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Physics Astrophysics

astro-ph Watch Astrophysics

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Astrophysics of Galaxies

Black hole spin-mass correlation and accretion disks at birth stage of dense star clusters

Zacharias Roupas

We review the accretion-driven channel of stellar black-hole growth and spin-up in gaseous star clusters, developed within the framework of our MSCA project "protoBH". Our detailed calculations involving semi-analytic modelling, dynamical and hydrodynamic simulations suggest that the growth and spin-up of initially low-mass stellar black holes is an integral element of the formation process of dense massive star clusters, such as the proto-globular clusters observed at high redshift. The black holes accrete residual gas, remaining from the first star formation event, and form accretion disks generated by gas angular momentum induced by the black-holes' own curved orbits. Assuming initial black hole masses below the pair-instability mass gap $\leq 55\,{\rm M}_{\odot}$, the gap gets populated with black-hole masses growing to $\sim 10^2\,{\rm M}_{\odot}$, and even reaching several hundred solar masses for sufficiently dense and massive proto-clusters. We predict a consistent spin-mass relation with low black hole spins $\lesssim 0.2$ for low black hole masses $\lesssim 20\,{\rm M}_{\odot}$, spanning all intermediate spins for higher masses and saturating to high spins $\gtrsim 0.8$ for high masses $\gtrsim 70\,{\rm M}_{\odot}$. We find evidence in favour of such an accretion-driven subpopulation of black holes in the GWTC-5.0 released by the LIGO-Virgo-KAGRA collaboration.
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High Energy Astrophysical Phenomena

Broadband non-thermal emission predictions based on 3D simulations of supernova explosions within active galactic nuclei jets

B. Longo, V. Bosch-Ramon, M. Perucho et al. (+1 more)

Thermonuclear and core-collapse supernovae are statistically expected to happen within extragalactic jets, as these jets cross the inner regions of their host galaxies, and supernova ejecta-jet interactions can potentially lead to strong non-thermal activity. We model the non-thermal emission from a supernova interacting with a jet on kiloparsec scales, using detailed numerical simulations of the interaction. Using a post-processing method, we applied a non-thermal model of the acceleration and transport of electron and their synchrotron and inverse Compton emissions, simplified and tuned for flexibility and computational speed, to the results of a three-dimensional relativistic hydrodynamics simulation of the ejecta of a supernova interacting with an extragalactic jet. For intermediate jet powers, radio, optical and X-ray fluxes from supernova ejecta-jet interactions may be detectable for distances < 100Mpc. The non-thermal luminosity budget and local conditions associated with these interactions could be enough to explain knots seen in kiloparsec scale jets at different energies. These conditions might also be suitable for the production of heavy ultra high-energy cosmic rays, but photon and neutrino generation from hadronic processes would be minor on kiloparsec scales. The leptonic gamma-ray fluxes are modest but might non-negligibly contribute in TeV for the nearest or more powerful jet sources.
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All authors B. Longo, V. Bosch-Ramon, M. Perucho, J.M. Martí

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Tidal Excitation of Relativistic Stars

Zhiqiang Miao, Junquan Su, Neev Khera et al. (+1 more)

How a relativistic star responds to a time-dependent tide has lacked a first-principles counterpart of the Newtonian normal-mode expansion. In general relativity, the tidal field is gauge sensitive, radiative modes are non-Hermitian and incomplete, and the direct and late-time responses are intrinsically nonmodal. In this work we present, to our knowledge, the first causal relativistic theory that treats all of these components on equal footing. We first develop the spectral decomposition of the retarded Green function of the matched stellar interior–Schwarzschild exterior, which classifies four separate regimes in time domain: acausal region, prompt wave, surface-reflected wave, and mode+tail. The prompt signal is identical to that of a Schwarzschild black hole with the same mass, which is combined with the surface-reflected wave to be referred as the "direct part". With the Green function and a complex bilinear form on the full metric–fluid phase space, we decompose the linear response of a nonrotating perfect-fluid star into direct, quasinormal-mode, and late-time-tail sectors. Crucially, every sector admits an explicit first-order driven evolution equation: discrete bilinear projections determine the dynamically evolving quasinormal-mode amplitudes, while continuum projections of the same tidal source onto branch-cut states determine the direct and tail amplitudes. The result is a complete modal–nonmodal decomposition of the spacetime and fluid perturbations, which is physically described by the dynamics of a discrete and a continuous-frequency set of oscillators. We verify the decomposition numerically under generic time-dependent tidal driving and discuss applications to black hole perturbations.
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All authors Zhiqiang Miao, Junquan Su, Neev Khera, Huan Yang

Astrophysics of Galaxies

EDGE-INFERNO: The chemical signatures of assembly history in reionization fossils

Eric P. Andersson, Martin P. Rey, Alexander P. Ji et al. (+9 more)

In galaxies, stellar populations represent a superposition of both in situ and accreted components, tracing internal chemical evolution as well as the histories of merged satellites. We investigate how assembly history shapes the chemical properties of present-day stellar populations in low-mass dwarf galaxies. We analyze a suite of EDGE-INFERNO star-by-star cosmological zoom-in simulations of galaxies with present-day halo mass $\sim1.4\times10^9\,{\rm M}_{\odot}$. We systematically vary galaxy growth while preserving the present-day halo mass, engineering our simulations to span a continuum of assembly histories. Early-forming systems form most of their stars in a single progenitor, with centrally concentrated star formation and a continuous enrichment history. In contrast, our late-forming systems assemble by accretion of multiple progenitors with their own stellar populations, resulting in fragmented star formation across several halos with independent chemical evolution tracks. These regimes produce qualitatively different chemical signatures: single-progenitor systems exhibit connected, well-defined trends in abundance space, while multi-progenitor systems show multiple, distinct stellar populations with limited overlap. We find that metallicity distribution functions provide initial constraints on assembly history for samples of at least $50$-$100$ member stars. Multi-element abundance analysis significantly improves the recovery of distinct components, although robust reconstruction still requires larger samples. Fully separating in situ and accreted populations likely requires kinematic information. Accreted stars can contribute substantially even at high metallicities in multi-progenitor systems, while external enrichment can cause accreted material to follow similar chemical trends as in situ stars, particularly in the single-progenitor regime.
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All authors Eric P. Andersson, Martin P. Rey, Alexander P. Ji, Justin I. Read, Oscar Agertz, Alexander H. Riley, Stacy Y. Kim, Astha Chaturvedi, Jennifer Mead, Kaley Brauer, Mordecai-Mark Mac Low, Andrew Pontzen

Instrumentation and Methods for Astrophysics

Ushering in high angular resolution observatories in the far-infrared: The case for a double-Fourier interferometer

C. S. Benson, M. Bonato, T. A. Davis et al. (+14 more)

A far-infrared (far-IR) interferometer from a space-based platform would bring about a transformational improvement in the spatial detail of astronomical observations that are inaccessible from ground-based observatories. This orders-of-magnitude improvement would significantly advance studies of newly formed and mature exoplanetary systems and their potential for supporting life, the earliest stages of star formation, and the evolution of galaxies up to the peak of the Universe's star formation activity and beyond. In this work, we discuss the potential for such an instrument and the science it enables in complement to current long-term plans of the global astronomical community and in preparation for the next generation of observatories. We also outline notable far-IR mission concepts, pathfinder instruments, and technology development platforms that have been studied and developed throughout the past few decades and briefly discuss key enabling technologies.
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All authors C. S. Benson, M. Bonato, T. A. Davis, T. Essinger-Hileman, D. Farrah, W. Grainger, D. Leisawitz, H. Matsuo, B. Matthews, P. Pokorny, S. E. Ragan, B. V. Ricketti, G. Savini, J. P. Scott, L. D. Spencer, C. M. Urry, D. Wilner

Cosmology and Nongalactic Astrophysics

Constraints on the cosmic reheating history from PTA data

Qi-Lin Yang, Shi-Jie Wang and Nan Li

The cosmic reheating is an important epoch in the very early Universe, and has significant impacts on the primordial black hole (PBH) abundance and the scalar-induced gravitational wave (SIGW) spectrum. The relevant energy scale and the constituents of cosmic medium are encoded in the reheating frequency $f_{\mathrm{reh}}$ and the equation of state parameter $w$. In this work, we perform a full parameter space Bayesian inference, using the NANOGrav 15-yr dataset to constrain the thermal history of reheating. Treating $f_{\mathrm{reh}}$ and $w$ as free parameters, we systematically investigate the Dirac $\delta$, narrow and broad log-normal primordial power spectra. Current pulsar timing array data can effectively constrain the peak frequency of the SIGW spectrum as $f_{\rm p}\sim 10^{-7.6}$–$10^{-7.0}$ Hz, along with $f_{\rm reh}\sim 10^{-9.0}$–$10^{-8.3}$ Hz and $w\sim 0.19$–$0.79$ (the $68\%$ confidence level), when the power spectrum has a relatively narrow width $\Delta \lesssim 1$. A broader power spectrum introduces a smoothing effect that obscures the characteristic frequency knee in the SIGW spectrum, leading to the loss of information about cosmic reheating. Furthermore, for the Dirac $\delta$ and narrow spectra, the PBH masses associated with the SIGWs are anchored at the planetary mass scale around $10^{-6}$–$10^{-4} M_{\odot}$. This establishes a consistent physical framework that naturally bridges the nanohertz gravitational wave background with the dark matter candidates implied by the Optical Gravitational Lensing Experiment microlensing events.
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High Energy Astrophysical Phenomena

Delving into the depths of NGC 3783 with XRISM VI. Evidence for a failed wind based on Fe xxv absorption line variability

Chen Li, Jelle S. Kaastra, Liyi Gu et al. (+7 more)

NGC 3783 exhibits a prominent Fe XXV absorption trough in the time-averaged XRISM/Resolve spectrum. To investigate its short-term variability, we present a time-resolved analysis of the Fe XXV absorption line during the continuous 10-day observation. We divided the resolved absorption profile into five fixed velocity intervals and measured their normalized equivalent widths in 19 time-resolved spectra. Three velocity intervals exhibit significant equivalent-width (EW) variability. Two velocity intervals respond differently to low- and high-flux states with less emission line contamination. The time-dependent photoionisation modelling is unable to reproduce the most significant observed EW variation ($3.5 \, \sigma$), possibly owing to uncertainties in the assumed initial equilibrium state, which prevent a precise density measurement. Instead, using photoionisation calculations and assuming the high-density limit, we derive approximate constraints on the ionisation parameters of the two relevant components. The low-velocity component (-320 to -680 km/s) shows a delayed inverse response, indicating a high ionisation parameter, while its relatively short lag timescale indicates a relatively high density and a distance upper limit of 0.05 pc. In contrast, the high-velocity component (-680 to -1040 km/s) manifests a positive response with a longer lag to the ionising continuum, implying a relatively low ionisation parameter. This component appears to be less dense, with an inferred distance upper limit of 0.25 pc. The low-velocity component is consistent with a failed wind, as its outflow velocity is below the local escape velocity, whereas the high-velocity component lies near the escape threshold. Together with the lower-ionisation failed wind detected in 2001, this supports a multiphase failed-wind scenario in the unobscured state of NGC~3783 over more than two decades.
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All authors Chen Li, Jelle S. Kaastra, Liyi Gu, Missagh Mehdipour, Keigo Fukumura, Matteo Guainazzi, Misaki Mizumoto, Ehud Behar, Shoji Ogawa, Keqin Zhao

High Energy Astrophysical Phenomena

Reconstruction of Interstellar Cosmic Ray Anisotropy via Heliospheric Propagation Modeling and SVD Inversion

Reilly Tom, Paolo Desiati, Juan Carlos Díaz-Vélez et al. (+1 more)

Ground-based experiments such as the IceCube Neutrino Observatory and the High-Altitude Water Cherenkov Gamma-Ray Observatory detect cosmic-ray anisotropy on Earth, but magnetic deflections within the heliosphere complicate interpretation. Understanding the original spatial distribution of cosmic rays in the interstellar medium requires modeling particle propagation across the heliospheric boundary. We constructed a simulated transport model that backtracks antiprotons from Earth to the interstellar medium and maps spatial transfer probabilities across energies using HEALPix representations. Because our transfer matrices are singular, inversion relies on singular value decom- position regularization. Ground-based observations lose the equatorial North-South anisotropy component, severely degrading interstellar map recovery. We developed a geometric circle-fitting algorithm to estimate and reintroduce the missing component into the observed signals. Our results show that restoring the North-South anisotropy en- ables more accurate recovery of the interstellar dipole structure. Furthermore, Poisson statistical fluctuations on the detected event counts dominate matrix-transformation errors when spread over multiple energies.
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All authors Reilly Tom, Paolo Desiati, Juan Carlos Díaz-Vélez, Perri Zilberman

Earth and Planetary Astrophysics

On the Orbital Evolution of Giant Planet Pair Embedded in a Gaseous Disk. III. simultaneous gas accretion and the final mass ratio

Bixuan Zhao, Hui Zhang, Yinhao Wu et al. (+1 more)

Recent exoplanet surveys reveal a systematic trend in the mass ratios of giant planet pairs ($> 30 M_\oplus$). Although the $M_{outer}/M_{inner}$ is broadly centered near unity, it exhibits a dependence on orbital separation. Compact pairs tend to have comparable masses, whereas widely separated pairs show outer-heavy configurations. To investigate the origin of this trend, we perform two-dimensional hydrodynamic simulations that couple gas accretion and orbital migration of two giant planet embryos with initial masses of $15-30 M_\oplus$. We explore the effects of disk viscosity, surface density slope, and initial mass ratio on the coupled evolution of planetary growth and migration. We find that convergent migration drives the planets to open a common gap, restructuring the gas flow. This configuration induces asymmetric accretion, in which the inner planet becomes starved as gap clearing suppresses its gas supply, while the outer planet continues to accrete from the high-density region at the outer gap edge. Consequently, the system naturally evolves toward mass-ratio convergence, and in many cases produces an inversion of the initial core-mass hierarchy. We further show that migration outcomes are highly sensitive to initial conditions. Systems with initially more massive inner cores tend to diverge, whereas steeper surface density profiles and more massive outer cores favor convergent migration and subsequent resonance capture. Overall, our results identify common-gap-driven asymmetric accretion as a unified mechanism linking orbital architecture, resonant capture, and the observed mass-ratio demographics of giant planet pairs.
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All authors Bixuan Zhao, Hui Zhang, Yinhao Wu, Ya-Ping Li

Cosmology and Nongalactic Astrophysics

Structure and evolution of cosmic voids within DESI DR1

Óscar Monllor-Berbegal, Susana Planelles and Vicent Quilis

Ongoing stage IV galaxy surveys such as DESI or Euclid offer an unprecedented amount of information to study the large-scale structure of the Universe by mapping tens of millions of galaxies. Within the context of cosmic voids, already released and future catalogues will help better understand the void structure and evolution as well as the cosmological model constraints derived from their statistics. With the recent DESI Data Release 1, our aim is to obtain a new void catalogue that allows us to study the properties of cosmic voids at different redshifts, hence providing insight not only on their structure but also on their evolution. We select the DESI BGS and LRG samples for this study. Before the void-finding process, the data goes through a preprocessing pipeline tackling redshift space distortions and reconstructing the mildly non-linear velocity field. After that, the new AVISM void finder is applied to the preprocessed data, obtaining two void catalogues in different redshift bins (0.1 < z < 0.3 and 0.4 < z < 0.8), both within a 1400^3 cMpc^3 cube. We successfully recover N_BGS = 1114 and N_LRG = 216 clean voids with sizes up to ~ 65 cMpc. The void size function, 3D shape variables, density profiles, and linear bias are obtained and analysed. Both the size function and the density profiles obtained are in agreement with previous theoretical studies. The expected mass depletion in void evolution is shown by the evolution of density profiles. We obtain a roughly constant linear bias inside r < Re with mean values of 1.31 +/- 0.02 and 2.14 +/- 0.04 for BGS and LRG, respectively. Both void catalogues are publicly released.
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Solar and Stellar Astrophysics

The EBLM project - XX. Absolute dynamical masses of five low-mass eclipsing binaries, and an evaluation of mass estimation methods

Adam T. Stevenson, Yasmin T. Davis, Daniel Sebastian et al. (+8 more)

Eclipsing binaries consisting of a solar-type primary and an M dwarf secondary are key laboratories to study objects at the bottom of the main sequence. Fundamental parameters of such stars have a direct impact upon exoplanetary studies, as searches for temperate Earth-sized planets focus on M dwarf hosts. Eclipsing binaries are essential to measure these parameters. However for stellar masses $<$ 0.35 M$_\odot$ , few double-lined eclipsing systems are known. Thus, stellar evolution models and empirical relations have had to rely on single-lined eclipsing binaries, for instance those from the EBLM project (Eclipsing Binary - Low Mass). Using high resolution spectroscopy to extract the weak signal of the secondary (flux ratio $<$ 1 per cent in the optical), we transform five more systems from single to double-lined, deriving absolute masses for both stars. We then compare methods typically employed to estimate stellar masses for field stars or single-lined binaries with the absolute dynamical masses we obtain, to assess their accuracy. Our results for SB1 and SB2 analyses are mostly consistent within 1-$\sigma$, though we identify a small systematic overestimation of SB1 masses derived from a combination of radial velocities and eclipse photometry. We show that the bias originates from primary radius overestimation during isochronal analysis, wherein the secondary light reduces photometric magnitudes and impacts the recovered radii by modifying the spectral energy distribution. With proper calibration, we can ensure the accuracy of using the full EBLM SB1 sample to constrain mass-radius-luminosity relationships for the smallest, yet most abundant, stars in the Galaxy
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All authors Adam T. Stevenson, Yasmin T. Davis, Daniel Sebastian, Amaury H. M. J. Triaud, Pierre F. L. Maxted, Alix V. Freckelton, Thomas A. Baycroft, Neda Heidari, David V. Martin, Nicola J. Miller, Alexandre Santerne

Solar and Stellar Astrophysics

The EBLM Project - XIX. The absence of radius inflation in a homogeneous analysis of 66 Northern low-mass eclipsing binaries

Yasmin T. Davis, Amaury H.M.J. Triaud, David V. Martin et al. (+30 more)

Precise and accurate measurements of host stars are crucial in the search for Earth-like exoplanets, and M-dwarfs are favourable targets in this quest. Low-mass eclipsing binaries offer unique opportunities to empirically determine stellar masses and radii for low-mass stars where stellar models may be systematically biased. We present results from the EBLM-North sample, the largest homogeneous study of low-mass eclipsing binaries with secondary characterisation yet, combining high-resolution and high-precision radial velocities from SOPHIE and TESS photometry. We measure a median precision for stellar companions of 4.2% in radius and 8.6% in mass within a sub-sample of 50 high-quality binaries, all with orbital periods $P_{\rm bin} > 5\,\rm days$. We compare our data to the Baraffe and MIST isochrones, and find our sample is statistically consistent with those models, producing reduced chi-squared values, $\chi^2_\nu\sim 1$. Our measured radius inflation is $0.3\pm 1.6$% indicating no statistically significant trend. We likewise detect no significant trend with metallicity, despite having the precision to identify such a relationship. As such, our observations do not appear to follow the general metallicity trend predicted in MIST. A $\chi_\nu^2 \sim 1$ indicates the scatter in our results is commensurate with our uncertainties alone. These results constrain the scope for unmodelled effects on the mass-radius relation that would produce radius deviations greater than 4.2%. However, our secondary effective temperatures do not reproduce this high level of agreement with the models, and we do not recover the predicted trends with metallicity.
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All authors Yasmin T. Davis, Amaury H.M.J. Triaud, David V. Martin, Alix V. Freckelton, Jenni R. French, Adam T. Stevenson, Annelies Mortier, Karen Collins, Pierre F. L. Maxted, Daniel Sebastian, Aleyna Adamson, Thomas A. Baycroft, Isabelle Boisse, Gavin A. L. Coleman, Georgina Dransfield, Yilen Gómez Maqueo Chew, Leslie Hebb, Neda Heidari, Vedad Kunovac, James McCormac, Nikki J. Miller, Richard Nelson, Martin Nielsen, Alexandre Santerne, Madison G. Scott, Owen Scutt, Alexis M. S. Smith, Matthew R. Standing, Amalie Stokholm, Matthew I. Swayne, Mathilde Timmermans, Peter J. Wheatley, Emma Willett

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

Cosmological Consequences of a Highly Decoupled Right-handed Neutrino

Stephen F. King, Rishav Roshan and Sudipta Show

In the minimal type-I seesaw, one right-handed neutrino (RHN) can decouple from neutrino mass generation. Such a state is usually neglected, yet its feeble couplings make it long-lived, and it can dominate the energy density of the Universe before decaying. We study this in a minimal $U(1)_{B-L}$ model, where the RHNs are produced through $B-L$ gauge interactions, for the cases of a decoupled lightest RHN $N_1$ and a decoupled heaviest RHN $N_3$. The resulting early matter-dominated era dilutes the baryon asymmetry, and for decoupled $N_3$ it also delays the equilibration of the charged-lepton Yukawa interactions, allowing a lighter $N_1$ to generate the asymmetry in the unflavoured regime. Breaking $U(1)_{B-L}$ forms cosmic strings whose gravitational-wave background acquires a spectral break from the early matter-dominated era, with a frequency set by the decoupled RHN mass and the lightest neutrino mass, within reach of future detectors such as SKA, THEIA, LISA, $\mu$ARES, DECIGO and ET.
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High Energy Astrophysical Phenomena

Two sides of the same spin: tracking optical and radio pulsations of SAX J1808.4-3658 from outburst to quiescence

C. Ballocco, A. Miraval Zanon, A. Papitto et al. (+25 more)

High-time-resolution optical and UV observations have revealed bright coherent pulsations from accreting millisecond pulsars, exceeding the luminosity expected from thermal emission from NS hotspots or X-ray reflection by the accretion disk. Characterizing optical pulsations over a wide range of accretion rates through coordinated multi-wavelength observations can shed light on their origin. We present a timing study of the AMSP SAX J1808.4-3658 during its 2022 outburst and quiescence, using optical TNG/SiFAP2 observations, simultaneous NICER X-ray data, LCO optical monitoring, and MeerKAT radio observations in quiescence. During the outburst, we detect coherent optical pulsations with pulsed luminosities of 1.3x10^(30)erg/s. Combined with previous detections, our results suggest that the optical pulsed amplitude increases as the X-ray flux decreases. The X-ray and optical pulsed luminosities show opposite trends with X-ray luminosity, suggesting different responses to changes in the accretion rate. We measure X-ray-to-optical delays of 0.88+-0.04ms and 0.51+-0.03 ms in two outburst observations, indicating that the relative timing between the signals is not constant. Together with the spectral energy distribution, these results support different emission mechanisms: non-thermal emission from relativistic particles for optical pulsations and channeled accretion onto the NS surface for X-ray pulsations. During quiescence, we detect no coherent optical pulsations, obtaining a 95% confidence upper limit of <2.2x10^(29)erg/s on the optical pulsed luminosity, corresponding to an optical efficiency comparable to those of spider radio millisecond pulsars. Simultaneous MeerKAT observations reveal no radio pulsations down to ~10{\mu}Jy, significantly improving previous constraints but not excluding an active rotation-powered pulsar whose radio emission may be absorbed by intra-binary material.
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All authors C. Ballocco, A. Miraval Zanon, A. Papitto, M. Burgay, M. C. Baglio, C. Malacaria, F. Ambrosino, A. Possenti, G. Illiano, E. D. Barr, R. P. Breton, L. Burderi, S. Campana, C. J. Clark, F. Coti Zelati, D. de Martino, T. Di Salvo, M. Kramer, R. La Placa, F. Lewis, A. Marino, D. M. Russell, A. Sanna, L. Stella, B. Stappers, J. D. Turner, M. Cecconi, A. Ghedina

High Energy Astrophysical Phenomena

Cell-based theoretical criteria on the onset and stability limit of thermonuclear detonation

Kazuya Iwata, Keiichi Maeda and Ken J. Shen

One of the key unresolved problems in thermonuclear explosions of white dwarfs (WDs), including type Ia supernovae, is the condition for ignition and propagation of thermonuclear flame. Given the limitation of hydrodynamic simulations in resolving the flame front involved in the explosion process, theoretical considerations for these criteria merit accurate prediction of the onset of deflagration and detonation (deflagration-to-detonation transition or direct initiation) and subsequent stable propagation. Application of cell-based theories, which are originally designed for terrestrial detonation incorporating the size of the cellular structure, to pure-helium detonation in a WD envelope was proven to be powerful. In the present work, we extend this for detonation in helium-carbon and carbon-oxygen mixtures, both of which are associated with the double-detonation model for type Ia supernovae. Comparing with previous hydrodynamic studies in terms of the minimum initiation energy and critical stellar mass for stable propagation, the agreement is satisfactory. For the helium-carbon detonation, it is theoretically substantiated that even an extremely low-mass WD envelope $\sim 10^{-3}$ M$_{\odot}$ can accommodate stable detonation. For the carbon-oxygen detonation, the oxygen-scale cell width is shown to be a good diagnosing indicator. In addition, it is indicated that direct initiation of the carbon-oxygen detonation is only available for a WD heavier than 0.6 M$_\odot$. The findings of this study enable first-order calibration of the explosion model by a simple calculation through the analogy between astrophysical and terrestrial burning, the latter of which can be tested and observed in a laboratory-scale experiment.
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Astrophysics of Galaxies

EMU detection of mysterious multiple component radio-continuum emission from nearby spiral Seyfert I type galaxy 'Sand-timer' (NGC 7213)

M. D. Filipović, Z. J. Smeaton, B. S. Koribalski et al. (+24 more)

We present an Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) radio-continuum detection of the nearby spiral Seyfert I type galaxy NGC 7213 which we nickname `Sand-timer' due to its morphological appearance. We find intriguing, peculiar emission extending from the central supermassive black hole (SMBH), which we refer to as galaxy hyperbubbles and/or active galactic nucleus (AGN) jets. Finally, we find two previously undetected kiloparsec-scale features in the polarised intensity image, which appear most likely also related to the central SMBH, as restarted bipolar radio jets, though somewhat obscured in the radio-continuum total intensity image. They resemble the bow shocks often seen in Fanaroff-Riley Class II (FR-II) radio galaxies, and so we propose they most likely represent an early episode of the `Sand-timer's' AGN jet activity. An alternative scenario is that the core of NGC 7213 may be a supermassive binary black hole (SMBBH) undergoing a tidal disruption event (TDE), potentially causing the peculiar radio-continuum emission.
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All authors M. D. Filipović, Z. J. Smeaton, B. S. Koribalski, R. Kothes, A. Ahmad, R. Z. E. Alsaberi, C. Bordiu, A. C. Bradley, E. J. Crawford, A. M. Hopkins, E. Järvelä, S. Lazarević, D. Leahy, J. L. Payne, S. F. ur Rahman, G. P. Rowell, H. Sano, M. Selby, S. S. Shabala, E. J. Stanton, S. Taziaux, K. Tsuge, D. Urosević, N. F. H. Tothill, J. Th. van Loon, V. Velović, G. L. White

Astrophysics of Galaxies

MUSE-DARK IV. Comparing Dark Matter Densities to Star Formation Histories in 375 intermediate-z galaxies

B. I. Ciocan, N. F. Bouché, J. Fensch et al. (+5 more)

(Abridged) Baryonic feedback is expected to transform cuspy dark-matter (DM) haloes into cores, but direct observational links between inner DM slopes and galaxy star-formation histories (SFHs) remain limited. We investigate and quantify the connection between halo inner slopes and baryonic assembly histories in a large sample of intermediate-z galaxies. We analyse 375 galaxies at 0.1<z<1.43 spanning 7<log(Mstar/Msun)<11.2 using 3D forward modelling of MUSE kinematics and disk-halo decompositions with mass-dependent (DC14-based) and generalised Navarro-Frenk-White (gNFW) halo profiles. Stellar population parameters are inferred from multi-band Spectral Energy Distribution fitting of UV-to-MIR photometry using a non-parametric SFH model. Bayesian model comparison shows that the DC14-based halo density profiles are statistically preferred over gNFW for a substantial fraction of the sample. The inferred inner slopes from gNFW fits nevertheless follow the DC14 expectation and reproduce the expected dependence on the stellar-to-halo mass ratio, despite this not being explicitly imposed. Partial correlation coefficient and random forest regression analyses consistently identify stellar mass (or, equivalently, the stellar-to-halo mass ratio) as the primary driver of the inner density slope, a result that holds robustly even when the analysis is restricted to the gNFW fits. In contrast, SFH-related quantities (e.g. formation time and 'burstiness' indicators) exhibit no independent predictive power on the DM halo inner slope once the dependence on stellar mass is accounted for. Cored systems preferentially occupy lower-mass, more bursty bins with later assembly times, whereas cuspy systems are associated with higher stellar masses, lower star formation activity, and earlier assembly epochs, in agreement with theoretical expectations of stellar-feedback-induced cores.
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All authors B. I. Ciocan, N. F. Bouché, J. Fensch, D. Krajnović, J. Freundlich, H. Desmond, A. Jeanneau, B. Famaey

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

Extrapolating Collisional Rate Coefficients for Molecules of Astrophysical Interest Using Neural Networks

Yigit Ergen and Jérôme Loreau

State-to-state rate coefficients for inelastic molecular collisions are essential inputs for non-local thermodynamic equilibrium radiative transfer models, yet their computation using quantum scattering methods is prohibitive for large molecules and highly excited rotational states. We investigate the ability of artificial neural networks to extend existing datasets of collisional excitation rate coefficients without performing additional scattering calculations. A multilayer perceptron model was trained using molecular quantum numbers, level energies, energy gaps, and kinetic temperature as descriptors, and optimized on logarithmic rate coefficients. The model was tested on diverse collision systems ranging from simple diatomic molecules (CO, SiO) to open-shell species (SO), small asymmetric tops (H$_2$O, SO$_2$), and complex organic molecules (benzonitrile and vinyl cyanide) colliding with H$_2$ molecules or He atoms. Extrapolations were performed toward higher rotational levels, higher temperatures, and combinations of both. For most systems, predictions of rate coefficients involving previously unseen rotational states yielded mean error factors between 1.1 and 1.5, with the dominant rate coefficients generally reproduced more accurately than weaker transitions. Temperature extrapolations proved particularly successful, while combined extrapolations in temperature and rotational levels remained accurate to within a factor of two in most cases. The prediction quality depends on the interplay between dataset size, temperature range, molecular complexity, and the presence of clear collisional propensity rules. Overall, the approach demonstrates that machine learning can provide a practical route to extending collisional datasets for astrophysical applications, especially for large molecules for which additional quantum-scattering calculations are computationally demanding.
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Astrophysics of Galaxies

Massive black holes in the first billion years with JWST

Hannah Übler

The James Webb Space Telescope has unlocked uncharted territory for the study of early black holes, enabling the detection of fainter and smaller black holes at larger cosmological distances than previously possible. Compared to nearby massive black holes, they are characterised by several unexpected attributes, such as their multi-wavelength properties or their relation to their host galaxies. These observational findings challenge our understanding of the past evolution of present-day supermassive black holes, and provide novel anchor points to constrain theoretical models of black hole formation and growth. This review summarises our current understanding of the observed properties of newly discovered, active black holes in the early Universe, discusses the status of mass measurements and the relation to their hosts, as well as open questions and future prospects.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Signature of GW from the Hidden Sector in light of the Recent LZ Event

Sujit Kumar Sahoo, Narendra Sahu and Vicky Singh Thounaojam

The LZ collaboration has recently reported a single nuclear-recoil event at $E_R=248\pm23_\text{stat}\pm23_\text{sys}$ keV, observed in a 2.84 tonne-year exposure with a local significance of $3.4\sigma$, pointing towards an inelastic dark matter (DM) interpretation. We explain this event within a gauged $U(1)_X$ hidden-sector model, spontaneously broken by a singlet scalar whose vacuum expectation value (VEV) gives rise to: (i) gauge boson mass, (ii) a small Majorana mass for the vector-like singlet fermion, the DM candidate, charged under the new symmetry, which splits the fermion into two pseudo-Dirac states (mass splitting proportional to the scalar VEV) thus resulting in a purely off-diagonal vector current, (iii) the frequency and the amplitude of the GW signal arising from the hidden sector symmetry breaking via first-order phase transition (FOPT). The symmetry-breaking scale thus provides a multi-messenger probe connecting terrestrial direct-detection kinematics at the LZ and early-universe FOPT thermodynamics while obtaining thermal DM relic abundance. We delineate the viable parameter space compatible with the LZ event, correct relic density, and detectable GW signals in the low frequency regimes at future interferometers like $\mu {\rm ARES}$ and THEIA while satisfying existing cosmological, astrophysical, and terrestrial bounds.
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High Energy Astrophysical Phenomena

Fast Radio Bursts from Monster Shocks and Flares of Inspiraling Binary Neutron Stars: A Kinetic Model for Double Pulsar

Jan Benáček, Benoît Cerutti, Martin Pohl et al. (+2 more)

The coalescence of binary neutron star systems offers unprecedented possibilities for multimessenger observations, including the detection of gravitational waves, gamma-ray bursts, kilonovae, and potentially fast radio bursts. For a detailed investigation of the latter, one requires a kinetic plasma model to describe the interacting magnetospheres of the stars. We present a three-dimensional particle-in-cell kinetic simulation of the combined magnetosphere of a binary neutron star in which the two stars physically orbit one another so that the orbital motion itself twists the magnetic loops. We find that the stellar magnetic-field intensity ratio controls the emergence of flares, while the stellar spins set the direction and modulation of the flare. We identify four spatially and dynamically distinct regions of strong electromagnetic energy release: (i) an expanding fast magnetosonic wave that steepens into a monster shock, (ii) a plasma flare being pushed by (iii) an expanding fireball and containing (iv) a reconnecting current sheet. The fast magnetosonic wave is a promising source of coherent radio emission. It is released when orbital motion cuts a closed plasma loop. The electric and magnetic wave amplitudes are similar and reach that of the background magnetic field. Our kinetic treatment yields particle spectra and plasma structures that can be used to assess coherent emission in kinetic-scale simulations. In conclusion, the stellar orbital motion constitutes a driving channel distinct from models with spin-driven magnetospheric twisting.
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All authors Jan Benáček, Benoît Cerutti, Martin Pohl, Tim Dietrich, Anna Neuweiler

High Energy Astrophysical Phenomena

Low-frequency spectra and scattering of pulsars towards the Gum Nebula with the MWA

Ting Yu, Zhifu Gao, Zhongli Zhang et al. (+1 more)

Context. The Gum Nebula is a nearby ionised complex with sight-line-dependent pulsar propagation. Aims. We test whether a smooth ionised structure can explain low-frequency spectral turnovers and pulse broadening, or whether smaller-scale material is required. Methods. We analysed Murchison Widefield Array observations of six pulsars at 80–240 MHz, combining sub-band flux densities with literature data. We compared power-law, free–free absorption (FFA), and turnover-constrained broken-power-law (BPL) spectra, and modelled scattering through pulse-profile convolution. PSR J0820-4114 and the Vela pulsar were fitted jointly across frequency. Results. All six spectra depart from a single power law. FFA is favoured for PSRs J0737-3039A and J0820-4114, and BPL for J0742-2822 and J0835-4510; the other two classifications depend on assumed error floors. Conditional FFA solutions imply emission measures of $10^4$–$10^5$ pc cm$^{-6}$ for electron temperatures of $3\times10^3$–$10^4$ K, far exceeding smooth-shell expectations. PSRs J0737-3039A and J0837-4135 have scattering laws consistent with $\tau_{\rm sc}\propto\nu^{-4}$. We obtain $\alpha_{\rm sc}=-3.07\pm0.11$ for J0742-2822 and $-1.59\pm0.44$ for J0820-4114 using a joint two-component model. The Vela pulsar is best described by an effective thick-screen model with $\alpha_{\rm sc}\simeq-2.74$. Neither tested Galactic electron-density model reproduces both independent distances and low-frequency scattering uniformly. Conclusions. The results favour a structured Gum–Vela magneto-ionic environment in which neighbouring sight lines probe different absorbing and scattering material; these effects need not arise in the same plasma component.
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All authors Ting Yu, Zhifu Gao, Zhongli Zhang, Weicong Jing

Solar and Stellar Astrophysics

MATISSE unveils a dusty disc in the interior of EP Aquarii. First evidence of a misaligned hierarchical triple system with a central AGB star?

J. Alonso-Hernández, C. Paladini, C. Sánchez Contreras et al. (+26 more)

Aims. We have mapped the dust and molecular gas emission distributions in the vicinity (a few stellar radii) of the asymptotic giant branch (AGB) star EP\,Aquarii, with a previously reported stellar companion at $\sim$50\,au, to search for binary-induced asymmetries. Methods. We present an analysis of new high-angular-resolution ($\gtrsim$4\,mas) images obtained with MATISSE (in the wavelength range $\sim$3–8\,\mum) as well as archival high-angular-resolution ($\gtrsim$20\,mas) ALMA $\rm^{12}$CO\,(c$J$=2-1) line and continuum emission observations ($\sim$230\,GHz), to study the circumstellar morphology and kinematics of the molecular gas on these spatial scales. Results. The MATISSE images display a bright central source and two slightly extended emission features ("blobs") located on opposite sides of the AGB star (at radial distances of $\sim$4–10\,au). These structures are consistent with previous mid-infrared interferometric observations, suggesting stability over decades. The central source is elongated along the direction defined by the blobs, in both the MATISSE and ALMA continuum images. The ALMA $\rm^{12}$CO\,($J$=2-1) maps display an asymmetric inner wind with a velocity gradient. Conclusions. The observations are consistent with an edge-on dusty equatorial overdensity (disc-like), hinting the presence of a close ($\lesssim$4\,au) companion. The inferred symmetry axis is almost perpendicular to the CO velocity gradient and the orbital plane proposed for the distant ($\sim$50\,au) companion. EP\,Aqr may represent the first misaligned hierarchical triple system with a central AGB star.
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All authors J. Alonso-Hernández, C. Paladini, C. Sánchez Contreras, J. Drevon, J. P. Fonfría, L. Planquart, T. Khouri, L. Siess, A. Jorissen, B. Aringer, F. Baron, E. De Beck, S. Höfner, J. Hron, F. Lykou, F. Millour, M. Montargès, N. Nardetto, K. Ohnaka, H. Olofsson, V. Răstău, J. Sanchez-Bermudez, L. Velilla-Prieto, W. Vlemmings, M. Wittkowski, G. Weigelt, W. C. Danchi, F. Kerschbaum, B. Lopez

Earth and Planetary Astrophysics

3D Global Climate Simulations of Synthetic Mars Warming

Tom N. Landefeld and Harald Lesch

Artificial warming via engineered aerosols presents a novel pathway to bypass volatile scarcity on modern Mars. Utilizing the Generic Planetary Climate Model, we evaluate the physical feasibility of aerosol-induced terraforming over a full Martian year (669 Sols). Unlike previous approaches that added aerosols to background dust or assumed continuous nanoparticle injection, we simulate the complete substitution of natural dust with a single-injection profile of radiatively active aluminium nanoparticles without continuous dumping. This tests whether initial infrared greenhouse forcing can overcome the severe ice-albedo cooling induced by a massive regional water-ice sheet ($3400 \text{ kg/m}^2$) localized in the Hellas Basin. Comparing this scenario against an unperturbed control run, we analyze surface temperature dynamics, sublimation fluxes, and water vapour concentration. Our 3D global climate simulations quantify the radiative-dynamical feedback thresholds and determine whether engineered aerosol forcing can trigger a self-sustaining water-vapour greenhouse effect or remains fundamentally limited by regional ice-albedo suppression in Hellas.
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Solar and Stellar Astrophysics

Dynamical and thermal evolution of localized reconnecting current sheets under varying guide-fields in the solar corona

Saksham Pande, Abhishekh Kumar Srivastava, Fabio Bacchini et al. (+9 more)

Although magnetic reconnection in coronal current sheets (CSs) is a fundamental energy release mechanism in the solar corona, the role of guide-fields in governing its formation and self-consistent evolution is not fully understood. Through 2.5D resistive magnetohydrodynamic (MHD) simulations, we investigate how guide-fields affect the formation and evolution of a localized reconnecting coronal CS. Strong guide-fields prevent oppositely directed field lines from approaching sufficiently to form a CS, delaying and suppressing its subsequent evolution. The reconnection rate exhibits a rising phase resembling a power-law, with exponent $\delta_1$ decreasing with rising guide-fields, indicating slower temporal growth of the reconnection rate. The aspect ratio of the CS follows a similar power-law trend with the exponent $\alpha_1$ decreasing with rising guide-fields. A subsequent slower growth phase of the reconnection rate shows a power-law exponent $\delta_2$ that increases with rising guide-fields, as does the corresponding aspect-ratio exponent $\alpha_2$. As the CS evolves, the latter phase is achieved due to a sharp decremental transition of the guide-field within the CS after a time when the increasing inflows are inefficiently resisted by the guide-field itself. In the reconnection regime during prior phases, the power-law exponents of the maximum temperature and the outflow velocities also decrease with rising guide-fields demonstrating that stronger guide-fields suppress the growth of these indicators also. This study suggests that a self-consistently formed CS displays phases of efficient and inefficient quenching of the reconnection mechanism, promoted by non-zero guide-fields. We also quantify this behavior for indicators of the reconnection process and discuss their applicability to observations of apparent CSs and probing background coronal conditions.
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All authors Saksham Pande, Abhishekh Kumar Srivastava, Fabio Bacchini, Sripan Mondal, Akash Bairagi, Balveer Singh, Kartika Sangal, Sudheer K. Mishra, Xinping Zhou, Ding Yuan, R. -Y. Kwon, B. N. Dwivedi

Instrumentation and Methods for Astrophysics

Charge Response Simulation of Liquid Argon Compton Cameras for Precise MeV Gamma-Ray Event Reconstruction

Shota Arai, Hirokazu Odaka, Satoshi Takashima et al. (+5 more)

We studied the detector response for a liquid-argon time-projection chamber (LArTPC) Compton camera targeting MeV gamma-ray astronomy by a Geant4-based Monte Carlo simulation. The simulation, implemented within ComptonSoft, incorporates electron-ion recombination, charge diffusion, and induction on the electrode pixels. We evaluated the angular resolution measure (ARM) and the energy reconstruction error as functions of electronic noise, pixel pitch, and the recombination correction method. An electronic noise level of 4 keV and a pixel pitch of 1 mm yield an ARM (FWHM) of about 3 degrees at 1332.5 keV and an energy reconstruction error better than 4% for incident energies of 1173.2 keV and above. Recombination correction using both scintillation light and charge signals improves the ARM and the energy error by factors of 1.7–2.3 and 2.2–5.4, respectively, compared to the charge-only correction, although the uncertainty of the recombination-fluctuation model remains. Since this simulation relies on idealized assumptions such as the use of the Monte Carlo truth in the event reconstruction, these values represent the best cases achievable under these detector conditions; nevertheless, they show that a large-scale LArTPC is a promising Compton camera for cosmic MeV gamma-ray observations.
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All authors Shota Arai, Hirokazu Odaka, Satoshi Takashima, Masashi Tanaka, Ryutaro Tatsumi, Hodaka Kawamura, Kouichi Hagino, Aya Bamba

High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Finite-Temperature Equations of State for Neutron-Star Mergers within the Quark Mean-Field Model

Shuochong Han, Xiangdong Sun, Zhenyu Zhu et al. (+1 more)

We extend the quark mean-field (QMF) model to finite temperature and systematically investigate the thermodynamic properties of uniform nuclear matter, using the relativistic mean-field (RMF) model as a reference. For each model, we consider two parameter sets calibrated to the same selected nuclear-matter saturation properties but with different nucleon Dirac effective-mass ratios at saturation. We examine the effective nucleon mass and the composition of $\beta$-equilibrium matter, together with the free energy, energy density, pressure, entropy, and heat capacities of symmetric nuclear matter, pure neutron matter, and $\beta$-equilibrium matter. The QMF and RMF models exhibit similar qualitative trends, but their predictions increasingly differ at high density, where the effective masses have distinct density dependences. These differences are particularly evident in the thermal pressure and thermal index. For the two parameter sets considered in this work, we further provide compact analytical representations of the thermal index, $\Gamma_{\rm th}(\rho_{\rm b},T,\beta)$ over baryon densities of 0.08-1.0 $\rm fm^{-3}$, temperatures of 5-100 MeV, and isospin asymmetries of 0-1. The fits reproduce the numerical results with an accuracy better than $2\%$ and can be directly implemented in binary neutron-star merger simulations. This study establishes a finite-temperature extension of the QMF framework and provides a basis for future assessments of how a quark-structure-based description of nuclear matter affects thermal support and post-merger dynamics in binary neutron-star mergers.
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All authors Shuochong Han, Xiangdong Sun, Zhenyu Zhu, Ang Li

Astrophysics of Galaxies

Radio ghosts: Radio polarimetry study of newly discovered cluster minihalo candidates or radio tailed galaxies

Sam Taziaux, Christopher J. Riseley, Stefan W. Duchesne et al. (+5 more)

Extended diffuse radio emission in the central regions of galaxy clusters is commonly associated with non-thermal processes in the intracluster medium (ICM), but its origin and the mechanisms responsible for sustaining it remain uncertain. We present the discovery and multi-wavelength analysis of two diffuse radio sources, MKTJ0355-4237 and MKTJ0355-4230, to assess their nature and investigate their radio spectral and magnetic field properties through radio polarimetric analysis. We use deep MeerKAT L-band (1.28 GHz) observations to perform spectral analysis of the diffuse emission and study its polarisation properties via rotation measure synthesis. These are complemented by eROSITA X-ray data and DESI photometric redshift catalogues to characterise the host cluster environments. MKTJ0355-4237 is confirmed as cluster-scale minihalo with extent of $\sim 400$ kpc, while the other diffuse source MKTJ0355-4230 remain uncertain and could be either associated with a radio minihalo or radio tailed galaxy. Both show steep spectra ($\alpha \approx -0.7$ to $-0.8$) that steepen toward the outskirts ($\alpha \lesssim -2.5$), consistent with spatial variations in electron ageing and re-acceleration. Polarised emission is detected in both systems, with fractional polarisation $\sim1\,\%$ in the centres and increasing in the outer regions of MKTJ0355-4237. MKTJ0355-4230 is associated with a previously uncatalogued cluster and shows an X-ray morphology offset from the brightest cluster galaxy, indicative of dynamical activity. MKTJ0355-4237 exhibits a sharply bounded internal radio deficit without a corresponding X-ray counterpart, within current sensitivity limits. The spectral steepening supports turbulent re-acceleration as the origin of the diffuse emission.
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All authors Sam Taziaux, Christopher J. Riseley, Stefan W. Duchesne, Francesca Loi, Alec J. M. Thomson, Aritra Basu, Timothy J. Galvin, Dominik J. Bomans

Instrumentation and Methods for Astrophysics · Cross-listed from cs.NI

Developments in Building Towards the Indian SKA Regional Centre

Rohit Sharma and Yogesh Wadadekar

The SKA Regional Centre Network (SRCNet) is a federated global network designed to archive, distribute, and process SKAO data products. This paper examines the evolving SRCNet architecture-focusing on the transition to version 0.2 (v0.2) requirements, including computation, orchestration, and multi-tiered storage-and details the strategy for establishing its proto-SRC infrastructure. We outline the prototype developments for the major and minor nodes in the context of v0.2. We describe the minor node compute and storage demands, establishing a pathway toward a fully operational Indian SKA Regional Centre (INSRC).
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Solar and Stellar Astrophysics

Simulating Ionospheric Distortions in Mock SKA-Low Solar Radio Observations

Rohit Sharma and Mitin

The Square Kilometre Array Observatory (SKAO) will provide unprecedented angular resolution for low-frequency solar radio imaging, enabling access to fine-scale coronal structures. However, the improved spatial resolution of SKA-Low also increases the sensitivity of solar images to ionospheric propagation effects. We investigate the impact of ionospheric fluctuations on simulated SKA-Low solar observations at 50, 100, 150, and 200 MHz using the Karabo simulator and turbulent, moving ionospheric phase screens. We quantify the resulting image distortions using spatial power spectral density (PSD) analysis and compare the SKA response with corresponding MWA simulations. The results show that ionospheric distortions are strongly scale- and frequency-dependent, with the maximum fractional PSD distortion decreasing with observing frequencies. SKA resolves ionospheric fluctuations over spatial scales that are largely smoothed by the MWA instrumental response, with significant distortions occurring on scales comparable to solar active-region structures. These results demonstrate that ionospheric propagation effects should be considered when interpreting high-resolution SKA-low solar radio images, particularly at the lower end of the frequency band.
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