdensities. Based on this finding and inspection of JWST morphologies, the authors argue that non-environmental mechanisms, such as mergers and violent disk instability, also trigger SMG starbursts. Their spatial analysis finds a redshift-dependent distribution, with SMGs more concentrated toward overdensity interiors at higher redshift.

PublicThis study asks whether galaxies detected at submillimeter wavelengths can help locate large regions where galaxies are unusually crowded. The researchers analyzed 449 such galaxies in the COSMOS field and compared their surroundings with those of more than 5000 other star-forming galaxies. Their method recovered 15 known clusters or developing clusters and identified 26 promising new candidates, which are not yet confirmed structures. Submillimeter galaxies were more likely than the comparison galaxies to mark crowded regions, but the fraction depended strongly on the criteria used: about 1–61% for the full sample and 12–71% for a smaller group with particular detected emission lines. Not all were associated with crowded regions. After also examining their shapes in JWST images, the authors argue that galaxy mergers and unstable disks may help trigger intense star formation without requiring a dense surrounding environment. They also find that, at higher redshifts, these galaxies tend to lie closer to the inner parts of crowded regions.

Young explorerThe researchers looked at special galaxies to see whether they could point to places where lots of galaxies gather together. These galaxies often helped them find crowded places, but not every one lived in a crowd. They found 15 galaxy groups that were already known and 26 possible new ones that still need checking. Looking at pictures, they suggest that galaxies bumping together or changes inside a galaxy might also help make lots of new stars. They also found that, when looking farther back in time, these special galaxies tended to be nearer the middle of the crowded places.

Chemical complexity in feedback from supernova remnants: first detection of PO+ in IC₄₄₃ and W44

G. Cosentino, F. Priestley, S. Scibelli+1 more

• High Energy Astrophysical Phenomena
• Solar and Stellar Astrophysics

AstronomerHigh-sensitivity IRAM 30m observations at 3 mm targeted PO+(2–1) and PN(2–1) at the interaction sites of W44 and IC443 with their associated molecular clouds. The authors report the first detections of PO+ toward supernova remnants, deriving abundances of approximately 8 × 10^-12 to 5 × 10^-11 under local thermodynamic equilibrium, but find no significant PN emission. PO+ is associated with strong SiO emission and has similar linewidths but velocity offsets, suggesting that it preferentially traces more compressed, more strongly ionised shock layers. Comparison with published abundances suggests that shock strength and shocked-medium density jointly influence PO+ abundance. The authors interpret the chemistry as favouring ions, likely because of enhanced cosmic-ray ionisation: in this proposed scenario, neutral PN is efficiently destroyed while ion–molecule reactions favour PO+ production. These findings suggest that supernova-remnant shocks can process phosphorus-bearing material in star-forming clouds; the proposed chemical mechanism is an interpretation rather than a direct measurement.

PublicResearchers used the IRAM 30m telescope to study phosphorus-containing molecules where the remains of two exploded stars, W44 and IC443, collide with molecular clouds. They detected the electrically charged molecule PO+ toward supernova remnants for the first time, but found no significant signal from the neutral molecule PN. PO+ appeared alongside silicon monoxide, a marker of shocked gas. Their spectral similarities and velocity differences suggest that PO+ comes mainly from especially compressed and strongly ionised parts of the shocks. The researchers propose that increased ionisation by cosmic rays helps produce PO+ while destroying PN, although this mechanism is not directly established by the observations. The work suggests that stellar explosions can alter phosphorus chemistry in clouds where stars form. Because phosphorus matters for biology, this could influence material later available to planetary systems, but the study does not demonstrate any effect on life.

Young explorerWhen a star explodes, its leftovers can send powerful pushes into nearby clouds of gas. Scientists looked at two places where this happens and found a tiny molecule called PO+ that contains phosphorus, an ingredient living things need. They did not find a clear signal from another phosphorus molecule they searched for. They think the pushes and tiny particles called cosmic rays may change which molecules form in the clouds, but they are not sure exactly how. This could change the ingredients around places where new stars form; it does not mean they found life.

Resolving the physics of Quasar Lyα Nebulae (RePhyNe): II. The dense and clumpy CGM of Quasars at z ∼ 3.5

Titouan Lazeyras, Sebastiano Cantalupo, Andrea Travascio+10 more

AstronomerThe study constrains the small-scale density distribution of cold circumgalactic gas by comparing MUSE observations of quasar nebulae at z ≈ 3.8 with mock observations from DaLya, COLIBRE, and HELLO under an assumption of maximal fluorescence. Except for the higher-resolution COLIBRE m5 run, simulated Lyα surface-brightness upper limits differ strongly from the observations, which generally exhibit a larger covering fraction of relatively bright emission. Under the fluorescence assumption, the observations suggest gas densities reaching at least 10 cm⁻³ at radial distances of 50–200 comoving kpc. The simulated density PDFs are consistent with skewed lognormal distributions, with medians near 10⁻² cm⁻³ and clumping factors of 16–102. Independently of maximal fluorescence, the observed HeII/Lyα ratio requires, if lognormal PDFs with simulation-like medians are assumed, a broader density distribution with a clumping factor at least eight times larger than predicted by the simulations. The authors interpret these discrepancies as evidence that higher resolution and/or additional physical mechanisms may be needed to reproduce the observed cold CGM.

PublicCold gas surrounding galaxies helps shape their evolution, but its small-scale structure remains uncertain. This study compares observed glowing gas around quasars at a redshift of about 3.8 with simulated views. Assuming the gas fluoresces at its maximum level, most simulations predict too little area covered by relatively bright hydrogen emission; the higher-resolution COLIBRE simulation is an exception. Within that assumption, the observations suggest that some surrounding gas reaches densities of at least 10 particles per cubic centimetre. A separate comparison of helium and hydrogen emission does not depend on maximum fluorescence. If the gas densities follow the assumed statistical pattern and have typical values like those in the simulations, that comparison indicates substantially more clumping than the simulations predict. The findings suggest that finer simulations, additional physical processes, or both may be needed, rather than establishing which explanation is responsible.

Young explorerGalaxies have cold gas around them. Scientists looked at glowing gas around very bright objects called quasars and compared it with computer-made pictures. Most computer pictures had less gas showing a bright glow than the real pictures, though one more detailed computer model was an exception. Different kinds of glow also gave clues that the real gas may be more bunched up than the models show. Those clues depend on some guesses about the gas. The scientists think they may need more detailed models, or more ways for the gas to behave, to make the pictures match.

Constraining the density distribution of the cold Circumgalactic Medium of quasars at z>2 through Lya, HeII and Ha emission

Andrea Travascio, Sebastiano Cantalupo, Titouan Lazeyras+16 more

AstronomerThe study extends analytical models with CLOUDY photoionization simulations to predict HeII/Hα in quasar-illuminated CGM, including log-normal density distributions. Non-resonant HeII and Hα help address the interpretive complications of resonant Lyα. Observations of 13 quasars at z≈2.2 with Keck/KCWI, followed by Keck/MOSFIRE targeting of systems with the most prominent extended Lyα and HeII, provide the first statistical quasar-CGM sample with combined measurements of all three lines. Stacked spectra in matched apertures extending to ≈35 proper kpc yield Lyα/Hα=9.1, HeII/Hα=0.54, and HeII/Lyα=0.06. In the models, the low HeII/Hα requires either single-density gas with n>10 cm^-3 or implausibly soft AGN spectra; broad log-normal distributions reproduce it at lower median densities but require a substantial emissivity-weighted high-density tail, formally corresponding to C≈10^3–10^4 in the adopted parameterization. Of 26 VLT/MUSE quasars at 3.1<z<4.5, 14 show co-spatial extended Lyα and HeII; Hα is inaccessible from the ground at these redshifts. The detected, emission-weighted HeII/Lyα component shows no evidence for strong evolution between z≈2.2 and z≈3.7, but this does not establish an invariant underlying density PDF.

PublicLarge clouds of cool gas surround distant quasars, but their commonly observed hydrogen glow, called Lyα, is difficult to interpret because the light can repeatedly interact with the gas. This study combines it with helium emission and another hydrogen line, Hα, to better constrain the gas. Researchers observed 13 quasars near redshift 2.2 and obtained Hα measurements for selected systems with especially prominent extended hydrogen and helium emission. Comparing the combined spectra with computer models, they found that a uniform-density explanation requires extremely dense gas or an implausible quasar spectrum. Models with a broad range of gas densities can instead match the measured helium-to-Hα ratio at lower typical densities, provided dense regions contribute substantially to the emitted light. This is a model-dependent interpretation, not a direct measurement of the gas's full density distribution. In a separate sample of 26 more distant quasars, 14 had overlapping extended hydrogen and helium emission. The detected helium-to-Lyα ratio showed no evidence of strong change between the two epochs, although the underlying mixture of gas densities could still differ.

Young explorerFar away, bright objects called quasars have big clouds of gas around them. Scientists looked at different kinds of light from those clouds, made by hydrogen and helium. Then they used computer models to test what the gas might be like. Models with both thinner gas and dense patches could explain the light, with the dense patches making an important part of the glow. That is a possible explanation, not a picture showing every patch. The scientists also compared clouds from two times in the universe's past. The balance of two kinds of light did not seem to change much, but that does not mean the clouds were exactly the same.

Weighing Galaxies Inside-Out: Small-Scale Lensing and the Stellar Mass Problem

Divya Rana, Henk Hoekstra, Konrad Kuijken+2 more

• Cosmology and Nongalactic Astrophysics

AstronomerThis study forecasts small-scale galaxy–galaxy weak-lensing constraints on the stellar initial mass function (IMF) from upcoming Euclid observations, using realistic mock catalogues for a DESI-like Bright Galaxy Survey expected to overlap about 9000 square degrees of the Euclid wide survey. Foreground lens light produces substantial scale-dependent biases in source detection, photometry, and shape measurement; Galfit subtraction reduces these biases by nearly an order of magnitude down to four half-light radii in the mocks. For central galaxies with 9.5 ≤ log(M*/h⁻² M☉) ≤ 11.5, the modeled signal over projected separations of 10–100 h⁻¹ kpc reaches a forecast signal-to-noise ratio of about 150 at intermediate stellar masses. Assuming an NFW dark-matter profile, the forecast precision on the stellar mismatch parameter α is approximately 8.5% for the full sample and 8.6% for massive galaxies. These are mock-based forecasts, not constraints from observed Euclid data, and their interpretation depends on the assumed dark-matter model.

PublicThe gravity of a foreground galaxy slightly distorts the apparent shapes of galaxies behind it. Measuring this weak lensing close to the foreground galaxy could help researchers investigate the mix of stellar masses with which its stars formed. Using simulated catalogues, the authors forecast what upcoming Euclid observations might achieve. A major obstacle is the foreground galaxy’s own light, which can interfere with detecting and measuring background galaxies. In the simulations, subtracting that light reduced these measurement biases by nearly a factor of ten. With an assumed model for the distribution of dark matter, the study forecasts roughly 8.5% precision on a parameter used to probe the stellar mass mix. This is a prediction of the method’s potential, not a result already obtained from Euclid observations.

Young explorerA galaxy’s gravity can make galaxies behind it look a little stretched. Scientists hope those tiny stretches will help them learn about the mix of small and big stars that a galaxy was born with. But the front galaxy’s bright light can make the shapes behind it hard to measure. The scientists tested pretend galaxy pictures and found that taking away the front galaxy’s light helped a lot. Their tests suggest that future Euclid observations could teach us more, but they have not made those real measurements yet, and their prediction depends on how they think invisible matter is spread through galaxies.

Galaxy Protoclusters as Drivers of Cosmic Reionization: II. Te-Based Metallicities of Lyman-α Emitters

C. Moya-Sierralta, C. L. Martin, L. F. Barrientos+15 more

AstronomerJWST/NIRSpec G395H spectroscopy of Lyman-alpha emitters in the LAGER-z7OD1 protocluster at z ≈ 6.93 provides five secure [O III] λ4363 detections and one upper limit. Direct electron-temperature-based abundances span 12+log(O/H) ≈ 7.2–8.0. Dust-extinction uncertainties from observed Balmer decrements are propagated through Monte Carlo simulations, producing asymmetric errors; stellar masses are inferred with BEAGLE from JWST/NIRCam and UltraVISTA photometry. The weighted spectral stack gives 12+log(O/H) = 7.76 (+0.06/−0.05), about 0.26 dex above comparable-redshift LAE stacks. Nevertheless, the fitted mass-metallicity relation, with slope γ = 0.232 ± 0.214 and normalization Z₀ = 7.888 ± 0.199, places these sources below established relations for normal galaxies and recent protocluster baselines at z ∼ 5–7. The authors interpret the enhanced abundance relative to other LAEs as suggesting accelerated assembly in the overdensity. The lower abundance at a given mass may reflect gas accretion accompanying stellar mass growth. Because the sample selects actively star-forming LAEs, pristine intergalactic inflow that fuels star formation while diluting interstellar gas is a proposed interpretation, not a directly demonstrated result.

PublicResearchers used the James Webb Space Telescope to measure oxygen in the gas of galaxies in an early-Universe region where a galaxy cluster is forming. They detected a key oxygen emission line securely in five galaxies and obtained an upper limit for another. Combining the spectra revealed more oxygen than in comparable samples of galaxies selected by their Lyman-alpha emission. Yet when stellar mass was taken into account, these galaxies fell below established mass–metallicity relations, meaning their gas was less enriched than those relations would suggest. The researchers propose that the crowded environment may speed up galaxy assembly, while incoming, relatively pristine gas could both support new star formation and dilute the oxygen already present. That explanation remains an interpretation, and the sample specifically targets actively star-forming galaxies.

Young explorerScientists used a space telescope to study gas in faraway galaxies growing close together. They found oxygen in the gas. Together, these galaxies had more oxygen than one group of similar galaxies, but less than expected for how much stuff they had in stars. Scientists think fresh gas might be flowing in, helping make new stars and mixing with the oxygen-rich gas. They have not shown for sure that this is happening.

Diverse Protoclusters at z∼3 Disclosed by Systematic Spectroscopy

Jun Toshikawa, Kentaro Koretomo, Nobunari Kashikawa+6 more

AstronomerFollow-up spectroscopy confirms three protocluster candidates at z≈3, selected as overdensities of U-dropout galaxies in Hyper SuprimeCam Subaru Strategic Programme imaging. Each shows spatial clustering both on the sky (>4σ overdensity) and in redshift (>98.4% confidence), providing clear evidence of genuine protoclusters. Their common selection dataset and technique support comparisons with minimized observational biases. Although the combined average galaxy population is consistent with field galaxies, individual protoclusters show distinct properties. One contains members with higher rest-frame Lyα equivalent widths and massive galaxies that remain highly star-forming; another shows comparatively suppressed star formation and systematically lower Lyα equivalent widths. The authors interpret this diversity as potentially reflecting different developmental phases. The proposed association of stronger Lyα emission with earlier cluster formation remains conditional on quenching galaxies marking more mature systems.

PublicSpectroscopic observations provide clear evidence that three candidate gatherings of galaxies at redshift about 3 are genuine protoclusters—galaxy clusters in the process of forming. Their galaxies are tightly grouped both across the sky and in redshift. All three were found using the same imaging survey and selection method, helping limit observational biases when comparing them. Taken together, their galaxies resemble galaxies outside these gatherings on average, but the individual protoclusters differ. In one, galaxies have stronger Lyman-alpha emission relative to their surrounding light, and even massive members are still actively forming stars. Another shows weaker relative Lyman-alpha emission and more suppressed star formation. The researchers suggest that these differences may reflect different stages of cluster development. If galaxies whose star formation is shutting down indicate a more mature system, stronger Lyman-alpha emission may be more common at earlier stages; this is an interpretation, not an established sequence.

Young explorerAstronomers checked three groups of galaxies and found clear signs that they are real groups growing into bigger galaxy clusters. The groups are not all alike. In one, even some big galaxies are still busy making stars. In another, star-making seems more slowed down. The scientists think the groups might be at different stages of growing up, but they do not know that for sure.

State of the Art in Direct Dark Matter Detectors: Technologies, Performance, and Future Directions

Muad Ghaith, Khaled Obaideen

• Instrumentation and Detectors

AstronomerThis review assesses direct dark-matter detection technologies through the physical trade-offs governing their reach, rather than reporting a new detection. Noble-liquid time projection chambers offer multi-tonne scalability and currently lead sensitivity to high-mass WIMPs, while cryogenic semiconductors and CCD-based sensors dominate searches for low-mass and sub-GeV candidates. The review emphasizes advanced reconstruction and machine learning as integral to detector performance. Looking ahead, coherent elastic neutrino–nucleus scattering creates an increasingly significant, ultimately irreducible background that can mimic dark-matter nuclear recoils—the neutrino fog. The authors argue for a complementary global program combining larger targets, lower energy thresholds, improved background discrimination, and directional and temporal observables to preserve discovery capability.

PublicScientists still do not know what kind of particle makes up dark matter. This review compares experiments designed to detect the tiny amounts of energy that dark-matter particles might leave when they collide with material on Earth; it does not report a dark-matter discovery. Large liquid-based detectors currently provide the greatest sensitivity to heavier candidates, while precise semiconductor detectors and CCD sensors lead searches for lighter ones. Sophisticated data analysis, including machine learning, is an important part of their performance. As experiments become more sensitive, neutrino collisions increasingly produce signals that resemble those expected from dark matter. The authors argue that future searches will need several complementary technologies, combining larger detectors, sensitivity to smaller energy deposits, better rejection of unwanted signals, and information about signal direction and timing.

Young explorerScientists are trying to find out what dark matter is made of. They build special detectors to look for tiny bumps that dark matter might make in ordinary material. This paper compares different kinds of detectors; it does not say dark matter has been found. Other tiny particles called neutrinos can make bumps that look similar, making the search harder. The scientists think using different detectors together, and checking when bumps happen and which way they come from, could help.

Evidence for inefficient dust production in a massive, metal-rich galaxy at z=7.13 uncovered by JWST and ALMA

Kasper E. Heintz, Darach Watson, Francesco Valentino+17 more

• Cosmology and Nongalactic Astrophysics

AstronomerA joint JWST–ALMA analysis of the magnified galaxy A1689-zD1 at z=7.13 (μ=9.6) combines rest-frame UV-to-far-infrared SED modeling with new JWST/NIRSpec IFU optical strong-line measurements and metallicity estimates. Despite an inferred dust mass of approximately 1.5×10^7 solar masses, the galaxy has low dust-to-gas and dust-to-metal mass ratios: DTG=(5.5 +3.5/−1.2)×10^−4 and DTM=(6.2 +4.2/−2.6)×10^−2. These reflect its high metallicity, 12+log(O/H)=8.36±0.10, and substantial gas mass, (2.8 +0.2/−1.7)×10^10 solar masses, inferred from [C II] luminosity and bounded by dynamics. Both ratios are about an order of magnitude below expectations for local galaxies with comparable chemical enrichment, consistent with the line-of-sight A_V/N_HI deficit. The authors find that similar deviations appear widespread among other metal-rich galaxies at z≳6. They interpret this as evidence that early-universe dust formation or destruction processes, or dust emissivity itself, may differ from those at later times.

PublicObservations from the James Webb Space Telescope and ALMA show that the distant galaxy A1689-zD1 contains a large amount of dust, yet surprisingly little compared with its gas and its supply of elements heavier than helium. The researchers combined measurements of the galaxy’s light with models to estimate these quantities; its gas mass was inferred from emission by ionized carbon and constrained by its dynamics. The estimated proportions of dust are about ten times lower than expected for nearby galaxies with similar chemical enrichment. Other chemically enriched galaxies in the early universe appear to show the same pattern. This suggests that dust may have formed or been destroyed differently then, or that early dust emits radiation differently; the study does not establish which explanation is correct.

Young explorerScientists used telescopes to study a galaxy from when the universe was much younger. It has lots of tiny dust grains, but compared with all its gas and the stuff that could make dust, it has less dust than expected. Other young galaxies seem similar. Maybe dust was made or broken apart differently back then, or maybe it gives off light differently. Scientists are not sure yet.

JWST View of the Supernebula in NGC 5253. II. Nebular Lines

Sara C. Beck, Jean L. Turner, Elm Zweig+7 more

AstronomerJWST MIRI/MRS spectroscopy over 5–25 micrometers detects more than 70 emission lines from H I, H₂, and metal ions in and around the compact radio-infrared supernebula in NGC 5253. The nebula is powered by a very young, embedded super star cluster with a luminosity of approximately 10⁹ solar luminosities. Comparing H I recombination emission with the free-free radio continuum yields an extinction curve that is nearly wavelength-independent across this infrared range. The nebular conditions are consistent with very massive stars no older than roughly 5 million years. All sampled regions show high excitation; the spatial distribution of high-excitation lines suggests that photons with energies near 50 eV escape the supernebula core despite a visual extinction of 35 magnitudes.

PublicUsing JWST, astronomers detected more than 70 infrared emission lines—distinct signatures of hydrogen and electrically charged metal atoms—in and around a compact nebula in the nearby dwarf galaxy NGC 5253. The nebula contains a hidden, very young star cluster shining with about a billion times the Sun’s luminosity. A comparison of hydrogen emission with radio emission indicates that light is dimmed by nearly the same amount across the observed infrared wavelengths. Conditions in the gas are consistent with very massive stars about 5 million years old or younger. The pattern of emission from highly energized gas suggests that some high-energy light escapes the nebula’s core, even though visible light is strongly obscured there.

Young explorerAstronomers used the JWST telescope to look at a bright group of young stars hidden inside a cloud in a nearby galaxy. They found more than 70 different signs of glowing gas in light our eyes cannot see. The gas gives clues that the stars are very big and young. The way the gas glows around the cloud suggests that some powerful light gets out, even though the cloud hides much of the light we could see with our eyes.

Eight New Ultramassive Black Hole Masses confirm Best Correlation with Galaxy Core Sizes

Stefano de Nicola, Jens Thomas, Roberto P. Saglia+3 more

AstronomerThe study examines high-mass black-hole scaling relations using 16 brightest cluster galaxies (BCGs) with no previous black-hole mass measurements. Direct dynamical detections using triaxial Schwarzschild models identify eight ultra-massive black holes, each exceeding 10 billion solar masses, doubling the known population. The BCGs are outliers in the canonical black-hole mass–stellar velocity dispersion relation, whereas depleted-core size provides a much better, unbiased mass predictor. The authors recommend it as a high-mass proxy. BCGs extend the previously established trends for massive core galaxies, including tight correlations of core size with sphere-of-influence radius and core density. These relations strongly support, but do not establish conclusively, the black-hole binary interpretation of central-core formation in the most massive galaxies.

PublicResearchers studied 16 of the brightest galaxies in galaxy clusters whose central black-hole masses had not previously been measured. By modeling motions within the galaxies, they identified eight black holes with masses greater than 10 billion Suns, doubling the number known in this category. These galaxies do not follow the usual relationship between black-hole mass and the spread of stellar speeds. Instead, the size of their central regions with unusually little starlight is a better guide to black-hole mass, and the researchers recommend using it for these very massive systems. The measured relationships also strongly support the idea that pairs of black holes helped form these light-deficient centers, although they do not prove that explanation.

Young explorerScientists looked at 16 very bright galaxies and studied how things move inside them. They found eight black holes, each heavier than 10 billion Suns put together. That made twice as many known black holes of this enormous kind. The size of a galaxy’s dim middle was a better clue to its black hole’s weight than how fast its stars move. The clues also fit an idea that two black holes together helped make the dim middle, but they do not prove it.

Starbursts hiding in the main sequence: a pathway toward quenching?

Florent Renaud, Katarina Kraljic, Jonathan Freundlich+10 more

AstronomerThe study identifies and tracks starbursts in the main sequence (SBMSs) in the NewHorizon cosmological simulation: galaxies with rapid, dense, compact star formation whose star-formation rates remain within the scatter of the stellar-mass–star-formation-rate relation. The authors interpret this behavior as a consequence of comparatively early stellar-mass assembly, particularly through more frequent, repeated mergers and highly productive interaction-triggered starbursts. SBMSs occur preferentially, but not exclusively, in the most massive simulated galaxies. Individual galaxies enter this regime intermittently, with episodes lasting approximately 30 Myr, while SBMS episodes occur across the simulated galaxy population throughout cosmic time. These findings and the proposed physical explanation come from a simulation rather than direct observational confirmation.

PublicGalaxies usually follow a pattern linking how much mass they have in stars to how quickly they make new ones. Some nevertheless form stars rapidly in small, dense regions without falling outside that usual pattern. Researchers studied these galaxies in the NewHorizon computer simulation. They explain their unusual behavior by earlier growth of their stellar mass, helped by repeated galaxy mergers that triggered especially productive bursts of star formation. In the simulation, this behavior is more common in the most massive galaxies, though smaller galaxies can show it too. Each episode lasts about 30 million years, and galaxies enter this state only intermittently. The explanation is based on simulated galaxies, not direct confirmation from observations.

Young explorerScientists used a computer to study galaxies, huge groups of stars. Some made new stars quickly in a tiny, crowded area, but still fit the usual pattern for galaxies their size. The scientists think these galaxies had built up lots of stars earlier, helped by galaxies joining together. In the computer model, this crowded star-making happened in short bursts, not all the time.

A Census of Na D-traced neutral ISM and outflows at 0.6<z<4

Yang Sun, Zhiyuan Ji, Francesco D'Eugenio+11 more

AstronomerUsing JWST/NIRSpec medium-resolution spectra from SMILES, JADES, Blue Jay, and Aurora, the authors census Na D-traced neutral ISM and outflows in 309 galaxies at 0.6 < z < 4. After stellar-continuum subtraction, modeling of the Na D doublet yields 63 robust ISM absorption detections, including four broad-line AGNs, and 10 tentative detections. Of the robust detections, 88% occur at log(M*/M☉) > 10. Massive galaxies show absorption in both star-forming and quiescent populations, while lower-mass detections occur only in star-forming systems. In massive quiescent galaxies, detectability appears related to star-formation history, favoring older systems with larger 4000 Å breaks and younger, rapidly quenching systems with strong Hδ_A absorption. Na D outflows are identified in 25 galaxies. Their correlations with star-formation properties in star-forming hosts are consistent with stellar driving. In quiescent hosts, the lack of association with residual star formation, often insufficient star-formation energy budgets, and a high AGN fraction suggest that AGNs dominate these neutral outflows at cosmic noon. Four quiescent galaxies are possible fossil-outflow cases, suggesting, rather than establishing, that AGN-driven outflows can outlast active accretion and help maintain quiescence.

PublicThe researchers used JWST spectra to study neutral gas in 309 galaxies across a broad range of redshifts. They looked for a pair of sodium absorption features, finding clear evidence of interstellar gas in 63 galaxies and tentative evidence in another 10. Most clear detections were in massive galaxies, including both galaxies forming stars and galaxies with little star formation. In less massive galaxies, detections occurred only in those forming stars. The team also identified gas outflows in 25 galaxies. In star-forming galaxies, the outflow properties track star formation, consistent with it powering the escaping gas. In galaxies with little star formation, the outflows often need more energy than the remaining star formation can supply. Combined with the frequent presence of active galactic nuclei, this suggests that activity around central black holes is the main driver in these quiet galaxies. Four quiet galaxies may contain lingering outflows from past nuclear activity. If that interpretation is correct, such outflows could persist after the active phase and help keep star formation low.

Young explorerScientists used the James Webb Space Telescope to look for gas in 309 galaxies, huge groups of stars. They found clear signs of gas in 63 galaxies and possible signs in 10 more. In 25 galaxies, they found gas moving outward. In galaxies making new stars, the clues suggest that star-making helps push the gas out. In galaxies making very few stars, the scientists think activity around a black hole may do most of the pushing. Four galaxies might still have gas moving outward from a time when their black holes were more active. That moving gas might help those galaxies stay quiet and make fewer new stars, but scientists are not sure yet.

Lyman-alpha Radiation Pressure in Dense Star Clusters: Implications for Star Formation and Winds at Cosmic Dawn

Shyam H Menon, Aaron Smith

AstronomerJWST observations in lensed fields suggest that cosmic-dawn galaxies may concentrate star formation in dense, compact clusters. To assess Lyα radiation pressure in these environments, the authors post-process radiation-hydrodynamic snapshots of dense cluster-forming clouds (Σ* ≳ 10³ M☉ pc⁻²) with COLT, spanning dust abundances Zd = 0–0.1 Zd,☉. They infer mild (~10%) effects on gas-to-star conversion efficiencies for Zd ≳ 0.01 Zd,☉, where ε* ≳ 60%; even dust-free models imply ε* ≳ 25%, compared with typical local values below 10%. Dense filaments that dominate stellar mass assembly (n ≳ 10⁴ cm⁻³) remain sub-Eddington, whereas the bulk of the gas volume (n ≲ 10³ cm⁻³) is super-Eddington, with noticeable fractions reaching fEdd ≳ 10. This suggests that Lyα could drive dynamically significant winds within ≲4 Myr, with possible consequences for ionizing-photon escape and galactic outflows. The force multiplier is strongly dust-dependent, reaching ≲3 at Zd = 0.1 Zd,☉ and ≲500 without dust; nevertheless, Lyα pressure exceeds UV and IR radiation pressure by factors of roughly 3–500 across the modeled dust range. These post-processing results support, rather than directly demonstrate observationally, a picture of efficient, bursty cluster formation accompanied by rapid outflows.

PublicJWST observations suggest that some galaxies in the early universe formed stars in extremely dense, compact clusters. This study uses computer simulations to investigate whether pressure from a particular kind of light, called Lyman-alpha, could disrupt the gas clouds that build those clusters. The analysis suggests that the densest gas can resist this pressure and continue forming stars efficiently: at least about 60% of the gas becomes stars in models with sufficient dust, and at least about 25% even without dust. Both are much higher than the below-10% efficiencies typical of nearby star-forming regions. Less dense gas is more vulnerable, and the calculations suggest that this light could push it into strong winds within about four million years. Dust greatly changes the strength of the push, but Lyman-alpha pressure still outweighs ultraviolet and infrared radiation pressure across the dust levels studied. The findings suggest that early galaxies could form stars in efficient bursts while rapidly losing some gas; possible effects on escaping radiation and larger galactic winds remain implications, not observed results of this study.

Young explorerA powerful telescope has given astronomers clues that some very early galaxies made stars in small, tightly packed groups. The scientists used computer models to ask what happens when light pushes on the gas where those stars grow. Their models suggest that thick clumps of gas can keep making lots of stars, while thinner gas may get pushed away like a wind. Tiny bits of dust change how strong the push is. This is what the models suggest, not something the telescope has shown happening directly.

Fractional-Dimension Gravity and the Milky Way Galaxy

Gabriele U. Varieschi

• General Relativity and Quantum Cosmology

AstronomerThe authors apply Fractional-Dimension Gravity (FDG), formerly Newtonian Fractional-Dimension Gravity, to the Milky Way using Gaia DR3 and earlier rotation-curve data. This alternative gravitational model does not require dark matter. They report successfully reproducing the observed rotation curves with a radius-dependent fractional dimension D(R), extending the methodology previously applied to other galaxies. An alternative dimension function D_m(R), derived from the mass-dimension field equation, gives less accurate fits. They also explore how additional weights in the FDG metric could affect special relativity in fractional-dimensional spacetimes. Effective superluminal motion in galactic regions with D<3 is presented as a very speculative theoretical possibility, not an observed finding.

PublicThe study tests a different way of describing gravity against measurements of how the Milky Way rotates, using Gaia DR3 and earlier data. Called Fractional-Dimension Gravity, the model does not require dark matter and allows the dimension describing space to vary with distance from the galaxy’s center. The authors report that this approach reproduces the observed rotation curves, while a second prescription for the dimension gives less accurate matches. These fits do not by themselves establish that the model is the correct description of gravity. The authors also consider possible changes to special relativity within their framework, including a very speculative possibility of effective faster-than-light motion in some galactic regions; they do not report observing such motion.

Young explorerScientists looked at measurements of how our galaxy, the Milky Way, spins. They tried a different rule for gravity that does not need the unseen matter called dark matter. By letting the rule’s description of space change across the galaxy, they could match the measured spinning pattern. Another version did not match as well. Matching the measurements does not prove the rule is right. They also wondered whether their rule might allow a kind of motion that acts faster than light, but that is a very uncertain idea, not something they saw.

Three New Likely Spider Millisecond Pulsar Binaries and Optical Kinematic Tracers of Intrabinary Shocks

Jay Strader, Rebecca Kyer, Laura Chomiuk+9 more

AstronomerMulti-wavelength follow-up of unassociated Fermi LAT sources identifies three candidate spider millisecond pulsars, with SOAR optical spectroscopy and Swift X-ray data. The counterparts near the localization centres of 4FGL J1020.4-5314 and 4FGL J1408.7-3747 are exceptionally strong redback candidates: both are spectroscopic binaries with orbital periods of 0.15–0.3 d and mass functions of 0.6–0.9 solar masses. In J1020.4-5314, bright H-alpha emission with FWHM 2100 km/s persists in all spectra obtained over two years. Its radial velocities are phase-offset from the secondary's absorption-line velocities and match the expected signal from emission near the primary. The authors identify this as the first demonstration in a spider that H-alpha emission can be associated with an intrabinary shock wrapping around the pulsar, suggesting optical emission lines could trace shock kinematics in some redbacks. The association of the third candidate with 4FGL J1429.8-0739 is less secure; its 30.5-hour orbit, possible subgiant secondary, and high X-ray luminosity motivate further investigation.

PublicAstronomers followed up three previously unidentified gamma-ray sources using visible-light spectra and X-ray observations, finding three candidate binary systems containing millisecond pulsars, known as spiders. Two are particularly strong candidates for the redback type, with measured orbits lasting 0.15–0.3 days. One, associated with 4FGL J1020.4-5314, showed bright, very broad hydrogen emission throughout observations spanning two years. The motion inferred from this emission differs from that of the companion star and matches what is expected from a source near the pulsar. The researchers link it to a shock between the stars that wraps around the pulsar—the first such demonstration for a spider system. This suggests that visible-light emission could help track the motion of these shocks in some redbacks. The third candidate's link to its gamma-ray source is less certain, but its 30.5-hour orbit, possibly evolved companion star, and high X-ray luminosity make it worth further study.

Young explorerAstronomers found three pairs of objects in space that might each include a tiny star spinning very fast, called a pulsar. Two pairs look like especially good matches, but they are still candidates. In one pair, glowing hydrogen moves differently from the companion star. The scientists say this glow can come from a shock wrapped around the pulsar, and it might help them study how the shock moves. The third pair is a less certain match and needs another look.

XClass: An Automated Multiwavelength Machine-Learning Pipeline for Classification of Extragalactic X-ray Sources. I. Pipeline Description

Blagoy Rangelov, Nicholas Moore, Haley Dutton+1 more

• Astrophysics of Galaxies
• Instrumentation and Methods for Astrophysics

AstronomerXClass is an end-to-end machine-learning pipeline for assigning extragalactic Chandra point sources to seven classes: AGN, LMXBs, HMXBs, CVs, low- and high-mass foreground stars, and supernova remnants. To bridge the mismatch between predominantly Galactic training photometry from PanSTARRS and 2MASS and target photometry from HST, it fits class-appropriate SED models and convolves them with HST filter curves to generate synthetic magnitudes. An asymmetric two-stage Random Forest first separates broad categories, then distinguishes LMXBs from HMXBs using features augmented with first-stage probabilities. Training sources come from ten Galactic catalogs and extragalactic SNR catalogs cross-matched with Chandra Source Catalog v2.1. Features include X-ray hardness ratios, translated HST colors, and X-ray-to-optical flux ratios. On the 11,374-source optical baseline, restricted to sources with at least one optical magnitude to avoid imputation artifacts, the authors report 99.6% accuracy, 0.90 balanced accuracy, and ECE = 0.002. These metrics describe the optical baseline, not demonstrated performance on M31 or M33; those applications are planned for a companion paper. The pipeline is designed to accommodate any HST filter configuration.

PublicMany X-ray sources found by Chandra in nearby galaxies have not yet been classified. The researchers present XClass, a machine-learning tool that sorts sources into seven types, including active galactic nuclei, two kinds of X-ray binary, cataclysmic variables, foreground stars in two mass groups, and supernova remnants. A major obstacle is that the examples used to train the tool were mostly measured with different light filters from those used by Hubble for the intended targets. XClass fits models of the training sources’ light and calculates how those models would appear through Hubble’s filters; these calculated brightnesses are not new Hubble observations. For a baseline of 11,374 sources with at least one optical brightness measurement, the authors report 99.6% accuracy, while a measure that gives equal weight to each class is lower, at 0.90. They also report that the tool’s confidence estimates are well calibrated. Applying XClass to the galaxies M31 and M33 is planned for a separate paper, rather than reported here.

Young explorerChandra sees spots in space that give off X-rays, but scientists do not yet know what many of them are. The researchers made a computer helper called XClass to sort the spots into seven groups. The pictures used to teach it were taken with different kinds of light filters, so the scientists used models to work out how the same objects would look through Hubble’s filters. The helper did very well in a check using objects that also had measurements of ordinary light, but it can still make mistakes. The scientists plan to use it on two nearby galaxies later; this paper does not yet show those results.

A Multi-Wavelength Picture of the Surprisingly Short 2024/25 Outburst from EXO 0748-676

Amy H. Knight, Lauren Rhodes, Noel Castro Segura+11 more

AstronomerEXO 0748-676 resumed outburst in March 2024 after sixteen years of quiescence, but returned to quiescence in January 2025 after approximately ten months, unlike its prolonged 1985–2008 outburst. This first multi-wavelength study of the 2024/25 event combines observations from nine facilities spanning radio to X-ray. Both the rise and decay were fully sampled in X-rays and optical light, whose fluxes remained reasonably stable rather than showing canonical transient low-mass X-ray binary outburst behaviour. Optical observations reveal a skewed orbital phase curve and an irradiation-dominated light curve. The authors associate the rapid terminal fading with the onset of hydrogen recombination in the outer disc at approximately 11,000 K. Early XMM-Newton and NICER spectra show substantial obscuration and a suppressed soft X-ray contribution. A clumpy, ionised absorber model describes these spectra, but the physical cause of the early obscuration remains uncertain. X-ray colours indicate a predominantly faint, hard state, with only marginal brightening near the end and no transition to a soft state, consistent with a failed-transition outburst.

PublicAfter sixteen quiet years, EXO 0748-676 became active again in March 2024. This episode lasted only about ten months, whereas its previous outburst ran from 1985 to 2008. Researchers combined observations from nine facilities, covering radio waves through X-rays, and tracked the full rise and fall in visible light and X-rays. The brightness stayed fairly steady through much of the episode, unlike a typical outburst of this kind. The optical light was dominated by material heated by incoming radiation. The researchers link the rapid final fading to hydrogen beginning to recombine in the outer disc at about 11,000 K. Early X-ray observations also showed that much of the lower-energy X-ray emission was obscured. A model involving clumpy, ionised gas fits this obscuration, but its exact cause is unknown. The source remained mostly faint with relatively high-energy X-ray emission and never shifted into a state dominated by lower-energy X-rays, behaviour characteristic of a failed transition.

Young explorerEXO 0748-676 grew brighter after being quiet for sixteen years. This time, it stayed active for about ten months, much less than before. Scientists watched it with nine observing places. Its light stayed fairly steady, then faded quickly. They think a change in the gas around it helped cause the quick fade. Some X-rays were hidden early on, but scientists are not sure exactly why.

X-ray Through Radio Observations and Modeling of the Soft X-ray Flash GRB 250419A

Genevieve Schroeder, Anna Y. Q. Ho, Gavin P. Lamb+24 more

AstronomerThe authors present X-ray, optical, and millimeter-to-centimeter radio observations of GRB 250419A, an X-ray flash with peak energy below 4 keV discovered by the Space-based multi-band astronomical Variable Objects Monitor. They observe a clear achromatic break in the X-ray and optical light curves and likely two radio spectral components. The afterglow resembles those of long-duration gamma-ray bursts but is slightly underluminous, with an unusually shallow optical decay during roughly the first two days. Their interpretation favors a high-Lorentz-factor jet with low kinetic energy, approximately 10^49–10^50 erg, and energy injection potentially associated with radial stratification and/or a marginally off-axis viewing angle. Although detailed multiwavelength coverage remains scarce for X-ray flashes, this event supports the conclusion that at least some are a lower-energy extension of classical gamma-ray bursts.

PublicX-ray flashes have several proposed explanations, and observations across different kinds of light are needed to distinguish them. For the X-ray flash GRB 250419A, researchers collected X-ray, visible-light, and radio data. The X-ray and visible-light afterglows showed a matching change in how their brightness faded, while the radio emission likely contained two distinct components. Overall, the afterglow resembled those of long-duration gamma-ray bursts, but was somewhat fainter and initially faded unusually slowly in visible light. The researchers interpret the observations as a very fast jet carrying relatively little energy, with additional energy supplied over time. The jet's structure and/or a viewing direction slightly away from its axis could help explain this behavior. The study suggests that some, not necessarily all, X-ray flashes belong to the lower-energy end of the gamma-ray-burst family.

Young explorerScientists watched a flash in space using different kinds of light. It looked a little like a dimmer cousin of a gamma-ray burst. They think a very fast stream of material with less energy could explain it. This suggests that some X-ray flashes and gamma-ray bursts may belong to the same family.

The X-ray and optical emission of the intermediate polar Swift J0614.0+1709

Nikita Rawat, Domitilla De Martino, David A. H. Buckley+5 more

AstronomerA pointed XMM-Newton observation and long-term TESS photometry provide the first detailed X-ray and optical study of the intermediate polar Swift J0614.0+1709. A coherent X-ray modulation at the approximately 1411 s white dwarf spin period confirms the system's magnetic nature. The pulse amplitude decreases with increasing energy, consistent with phase-dependent absorption; phase-resolved spectroscopy indicates that changes in the partial-covering absorber's covering fraction primarily drive the spin variability. The broadband spectrum is well fitted by a partially absorbed thermal plasma at approximately 12 keV plus a soft blackbody component at approximately 63 eV. The inferred bolometric luminosity is approximately 5 × 10^34 erg s^-1, placing the source among the more luminous intermediate polars. In TESS data, the spin signal remains dominant, while the relative orbital and spin strengths vary substantially between sectors. The beat modulation varies and disappears in one sector, suggesting changes in the contribution of reprocessing regions. Orbital and, more weakly, spin amplitudes tend to increase in brighter optical states, potentially linking the variability to changes in mass transfer. Changing pulse morphology and recurrent brightenings motivate future simultaneous optical and X-ray observations.

PublicResearchers studied the magnetic white dwarf system Swift J0614.0+1709 using X-rays from XMM-Newton and visible-light measurements from TESS. Its X-ray brightness pulses regularly about every 1411 seconds as the white dwarf spins, confirming the system's magnetic nature. The pulses are weaker at higher X-ray energies, and the spectral analysis indicates that much of the variation comes from changes in how much of the X-ray source is obscured by material flowing toward the star. The estimated total luminosity places it among the more luminous systems of its class. Its visible-light behavior is more complicated: the spin-related signal stays dominant, but other repeating signals change in strength, and a beat signal disappears during one observing interval. This may reflect changes in regions that absorb and re-emit radiation. Some brightness variations also tend to strengthen when the system is brighter, suggesting that changes in the supply of material may play a role. The researchers identify it as a promising target for future observations made in X-rays and visible light at the same time.

Young explorerScientists watched a little star called a white dwarf that has a strong magnetic field. As it spins, its X-ray light gets brighter and dimmer in a steady pattern. Their study shows that this mostly happens because moving material hides different amounts of the X-ray light. The light we can see with our eyes changes in more complicated ways, and one repeating pattern even goes away for a while. Scientists think changes in the material around the star may help explain this, but they want to watch both kinds of light together to learn more.

AT2018hyz: Predictions for a Sky Projection from a Delayed Off-Axis Jet

Ranadeep Ghosh Dastidar, Paul C Duffell

AstronomerAT2018hyz, an optically discovered tidal disruption event, was first detected in radio 972 days later and showed radio brightening at 1370–2160 days. Proposed explanations include an off-axis jet afterglow or a delayed mildly relativistic outflow. This study explores the delayed off-axis jet scenario and finds that different combinations of launch delay and viewing angle can reproduce the observed radio behavior. Larger angles from the jet core imply shorter inferred launch delays, creating a degeneracy. Predicted sky-image extents range from 0.6 milliarcseconds for a viewing angle of 30 degrees to 0.3 milliarcseconds for a view perpendicular to the jet core. The authors propose that future VLBI imaging, combined with the radio light curve, could constrain the viewing angle and launch delay; these image extents are model estimates, not reported resolved observations.

PublicThe tidal disruption event AT2018hyz was discovered in visible light, then first detected in radio waves 972 days later. Its radio emission brightened between 1370 and 2160 days. One possible explanation is a jet launched after a delay and viewed away from its central direction; another is a delayed outflow moving at mildly relativistic speed. This study examines the jet explanation. The models can account for the radio brightening with different combinations of viewing angle and launch delay: viewing the jet farther from its central direction requires a shorter delay. The researchers predict slightly different apparent radio-image sizes for these possibilities. Future high-resolution radio observations using VLBI could distinguish them, especially when combined with the changing radio brightness. The study does not establish that a delayed jet is the unique explanation.

Young explorerAstronomers watched an event in space called AT2018hyz. They first saw it with ordinary light, and much later they detected radio waves from it. Those radio waves later grew brighter. The scientists tested an idea: maybe a jet of material started late, and we are looking at it from the side. Different starting times and directions can explain the brightening, so they do not yet know which is right. They predict that very sharp radio pictures could help tell these possibilities apart. Those pictures are a plan for future observations, not something they have already seen.

Early Emergence of SSS emission in RS Oph

J.-U. Ness, J.P. Osborne, M. Orio+3 more

• Solar and Stellar Astrophysics

AstronomerAn XMM-Newton observation of RS Oph at an early stage of its 2021 outburst closely resembles the unusual spectrum observed on day 26.1 of the 2006 outburst. The spectrum combines a slowly fading shock component, evolving over days, with a soft component that varies over hours, dominates the variability, and contains several unidentified features. A blackbody reproduces the low-resolution 2006 EPIC/pn spectrum but fails for the simultaneous high-resolution RGS data, demonstrating that low-resolution spectra can conceal complex, line-dominated emission. No significant 35-s periodicity is detected in this analysis. The rapid soft variability, radiative recombination continua, Fe X emission, and previously detected 35-s period suggest, rather than establish, a hidden photoionising source. The authors classify these spectra, together with those of V1494 Aql and V1716 Sco, as intermediate between the SSe and SSa categories of Ness et al. (2013); they do not resemble the persistent SSS Cal 87. Future modelling is needed to assess the relative contributions of photoionisation, charge exchange, and other processes.

PublicDuring its 2021 eruption, the recurrent nova RS Oph produced an unusual X-ray spectrum closely resembling one seen early in its 2006 eruption. The observations separate two components: emission from shocks that fades slowly over days, and lower-energy X-ray emission that changes over hours and causes most of the observed variability. Detailed spectra reveal several features whose origins remain unidentified. A simple blackbody model fits the less detailed 2006 spectrum but cannot explain the fine structure seen at the same time, showing why high-resolution observations matter. The researchers did not detect a significant repeating signal every 35 seconds in this analysis, although such a signal had been detected previously. That earlier signal and other spectral clues suggest an unseen source that ionises surrounding gas, but this interpretation remains uncertain. The authors place RS Oph and two similar novae in an intermediate spectral class; further modelling is needed to determine which physical processes create these spectra.

Young explorerRS Oph is a star that has erupted more than once. Scientists found that its X-ray light in the 2021 eruption looked much like its light in the 2006 eruption. One part faded slowly over days, while another changed much faster, over hours. Looking closely showed puzzling features that a less detailed picture could hide. The scientists think a hidden source of light might help explain what they see, but they are not sure yet. They need more work to understand what makes these strange patterns.

Optimal Pulsar Timing Array Strategies with the Deep Synoptic Array

Tyler Cohen, Paul B. Demorest, Jeremy G. Baier+50 more

• Instrumentation and Methods for Astrophysics

AstronomerPTAs have found evidence for a nanohertz gravitational-wave background through coordinated timing of millisecond pulsars; its progenitor or progenitors remain to be identified. This study presents a timing-simulation framework to predict the optimal telescope, observing frequency, and integration time for each pulsar. It applies the framework to NANOGrav’s 85-pulsar source list using configurations involving the Green Bank Telescope, Very Large Array, CHIME, and the DSA, which is under construction in Nevada. The analysis indicates that intrinsic pulse-phase jitter is not the dominant timing-noise contribution for most sources and identifies targets best assigned to DSA plus CHIME or DSA alone. The simulations predict that a DSA PTA built from scratch would be more sensitive than one using current instruments. Under a fixed observing-time budget, the authors optimize integration times to maximize GWB signal-to-noise. Monte Carlo realizations yield only about a 5% sensitivity improvement over equal time per source for an early-science DSA scenario with a fixed source list, indicating limited benefit from integration-time optimization in that setting.

PublicAstronomers have found evidence for a background of extremely low-frequency gravitational waves by tracking the radio pulses of rapidly spinning stars called millisecond pulsars. The sources of that background are not yet established. This study uses simulations, rather than observations with the still-under-construction Deep Synoptic Array (DSA), to explore how best to time 85 pulsars with several radio telescopes. The model predicts which telescope, radio frequency, and observing duration should work best for each pulsar. It finds that variations in the pulses themselves are not the main limit on timing precision for most of these stars, and predicts that a pulsar-timing program built around DSA would be more sensitive than one using current instruments. However, finely adjusting the observing time for each star offers only a modest gain: about 5% in simulated gravitational-wave sensitivity for an early-science DSA program with a fixed target list and time budget.

Young explorerSome spinning stars send out radio pulses like ticking clocks. By watching lots of these clocks, scientists have found clues to very slow ripples in space. They do not yet know what makes those ripples. This study used computer pretend-observations to plan how telescopes could watch the stars. It predicts that a new telescope being built could help. Giving some stars more watching time than others helped only a little in the computer tests.

Towards Retrieval Augmented Generation in High-Energy and Astroparticle Physics

Jacky Kumar, Sajan Kumar

• High Energy Physics - Phenomenology

AstronomerThe authors develop an open-source retrieval-augmented generation pipeline for focused literature surveys in high-energy and astroparticle physics. It embeds approximately 230,000 arXiv papers from hep-ph and astro-ph.HE, combines keyword and semantic retrieval, and refines the candidates with a cross-encoder reranker. Google DeepMind’s Gemma-4-E4B language model then assesses relevance and synthesizes a concise report with references. The intended use is to help researchers, editors, and referees establish prior work and identify open questions. The authors claim capabilities beyond classical keyword search, but the abstract provides no quantitative evaluation of retrieval performance or report accuracy; this is a literature-search tool, not a new astrophysical finding.

PublicThe authors describe an open-source AI tool designed to help people navigate the vast research literature on high-energy particles and related cosmic phenomena. It searches approximately 230,000 arXiv papers using both matching words and similarity in meaning, ranks the most promising papers, and uses a language model to assess their relevance and write a short summary with references. The goal is to help researchers and reviewers quickly understand what has already been studied and what questions remain. Although the authors say the approach goes beyond ordinary keyword searches, the abstract does not report tests showing how accurate or reliable its summaries are.

Young explorerThere are so many papers about tiny particles and things in space that it is hard to find the ones you need. The authors made a computer helper that looks for papers about your question and writes a short explanation, with a list of the papers it used. It looks for both matching words and matching ideas. It is meant to help people learn what others have already studied, not to discover something new in space. The description does not tell us how often the helper gets things right.

High-energy neutrinos from shocked circumnuclear material around optically-bright and infrared-only tidal disruption events

Mainak Mukhopadhyay, Shigeo S. Kimura, Tatsuya Matsumoto

• High Energy Physics - Phenomenology

AstronomerThis study semi-analytically models neutrino production from sub-relativistic TDE outflows shocking circumnuclear material, including cosmic-ray acceleration and transport, proton–proton interactions, and radiative cooling and compression. It compares optically bright TDEs with IR-only events, motivated by luminous IR transients with weak or absent optical counterparts that are consistent with dusty, obscured TDEs. In the model, optical TDEs have low proton–proton efficiencies and small neutrino yields, whereas radiative compression in dense IR-only environments can raise the target density enough to approach calorimetric efficiency. Depending on event-rate uncertainties, the latter population could supply up to approximately 10% of the observed diffuse neutrino flux at 100 TeV. These are model estimates, not detections of TDE neutrinos. Long emission durations and low individual yields motivate electromagnetically informed stacking searches. Forecasts for IceCube, IceCube-Gen2, KM3NeT, and HUNT indicate that a future approximately 30 km³ neutrino observatory could reach 3σ sensitivity to nearby IR-only TDEs at z ≲ 0.4 using multi-year windows.

PublicWhen a star is torn apart by a black hole, the event can send material outward, creating shocks in the surrounding gas. This study models how those shocks could accelerate particles that collide with the gas and produce high-energy neutrinos. The researchers compare events bright in visible light with events seen mainly in infrared light, which may be hidden by dust. Their calculations suggest that visible-light events produce relatively few neutrinos, while cooling and compression in dense, dust-obscured environments could make neutrino production much more efficient. Depending on how common these events are, the infrared-only population could account for up to about 10% of the measured diffuse neutrino flux at an energy of 100 TeV. This is a prediction, not a detection from these events. Because each event is expected to give a weak but long-lasting signal, the team proposes combining searches across many events over several years. They forecast that a future neutrino observatory with a volume of about 30 cubic kilometres could find statistical evidence for the nearby infrared-only population.

Young explorerWhen a black hole tears a star apart, some material can rush outward and bump into gas nearby. Scientists used a model to work out whether those bumps could make tiny particles called neutrinos. They think star-tearing events hidden behind lots of dust might make more neutrinos than ones we can see in ordinary light. They have not shown that these events really make the neutrinos we detect. To test the idea, they suggest using a future giant detector to look for tiny clues from many events over several years.

Eight Gamma-Ray Bursts Observed with the Fermi Gamma-ray Burst Monitor: Significant Quasi-Thermal Components and Conditional Jet Constraints

Ze-lian Du, Zhao-Yang Peng, Jia-Ming Chen+2 more

AstronomerThe study analyzes eight Fermi GBM GRBs with reported redshifts, selected from 126 events using prespecified fluence and spectral criteria. After unstable compound-model DIC evaluations are excluded, the stable added-blackbody comparison yields ΔDIC > 10 in 203 of 215 accepted bins, while an independent mBB+PL decomposition assigns more than half the flux to mBB in 214 of 215 bins. These spectral results are model-dependent: CPL–mBB correlations of 0.83 and 0.78 exceed Band–mBB correlations of 0.41 and 0.48, and time-integrated simple-BB fractions range from 0.005 to 0.311, with six of eight below 0.12. Applying the H2013 and G2015 non-dissipative photosphere prescriptions gives conditional, rather than unique, jet constraints. At assumed launch radii of 21, 100, and 1000 km, H2013 yields εTh > 0.5 in 1/2, 1/4, and 2/8 valid solutions, respectively; G2015 yields σ0 < 1 in 0/1, 1/4, and 1/8. Boundary or physically inadmissible inversions are excluded. At 21 km, six H2013 and seven G2015 solutions are invalid, indicating incompatibility between that radius and the adopted inversion for most events. For bursts with valid solutions at multiple radii, increasing the radius generally lowers εTh and raises σ0. Launch radius, efficiency, and spectral decomposition therefore dominate the inferred constraints; the analysis establishes neither a universal jet class nor a unique non-thermal emission mechanism.

PublicWhat gamma-ray burst jets are made of remains uncertain. Researchers examined eight bursts observed by Fermi’s Gamma-ray Burst Monitor, chosen from 126 events using predefined criteria and having reported redshift information. After removing unstable model comparisons, adding a blackbody component was statistically favored in 203 of 215 accepted time intervals. A different model, combining a multicolor blackbody with a power law, attributed most of the radiation to the multicolor component in 214 intervals. These findings do not give a single, model-independent measure of thermal radiation: the simple-blackbody contribution across each burst was much smaller, ranging from 0.5% to 31.1%, and other spectral comparisons also depended on the model used. The researchers then used two theoretical descriptions to infer jet properties. Those inferences depended strongly on the assumed jet launch radius, efficiency, and spectral model. Many calculations produced invalid solutions at the smallest assumed radius, showing that this choice was incompatible with the adopted calculation for most bursts. The study therefore does not identify one jet type shared by all bursts or a unique explanation for their non-thermal radiation.

Young explorerGamma-ray bursts are powerful flashes in space with jets, but scientists are still unsure what those jets are made of. They studied the light from eight bursts and tried different ways of describing it. The answers changed depending on which description they used. They also used models to work backward from the light to the jets. Some guesses about where the jets started did not give sensible answers. So the scientists have clues, but they cannot yet say that all these jets are the same kind or that their light is made in just one way.

Superorbital Phase Evolution and Identification of New Anomalous Low State Candidates for Her X-1

Yi Chou, Jun-Lei Wu

AstronomerA 35-year, multi-instrument X-ray study of Her X-1 examines its 35-day superorbital modulation. A new Rank-Searching method, based on peak main-high-state intensity, provides an objective, reproducible criterion for anomalous low states (ALSs). It recovers known ALSs and the recently reported ALS 2025, while identifying ALS 1991 and ALS 2015 as previously unrecognized candidates. The superorbital phase evolution separates into seven epochs alternating between smooth and variable behavior, with an empirical cubic trend for the smooth component and a characteristic recurrence timescale of approximately 3400 days for the variable epochs. In a first-order tilted-disk interpretation, the secular evolution corresponds to an inferred cumulative disk-mass increase of about 1.8% and outer-radius expansion of about 0.9%; disk-mass variations of at most about 2.4% can reproduce the short-term phase excursions. These are model-dependent inferences rather than direct measurements of disk changes. A viscous diffusion timescale of approximately 168 days characterizes the short-term disk response. The stable phase relation and similar profiles of the main and short high states support a remarkably stable global warped-disk geometry across the baseline.

PublicResearchers studied 35 years of X-ray observations of Her X-1 to track changes in its roughly 35-day brightness cycle. Their new method reliably identifies unusually faint episodes, recovering previously known events and flagging two additional candidates in 1991 and 2015. The cycle's timing passes through seven periods that alternate between smoother and more variable behavior; the variable periods recur on a characteristic timescale of about 3400 days. Using a simplified tilted-disk model, the researchers interpret the long-term timing changes as a small increase in the disk's mass and outer size. Small mass changes can also reproduce the shorter-term timing shifts, with approximately 168 days serving as a characteristic response time. These disk changes are inferred from a model, not measured directly. The consistent timing relationship and similar shapes of the two bright portions of the cycle suggest that the warped disk's overall shape stayed remarkably stable.

Young explorerHer X-1 gets brighter and dimmer in X-rays in a cycle lasting about 35 days. Scientists looked at 35 years of observations and found two possible dim spells they had not noticed before. The cycle's timing sometimes changed smoothly and sometimes more unevenly. A model suggests that small changes in a disk of material could explain this, but that is not something they measured directly. The disk's overall shape seems to have stayed much the same.

25 Years of Mrk 421 with XMM-Newton: Unveiling Structured Jets and Energy-Dependent Escape

Tek P. Adhikari, Gopal Bhatta, Sangeetha Kizhakkekalam+4 more

• Astrophysics of Galaxies

AstronomerAn analysis of 76 archival XMM-Newton/pn epochs from 2000–2025, using IMAGING and TIMING modes, traces the long-term X-ray spectral and timing behavior of the TeV blazar Mrk 421. Flux varies by roughly an order of magnitude and exhibits a harder-when-brighter trend, although hardness-ratio scatter shows that flux does not uniquely specify the spectral state. Hard-band (2–10 keV) and soft-band (0.3–2 keV) fractional variability are tightly correlated, with stronger variability at higher energies. The flux distribution is non-Gaussian and lognormal-like, with a bright-flare tail. A simple power law is insufficient: 59 epochs favor a broken power law and 17 a log-parabola. The authors interpret this changing model preference as possible transitions between a distinct acceleration shockfront and downstream stochastic turbulence. Broken-power-law break energies cluster near 2 keV across flux states, with mild mean steepening of ΔΓ ≈ 0.19, inconsistent with standard one-zone cooling models. These findings support structured-jet scenarios or energy-dependent electron escape, without uniquely establishing either explanation.

PublicResearchers examined 76 sets of X-ray observations of the blazar Mrk 421 taken by XMM-Newton between 2000 and 2025. Its brightness changed by about a factor of ten, alternating between flares and quieter periods. When brighter, it generally produced a greater proportion of higher-energy X-rays, but brightness alone did not fully explain its spectrum. Higher-energy X-rays also varied more strongly than lower-energy ones. Most observations favored a spectrum with a change in slope, while the others favored a smoothly curved spectrum. The change in slope usually occurred near 2 keV and was too mild to match standard models in which electrons cool within a single emission region. The authors suggest that changes in particle acceleration, structure within the jet, or electrons escaping differently depending on their energy could help explain the findings. These are interpretations of the observations, not directly demonstrated mechanisms.

Young explorerScientists looked at years of X-ray pictures of a space object called Mrk 421. It sometimes shone much brighter and sometimes grew quieter. When it was brighter, it usually gave off more of the stronger-energy X-rays, and those X-rays changed more than the gentler ones. But brightness did not tell the whole story. The scientists think different things may be happening inside its fast-moving jet, such as particles gaining energy or escaping. They have clues, but they do not yet know exactly which explanation is right.

Detection of kilosecond hard lags in the new pulsating ULX candidate NGC 7456 ULX-1

W. Leone, F. Pintore, C. Pinto+19 more

• Astrophysics of Galaxies

AstronomerAnalysis of the two deepest XMM-Newton observations of NGC 7456 ULX-1, from 2018 and 2023, detects significant hard X-ray lags of approximately 1,000 s during rapid flux variability. Adaptive-binned cross-correlations of the 1–10 keV and 0.3–1 keV light curves were evaluated in consecutive 10 ks intervals; the lowest-energy photons primarily drive the delays. Spectral modeling indicates a Comptonization-dominated flow with a cooler, extended outer region and a hotter, compact inner region embedded in an optically thick wind. The authors interpret the lags as inward propagation of accretion-rate fluctuations combined with photon diffusion through the dense outflow, rather than standard reverberation. The small inferred inner emitting radius disfavors, but does not exclude, an intermediate-mass black hole. The results support an important role for propagation and radiative transfer in shaping super-Eddington timing behavior, without uniquely establishing the proposed mechanism.

PublicObservations of the unusually bright X-ray source NGC 7456 ULX-1 reveal that, during rapid brightness changes, higher-energy X-rays arrive about 1,000 seconds after lower-energy X-rays. This delay was detected in XMM-Newton observations from both 2018 and 2023. Models of the source’s spectrum suggest that cooler outer gas surrounds a hotter, compact inner flow, with a dense wind around it. The researchers propose that changes in the incoming gas first brighten the cooler region, then travel inward, while repeated interactions between photons and the surrounding material further delay their escape. This explanation is an interpretation of the measurements, not a directly observed sequence. The delays argue against a standard light-echo explanation, and the inferred small size of the inner emitting region makes an intermediate-mass black hole less likely.

Young explorerScientists watched a very bright source of X-rays in space. When its brightness changed quickly, some higher-energy X-rays showed up many minutes after lower-energy ones. The scientists think changes may start in cooler gas farther out and then move into hotter gas closer in. The X-rays may also take time to work their way through a thick cloud of flowing gas. That could explain why some arrive later, but scientists have not proved that this is exactly what happens.

Disk-Like Matter Outflow from a Kerr-Type Wormhole: Possible Observational Manifestations and Magnetic Effects

Mikhail Piotrovich, Stanislava Buliga, Tinatin Natsvlishvili

AstronomerThis phenomenological study considers a hypothetical traversable Kerr-type wormhole connecting two distinct asymptotic regions, with one mouth in an accreting active galactic nucleus and the other in a comparatively quiescent nucleus. Matter entering from the active side may emerge through the other mouth; its angular momentum is expected to favor an equatorial, disk-like outflow rather than a conventional black-hole accretion disk. The authors classify possible outer-flow regimes by outflow speed relative to local escape and orbital speeds, explicitly restricting this Newtonian treatment to weak fields at large radii. Near-throat dynamics instead require general-relativistic and magnetohydrodynamic treatment. They discuss possible observational, thermal, and recombination signatures, magnetic effects, and jet formation without a conventional accretion disk, including how magnetic stresses, energy extraction, and an intrinsic dipolar field could affect the flow's inherited energy and angular momentum. These are hypothetical scenarios and possible signatures, not observational evidence for wormholes.

PublicThe study explores what might happen if a hypothetical wormhole linked an actively feeding galactic center to a quieter one. Gas entering one end could pass through and emerge from the other. Because the gas carries rotational motion, the emerging flow is expected to spread mainly into a disk-like shape, unlike the usual disk of gas falling toward a black hole. Its behavior would depend on its speed compared with the speeds needed to orbit or escape. The authors discuss possible heat, light, and magnetic effects, including whether a jet could form without a normal accretion disk. They emphasize that a simpler description of gravity applies only far from the wormhole; the region near its narrow passage needs a treatment that includes relativity and magnetic fields. The work describes possibilities, not a detected wormhole or confirmed signals.

Young explorerImagine a pretend tunnel joining the centers of two galaxies. One end has gas falling into it, and the other end is in a quieter place. The scientists ask whether that gas could come out of the quiet end and spread into a flat shape because it is spinning. They also wonder whether it could make a narrow stream of gas called a jet. This is an idea they are exploring, not a tunnel they have found.

Slingshot on compact binaries in the nuclear region of galaxies as the origin of large offset gamma-ray bursts

Juan C. Rodríguez-Ramírez, Viviane Alfradique, Clécio R. Bom+1 more

AstronomerSome observed GRBs lie at large projected offsets from their putative host-galaxy centres, reaching several tens of kiloparsecs. For kilonova-associated GRBs, neutron-star natal kicks offer an explanation. This study explores an alternative: gravitational-slingshot ejection of bound NS-NS, NS-BH, and NS-WD binaries from galactic nuclei by an intermediate-mass black hole or a secondary supermassive black hole. The authors analytically derive binary-survival conditions and parametrise post-encounter velocities, then numerically integrate centre-of-mass trajectories in elliptical-like and spiral-like potentials containing a primary SMBH, stars, and dark matter. In the sampled models, NS-NS and NS-WD systems typically merge farther out than NS-BH systems. Approximately 30–45% of successful ejections yield mergers at three-dimensional distances exceeding 100 kpc, occurring roughly 0.1–10 Gyr after ejection. These model-dependent, three-dimensional offsets are distinct from observed projected offsets; the results support the mechanism as a candidate channel, not an established explanation for particular transients.

PublicSome gamma-ray bursts appear far from the centres of galaxies thought to host them. When a burst accompanies a kilonova, it is expected to involve a pair of compact objects containing at least one neutron star. A kick received when the neutron star formed could explain the displacement. This study models another possibility: a black hole near a galaxy’s centre could gravitationally fling a compact pair outward while leaving it bound together. The calculations follow pairs containing a neutron star and either another neutron star, a black hole, or a white dwarf. In the sampled models, about 30–45% of successful ejections lead to mergers more than 100 kiloparsecs from the galaxy’s centre, roughly 100 million to 10 billion years later. These are predicted distances in three dimensions, not measured sky offsets. The mechanism remains a possible explanation for very distant transient events.

Young explorerAstronomers have seen bright space flashes far from the middles of galaxies they think the flashes belong to. They wondered whether a black hole could fling two tiny, heavy star leftovers far away while the pair stayed together. Their calculations showed that some pairs could travel very far before joining together. This might help explain some distant flashes, but it does not prove that a black hole sent them there.

Recycling serendipitous observations of XRISM for dark matter searches

Lidiia Zadorozhna, Denys Malyshev, Oleg Ruchayskiy

AstronomerThe authors propose a strategy for low-count-rate XRISM/Resolve observations and search the 3.48–3.56 keV band for radiative decay emission from keV-mass dark matter in the Milky Way halo. Despite lower exposure, they obtain stronger bounds than those from XRISM galaxy-cluster observations. They also report a residual at 3.5311 keV with approximately 3σ local significance, coincident with a previously reported unidentified feature and with no plausible atomic or instrumental counterpart identified. This is not a confirmed dark-matter detection. They expect the bounds to tighten as additional pointings become available.

PublicResearchers used XRISM/Resolve to search for an X-ray signal that might come from dark matter decaying in the halo surrounding the Milky Way. Their analysis places tighter limits on such a signal than XRISM observations of galaxy clusters, despite using less exposure time. They also found a possible feature at the same X-ray energy as an earlier unexplained signal. Its statistical significance is about three sigma locally, meaning at that particular energy, so it does not establish a dark-matter discovery. The authors identify no plausible explanation involving atoms or the instrument and expect more observations to improve the limits.

Young explorerScientists are looking for a special kind of light that might come from dark matter, invisible stuff around our galaxy. They used an X-ray telescope to put a stricter limit on how much of that light could be there. They also saw a small hint of extra light, but they do not know whether it comes from dark matter. They expect more looks at the sky to help them check.

Stationarity and angular momentum conservation in pulsar spin noise

Reginald Christian Bernardo

• Instrumentation and Methods for Astrophysics
• Statistical Mechanics

AstronomerThe study analyzes pulsar spin wandering with two physically motivated crust–superfluid models: a singular, nonstationary model with diffusive total angular momentum and a minimal, stationary model with conserved total angular momentum. Using scalable Gaussian process methods on mock data, the authors show that the models are testable and distinguishable given simultaneous, independent observations of both rotational states. Joint continuous gravitational-wave observations and radio timing are proposed as a potential route to testing stationarity, not reported as an accomplished measurement. With only one component accessible, robust inference and prediction are more difficult and depend on priors and data quality.

PublicThe researchers compare two explanations for irregular changes in pulsar rotation, treating the crust and the superfluid as separate spinning components. In one model, their combined angular momentum wanders randomly; in the other, it stays conserved and the spin fluctuations have statistical properties that remain steady over time. Tests with simulated data show that the models can be distinguished if both components’ rotation can be measured independently at the same time. Combining radio timing with continuous gravitational-wave observations might make such a test possible. The paper does not report that observational test, and warns that measuring only one component makes conclusions and predictions less reliable and more dependent on data quality and starting assumptions.

Young explorerImagine a spinning object in space with an outside part and an inside part. Scientists made two models for how its spinning might wiggle. In one, the two parts’ total amount of spin wanders; in the other, that total stays the same. They tried the models with pretend measurements and found they could tell them apart if they could watch both parts spin at once. They hope two kinds of signals from space might help them do that. Watching just one part makes it harder to know which model fits or what will happen next.

Intrinsic versus observation induced spin nonstationarity in pulsar timing

Reginald Christian Bernardo

• Instrumentation and Methods for Astrophysics

AstronomerThe authors develop a Gaussian-process test of spin-noise stationarity using crust rotational phases, the quantity accessible to radio pulsar timing. In two-component models, stationarity concerns internal angular-momentum conservation versus exchange through independent stochastic torques on the crust and superfluid. Exact phase means and semiseparable covariances for a singular nonstationary model and a minimal stationary model enable a likelihood with linear scaling in observation count and analytic timing-model marginalization. Tests use simulated data, not observations of an actual pulsar. Observing both components decisively distinguishes the models and recovers generating parameters; crust-only phases fit both models comparably across much of parameter space, with order-unity, prior-limited Bayes factors. Integration, timing-model removal, and differentiation preserve the underlying distinction but affect its detectability in finite noisy data. The minimal stationary model predicts a superfluid–crust phase relation controlled by the superfluid inertia fraction. An independent estimate of that fraction, potentially from glitches, would make this prediction testable by a continuous gravitational-wave observation probing the interior.

PublicA neutron star’s uneven spinning may reflect how its outer crust and inner superfluid share angular momentum or exchange it with their surroundings. Radio pulsar timing tracks only the crust, leaving the interior hidden. The researchers developed an efficient statistical method to test whether the character of these spin fluctuations stays constant over time. They tested it on simulated signals from two models, one stationary and one nonstationary. When the simulations reveal both components, the method clearly distinguishes the models. When only the crust is visible, both models often explain the signal equally well, and the comparison depends on assumptions made beforehand. One model nevertheless predicts a specific connection between the crust’s motion and the hidden interior’s motion. Independently estimating the superfluid’s share of rotational inertia could allow a future gravitational-wave observation to test that prediction.

Young explorerImagine a spinning star with an outside and a hidden inside that can turn differently. Scientists made pretend star signals to test a way of studying little changes in its spinning. Seeing both parts helped them tell two ideas apart, but seeing only the outside often did not. One idea also predicts how the inside should move. A future observation might check whether it is right.

The Impact of a Clumpy Ambient Medium on the Dynamics and Synchrotron Emission of AGN Jets

Ivan Almeida, Christian Fendt, Bhargav Vaidya

• Astrophysics of Galaxies

AstronomerThis study uses 3D special-relativistic magnetohydrodynamic simulations with PLUTO to examine a Lorentz-factor-10 AGN jet propagating through a parsec-scale medium. A homogeneous environment is compared with clumpy models having cloud volume filling factors of 0.1% and 1%. In the simulations, jet-cloud interactions deflect the flow, enhance shock formation, create a more asymmetric cocoon, and alter turbulence and mixing. Entrained mass rises from 0.43 solar masses in the homogeneous run to 5.3 and 8.8 solar masses in the clumpy runs, respectively. Synthetic synchrotron maps and spectra, computed from Lagrangian macro-particles accelerated by diffusive shock acceleration, show brighter, more irregular emission in the clumpy models. For identical injected jets, frequency-integrated synchrotron emission is stronger, with the largest spectral energy distribution differences spanning submillimetre through infrared/optical bands. These are simulation results, not observational measurements, and indicate that small-scale ISM structure can substantially affect young-jet dynamics and radiation.

PublicComputer simulations explore how fast jets from active galactic centres behave when they encounter uneven gas rather than a smooth environment. The researchers compared the same jet moving through uniform gas and through two environments containing dense clouds. In the cloud-filled simulations, collisions bend the jet, create more shocks, and make the surrounding envelope of jet material more lopsided. The jet also picks up much more surrounding gas, while turbulence and mixing change. Calculated radiation is brighter and less regular, with the greatest spectral differences from submillimetre wavelengths through infrared and visible light. These findings come from simulations and synthetic radiation calculations, not observations of actual jets. They suggest that even clouds occupying a small fraction of the surrounding space can strongly influence a young jet.

Young explorerScientists used a computer to imagine a very fast stream of stuff coming from the middle of a galaxy. They tried sending it through smooth gas and through gas with little clouds in it. In their computer worlds, the clouds bent the stream, made more bumps and shocks, and let it pick up more gas. The computer also showed that its glow would be brighter and more uneven. This is what happened in the simulations, not something the scientists watched happen in a real galaxy.

Normalizing Flow Emulator for Gravitational Wave Detection Probability in the LIGO/Virgo/KAGRA O4 Observing Run

Julius Gassert, Ignacio Magaña Hernandez, Ariel J. Amsellem+2 more

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

AstronomerThe authors present a Normalizing Flow (NF) approach to estimating gravitational-wave detection probability from source parameters for an O4-like LIGO/Virgo/KAGRA network configuration. They train and test the model using a publicly available injection dataset, assessing its generative performance by its ability to recover the parameter distributions of detected events. Detection efficiencies predicted by the NF emulator agree well with Monte Carlo importance-sampling estimates. For a wide range of population models, including those with sharp features, the emulator can provide more precise efficiency estimates than importance sampling. The work demonstrates its use in gravitational-wave population analysis, with training code and trained models publicly available. These findings concern an emulator tested on injection data, rather than new astrophysical detections.

PublicTo study populations of gravitational-wave sources, researchers need to estimate how likely their detectors are to detect different kinds of events. The usual approach involves computationally expensive tests using simulated signals. This study presents a machine-learning alternative for a detector configuration resembling the LIGO/Virgo/KAGRA O4 network. Trained and tested on publicly available simulated-signal data, the model reproduces the distributions of detected events and predicts detection efficiencies that agree well with a standard statistical method. Its estimates can also be more precise for a variety of source populations, including ones with sharply changing properties. The authors demonstrate its use in population studies and release their code and trained models. The study tests a prediction tool; it does not report new gravitational-wave discoveries.

Young explorerGravitational waves are signals that special detectors try to catch. Some signals are easier to catch than others. The researchers taught a computer using pretend signals to guess how often detectors would catch different kinds. In their tests, its guesses matched another way of working out the answer, and sometimes they were more precise. This could help scientists study groups of things that make gravitational waves. The team tested a computer helper, not a newly discovered signal.

Coexistence of strange quark stars and neutron stars: metastability and nucleation in proto-neutron stars

Mirco Guerrini, Giuseppe Pagliara, Luca Passarella+1 more

• Nuclear Theory

AstronomerAssuming absolutely stable strange quark matter (SQM), the two-families scenario permits hadronic neutron stars and strange quark stars to coexist, but requires some hot proto-neutron stars to avoid conversion. This theoretical study examines thermal nucleation of critical SQM droplets under representative proto-neutron-star conditions, including flavor-composition fluctuations and suppression of color-superconducting pairing in droplets smaller than the diquark coherence length. Nucleation conditions are defined by the statistical expectation of a critical droplet forming within the system’s characteristic dynamical timescale. At these conditions, the calculated reduced barrier is nearly universal, W*/T ≈ 167, varying by only a few units. Across the explored SQM parameter space, requiring a 1.4-solar-mass hadronic neutron star to survive its proto-neutron-star stage yields a lower bound on the hadron–quark surface tension of approximately 67 MeV fm^-2. This is a conditional theoretical constraint, not an observational measurement.

PublicIf strange quark matter is the most stable form of matter, ordinary neutron stars might coexist with stars made of strange quark matter. The puzzle is why every newborn, hot neutron star would not quickly change into a strange quark star. The researchers theoretically studied whether heat could produce the first sufficiently large droplet of strange quark matter that triggers this change. Their calculations account for fluctuations in the types of quarks present and for effects that depend on droplet size. At conditions where such a droplet is expected to form within the system’s characteristic dynamical time, they find a nearly constant ratio of the formation barrier to temperature. Within the models explored, allowing an ordinary neutron star with 1.4 times the Sun’s mass to survive its hot newborn stage requires the surface tension between the two forms of matter to be at least about 67 MeV fm^-2. This limit depends on the study’s assumptions; it is not a measured surface tension.

Young explorerA newborn neutron star is very hot. Scientists wondered whether a tiny drop of a different kind of matter could grow inside it and make the star change. They used calculations, not observations, to study when that first drop might form. In their model, the boundary around the drop must be hard enough to make for an ordinary neutron star to stay as it is while it is young and hot. This idea depends on whether that different kind of matter really is the most stable kind.

Trace-anomaly decomposition and universal dark matter scaling in compact stars

Adamu Issifu, Constança Providência, Tobias Frederico

• Nuclear Theory
• High Energy Physics - Phenomenology

AstronomerThis theoretical study models dark-matter-admixed neutron-star matter as a single fluid, imposing n_chi = F_chi n_B, and derives an exact microscopic decomposition of the total trace anomaly. For the collider-motivated Higgs-portal benchmarks considered, explicit Higgs, vector-mediator, and contact-interaction terms are negligible. Heavy nonrelativistic dark matter instead contributes mainly through its rest-mass energy fraction, with an intrinsic trace anomaly near 1/3, yielding a smooth upward shift in the total anomaly of up to about 0.1 at F_chi about 0.2%. In the pressureless, comoving heavy-WIMP regime, numerical calculations at fixed mass-loading parameter lambda = F_chi m_chi/m_N give overlapping trace-anomaly, sound-speed, and mass–radius responses for a given baryonic equation of state. In modeled hybrid stars, dark matter barely changes the coexistence pressure or chemical potential, while first-order hadron–quark deconfinement creates sharp discontinuities in squared sound speed and trace-anomaly diagnostics. The combined softening reduces the maximum stellar mass substantially, putting F_chi about 0.2% in tension with observed two-solar-mass neutron stars. These model results suggest that the density dependence of the trace anomaly can distinguish smooth dark-matter effects from a first-order deconfinement transition; they do not establish that neutron stars contain dark matter.

PublicThe researchers calculated how a small admixture of dark matter could change matter inside neutron stars. Their model treats ordinary matter and dark matter as one fluid with a fixed ratio of particle numbers. For the dark-matter scenarios studied, the main effect comes from the extra rest-mass energy, rather than explicit interaction contributions. This produces a smooth change in the trace anomaly, a measure relating the matter’s pressure and energy density. By contrast, a modeled abrupt transition from hadronic matter to quark matter produces sharp jumps in this measure and in the speed of sound. In the heavy, pressureless dark-matter regime, different dark-matter masses and abundances give matching model responses when their mass-loading parameter is the same. Combining dark matter with the quark transition also lowers the largest mass the modeled stars can support. A dark-matter particle-number fraction of about 0.2% is therefore in tension with the observed existence of neutron stars twice the Sun’s mass. These are theoretical results, not a detection of dark matter or quark matter inside neutron stars.

Young explorerA neutron star is a star made of very tightly packed matter. Scientists used a model to ask what might happen if a little dark matter were mixed inside it. In their calculations, dark matter changed the star’s matter smoothly. A sudden change to a different kind of matter, called quark matter, made sharp jumps instead. Together, these changes made the model stars able to hold less mass before reaching their limit. Some versions had trouble matching the very heavy neutron stars we have seen. This does not mean scientists found dark matter inside a star; they worked out what it might do.

Unveiling Multimessenger Emission from Hidden Cores of Microquasars

Yu-Jia Wei, Kohta Murase, B. Theodore Zhang

AstronomerMotivated by detections of approximately 100 TeV photons from Cygnus X-1 and multi-PeV photons from Cygnus X-3, the authors use the Astrophysical Multimessenger Emission Simulator (AMES) to model emission from radio to ultrahigh-energy gamma rays. The modeling suggests highly efficient particle acceleration in the jets. Depending on emission-zone location and conditions, either proton–photon or proton–proton interactions can account for the observed gamma rays above roughly 0.1 PeV while reproducing the lower-energy spectra. The models predict a deep valley, mild suppression, or power-law spectrum in the poorly constrained 0.1–10 TeV band. Compact zones comparable to the orbital separation predict strong variability, whereas extended, static external zones predict more stable emission. Changes in Doppler factor and external gamma–gamma absorption offer a possible qualitative explanation for energy-dependent modulation. Modeling the PeV emission from Cygnus X-3 favors a compact zone requiring a magnetic field of order 100 G; this is a model inference, not a field measurement. Pion and muon cooling suppress the predicted neutrino flux, making detection more challenging than previously thought.

PublicMicroquasars are pairs of stars containing an X-ray source that launches fast jets and emits radio waves. Recent detections of extremely energetic gamma rays from Cygnus X-1 and Cygnus X-3 motivated researchers to simulate how these systems produce radiation across a wide range of energies. Their models suggest that the jets can accelerate particles very efficiently. Collisions of protons with either light or other protons could explain the highest-energy gamma rays, depending on where the radiation is produced. The study does not establish which explanation is correct. Instead, it predicts differences that observations could test: distinct patterns in a poorly measured energy range, and stronger brightness changes for small emitting regions than for larger, stationary ones. Changes in how the jet's motion affects the light we receive, together with absorption by surrounding light, may explain some energy-dependent brightness patterns. For Cygnus X-3, the modeling favors a small emitting region with a magnetic field of about 100 gauss. The models also predict fewer neutrinos after accounting for energy lost by particles that produce them, suggesting that neutrino detection will be harder than previously expected.

Young explorerAstronomers have seen very powerful light from two space systems that shoot out fast jets. They used a computer to try out ideas about how the jets make that light. The models suggest that tiny particles could get a big boost in the jets and make powerful light when they bump into light or other particles. More than one idea could work, so the scientists do not yet know which is right. Their models say that a small place making the light should change brightness a lot, while a bigger, steady place should change less. Watching for those changes could help test the ideas. The models also suggest that tiny particles called neutrinos may be harder to find than scientists had thought.

Search for Anisotropic Pair Halos Associated with Blazar Jets

Ao Zhang, Wenlei Chen, Manel Errando

AstronomerThe study searches for gamma-ray pair halos from electromagnetic cascades around TeV-emitting blazars, exploiting their expected anisotropic morphology relative to projected jet directions. Monte Carlo modeling guides the selection of 21 high-synchrotron-peaked BL Lac objects with radio-interferometric jet position angles. Rotating and stacking Fermi-LAT observations along those directions preserves anisotropic extended emission that orientation-agnostic stacking would dilute. A likelihood analysis yields evidence for a non-zero intergalactic magnetic field, rejecting the null hypothesis at 3.8 sigma, with a best-fit B0 = 2.8 × 10^-16 G and a 99% confidence interval of 0.9 × 10^-16 G < B0 < 8.9 × 10^-16 G. This is an indirect field inference, not a direct magnetic-field image or an explanation of the fields’ origin. The result is consistent with previous spectral, spatial, and temporal constraints. Direct imaging of pair halos and mapping of void magnetic fields are presented as possibilities for future higher-angular-resolution gamma-ray observations.

PublicResearchers report evidence for extremely weak magnetic fields in the space between galaxies, whose origin remains unknown. They searched for extended gamma-ray emission around 21 blazars, using simulations to model the expected shape and radio observations to establish the directions of the blazars’ jets. They then rotated and combined Fermi-LAT observations so those directions lined up, making the predicted uneven halos easier to identify. Their statistical analysis disfavors the no-field hypothesis at 3.8 sigma and gives a best-fit strength of 2.8 × 10^-16 gauss, with a 99% confidence range from 0.9 × 10^-16 to 8.9 × 10^-16 gauss. This is evidence inferred from the gamma-ray observations, rather than a direct image of the magnetic fields, and it agrees with earlier constraints. Sharper future gamma-ray observations might directly reveal these halos and help map magnetic fields in cosmic voids.

Young explorerScientists want to know whether the big spaces between galaxies have very weak magnetic fields. They looked at special light called gamma rays from 21 bright objects with jets. Computer models helped them work out what faint patches of light around these objects might look like. They lined up the jet directions in the pictures and put the pictures together to make the faint pattern easier to spot. What they found is a clue that magnetic fields are there, but it is not a sure answer or a direct picture of the fields. Better pictures in the future might help them see the faint patches more clearly.

Gravitational wave detectability range informed by external messengers

S. Ronchini, A. Chopra, T. Dal Canton+3 more

• General Relativity and Quantum Cosmology

AstronomerThe authors introduce the Targeted Detectability Range (TDR), a computationally inexpensive estimate of compact-binary-coalescence gravitational-wave detectability under the hypothesis that a merger is associated with an external electromagnetic or neutrino signal. Unlike the standard GW range based on averaged source parameters, TDR incorporates external-messenger information about sky location, inclination, and physically motivated component-mass bounds. They report TDR estimates for all short- and long-duration gamma-ray bursts observed during the first three Advanced LIGO and Advanced Virgo observing runs, and validate the method through systematic comparison with the 90% exclusion distances from modeled targeted GW searches. When all-sky, all-time GW searches yield no coincident detection, TDR offers a rapid quantitative constraint on a possible merger origin, not proof of an association or its absence. Low-latency implementation and public availability are presented as ways to improve follow-up prioritization and resource allocation.

PublicThe study introduces a quick way to estimate whether gravitational waves from two merging compact objects could be detected if the merger were linked to a flash of light or a neutrino signal. Called the Targeted Detectability Range, it uses clues from that other signal, such as its position in the sky and constraints on the system's orientation and masses, instead of relying on average source properties. The authors calculate this range for short and long gamma-ray bursts observed during the first three Advanced LIGO and Advanced Virgo observing runs. They check the method against distance limits from targeted gravitational-wave searches. If a broad gravitational-wave search finds no matching signal, the estimate can help constrain whether a merger could explain the burst, but it does not settle that question by itself. Making the method publicly available and able to run promptly could help astronomers choose which events to follow up.

Young explorerSometimes astronomers see a bright flash in space and wonder whether two very small, heavy objects came together and made ripples in space. The researchers made a quick way to work out how far away such a crash could be and still have its ripples detected, using clues from the flash. They tried it on gamma-ray flashes and checked it against more detailed searches for ripples. Not finding matching ripples can help them judge whether a crash might explain a flash, but it does not give a sure answer. The tool could help astronomers decide which flashes to study next.

Ring Position Angles and Spin in M87* and Sgr A*

Nicholas S. Conroy, Michi Bauböck, Vadim Bernshteyn+4 more

AstronomerThis study extends analysis of EHT ring brightness asymmetry from its magnitude, a1, to the position angle of its peak, PA1, using GRMHD models. For the reported spin regimes a*>0 and a*≲−0.5, the mean PA1 lies within 1σ of the approaching limb across the inclinations, disk magnetizations, and sources considered. Comparing observed M87* distributions of (a1, PA1) with the models mildly disfavors low-magnitude spins and strongly disfavors all spin vectors pointing toward Earth. The alignment of PA1 with respect to the large-scale jet axis may indicate that the disk is not substantially tilted. Under optimistic 2026 M87* video conditions, combining PA1 with measured pattern speed is forecast to distinguish prograde from retrograde configurations with approximately 84% accuracy; this is not a reported observational classification. A detection of (a1, PA1) in Sgr A* could constrain its spin magnitude and direction. For a larger future EHT source sample, ring diameter, asymmetry magnitude, and asymmetry angle could jointly provide robust constraints on mass, spin, and inclination.

PublicEHT images show black holes as rings that are brighter on one side. Researchers used computer models to investigate what the location of that bright region can reveal about a black hole's spin. In the reported model spin ranges, the average bright-region position stays close to the side approaching us, despite differences in viewing angle and disk magnetization. Comparing the models with M87* observations makes weak spins somewhat less likely and strongly disfavors spin directions pointing toward Earth. The bright region's alignment relative to the large jet may also suggest that the disk is not greatly tilted. The authors predict that, under optimistic conditions for 2026 EHT movies, combining the bright region's angle with the motion of brightness patterns could distinguish whether M87* spins with or against its disk with about 84% accuracy. Similar measurements could help constrain Sgr A*'s spin, while future EHT expansion could extend these methods to more black holes.

Young explorerPictures of black holes look like rings with one side brighter than the other. Scientists made computer models to see whether that bright spot can help tell how a black hole spins. Comparing the models with pictures of a black hole called M87* makes some ways of spinning seem less likely, but does not give a certain answer. The scientists think future movies could help tell whether the black hole and its disk spin the same way or opposite ways. That is a prediction, not something they have already seen.

Relativistic outflows power a quasi-periodic eruption: constraints on energetics, mass loss, and emission mechanisms

Joheen Chakraborty, Erin Kara, Wenbin Lu+17 more

• Astrophysics of Galaxies

AstronomerNew XMM-Newton observations of the quasi-periodic eruptions (QPEs) in ZTF19acnskyy, or Ansky, provide the deepest observations of individual QPE bursts to date. Time-evolving P Cygni profiles show blueshifted absorption and redshifted emission in Fe XIX–XXIV L-shell transitions, with inferred column densities of approximately 10^22–10^23 cm^-2 and bulk speeds near 0.2c, indicating relativistic mass ejection during each eruption. A time-dependent analytical model of a wind turning on can reproduce both the light curve and spectral lines with a wide-angle outflow at approximately 10^-9–10^-8 solar masses per second and an X-ray-to-kinetic-power ratio of about 0.1. For an assumed covering fraction of about 0.5, the inferred ejecta per burst are approximately 10^-3 solar masses and at least 10^49 erg of kinetic energy. A reservoir of approximately one solar mass would therefore limit activity to roughly 1,000 bursts or fewer. Detectable multiwavelength reverberation and feedback signatures are suggested, not reported detections. The findings constrain QPE energetics and emission models, while the underlying origin of the recurring eruptions remains uncertain.

PublicSome supermassive black holes produce recurring bursts of X-rays called quasi-periodic eruptions, but what drives them is still uncertain. New XMM-Newton observations of a source nicknamed Ansky reveal changing patterns of absorption and emission from iron in the X-ray spectrum. These patterns indicate that gas is expelled during each burst at about one-fifth the speed of light. The researchers developed a mathematical model in which a broad outflow powers the X-rays using about 10% of its kinetic power; the model can explain both the changing brightness and the spectral features. Assuming the outflow covers about half the surrounding directions, they estimate that each burst ejects about one-thousandth of the Sun's mass. If the available gas totals about one Sun's mass, that supply would allow roughly 1,000 bursts or fewer. The expelled material might also produce detectable effects at other wavelengths as it interacts with the black hole's surroundings, but those effects have not been reported as detections here.

Young explorerA giant black hole called Ansky has repeated flashes of X-ray light. Scientists studied those flashes and found clues that gas rushes outward very fast—about one-fifth as fast as light. They made a math model showing how the rushing gas could help make the flashes. That is a possible explanation, not something they know for sure. If there is only a limited supply of gas, the flashes cannot keep happening forever. Scientists still do not know exactly why the flashes repeat.

U-spin symmetry energy and hyperon puzzle in Λ-admixed neutron stars

Hao-Song You, Ting-Lan Yu, Sophia Han+2 more

• High Energy Physics - Phenomenology

AstronomerThe authors propose a U-spin symmetry energy E_U(n_b) to describe binding-energy changes associated with hyperons, analogous to the I-spin nuclear symmetry energy E_sym(n_b). They constrain a dense-matter model containing Lambda hyperons, but no other hyperon species, through Bayesian inference using nuclear physics and astrophysical observations. The inferred E_U is much smaller than 9E_sym, indicating weaker sensitivity of the adopted binding-energy functional to U-spin asymmetry than to the corresponding I-spin asymmetry. In this model, the Lambda potential rises with density and becomes repulsive at high density. The posterior assigns more than 50% probability to Lambda emergence; when they appear, their onset is typically at 2–5 n_0, corresponding to central densities of neutron stars more massive than 1.0 solar mass. Lambdas are likely to disappear again at densities at or above roughly 5 n_0. These are model-dependent inferences, not direct detections of hyperons in neutron stars.

PublicThe study proposes a way to describe how the binding energy of very dense matter changes when particles called Lambda hyperons are included. The researchers combine nuclear-physics information and astronomical observations to constrain their model, which leaves out other kinds of hyperons. Their analysis suggests that the binding energy is less sensitive to the proposed hyperon-related imbalance than to the corresponding neutron–proton imbalance. The model assigns more than a 50% probability to Lambda hyperons appearing, but predicts that they would likely disappear again at still higher densities as their interaction becomes repulsive. When they appear, the required densities correspond to conditions at the centers of neutron stars more massive than the Sun. This is an inference about possible neutron-star interiors, not an observation of the particles themselves.

Young explorerScientists want to know what could be inside very tightly packed stars called neutron stars. They made a model that allows particles called Lambda hyperons to join the matter inside, and used clues from astronomy and nuclear physics to check it. The model suggests these particles might appear when the matter is squeezed enough, but could disappear if it is squeezed even more. The scientists have not seen these particles inside a star, and their model leaves out other kinds of hyperons.

Testing the wormhole echo hypothesis for GW231123

Qi Lai, Qing-Yu Lan, Zhan-He Wang+1 more

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

AstronomerGW231123 is a short-duration, burst-like gravitational-wave event with no clear inspiral and component masses inferred to fall in the pair-instability mass gap. Motivated by its phenomenological similarity to GW190521, the authors test a wormhole-echo interpretation using a phenomenological sine-Gaussian model for a leading echo pulse. Bayesian comparison with the IMRPhenomXPHM-SpinTaylor binary black hole waveform gives ln B(Echo/BBH) = 1.87. However, this preference depends on the BBH waveform family and echo priors, and the statistic is not unusual in the targeted BBH-null ensembles. The positive Bayes factor is therefore not robust evidence for wormhole echoes; the analyses considered support the standard binary black hole interpretation.

PublicThe gravitational-wave event GW231123 was a short burst with no clear signal of two objects spiraling toward each other. Under the standard binary black hole interpretation, its inferred black hole masses fall in a range called the pair-instability mass gap. Because the event resembles GW190521, researchers tested whether it could instead be an echo associated with a wormhole. Their comparison gave a modest preference to the echo model, but that preference changed with modeling assumptions and was not unusual in tests where a binary black hole signal was assumed. The study therefore finds no robust evidence for a wormhole echo and supports the standard explanation of two merging black holes.

Young explorerScientists caught a short ripple in space called GW231123. They checked whether it could be an echo from a wormhole instead of a signal from two black holes joining together. One test leaned a little toward the echo idea, but the answer depended on how they set up the test. A signal from two black holes could also give that kind of answer. So this study does not give strong evidence for a wormhole and supports the two-black-hole explanation.

Hadronic description of nuclear matter and neutron star properties

Yao Ma, Yong-Liang Ma, Jia-Ying Xiong

• Nuclear Theory

AstronomerThe authors perform a joint Bayesian analysis within a generalized quantum hadrodynamics model containing nucleons and the σ, ω, ρ, and a₀ mesons. Constraints include experimental nuclear-matter data, heavy-ion flow pressure, mass–radius inferences for PSR J0740+6620, PSR J0437−4715, PSR J0614−3329, and HESS J1731−347, and the GW170817 tidal posterior. They find that a purely hadronic description can jointly accommodate the nuclear and astrophysical constraints. The inferred model develops a non-monotonic, peak-like sound-speed profile, absent in the comparison models TM1, NL3, and FSU-δ6.7. A soft-to-stiff transition accompanied by pronounced symmetry-energy softening yields R₁.₄ ≃ 11.1–11.4 km and maximum masses of 2.2–2.3 solar masses. These are model-dependent findings, not direct measurements of neutron-star composition. The authors argue that future mass–radius measurements, especially for intermediate-mass stars, will be crucial for distinguishing purely nucleonic stars from hybrid stars.

PublicWhat is inside a neutron star remains uncertain. This study combines laboratory information about nuclear matter with astronomical estimates of neutron-star masses, sizes, and tidal responses to test a model containing only hadronic matter. The authors find that this model can account for the combined constraints, so these data do not by themselves establish that a different type of matter is required. In the model, matter changes from being relatively easy to compress to resisting compression more strongly, and the speed of sound shows a peak. The model predicts radii of about 11.1–11.4 kilometres for stars with 1.4 times the Sun’s mass, while allowing a maximum mass of 2.2–2.3 times the Sun’s mass. These values are model results rather than new direct measurements. The authors emphasize that future measurements of neutron-star masses and sizes could help distinguish competing descriptions of their interiors.

Young explorerA neutron star is a very small, very heavy star, and scientists are still trying to work out what is inside it. They used clues from space and laboratory experiments to test a mathematical picture of its matter. Their picture could match those clues: the matter was easier to squeeze at first and harder to squeeze later. But a picture that fits the clues does not prove what is really inside. The scientists say that measuring how heavy and how big more neutron stars are could help tell different ideas apart.

Diffuse Supernova Neutrinos with Secret Neutrino Interactions

Praveen Bharadwaj, Utpal Chattopadhyay, Dilip Kumar Ghosh+1 more

• High Energy Physics - Phenomenology

AstronomerThis theoretical study forecasts how scalar-mediated non-standard neutrino self-interactions could modify the diffuse supernova neutrino background (DSNB), the isotropic flux from stellar core collapses throughout cosmic history. The calculation retains the full three-flavor PMNS structure and considers universal, electron-, muon-, and tau-specific flavor-diagonal couplings. Resonant scattering on the lightest, relativistic cosmic neutrino background state produces broad spectral depletion, with patterns across the six flavor fluxes that depend on the coupling structure and neutrino mass ordering. Predicted event spectra for JUNO, gadolinium-loaded Hyper-Kamiokande, and DUNE yield projected 3σ sensitivities reaching g approximately 10^-8 for scalar masses of approximately 100–300 eV, with improvements over existing bounds by up to a few orders of magnitude in the sub-100 eV mass range. These are sensitivity projections, not detections. If a signal is detected, its flavor-dependent signatures could help distinguish the interaction’s flavor structure, unlike the flavor-blind cosmological and supernova bounds discussed in the abstract.

PublicCollapsing stellar cores across cosmic history are expected to leave a faint, all-sky background of neutrinos, tiny particles that travel through space. This study calculates what could happen if those neutrinos interact in a new way with an older background of neutrinos already filling the universe. A hypothetical particle carrying the interaction could reduce the incoming neutrino flux over broad energy ranges. The predicted pattern depends on which neutrino types participate and on the ordering of neutrino masses. The researchers calculate how these patterns could appear in JUNO, Hyper-Kamiokande with gadolinium, and DUNE, and forecast that the experiments could test very weak interactions, potentially improving substantially on existing limits in some mass ranges. No such interaction is reported as detected here: the results are predictions of experimental sensitivity. A future detection could help identify which neutrino types are involved.

Young explorerWhen the centers of stars collapse, they send out tiny particles called neutrinos. Many of these particles travel through space toward us. Scientists worked out what might happen if they bumped into other neutrinos in a new way, with help from a tiny particle that might exist. Those bumps could mean fewer neutrinos reach us at some energies. Different kinds of neutrinos could leave different clues. Big detectors might one day find those clues, but this study is a prediction, not a discovery.

Asteroseismic Detection of a Massive Unseen Companion to the δ Scuti Star TIC 160582982

Chenglong Lv, J. Pascual-Granado, Ali Esamdin+4 more

AstronomerTIC 160582982 is an eccentric δ Scuti binary with a dynamically massive, unseen companion. Phase modulation of six coherent pressure modes yields an orbital period of 89.29 ± 0.19 days, eccentricity of 0.539 (+0.040/−0.037), and mass function of 0.416 (+0.032/−0.028) solar masses; independent frequency modulation of the two strongest modes gives a consistent solution. Rotating MIST isochrones constrained by atmospheric parameters and the spectral energy distribution give a primary mass of 1.93 ± 0.19 solar masses, implying a formal edge-on minimum companion mass of approximately 1.80 solar masses. Assuming a luminous main-sequence companion and a non-eclipsing geometry yields a companion mass of 2.19 (+1.24/−0.34) solar masses and inclination of 61.5 (+16.6/−19.6) degrees. However, neither photometry nor spectroscopy clearly reveals a luminous counterpart. A neutron star or stellar-mass black hole is therefore suggested, not established. Future phase-resolved high-resolution spectroscopy is needed for an independent orbital constraint and clarification of the companion’s nature.

PublicAstronomers used six steady pulsations in the star TIC 160582982 as clocks to trace its motion around an unseen companion. Their timing analysis indicates an elongated orbit lasting about 89 days, and a separate analysis of two pulsations supports that result. Combining the orbital measurements with an estimated mass for the visible star gives a minimum companion mass of about 1.8 times the Sun’s mass. Yet neither the brightness data nor the spectra clearly show light from this companion. That makes a compact object, such as a neutron star or a stellar-mass black hole, a possible explanation, but its identity is not confirmed. Future high-resolution spectra taken at different points in the orbit will help test the orbit and determine what the companion is.

Young explorerA star has a steady beat, a little like a ticking clock. Astronomers used that beat to work out that the star moves around with a heavy partner they cannot see. One trip around takes about 89 days. The hidden partner might be a neutron star, which is a very squashed leftover of a star, or it might be a black hole. But the astronomers do not know yet. They need to study the star’s light more carefully to find out.

Gaia neutron stars: demographics, birth rates, and connections to other neutron star populations

Cheyanne Shariat, Natsuko Yamaguchi, Kareem El-Badry+1 more

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena

AstronomerThe study infers the intrinsic demographics of neutron stars in au-scale orbits with solar-type companions from 27 Gaia DR3 candidates, accounting for astrometric selection biases in a hierarchical Bayesian framework. The inferred population favors a decreasing orbital-period distribution with power-law slope α_P = −0.75 ± 0.35, companion masses peaked near 0.85 solar masses with a width of about 0.2 solar masses, neutron-star masses peaked near 1.3 solar masses with a higher-mass tail, and moderate-to-large eccentricities. The estimated space density within 2 kpc is about 120 per cubic kiloparsec, implying that only about 3% of the local population has been discovered. Forecasts, rather than observed results, suggest Gaia DR4 could yield about 300–650 candidates and extend coverage to longer periods, enabling direct tests of formation models. The inferred fraction of neutron stars born into these systems is 0.01%–1%; their birth rate is 10–100 times below that of high-mass X-ray binaries and broadly comparable to that of symbiotic X-ray binaries. Their formation pathway remains unclear.

PublicGaia has identified 27 candidate systems in which a neutron star orbits with a star similar to the Sun, but its ability to detect these pairs strongly shapes the sample. By modeling that detection bias, researchers estimate that the underlying population favors shorter orbital periods and moderately to strongly elongated orbits. Their analysis places the typical companion mass near 0.85 times the Sun’s mass and the neutron-star mass near 1.3 times the Sun’s mass, with some neutron stars extending to higher masses. They estimate that only about 3% of the local population has been found. Their forecast predicts roughly 300–650 candidates in Gaia’s next data release, including pairs with longer orbital periods that could help test how these systems form. The study estimates that only 0.01%–1% of neutron stars are born into such pairs; their origin is still uncertain.

Young explorerGaia has found 27 possible star pairs, each with a neutron star and a star like our Sun. Some pairs are easier for Gaia to notice than others. The researchers used a model to work out what the harder-to-see pairs might be like. They think many more pairs remain to be found, and that these stars often follow stretched-out paths around each other. They predict Gaia’s next set of information could reveal hundreds of possible pairs, but that has not happened yet. Scientists still do not know how these unusual pairs form.

Eppur binaria non è esclusa: Pulsations in CZ Tuc appear to be tidally excited by its veiled companion

Piotr A. Kołaczek-Szymański, Patryk Iwanek, Jim Fuller+3 more

AstronomerLong secondary periods (LSPs), seen in about one-third of pulsating red giants, remain unexplained, with binarity and non-radial oscillations the leading hypotheses. An interacting, eccentric binary containing a red giant and a substellar companion could produce tidally excited oscillations (TEOs), offering an independent test of the binary interpretation. An approximately 80-year light curve combining DASCH, Hipparcos, and ASAS photometry yields a pulsation period of 55.4734 ± 0.0074 days and an LSP of 443.62 ± 0.12 days for CZ Tucanae. Their ratio, 7.9970 ± 0.0024, is consistent with a TEO. Theoretical models adopting the star’s estimated fundamental parameters can reproduce the candidate TEO’s observed amplitude. The authors identify CZ Tuc as the first candidate LSP star with a TEO, providing evidence for binarity in at least a subset of LSP variables, rather than confirming the origin of all LSPs.

PublicAbout one-third of pulsating red giant stars show an additional, much longer cycle whose cause is still unknown. Using roughly 80 years of brightness measurements, researchers found that CZ Tucanae has a pulsation cycle of about 55.47 days and a longer cycle of about 443.62 days. The longer cycle is consistent with lasting eight times as long as the shorter one. This relationship fits the possibility that a companion’s tidal pull excites the star’s pulsation. Theoretical models also show that this mechanism could produce the observed strength of the pulsation, using estimated properties of the star. CZ Tucanae is the first proposed example of such a tidally excited oscillation in a star with a long secondary period. It supports the companion explanation for at least some of these stars, but does not establish it as the cause of every long secondary period.

Young explorerA big red star called CZ Tucanae gets brighter and dimmer in two repeating patterns. Scientists looked at about 80 years of measurements and found that the slower pattern takes about eight times as long as the faster one. A smaller neighbor might be pulling on the star and making it wiggle. Their calculations show that this idea could work, but they have not proved that a neighbor is causing the wiggle.

Theoretical RR Lyrae Instability Strip from MESA-RSP Pulsation models and updated BaSTI Evolutionary Tracks

M. Deka, M. Marconi, R. Molinaro+6 more

AstronomerThis modeling study updates RR Lyrae instability-strip boundaries and period-luminosity-metallicity (PLZ) and period-Wesenheit-metallicity (PWZ) relations using updated BaSTI horizontal-branch tracks and a grid of linear non-adiabatic radial pulsation models computed with mesa-rsp. The grid spans −2.2 ≤ [Fe/H] ≤ +0.06 dex and explores seven convection configurations, including a recently empirically calibrated prescription. Analytical boundaries for RRab and RRc pulsators are mapped into Gaia, OGLE, 2MASS, and LSST photometric systems and the Kiel diagram. Updated evolutionary models produce no substantial change in pulsation predictions: RRab boundaries agree well with previous results, while the RRc red edge shifts slightly redward. Increasing alpha_MLT systematically narrows the predicted instability strip, and RRc predictions are relatively more sensitive to convection treatment. Near-infrared PLZ and PWZ relations agree well with previous empirical and theoretical calibrations, but the best-matching convection prescription depends on wavelength. These are model predictions, not new observational measurements; their coupled dependence on pulsation mode, metallicity, and convection prevents any one prescription from performing uniformly best across all observational planes.

PublicRR Lyrae stars help astronomers trace old stellar populations and estimate distances. This study uses updated computer models of stellar evolution and pulsation to predict which RR Lyrae stars should pulsate and how their pulsation periods, brightnesses, and metal contents are related. The researchers tested seven ways of modeling convection, the transport of heat by moving material inside a star. The updated evolution models largely preserve earlier predictions, although one type of RR Lyrae has a slightly cooler predicted boundary for pulsation. Changing the convection settings changes the predicted range of temperatures where pulsation occurs, with one pulsation type more sensitive than the other. Predicted near-infrared brightness relations agree well with earlier observational and theoretical calibrations. However, no single convection treatment works best for every wavelength and pulsation type. The study provides updated predictions rather than new measurements of stars.

Young explorerSome stars called RR Lyrae get brighter and dimmer over and over. Astronomers use them to help work out how far away things are. Here, scientists made computer models to learn when these stars should pulse and how bright they should be. Most answers were close to earlier ones. But changing how heat moves inside the pretend stars changed some answers, and no one choice worked best for everything. These are computer predictions, not new pictures or measurements of stars.

Unresolved triples in the open cluster NGC 2437 (M 46) confirmed by the KMOS VVVX-GalCen Spectroscopic Survey

D. Minniti, T. Palma, C. O. Obasi+31 more

AstronomerUsing Gaia DR3 and VVVX photometry, the study identifies candidate unresolved multiple systems in the open cluster NGC 2437 (M 46), at a distance of 1.6 kpc. It confirms a photometric binary sequence and reports a triple-system sequence above the equal-mass binary sequence. Radial velocities from the ESO KMOS VVVX-GalCen survey corroborate cluster membership for 13 binary candidates and 8 triple candidates; the authors report spectroscopic confirmation for 95% of selected VVVX targets. This spectroscopic support secures the cluster association of the photometric sequences, rather than directly resolving their stellar components. A color-selected K-dwarf sample provides a controlled comparison with the Solar neighborhood. The inferred unresolved triple and quadruple fraction exceeds that in the older cluster Trumpler 19, studied with a similar setup. The authors interpret this difference as suggesting that such systems merge into blue stragglers or dissolve over time, not as direct evidence of those processes. They report that single stars account for 60% of the cluster mass and unresolved multiple systems for 40%.

PublicAstronomers studied NGC 2437, also called M 46, to find groups of stars that appear as single points of light because their members cannot be seen separately. Gaia and VVVX brightness and color measurements reveal a known pattern of likely pairs and a newly identified pattern of likely triples. Spectroscopic measurements of motion confirm cluster membership for 13 likely pairs and 8 likely triples, strengthening the evidence that these patterns belong to the cluster. The study finds a larger fraction of unresolved triples and quadruples than in the older cluster Trumpler 19. This suggests that some multiple systems may merge or break apart as clusters age, but the comparison does not directly demonstrate either process. The authors estimate that 40% of NGC 2437’s mass is in unresolved multiple systems and 60% is in single stars; these are mass shares, not percentages of the number of stars.

Young explorerSometimes two or three stars are so close together in the sky that they look like one little dot. Scientists looked at a big group of stars called M 46 and found patterns that suggest some dots are pairs and some are triples. They measured how the stars move to check that many of these dots really belong to the group. They also found more signs of triples and groups of four than in an older star group. Maybe some star families join together or split apart as they get older, but the scientists have not shown that happening here.

1RXS J174320.1-042953: another polar with a red-shifted absorption component in emission line wings

Diego H. González-Buitrago, Ma. T. García-Díaz, Sergey Zharikov+5 more

• High Energy Astrophysical Phenomena

AstronomerSpectroscopy and multi-band photometry of the magnetic cataclysmic variable 1RXS J174320.1-042953 confirm an orbital modulation with P_orb = 0.0864 ± 0.0001 days. Adopting an estimated secondary mass of approximately 0.15 solar masses and an X-ray-based white dwarf mass of approximately 0.75 solar masses yields q ≈ 0.2 and an inclination of 47° ± 10°. Strong, asymmetric, highly variable, single-peaked Balmer, He I, and He II emission, together with the absence of evidence for a Keplerian accretion disc in Doppler tomography, supports a polar classification. Hβ and He II each contain at least two components: low-velocity semi-amplitudes are approximately 170 and 147 km/s, respectively, while high-velocity semi-amplitudes are approximately 317 and 460 km/s. The low-velocity emission is interpreted as originating on the irradiated face of the secondary and/or near L1, whereas the high-velocity emission is associated with the accretion stream. Redshifted absorption in the line wings near orbital phase 0.0 reaches approximately 1400 km/s and is likely caused by stream material crossing the line of sight.

PublicObservations of the binary star system 1RXS J174320.1-042953 show a repeating brightness pattern corresponding to an orbital period of 0.0864 ± 0.0001 days, or roughly two hours. The system contains a magnetic white dwarf and a companion star. Its changing light spectrum and the lack of evidence for an orbiting gas disc support its classification as a polar, a type of magnetic binary in which gas is transferred toward the white dwarf. Using estimated stellar masses, the researchers infer that the system is tilted by about 47° ± 10° to our line of sight. The spectra reveal at least two emission components with different speeds. The slower component likely comes from the companion's illuminated face and/or the region where gas leaves it; the faster component is linked to the gas stream. Absorption seen near one orbital phase reaches speeds of about 1400 km/s and is likely caused by stream material passing in front of the emitting region. These proposed locations explain the observations but are not all uniquely established.

Young explorerTwo stars in this system circle each other about every two hours. One is a small star called a white dwarf that has a strong magnetic field. Astronomers studied the changing light and found signs of gas moving at different speeds. They think some light comes from the side of the other star facing the white dwarf, or from nearby gas, and some comes from a stream of gas flowing toward the white dwarf. They did not find signs of a spinning gas disc. They also saw some light being blocked, probably by gas passing in front, but they are not completely sure.

Probing Accretion and Outflow in V1180 Cas through High-Resolution Optical Spectroscopy

Tarak Chand, Saurabh Sharma, Koshvendra Singh+9 more

AstronomerA high-resolution Keck/HIRES optical spectrum of V1180 Cas in a bright photometric state shows strong permitted and forbidden emission indicative of ongoing accretion and mass loss. Weak Li I 6708 absorption confirms its youth; this feature and selected Fe I emission lines yield the first reported radial velocity, −16 ± 3 km/s. Asymmetric Hα and Hβ profiles with blueshifted absorption suggest line-of-sight outflows. He I 5876 has a narrow component likely associated with post-shock accretion regions and a broad, slightly blueshifted component probably originating in magnetospheric flows and/or inner disk winds. Low- and high-velocity components of [O I] 6300 are interpreted as a slow disk wind and a fast jet. The forbidden [O I] line gives a first disk-inclination estimate of approximately 50°. Derived jet mass-loss and accretion rates imply a ratio of approximately 0.01–0.03, low but consistent with values observed for Class II young stellar objects. Forbidden-line diagnostics indicate densities near 10³ and 10⁶ cm⁻³ and temperatures near 10⁴ K, supporting an actively accreting, moderately inclined system with a multi-component outflow.

PublicAstronomers studied a detailed optical spectrum of the young star V1180 Cas with the Keck Observatory while it was bright. Its strong emission lines indicate that it is gathering material while also losing gas. A weak lithium absorption feature confirms the star’s youth, and the researchers report its first measured velocity along our line of sight: −16 ± 3 km/s. The shapes of several spectral lines suggest outflowing gas. The researchers interpret two components of an oxygen line as a slower wind from the surrounding disk and a faster jet, and use that line to estimate a disk inclination of about 50°. Their estimates indicate that the jet carries away about 1–3% as much mass as the system accretes, a low but consistent value compared with observations of Class II young stellar objects. The gas diagnostics support an outflow with multiple components, although the origins of some emission features remain uncertain.

Young explorerAstronomers looked closely at the light from a young star called V1180 Cas while it was bright. The light gives clues that the star is taking in material and sending some gas away. The clues suggest that gas leaves in different ways: a slower wind from the disk around the star and a fast jet. The scientists also estimated how tilted the disk is. Some clues could come from more than one place, so they are not sure exactly where all the glowing gas comes from.

Structure of Convective-Reactive Zone in a Supernova Progenitor

M. Mocak, C. Meakin, F. Rizzuti+5 more

• High Energy Astrophysical Phenomena

AstronomerThis study analyses a 3D hydrodynamic simulation of an oxygen–neon shell merger in a massive pre-supernova star, using the Reynolds-Averaged Navier-Stokes mean-field composition transport equation. In this convective-reactive regime, turbulent mixing and nuclear burning operate on comparable timescales. The simulated merged convection zone develops multiple nested convective-reactive shells within a single convection zone. Their structure depends on mean stratification and mixing as well as the emergent collective behaviour of nuclear reactions involving individual isotopes. Almost all layers exhibit a quasi-steady balance between burning and mixing. The authors classify these layers and contrast their treatment with that in 1D stellar evolution codes. These findings describe the simulation, rather than direct observations of a star.

PublicInside some evolving stars, turbulent motion mixes material about as quickly as nuclear reactions change it, so mixing and burning strongly affect one another. Researchers studied a three-dimensional computer simulation in which oxygen and neon shells merge inside a massive star before a supernova. In the simulation, the resulting single mixing region develops several nested layers with distinct interactions between mixing and nuclear burning. The structure depends both on how material is arranged and transported and on how the nuclear reactions act together. Nearly all layers reach an approximately steady balance between mixing and burning. The researchers compare these simulated layers with how simpler, one-dimensional stellar models treat them; the abstract does not report direct observations of this structure.

Young explorerScientists used a computer to model the inside of a big star before it explodes. In their model, two layers joined together. The joined part did not become evenly mixed: it formed smaller layers inside it. Star material swirled around while tiny particles changed through nuclear reactions. In nearly all the layers, the swirling and the changes stayed roughly in balance. This happened in the computer model; the scientists did not watch it happen inside a real star.

Towards solar many-line inversions

Johannes Hölken

• Mathematical Physics
• Instrumentation and Detectors

AstronomerThis work develops techniques for resolving small-scale solar atmospheric structures relevant to atmospheric heating, the solar dynamo and activity cycle, and space-weather prediction. It describes calibration of very-high-spatial-resolution spectropolarimetry and assembles building blocks toward a mathematical proof of the MOMFBD image-reconstruction algorithm. The FISS-SP prototype is designed to exploit a 1.6 m telescope's resolution and provide spectropolarimetric data suitable for reconstruction down to the diffraction limit. Building on theoretical work showing improved noise robustness from simultaneous interpretation of multiple spectral lines, the author applies this approach to FISS-SP observations to retrieve a coherent local atmospheric model resolving horizontal structures of about 49 km. Application to a solar pore reveals small-scale structures not previously resolved spectropolarimetrically. Dark boundary striations with bright grains moving into the pore are interpreted as convective features. The abstract presents observational and methodological advances, not demonstrated improvements in heating models or space-weather forecasts.

PublicEvents only tens of kilometres across can strongly influence the Sun's atmosphere, but studying them requires exceptionally sharp observations. This work describes how to calibrate measurements of solar light and its polarization, reconstruct sharper images, and use a prototype instrument called FISS-SP designed for a 1.6-metre telescope. Earlier theoretical work suggested that analysing several spectral lines together could make atmospheric estimates more resistant to noise. Here, that idea is applied to observations to build a consistent model of the local solar atmosphere, distinguishing structures about 49 kilometres across. In observations of a solar pore, the author interprets dark streaks and bright grains moving inward as features of convection. These methods are intended to help investigate solar heating and activity; improved space-weather predictions are a motivation, not a demonstrated result.

Young explorerTiny things happen in the Sun's outer layers, and scientists want to see them more clearly. This work uses a special instrument and ways to study sunlight to make a detailed picture of those layers. It can pick out things about 49 kilometres wide. In one place called a solar pore, bright little spots move inward beside dark streaks. The scientist thinks these are signs of moving solar material.

Solarprop 2.0: Modern charge-sign dependent solar modulation for everyone

Henning Gast

• High Energy Astrophysical Phenomena
• Instrumentation and Methods for Astrophysics

AstronomerThe author presents an improved version of SOLARPROP, an open-source framework for modeling charge-sign-dependent solar modulation of cosmic rays in the heliosphere. It solves the charged-particle transport equation through stochastic differential equations (SDEs). The update includes the full two-dimensional SDE system, permitting magnetic fields with latitudinal components, and generalizes the framework to accommodate three-dimensional models. Parallelization and optimization yield a reported speedup of up to three orders of magnitude over the original version, and Python bindings improve usability. Comparisons with published model calculations show excellent agreement in many cases but important discrepancies for two model implementations. Possible causes of those discrepancies were investigated, but the abstract does not establish a definitive explanation. These comparisons test model calculations, not agreement with observational data.

PublicSOLARPROP is free, open-source software for modeling how the Sun’s influence changes the travel of cosmic rays through the region around it, with different effects depending on whether particles have positive or negative electric charge. This update supports more complete two-dimensional models and can accommodate three-dimensional models. Computing improvements make it up to 1,000 times faster than the original version, and a Python interface makes it easier to use. Its calculations agree very well with many previously published model calculations, but differ substantially from two model implementations. The author investigated possible reasons for these differences without reporting a settled explanation in the abstract. The checks described are comparisons between models, not tests against measurements of cosmic rays.

Young explorerTiny particles from space travel through the area around the Sun. A computer program called SOLARPROP helps scientists work out how the Sun changes their journeys. Particles with positive and negative electric charge can be affected differently. The new program can make more detailed models and can run much faster than the old one. Its answers matched many other computer models very well, but two gave importantly different answers. The scientist looked for reasons, but this summary does not say the mystery is solved. These were checks against other models, not against particles measured in space.

Delayed, Line-dependent Reorganization of Pore Oscillations Following a Compact C8.2 Flare Observed by Sunrise III/SUSI

Shahin Jafarzadeh, David B. Jess, Marco Stangalini+34 more

AstronomerSUSI observations aboard Sunrise III reveal a delayed redistribution of oscillatory power in a magnetic pore partially crossed by a C8.2 flare ribbon. Around 30 minutes after the flare peak, core-intensity power at 4.2–7.0 mHz exceeds pre-event levels by factors of 1.60–8.71 in all eight spectral lines studied between 327 and 329 nm. At 7.0–11.5 mHz, power falls to approximately 0.13–0.41 of its pre-event value in seven lines. Line-center velocities also support the lower-frequency enhancement. The line-dependent shift is consistent with flare-induced changes in wave transmission, reflection, or resonant response, but the observations do not yet distinguish thermodynamic effects from changes in the magnetic waveguide.

PublicResearchers studied oscillations in a small magnetic region on the Sun that was partly crossed by the bright ribbon of a solar flare. Using the SUSI instrument on Sunrise III, they measured brightness variations in eight spectral lines. About 30 minutes after the flare peaked, slower oscillations had 1.60–8.71 times their earlier power in all eight lines, while faster oscillations had only about 13–41% of their earlier power in seven lines. Measurements of motion also supported the increase in slower oscillations. The pattern could reflect changes in how waves travel, bounce back, or resonate after the flare, but researchers cannot yet separate the effects of changes in the region’s magnetic structure from changes in its temperature and other thermodynamic conditions.

Young explorerA small magnetic patch on the Sun was partly touched by a bright flare. Scientists watched how the patch’s light flickered. About half an hour after the flare was brightest, slower flickers were stronger, and faster flickers were weaker in most of the kinds of light they checked. The flare may have changed how waves move or bounce inside the patch, but scientists do not yet know exactly what caused the change.

Ensemble pulsational characteristics of eclipsing binaries containing β Cep stars observed by the TESS mission

C. I. Eze, G. Handler, M. Vanrespaille+4 more

AstronomerThe study analyses 65 β Cep pulsators in eclipsing binaries, combining pulsation constraints with MESA evolutionary grids and StORM frequencies to infer interior properties, ages, and rotation. Rotationally split modes yield interior rotation rates for 14 systems. Differential rotation is tentatively inferred for HD 112485; the remaining systems, except CZ Vel, are consistent with quasi-rigid rotation. Detailed forward asteroseismic modelling of HD 112485 and EK Cru identifies their reproduced zonal modes: the first radial-order dipole pressure mode and second radial-order quadrupole gravity mode in HD 112485, and the second-order quadrupole mixed mode and third-order dipole pressure mode in EK Cru. The modelling places HD 112485 among the least evolved β Cep stars studied asteroseismically, with a core hydrogen mass fraction of 0.501, with lower and upper uncertainties of 0.013 and 0.009. Multivariate regression finds a negative correlation between pulsation amplitude and frequency, but no statistically significant relationship of either amplitude or frequency with orbital period in this sample.

PublicResearchers studied 65 massive, vibrating stars called β Cep stars in pairs whose members eclipse one another. These eclipses provide precise stellar properties, while the vibrations help probe the stars’ hidden interiors through comparison with stellar models. Patterns in the vibrations allowed the team to infer internal rotation rates for 14 systems. Most are consistent with their interiors rotating at nearly the same rate throughout, although CZ Vel is an exception and HD 112485 shows tentative evidence of different rotation rates in different regions. Detailed modelling of HD 112485 and EK Cru also identified particular vibration patterns. The models suggest that HD 112485 is among the least evolved β Cep stars examined with this technique. Across the sample, faster vibrations tend to have smaller amplitudes. The study found no statistically significant link between the time taken to complete an orbit and either vibration frequency or amplitude; this does not establish that such links are absent in all systems.

Young explorerSome big stars wobble, a little like a ringing bell. Scientists studied 65 of these stars that have a star partner passing in front of or behind them. Their wobbles, compared with computer models, give clues about what is happening inside. For 14 pairs, the scientists could work out how fast the wobbling star spins inside. Most seemed to spin almost together throughout, but there were exceptions, and one star may spin differently in different parts. Stars with quicker wobbles tended to have smaller wobbles. The scientists did not find a clear link between the wobbles and how long the star partners take to go around each other.

LACHESIS: Robust stellar parameters through Bayesian model averaging of isochrone grids

Jose I. Vines, Austin T. Ware

AstronomerLACHESIS is a Python package for inferring stellar masses, radii, and ages from photometry and spectroscopy while accounting for systematic uncertainty associated with stellar evolution grid choice. It interpolates five independent isochrone grids in metallicity, log age, and equivalent evolutionary phase, samples each with nested sampling, and combines their posteriors through Bayesian model averaging weighted by Bayesian evidence. Validation against Kepler asteroseismic dwarfs and subgiants yields robust scatters of about 4% in mass, 2% in radius, and 30% in age, with radius bias below 1% and a mass systematic of about 3%. Age performance depends strongly on evolutionary state; grid-to-grid differences contribute an approximately 9% uncertainty floor, which is subdominant but omitted by single-grid fits. Model-averaged credible intervals approach nominal coverage when reference uncertainties are included. In injection tests, coverage remains near nominal even when the generating model is outside the grid ensemble. The method incorporates grid-choice uncertainty into the reported posteriors for applications to exoplanet hosts and stellar populations.

PublicEstimating a star’s mass, size, and especially age usually requires comparing its light with models of how stars evolve. Different model sets can give different answers, and using just one can leave out an important source of uncertainty. The researchers present LACHESIS, software that combines estimates from five model sets, giving each a weight based on how well it accounts for the data. Tested against a benchmark of Kepler stars whose properties were assessed using stellar oscillations, its estimates showed scatter of about 4% for mass, 2% for radius, and 30% for age. Radius bias was below 1%, while mass estimates had a systematic difference of about 3%. Age estimates were much more sensitive to the star’s evolutionary stage, and differences between models contributed an uncertainty floor of about 9%. Combining models produced more reliable uncertainty ranges than choosing a single model, though the benchmark comparison needed to include uncertainty in the reference values. Simulated tests also supported this improvement, including cases generated with a model outside the five used by the software.

Young explorerScientists look at a star’s light to work out how big it is, how much stuff it has, and how old it is. They use computer guides, but different guides can give different answers. A new program called LACHESIS compares five guides and mixes their answers, while showing how unsure it is. When scientists tested it on stars with other estimates to compare against, it did better at finding their size and amount of stuff than their age. A star’s age is still tricky to figure out, and how far it has grown and changed matters a lot. Using several guides helps the program show uncertainty that one guide alone could miss.

Wolf-Rayet formation through L/M-dependent superwinds

Aisling McKeown, Ciarán Furey, Gautham N. Sabhahit+1 more

AstronomerThis modeling study compares late-stage evolution under traditional luminosity-dependent red-supergiant mass-loss prescriptions and a proposed luminosity-to-mass (L/M) prescription. MESA models span initial masses of 10–40 solar masses. For a 25-solar-mass star, the L/M prescription produces a mass-loss rate about an order of magnitude higher than traditional prescriptions, regardless of the stellar-envelope treatment. Because RSG luminosity is set mainly by core mass and is largely insensitive to current total mass, the inverse mass dependence produces positive feedback and runaway envelope stripping. In these models, stars initially around 20 solar masses can lose their hydrogen envelopes and become classical Wolf-Rayet stars; this classification is supported by both their HR-diagram locations and emission-line spectra predicted with PoWR. Stars initially below 20 solar masses do not strip completely and expand after core helium burning. A generic analytical model finds that stronger inverse mass scaling rapidly increases the tendency toward runaway stripping. These results demonstrate a viable modeled single-star route to yellow-supergiant and Wolf-Rayet stages, with consequences for supernova progenitors, including partially stripped type IIb events. They do not establish which wind prescription describes real RSGs.

PublicHow red supergiants lose their outer layers remains uncertain. The researchers simulated massive stars using different rules for this mass loss. Traditional rules depend on a star’s brightness, while a proposed rule also depends on its mass. Under the proposed rule, losing mass can make further loss faster: the star stays nearly as bright because its core largely controls its brightness. For a modeled star of 25 solar masses, this rule gave a mass-loss rate about ten times higher than traditional rules. The simulations suggest that stars born with around 20 solar masses can shed their hydrogen envelopes and become Wolf-Rayet stars, supported by predicted spectra as well as their modeled temperatures and brightnesses. Lower-mass models retain some hydrogen and expand later. The findings offer a possible route for single stars to reach these stages and affect the kinds of supernova progenitors they become, but they are predictions from models, not direct observations confirming the proposed rule.

Young explorerBig red stars can lose some of their outside gas, but scientists do not yet know exactly how. They made computer models to try different rules. With one rule, losing gas makes a star lose even more gas, while it stays nearly as bright. Some model stars lost all their outer hydrogen and became a different kind of star called a Wolf-Rayet star. Others kept some hydrogen and grew bigger later. This could help explain stars before they explode, but real stars have not yet been shown to follow this rule.

A New Framework for Modeling Solar Flares from MHD to Kinetic Processes

Joel C. Allred, Graham S. Kerr, Silvina E. Guidoni+4 more

AstronomerThis study presents a linked solar-flare simulation framework spanning magnetic energy release, particle acceleration, transport, thermalization, and lower-atmosphere heating. The 2.5D ARMS MHD model simulates magnetic stressing, current-sheet formation, reconnection, and flare-loop evolution. Current-sheet conditions initialize kglobal, which predicts time-dependent nonthermal electron and proton distributions. RADYN+FP then injects these distributions into a newly reconnected ARMS loop and computes particle transport, atmospheric heating, and radiative emission. The authors report the first detailed RADYN+FP simulation tracking nonthermal electrons and protons in the same loop, with a simulated white-light emission height consistent with observations. The framework links specialized models rather than providing a single unified calculation and represents an initial step toward fully 3D flare modeling.

PublicSolar flares involve processes across such a wide range of sizes and timescales that modeling all of them in one calculation remains computationally impractical. This work connects three specialized computer models: one simulates changes in the Sun’s magnetic field and the release of energy, another predicts how electrons and protons gain energy, and a third follows those particles as they travel into and heat the lower solar atmosphere. The authors present the first detailed simulation with RADYN+FP that follows both energetic electrons and protons in the same flare loop. The simulated height of the flare’s visible, white-light emission is consistent with observations, but this is a modeling result, not a new observation. The work is a first step toward a fully three-dimensional flare model.

Young explorerA solar flare is a burst of energy on the Sun. Scientists joined three computer models to show how the Sun’s magnetic fields can release energy, how tiny particles get faster, and how those particles travel and heat part of the Sun. They followed two kinds of tiny particles, electrons and protons, together in one loop. In their computer flare, bright light came from a height that fits what people have seen on the Sun. This is a computer model, not a real flare, and the scientists still want to make it more complete.

Black hole astrometric binaries in the Roman Galactic Bulge Time Domain Survey

Casey Y. Lam, Jessica R. Lu, Kareem El-Badry+6 more

• Astrophysics of Galaxies

AstronomerUsing a synthetic population, the authors forecast the detectability of unresolved astrometric binaries, especially systems with compact-object companions, in Roman’s planned Galactic Bulge Time Domain Survey. The survey is expected to provide approximately 50,000 epochs of photometry and astrometry for about 100 million sources over 1.7 square degrees. Its astrometry is described as comparable to Gaia DR4 in source count, precision, and time baseline, while complementary in wavelength and sky coverage. Assuming black-hole and neutron-star occurrence rates of 10^-7 and 10^-6, respectively, in AU-scale stellar orbits, and astrometric precision of 1% of a pixel, the simulations predict roughly ten detectable detached binaries of each type. Predicted median black-hole mass uncertainties are about 25%, and the black-hole detections would triple the existing detached astrometric sample. Combined with roughly 100 isolated black holes expected from Roman microlensing and roughly ten additional detached black-hole binaries anticipated from Gaia DR4, the authors argue that these discoveries would provide a representative view of quiescent Galactic stellar-mass black holes. These are conditional forecasts, not reported detections.

PublicThe planned Roman telescope survey will repeatedly measure the brightness and positions of about 100 million sources toward the Milky Way’s central bulge. This study uses simulated sources to ask whether small changes in a star’s position could reveal an unseen black hole or neutron star orbiting with it. If these companions occur as often as the authors assume, and Roman reaches the assumed measurement precision, the survey could detect roughly ten star–black-hole pairs and ten star–neutron-star pairs. The predicted black-hole mass measurements would have typical uncertainties of about 25%. These are predictions, not discoveries. The authors suggest that combining these potential detections with black holes expected from Roman’s gravitational microlensing searches and Gaia observations could give a representative picture of the Milky Way’s quiet stellar-mass black holes.

Young explorerScientists made a pretend sky on a computer to see what the planned Roman space telescope might find. A star moving in a little wobble could have a hidden black hole or neutron star beside it. If their guesses are right and the telescope measures carefully enough, it might find about ten pairs of each kind. They have not found these pairs yet.

How eccentric is the debris disk of epsilon Eridani? ALMA reveals a near-circular belt

Oto Ulrich, Joshua B. Lovell, David J. Wilner+2 more

• Solar and Stellar Astrophysics

AstronomerA reanalysis of ALMA Band 6 (1.29 mm) observations of ε Eridani, a K2V star at 3.2 pc hosting a debris disk and the Jupiter analog ε Eridani b, constrains the outer belt’s eccentricity using separate forced- and proper-eccentricity models. The respective 99.7th-percentile upper limits are e_f < 2.6% and e_p < 6.8%, with tentative evidence for e_f = 1.62 (+0.39/−0.40)% at the 4σ level. The authors report the lowest millimeter-derived forced-eccentricity upper limit for any debris disk to date; together, the limits suggest a nearly circular, dynamically cold belt. Combining these results with Spitzer/IRAC, JWST/NIRCam F444W, and JWST/MIRI F2550W data constrains possible additional planets beyond ε Eridani b to masses of approximately 2 × 10^-4–0.3 Jupiter masses at orbital separations of approximately 6–60 au, rather than establishing new planet detections.

PublicThe nearby star ε Eridani has a known Jupiter-like planet and an outer ring of debris. Researchers reexamined ALMA telescope observations to test whether the ring is stretched away from a circle, possibly by a planet’s gravitational influence. Their modeling indicates that the ring is nearly circular, although they report tentative evidence for a small distortion. They set tight limits on two kinds of orbital eccentricity, or departure from circularity. Combining this analysis with infrared observations from Spitzer and JWST also restricts the masses and distances of any additional planets that could fit the data; it does not demonstrate that those planets exist.

Young explorerA nearby star has a big planet and a ring of little bits of material around it. Scientists looked again at telescope pictures to see whether the ring is round or a little stretched. It seems almost round, but there might be a tiny stretch. They also worked out what other planets could fit the clues, without finding any new planets for sure.

Correlations between the Carbon-to-Oxygen Ratio and the Orbital and Physical Properties of Exoplanets

Noah Ferich, Robert Royer III, Cody Shakespeare+1 more

AstronomerThis simulation study examines planet formation across varying carbon-to-oxygen ratios, using the REBOUND N-body integrator with data from a sequential dust condensation model. It addresses how differences in protoplanetary disk surface density profiles could affect system architectures and planetary iron and siderophile contents, a topic the authors identify as lacking detailed treatment in previous work. Prior studies suggest that high-C/O disks can form carbon-dominated rather than silicon-dominated terrestrial planets. The authors find that bulk density could help distinguish silicon-rich from carbon-rich planets, but caution that it may not be reliable as a standalone diagnostic. The abstract reports no specific architectural or compositional outcomes beyond this density-based finding.

PublicPlanets form from disks of material around stars, and the balance of carbon and oxygen in those disks may influence what the planets are made of. Earlier studies suggest that disks with high carbon-to-oxygen ratios could produce rocky planets dominated by carbon rather than silicon. This study uses computer simulations to investigate how different disk material distributions could affect planet arrangements and their iron and related metal contents. The simulations suggest that a planet’s average density could help distinguish carbon-rich from silicon-rich planets, but density alone may not provide a dependable answer.

Young explorerNew planets grow from material in a disk around a star. Scientists used a computer to explore how planets might grow when that material has different amounts of carbon and oxygen. Some planets might be rich in carbon, while others are rich in silicon. The computer study suggests that checking how much stuff is packed into a planet could help tell the two kinds apart, but that clue alone might not be enough.

Planetary eccentricity enhances inward comet transport but suppresses gentle impacts

Qunfeng Jiang

AstronomerNumerical simulations test whether modest planetary eccentricity preserves low-velocity comet delivery through compact planetary chains. The main suite follows 64,000 comets from between the two outermost planets of an eight-planet chain toward an Earth-mass planet on a temperate orbit around a 0.1-solar-mass star. A second suite isolates the final transfer to the innermost planet for initial planetary eccentricities of 0–0.05 and separations of 10 and 30 mutual Hill radii; a separation of 12 provides a comparison to test the influence of the near-3:2 period ratio at 10. At an initial eccentricity of 0.05, interception by the outermost planet falls by 11 per cent and 6 per cent more comets reach the inner region. The innermost planet's impact probability changes by less than 3 per cent, but the share of impacts below 15 km/s drops from 25 to 18 per cent, reducing the fraction of all injected comets producing such impacts by 30 per cent. Simulated pre-encounter speeds indicate preferential loss of the slowest approaches. An applied impact-chemistry model yields a 31 per cent reduction in HCN survival-equivalent yield. These model results suggest that enhanced inward transport need not translate into greater delivery of prebiotic material under chemically favourable impact conditions.

PublicComets may bring volatile substances and molecules relevant to the origins of life to rocky planets, but fragile molecules must survive atmospheric entry and impact. Researchers used computer simulations to ask whether slightly elongated planetary orbits disrupt the gentle comet deliveries possible in tightly packed planetary systems. They followed 64,000 simulated comets through an eight-planet system around a star one-tenth the Sun's mass, with additional simulations examining the final transfer to the innermost planet. With an initial orbital eccentricity of 0.05, more comets reached the inner region, while the innermost planet's chance of being hit changed by less than 3 per cent. However, the share of impacts slower than 15 km/s fell from 25 to 18 per cent. Across all comets introduced into the simulations, these slower impacts became 30 per cent less common. A chemical model estimated a 31 per cent lower survival-equivalent yield of HCN, a molecule relevant to prebiotic chemistry. The study therefore predicts that slightly elongated planetary orbits can send more comets inward yet reduce delivery under conditions favourable to fragile molecules; it does not report observations of actual comet impacts.

Young explorerComets can carry ingredients that might help life get started, but those ingredients can be damaged when a comet hits a planet too fast. Scientists used a computer to imagine comets passing along a row of planets. When the planets followed slightly stretched-out paths instead of round ones, more comets moved toward the inner planets, but fewer hit gently. Another computer model suggested that less of one fragile ingredient would survive. So sending more comets toward a planet does not always mean delivering more useful ingredients. This was a computer experiment, not something scientists watched happen in space.

Constraining Particle Stiffness in Asteroid Regolith from Early-Time High-Speed Penetrator Dynamics under Local Granular Variability

Zichen Wang, Yang Yu, Chenyang Huang+4 more

• Instrumentation and Methods for Astrophysics

AstronomerThis numerical study tests whether early-time high-speed penetration dynamics can constrain particle Young’s modulus in rubble-pile asteroid regolith. A bidirectionally coupled EDEM–Adams discrete-element–multibody model screens six contact parameters, then compares five modulus levels at 17 matched locations in a single settled granular bed, for 85 simulations. At penetration speeds of 75–90 m s^-1, Young’s modulus produces the clearest systematic changes in probe deceleration; the other parameters have weaker effects within their tested ranges. Validation that withholds all modulus cases at each location in turn shows that the early response distinguishes broad modulus ranges better than adjacent levels. Mesoscale analysis associates increasing modulus with concentrated interface load sharing and spatially extended, three-dimensional high-capacity contact paths. These controlled simulations support narrowing particle-stiffness ranges despite local granular variability, but quantitative inference for real asteroid regolith requires further experimental validation.

PublicResearchers used computer simulations to ask whether the rapid slowing of a probe entering an asteroid’s loose surface material could reveal how stiff its individual particles are. They compared five particle-stiffness settings at the same 17 locations in one simulated bed of grains. For probe speeds of 75–90 metres per second, stiffness changed the slowing pattern more consistently than the other material and contact properties tested. Tests on locations left out of the analysis showed that the early motion was better at separating broad stiffness ranges than closely spaced settings. The simulations linked these differences to how contacting grains share and transmit loads. This is a possible way to narrow estimates of particle stiffness, not a measurement of a real asteroid: experiments are still needed before the method can be applied quantitatively.

Young explorerSome asteroids are piles of rocks and loose grains. Scientists made a pretend pile in a computer and pushed a fast-moving probe into it. They changed how stiff the grains were and watched how the probe slowed down. In these computer tests, the slowing helped tell very different stiffnesses apart, but nearby stiffnesses were harder to tell apart. Where the probe hit also mattered. Scientists still need real experiments to find out how well this idea works for asteroid material.

Interpreting effective homogeneous rheologies through a local differential map with application to the Moon

Yeva Gevorgyan

AstronomerThe authors develop a local interpretation of equivalent homogeneous rheologies by linearizing the layered-to-homogeneous mapping around a fixed-geometry baseline, varying selected layer rigidities and viscosities. A pole-residue representation of the degree-two Love number yields a physical-to-effective transfer matrix; singular values, a resolution matrix, and a mode-dominance matrix characterize parameter visibility and its expression in effective coordinates. In a five-layer lunar model, the full degree-two response is sensitive to seven of eight solid-layer rheological parameters. Inner-core rigidity is the sole near-null direction, consistent with fluid-outer-core shielding and weak sensitivity to core elastic structure. Fewer physical directions remain visible over the lunar laser ranging frequency interval, where an elastic spring, an isolated dashpot, and two Voigt elements reproduce the nine-pole response to first order. Finite-perturbation tests agree with the tangent prediction within a few percent, but a nearly degenerate pair of long-timescale modes limits the range of validity. These are model-based sensitivity results, not observational determinations of lunar layer properties.

PublicA planet or moon’s layered interior affects how it deforms and dissipates energy under tidal forces. Calculating that response repeatedly can be costly, so researchers often replace the layers with a simpler mathematical model. This study develops a way to interpret which small changes in individual layers that simpler model can represent. In a five-layer model of the Moon, the complete tidal response was sensitive to seven of eight tested material properties; the inner core’s stiffness had very little effect, consistent with shielding by the fluid outer core. Over the frequency range used in lunar laser ranging, fewer independent changes could be distinguished, and a compact spring-and-damping model reproduced the more complex response to first order. Tests with finite changes matched the local predictions within a few percent, but the approximation has a limited range of validity. The study analyzes a lunar model rather than measuring the Moon’s interior.

Young explorerThe Moon has layers inside, and tidal pulls can make it change shape a little. Scientists used a pretend Moon in a computer to see which changes inside would change how it bends. They found that most of the things they tested mattered, but making the very middle stiffer hardly changed the answer. They also made a simpler pretend Moon that gave nearly the same answers for small changes. It does not work for every change, and this was a computer study, not a new look inside the real Moon.

Two-stage disruption of resonant chains

Nick Choksi, Yoram Lithwick, Eugene Chiang+1 more

AstronomerObservations of young transiting systems enabled by TESS suggest that most close-in planets formed in mean-motion resonant chains that disrupt on a characteristic timescale of roughly 100 Myr, despite the stabilizing effects of the dissipative forces responsible for resonance capture. The authors investigate a two-stage disruption scenario for super-Earth chains: excitation of free eccentricities to a few percent, followed by dynamical instability on an approximately 100 Myr timescale. Their analysis finds that any mechanism providing this initial excitation can initiate the second stage. One proposed trigger is accretion of a handful of Mercury-sized bodies totaling a few percent of the system's planetary mass; this scenario reproduces the observed decline in resonance incidence and could also explain period ratios narrow of commensurability in some young systems. Growth of these impactors from leftover planet-formation debris is sketched rather than established. The authors also identify observational trends of declining multiplicity on the resonance-disruption timescale and greater resonance occupation at higher multiplicity.

PublicTESS observations of young stars suggest that many planets orbiting close to their stars began in coordinated arrangements, with their orbital periods linked by simple numerical ratios. These arrangements appear to break apart over roughly 100 million years. That is puzzling because the forces that originally arrange the planets this way should also help keep their orbits stable. The authors explore a two-step explanation: first, something makes the planets' orbits slightly more elongated; then, the system becomes unstable over about 100 million years. They find that an initial orbital distortion of a few percent is enough to start this process. A possible cause is collisions with a handful of bodies about the size of Mercury, together amounting to a few percent of the planetary system's mass. This proposed explanation reproduces the observed decrease in coordinated orbits, but the collisions themselves are not established by the observations. The data also show that the number of planets seen per system declines on a similar timescale, and that systems with more planets are more likely to have coordinated orbits.

Young explorerSome young planets go around their stars in a matching rhythm, like dancers keeping time together. Observations suggest that many lose this rhythm after about 100 million years. The scientists studied one possible reason: something first makes their paths a little more stretched out, and later their dance becomes unstable. Bumps from smaller worlds might give them that first push, but scientists have not shown that these bumps really happened. They also found that groups where we see more planets are more likely to keep a matching rhythm.

Early Planet Formation in Embedded Disks (eDisk). XXV. Inclination-Induced Minor-Axis Brightness Asymmetries Reveal Limited Dust Settling in Embedded Protostellar Disks

Sidhant Kumar Suar, Zhe-Yu Daniel Lin, Zhi-Yun Li+9 more

• Solar and Stellar Astrophysics

AstronomerThe study uses minor-axis continuum brightness asymmetry in highly inclined disks to constrain vertical dust structure in embedded Class 0/I systems. RADMC-3D radiative transfer simulations show that inclination, optical depth, and dust scale height can naturally produce the observed asymmetry. MCMC fits apply this framework to nine ALMA eDisk disks. Independent outflow constraints agree with the modeled near- and far-side orientations in all eight sources with useful outflow information, supporting the inferred geometry. Most disks show no strong evidence for significant dust settling, with inferred dust scale heights comparable to those of the gas. Combined with literature evidence that Class II disks tend to be well settled, these results support significant settling during the Class I transition rather than directly measuring its timing. The apparent broad coincidence between settling and widespread dust substructure motivates the tentative interpretation that gravitationally driven vertical dust concentration may trigger substructure formation.

PublicDust settling into a thinner layer inside a young star’s disk could help create the concentrations needed to build planets, but measuring that layer is difficult when the system is still embedded in surrounding material. Researchers modeled how differences in brightness across a tilted disk depend on its viewing angle, opacity, and dust thickness, then fitted observations of nine young disks. Separate observations of outflowing material supported their inferred disk orientations in eight cases where useful checks were available. Most disks showed no strong evidence that the dust had settled into a much thinner layer than the gas. Comparison with studies of later-stage disks suggests that substantial settling happens during the intermediate Class I stage. A possible connection between settling and the appearance of dust structures remains an interpretation, not an established cause.

Young explorerBaby stars have disks of gas and dust around them. Scientists studied nine young disks and used computer models to see what their brighter and dimmer sides could tell us. In most, the dust did not seem to have sunk into a very thin layer. It may settle down as the stars grow. That could help make the dusty clumps needed to build planets, but scientists are still figuring out how.

Inferring radio beams from sparse sampling patterns: a case study with the Murchison Widefield Array

Michael J. Wilensky, Aman Chokshi

• Cosmology and Nongalactic Astrophysics

AstronomerReprocessed satellite observations are used to infer the 137-MHz, zenith-pointed power beams of Murchison Widefield Array receiving elements. Two complementary Bayesian approaches quantify departures from nominal electromagnetic simulations: a physically motivated model of complex dipole-to-dipole variations and a hierarchical spline model of direction-dependent structure. The inferred beams show shallower, displaced nulls and coherent sidelobe deformations. The dipole model captures much of the broad morphology, while the spline recovers additional localised features and remains largely robust to isolated pass-shaped artefacts. Four independent 20-day subsets, each comprising approximately 20% of the full dataset, recover consistent null and sidelobe morphology across the visible hemisphere despite sparse, differing sampling. This supports practical, repeatable power-beam reconstruction from opportunistic satellite transmissions. Accurate beam models are important for limiting foreground contamination in Epoch of Reionisation 21-cm searches; future chromatic, phase-referenced measurements of the full Jones response remain a proposed extension, not a result of this study.

PublicA radio telescope’s sensitivity varies across the sky, and errors in modelling that pattern can let bright foreground radio emission contaminate the faint signal sought from the Epoch of Reionisation. Researchers used reprocessed satellite observations to map this sensitivity pattern for Murchison Widefield Array receiving elements at 137 MHz, with the elements pointed overhead. Compared with electromagnetic simulations, the measurements showed that low-sensitivity regions were less deep and shifted in position, while secondary response regions were systematically reshaped. Two statistical models captured these differences: one described variations among individual antenna dipoles, and the other mapped more localised features while being largely resistant to isolated artefacts. Four independent 20-day portions of the observations produced consistent patterns despite sampling the sky differently. The study supports satellite transmissions as a practical, repeatable way to reconstruct these beam patterns, but broader measurements of their frequency dependence and full polarisation response are left for future work.

Young explorerA radio telescope hears signals from some parts of the sky better than others. Scientists used signals from satellites to make a map of where parts of one telescope hear well and where they hear poorly. The map was a little different from what computer models expected: some quiet spots were not as quiet, and some were in different places. The scientists tried two ways to draw the map and checked it using four separate groups of observations. They found similar shapes each time. That is a good sign that satellite signals can help them make reliable maps. They still want to make more kinds of measurements later.

NASA ASTRA White Paper : A Chandra Successor in the 2030s

C. S. Reynolds, E. Hodges-Kluck, E. A. Kara+19 more

• High Energy Astrophysical Phenomena

AstronomerThis mission-concept paper argues for a Chandra successor providing soft X-ray spectral imaging with approximately 1 arcsec angular resolution, more than 10 times Chandra’s sensitivity, and more than 50 times its survey speed. Chandra has established the broad scientific value of such imaging, but the authors argue that its sensitivity is insufficient to complement upcoming major facilities. They highlight four science drivers: supermassive black hole formation, stellar and AGN feedback in galaxies, the effects of high-energy stellar activity on exoplanet atmospheres, and black hole mergers. Using the NASA Probe concept study report for AXIS, they sketch AXIS-Deep, AXIS-Classic, and AXIS-Fast to explore science–instrument trade-offs, with a breakthrough science case and additional design-driving cases for each. The enhanced capabilities and scientific payoffs are proposed, not demonstrated results. The authors also argue that a successor in the 2030s could demonstrate X-ray mirror technology for a future flagship and sustain the US high-energy astrophysics workforce.

PublicThe authors make the case for a new X-ray space telescope to follow Chandra. Chandra has shown how valuable sharp X-ray images are across astronomy, but the authors say a more sensitive telescope is needed to work alongside upcoming major observatories. They envision a successor with more than ten times Chandra’s sensitivity and more than fifty times its survey speed. It would help investigate how supermassive black holes formed, how stars and active galactic centers affect their galaxies, how energetic stellar activity changes the atmospheres of planets around other stars, and how black holes merge. The paper outlines three possible designs, called AXIS-Deep, AXIS-Classic, and AXIS-Fast, rather than reporting new observations or a completed mission. A launch in the 2030s could also help prepare mirror technology and maintain expertise for a later, larger X-ray observatory.

Young explorerChandra is a space telescope that sees a kind of light called X-rays. It has helped scientists learn about space. Now scientists are suggesting a new telescope that could see fainter things and look across the sky faster. They hope it could help explain how giant black holes began, how stars change galaxies, how stars affect the air around faraway planets, and how black holes join together. They describe three possible telescope designs. These are ideas for a future telescope, not things a new telescope has already discovered.

Automated multi-stressor optical fiber focal ratio degradation and throughput characterization system for future massive multiplex spectroscopic survey

Daksh Singh, Ting S. Li, Sarik Jerma+1 more

AstronomerThe authors present an automated platform for measuring focal ratio degradation (FRD) and relative throughput in optical fibers while varying input angle, wavelength, bend radius, twist angle, and applied load, individually or in combination. Software automates hardware control, acquisition, and analysis to support characterization campaigns with minimal user intervention. Validation measurements on a multimode fiber resolve both pronounced and subtle stress-dependent changes: FRD exhibits the expected dependence on input angle and bend radius, comparatively weak sensitivity to compressive loading under the tested conditions, and a reproducible periodic dependence on twist angle. Relative throughput decreases with increasing input angle in a manner not explained solely by a simple projected-area model. The platform is intended to support large-scale fiber characterization for future facilities such as Spec-S5 and WST, each expected to contain more than 25,000 fibers; the reported validation does not establish performance across those full fiber populations.

PublicFuture telescope facilities such as Spec-S5 and WST will use more than 25,000 optical fibers to carry light for analysis. Testing all those fibers by hand would take too long, so the researchers built an automated system that measures how much light a fiber transmits relative to a reference and how the light spreads as it emerges. The system can vary the light’s entry angle and wavelength, as well as bending, twisting, and pressure on the fiber. Tests on a multimode fiber found the expected changes in light spreading with entry angle and bending, relatively little response to squeezing under the tested conditions, and a repeating pattern as the fiber was twisted. Light transmission also fell as the entry angle increased, beyond what a simple geometric explanation could account for. These tests demonstrate the system’s capabilities; its proposed role is to make much larger testing campaigns practical.

Young explorerTelescopes can use lots of thin threads to carry light. Scientists built a machine to test these threads automatically. In a test of one thread, changing how light went in, bending the thread, or twisting it changed how the light spread out when it came out. Twisting made a pattern that repeated. Squeezing had only a small effect in the tests they tried. The scientists hope this machine will help them check many more threads without testing each one by hand.

Prototyping the Next-Generation Spectrograph for Space Exploration: Digital Micromirror Device-based Multi-Object Spectrograph (DMD-MOS) Calibration and Performance Assessment

Jiayi Emma Xu, Sarik Jeram, Shaojie Chen+7 more

AstronomerDMD-MOS uses an addressable array of microscopic mirrors, each with two discrete tilt positions, to create configurable slit masks for multi-object spectroscopy. Its two optical channels associate one mirror position with imaging for target selection and the other with spectroscopy, allowing simultaneous imaging of the telescope field and routing of selected targets' light to the spectrograph. The authors report laboratory tests of spectral resolution, line spread function, wavelength coverage, and the mapping between the DMD and imaging planes. This mapping enables the control software to configure the mirrors instantaneously for selected targets in the acquisition field. The abstract gives no numerical performance values and reports laboratory testing rather than on-sky results.

PublicThe researchers have designed and tested a device that uses tiny movable mirrors to select which objects' light goes into a spectrograph, an instrument that separates light by wavelength. Each mirror can tilt in two directions: one sends light to an imaging channel used to choose targets, and the other sends it to the spectrograph. This lets the device make an image of the telescope's view while directing light from chosen objects for spectral analysis. Laboratory tests examined how well it separates wavelengths, how it records narrow spectral lines, which wavelengths it covers, and how image locations correspond to mirror locations. That correspondence lets the software quickly set the mirrors for selected targets. The abstract does not provide performance numbers or results from observations through a telescope.

Young explorerImagine lots of tiny mirrors that can tip two ways. One way sends light to a camera that makes a picture. The other way sends light to a tool that sorts it by color. Scientists can choose things in the picture and tip the right mirrors to send their light to that tool, while still making a picture. They tested the device in a laboratory, including checking which mirrors match which places in the picture. They do not say here how well it worked when looking at the sky.

Measuring the linear gain performance for the OrcaQuest CMOS imaging sensor

Zain Azama, Aditya Khandelwal, Ryan Dungee+3 more

AstronomerExposure tests and data-reduction pipelines characterize a non-linear gain curve in Hamamatsu Photonics’ OrcaQuest CMOS sensor at short exposure times. The report provides a more accurate gain characterization curve. These calibration data could support more consistent measurements of pixel gain and linearity, as well as more consistent high-frame-rate imaging; the abstract does not quantify the non-linearity or the resulting improvements.

PublicTests found that the gain of Hamamatsu Photonics’ OrcaQuest camera sensor does not behave linearly when exposures are very short. The report describes how this behavior was tested and analyzed, and provides a more accurate curve for characterizing the sensor’s gain. This information could help make sensor measurements and fast image sequences more consistent, though the abstract does not say how large the improvement would be.

Young explorerScientists tested a camera sensor called OrcaQuest. When it takes pictures very quickly, its response does not follow a simple, steady pattern. They made a better guide to that pattern. The guide could help people understand the sensor and make fast pictures more consistent.

Near-Noiseless Single-Photon Detection in the Infrared with a Megapixel Semiconductor Array for Low-Background Astronomy

Guillaume Huber, Pavaman Bilgi, Charles-Antoine Claveau+7 more

AstronomerThe authors demonstrate single-photon-resolving operation in a megapixel-format HgCdTe linear-mode avalanche photodiode array at conventional cryogenic temperature. Avalanche gain lifts photon-induced steps in non-destructive up-the-ramp data above the readout-noise floor while leaving the dark signal largely unamplified. The reported false-positive rate is approximately two false counts per thousand reads per pixel. The demonstration supports LmAPDs as a promising route toward infrared photon-counting focal planes for future low-background observatories, rather than establishing their performance in those observatories.

PublicDetecting extremely faint infrared light is difficult because a sensor’s own noise can hide individual photons. The researchers demonstrated that a semiconductor detector array with a million pixels can distinguish individual photon arrivals while operating at conventional cryogenic temperatures. It amplifies the light-generated signal before readout while leaving most of the unwanted dark signal unamplified. It still makes occasional mistakes: about two false counts per thousand readings of each pixel. This offers a promising alternative to superconducting infrared detectors, which require temperatures near absolute zero and substantially more power, but its use in future low-background observatories remains a prospect.

Young explorerLight comes in tiny bits called photons. Scientists tested a very cold light sensor that can spot these tiny bits of infrared light one at a time. It makes the light’s signal bigger so it is easier to notice, but sometimes it counts a bit of light that was not really there. This kind of sensor could help future telescopes see very faint light.

LeoNet: A Machine Learning Method for Binary Pulsar Classification

Zhaocheng Gong, Jack White, Zeyu Yang+3 more

AstronomerLeoNet is a convolutional neural network for identifying binary-pulsar candidates whose signals are affected by orbital Doppler shifts. Ten learnable filters produce a compact feature map in place of an explicitly sampled acceleration–jerk response grid, followed by convolutional classification. On simulated 500 s observations, it achieved a mean relative reduction in false-negative rate of 55.5% across five sampling intervals compared with the evaluated PRESTO acceleration-search configuration. TensorRT-optimised FP32 processing on an NVIDIA H100 PCIe GPU took 3.44–4.37 ms per observation across eight sampling intervals, including preprocessing and postprocessing. At 128 microsecond sampling, the mean time was 3.54 ms versus 1.767 s for PRESTO FDAS on an AMD EPYC 9825 CPU with a 96–1000 Hz search range, giving an approximately 499-fold measured speedup. This comparison uses different hardware, and the detection results are simulation-based; the findings support LeoNet’s potential as a real-time candidate-identification stage rather than demonstrate discoveries in observational data.

PublicPulsars in orbit with another object can help test gravity, but their orbital motion shifts their signals and makes them harder to find. The researchers developed LeoNet, an artificial-intelligence system that learns patterns in these shifted signals and flags possible pulsars. In simulated 500-second observations, it reduced the rate of missed signals by an average of 55.5% relative to the tested configuration of an existing search program, PRESTO. LeoNet also processed each simulated observation in just a few milliseconds on a graphics processor. One timing comparison found it about 499 times faster than PRESTO, although the programs ran on different hardware. These tests suggest that LeoNet could help screen incoming telescope data quickly; they do not establish that it has found real pulsars.

Young explorerSome stars called pulsars send out signals like a repeating beat. When a pulsar moves around with a partner, that beat can be harder for a computer to spot. Scientists made a computer helper called LeoNet and tested it with pretend observations. It missed fewer signals than the other search program they tested, and it worked very quickly. The programs used different kinds of computers, so the speed comparison needs care. LeoNet might help scientists look for real pulsars, but these tests did not show it finding any.

Comparing Optimized Systematic Error Correction Methods on Selected TESS Light Curves

David Rapetti, Jon Jenkins, Joseph Twicken+2 more

• Earth and Planetary Astrophysics

AstronomerThe authors present SysCoCoPy, a software package and analysis framework for comparing systematic-error correction in TESS light curves. It compares the SPOC pipeline’s Presearch Data Conditioning (PDC) method with three community correctors implemented through Lightkurve, focusing on scattered-light contamination from Earth and the Moon. The framework automatically optimizes corrector parameters and supplies qualitative and quantitative comparisons for individual cases and statistical results for selected samples. Two correctors whose designs favor scattered-light removal achieve a significant number of successful corrections with this optimization. However, the statistical analysis of the largest sample currently indicates that PDC is more robust overall, achieving a higher success level according to the metrics used.

PublicTESS records changes in the brightness of stars, but scattered light from Earth and the Moon can contaminate those records. The authors developed software called SysCoCoPy to compare four methods for correcting these and other systematic errors: the standard pipeline’s PDC method and three community-developed alternatives. The software automatically adjusts settings and helps assess performance both for individual cases and across samples. Two methods designed to favor scattered-light removal successfully corrected many cases after automatic adjustment. Even so, in the largest sample studied, PDC currently performed more reliably overall according to the study’s evaluation measures.

Young explorerTESS watches how bright stars look, but light scattered from Earth and the Moon can get in the way. The researchers made a computer program to compare four ways of cleaning up the star brightness records. Two ways did well at removing the unwanted light in many cases after the program adjusted their settings. But in the biggest group they checked, the usual way, called PDC, worked more reliably overall by the checks they used.

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

Harry T. J. Bevins

• Cosmology and Nongalactic Astrophysics

Astronomerhyprfine is an analytic, GPU-native simulation of the sky-averaged 21-cm signal over z = 1100–6, implemented in JAX and Python. It models the signal’s mean temperature as a function of cosmic time, Λ-CDM cosmological parameters, and the astrophysics of the first stars and galaxies. The authors report subsecond execution, efficient GPU parallelisation, and differentiability through the Dark Ages at z ≥ 35. To their knowledge, it is the first analytic GPU-native simulation of this signal. These are modeling and software capabilities, not observational findings.

PublicThe researchers describe hyprfine, a computer simulation of how the average temperature of the sky’s 21-centimeter signal changes over cosmic history. Its predictions depend on parameters of the Λ-CDM cosmological model and on how the first stars and galaxies behave. Written in Python using JAX, it is designed to run directly on graphics processing units, or GPUs. The authors report that it runs in a fraction of a second and efficiently carries out calculations in parallel. During the period called the Dark Ages, the code also supports calculating how its predictions respond to changes in its inputs. They believe it is the first analytic GPU-native simulation of this signal; the abstract describes software, not a new sky measurement.

Young explorerScientists made a computer program called hyprfine to pretend how a signal from space changed as the universe grew older. It works out an average for the whole sky, using ideas about the universe and its first stars and galaxies. The scientists say it can finish in less than a second on a special computer chip. It is a computer model, not a new picture or measurement of the real sky.

Radio Interferometric Calibration with the Exponential Map

L. Cabral, M. Fernandez-Corazza, G. Gancio+1 more

• Signal Processing

AstronomerThe authors develop a maximum-likelihood estimator for multiplicative and additive signal-path perturbations in radio interferometry, using the exponential map and Lie groups. They evaluate its performance against the Cramér–Rao lower bound, compare its estimation time with that of an expectation-maximization maximum-likelihood estimator, and apply it to a Submillimeter Array observation of the protoplanetary disk AS 209. They report that the estimator meets the Cramér–Rao lower bound and runs approximately 40 times faster than the expectation-maximization algorithm in their evaluation. The abstract does not specify the test conditions or establish that this speed advantage holds generally.

PublicRadio interferometers combine signals from multiple antennas to study astronomical sources. Effects along the signal path can change those signals, so astronomers use calibration to correct them. This study develops a new mathematical method for estimating those effects. The authors compare its accuracy with a theoretical limit and its speed with an existing method called expectation maximization. They also apply it to a real Submillimeter Array observation of AS 209, a disk where planets may form. In their evaluation, the new method reaches the theoretical accuracy benchmark and is about 40 times faster than the comparison method; the abstract does not establish whether that advantage applies to all observations.

Young explorerAstronomers use several radio antennas together to look at things in space. The signals can get changed on their way through the equipment, so scientists need to work out how to correct them. These researchers made a new way to do that and tried it on a real observation of a disk around a star. They say their method did as well as a mathematical rule says it could and was about 40 times faster than another method in their tests. That does not mean it will always be that much faster.

Spurious sources in high-resolution VLA surveys

Eric F. Jiménez-Andrade, Emmanuel Momjian, Eric J. Murphy+2 more

AstronomerThe authors investigate excess spurious detections in high-resolution radio continuum surveys using the VLA 10 GHz GOODS-N mosaic, which has a native resolution of 0.22 arcsec and a nearly Gaussian pixel-noise distribution. The increased number of independent resolution elements explains part of the excess, while residual wide-field effects associated with the primary-beam response contribute only modestly. After accounting for these effects, the observed false-detection fraction remains several times the Gaussian-noise prediction. Noise-autocorrelation analysis indicates that sparse uv coverage leaves significant dirty-beam sidelobes, producing correlated noise fluctuations that enhance false detections. The authors interpret the excess as an intrinsic consequence of incomplete uv sampling rather than the imaging methodology, and argue that future deep surveys need sufficiently dense uv coverage alongside high angular resolution.

PublicVery sharp radio images can contain apparent sources that are actually noise. The researchers studied a high-resolution image of the GOODS-N field made with the Very Large Array. Although the noise values across the image follow a nearly bell-shaped distribution, false detections occur several times more often than a simple model of that noise predicts, even after other contributing effects are accounted for. Searching more independently resolved patches explains part of the increase, and effects related to the telescope’s sensitivity across the field explain only a modest amount. The analysis points to incomplete sampling of the radio signals needed to construct the image: this leaves response patterns that link noise fluctuations across the image and make them more likely to resemble real sources. The authors conclude that future deep radio surveys need more complete sampling, not just sharper images, to reduce false detections.

Young explorerA radio telescope makes pictures using radio waves from space. Sometimes a spot in a picture looks like something real, but it is only noise. The scientists studied one very sharp picture and found more of these pretend spots than a simple noise model expected. Their study suggests that missing pieces of the information used to make the picture leave patterns that make noise look like real spots. They say future radio pictures need more complete information, not just sharper detail, to have fewer pretend spots.

Bayesian Image Reconstruction with Spatially Variant PSFs in X-ray Astronomy

Vincent Eberle, Matteo Guardiani, Margret Westerkamp+4 more

AstronomerThe authors combine Bayesian inference grounded in information field theory (IFT) with a fast, spatially variant point spread function (PSF) representation to estimate the posterior mean and uncertainty of X-ray flux under minimal physically motivated priors. In a synthetic benchmark that neglects spatial PSF variability, IFT-based deconvolution outperforms three Richardson-Lucy variants according to SSIM, RMSE, and NLL. Separately, tests on simulated PSF data show that an interpolated patch-based convolution scheme accurately reproduces the complex Chandra PSF. Combining these components for real Chandra observations of Cassiopeia A yields a reconstruction that appears visually sharper than the exposure-corrected data, with residuals consistent with pure noise. Comparison with a highly resolved reference dataset supports this assessment. These results indicate, rather than prove, an accurate instrument-and-sky model. Cross-calibration among observations or X-ray instruments is presented as a future application, not a demonstrated result.

PublicX-ray images are blurred by the telescope, and photon counts fluctuate because of statistical noise. This study uses a Bayesian method to reconstruct the underlying X-ray brightness while estimating uncertainty and accounting for how the blur changes across an image. On an artificial test image, the method performed better than three versions of an established deblurring algorithm. A separate simulation showed that its model could accurately reproduce Chandra's complex blur pattern. Applied to real Chandra observations of the supernova remnant Cassiopeia A, the reconstruction looked sharper than the exposure-corrected image. The remaining differences between the model and the data were consistent with noise, and comparison with a highly resolved reference dataset supported the apparent improvement. These checks suggest that the model represents both the telescope and the source well; they do not establish a perfectly recovered image. Using the framework to compare and calibrate different observations or instruments remains a possibility for future work.

Young explorerAn X-ray telescope can make a space picture blurry and speckly. Scientists made a computer method to help clean up those pictures and show which parts are still uncertain. It did better than three other methods on a pretend picture. They also tested how well the computer copied the telescope's changing blur. Then they used it on a real picture of Cassiopeia A, the remains of an exploded star. The new picture looked sharper, and checking another detailed picture helped support that. It is still an estimate, not a perfectly clear picture.

A comprehensive simulation framework for multi-modal kilonova observations from all-sky surveys

Felipe Fontinele Nunes, Andrew Toivonen, Farhana Taiyebah+5 more

AstronomerThe authors propose kilonova-multimodal-emulator, a simulation pipeline designed to generate realistic kilonova photometry, spectra, and images for multimodal AI training. The motivation is the scarcity of observed kilonovae and the difficulty of identifying them among millions of nightly transient candidates from surveys such as Rubin’s Legacy Survey of Space and Time and ZTF. They demonstrate the pipeline for ZTF-type observations, using historical Bright Transient Survey cadence and limiting-magnitude information together with radiative-transfer kilonova models. The resulting dataset is simulated and intended for training large AI models; the abstract does not report improved classification performance or validation against observed kilonovae.

PublicSky surveys produce millions of candidates for changing or short-lived astronomical events each night, making kilonovae difficult to pick out. Because relatively few kilonovae have been observed, there is limited real data for training artificial intelligence to recognize them. The authors propose a simulator that creates several kinds of synthetic observations: brightness measurements, spectra showing how light is distributed across wavelengths, and images. They demonstrate it for observations like those made by ZTF, combining kilonova models with historical information about when the survey observed and how faint an event it could detect. The dataset is intended to train AI, but the abstract does not show that it improves the identification of real kilonovae.

Young explorerTelescopes find lots of things in the sky that change, and special events called kilonovae can be hard to spot. Scientists have only a few real examples to help teach a computer what to look for. This team made a tool that uses models to create pretend telescope pictures and light measurements of kilonovae. These practice examples are meant to help teach computers, but the team has not shown here that they help computers find real kilonovae better.

Best practices in software citation

Phil R. Van-Lane, Floor S. Broekgaarden, Daniel S. Katz+11 more

• Digital Libraries

AstronomerDrawing on a NASA-funded community workshop held in April 2026, this analysis examines software citation as a problem of research infrastructure and scholarly practice. The authors describe current citations as inconsistent, incomplete, and rarely machine-actionable, arguing that infrastructure built for papers and data does not adequately support software. They organize the discussion around cultural barriers, unclear community norms, technical and workflow gaps, and challenges from AI-assisted research. For each theme, they propose targeted interventions and assign stakeholder responsibilities. Their central conclusion is that technical and cultural changes must proceed together, with journal editors and publishers identified as the highest-leverage actors. These are workshop-informed assessments and recommendations, not demonstrated outcomes of the proposed interventions.

PublicResearch depends on software, and software itself can be an important research product. Yet researchers do not consistently cite it in ways that give its creators credit or let computers readily process the references. The authors argue that this makes research harder to reproduce and hides some of the work behind it. Based on a NASA-funded community workshop in April 2026, they examine habits, citation rules, technical systems, and new challenges from AI-assisted research. They recommend coordinated changes, especially from journal editors and publishers, so that citing software correctly becomes easy within researchers’ usual routines. The abstract presents an analysis and proposed actions, rather than evidence that those actions have already worked.

Young explorerScientists use computer programs to help them do their work. But they do not always clearly say which programs they used or who made them. That can make it harder for other scientists to do the same work and can leave the program makers without credit. After a group discussion, the authors suggest clearer rules and easier ways to give credit. They think the people who help publish research can do a lot to help. These are ideas for making things better, not changes they have already shown to work.

Markov Chain Monte Carlo for Bayesian Parametric Galaxy Modeling in LSST

James J. Buchanan, Michael D. Schneider, Kerianne Pruett+1 more

AstronomerThe authors apply MCMC to parametric galaxy modeling for more than 100,000 coadded galaxy images from DC2, a simulated survey resembling Rubin Observatory’s LSST. The analysis is restricted to truly unblended galaxies detected as single objects. Using a physically informed prior and selection-corrected likelihood, they estimate posterior distributions for properties including ellipticity and brightness and systematically assess posterior bias and calibration. The resulting samples support probabilistic inference of model parameters and uncertainties, including for low-signal-to-noise galaxies often excluded from cosmological analyses. The modeling and inference are implemented in the freely available Joint Image Framework (JIF). These findings concern simulated images and do not establish performance for blended galaxies.

PublicResearchers tested a statistical method for estimating galaxy shapes and brightnesses, along with how uncertain those estimates are. They analyzed more than 100,000 combined galaxy images from DC2, a simulated telescope survey designed to resemble Rubin Observatory’s LSST. Their method uses physically informed assumptions and accounts for how galaxies are selected for analysis; they also examined whether its estimates were biased and its uncertainties well calibrated. It supports estimates even for galaxies whose signals are weak compared with image noise, which are often left out of cosmological studies. The test included only galaxies that did not overlap with others and were detected as single objects. The researchers made their modeling software, JIF, freely available.

Young explorerScientists used more than 100,000 pretend pictures of galaxies to test a computer tool. The tool estimates how bright each galaxy is and how stretched its shape looks, while showing how unsure it is. It can help even when a galaxy is hard to see clearly in a messy picture. They only tested galaxies that were separate from other galaxies and found as one object. They also shared the tool so other people can use it.

Selective state space model for photon energy estimation in microwave kinetic inductance detectors

Benjamin A. Mazin

AstronomerMKIDs measure individual photon energies and arrival times, but their energy resolving power, R = E/ΔE, is constrained by violations of the stationary-noise, linear-response, and energy-independent-pulse assumptions underlying Wiener optimal filtering. Venom is a Mamba-based selective state space model with 3,314 trainable parameters that replaces the coordinate transform and optimal filter by processing raw in-phase/quadrature timestreams. Training uses synthetic pulses generated through streaming principal component analysis, sampling energies continuously between calibration wavelengths. All reported performance is evaluated on a stratified 15% held-out validation set, with R derived from kernel density estimates. For an InHf bilayer resonator calibrated at ten wavelengths spanning 254–1310 nm, one Venom model achieves mean R = 26.4, versus 24.2 for ten published per-wavelength filter templates, a 9% improvement. Its R = 38.6 at 254 nm is reported as a record for an ultraviolet-to-near-infrared MKID suitable for dense arrays. For a PtSi resonator calibrated at five wavelengths spanning 808–1310 nm, Venom matches the published shared-920-nm-template baseline: mean R = 9.1 versus 8.8 at the three interior wavelengths. Deployment on MKIDGen3 and future system-on-chip readouts is a target, not a demonstrated result.

PublicMicrowave Kinetic Inductance Detectors, or MKIDs, are superconducting detectors that record both the energy of each incoming light particle and when it arrives. The usual method for estimating energy relies on assumptions these detectors do not fully satisfy. The researchers introduce Venom, a compact neural-network model that works directly with the detector signals. To supplement small calibration datasets, they train it using synthetic signals representing photon energies between the calibration points. In tests on a held-out 15% of the data, Venom improved average energy resolving power by 9% for one InHf detector, replacing ten wavelength-specific filters with a single model. At 254 nanometers, the researchers report the highest resolving power yet recorded for an ultraviolet-to-near-infrared MKID suitable for a dense detector array. On a second detector, made with PtSi, Venom performed comparably to the existing method rather than showing the same improvement. These are validation results for the tested detectors; operation on the intended readout hardware remains a development goal.

Young explorerThese special detectors notice tiny bits of light and measure how much energy each bit has and when it arrives. Scientists made a new computer helper called Venom to read the detector signals. They taught it using pretend signals, then tested it on data kept aside. For one detector, it told light energies apart better than the old method. For another detector, it did about as well as the old method. The scientists hope to put the helper into the equipment that reads the detectors, but they have not shown that step yet.

ArxSP: A Python-Based Modular Application for the Reduction of Digitized Archival Spectra

Ildana Izmailova, Adel Umirbayeva, Manas Khassanov+2 more

• Astrophysics of Galaxies

AstronomerThe authors present a reduction methodology and an interactive Python/PyQt5 package for archival photographic spectra, primarily those recorded with electron-optical converters. These data have geometric distortions caused by the registration system’s magnetic field and require conversion from photographic optical density to relative intensity, tasks the abstract states cannot be handled by standard packages such as IRAF. The software retains and extends the logic of FAI’s legacy Microsoft QuickC reduction program, which is incompatible with modern operating systems. Implemented operations include rotation, cropping, geometric correction, construction of the optical-density–intensity characteristic curve, and direct conversion of object-spectrum pixel values. The Fesenkov Astrophysical Institute archive contains about 10,000 photographic plates. The authors describe the package as enabling reproducible, cross-platform reduction with scope for future extensions; the abstract provides no quantitative accuracy tests or scientific results from reduced spectra.

PublicThe authors have developed software to help process old photographic records of spectra, which show how light is spread across different wavelengths. Their main target is records made with electron-optical converters, whose recording systems introduce magnetic-field-related distortions. Processing these records also requires translating the darkness of the photographic material into relative light intensity. The Fesenkov Astrophysical Institute holds about 10,000 photographic plates, and its older processing program no longer works on modern operating systems. The new Python software offers an interactive interface for rotating and cropping images, correcting distortions, and converting photographic darkness into intensity. The authors describe it as a reproducible tool that works across operating systems, but the abstract does not report numerical tests of its accuracy or new astronomical discoveries.

Young explorerSome old astronomy pictures show light spread into a pattern, like a rainbow. The machine that made some of these pictures bent the pattern out of shape, and the dark marks on the pictures need to be turned into information about how strong the light was. The authors made a new computer program to help straighten the patterns and read those marks. It replaces an old program that does not work on modern computers. This work is about making old pictures easier to use, not about finding a new star or planet.