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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 20 May

Instrumentation and Methods for Astrophysics · Cross-listed from physics.ao-ph

Three-Dimensional Velocity Analysis and Particle Size Dynamics from Multi-Site RGB-Photometry of Noctilucent Clouds

Oleg S. Ugolnikov, Olga Yu. Golubeva and Egor O. Ugolnikov

A method for measuring the altitude and particle size of noctilucent clouds, based on positioning and photometry from wide-angle three-color cameras, has been developed to determine the three velocity components, particle radius, and its derivative with respect to time for different cloud fragments. The updated method is applied to observational data of bright clouds during the summers of 2023-2025. Meridional motion of the cloud is found to be the principal factor driving the change in particle size. The effect of particle size evolution in the presence of a strong latitudinal temperature gradient is also studied.
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Earth and Planetary Astrophysics

Bayesian Modeling of NICER Cometary X-ray Spectra: A Legacy Survey of Solar-Wind Charge Exchange

T. K. Deskins, Dennis Bodewits, Steven Bromley et al. (+3 more)

We present a uniform, epoch-resolved analysis of soft X-ray observations of eight comets obtained with NICER, using Bayesian statistics to identify charge-exchange line components, measure relative ion fluxes, and infer nominal solar-wind freeze-in temperatures. The sample exhibits recurring spectral morphologies that fall into distinct families: carbon-dominated, intermediate, and nitrogen-/oxygen-dominated. Epoch-resolved flux ratios yield a robust separation between diagnostics: carbon-derived freeze-in temperatures cluster near T_freeze(C) about 1.4-1.7 MK, while nitrogen- and oxygen-derived diagnostics are systematically higher, typically T_freeze(N,O) about 2.0-2.3 MK. Short-timescale variability in inferred freeze-in conditions is common, indicating that instantaneous solar-wind charge-state fluctuations, rather than large changes in coma composition, dominate the spectral differences. We discuss instrumental and modeling limitations, demonstrate how our Bayesian fitting method mitigates degeneracies via physically motivated priors and Bayesian model selection, and recommend laboratory measurements and coordinated high-resolution X-ray observations to refine charge-exchange diagnostics and validate low-resolution inferences.
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All authors T. K. Deskins, Dennis Bodewits, Steven Bromley, Konrad Dennerl, Damian J. Christian, Dusan Odstrcil

Solar and Stellar Astrophysics

The Absolute Age of the Open Cluster NGC 6791 and Its Implications for Galactic Archaeology and Asteroseismic Calibration

George Dufresne, Brian Chaboyer and Rayna Rampalli

We present a new absolute age determination for NGC 6791, one of the Milky Way's oldest and most metal-rich open clusters. Its unusual properties make it an important probe of inner-disk evolution and asteroseismic calibration, but its age has remained difficult to determine because of coupled uncertainties in reddening, distance, photometry, and stellar-model physics. Gaia DR3 photometry together with detached eclipsing binaries (DEBs) in NGC 6791 are combined with 10,000 Monte Carlo isochrone sets (marginalizing over uncertainties in composition, convective mixing processes, opacities, diffusion, nuclear reaction-rates, distance modulus, and reddening) to determine the age of NGC 6791. For each isochrone we build a synthetic color-magnitude diagram (CMD) that matches the observed star count in the MSTO and subgiant-branch window and injects empirical photometric scatter perpendicular to the ridgeline, enabling CMD comparisons without artificial-star tests. We assess CMD morphology using a bootstrap-calibrated two-dimensional Kolmogorov-Smirnov statistic, and add an external check based on the nearest-point metric: a coeval DEB statistic in $(M,L)$ space. These statistics are mapped to probability-density weights via bootstrap-resampling and combined into a single isochrone weight. NGC 6791 is determined to have an age of $8.46\pm0.66$ Gyr, $[\mathrm{Fe/H}]=+0.280\pm0.079$, $Y=0.2968\pm0.0158$, $(m{-}M)_V=13.333\pm0.058$, and $E(B{-}V)=0.183\pm0.024$. Our error budget shows no single dominant contributor, and highlights differences between open-cluster and globular-cluster age errors. Combined with its super-solar metallicity, our age estimate favors an inner-Galaxy origin for NGC 6791 and subsequent outward migration, provides a benchmark for asteroseismic calibration at high metallicity, and extends the absolute cluster age–metallicity relation to an old, metal-rich open cluster.
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Solar and Stellar Astrophysics

29SiO and 30SiO J=1–0 maser signatures in Galactic AGB stars: the impact of third dredge up and turbulence velocity

M.O. Lewis, L.O. Sjouwerman, Y.M. Pihlström et al. (+3 more)

J=1–0 SiO masers at 43 GHz have a well-established distinctive signature in asymptotic giant branch (AGB) stars. 28SiO transitions typically dominate these spectra with the v=1 and v=2 emission being especially prominent and ubiquitous. Several predictions about enhanced 29SiO abundances in exotic stars prompt us to catalog the cases where 29SiO maser emission is enhanced compared to 28SiO. Our purpose is to catalog the known cases of 43 GHz spectra dominated by emission from isotopologue transitions (iso-dom spectra), to explore the commonalities in these sources, and to explain the cause of such maser signatures. Our catalog is drawn from SiO maser line ratios in the infrared-color-selected BAaDE survey and supplemented with a literature detection. The BAaDE catalog has cemented the typical signature of 43 GHz SiO masers, showing it is dominated by the v=1 and v=2 lines. Thirty-five iso-dom spectra are identified, meaning that this signature is seen in about 0.2% of our SiO maser-bearing stars. Their infrared colors are blue compared to other sources of the same period, similar to all sources displaying isotopologue masers. It is clear that the iso-dom nature of sources is variable, but unclear whether this is tied to stellar phase. A large abundance abnormality among the iso-dom sources is disfavored as the iso-dom sources do not appear significantly different from other stars which host isotopologue masers. Maser pumping, affecting the population inversions of specific transitions, can instead explain the enhanced signatures. We posit that iso-dom spectra appear in AGB stars which have undergone third-dredge up (enhancing the 29SiO and 30SiO abundance slightly) and which, in addition, are experiencing very low turbulence velocity (<1 km/s), creating a line overlap which pumps the maser transitions very efficiently.
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All authors M.O. Lewis, L.O. Sjouwerman, Y.M. Pihlström, H.J. van Langevelde, R. Bhattacharya, M.C Stroh

Astrophysics of Galaxies · Cross-listed from physics.plasm-ph

Numerical simulations of shock-driven, supersonic interstellar turbulence in colliding three-temperature laboratory plasmas

Stefano Merlini, James R. Beattie and Vicente Valenzuela-Villaseca

Shock-driven turbulence is central to astrophysical plasmas in which explosions and compressive driving inject energy through shocks rather than steady stirring. We present three-dimensional, three-temperature (ion, electron, and radiation; 3T) radiation-hydrodynamic simulations of a laboratory platform in which two offset CH mesh targets are irradiated by a $30\,\rm ns$ X-ray pulse. Mesh ablation launches counter-streaming supersonic flows whose vorticity is seeded baroclinically at mesh-cell corners, advected into collimated channels over $\sim15\,\rm ns$, and injected into the outgoing streams before collision. The flows first collide at $t\simeq75\,\rm ns$, forming a shocked turbulent mixing layer that persists for at least $300\,\rm ns$, reaches $\ell_0\simeq4.5\,\rm mm$, and evolves toward an effectively isothermal equation of state with $\gamma_{\rm eff}\simeq1.1$. After stagnation, $u_0(t)\propto t^{-1.1}$ while $t_0/t_{c_s}\simeq0.2$ remains nearly fixed. Compression and stretching dominate the vorticity budget, and the velocity field relaxes toward a kinetic-energy partition of approximately $70\%$ solenoidal and $30\%$ compressive. The Reynolds stress is strongly anisotropic at the outer scale and remains measurably anisotropic over much of the resolved inertial interval, indicating directional memory of the collision axis and mesh geometry across many scales. The solenoidal strain spectrum implies $\ell_{\nu,\rm s}\simeq92\,\mu\rm m$, $\ell_0/\ell_{\nu,\rm s}\simeq49$, and an effective Reynolds number $\mathrm{Re}\sim2\times10^2$. The density-gradient spectrum is directly tied to the compressive mode spectrum, which evolves independently from the incompressible cascade. Abridged.
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Astrophysics of Galaxies

JWST Advanced Deep Extragalactic Survey (JADES) Data Release 5: stellar population catalogue for galaxies in GOODS-N and GOODS-S

Qiao Duan, Sandro Tacchella, Benjamin D. Johnson et al. (+37 more)

We present the galaxy stellar population catalogue from the JWST Advanced Deep Extragalactic Survey (JADES) Data Release 5 (DR5), providing homogeneous Bayesian inference of physical galaxy properties in GOODS-N and GOODS-S. Using deep JWST/NIRCam and MIRI imaging combined with ancillary multi-wavelength data, we model the spectral energy distributions of ~500,000 sources with the Prospector framework. Our modelling incorporates flexible non-parametric star-formation histories (SFHs), nebular emission, dust attenuation, metallicities, and mid-infrared AGN and dust emission. We adopt an evolving star-forming main sequence (SFMS) prior for modelling the SFHs, which provides a physically-motivated long-term shape of SFHs while retaining non-parametric flexibility. The prior links stellar mass growth and SFR through the observed redshift-dependent SFMS, shaping the global behaviour of the inferred SFHs but allowing substantial deviations and scatters wherever supported by the data. We derive posterior distributions for stellar masses, SFRs, SFHs, dust attenuation, metallicities, and AGN contributions. The depth and wavelength coverage of JADES enable robust stellar mass measurements down to low-mass limits, as well as improved constraints on recent star-formation activity for ~350,000 galaxies at z = 1 - 9. The adoption of a physically motivated prior mitigates unphysical solutions and reduces degeneracies between redshift, age, dust, and metallicity, particularly for faint sources. We validate the catalogue through consistency checks and comparison to spectroscopic redshifts where available. The resulting value-added catalogue provides a uniform set of stellar population parameters suitable for statistical studies of galaxy growth, quenching, and the build-up of stellar mass across cosmic time. The full catalogue and posterior summaries are publicly released as part of JADES DR5.
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All authors Qiao Duan, Sandro Tacchella, Benjamin D. Johnson, Brant Robertson, Charlotte Simmonds, William M. Baker, Andrew J. Bunker, Stefano Carniani, Courtney Carreira, Stéphane Charlot, Jacopo Chevallard, Emma Curtis-Lake, A. Lola Danhaive, Francesco D'Eugenio, Daniel J. Eisenstein, Sophia Geris, Kevin N. Hainline, Ryan Hausen, Jakob M. Helton, Patricia Iglesias-Navarro, Yuki Isobe, Zhiyuan Ji, Maria Koller, Tobias J. Looser, Roberto Maiolino, Robert G. Pascalau, Pablo G. Pérez-González, Dávid Puskás, Marcia Rieke, Bruno Rodríguez Del Pino, Pierluigi Rinaldi, Jan Scholtz, Amanda Stoffers, Yang Sun, James A. A. Trussler, Hannah Übler, Christina C. Williams, Lily Whitler, Zihao Wu, Yongda Zhu

Astrophysics of Galaxies

Advancing the detection of low surface brightness galaxies. I. ATTILA: multi-tAsking deTecTIon tool for Lsb gAlaxies

E. Borsato, F. Fonzo, N. Bellucco et al. (+15 more)

Context. Ultra-diffuse galaxies (UDGs) lie at the extreme end of the size-luminosity distribution of low surface-brightness (LSB) galaxies. Their detection and characterization require deep imaging and reliable source detection techniques that can handle low signal-to-noise ratios and severe source blending. Aims. We aim at improving the detection and characterization of the LSB galaxies and UDG candidates in different environments. To this end, we have developed a new automated detection Python-based tool, named ATTILA. Methods. We use deep g- and r-band imaging from the VST Early-type GAlaxy Survey (VEGAS), covering the central region of Hydra I and three new additional fields. Sources are identified combining tiling processing, source detection, and iterative deblending. The structural parameters are derived through surface brightness profile analysis and Sérsic modelling. Cluster membership is determined using the early-type galaxies colour-magnitude relation. Results. We identify 24 new UDGs, doubling the known population in the Hydra-I cluster to 48, consistent with expectations from halo mass scaling relations, and 92 additional LSB galaxies. In real data, ATTILA recovers more than 80% of previously known LSB galaxies and significantly improves the automated detection rate relative to standard methods. Conclusions. By improving the recovery of faint and diffuse sources while mitigating blending and contamination effects, ATTILA enables a more complete census of the LSB galaxy population, including UDGs.
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All authors E. Borsato, F. Fonzo, N. Bellucco, E. Iodice, E. M. Corsini, M. Spavone, S. Pasquato, C. Buttitta, M. Cantiello, M. D'Onofrio, M. Gullieuszik, A. La Marca, A. Moretti, A. Nucita, M. Paolillo, A. Pizzella, E. Portaluri, C. Tortora

Astrophysics of Galaxies

Predicting intermediate-mass black hole formation in star clusters with machine learning

Konstantinos Kritos, Digvijay Wadekar and Emanuele Berti

Whether intermediate-mass black holes reside in nearby star clusters has remained contested for decades. We address this question by training neural network and random forest regressors on synthetic catalogs generated with the Rapster cluster evolution code, mapping observable cluster properties such as total mass and half-mass radius onto the mass of the heaviest black hole built up through repeated mergers. Applying these models to nearby globular and nuclear star clusters, we forecast the intermediate-mass black hole population that each system may host. Globular clusters are unlikely to contain black holes more massive than $\sim 100\,M_\odot$, with an occupation fraction near 0.02, although they can produce remnants within the upper mass gap with masses approaching $100\,M_\odot$. Among nuclear star clusters, a handful of cases, including NGC 5102 and NGC 5206, yield predicted central black hole masses above $100\,M_\odot$, which we contrast with kinematically inferred estimates. Where the observationally claimed masses exceed our predictions, the implication is that the assembly history involved processes beyond hierarchical mergers, most plausibly accretion of gas and stars. Finally, we employ a normalizing flow to quantify, for individual globular clusters, the likelihood that their initial conditions were favorable to a collisional runaway during the first few million years after formation.
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Astrophysics of Galaxies

Molecular gas properties of star-forming brightest group galaxies at $z \sim 0.3$

Greta Toni, Gianluca Castignani, Françoise Combes et al. (+4 more)

Recent efforts to characterise the molecular gas content of brightest cluster galaxies (BCGs) at intermediate redshift have revealed a sub-population of gas-rich systems, whose star formation activity is likely influenced by environmental processing. In this study, we aim to investigate the molecular gas reservoirs and star formation fuelling of central galaxies in groups, also known as brightest group galaxies (BGGs), at intermediate redshifts. We present targeted carbon monoxide (CO) line observations of three BGGs in the COSMOS field at $z \sim 0.3$, obtained with the IRAM 30m telescope. The galaxies exhibit disturbed morphologies, extended blue substructures, and interaction signatures. Furthermore, they exhibit significant star formation rates derived from multiwavelength diagnostics. We detect CO(1$\rightarrow$0) emission in one system, revealing a substantial molecular gas mass of $M_{H_2} \sim 3 \times 10^{10}$ M$_\odot$, while for the other two BGGs, CO emission lines remain undetected, yielding stringent upper limits of $M_{H_2} \lesssim 10^{10}$ M$_\odot$. By combining molecular gas constraints with fiducial star formation rates derived from total infrared emission, we infer gas depletion timescales in the range of $\lesssim 0.5-1.5$ Gyr. These results may indicate that, despite their active star formation and interaction signatures, some BGGs could already experience efficient gas exhaustion or suppressed gas replenishment, suggesting that gas depletion precedes star formation quenching. Our findings hint that environmental processes in galaxy groups could strongly regulate the availability of cold gas and drive rapid evolutionary phases in central galaxies, possibly bridging the gap between gas-rich BCGs and passively evolving systems.
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All authors Greta Toni, Gianluca Castignani, Françoise Combes, Philippe Salomé, Angel Bongiovanni, Lauro Moscardini, Matteo Maturi

Astrophysics of Galaxies

A Magnetized Black Hole Envelope Model for Little Red Dots

Shinsuke Takasao and Kohei Inayoshi

Recent observations have revealed a unique class of active galactic nuclei (AGNs), termed little red dots (LRDs). These objects are hypothesized to be powered by massive black holes rapidly accreting in dense gaseous environments. Theoretical studies suggest that the circum-nuclear gas can form an optically thick black hole envelope (BHE), whose structure resembles the atmospheres of convective stars near the Hayashi limit. Given that such cool stars typically generate magnetic fields, we propose a dynamical and spectral model for an LRD enshrouded by a magnetized BHE. Assuming spherical free-fall accretion onto a rotating, magnetized BHE, our model accounts for key observational properties of LRDs. We propose that the Doppler component of broad emission lines originates from plasma clumps co-rotating within the BHE magnetosphere. Including additional broadening due to electron scattering allows the resulting line profile to be fitted by a combination of a Gaussian core and an exponential tail. This model can reproduce Doppler components up to a few thousand ${\rm km~s^{-1}}$. We suggest that conventional black hole mass estimation methods based on the virial relation may yield erroneous results. Furthermore, our model is consistent with X-ray non-detections in LRDs. We evaluate the X-ray luminosities of two potential sources: the post-shock region of accretion shocks and a magnetically heated corona. We find that these X-ray luminosities are constrained to $\lesssim 10^{41}~{\rm erg~s^{-1}}$ across a wide range of black hole masses ($10^5 M_\odot \lesssim M_{\rm BH}\lesssim 10^7M_\odot$) and accretion rates, consistent with current upper limits on X-ray emission.
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Astrophysics of Galaxies

Decomposing cool stellar populations with H-band spectral fluctuations: Long-period variable stars in NGC 5128 and carbon stars in NGC 5102

Russell J. Smith and Anastasia Gvozdenko

We analyse new H-band integral-field unit observations of two galaxies at ~4 Mpc, using a principal components analysis of pixel spectra to probe their giant star content. In both galaxies, the signals arise in near-resolved point-like sources without large-scale variation, consistent with each pixel sampling stars randomly from a common underlying population. In the (mostly) old bulge of NGC 5128, the observed pixel-to-pixel variation is dominated by a component with a mid-M giant spectrum with prominent CO bandheads. We also recover a smoother second spectral component, apparently driven by contributions from later spectral types. This component is not present in predictions from Poisson-sampled models of old stellar populations; we suggest that it arises from the cool phases of long-period variable stars. (An appendix provides direct evidence for such variables in complementary two-epoch MUSE observations.) In the contrasting galaxy NGC 5102, where a post-starburst stellar population is known to be present, we again find two distinct components. As before, the first component carries the CO bands typical of M-giants. The second eigenspectrum in this younger galaxy shows a strong 1.77 micron C2 bandhead, a feature which is characteristic of carbon stars. Our results highlight the ability of integral field data to access information beyond the total spectrum, even when individual stars cannot be classically resolved.
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Cosmology and Nongalactic Astrophysics

Still non-accelerating: age-bias correction in supernova cosmology is robust to host-progenitor age mapping

Chul Chung, Junhyuk Son, Seunghyun Park et al. (+4 more)

We re-examine the claim by Wiseman et al. (2026) that progenitor-age bias has a negligible impact on cosmological inferences from Type Ia supernovae (SNe Ia). We show that their inferred host-age-Hubble residual (HR) slope is severely underestimated because their combined SN Ia sample spans an unusually wide redshift range ($0.04 < z < 0.42$), over which the mean host age evolves by $\sim$\,3 Gyr. As a result, SNe Ia spanning substantial host-age differences are effectively assigned similar HR values prior to regression, artificially flattening the inferred age-HR relation. In addition, their application of the Pantheon+ host-mass correction further suppresses the slope, but the underlying dust model is highly incompatible with the measured dust attenuation curves of galaxies. We also demonstrate that our age bias correction is robust to uncertainties in host-progenitor age mapping arising from different choices of the SN Ia delay-time distribution. The reduced progenitor-age evolution argued by Wiseman et al. (2026) must, by the same logic, be accompanied by a steeper inferred progenitor-age-HR slope. When these two effects are consistently combined in computing the redshift-dependent magnitude correction, the final correction, and hence the resulting cosmological impact, remain largely unchanged from Son et al. (2025).
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All authors Chul Chung, Junhyuk Son, Seunghyun Park, Suk-Jin Yoon, Hyejeon Cho, Dongwook Lim, Young-Wook Lee

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

Wave-optics gravitational wave lensing in modified gravity

Alice Garoffolo and Gianmassimo Tasinato

We initiate the study of gravitational-wave lensing in the wave-optics regime within modified gravity. We consider a phenomenological setup in which the gravitational-wave amplitude obeys a curvature-coupled propagation equation. This framework reproduces the standard GR behaviour in the geometric-optics regime, while leading to qualitatively different infrared dynamics. In particular, the usual argument implying that the amplification factor approaches unity in the zero-frequency limit no longer applies. This is due to the persistence of curvature-induced interactions in the infrared, which modify the natural propagation basis itself. As a result, the standard Fresnel treatment ceases to be valid at sufficiently low frequency. The correct infrared regime is instead controlled by an interacting static Green function, with a finite-frequency completion provided by a partial-wave formulation. We show that this structure admits an equivalent distorted-wave interpretation, in which the curvature interaction is absorbed into a dressed reference propagation basis, while the residual lensing effect is encoded in finite-frequency phase shifts. We further demonstrate that these phenomena admit a natural interpretation in the language of scattering amplitudes. Wave-optics lensing can therefore probe propagation-level departures from GR that remain entirely invisible in geometric optics.
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High Energy Astrophysical Phenomena

Massquerade: Impacts of Mass Ratio Reversals on Binary Black Hole Merger Rates and Mass Distributions

Tyler B. Smith, Floor Broekgaarden, Sasha Levina et al. (+4 more)

We investigate the role of mass ratio reversal (MRR), in which the initially less massive star in a binary forms the more massive compact object, in shaping the astrophysical binary black hole (BBH) merger rate and mass distribution inferred by LIGO-Virgo-KAGRA, comparing simulation outcomes from population synthesis frameworks COMPAS and SEVN. We find that the observational imprint of MRR differs qualitatively between the two models. In COMPAS, MRR systems dominate the merger rate density at high primary masses ( $\gtrsim$ 12 M$_\odot$), high secondary masses ( $\gtrsim$ 20 M$_\odot$), and high mass ratios ($q>0.6$), whereas in SEVN, MRR systems remain subdominant across the BBH mass distribution. This implies that the initially less massive star can massquerade as the observed primary black hole, such that the primary-mass distribution is not a direct tracer of the initially more massive stars, but instead a superposition of physically distinct evolutionary populations. We identify in the simulations three distinct evolutionary pathways leading to MRR systems: core-growth, in which stable mass transfer increases the helium-core mass of the secondary; PPISN-shrinking, where pulsational pair-instability episodes reduce the primary remnant mass; and asymmetric-CCSN, where differential supernova mass loss drives the reversal. When weighted by the local BBH merger-rate density, the core-growth channel dominates almost exclusively. MRR systems predominantly originate from massive ($\gtrsim$ 50 M$_\odot$), low-metallicity progenitors, with most of the systems forming below 0.1 $Z_\odot$. Our results demonstrate that MRR is a physically distinct and potentially observable feature of isolated binary evolution. Accounting for MRR will be important for robustly connecting future gravitational-wave observations to the physics of massive binary evolution and compact-object formation.
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All authors Tyler B. Smith, Floor Broekgaarden, Sasha Levina, Amedeo Romagnolo, Manasvini Komandur, Melanie Santiago, Kyle A. Rocha

Astrophysics of Galaxies

Interstellar Medium-Driven Orbital Transport – I. Radial Heating and Migration

Shaunak Modak, Chris Hamilton, Eve C. Ostriker et al. (+1 more)

Interstellar medium (ISM) structures gravitationally perturb stellar orbits in galactic disks, driving orbital heating and migration. However, studies of these transport processes tend to model the ISM very crudely, e.g., as a collection of compact, spherical “clouds” moving in the disk plane. Here, we revisit this problem with more realistic models of ISM density fluctuations drawn from the TIGRESS-NCR magnetohydrodynamic simulations, which follow the physics governing the ISM in Milky-Way-like conditions at high resolution. By integrating test-particle trajectories through time-dependent TIGRESS-NCR structures, we uncover transport behavior that contrasts sharply with conventional theoretical expectations. Notably, radial heating scales as $\sigma_R \propto t^{1/2}$ for initially cold orbits at early times, and $\sigma_R \propto t^{1/5}$ for warmer orbits at late times, contrary to the classic $\sigma_R \propto t^{1/3}$ prediction. The ISM drives substantial radial migration, accounting for $\gtrsim 30\%$ of that observed in the solar neighborhood (even without stellar spiral structure), and leads to a very low heating-to-migration ratio of $\mathrm{rms}\,\delta J_R\,/\,\mathrm{rms}\,\delta J_\varphi \approx 0.055$, where $J_R$ and $J_\varphi$ are the radial and azimuthal actions respectively. Vertical motion suppresses the amplitude of radial transport, but does not change the basic scalings. All our simulation results can be explained using quasilinear diffusion theory, accounting for the fact that the dominant ISM fluctuations have wavelengths of $\lambda_* \sim 600\,$pc and correlation timescales of $\tau_* \sim 70\,$Myr. We provide simple fitting formulae for the corresponding diffusion coefficients. In Paper II, we study the ISM's role in vertical disk heating.
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All authors Shaunak Modak, Chris Hamilton, Eve C. Ostriker, Scott Tremaine

High Energy Astrophysical Phenomena

Gravitational wave detectability range informed by external messengers

S. Ronchini, A. Chopra, T. Dal Canton et al. (+3 more)

A rapid estimate of gravitational-wave (GW) detectability associated with astronomical transients is crucial for optimizing multi-messenger follow-up strategies and for constraining the physical origin of the transient itself. We introduce here the Targeted Detectability Range (TDR), designed to evaluate, with minimal computational effort, the detectability of compact binary coalescences under the hypothesis of association with an external messenger, such as an electromagnetic or neutrino signal. Unlike the standard GW range, which is based on averaged source parameters, the TDR incorporates prior information from observations of the external messenger, including sky localization, inclination constraints, and physically motivated bounds on component masses. We report the TDR of all short- and long-duration gamma-ray bursts, observed during the first three observing runs of Advanced LIGO and Advanced Virgo. The method is validated by performing a systematic comparison with the 90$\%$ exclusion distances provided by modeled targeted GW searches. In the absence of a coincident detection by all-sky, all-time GW searches, the TDR provides a rapid and quantitative constraint on a possible merger origin of the astrophysical source. Its low-latency implementation and public availability would enable timely prioritization of follow-up observations and optimized allocation of observational resources, with direct impact on the physical interpretation of astronomical transients.
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All authors S. Ronchini, A. Chopra, T. Dal Canton, B. Banerjee, A. L. De Santis, M. Branchesi

Astrophysics of Galaxies

Investigating central star formation in local AGN host galaxies: is there tension between coeval growth and AGN feedback?

Q. Ni, K. Nandra, A. Merloni et al. (+3 more)

It has been argued that supermassive black holes (BHs) coevolve with the central parts of galaxies, as a result of the common fuel for both the BH and star formation in the galaxy central region, as supported by the particularly significant relation between BH growth and the central mass density within 1 kpc found among star-forming galaxies. In the context of this scenario, one would naturally expect a close observational link between AGN activity and star formation activity in the central regions, e.g., the surface star formation rate density in the central 1 kpc region ($\Sigma_{\rm SFR, 1~kpc}$), as the manifestation of coeval growth. With ~3000 galaxies in the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey that have X-ray coverage from SRG/eROSITA, XMM-Newton, or Chandra, we studied how the X-ray AGN fraction varies with $\Sigma_{\rm SFR, 1~kpc}$. We found that the fraction of X-ray AGNs with relatively higher specific BH accretion rates increases with $\Sigma_{\rm SFR, 1~kpc}$, consistent with the expectation. Comparison of the mean star formation rate surface density ($\Sigma_{\rm SFR}$) profiles of the host galaxies of these AGNs and normal galaxies sharing similar properties reveals elevated $\Sigma_{\rm SFR}$ in AGN hosts across the entire central region. As for optically-selected AGNs, their hosts also tend to show high $\Sigma_{\rm SFR}$ in the central regions on average compared to normal galaxies, but are discrepant with X-ray AGNs in terms of the trend of AGN fraction vs. $\Sigma_{\rm SFR, 1~kpc}$, which can be explained by selection effects. While these general trends all support the coeval growth scenario, they do not contradict observational evidence for AGN feedback, as the time-averaged effects from local AGN feedback are modest in star-forming regions.
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All authors Q. Ni, K. Nandra, A. Merloni, J. Comparat, D. Tubín-Arenas, Y. Zhang

High Energy Astrophysical Phenomena

First-Principles Turbulence-Driven Deflagration-to-Detonation Transition Mechanism for Near-Chandrasekhar Mass White Dwarf Progenitors

Krut Patel, Akshay Dongre, Robert Fisher et al. (+4 more)

Type Ia supernovae (SNe Ia) play an important role throughout astrophysics, most notably as standardizable cosmological candles. Yet, their stellar progenitors and explosion mechanism remain areas of active investigation. For decades, the canonical model for normal brightness SNe Ia used in cosmology was a carbon-oxygen white dwarf (WD) accreting from a non-degenerate stellar companion, approaching the Chandrasekhar mass (M_Ch). Previously, all models of near-M_Ch SNe Ia invoked an ad hoc assumption on the critical process of detonation initiation, and could therefore be tuned to a variety of outcomes. Here, we present global 3D hydrodynamical simulations of near-M_Ch progenitors, which incorporate, for the first time, a laboratory-validated ab initio mechanism for the turbulence-driven deflagration-to-detonation transition (tDDT). The tDDT detonation mechanism is highly efficient, leading to detonation initiation which is prompt in comparison to most prior work. Despite spanning a factor of six in central ignition density and qualitatively distinct ignition topologies, all models converge on nearly identical synthetic spectra at peak luminosity, spectroscopically matched to the overluminous SN 1999aa. The turbulence-driven Chapman-Jouguet criterion drives each progenitor to a common detonation configuration from diverse initial conditions, providing a physical foundation for the ignition-insensitive detonation outcomes implicit in the empirical standardizability of SNe Ia. This provides the first physically motivated, self-consistent pathway for delayed detonation in SNe Ia simulations. Further work is necessary to understand how this mechanism might produce more delayed detonation initiation and potentially fail, thereby yielding SNe Iax.
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All authors Krut Patel, Akshay Dongre, Robert Fisher, Alexei Poludnenko, Vadim Gamezo, Mark Ugalino, Chris Byrohl

Astrophysics of Galaxies

(LRDs)$^2$: The Low-ReDshift Little Red Dots Survey. II. DESI DR1 Sample

Xiaojing Lin, Xiaohui Fan, Zheng Cai et al. (+12 more)

JWST has revealed a substantial population of "Little Red Dots" (LRDs) at $z>4$, challenging conventional AGN frameworks. However, the low-redshift regime remains largely unexplored. In the second paper of the (LRDs)$^2$ series, we present a systematic selection from DESI DR1 and identify 27 LRDs at $z=0.2-0.9$, yielding a number density lower limit of $7.5\times10^{-10}$ cMpc$^{-3}$. We conducted near-IR spectroscopic follow-up observations for 21 of them, revealing their full SED shapes and emission lines. These low-$z$ LRDs share the hallmark properties of their high-$z$ counterparts: compact morphology, V-shaped UV-optical continua, broad Balmer emission with extreme decrements (median H$\alpha$/H$\beta\sim15$), frequent Balmer absorption (70%), and blackbody-like optical-to-near-IR continua. All have low metallicity, occupy the same regions in the BPT diagram as high-$z$ LRDs, and have softer ionizing spectra than typical AGNs. The consistency between low-$z$ and high-$z$ LRD properties indicates the same physical processes at work. The correlation between broad-line Balmer luminosity and $L_{5100}$ deviates from that of local type-1 AGNs, limiting the direct application of local BH mass calibrations. Ionized [O III] outflows are ubiquitous (78%). One LRD at $z=0.196$, J1717+3807, shows robust long-term variability in $i$ and WISE bands. The optical-to-NIR continua of LRDs reveal a wide range of temperatures $\sim2000-4700$ K (peak $0.6-1.4$ $\mu$m), with a subset showing cooler and larger envelopes than those at high $z$. Low-$z$ LRDs serve not only as proximate laboratories for probing the nature of LRDs, but also trace the cosmic evolution of this population from the cosmic dawn to the present day.
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All authors Xiaojing Lin, Xiaohui Fan, Zheng Cai, Yichen Liu, Fengwu Sun, Fuyan Bian, Mingyu Li, Junjie Mao, Jenny E. Greene, Hanpu Liu, Jiaxuan Li, Weizhe Liu, Yilun Ma, Zechang Sun, Zijian Zhang

Cosmology and Nongalactic Astrophysics

Information Content of the Cosmic Web

Juan Garcia-Bellido

We present an information-theoretic analysis of the Cosmic Web that goes beyond the scalar density contrast and exploits the full structure of the tidal deformation tensor. The three eigenvalues ($\lambda_1, \lambda_2, \lambda_3$) of the tidal Hessian furnish a natural morphological classifier: clusters, filaments, walls, and voids correspond to (+,+,+), (+,+,-), (+,-,-), and (-,-,-) sign patterns, and their joint probability distribution function (PDF), known analytically in the linear regime from Doroshkevich (1970), defines a continuous Shannon entropy that quantifies the information encoded in the geometry of large-scale structure. Additional information resides in the shear invariants ${\cal Q} = {\rm Tr}(T^2)$ and ${\cal A} = {\rm Tr}(T^3)$, independent of the density. We derive the Log-Doroshkevich distribution, and show the $\mathbb{Z}_2$ symmetry survives the nonlinear map, broken only in matter fractions. Gravitational collapse breaks it through the density skewness: an Edgeworth treatment gives the cluster–void asymmetry $\mathcal{R}_{\rm cv}-1=0.609\,\varepsilon_3$ and entropy difference $\Delta H_{\rm CV}=0.107\,\varepsilon_3$ bits, with $\varepsilon_3=S_3^{\rm tot}(R)\,\sigma_0(R)\,D(z)$. The total skewness combines a gravitational term $S_3^{\rm grav}=34/7+n_{\rm eff}(R)$ and a primordial one $S_3^{\rm PNG}=S_3^{(1)}(R)\,f_{\rm NL}$ with $S_3^{(1)}(8\,h^{-1}{\rm Mpc})\simeq3\times10^{-4}$, smaller by four to five orders of magnitude, so the one-point asymmetry is gravity-dominated and only weakly sensitive to $f_{\rm NL}$. The multifractal entropy rate obeys $\dot H_{\rm mf}(z)=-3f(z)/(1+z)$, a growth probe complementary to $f\sigma_8$.
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Cosmology and Nongalactic Astrophysics

Velocityformer: Broken-Symmetry-Matched Equivariant Graph Transformers for Cosmological Velocity Reconstruction

Tilman Tröster, David Mirkovic, Veronika Oehl et al. (+1 more)

Precise measurement of the kinematic Sunyaev-Zel'dovich (kSZ) effect - a probe of the large-scale distribution of baryonic matter, a key observable for cosmological inference - requires accurate reconstruction of galaxy velocities from spectroscopic surveys. The signal-to-noise ratio (SNR) of kSZ measurements scales directly with the correlation coefficient $r$ between reconstructed and true velocities. We introduce Velocityformer, an equivariant graph transformer architecture designed to match the specific symmetry of the observational data. While the underlying physics is equivariant with respect to translations and rotations, observational effects break this symmetry due to the preferred line-of-sight direction. Matching the model's inductive bias to the data's broken symmetry consistently improves performance across all model sizes and training volumes, with Velocityformer improving $r$ by 35% over the standard linear theory baseline and outperforming ML baselines at every data volume. By matching the model's inductive bias to the data and conditioning on the physics-based long-wavelength solution, Velocityformer is highly data-efficient, training to high accuracy on as few as 4 low-fidelity simulations, and generalises zero-shot across input geometry, cosmological parameters, and galaxy sample. On high-fidelity simulated galaxy catalogues, this yields a 30% improvement in $r$ over the physical baseline, directly translating to the same SNR gain on observational data.
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All authors Tilman Tröster, David Mirkovic, Veronika Oehl, Arne Thomsen

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

Opening the Window of Ultra-Light PBHs by Exorcising the Poltergeist

Yann Gouttenoire, Nicholas Leister and Pedro Schwaller

The hot Big Bang may have emerged from evaporation of primordial black holes (PBHs) lighter than $10^9$g. Standard monochromatic treatments predict nearly simultaneous evaporation, abrupt reheating, and a large Poltergeist scalar-induced gravitational wave signal. We confront this expectation with the irreducible collapse mass tail predicted by general relativity, $df_{\rm PBH}/d\ln M\propto M^{3.78}$, which smooths reheating, suppresses the signal by orders of magnitude, and reopens the ultra-light PBH window.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Gravitational Waves from Black Hole Reheating: The Scalar-Induced Component

Yann Gouttenoire, Nicholas Leister and Pedro Schwaller

The reheating of the universe by the evaporation of light primordial black holes (PBHs) can leave a stochastic gravitational-wave (GW) background in the early Universe. In the monochromatic limit, their simultaneous evaporation produces an abrupt matter-to-radiation transition, triggering the so-called Poltergeist GW signal, usually predicted to be dominant and observable. We revisit this result by including the irreducible mass spread implied by gravitational collapse in General Relativity, whose infrared tail scales as $d f_{\rm PBH}/d\ln M_{\rm PBH}\propto M_{\rm PBH}^{3.78}$. We show that this minimal width smooths reheating enough to suppress the Poltergeist background by orders of magnitude, down to the level of the scalar-induced GW signal produced during a generic early matter era, such as one driven by the decay of a heavy relic. We provide a complete decomposition of the scalar-induced spectrum into eight production channels and find that none, except the one from PBH formation, reaches either the $\Delta N_{\rm eff}$ bound or the projected sensitivity of future GW observatories. This reopens regions of ultra-light PBH parameter space previously thought to be excluded by these constraints.
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High Energy Astrophysical Phenomena

The giant pulse population of PSR B0355+54

Sergei L. Kurdubov and Dmitry A. Marshalov

Giant pulses are rare bright radio bursts that occur in restricted ranges of pulsar rotational phase. Here we report giant pulses from PSR B0355+54, a pulsar with spin period ~0.156 s. Using 7.97 hours of observations centred at 1.46 GHz, with 128 MHz bandwidth in each circular polarizations, we identify 432 pulse periods containing bright pulses. The giant pulses recur in two compact longitude regions inside the radio emission window. They are narrow compared with the mean profile, with median W50=290.3 us, and reach relative peak flux density ratios up to 149.7. The early longitude group has a timing scatter of 139.7 us, or 0.00089 of a rotation. The first longitude group favours right, while the second favours left circular polarization.
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Cosmology and Nongalactic Astrophysics

Negative neutrino mass or negative dark energy?

Cihad K{\i}br{\i}s, Willem Elbers, Özgür Akarsu et al. (+1 more)

Recent cosmological analyses based on DESI and CMB data have revealed a tension between the inferred sum of neutrino masses and the minimum value allowed by neutrino oscillation experiments, when assuming an underlying $\Lambda$CDM model of cosmology. In this work, we perform a systematic exploration of alternative dark energy models, including models that can supply a negative dark energy density capable of reproducing the cosmological effects of negative effective neutrino masses. We argue that dark energy models can alleviate the tension by modifying the cosmic expansion rate over a specific redshift range relevant for CMB lensing, while matching BAO distance measurements from DESI at lower redshifts. Among the models considered, we find that a sign-switching cosmological constant model, $\Lambda_\mathrm{s}$CDM, is uniquely capable of recovering positive neutrino masses by modifying the expansion history in this way. For the combination of DESI DR2 BAO, CMB, and DES-Dovekie supernova data, the constraint on the effective neutrino mass shifts from $\sum m_{\nu,\mathrm{eff}}=-0.075^{+0.039}_{-0.053}$ eV (68%) for $\Lambda$CDM to $\sum m_{\nu,\mathrm{eff}}=0.055\pm0.050$ eV (68%) for $\Lambda_\mathrm{s}$CDM, with a 95% lower bound on the dark energy transition redshift, $z_\dagger>2.4$. Although $\Lambda_\mathrm{s}$CDM does not have the strongest overall statistical support among the models considered, when the $\sum m_{\nu,\mathrm{eff}}$ parameter is allowed to vary, our findings point toward a specific sign- and redshift-structured contribution to the late-time expansion history as a viable way to alleviate the neutrino mass tension.
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All authors Cihad K{\i}br{\i}s, Willem Elbers, Özgür Akarsu, Eleonora Di Valentino

Cosmology and Nongalactic Astrophysics

Euclid preparation: Testing multi-field inflation with galaxy power spectrum and bispectrum

Euclid Collaboration: D. Linde, A. Moradinezhad Dizgah, G. Parimbelli et al. (+280 more)

Primordial non-Gaussianity (PNG) is a powerful probe of the origin of cosmic structure. Stage-IV surveys like \Euclid will measure galaxy $2$- and $3$-point clustering at high signal-to-noise, whose exploitation requires robust joint analysis. We prepare for Euclid's spectroscopic sample by validating a redshift-space power-spectrum and bispectrum pipeline (one-loop $P_\ell$, tree-level $B_\ell$) on Euclid-like mocks from Abacus-PNG $N$-body simulations with Gaussian and local-PNG initial conditions, using a halo occupation distribution (HOD) tuned to Euclid Flagship 2. We stress-test analysis choices – PNG-bias parametrisation, priors, and scale cuts – and perform null tests without PNG. In a `prior-agnostic setup', detection of the dominant PNG term $\propto f_{\rm NL} \, b_\phi$ in single redshift bins is difficult; nevertheless, the bispectrum provides constraints on other PNG combinations that partially lift degeneracies. We propose a physically motivated prior on $b_\phi$ that yields unbiased $f_{\rm NL}$ while accounting for theory uncertainty, and determine scale cuts that give unbiased $\Lambda$CDM and $f_{\rm NL}$. With $V_{\rm eff}=16\,h^{-3}\,{\rm Gpc}^3$ across four snapshots ($0.8\le z\le1.7$), our likelihood analyses recover $<1\sigma$ bias in $f_{\rm NL}$ and $\Lambda$CDM. At fixed cuts, $B_\ell$ alone reduces $\sigma({f_{\rm NL}})$ by $\sim29$–$46\%$ relative to $P_\ell$, and joint power spectrum-bispectrum analysis tightens a further $\sim8$–$13\%$; the cumulative gain from $z=0.8$ to $1.7$ is $\sim2.3$ for the joint case. The bispectrum quadrupole is key. Our strongest results are at $z=1.7$: $1.9\sigma$ for $f_{\rm NL} \, b_\phi$ (prior-agnostic) and $2.35\sigma$ for $f_{\rm NL}$ (prior-based). Joint analyses thus offer strong prospects for testing multi-field inflation, pending end-to-end validation in the full Euclid geometry with observational systematics.
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All authors Euclid Collaboration: D. Linde, A. Moradinezhad Dizgah, G. Parimbelli, K. Pardede, E. Sefusatti, M. S. Cagliari, G. D'Amico, V. Desjacques, A. Eggemeier, M. Biagetti, A. Veropalumbo, B. Camacho Quevedo, A. Chudaykin, M. Crocce, L. Castiblanco, E. Castorina, A. Farina, M. Guidi, M. Karcher, A. Pezzotta, A. Pugno, B. Altieri, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, S. Bardelli, P. Battaglia, A. Biviano, E. Branchini, M. Brescia, S. Camera, G. Canas-Herrera, V. Capobianco, C. Carbone, J. Carretero, S. Casas, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, H. Degaudenzi, S. de la Torre, G. De Lucia, H. Dole, M. Douspis, F. Dubath, X. Dupac, S. Escoffier, M. Farina, R. Farinelli, S. Ferriol, F. Finelli, P. Fosalba, S. Fotopoulou, M. Frailis, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, W. Holmes, F. Hormuth, A. Hornstrup, K. Jahnke, B. Joachimi, S. Kermiche, A. Kiessling, B. Kubik, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, S. Mei, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, L. Moscardini, C. Neissner, S.-M. Niemi, J. W. Nightingale, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, S. Pires, G. Polenta, M. Poncet, L. A. Popa, F. Raison, A. Renzi, J. Rhodes, G. Riccio, E. Romelli, M. Roncarelli, R. Saglia, Z. Sakr, A. G. Sanchez, D. Sapone, B. Sartoris, A. Secroun, G. Seidel, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, A. Spurio Mancini, L. Stanco, P. Tallada-Crespi, A. N. Taylor, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, L. Valenziano, J. Valiviita, T. Vassallo, G. Verdoes Kleijn, Y. Wang, J. Weller, G. Zamorani, F. M. Zerbi, E. Zucca, M. Ballardini, E. Bozzo, C. Burigana, R. Cabanac, M. Calabrese, T. Castro, J. A. Escartin Vigo, J. Garcia-Bellido, J. Macias-Perez, R. Maoli, J. Martin-Fleitas, N. Mauri, R. B. Metcalf, P. Monaco, M. Pontinen, I. Risso, V. Scottez, M. Sereno, M. Tenti, M. Tucci, M. Viel, M. Wiesmann, Y. Akrami, I. T. Andika, G. Angora, M. Archidiacono, F. Atrio-Barandela, S. Avila, L. Bazzanini, J. Bel, D. Bertacca, M. Bethermin, F. Beutler, A. Blanchard, L. Blot, H. Bohringer, M. Bonici, S. Borgani, M. L. Brown, S. Bruton, A. Calabro, F. Caro, C. S. Carvalho, F. Cogato, A. R. Cooray, S. Davini, G. Desprez, A. Diaz-Sanchez, S. Di Domizio, J. M. Diego, V. Duret, M. Y. Elkhashab, A. Enia, Y. Fang, A. Finoguenov, A. Franco, K. Ganga, T. Gasparetto, F. Giacomini, F. Gianotti, G. Gozaliasl, A. Gruppuso, C. M. Gutierrez, A. Hall, C. Hernandez-Monteagudo, H. Hildebrandt, J. Hjorth, J. J. E. Kajava, Y. Kang, V. Kansal, D. Karagiannis, K. Kiiveri, J. Kim, C. C. Kirkpatrick, S. Kruk, M. Lattanzi, L. Legrand, M. Lembo, F. Lepori, G. Leroy, G. F. Lesci, J. Lesgourgues, T. I. Liaudat, S. J. Liu, G. Maggio, M. Magliocchetti, A. Manjon-Garcia, F. Mannucci, C. J. A. P. Martins, L. Maurin, C. Moretti, G. Morgante, S. Nadathur, K. Naidoo, A. Navarro-Alsina, S. Nesseris, L. Pagano, D. Paoletti, F. Passalacqua, K. Paterson, L. Patrizii, C. Pattison, A. Pisani, D. Potter, G. W. Pratt, S. Quai, M. Radovich, K. Rojas, W. Roster, S. Sacquegna, M. Sahlen, D. B. Sanders, E. Sarpa, A. Schneider, M. Schultheis, D. Sciotti, E. Sellentin, L. C. Smith, K. Tanidis, F. Tarsitano, G. Testera, R. Teyssier, S. Tosi, A. Troja, A. Venhola, D. Vergani, F. Vernizzi, G. Verza, S. Vinciguerra, N. A. Walton, A. H. Wright, H. W. Yeung

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

Cosmological Collider Signatures from Right-Handed Neutrino Loop

Jingtao You, Linghao Song, Chengcheng Han et al. (+3 more)

We study cosmological collider (CC) signatures generated by right-handed neutrino loops in the setup of inflation combined with the neutrino seesaw mechanism. We formulate the inflaton interaction with the right-handed neutrinos through a unique dimension-5 operator respecting shift symmetry, which induces an effective chemical potential in the slow-roll background, leading to helicity-dependent production of right-handed neutrinos and enhancing the CC signatures. The right-handed neutrino is described by a two-component Weyl spinor with a Majorana mass term. Using the Schwinger-Keldysh formalism, we derive a set of seed integrals for fermion propagators of the right-handed Majorana neutrino. With these, we compute the factorized nonlocal contributions to the three-point inflaton correlator generated by the triangle loop of right-handed neutrinos. We show that the chemical potential can substantially soften the heavy-mass Boltzmann suppression and amplify the oscillatory non-Gaussianity signatures associated with the dominant helicity mode. We systematically analyze the spinor structure, the factorization of fermion triangle loop, the loop-momentum integrals and the time seed integrals, which give a controlled computation of the nonlocal contributions to the CC signals of the right-handed neutrinos.
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All authors Jingtao You, Linghao Song, Chengcheng Han, Hong-Jian He, Xingang Chen, Zhong-Zhi Xianyu

Solar and Stellar Astrophysics

Lithium Enrichment in a Subgiant Star with a Brown Dwarf Companion: A Planetary Engulfment Candidate

Brooke Kotten, Melinda Soares-Furtado, Ricardo Yarza et al. (+11 more)

Theoretical models predict that subgiants within a narrow mass regime can retain detectable lithium enrichment signatures from planetary engulfment. We test this prediction using TOI-5882, selected because it occupies this favorable subgiant parameter space and hosts a massive brown dwarf ($22 \, M_{ \rm J}$, $P=7.1 \,{\rm d}$) companion capable of dynamically perturbing inner planets. We investigate whether: (1) TOI-5882 exhibits lithium enhancement among similar subgiants, (2) planetary material would be deposited in the convective zone, and (3) the required engulfed mass lies within a plausible range for planetary engulfment. Using spectra from the Tillinghast Reflector Echelle Spectrograph, we measured a Li I equivalent width of $75.39 \pm 3.58$ mA and an abundance of A(Li) $=2.49 \pm 0.12$ dex. Comparing these values to a control sample of 61 subgiants from the GALactic Archaeology with HERMES (GALAH) DR4 survey, we find that TOI-5882 ranks in the 98.4th percentile in both metrics, confirming significant lithium enrichment. We evaluate the engulfment scenario by modeling convective zone deposition and estimating the mass required to reproduce the observed enhancement relative to the control sample. We perform an estimate of the engulfed planetary mass incorporating CI chondritic Li abundances, as planets formed via core accretion are enriched in heavy elements and lithium partitions with these metals. This yields a required engulfed mass of $9$-$95\,M_\oplus$–an order of magnitude lower than the $5.6 \, M_{\rm J}$ implied by proto-solar assumptions. TOI-5882's lithium excess can plausibly result from the ingestion of a super-Earth to Neptune-mass planet, motivating further studies to test this scenario.
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All authors Brooke Kotten, Melinda Soares-Furtado, Ricardo Yarza, Andrew C. Nine, Seth A. Jacobson, Noah Vowell, Olivia Maynard, Allyson Bieryla, Andrew Vanderburg, Jack Schulte, Claudia Aguilera-Gomez, Enrico Ramirez-Ruiz, Joseph E. Rodriguez, David W. Latham

Earth and Planetary Astrophysics

Producing planetary debris exterior to white dwarf Roche radii through sublimative rotational fission

Dimitri Veras, Jordan K. Steckloff and Kathryn Volk

The majority of white dwarfs that host periodic transiting planetary debris do so at distances that exceed the rubble-pile Roche limit, in disagreement with canonical formation models that focus on the tidal disruption of minor planets. Here, we quantify the conditions by which rotational fission due to sublimative outgassing ("SYORP" break-up) can occur outside of the Roche sphere in the distance range of 1-5 Roche radii. We use the Many Materials Orbital Sublimation (MaMOS) model to quantify the outgassing properties of three representative types of planetary materials: cores (iron), mantles (forsterite olivine) and comets (water ice), and characterise the resulting spin-up rate analytically by adopting SYORP coefficients in the range of $10^{-5}-10^{-3}$. We then compare this rate to that generated by the radiative YORP effect with YORP coefficients of $10^{-3}-10^{-2}$, and focus on planetesimals with radii of 0.1, 1.0, and 10 km. We find that for white dwarf cooling ages of up to $\sim$ 1 Gyr, sublimative fission of planetesimals and fragments $\lesssim$ 0.1 km in size due to water ice outgassing occur on observable timescales (within 10 yr), regardless if the spin-up is monotonic or stochastic. Further, these timescales are orders of magnitude shorter than the corresponding YORP fission timescales. For drier planetesimals, both iron and forsterite outgassing can be effective at 10-100 Myr cooling ages. Our results do not substantially differ for strengthless rubble piles versus objects with 1 kPa of internal strength. These findings add to growing evidence that gravitationally scattered comets and asteroids do not need to adopt pericentres within a white dwarf's Roche radius to eventually enrich, or pollute, the star with metals.
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High Energy Astrophysical Phenomena

Compact Object Astrophysics with Frontline Astrometry

P. Gandhi

Astrometry - the precise measurement of celestial positions and motions - is entering the micro-arcsecond ($\mu$as) era at multiple wavelengths, enabling new insights on compact objects across all mass scales. Here we review how high-precision astrometry is advancing our understanding of compact objects - neutron stars (NSs) and black holes (BHs). We provide the context for high precision astrometry before discussing natal kicks and the latest results from Gaia Data Release 3 (DR3). We highlight the evidence for mass-dependent peculiar velocities of accreting binaries, and also reveal a close similarity between NSs and BHs. Next-generation surveys will find recoiling supermassive BHs (SMBHs) in galactic nuclei, exploring how gravitational-wave-induced kicks operate. Exploitation of scientific opportunities on the lunar surface could facilitate much larger collecting areas and astrometric precision in X-rays than currently feasible.
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