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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 31 March

High Energy Astrophysical Phenomena

Traces of Helium Detected in Type Ic Supernova 2014L

Jing Lu, Wolfgang E. Kerzendorf, John T. O'Brien et al. (+6 more)

The absence of helium features in optical spectra is one of the classification criteria for Type Ic supernovae (SNe Ic). However, it is highly debated whether helium is truly absent in ejecta or spectroscopically undetectable in the optical region. The near-infrared (NIR) region contains cleaner He lines that are less blended with other common ions in SNe Ic ejecta. We perform full spectral modeling on the near-peak-light optical and NIR spectra of the SN Ic 2014L to quantitatively constrain helium and other outer-ejecta properties, using the radiative transfer code TARDIS. We employ a deep-learning emulator for SNe Ic spectra that serves as a fast surrogate for TARDIS simulations. We then integrate the emulator within the Bayesian inference framework to infer the ejecta properties. The emulator achieves a mean fractional error of 1% between the emulated and TARDIS fluxes across all wavelengths and all samples in the test dataset. We constrain 0.018 to 0.020 M_sun (16% to 84% posterior percentile) of He above the photosphere near peak light in SN 2014L, inferred from the observed spectra covering 3500A to 24000A. A Bayesian statistical test shows that the observed spectra are inconsistent with no helium. Furthermore, the posterior favors a power-law density exponent of -7.04 to -6.88 (16% to 84% credible interval), consistent with theoretical calculations of radiation-dominated explosions. This work demonstrates that Bayesian radiative-transfer inference over a wide wavelength range provides a powerful path toward systematic constraints on He in SNe Ic.
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All authors Jing Lu, Wolfgang E. Kerzendorf, John T. O'Brien, Maryam Modjaz, Jared A. Goldberg, Nutan Chen, Erin Visser, Joshua V. Shields, Andrew G. Fullard

Solar and Stellar Astrophysics

Formation of dust grains in the winds of cool giants, PhD thesis 1992

C. Dominik

Interstellar dust forms during stellar mass-loss events, occurring either during a star's giant phase or during supernova explosions. This PhD thesis provides an in-depth investigation into the theory of dust condensation and growth, specifically applied to the winds of cool giants such as Asymptotic Giant Branch (AGB) stars. The thesis begins with a theoretical description of the chemical reactions that initiate seed formation within a cooling flow. It then details an efficient mechanism - a moment method based on size-weighted moments of the grain size distribution - to compute dust evolution during growth. This theoretical framework is applied to dust-driven winds from carbon-rich AGB stars. By deriving wind equations and self-consistently incorporating dust formation, the research demonstrates that radiation pressure on dust forming in the expanding atmosphere can drive a stellar wind. Furthermore, a parameter study covering the giant region of the Hertzsprung-Russell (HR) diagram is used to derive mass-loss formulas for these winds. The final chapter expands the dust formation theory to investigate the condensation of heterogeneous grains.
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Instrumentation and Methods for Astrophysics

Pegasi Ascendant: Ranking Constellation Genitives on their Aesthetic Merit

Pranav Nagarajan

Despite their ubiquity in the astronomical literature, there is no consensus tier list of the genitive forms of the 88 constellations officially recognized by the International Astronomical Union. To address this pressing open question, I conduct an anonymous pair comparison survey of 74 professional astronomers to rank these constellation genitives on their aesthetic merit. After each survey response, I use active sampling to select a new set of pair comparisons that maximizes expected information gain, and update overall scores based on a fully Bayesian framework. I find that Pegasi is the most aesthetically pleasing constellation genitive overall, narrowly edging out Centauri and Andromedae. While most astronomers self-report Orionis to be their top choice before taking the survey, this well-recognized constellation genitive only places seventh in the final ranking. Gruis, meanwhile, receives the dubious honor of last place. When breaking down the ranking by career stage, I find tentative evidence for generational differences in aesthetic taste. A larger sample of faculty members is needed to confirm this result. Finally, I offer unsolicited commentary on the phonetic appeal and cultural significance of the genitives ranked in the top and bottom five.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Does a wormhole survive a cosmological bounce?

Daniela Pérez, Gustavo E. Romero and Santiago E. Perez Bergliaffa

We investigate whether a dynamical wormhole could survive in a universe that undergoes a cosmological bounce. First, the conditions under which a wormhole could persist from a contracting to an expanding phase of the cosmos are presented. Then, the only two known cosmological solutions of Einstein's equations representing wormholes are analyzed, and it is shown that both dynamical wormholes exist for all cosmic times on both sides of a bouncing universe and at the bounce itself. We also provide a detailed analysis of the causal structure of such spacetimes and the matter content of the wormhole. Finally, some possible astrophysical manifestations of surviving wormholes in a bouncing universe are mentioned. Our results show that, at least for the Kim and Pérez-Raia Neto solutions, there is no topology change in the chosen cosmological model with a bounce.
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Astrophysics of Galaxies

The Star Formation Factory revisited I. The impact of metallicity on collapsing star-forming clouds

S. Jiménez, D. Kománek, R. Wünsch et al. (+4 more)

Context. Stellar feedback regulates star formation and shapes the interstellar medium, yet its role during the collapse of molecular clouds remains uncertain over a wide range of initial conditions. Aims. We explore how stellar winds and supernovae influence star formation in collapsing gas clouds that span a broad parameter space in mass, size, and metallicity. Methods. Using a one-dimensional numerical model, we follow the evolution of feedback-driven bubbles produced by embedded clusters, incorporating time-dependent energy and mass injection, self-gravity, integrated cloud collapse, radiative cooling, shell instabilities, and triggered star formation. Our treatment of gas cooling in the hot bubble explicitly accounts for heat transfer across the bubble-shell interface. Results. We find that metallicity acts as a key regulator of feedback, comparable in importance to cloud mass and radius. In low-metallicity clouds, reduced radiative cooling is offset by weaker stellar winds, leading to prolonged star formation and higher efficiencies. Across a substantial portion of parameter space, the expanding shell undergoes a stalling phase that further enhances the star formation efficiency, an outcome that is not observed at higher metallicities. Conclusions. Our results suggest that the diverse properties of star clusters across cosmic time may arise from the metallicity-dependent interplay between stellar feedback and gas cooling.
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All authors S. Jiménez, D. Kománek, R. Wünsch, J. Palouš, S. Ehlerová, S. Martínez-González, A. Srbljanović

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Lectures on Light Particles and Compact Objects

Alessandro Lella and Jamie McDonald

This document is based on lectures delivered at a recent COSMIC WISPers COST Action training school in Annecy in September 2025. They examine detection of weakly interacting slim particles (WISPs), specifically axions and high-frequency gravitational waves, with compact objects. These slightly expanded notes focus on searches for axion dark matter and axion-like particles with neutron stars, superradiance, white dwarfs and astrophysical searches for high-frequency gravitational waves. They are accompanied by a set of practical exercises. Comments on these notes are gratefully received.
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Cosmology and Nongalactic Astrophysics

Eppur non si trovano Vol. 2: No Planetary-mass Primordial Black Holes toward the Andromeda Galaxy

Przemek Mróz and Andrzej Udalski

A recent preprint by Sugiyama et al. reported the discovery of twelve candidates for short-timescale (less than one day) gravitational microlensing events based on high-cadence photometric observations of the Andromeda Galaxy (M31) using the Subaru Hyper Suprime-Cam. These detections were attributed to a large population of planetary-mass primordial black holes (PBHs) that could account for the entirety of the dark matter in the Milky Way and M31 halos. However, these results are in clear tension with previous searches for short-timescale microlensing events toward the Magellanic Clouds, such as those by the OGLE survey. In addition, both the temporal and spatial distributions of the Subaru candidates are inconsistent with expectations for microlensing events. Here, we reanalyze the Subaru data using an independent difference image analysis photometric pipeline. We find that all twelve candidates identified by Sugiyama et al. exhibit asymmetric light curves and/or variability on multiple nights of Subaru observations. Our analysis reveals that among them ten objects are RR Lyrae stars, one is an eclipsing binary, and one is an unclassified variable star. We find no compelling evidence for short-timescale microlensing events among the candidates identified in the Subaru data set, nor for a significant population of planetary-mass PBHs as dark matter components. Our results underscore the necessity of robust variable-star rejection in high-cadence microlensing searches using large telescopes.
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Astrophysics of Galaxies

The Impact of Seyfert Jets on Galaxy Evolution Across Major Scaling Relations

Julianne Goddard, Isaac Shlosman and Emilio Romano-Diaz

We analyze a suite of high-resolution cosmological zoom-in simulations of jetted Seyfert galaxies over $z\leq10$ projected on the major scaling relations, comparing trajectories of `normal' versus jet-hosting galaxies. Models include thermal and mechanical jet feedback launched from supermassive black holes (SMBHs) seeded at $z\sim9.1$ and $z\sim3.7$ with $M_\bullet\sim10^6\,M_\odot$ in galaxies within dark matter halos of ${\rm log}\,M_{\rm halo}/M_\odot\sim11.8$ at $z=0$. A single parameter, the SMBH accretion efficiency, has been varied resulting in $L_{\rm jet}\sim10^{40-42}\,{\rm erg\,s^{-1}}$, and SMBH accretion rates range between $\sim 0.2-10^{-4}$ of the Eddington rate. We find that jet feedback (1) suppresses central star formation rates (SFRs), redistributes gas to larger radii, (2) generates long-lived expanding shocks that couple to the ISM and CGM, (3) reduces stellar mass ($M_*$), shifting galaxies toward lower central concentrations, and (4) alters host trajectories on the $M_{\rm halo}-M_*$, specific SFR$-M_*$, $M_\bullet-\sigma_{\rm bulge}$, Mass$-$Metallicity, Kennicutt-Schmidt, and baryonic Tully-Fisher relation planes. Specifically, we find that jetted Seyferts live longer in the green valley and more frequently move to the quenched region in comparison to the non-jetted galaxies. Despite producing only transient quenching, Seyfert jets cause persistent structural, kinematic and chemical signatures, including flatter rotation curves, elevated CGM metallicities, and reduced cold gas clumping. (5) Early SMBH seeding and stronger jets amplify these effects, yielding galaxies that lie systematically closer to some of the empirical relations, e.g., $M_{\rm halo}-M_*$, while showing offsets for others, e.g., Kennicutt-Schmidt, and demonstrating that low-luminosity Seyfert jets can exert a significant long-term influence on galaxy evolution.
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High Energy Astrophysical Phenomena

Generalized Predictions for the Electromagnetic Signatures of Mirror Stars

Franco Cabral, Stuart Williamson, David Curtin et al. (+1 more)

Mirror Stars are a generic prediction of dissipative dark matter models, including minimal atomic dark matter and twin baryons in the Mirror Twin Higgs. Mirror Stars capture regular atoms from the interstellar medium through highly suppressed kinetic mixing interactions between the regular and the dark photon. This results in the accumulation of a "nugget", which draws heat from the mirror star core and emits distinctive X-ray and optical signals. In this work, we solve the stellar structure equations of optically thick nuggets across a wide range of the effective mirror star parameter space, and characterize their emission spectra using stellar atmosphere models. This complements an earlier analysis of lower-mass optically thin nuggets. We find that optically thick mirror star nuggets occupy distinct regions of the (stellar surface temperature, luminosity, surface gravity) space, and can be distinguished from regular stars in both HR diagrams and temperature-surface-gravity diagrams using astrometric and spectroscopic stellar catalogues. Our detailed predictions, which are publicly available, now give for the first time a general picture of mirror star signals in the optical and IR to enable realistic mirror star searches using existing catalogues and new telescope observations.
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All authors Franco Cabral, Stuart Williamson, David Curtin, Christopher D. Matzner

Instrumentation and Methods for Astrophysics

Optimisation of calibration sources for global 21-cm experiments: the REACH case

Adarsh Kumar Dash, Dominic Anstey, Harry T. J. Bevins et al. (+41 more)

The spin-flip 21-cm signal from the Cosmic Dawn and the Epoch of Reionization is an essential probe of the conditions that led to the formation of the first luminous objects in the early Universe. However, its detection remains a major challenge owing to its low strength compared to the bright foregrounds and the requirement of precise calibration of the instrument to prevent systematics that could hinder a detection or lead to false inferences. REACH (Radio Experiment for the Analysis of Cosmic Hydrogen) is a radiometer experiment designed to detect this sky-averaged signal in the frequency range of 50–130~MHz. Using a wide-beam antenna, REACH calibration relies on internal reference sources, covering a broad range of temperatures and reflection coefficients. The choice of type and number of calibrators used significantly influences the quality of the calibration. This work investigates these effects and introduces a novel method for selecting an optimal set of calibration sources. With an optimised set, we aim to reduce calibration time, thereby increasing sky integration time while preserving calibration accuracy. We explore two optimisation strategies: one applied across the full receiver band and another performed on a frequency-by-frequency basis. Finally, we demonstrate that, with a total calibration time comparable to the conventional full-calibrator set, an optimised set with fewer calibrators achieves approximately a $15~\%$ reduction in calibrated temperature noise and improved absolute calibration of the instrument. This has implications for better calibration strategies in similar radiometer experiments.
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All authors Adarsh Kumar Dash, Dominic Anstey, Harry T. J. Bevins, Eloy de Lera Acedo, Gary Allen, Kaan Artuc, Gianni Bernardi, Martin Bucher, Steve Carey, Jean Cavillot, Ricardo Chiello, Adelicia S. Chu, Wessel Croukamp, John Cumner, Saswata Dasgupta, Dirk I. L. de Villiers, Jiten Dhandha, Aleksandra Dragovic, John A. Ely, Anastasia Fialkov, Thomas Gessey-Jones, Will J. Handley, Christian Kirkham, Girish Kulkarni, Samuel A. K. Leeney, Alessio Magro, P. Daan Meerburg, Shikhar Mittal, Daniel Molnar, Rohan S. Patel, Joe H. N. Pattison, Saurabh Pegwal, Carla M. Pieterse, Jonathan R. Pritchard, Gabriella Rajpoot, Nima Razavi-Ghods, Daniel Robins, Ian L. V. Roque, Anchal Saxena, Killian H. Scheutwinkel, Emma Shen, Peter H. Sims, Marta Spinelli, Jiacong Zhu

Astrophysics of Galaxies

The Kormendy Relation in the First Billion Years: Evidence from $JWST$

Anshuman Borgohain and Kanak Saha

Galaxy scaling relations encode key information about the structural, dynamical, and mass assembly histories of galaxies, and provide constraints on galaxy formation models as well as the onset of galaxy assembly. While these relations are well characterized out to intermediate redshifts, their existence during the first billion years of cosmic history remains largely unconstrained due to observational limitations. In this work, we investigate the Kormendy relation (KR) for spheroidal systems at $z~\ge~6$ using rest-frame $B$-band structural parameters derived from publicly available deep JWST imaging of the GOODS, CEERS, PRIMER-UDS, and PRIMER-COSMOS fields. We find that spheroidal galaxies at these epochs already occupy a well-defined locus in the mean effective surface brightness $(\langle~\mu_{\rm e}~\rangle)$ and effective radius ($\rm~R_{\rm e}$) plane, demonstrating that a KR is already in place when the universe was less a gigayear old. The best-fit relation has a slope of $\beta~=~4.25^{+0.40}_{-0.39}$ and a zero-point of $\alpha~=~15.89^{+0.17}_{-0.17}$, indicating a steeper relation and systematically higher surface brightness compared to the local relation. This steepness reflects the compact sizes and high central stellar-mass densities of these systems, consistent with rapid, dissipative assembly in environments with high gas fractions, likely driven by efficient gas inflows, and gas-rich mergers. The presence of dense bulges embedded in some of these galaxies at similar redshifts further supports a common formation pathway for both bulges and spheroids. Altogether, these findings indicate a predominantly dissipative mode of assembly for the first spheroidal systems which may evolve into the compact quiescent galaxies observed at later cosmic epochs.
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High Energy Astrophysical Phenomena

Searching for unresolved massive black hole pairs through AGN photometric variability

Lorenzo Bertassi, Maria Charisi, Fabio Rigamonti et al. (+2 more)

Since their discovery, AGN light curves are known to be intrinsically variable. In the optical/UV band, this variability is consistent with correlated or red noise and is particularly well described by the damped random walk (DRW) model. In this work, we evaluate the feasibility of a new method for identifying spatially unresolved couples of AGN through a fully Bayesian time-domain analysis of the observed light curves (LCs). More specifically, we check whether observed LCs are better described by a single DRW, which we interpret as emitted by a single massive black hole (MBH), or a pair of independent DRWs, generated by a pair of MBHs. We test the method on mock LCs associated with a single MBH and pairs generated with different cadences and lengths of observational campaigns. We constrained the occurrence of false positives, that is, the percentage of single MBH LCs that show substantial evidence in favour of the unresolved MBH pair scenario, finding a fraction of 0.2% and 0.59% in the even and uneven sampling scenarios. We discuss how well the method recovers the model parameters, showing that about 51% and 7% of the simulated LCs have all the recovered parameters within 20% of their true values in our best scenario of evenly sampled LCs for the single MBH and MBH pair scenarios, respectively. We finally study the region of the parameter space in which the detection of an MBH pair is possible, finding that such objects can be correctly identified if the timescales of the process describing the noise are very different, with a ratio smaller than ~0.2, and the variability amplitudes are similar, with their ratio bigger than ~0.2. When limiting to such a region of the parameter space, the fraction of pairs with all the recovered parameters within 20% of the injected values increases up to about 14% and 8% for evenly and unevenly sampled LCs, respectively.
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All authors Lorenzo Bertassi, Maria Charisi, Fabio Rigamonti, Stefano Covino, Massimo Dotti

Astrophysics of Galaxies

Imladris: a detailed and flexible model for galaxy simulations with individual stars

Matthew C. Smith

Coupling stellar feedback to the evolution of individual stars, as opposed to averaging over the initial mass function (IMF), substantially improves the fidelity of galaxy formation simulations by capturing stochastic population effects. Existing treatments can typically only operate at a narrow mass resolution range, limiting their applicability. We present Imladris, a detailed model for star formation and stellar feedback with individual stars. At high resolution, each star can be represented by its own particle ("star-by-star"). At coarser resolution, star particles represent specific realisations of stellar populations sampled from the IMF. Both methods share a unified implementation of stellar feedback tied to the individually tracked stars, including supernovae, stellar winds and radiation. Imladris has been optimised for both computational efficiency and memory footprint. We demonstrate the model with idealised galaxy simulations ($M_\mathrm{vir}\sim10^{10}-10^{11}\,\mathrm{M_\odot}$) spanning a baryonic mass resolution range of $2.5-1000\,\mathrm{M_\odot}$. Without re-calibration, the time-averaged star formation rate (SFR), galactic wind mass and energy loadings close to the disc are converged up to a resolution of $20\,\mathrm{M_\odot}$ within a factor of 1.1, 1.1 and 1.3, respectively, and 1.4, 1.6 and 2.5 up to $100\,\mathrm{M_\odot}$. Above this, SFRs become more bursty, while loading factors increase substantially. This is linked to resolution-dependent supernova clustering, which represents a fundamental barrier to convergence for any scheme attempting to model a self-consistent stellar feedback-regulated interstellar medium. Regardless, the ability to deploy the scheme across a wide range of resolutions (and to carry out in-depth resolution convergence studies) makes Imladris a powerful tool for numerical investigations of galaxy formation.
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Astrophysics of Galaxies

The multi-age stellar populations of Terzan 5 as revealed by JWST

G. Zullo, C. Pallanca, F. R. Ferraro et al. (+10 more)

The James Webb Space Telescope provides an exciting opportunity to investigate stellar systems located in heavily obscured regions like the Galactic bulge. Possibly, the most enigmatic among them is Terzan 5: long classified as a globular cluster, it is now known to host distinct stellar populations with different iron abundances (ranging approximately from [Fe/H]=-$0.8$ to [Fe/H]=$+0.3$ dex). Indeed the chemical and structural properties collected so far suggest that it is the remnant of one of the primordial clumps that contributed to the early assembly of the bulge, a so-called "Bulge Fossil Fragment". Here we present a new photometric analysis of Terzan 5 based on JWST/NIRCam observations in the F115W and F200W filters, as well as archival HST/ACS optical (F606W and F814W) data. The dataset overcomes the severe and spatially variable extinction along the line of sight and yields the deepest color-magnitude diagram ever obtained for Terzan 5. Proper motion selections and high-resolution differential reddening corrections allow us to isolate bona fide cluster members and to provide an unprecedented view of the main-sequence turn-off region. We clearly identify two main components and determine their respective ages: the old, sub-solar component has an age of 12.5 $\pm$ 0.5 Gyr, while the super-solar component is significantly younger with an age of 4.7 $\pm$ 0.5 Gyr. Interestingly, we also find hints of an even younger main sequence turn-off and sub-giant branch, consistent with the presence of a further stellar component with an age of 3.8 $\pm$ 0.5 Gyr. There is also evidence of a blue plume populated by stars as bright as $m_{\rm F115W}\sim 17.4$, suggesting a prolonged period of star formation extending up to 2.5 Gyr ago.
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All authors G. Zullo, C. Pallanca, F. R. Ferraro, B. Lanzoni, L. Origlia, D. Massari, E. Dalessandro, C. Fanelli, M. Cadelano, E. Vesperini, C. Crociati, R. M. Rich, E. Valenti

Cosmology and Nongalactic Astrophysics

Lagrangian Bias as a Gaussian Random Field

Arka Banerjee

Halo bias is typically treated as a set of coefficients in a perturbative expansion. We show instead that every point in a Gaussian density field has a well-defined scale-independent Lagrangian bias, thereby defining a bias field. This property can be extended to any linear operator acting on the Lagrangian density field, generating secondary bias fields. Halo bias then arises from geometric selection of Lagrangian patches within this pre-existing field, rather than being generated by collapse. We demonstrate that this framework predicts the measured $b(M)$ relation for halos. The multivariate Gaussian structure of the fields naturally explains the Gaussian distribution of halo bias at fixed mass and assembly bias. The results presented here motivate combining this framework with a forward model of halo collapse, yielding an ab initio model for halo clustering.
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Astrophysics of Galaxies

Revealing the stellar population of the ultra-obscured Galactic globular cluster Glimpse-C02

M. Loriga, M. Cadelano, C. Pallanca et al. (+10 more)

In this paper, we present the results of a detailed photometric analysis of Glimpse-C02, one of the most extincted globular clusters of the Milky Way. We built a deep color magnitude diagram spanning $\approx$ 10 magnitudes, enabling the first identification of the cluster's main sequence turnoff. Due to the extreme reddening affecting the region, a differential reddening correction was necessary. The resulting reddening map reveals variations up to $\delta E(B-V) \approx 2.5$ mag. From isochrone-fitting of the differential reddening corrected color-magnitude diagram, we derived a mean color excess $E(B-V)=6.33^{+0.05}_{-0.04}$, and a distance modulus $(m-M)_0=14.00^{+0.26}_{-0.11}$, corresponding to a distance of $d=6.3^{+0.8}_{-0.3}$ kpc from the Sun, and a Galactocentric distance of $2.6^{+0.6}_{-0.7}$ kpc. This distance value, within the associated uncertainties, suggests that the cluster may be located closer to the Galactic Center compared to previous estimates, possibly supporting its classification as a bulge globular cluster. We obtained a photometric metallicity estimate of [Fe/H]$=-0.30^{+0.10}_{-0.08}$ and the first absolute age determination for Glimpse-C02, resulting in $t=11.9^{+0.7}_{-0.6}$ Gyr, as typically measured for Galactic globular clusters at this metallicity. We also derived a new estimate of the center of gravity of the cluster and determined its projected density profile from resolved star counts, finding a high King concentration parameter ($c = 1.97_{-0.67}^{+0.51}$) and a core radius $r_c =8.72^{+0.40}_{-0.35}$ arcsec. Finally, from the surface brightness profile of the system, we derived an integrated $H$-band magnitude $M_{\rm H}=-7.9$, corresponding to a mass of $M=3.57^{+0.22}_{-0.19}\times 10^4 M_{\odot}$. Thus, our work classifies Glimpse-C02 as an old and metal-rich globular cluster that is in an advanced stage of its dynamical evolution.
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All authors M. Loriga, M. Cadelano, C. Pallanca, F. R. Ferraro, B. Lanzoni, L. Chiappino, C. Crociati, E. Dalessandro, C. Giusti, S. Leanza, D. Massari, L. Origlia, E. Vesperini

High Energy Astrophysical Phenomena

A Solar Probe of Dark Matter Decay in the Galaxy

Maximilian Detering and Shyam Balaji

Dark matter (DM) particles decaying in the Galactic halo can inject energetic $e^\pm$ that inverse-Compton scatter (ICS) solar photons into $\gamma$-rays, producing a diffuse and extended halo of emission around the Sun. We present the first quantitative study of this signal as an indirect probe of decaying DM. The intense solar photon field in the inner heliosphere amplifies the inverse-Compton emissivity by many orders of magnitude relative to the interstellar radiation field, making the Sun an unusually sensitive local converter of sunlight into $\gamma$-rays via scattering with injected $e^\pm$. Using 15 years of Fermi-LAT solar-halo data, we derive stringent limits on the DM lifetime for 10 GeV-10TeV masses at the level of $\tau_\chi \sim 10^{27}\,\mathrm{s}$ in leptonic decay channels. The predicted surface brightness rises steeply toward the Sun, and the $\gamma$-ray flux falls off at high energy due to Klein-Nishina suppression. Solar ICS $\gamma$-rays measured with degree scale angular resolution therefore provide a novel and complementary probe of DM decays, adding a local $\gamma$-ray search channel that is systematically distinct from both Galactic diffuse analyses and direct charged-particle measurements.
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Cosmology and Nongalactic Astrophysics

Non-Cold Dark Matter from Memory-Burdened Primordial Black Holes

Valentin Thoss, Laura Lopez-Honorez, Florian Kühnel et al. (+1 more)

Non-cold dark matter particles can arise from the evaporation of primordial black holes (PBHs). In this paper, we further investigate how the memory-burden effect, which delays the full evaporation of black holes, affects the Lyman-$\alpha$ bound on such non-cold dark matter (NCDM) particles. We mainly focus on scenarios in which PBHs have fully evaporated by today, undergoing a semi-classical evaporation phase followed by a memory-burden dominated phase. In this framework, PBH evaporation generically leads to two distinct dark-matter populations with different velocity dispersions, which can imprint observable signatures on the matter power spectrum. We compute the resulting NCDM phase-space distribution and its impact on small-scale overdensities using the $\texttt{BlackHawk}$ and $\texttt{CLASS}$ codes. This is then used to reinterpret Lyman-$\alpha$ forest constraints for thermal warm dark matter, deriving both a velocity-dispersion-based and a matter-power-spectrum-based estimate. In particular, we discuss how we obtain constraints on scenarios in which NCDM particles constitute only a fraction of the total relic dark matter. Finally, we discuss the viable parameter space as a function of dark matter masses, PBH initial conditions, and memory-burden parameters. We show that even subdominant NCDM components from PBH evaporation can be constrained, and confirm that NCDM can only account for all of the dark matter in the absence of PBH domination, as in the semi-classical case.
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All authors Valentin Thoss, Laura Lopez-Honorez, Florian Kühnel, Marco Hufnagel

Astrophysics of Galaxies

Large Scale Structure and Environmental Effects on Dwarf Galaxy Growth

Mac M. McMullan, Sownak Bose, Azadeh Fattahi et al. (+3 more)

Dwarf galaxies serve as key models for understanding galaxy assembly in the early universe, with their final properties influenced by environmental factors. Using the dark matter-only simulation "Copernicus Complexio" (COCO) and the semi-analytic model GALFORM, we examine the stellar mass assembly of dwarf galaxies across different cosmic web regions, defined by the NEXUS+/CACTUS algorithm. We identify significant variations in stellar mass assembly based on final mass, with the largest dwarf galaxies assembling, on average, 50% of their mass 7.7 Gyrs later than the smallest ones. Central galaxies also differ in their assembly from satellites of comparable final mass, forming 50% of their mass 2.5 Gyrs later. The location within the cosmic web further influences assembly, with satellite galaxies showing greater differences than centrals. Satellites in the densest regions assemble their mass 1.5 Gyrs earlier than those in the least dense regions, compared to 0.69 Gyrs for central galaxies. This disparity arises from varying infall times, with satellites in dense environments infalling 5.2 Gyrs earlier than those in voids. Additionally, we investigate the impact of reionisation parameters, specifically the timing ($z_{cut}$) and filtering scale ($v_{cut}$) of reionisation. The stellar-to-halo-mass relation shows a power law break between $10^8~\mathrm{M}_\odot < M_{200} < 10^{10}~\mathrm{M}_\odot$, with earlier $z_{cut}$ or higher $v_{cut}$ leading to more star formation suppression in lower-mass haloes. The halo occupation fraction is also affected, with later $z_{cut}$ or lower $v_{cut}$ resulting in fewer lower-mass haloes being occupied at $z=0$. Our investigation provides a valuable theoretical framework for interpreting upcoming observational data in this mass regime.
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All authors Mac M. McMullan, Sownak Bose, Azadeh Fattahi, Isabel Santos-Santos, Wojciech A. Hellwing, Tilly A. Evans-Hofmann

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Big Bang revisited

Frans R. Klinkhamer

The Friedmann cosmological solution of the standard Einstein gravitational field equation has a curvature singularity at a moment in time known as the Big Bang. It has been suggested that this Big Bang curvature singularity can be eliminated by use of a degenerate spacetime metric. This proposal was the main topic of our talk at the Workshop, but, here, we also discuss the possible appearance of CPT-conjugated worlds and the conjectured relevance of an extended version of Einstein's field equation.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Wormhole Dynamics: Nonlinear Collapse and Gravitational-Wave Emission

Nikita M. Shirokov

We present 3D numerical-relativity evolutions of the unstable Ellis-Bronnikov wormhole using GRTeclyn, starting from exact isotropic initial data for the coupled Einstein-phantom-scalar system. With a flat initial lapse (alpha=1) and full phantom support, truncation-level noise eventually drives the rarefactive instability and rapid throat expansion. To force a clean collapse while breaking spherical symmetry, we reduce the phantom stress-energy support to S_support=0.5 and add a quadrupolar scalar-field perturbation (A_phi=+0.02, sigma_phi=0.5). The resulting compressive evolution forms a trapped surface and emits a gravitational-wave signal whose peak propagates between extraction radii at v approx c, distinct from superluminal CCZ4 constraint modes. After horizon formation the swallowed phantom matter triggers a violent rebound ("phantom bounce") that launches an outward curvature shock. For the moderate perturbation amplitude simulated here, an intermediate-mass (10^3 solar mass) wormhole at D=1 Mpc falls slightly below the Advanced LIGO design sensitivity; detection requires either closer sources, larger initial asymmetries, or next-generation detectors.
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Instrumentation and Methods for Astrophysics

Independent Replication of Nuclear Test-Transient Correlations and Earth Shadow Deficit in POSS-I Photographic Plates

Brian Doherty

Transient sources on astronomical photographic plates are objects that appear on a single exposure but have no counterpart in modern sky surveys or on temporally adjacent plates. I present an independent replication of two findings reported by Bruehl and Villarroel (2025) and Villarroel et al. (2025): (1) a temporal correlation between transient detections on Palomar Observatory Sky Survey (POSS-I) photographic plates and atmospheric nuclear weapons tests, and (2) a deficit of transient sources within Earth's geometric shadow cone at geosynchronous orbit altitude. Using the original dataset provided by the authors, I reproduce the chi-square contingency analysis (relative risk = 1.45, p = 0.011), extend the analysis with negative binomial regression controlling for precipitation, lunar illumination, and cloud cover (all-transient incidence rate ratio = 1.80; sunlit-only IRR = 3.98, reproducing the original paper's reported findings), and confirm temporal specificity of the association via a 10,000-iteration permutation test (p = 0.006). The Earth shadow classification identifies 499 transients (0.46%) within the umbral cone in the full catalog and 142 (0.45%) in the more stringent center-of-plate subset, both significantly below the geometric expectation of approximately 1.4%, consistent with the findings of Villarroel et al. (2025). All transients predate the launch of Sputnik 1. These results confirm the core statistical claims of the original papers based on an independent analysis.
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Instrumentation and Methods for Astrophysics

The WEAVE acquisition and guiding software: pattern recognition-based acquisition and multi-fibre guiding

Emanuel Gafton, Gavin B. Dalton, Don Carlos Abrams et al. (+19 more)

We present the architecture, implementation, and on-sky validation of the fully automated acquisition and guiding system (AG) developed for the WEAVE instrument on the William Herschel Telescope. The AG operates in two distinct modes, corresponding to the observing modes of WEAVE. For the large integral field unit (LIFU), an off-axis imaging guider is used, for which we have devised an automatic acquisition method based on pattern recognition of stellar asterisms matched against Gaia predictions. For the multi-object spectrograph (MOS) and the mini-integral field units (mIFU), a multi-fibre guider uses up to eight coherent image guide fibre bundles to derive and apply continuous corrections in azimuth, altitude, and rotation. The system performs complete astrometric calculations, including atmospheric differential refraction and instrument flexure, for each guide frame, enabling accurate target placement and stable closed-loop guiding in all configurations. To support development, commissioning, and operational validation, we have also built a high-fidelity simulation mode that reproduces the behaviour of the telescope control system and of the AG cameras, and we release the standalone camera simulator as open-source software. Using two years of routine WEAVE operations spanning commissioning and early survey phases, we present a statistically robust characterization of AG performance, demonstrating that both modes meet design requirements and are ready for sustained survey operations.
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All authors Emanuel Gafton, Gavin B. Dalton, Don Carlos Abrams, Jure Skvarč, Sergio Picó, Lilian Domínguez-Palmero, Illa R. Losada, Sarah Hughes, Neil O'Mahony, Frank J. Gribbin, Andy Ridings, David L. Terrett, Cecilia Fariña, Chris R. Benn, Esperanza Carrasco, P. Joel Concepción Hernández, Kevin Dee, Rafael Izazaga, Shoko Jin, Ian J. Lewis, J. Alfonso L. Aguerri, Gonzalo Páez

Astrophysics of Galaxies

An inverted infall profile for the collapse of the massive star-forming IRDC SDC335.579-0.292

Jinjin Xie, Gary A. Fuller, Di Li et al. (+8 more)

There is increasing evidence for global collapse of clumps over parsec-scales in massive star formation regions. Such collapse may result in characteristic molecular line emission profiles but the spatial variation of such lines has rarely been quantitatively examined. Here we explore the infall properties using the spatially-resolved HCO$^+$ J=1–0 and H$^{13}$CO$^+$ J=1–0 maps of the massive infrared dark cloud (IRDC) SDC335.579-0.292. We compare the observations with the analytical Hill5 model and radiative transfer models. This shows that the best-fit infall velocity towards the cloud centre to be well-constrained to $-0.6$ to $-1.6$ km s$^{-1}$ and the mass infall rate between a few $\times10^{-3}$ and $10^{-2}$ M$_{\odot}$yr$^{-1}$. The comparison also highlights some limitations of the Hill5 method. We demonstrate that the width of optically thin spectral lines, which are usually interpreted as resulting from turbulent motions, are in fact dominated by unresolved, ordered infall motions within the beam. Our results suggest a complex collapse situation where there is a minimum in the infall velocity at $\sim2\times10^{18}$ cm (0.7 pc) with the infall velocity increasing at both smaller and larger radii. The parsec-scale infall with an inverted velocity profile indicates that the accretion in this massive star-forming cloud should have intermediate scales, at which fragmentation or filament formation has to occur before material flows onto the cloud centre.
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All authors Jinjin Xie, Gary A. Fuller, Di Li, Rowan Smith, Nicolas Peretto, Jingwen Wu, Yongxiong Wang, Yan Duan, Jifeng Xia, Jarken Esimbek, Willem A. Baan

Instrumentation and Methods for Astrophysics

Enabling fundamental understanding of Nature with novel binning methods for 2D histograms

Igor Vaiman

Context. Visualization of 2D distributions is an essential task, commonly done with a 2D histogram. The histogram is built by subdividing the sample space into regions and color-coding the number of samples in each region. Aims. We aim to solve long-standing problems with common 2D histogram methods: lack of thematic, visual, and conceptual unity with underlying data, and general stagnation in the field. Methods. We develop a new method for plotting 2D histograms with arbitrary bin shapes, including aperiodic tilings and geographic maps. We apply the method to several common plot types from the literature. Results. We find our method performs best across all tasks, solving the problems and propelling the scientific progress forward.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

What does the Universe sound like?

Francesco Iacovelli

Unlike electromagnetic telescopes, gravitational-wave (GW) detectors cannot produce pretty pictures, but we can convert GW signals into sound. I compute what the Universe actually sounds like by averaging over $\sim10^6$ synthetic compact binary coalescence events occurring throughout 2026. The result: a soothing, low-frequency rumble, perfect for sleeping, meditation, or contemplating the violent nature of spacetime. This is the $Universal\ harmony$, audio file included!
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Instrumentation and Methods for Astrophysics

The Hollyfeld Gambit in Astrophysics

Benne Holwerda

We estimate the Hollyfeld Gambit for the Powerball lottery and its return on investment compared to present and extrapolated federal funding for astrophysical grants. Using a Monte Carlo estimation of rate of return for the Powerball, we conclude a Hollyfeld Gambit is a better bet than a federal grant by the end of the decade if current trends hold.
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High Energy Astrophysical Phenomena

A Therapy Session with Sgr A*

Mayura Balakrishnan, Robert Frazier and Joseph Michail

The nature of Sagittarius A* (Sgr A*) has been the subject of intense study and debate for over half a century. Herein, we present the first successful interview with an astrophysical object, exploring the perspective of this supermassive black hole and, in doing so, challenging the traditional observational paradigm of astrophysics. Rather than treating astrophysical systems as purely passive entities characterized through indirect measurements, we introduce an interaction-based framework via a therapeutic-style interview enabled by the ARMCHAIR communication methodology. Using structured, psychotherapeutic dialogue, we probe Sgr A*'s responses to key aspects of its astrophysical characterization, including eating habits, its name, and concerns about privacy. These exchanges offer an alternative lens through which to interpret familiar observational phenomena. This work highlights potential limitations in strictly reductionist approaches and suggests a modest expansion of standard astrophysical methodology to leave room for considering how the objects we study might feel about the attention they receive.
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Cosmology and Nongalactic Astrophysics

Constraining Lyman-Werner Feedback from Velocity Acoustic Oscillations in the Cosmic Dawn 21 cm Signal

Xi Du, Bin Yue, Furen Deng et al. (+4 more)

During Cosmic Dawn, Pop III stars could be formed in minihalos through molecular hydrogen (H$_2$) cooling. The minimum halo mass required for H$_2$ cooling is highly sensitive to Lyman-Werner (LW) radiation, which dissociates H$_2$ and regulates star formation. However, the efficiency of LW feedback remains poorly constrained due to the lack of direct observations of Pop III stars. The dark matter-baryon relative streaming velocity suppresses star formation in low-mass halos and imprints characteristic Velocity Acoustic Oscillation (VAO) features in the 21 cm power spectrum. These features are particularly sensitive to the cooling threshold mass: if LW feedback raises the minimum halo mass above the streaming-sensitive regime, the VAO signal is strongly suppressed. This makes the VAO wiggles a promising indirect probe of LW feedback during Cosmic Dawn. We investigate the feasibility of constraining LW feedback parameters using semi-numerical 21 cm lightcone simulations. We compute the multi-frequency angular power spectrum (MAPS) to isolate the VAO features and train a Convolutional Neural Network (CNN) to infer the LW feedback efficiency and the baseline cooling threshold. We find that in the absence of instrumental noise, the LW feedback efficiency can be accurately recovered from the VAO features. However, for the SKA-low AA* configuration, meaningful constraints require integration times exceeding $10^4$ hours under optimistic foreground assumptions. Nonetheless, our results demonstrate that VAO features provide a physically robust and potentially powerful probe of LW feedback at Cosmic Dawn.
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All authors Xi Du, Bin Yue, Furen Deng, Yidong Xu, Yan Gong, Ely D. Kovetz, Xuelei Chen