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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 11 November

Astrophysics of Galaxies

Highly Efficient Identification of Extreme Emission Line Galaxies in the Local Universe: >8000 New Green Pea Candidates at 0.12 < z < 0.36

Heather Samonski, Samir Salim and John Salzer

The currently known compact extreme emission-line galaxies (the "Green Peas", GPs) in SDSS are rare and were mostly found among serendipitous spectroscopic targets, thus leaving open the possibility that a substantial population of GPs is missed. A significantly larger number of identified GPs in the Local Universe might provide a better characterization of their high-redshift analogs and Lyman continuum escape. In this paper, we confront the challenges of robustly identifying GPs without spectroscopic information, a needed approach considering the incompleteness of spectroscopic surveys for compact sources. The principal difficulty stems from a significant contamination of photometric candidates by stars and quasars of similar color. To solve this, we introduce an SED matching method, which separates candidate GPs from contaminants on the basis of SDSS and WISE photometry of spectroscopically confirmed stars, quasars and galaxies. The method has an effectiveness of 85%, and a contamination rate of ~10%. With it we identify ~9600 GP candidates expected to lie in the 0.12 < z < 0.36 range - a tenfold increase over what would be selected using SDSS DR18 spectra. Some of the new GPs are as bright as r~19, and 1200 are predicted to have [OIII]5007 equivalent widths in excess of 500 A. The new population contains many "Extended Peas", which are absent among known GPs and possibly represent merging systems. We provide catalogs containing 8313 newly identified GP candidates, as well as 917 GPs confirmed using SDSS spectroscopy and 521 GPs with spectroscopic redshifts from LAMOST and other sources.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

Massive Inflationary Amplitudes: New Representations and Degenerate Limits

Zhong-Zhi Xianyu and Jiaju Zang

The particle model building of cosmological collider physics often involves boost-breaking bilinear mixing between a heavy particle and the nearly massless inflaton mode. In cosmological correlators, such a mixing is obtained by taking a folded limit of a generic tree graph, which is a special case of degenerate kinematics. In this work, we continue our exploration of massive inflationary amplitudes with a focus on degenerate kinematics. With a suitable change of variables, we derive new differential equations and full analytical solutions for generic tree graphs, making it trivial to take the folded limit and partial-energy limit at a vertex. Our result shows that folded tree graphs generally involve functions of smaller transcendental weights than their nondegenerate counterparts. In particular, the inflaton bispectrum with triple massive exchanges can be expressed in terms of a trivariate Kampé de Fériet function and simpler hypergeometric functions.
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Astrophysics of Galaxies

Evidence for in-situ acceleration of relativistic particles in the wings of X-shaped radio galaxies

Dusmanta Patra, Gopal-Krishna and Ravi Joshi

We report evidence for in-situ acceleration/re-acceleration of relativistic particles in 11 radio wings out of a total of 68 wings sufficiently well-resolved for spectral mapping, which belong to our sample of 40 X-shaped radio galaxies (XRGs). This representative XRG sample includes 15 XRGs newly reported here, which we selected from the LOTSS-DR2 survey, following well-defined criteria. The evidence for in-situ particle acceleration comes from the observed cessation of steepening, or even flattening (i.e., gradient reversal) of the spectral index profile along the lobe into the associated wing, as determined here by combining the LoTSS-DR2 (144 MHz) and FIRST (1.4 GHz) maps. Interestingly, the afore-mentioned trends in spectral gradient, indicative of in-situ particle acceleration, are mostly found to set in near the region where the lobe plasma stream bends to connect to the wing. Such a spatial coincidence with bending of radio lobe/tail has been noticed in recent years for just a couple of radio galaxies. The large increase in such examples, as reported here, is expected to give a fillip to observational, theoretical and numerical simulation follow-up investigations of this important clue about the occurrence of in-situ particle acceleration in lobes of radio galaxies.
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Solar and Stellar Astrophysics

The binary landscape of massive stars at low $Z$: Insights from the BLOeM Campaign

J. I. Villaseñor, H. Sana, J. Bodensteiner et al. (+4 more)

We present an overview of our recent results from the BLOeM campaign in the Small Magellanic Cloud ($Z=0.2\,{\rm Z}_{\odot}$). Using nine-epoch VLT/FLAMES spectroscopy, we investigated the multiplicity of 929 massive stars. Our findings reveal contrasting binary properties across evolutionary stages: O-type stars show an intrinsic close-binary fraction of $70\%$, and early B-type dwarfs/giants reach ${\sim80}\%$, exceeding higher-metallicity samples. In contrast, B0-B3 supergiants drop to ${\sim40}\%$, and A-F supergiants to ${\sim8}\%$; intrinsic variability likely inflates the latter, so the true multiplicity may be lower. OBe stars display distinct binary properties consistent with a post-interaction origin. These results have profound implications for massive-star evolution at low metallicity, including the production of exotic transients, gravitational-wave progenitors, and ionising radiation in the early Universe.
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All authors J. I. Villaseñor, H. Sana, J. Bodensteiner, N. Britavskiy, L. R. Patrick, T. Shenar, the BLOeM Collaboration

Astrophysics of Galaxies

Where Giants Dwell: Probing the Environments of Early Massive Quiescent Galaxies

Gabriella De Lucia, Lizhi Xie, Michaela Hirschmann et al. (+1 more)

We investigate the environments of massive quiescent galaxies at 3 < z < 5 using the GAlaxy Evolution and Assembly (GAEA) theoretical model. We select galaxies with stellar mass ~10^10.8 Msun and specific star formation rate below 0.3x t_Hubble, yielding in a sample of about 5,000 galaxies within a simulated volume of ~685 Mpc. These galaxies have formation times that cover well the range inferred from recent observational data, including a few rare objects with very short formation time-scales and early formation epochs. Model high-z quiescent galaxies are alpha-enhanced and exhibit a wide range of stellar metallicity, in broad agreement with current observational estimates. Massive high-z quiescent galaxies in our model occupy a wide range of environments, from void-like regions to dense knots at the intersections of filaments. Quiescent galaxies in underdense regions typically reside in halos that collapsed early and grew rapidly at high redshift, though this trend becomes difficult to identify observationally due to large intrinsic scatter in star formation histories. The descendants of high-z massive quiescent galaxies display a broad distribution in mass and environment by z=0, reflecting the stochastic nature of mergers. About one-third of these systems remain permanently quenched, while most rejuvenation events are merger-driven and more common in overdense regions. Our results highlight the diversity of early quiescent galaxies and caution against assuming that all such systems trace the progenitors of present day most massive clusters.
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All authors Gabriella De Lucia, Lizhi Xie, Michaela Hirschmann, Fabio Fontanot

Astrophysics of Galaxies

An almost NIRCam-dark dusty star-forming galaxy at z=6.63

Longji Bing, Seb Oliver, Mengyuan Xiao et al. (+28 more)

We present AC-2168, an almost NIRCam-dark, millimetre-bright galaxy in the COSMOS field. The source was identified blindly in ALMA Band-4 continuum data and remains undetected in the COSMOS-Web DR1 NIRCam catalogue. We spectroscopically confirm a redshift of $z_{\rm spec}=6.631$ from [CII] 158 $\mu$m and four tentatively detected CO lines in NOEMA and ALMA data. SED fitting to near-IR to millimetre photometry yields $\rm L_{IR}=1.6\times10^{12}\,L_\odot$, an SFR of $\rm 244\,M_\odot/yr$, heavy dust attenuation $\rm A_V=5.4$ mag, and a stellar mass $\rm M_\star=3.7\times10^{10}\,M_\odot$. From the millimetre continuum and [CII] emission, we infer a warm ISM with $\rm T_{\rm dust}=60K$, $\rm M_{dust}=3.0\times10^{8}\,M_\odot$ and $\rm M_{gas}=4.1\times10^{10}\,M_\odot$. AC-2168 has a gas fraction ($f_{\rm gas}=M_{\rm gas}/(M_\star+M_{\rm gas})$) of $\sim52\%$, a short depletion time of $\rm \sim170Myr$, a compact ($\rm \sim1kpc$) dust-continuum size, and an SFR consistent with the star-forming main sequence at its mass. These properties match expectations for progenitors of massive quiescent galaxies at the peak of their assembly, as implied by NIRSpec-based SFHs of $z\sim4-5$ systems. Using the blind detection, we estimate a space density of $\rm 7.8^{+18.0}_{-6.5}\times10^{-6}\,cMpc^{-3}$ for AC-2168-like NIRCam-dark galaxies at $z\sim6-7$, $\sim42\%$ of the abundance of massive quiescent galaxies at $z\sim4-5$. No overdensity of Ly$\alpha$ emitters or Lyman-break galaxies is found nearby, suggesting AC-2168 does not lie in a prominent protocluster and highlighting the importance of unbiased blind surveys for this population.
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All authors Longji Bing, Seb Oliver, Mengyuan Xiao, Guilaine Lagache, Sylvia Adscheid, Daizhong Liu, Benjamin Magnelli, Roberto Neri, Miroslava Dessauges-Zavadsky, Anton M. Koekemoer, Maximilien Franco, Shuowen Jin, Olivia R. Cooper, Andreas L. Faisst, Catilin M. Casey, Jeyhan S. Kartaltepe, Hollis Akins, Alexandre Beelen, David Elbaz, Steven Gillman, Santosh Harish, Arianna S. Long, Henry Joy McCracken, Pascal Oesch, Louise Paquereau, Nicolas Ponthieu, Jason Rhodes, Brant Robertson, David B. Sanders, Marko Shuntov, Stephen Wilkins

Astrophysics of Galaxies

JWST/NIRSpec Reveals a Small Population of Dominant Dust-Obscured Ionizing Sources in Galaxies at 1 < z < 3

Si-Rui Ge, Nikko J. Cleri, Joel Leja et al. (+2 more)

Rest-frame optical emission line diagnostics are often used to help classify ionizing sources within galaxies. However, rest-frame optical tracers can miss sources with high dust attenuation, leading to misclassification of the dominant ionizing source. Longer wavelength tracers, such as those in the near-infrared, carry the power to diagnose ionizing sources while being more robust than optical tracers to the presence of dust. The diagnostics used in this work employ the ratios of bright near-infrared emission lines [S III] 9530, [Fe II] 12566 and [Fe II] 16443 to Paschen lines in publicly-available JWST/NIRSpec MSA medium-resolution spectroscopy of 55 galaxies at z < 3. We compare the rest-frame near-infrared and rest-frame optical diagnostics and find that ~90% of our sample have consistent classifications across wavelengths (49/55), while the remaining sources can be explained through ionizing radiation obscured by dust and/or elevated N/Fe abundances. We identify three objects classified as star-forming in the rest frame optical and as active galactic nuclei (AGN) in the rest-frame near-infrared, which we interpret as obscured AGN. We also identify three objects which are classified as AGN in the rest-frame optical and star forming in the rest-frame near-infrared. We interpret two of these objects as AGN with obscured star formation and the other with elevated N/Fe. We discuss how future spatially-resolved and/or mid-infrared spectroscopy can test the relative contributions of AGN and stars to the ionizing photon budgets of these disagreeing sources.
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All authors Si-Rui Ge, Nikko J. Cleri, Joel Leja, Antonello Calabro, Vital Fernandez

Astrophysics of Galaxies

Bridging scales: How much do supermassive black holes grow in the suppressed Bondi regime?

Kung-Yi Su, Angelo Ricarte, Priyamvada Natarajan et al. (+6 more)

The co-evolution of supermassive black holes (SMBHs) and their host galaxies remains one of the central open questions in cosmology, rooted in the coupling between accretion, feedback, and the multi-scale physics that links the event horizon to the circumgalactic medium. Here we bridge these scales by embedding a first-principles, GRMHD-informed prescription for black hole accretion and feedback–derived from multi-zone simulations that self-consistently connect inflows and outflows from the horizon to the Bondi radius–within cosmological magnetohydrodynamic zoom-in simulations of $\sim10^{14}\,M_\odot$ halos. These GRMHD results predict a "suppressed Bondi" regime in which magnetic stresses and relativistic winds strongly reduce effective accretion rates in a spin-dependent manner. We find that black holes cannot grow efficiently by accretion until they exceed $\sim10^{7}\,M_\odot$, regardless of the feedback strength. Beyond this threshold, systems bifurcate: low-spin ($\eta\!\sim\!0.02$) black holes continue to accrete without quenching star formation, while high-spin ($\eta\!\gtrsim\!0.3$) black holes quench effectively but become starved of further growth. Early, massive seeding partially alleviates this tension through merger-driven assembly, yet an additional cold or super-Eddington accretion mode appears essential to reproduce the observed SMBH population and the empirical black hole–galaxy scaling relations. Our results demonstrate that GRMHD-informed feedback models can account for the maintenance-mode behavior of low-luminosity AGN like M87*, but cannot by themselves explain the full buildup of SMBH mass across cosmic time. A unified, multi-regime framework is required to capture the evolving interplay between spin-dependent feedback, cold inflows, and mergers in driving co-evolution.
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All authors Kung-Yi Su, Angelo Ricarte, Priyamvada Natarajan, Antonio J. Porras-Valverde, Hyerin Cho, Ramesh Narayan, Claude-André Faucher-Giguère, Philip F. Hopkins, Ben S. Prather

Cosmology and Nongalactic Astrophysics

Exploring the Impact of Systematic Bias in Type Ia Supernova Cosmology Across Diverse Dark Energy Parametrizations

Drishti Sharma, Purba Mukherjee, Anjan A Sen et al. (+1 more)

We investigate the impact of instrumental and astrophysical systematics on dark energy (DE) constraints from Type Ia supernova (SN-Ia) observations. Using simulated datasets consistent with current SN-Ia measurements, we examine how photometric calibration, intergalactic dust, progenitor evolution in luminosity and light-curve stretch, intrinsic color scatter, and matter density mismatch affect the inferred DE equation of state (EoS) parameters $(w_0,w_a)$. We test the Generalised Scale Factor (GEN) parametrization against three time-evolving DE models: Chevallier-Polarski-Linder (CPL), Jassal-Bagla-Padmanabhan (JBP), and Logarithmic (LOG). Calibration and progenitor-related effects emerge as the dominant sources of bias. {In particular, a calibration offset of $\Delta M_B=0.02$ can shift the inferred parameters by up to $\Delta w_0 \simeq -0.12$ and $\Delta w_a \simeq +0.60$ in JBP, while the corresponding shift in GEN is much smaller, with $\Delta w_0 \simeq -0.02$ and $\Delta w_a \simeq -0.04$. Progenitor-stretch evolution also induces substantial shifts, whereas intergalactic dust and color-scatter systematics produce only minor deviations for the fiducial amplitudes adopted here. Overall, JBP is the most sensitive to injected systematics, CPL and LOG show intermediate sensitivity, and GEN remains the most stable. We also quantify the deviation from the fiducial $\Lambda$CDM ($w_0=-1,\, w_a=0$) for the injected-systematic cases, and find that the second set of systematic injections supports the same qualitative hierarchy. These results highlight the need for sub-percent calibration precision and improved astrophysical modelling for robust DE inference from present and future SN-Ia cosmology experiments. More broadly, our results motivate model-independent tests of late-time physics, with phenomenological $(w_0,w_a)$ parametrizations used as summary statistics.
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All authors Drishti Sharma, Purba Mukherjee, Anjan A Sen, Suhail Dhawan

Cosmology and Nongalactic Astrophysics

Early Formation of Supermassive Black Holes via Dark Star Gravitational Instability

Katherine Freese, George M. Fuller, Sohan Ghodla et al. (+4 more)

We show that dark stars, which are dark-matter-powered stars in the early universe, can grow by accretion to masses in the range $\mathscr{O}\left ({10}^4\right )-\mathscr{O}\left ({10}^7\right)\,{M_\odot}$ before the general-relativistic Feynman-Chandrasekhar instability causes their dynamical collapse to black holes. These accreting dark star configurations avoid standard stellar nuclear- and weak-interaction evolution that would lead to their demise long before they reached this supermassive size. Remarkably, this mechanism for supermassive black hole (SMBH) genesis is relatively robust to initial dark star mass, formation epoch, accretion rate and its history. The SMBHs produced this way can serve as seeds for even larger SMBHs $({\gtrsim}10^9\,M_\odot)$ that have been discovered at high redshift.
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All authors Katherine Freese, George M. Fuller, Sohan Ghodla, Cosmin Ilie, Kyle S. Kehrer, Tanja Rindler-Daller, Evangelos I. Sfakianakis

Cosmology and Nongalactic Astrophysics

Dark winds on the horizon: Prospects for detecting neutrino and hot dark matter wakes in large-scale structure

Caio B. de S. Nascimento and Marilena Loverde

We explore the cosmological signatures of neutrino and Hot Dark Matter (HDM) wakes, which refers to the preferential accumulation of neutrinos (or, more broadly, HDM particles) downstream of moving cold dark matter structures. We improve on existing theoretical models, and provide forecasts for the detectability of the effect in future surveys under more realistic conditions than previously considered in the literature. We show that neutrino and HDM wakes are unlikely to be ever observed with the most natural tracer of a hot subcomponent of the total dark matter on cosmological scales, i.e. 2D weak lensing surveys. However, the effect can be detected at a high significance with idealistic 3D maps of a tracer of HDM, for sufficiently small values of the effective free-streaming length (e.g. present-day values of $k_{\textrm{fs},0} \gtrsim 0.03\textrm{Mpc}^{-1}$ to reach $\textrm{SNR} \gtrsim 1$, for a HDM species accounting for a percent of the total dark matter). HDM wakes are a smoking gun of the effects of free-streaming, which cannot be mimicked by changes to the background expansion history (such as allowing for the dark energy to be dynamical), and hence offer another avenue to search for massive neutrinos, and hot subcomponents of the total dark matter more broadly, in a way that complements traditional observables.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Metastable Strings and Gravitational Waves in One-Scale Models

James Ingoldby, Valentin V. Khoze and Jessica Turner

Metastable cosmic strings provide a minimal and predictive origin for the stochastic gravitational-wave background reported by Pulsar Timing Array experiments. We analyse this possibility in electroweak-like dark sectors with a single-stage breaking $SU(2)\times U(1)\!\to\!U(1)$ driven by one Higgs field. In the regime with dark sector Higgs mass below the $Z'$ mass, and for sufficiently small $W'$ mass, the resulting $Z$-string is classically stable but undergoes quantum decay via nucleation of monopole–antimonopole pairs along the string. We compute the corresponding semiclassical bounce action in a thin-defect approximation, treating both the string core and the monopole endpoints as localised defects whose sizes are small relative to their separation in the tunnelling configuration. This yields a decay rate per unit length that depends on the gauge couplings and the mass hierarchy. We delineate the parameter space in which single-scale dark-sector models reproduce the PTA signal, demonstrating the applicability of the thin-defect approximation throughout the phenomenologically favoured region and without invoking extended Higgs sectors or multi-stage symmetry breaking.
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High Energy Astrophysical Phenomena

A Novel Parameterization for Rapid Cooling in Supernova Remnants, with applications to the Pa 30 nebula

Miranda Pikus, Paul Duffell, Soham Mandal et al. (+1 more)

We systematically study how cooling creates structural changes in supernova remnants as they evolve. Inspired by the peculiar morphology of the Pa 30 nebula, we adopt a framework in which to characterize supernova remnants under different degrees of cooling. Our cooling framework characterizes remnants with a singular parameter called $\beta$ that sets how rapidly the system's thermal energy is radiated or emitted away. A continuum of morphologies is created by the implementation of different cooling timescales. For $\beta \gtrsim 400$, or when the cooling timescale is shorter than $\approx \frac{1}{400}$ of the Sedov time, the ejecta is shaped into a filamentary structure similar to Pa 30. We explain the filament creation by the formation of Rayleigh-Taylor Instability fingers where cooling has prevented the Kelvin-Helmholtz Instability from overturning and mixing out the tips. The ejecta in these filaments have not decelerated and are moving almost completely ballistically at $\approx 95-100\%$ their free expansion speed. In this rapid cooling regime, an explosion energy $\approx 3.5 \times 10^{47}$ erg is inferred. We also propose the cooling mechanism required to create these structures necessitates removing energy at a rate of $2\%$ of $E_{\rm ej}/t$, which implies a cooling luminosity of $\approx 10^{36}$ erg/s.
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All authors Miranda Pikus, Paul Duffell, Soham Mandal, Abigail Polin

Solar and Stellar Astrophysics

Growth of Metal-Enriched Supermassive Stars by Accretion and Collisions

Devesh Nandal and Sunmyon Chon

Supermassive stars (SMSs) are candidate progenitors of massive black hole seeds and may contribute to anomalous abundance patterns in high-redshift galaxies and globular clusters. Recent radiation-hydrodynamic simulations indicate that SMSs can form at finite metallicity, not only in metal-free direct-collapse conditions. We model SMS growth with GENEC over $Z/Z_\odot=10^{-5}$-$10^{-2}$ using simulation-motivated accretion histories. The final masses reach $\sim7.2\times10^{4}\,M_\odot$ at $10^{-5}\,Z_\odot$ and $\sim2.3\times10^{3}\,M_\odot$ at $10^{-2}\,Z_\odot$. Models are evolved through the pre-main sequence and core H-burning phases, terminating at the onset of general-relativistic instability for $Z\lesssim10^{-4}\,Z_\odot$ or at core He exhaustion for $Z\gtrsim10^{-3}\,Z_\odot$. The dominant mass growth channel transitions from collision-driven to accretion-driven between $Z=10^{-4}$ and $10^{-3}$. With stellar lifetimes remaining nearly constant at $1.8$-$2.0$ Myr, collisions do not significantly rejuvenate the star, implying that collision driven runaway collapse cannot proceed in isolation and must be supplemented, and likely dominated by gas accretion. We further compute the critical inflow rate required to keep the stellar envelope inflated, $\dot{M}_{\rm crit}$, which decreases with increasing $Z$ and decreasing central mass fraction of hydrogen ($X_{\rm c}$). The critical rate falls below $10^{-5}\,M_\odot\,{\rm yr^{-1}}$ at $X_{\rm c}=0.60$ for $10^{-2}Z_\odot$. This indicates that SMSs with $0.01~Z_\odot$ are cool supergiants during most of their lifetimes, where UV photon emissivity and radiative feedback is strongly suppressed. Overall, SMS evolution remains viable up to $Z\simeq0.01\,Z_\odot$, supporting SMS formation in proto-globular clusters and other metal-enriched dense environments.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Nonlinear Gravitational Wave Memory : Universal Low-Frequency Background

Caner Ünal and Doğa Veske

A universal contribution exists in the infrared (low frequency) regime of all gravitational waves, which results from nonlinear memory. Nonlinear memory is sourced by linear order gravitational waves and exists for any gravitational-wave background. We calculate the stochastic nonlinear memory signal of various stochastic backgrounds of cosmological (scalar induced, reheating, phase transition, topological defect, turbulence) and astrophysical (binary mergers of stellar-mass, intermediate mass, supermassive, and primordial black holes) origins. These results allow us to derive the complete frequency spectrum of cosmological and astrophysical SGWB. We calculate how to probe the thermal state of the universe, i.e. the equation of the state, via the memory spectrum's slope and also discuss the detection prospects at various frequency bands with future experiments.
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Earth and Planetary Astrophysics

Lunar Dust: Formation, Microphysics, and Transport

Slava G. Turyshev

Lunar dust – the sub-millimeter fraction of the regolith – controls the optical, thermophysical, electrical, mechanical, and environmental behavior of the Moon's surface. These properties set the performance envelopes of remote-sensing retrievals, regolith geotechnics, volatile cycles, and exploration systems, while also posing operational and biomedical risks. We synthesize Apollo sample analyses and in-situ observations (Surveyor, Lunokhod, Apollo) with contemporary datasets from the LRO Diviner Lunar Radiometer, the LADEE/LDEX exospheric dust measurements, and Chang'e-4 Lunar Penetrating Radar (LPR). We also incorporate 2024-2025 results: Chandrayaan-3 ChaSTE thermophysics at the Vikram lander's site, SCALPSS plume-surface diagnostics from Intuitive Machines Mission 1 (IM-1), and Negative Ions at the Lunar Surface (NILS) detections of a dayside near-surface H$^{-}$ population on Chang'e-6. The review links (i) production and modification processes to (ii) grain-scale physical/chemical/electrical/optical/mechanical properties, then to (iii) mobilization pathways (meteoroid ejecta, electrostatic hopping, rocket-plume entrainment), and finally to (iv) region-specific design ranges across maria, highlands, pyroclastic units, magnetic swirls, and permanently shadowed regions (PSRs). We quantify temperature-illumination dependence across day/night and PSR-equator regimes through a two-channel $k(T,\rho)$ model and charge-relaxation scaling. We provide closed-form expressions for adhesion-aware lift thresholds and for near-surface (0-3~m) dust transport at apex/hover heights as functions of sheath structure. The result is a design-ready set of relations, figures, and tables that propagate microphysics and composition into engineering parameters for upcoming landed and rover operations.
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Instrumentation and Methods for Astrophysics

A Simple Ray Acceleration Structure for Non-LTE Radiative Transfer

Christopher M. J. Osborne

We present a novel ray acceleration structure for radiative transfer outside of local thermodynamic equilibrium (non-LTE), leveraging techniques from computer graphics to improve computational efficiency. By applying mipmapping (local recursive spatial averaging) and sparse voxel grids, we exploit spatial coherence and sparsity in astrophysical models to accelerate the formal solution of the radiative transfer equation. We introduce a variance-limited mipmapping (VLM) scheme with tunable error control, and extend it to handle anisotropic emission via two methods: velocity interpolation, and so-called "Core and Voigt". Our approach integrates a hierarchical digital differential analyzer (HDDA) for efficient ray traversal, which, combined with the mipmapping scheme achieves an order of magnitude speedup with less than 0.5 % error in the 99.9th percentile of the level populations. These methods are implemented in the DexRT code and demonstrate significant performance gains in realistic solar atmospheric models.
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Cosmology and Nongalactic Astrophysics

Accelerated inference of microlensed gravitational waves with machine learning

Marienza Caldarola, Srashti Goyal, Nihar Gupte et al. (+2 more)

Gravitational waves (GWs) within the LIGO-Virgo-KAGRA sensitivity band can be microlensed by stellar and intermediate-mass black holes, producing a frequency-dependent modulation of the signal amplitude. Microlensing analyses, however, are costly due to the increased dimensionality of the parameter space and waveform computation time. As a proof of concept, we show that the deep-learning-based framework Deep Inference for Gravitational-Wave Observations (DINGO), which employs a simulation-based inference approach to estimate posterior distributions, can perform efficient parameter inference for GW microlensing by an isolated point-mass lens. Using simulated microlensed GW signals, we train a lensed-DINGO network and compare its performance with traditional Bayesian parameter estimation carried out with Bilby. Our framework can be used to rapidly identify microlensed events in large GW catalogs. When the lensed-DINGO network is combined with importance sampling, we find that although sample efficiencies are somewhat reduced compared to the unlensed-DINGO network, owing to the richer structure of microlensed signals, it still achieves $\mathcal{O}(10\times)$ speed-up relative to Bilby. We further show that this framework is useful to efficiently estimate the background Bayes-factor distribution, which is crucial for assessing the significance of candidate lensed events. However, for foreground (lensed) events, the sampling efficiency can sometimes drop when analysed with the unlensed-DINGO network, providing a diagnostic indicator of out-of-distribution data. Our approach can be straightforwardly generalised to more complex and realistic lens models, enabling detailed studies of microlensed GWs.
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All authors Marienza Caldarola, Srashti Goyal, Nihar Gupte, Stephen R. Green, Miguel Zumalacárregui

Solar and Stellar Astrophysics

Stellar cycle variability in Mount Wilson stars and dynamo models: Rotation rate and dynamo number dependency

Suyog Garg, Bidya Binay Karak and Rohan B. Mandrai

Similar to the solar cycle, the magnetic cycles of other solar-type stars are also variable. How the variability of the stellar cycle changes with the rotation rate or the dynamo number is a valuable information for understanding the stellar dynamo process. We examine the variability in the stellar magnetic cycles by studying 81 stars from the data of the Mount Wilson Observatory, which started observations in 1966. For 28 stars, we have time series data available till 2003, while for others, the data are limited till 1995. We specifically explore how the variability changes with respect to three rotation-related parameters. We find a modest positive correlation between the variability and the stellar rotation period. In addition, we find suggestive negative correlations between the variability and the inverse squared Rossby number ($Ro^{-2}$), and the ratio of the mean cycle duration and rotation period ($\log \, (\langle P_{\rm cyc} \rangle / P_{\rm rot})^2$). Variability computed from the magnetic field of stellar dynamo models also show similar trends. Finally, inspired by previous studies, we examine dynamo number scaling in our model data and find that $Ro^{-0.6}$ (instead of $Ro^{-2}$ as suggested in the linear $\alpha \Omega$ dynamo theory) and $(\langle P_{\rm cyc} \rangle /P_{\rm rot})^{0.6}$ (instead of $\log \, (\langle P_{\rm cyc} \rangle / P_{\rm rot})^2$ as predicted in previous observations) are a good measure of the dynamo number. In conclusion, our results demonstrate that the stellar magnetic cycle variability decreases with the increase of the rotation rate or the dynamo number.
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Astrophysics of Galaxies

Supermassive Dark Stars and their remnants as a possible solution to three recent cosmic dawn puzzles

Cosmin Ilie, Jillian Paulin, Andreea Petric et al. (+1 more)

The James Webb Space Telescope (JWST) has begun to revolutionize our view of the Cosmos. The discovery of Blue Monsters (i.e., ultra-compact yet very bright high-z galaxies) and the Little Red Dots (i.e., very compact dustless strong Balmer break cosmic dawn sources) pose significant challenges to pre-JWST era models of the assembly of first stars and galaxies. In addition, JWST data further strengthen the problem posed by the origin of the supermassive black holes that power the most distant quasars observed. Stars powered by Dark Matter annihilation (i.e., Dark Stars) can form out of primordial gas clouds during the cosmic dawn era and subsequently might grow via accretion and become supermassive. In this paper we argue that Supermassive Dark Stars (SMDSs) offer natural solutions to the three puzzles mentioned above.
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All authors Cosmin Ilie, Jillian Paulin, Andreea Petric, Katherine Freese

Earth and Planetary Astrophysics

HARPS-N, TESS, and CHEOPS discover a transiting sub-Neptune and two outer companions around the bright solar analogue HD 85426

F. Lienhard, A. Mortier, A. Collier Cameron et al. (+96 more)

We provide a detailed characterisation of the planetary system orbiting HD 85426 (TOI-1774). This bright G-type star ($M_{\ast}$: 0.99 $\text{M}_{\odot}$; $R_{\ast}$: 1.13 $\text{R}_{\odot}$; age: 7.4 Gyr; V mag: 8.25) hosts a transiting sub-Neptune, HD 85426 b, with an orbital period of 16.71 days and a blackbody equilibrium temperature of $824^{+11}_{-11}$ K. By jointly analysing HARPS-N RVs, TESS, and CHEOPS photometric data and using two different stellar activity mitigation techniques, we constrain planet b's mass to $6.0^{+1.5}_{-1.6}$ $\text{M}_{\oplus}$ and $8.5^{+1.3}_{-1.4} $ $\text{M}_{\oplus}$, depending on the mitigation technique. We investigate the dependence of these results on the priors, data selection, and inclusion of other Keplerians in the modelling. Using this approach, we identify the presence of two non-transiting planetary companions with minimum masses near 10 $\text{M}_{\oplus}$ and orbital periods of 35.7 and 89 days. Additionally, we reject the initial hypothesis that the 35.7-day periodic signal was due to stellar activity. We also determine HD 85426 b's radius to be $2.78^{+0.05}_{-0.04}$ $\text{R}_{\oplus}$ and compute a transmission spectroscopy metric in the range of 82 to 115, making this planet a highly valuable target for atmospheric characterisation.
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All authors F. Lienhard, A. Mortier, A. Collier Cameron, M. Cretignier, L. Borsato, A. Anna John, J. A. Egger, M. Stalport, T. G. Wilson, A. Deline, A. Fortier, D. W. Latham, L. Malavolta, P. F. L. Maxted, S. G. Sousa, S. L. Grimm, L. Buchhave, Y. Alibert, B. S. Lakeland, X. Dumusque, J. Cabrera, L. Naponiello, A. C. M. Correia, F. Rescigno, L. Fossati, A. Sozzetti, R. Alonso, T. Bárczy, D. Barrado, S. C. C. Barros, W. Baumjohann, W. Benz, N. Billot, A. Brandeker, C. Broeg, K. Collins, Sz. Csizmadia, P. E. Cubillos, M. B. Davies, M. Deleuil, O. D. S. Demangeon, B.-O. Demory, A. Derekas, B. Edwards, D. Ehrenreich, A. Erikson, M. Fridlund, D. Gandolfi, K. Gazeas, M. Gillon, M. Güdel, M. N. Günther, R. Haywood, A. Heitzmann, Ch. Helling, K. G. Isaak, J. M. Jenkins, L. L. Kiss, J. Korth, K. W. F. Lam, J. Laskar, A. Lecavelier des Etangs, A. Leleu, M. Lendl, D. Magrin, A. F. Martínez Fiorenzano, B. Merín, C. Mordasini, V. Nascimbeni, G. Olofsson, H. P. Osborn, R. Ottensamer, I. Pagano, L. Palethorpe, E. Pallé, G. Peter, D. Piazza, G. Piotto, D. Pollacco, D. Queloz, R. Ragazzoni, N. Rando, H. Rauer, I. Ribas, K. Rice, N. C. Santos, G. Scandariato, D. Ségransan, A. E. Simon, A. M. S. Smith, S. Sulis, Gy. M. Szabó, S. Udry, S. Ulmer-Moll, V. Van Grootel, J. Venturini, E. Villaver, N. A. Walton, T. Zingales

Solar and Stellar Astrophysics · Cross-listed from physics.space-ph

Monitoring the Solar Wind Before It Reaches L1

Erika Palmerio

Space weather predictions of the solar wind impacting Earth are usually first based on remote-sensing observations of the solar disc and corona, and eventually validated and/or refined with in-situ measurements taken at the Sun$-$Earth Lagrange L1 point, where real-time monitoring probes are located. However, this pipeline provides, on average, only a few tens of minutes of lead time, which decreases to $\sim$30 minutes or less for large solar wind speeds of $\sim$800 km/s and above. The G5 geomagnetic storm of 2024 May provided an opportunity to test predictions generated employing real-time data from the STEREO-A spacecraft, placed 13{\deg} west of Earth and 0.04 au closer to the Sun than L1 at the time of the event, as shown recently by Weiler et al. (2025). In this Commentary, we contextualise these results to reflect upon the advantages of measuring the solar wind in situ upstream of L1, leading to improvements in both fundamental research of interplanetary physics and space weather predictions of the near-Earth environment.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Bounds on screened dark energy from near-Earth space-based measurements

Fabiano Feleppa, Welmoed Marit de Graaf, Philippe Brax et al. (+1 more)

We test screened dark energy with near-Earth, space-based measurements. In a post-Newtonian framework, we compute leading corrections to geodetic precession (Gravity Probe B), LAGEOS-2 pericenter advance, and the Sagnac delay in a prospective orbital configuration, yielding bounds on chameleon, symmetron, and dilaton models. LAGEOS-2 sets the strongest Earth-orbit limits on symmetron and dilaton, while a Sagnac setup at the projected sensitivity of state-of-the-art space clocks gives the tightest chameleon constraint. These results show that low-density, space-based experiments sensitively probe screened dark energy and exclude previously allowed parameter space. Notably, at nuclear-clock precision $\mathcal{O}\big(10^{-19}\big)$, a Sagnac test would exclude the entire chameleon parameter space considered.
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All authors Fabiano Feleppa, Welmoed Marit de Graaf, Philippe Brax, Gaetano Lambiase

Astrophysics of Galaxies

Isolated massive star candidates in NGC 4242 with GULP

Pietro Facchini, Eva K. Grebel, Anna Pasquali et al. (+16 more)

$\textit{Context.}$ There is considerable debate on how massive stars form, including whether a high-mass star must always form with a population of low-mass stars or whether it can also form in isolation. Massive stars found in the field are often considered to be runaways from star clusters or OB associations. However, there is evidence in the Milky Way and the Small Magellanic Cloud of high-mass stars that appear isolated in the field and cannot be related to any known star cluster or OB association. Studies of more distant galaxies have been lacking so far. $\textit{Aims.}$ In this work, we identified massive star candidates that appear isolated in the field of the nearby spiral galaxy NGC 4242 (distance: 5.3 Mpc), to explore how many candidates for isolated star formation we find in a galaxy outside the Local Group. $\textit{Methods.}$ We identified 234 massive ($M_{ini}\geq15M_{\odot}$) and young ($\leq 10$ Myr) field stars in NGC 4242 using the Hubble Space Telescope's Solar Blind Channel of the Advanced Camera for Surveys, the UVIS channel of the Wide Field Camera 3 from the Galaxy UV Legacy Project (GULP) and optical data from the Legacy ExtraGalactic UV Survey (LEGUS). We investigated the surroundings of our targets within the range of projected distances expected for runaway stars, $74$ pc and $204$ pc. $\textit{Results.}$ We find that between $9.8\%$ and $34.6\%$ of our targets have no young stellar groups or massive stars within the threshold radii, making them appear isolated. This fraction reduces to $3.2\%-11.5\%$ when we consider the total number of massive stars expected from the observed UV star formation rate. $\textit{Conclusions.}$ Our results show that there is a small population of young and massive, potentially isolated field stars in NGC 4242.
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All authors Pietro Facchini, Eva K. Grebel, Anna Pasquali, Elena Sabbi, Beena Meena, Varun Bajaj, John S. Gallagher III, Bruce G. Elmegreen, Luciana Bianchi, Angela Adamo, Daniela Calzetti, Michele Cignoni, Paul A. Crowther, Jan J. Eldridge, Mario Gennaro, Ralf S. Klessen, Linda J. Smith, Aida Wofford, Peter Zeidler

Cosmology and Nongalactic Astrophysics

Galactification: painting galaxies onto dark matter only simulations using a transformer-based model

Shivam Pandey, Christopher C. Lovell, Chirag Modi et al. (+1 more)

Connecting the formation and evolution of galaxies to the large-scale structure is crucial for interpreting cosmological observations. While hydrodynamical simulations accurately model the correlated properties of galaxies, they are computationally prohibitive to run over volumes that match modern surveys. We address this by developing a framework to rapidly generate mock galaxy catalogs conditioned on inexpensive dark-matter-only simulations. We present a multi-modal, transformer-based model that takes 3D dark matter density and velocity fields as input, and outputs a corresponding point cloud of galaxies with their physical properties. We demonstrate that our trained model faithfully reproduces a variety of galaxy summary statistics and correctly captures their variation with changes in the underlying cosmological and astrophysical parameters, making it the first accelerated forward model to capture all the relevant galaxy properties, their full spatial distribution, and their conditional dependencies in hydrosimulations.
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All authors Shivam Pandey, Christopher C. Lovell, Chirag Modi, Benjamin D. Wandelt

Instrumentation and Methods for Astrophysics

WFC3/IR Starter Guide

P. R. McCullough and Joel D. Green

In this starter guide, we provide a high-level overview of analysis of WFC3/IR data available from the Mikulski Archive for Space Telescopes (MAST). We intend this guide as a starting point for users examining WFC3/IR data for the first time, or for those refreshing their memory on WFC3/IR data analysis. Therefore, we focus on the analysis of archival data, not preparing new observations. Three appendices include A) a summary of the instrument and an optical schematic, B) examples from the Exposure Time Calculator, and C) a glossary of uncommon acronyms. This report addresses only data from WFC3's IR channel; not the UVIS channel.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.acc-ph

High Power RF Pulse Shaping Tests with NG-LLRF and Cool Copper Collider Prototype Structure

Chao Liu, Ankur Dhar, Ronald Agustsson et al. (+4 more)

RF pulse modulation techniques are widely applied to shape RF pulses for various types of RF stations of particle accelerators. The amplitude and phase modulations are typically implemented with additional RF components that require drive or control electronics. For the RF system-on-chip (RFSoC) based next generation LLRF (NG-LLRF) platform, which we have developed in the last several years, RF modulation and demodulation are fully implemented in the digital domain. Therefore, arbitrary RF pulse shaping can be realized without any additional analogue components. We performed a range of high-power experiments with the NG-LLRF and a prototype Cool Copper Collider (C3) structure. In this paper, the RF field measured at different stages with different pulse shapes and peak power levels up to 5.4 MW and pulse width about 1 microsecond will be demonstrated and analyzed. The high precision pulse shaping schemes of the NG-LLRF can be applied to realize the phase modulation for a linear accelerator injector, the phase reversal for a pulse compressor, or the modulation required to compensate for the beam loading effect.
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All authors Chao Liu, Ankur Dhar, Ronald Agustsson, Diego Amirari, Dennis Palmer, Martin Breidenbach, Emilio Nanni

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

Evading the BBN bound with a soft stiff period

Lucy Brissenden, Konstantinos Dimopoulos and Eemeli Tomberg

Cosmic inflation is the leading theory to explain early Universe history and structure formation. Non-oscillatory inflation is a class of models which can naturally introduce a post-inflationary stiff period of the Universe's evolution which boosts the signal of primordial gravitational waves (GWs), making it possible to observe them in forthcoming GW experiments. However, this pushes the GW energy density high enough to destabilise the process of Big Bang Nucleosynthesis (BBN). This problem can be overcome by "softening" the stiff period, so that the field is gradually tending towards freefall from a frozen start. Here, we consider a modified hybrid inflation model where the stiff period is driven by the waterfall field, allowing the barotropic parameter of the Universe to vary, so that it does not violate the BBN constraint but produces a characteristic gravitational wave spectrum soon to be observable.
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High Energy Astrophysical Phenomena

Revisiting the Possibility of a Sharp Phase Transition in Cold Neutron Stars

Bao-Jun Cai, Bao-An Li and Yu-Gang Ma

First-order phase transitions (FOPTs) in cold neutron stars (NSs) have been extensively studied and have provided valuable insights into the behavior of the densest matter visible in our Universe, although a strong consensus has yet to emerge. Revisiting the possibility of a hadron-quark FOPT from a new perspective, we examine the interplay between the coupled nature of gravity and microscopic interactions in Tolman–Oppenheimer–Volkoff (TOV) equations and the fundamental requirements of thermodynamic consistency in NSs. We demonstrate that a sharp FOPT manifested as a plateau in the equation of state (EOS) $P(\varepsilon)$, i.e., pressure $P$ versus energy density $\varepsilon$, is intrinsically incompatible with the regularity conditions of the TOV solutions. Although numerical integrations of the TOV equations with EOSs incorporating FOPTs may yield seemingly reasonable mass-radius relations consistent with current observations, such results can mask underlying inconsistencies. Our analysis thus establishes a structural consistency criterion for constraining dense-matter EOSs using NS observables, complementing existing studies of possible phase transitions in NS interiors.
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Solar and Stellar Astrophysics

Effect of gravity darkening and oblate factor in rapidly rotating massive stars

Bhawna Mukhija, Michel Curé, Ignacio Araya et al. (+2 more)

Context. Rapid rotation in massive stars leads to gravity darkening and oblateness, significantly affecting their radiation-driven winds. These effects can alter wind dynamics and play a role in forming slowly equatorial outflowing winds. Aims. This work investigates the transition region where the fast solution (i.e. high terminal velocities) of radiation-driven winds in a massive rotating star, in the frame of the modified-CAK theory, switches to the Omega-slow solutions (a denser and slower wind) when the effects of gravity darkening and oblateness are considered. This Omega-slow solution appears when the rotational speed is higher and equal to 75% of the critical rotation speed. Methods. To explore the transition region for various equatorial models of B-type stars, we focus on the co-existence interval where both solutions simultaneously exist and the transition point where fast solutions switch to Omega-slow solutions. Results. Using our stationary numerical code Hydwind, we first analyse the individual effects of gravity darkening and stellar oblateness caused by high rotational speeds and then examine their combined impact on the wind solutions. Conclusions. We find that for a certain range of rotational speeds, both the fast and Omega-slow solutions can co-exist, and the co-existence range strongly depends on the initial conditions. When only gravity darkening is considered, the co-existing interval shifts towards higher rotational speeds. While in the presence of the oblateness, the co-existing interval also occurs at higher rotational speeds; however, it is less than the gravity darkening effect. We also explored how line-force parameters affect the critical point, the location of the co-existing interval, and where the solution switches.
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All authors Bhawna Mukhija, Michel Curé, Ignacio Araya, Catalina Arcos, Alejandra Christen