Solar and Stellar Astrophysics
Spectral characteristics of fast rotating metal-poor massive stars
Brankica Kubátová and Dorottya Szécsi
Low-
metallicity massive
stars are assumed to be progenitors of certain
supernovae, gamma-ray bursts, and gravitational wave emitting mergers. These exotic phenomena contribute to their host
galaxies through strong ionizing radiation and mechanical feedback. Here we investigate a certain type of very metal-poor (0.02 Zsun) hot massive single
stars that rotate fast and evolve chemically homogeneously. Combining state-of-the-art theories of
stellar evolution and
stellar atmospheres modelling we predict synthetic spectra of these
stars corresponding to different masses and evolutionary phases. The predicted spectra in early evolutionary phases is classified mainly as an early-O type
giant or supergiant while in later evolutionary phases most of our model spectra are assigned to the WO-type spectral class. The Hubble Space
Telescope's (HST) Ultraviolet Legacy Library of Young
Stars as Essential Standards (ULLYSES) program will enable us to compare our predicted spectra with observations of
stars of similar nature (e.g., metal-poor
stars in Sextant A).
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Astrophysics of Galaxies
Recovering the infall mass for Milky Way satellite galaxy Sextans
Tingting Tian, Jiang Chang, Go Ogiya et al. (+2 more)
Understanding the formation and
evolution of the Milky Way (MW) requires detailed knowledge of its satellite
galaxies. In this study, we focus on the Sextans
dwarf spheroidal (dSph)
galaxy, a faint, dark matter (DM)-dominated satellite, to investigate the role of
tidal and baryonic effects in shaping its observed properties. Using tailored $N$-body simulations, we explore possible orbits of Sextans in different MW models to reconstruct its progenitor's properties. Our simulations demonstrate the
stars in Sextans are only mildly affected by
galactic tides and the
stellar kinematics provide robust constraints on its dynamical mass within the half-light radius, while the
tidal mass loss of its DM component depends primarily on MW mass. The recovered infall mass of Sextans ranges from $1.22$ to $3.14\times10^9\rm\,M_\odot$ for MW masses from $0.8$ to $2\times10^{12}\rm\,M_\odot$. If the DM density remained as cuspy as NFW profile, the infall mass would be smaller by a factor of 2. Although with large ranges, the possible infall masses of Sextans recovered by our simulations are consistent with the
stellar mass-
halo mass relation in TNG50 and abundance matching results. We find some cases for the cuspy DM density profile where the infall mass is smaller than $10^9\rm\,M_\odot$, possibly indicating that
star formation in Sextans is more efficient than in other satellites. The recovered DM
halo structural parameters from our simulations provide valuable constraints for future studies on the DM content and formation history of Sextans.
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All authors Tingting Tian, Jiang Chang, Go Ogiya, Xi Kang, Renyue Cen
High Energy Astrophysical Phenomena
Accretion Disk Evolution in GX 339-4 Across Spectral States Using NuSTAR, NICER, and Insight-HXMT Observations
Ruchika Dhaka, Ranjeev Misra and Suraj Kumar Chaurasia
We present a broadband spectral analysis of the black hole X-ray binary GX 339-4 during its 2021 outburst, covering both hard and soft spectral states. Using simultaneous observations from NuSTAR, NICER, and Insight-HXMT, we investigate the
evolution of the
accretion disk with a focus on the disk normalization derived from the diskbb component, which serves as a proxy for the apparent inner disk radius. In the standard single Comptonization model, the disk normalization in the hard state is more than an order of magnitude lower than in the soft state ($\sim$0.3$\times$10$^3$ vs. $\sim$3.0$\times$10$^3$). This result contradicts the widely accepted view that the disk radius is smaller in the soft state than in the hard state. By incorporating an additional warm Comptonization component, the disk normalization in the hard state increases to values ($\gtrsim 10^4$) exceeding those in the soft state ($\sim 10^3$), yielding results consistent with a physically truncated, cooler
accretion disk. The results of this work support the presence of a dual-corona geometry in the hard state, comprising both a hot, optically thin corona and a warm, optically thick corona, while the soft state spectrum is well described by a single hot Comptonization component alone. Our findings emphasize the importance of including a warm corona in hard-state spectra, as it leads to a more physically consistent picture of the
accretion geometry across spectral states.
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High Energy Astrophysical Phenomena
Do the Amati and Yonetoku Relations Evolve with Redshift for Swift GRBs?
Ali M. Hasan and Walid J. Azzam
Gamma-ray bursts (GRBs) are extremely powerful
stellar explosions that have been observed to huge distances with
redshifts exceeding 9. Although GRBs are not standard candles, one may standardize them by calibrating certain correlations that link an intrinsic parameter to an observed one. Two such correlations that have been discovered are the Amati relation and the Yonetoku relation. In this paper, we compile a large sample of 241 Swift long GRBs for the purpose of examining whether the Amati and Yonetoku relations are immune to
redshift evolution. Our methodology encompasses two approaches: the first involves binning the data by
redshift and fitting the two relations for each bin, then checking whether the fitting parameters evolve with
redshift; the second approach involves using a
redshift cutoff to divide the data into a low-
redshift group and a high-
redshift group, then checking whether the fitting parameters for the two relations are consistent with one another. Our results indicate that the Amati and Yonetoku relations are robust in the sense that they do not show any systematic or significant
redshift evolution. Moreover, our results indicate that the high
redshift bins show better fits compared to the low
redshift bins, which indicates that the Amati and Yonetoku relations are more reliable for high
redshift and hence are promising cosmological probes.
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Instrumentation and Methods for Astrophysics
Rederivation of STIS Secondary Echelle Mode Traces
Matthew R. Siebert, TalaWanda Monroe and Svea Hernandez
The STIS echelle gratings can be used with a variety of different central wavelength settings. "Secondary" wavelength settings, designed to cover select absorption or emission lines, have not been calibrated as precisely as their primary mode counterparts. In particular, secondary echelle mode traces (and subsequent extraction regions) have been previously defined using straight line fits to each spectral order. In this work, we define a new general method for defining echelle traces that utilizes Gaussian process regression and accounts for the detailed
curvature of each order across the detector. Across a variety of echelle grating and central wavelength settings, we find that this method can improve flux throughput by $\sim4\%$ especially near wavelengths located close to the edge of the detector. We have used this method to provide new traces and update reference files for 9 different echelle modes for both pre- and post-Servicing Mission 4 (SM4; in 2009) observations.
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Instrumentation and Methods for Astrophysics
Recalibration of Pre-SM4 STIS Echelle Throughputs
Matthew R. Siebert, Joleen K. Carlberg, Svea Hernandez et al. (+1 more)
Recent improvements to
stellar atmospheric models have merited updated flux calibration for high priority STIS observing modes. Specifically, in the FUV and NUV, continuum differences of 1-3% are present between the newest models (CALSPECv11) and previous models (CALSPECv04-v07). As a result of these improvements the STIS team has derived updated sensitivity curves and blaze shift coefficients for a variety of echelle modes in order to meet targeted flux accuracies. The first series of echelle sensitivity updates primarily targeted post-Servicing Mission 4 (SM4; in 2009) observations. In this ISR, we investigate instead applying a simple scaling (derived from the ratio of new vs old CALSPEC model continua) to the previously determined throughputs of STIS echelle modes. This alternative approach has a straightforward implementation and provides reasonable accuracy, especially in cases where available calibration data are lacking (e.g., pre-SM4 era). Adopting this scaling approach, we delivered pre-SM4 throughput updates for 8 echelle modes, resulting in typical improvements of 0.5-2.4% across the FUV and NUV.
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All authors Matthew R. Siebert, Joleen K. Carlberg, Svea Hernandez, TalaWanda Monroe
High Energy Astrophysical Phenomena
Matter- and magnetically-driven flavor conversion of neutrinos in magnetorotational collapses
Marco Manno, Pablo Martínez-Miravé and Irene Tamborra
The magnetorotational collapse of massive
stars copiously emits
neutrinos of all
flavors, with a prominent hierarchy between the non-electron and electron
flavor average energies. Relying on a three-dimensional
neutrino-magnetohydrodynamic simulation of a $13 M_\odot$ progenitor, we investigate
flavor conversion in matter. We find that, in addition to resonant
flavor conversion of
neutrinos and antineutrinos in matter, (anti)
neutrinos experience chirality-flipping interactions due to their non-zero
magnetic moment ($\mu \lesssim 10^{-12} \mu_B$) and large
magnetic field in the source ($B \simeq 10^{15}$ G). For Majorana
neutrinos, this leads to resonant
flavor-changing
neutrino-antineutrino mixing. The event rate expected from a
Galactic collapse at current and next-generation
neutrino telescopes, such as IceCube and Hyper-Kamiokande, strongly depends on the orientation of the magnetorotational collapse with respect to the observer direction and
flavor conversion scenario. The event rate is expected to be larger for an observer facing head on the jet launched during the
stellar collapse and peaks around $400$-$600$ ms after bounce. Our work highlights that understanding the rich phenomenology of
flavor conversion in magnetorotational collapses is essential to take full advantage of the joint detection of
neutrinos and gravitational waves from these sources.
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Cosmology and Nongalactic Astrophysics · Cross-listed from cond-mat.quant-gas
Analog Simulation of Massive Relativistic Quantum Fields in 2 + 1 Dimensions
Yansheng Zhang, Feiyang Wang, Paul H. C. Wong et al. (+8 more)
Quantum field theories provide fundamental models of complex interacting systems, from high-energy physics and cosmology to condensed matter. However, solving these models in non-perturbative and dynamical regimes is often challenging, particularly in more than one spatial dimension. Analog simulation using tunable synthetic
quantum systems can both verify existing theoretical predictions and lead to new physical insights. Here, we realize analog simulation of massive relativistic
quantum fields in $2+1$ dimensions (two spatial dimensions and time), using two coherently coupled
spin components in a uniform two-dimensional atomic Bose–Einstein condensate. Specifically, we encode the paradigmatic sine-Gordon model in the long-wavelength modes of the field describing the relative phase, $\phi$, of the two components. In the perturbative regime, collective field excitations exhibit a relativistic dispersion with a tunable mass gap. We also observe explicitly non-perturbative phenomena, including the existence of topological domain walls across which $\phi$ rapidly winds by $2\pi$. Our work opens possibilities for studies of cosmologically relevant phenomena including preheating, dynamics of topological defects, and relativistic false-
vacuum decay.
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All authors Yansheng Zhang, Feiyang Wang, Paul H. C. Wong, Alexander C. Jenkins, Yi Jiang, Konstantinos Konstantinou, Gehrig Carlse, Nishant Dogra, Joseph H. Thywissen, Christoph Eigen, Zoran Hadzibabic
Astrophysics of Galaxies
16 new quasars at the end of the reionization unveiled by self-supervised learning
L.N. Martínez-Ramírez, Julien Wolf, Silvia Belladitta et al. (+8 more)
Luminous
quasars at $z > 6$ are key probes of early supermassive black hole (SMBH) growth, massive
galaxy evolution, and intergalactic medium properties during
cosmic reionization. However, their discovery is very challenging due to their scarcity and overwhelming contamination, as foreground ultracool
dwarfs (UCDs) outnumber $z>6$
quasars by 2-4 orders of magnitude. In this work, we leverage the extensive coverage of DESI Legacy Survey DR10 to conduct a self-supervised search for
quasars at $z > 6$, directly analyzing multiband optical images and minimizing the biases of traditional catalog-driven color-color selection criteria. By applying a contrastive learning (CL) method followed by spectral energy distribution (SED) fitting prioritization, we identified 1139 high-priority
quasar candidates, for which we expect a competitive $\sim$1:1
quasar-to-UCD ratio based on literature samples. We spectroscopically confirm 16 new
quasars at $z = 5.94$-6.45, achieving a 45% success rate. Remarkably, all 16 objects are relatively bright ($M_{1450} < -25.5$)
quasars, including several with unusual properties such as narrow Ly$\alpha$ emission (FWHM $< 2600$ km s$^{-1}$), strong Ly$\alpha$+NV emission with equivalent width $>100$ Å, and mildly red observed-frame near-infrared (NIR) continua ($z - J > 0.4$). Notably, three of them would have been missed by traditional color-color selections. These results highlight the power of self-supervised machine learning combined with SED fitting prioritization to uncover rare distant sources beyond conventional techniques. Our approach offers a scalable and robust framework for data mining and can be readily extended to forthcoming wide-field surveys such as Rubin/LSST, 4MOST, Euclid, and Roman, improving the census of high-
redshift quasars and constraints on SMBH formation and
evolution in the first billion years of the Universe.
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All authors L.N. Martínez-Ramírez, Julien Wolf, Silvia Belladitta, Eduardo Bañados, F. E. Bauer, Raphael E. Hviding, Daniel Stern, Chiara Mazzucchelli, Romain A. Meyer, Ezequiel Treister, Federica Loiacono
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Axion-neutrino interactions in seesaw models and astrophysical probes
P.Kivokurtseva
We study
axion-
neutrino interactions in
neutrino-mass extensions of the Standard Model, focusing on the Type-I and inverse seesaw. In these frameworks the effective coupling $g_{a\nu}$ is tied to the
axion scale and can be constrained using existing astrophysical limits on
axion couplings to electrons. We then estimate the impact of
axion-mediated scattering on
neutrino propagation in two
benchmarks: resonant interactions with the C$\nu$B and scattering on
axion dark matter. In the parameter space allowed by current bounds, the resulting optical depths are extremely small, implying no observable signatures with present sensitivities.
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Cosmology and Nongalactic Astrophysics
Detecting Axion-like particles using Cosmic Variance Cancellation with CMB and Radio surveys
Harsh Mehta, Anaya Dixit, Suvodip Mukherjee et al. (+1 more)
Axions and
axion-like particles (ALPs) arise naturally in many extensions of the Standard Model and are among the well-motivated candidates for dark matter. In the presence of
magnetic fields of
galaxy clusters, the
Cosmic Microwave Background (CMB)
photons can convert to ALPs, with the efficiency of the process governed by the cluster electron density and
magnetic field profiles, the
photon-ALP coupling strength (${g_{a\gamma}}$), as well as the frequency ($\nu$) of the
photon at the
redshift of the cluster. The CMB blackbody spectrum suggests this resonant conversion takes place at
radio wavelengths as well, following the spectral behaviour of the ALP distortion signal. This opens up a new window to search for ALPs using
cosmic variance cancellation (CVC), with multi-frequency tracers of the same phenomenon in CMB
photon-ALP resonant conversion. The constraints on the ALP signal ratios from different combinations of microwave and
radio bands of Simons Observatory (SO) and Square Kilometer Array (SKA), can be significantly improved using CVC as compared to the case of using auto-only spectra from the two experiments. With the large number of
galaxy clusters that will be observed by SO and SKA, we will be able to obtain much more information using CVC, especially for the case of low-mass ALPs with stronger signals. Using the auto-only spectra from
galaxy clusters up to
redshift $z = 1$ for inference of normalized ratio parameter, we obtain a standard deviation of $5.9 \times 10^{-2}$ for ALP mass $m_a = 10^{-14} \, \rm{eV}$, which improves to $1.3 \times 10^{-2}$ using CVC. Not only is this method a universal probe of the ALP distortion signal using its spectral dependence, but will be able to provide a more robust consistency check, helping to identify and mitigate potential spurious signals that might arise in CMB-only analyses, based on its frequency behavior in different bands.
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All authors Harsh Mehta, Anaya Dixit, Suvodip Mukherjee, Joseph Silk
Solar and Stellar Astrophysics
Red-Giant Asteroseismology of Low-Mass Population III Stars
Thiago Ferreira, Earl P. Bellinger, Ebraheem Farag et al. (+1 more)
Low-mass
stars from the first epoch of
star formation may still persist in the Milky Way and its satellite
dwarf galaxies today; however, their detection is confounded by surface pollution from interstellar
accretion and internal mixing, which obscure their
primordial composition and blur their distinction from second-generation
stars. Asteroseismology offers a probe of the internal structure and evolutionary state of
stars, and hence may aid in the search for
primordial stars. In this second paper of the series, we present the first non-radial adiabatic pulsation analysis of low-mass, metal-free
stellar models. We use a $0.85\,M_\odot$ red
giant as a case study and compare its seismic signatures with those of higher-
metallicity models. At the same central hydrogen fractions, Pop III main-sequence models display systematically higher $r_{02}\equiv\delta\nu_{02}/\Delta\nu$ ratio and lower $\Delta\nu$ than metal-enriched analogues, a direct consequence of their larger internal sound speeds and steeper core-envelope stratification. To interpret the structural dependence during
giant evolution, we introduce a composite asteroseismic diagnostic, $\psi\equiv\Delta\nu/\Delta\Pi_1$, which traces how
metallicity influences the balance between acoustic and buoyancy cavities through its imprint on opacity, core contraction, and mean molecular-weight gradients. Pop III models occupy a distinct locus in the $\psi-\Delta\Pi_1$ plane due to their radiative interiors with lower mean densities and delayed development of core mean molecular weight gradients. We find that asteroseismology is a powerful diagnostic for identifying relic Pop III
stars despite potentially polluted surfaces, providing a clear pathway for future searches of the
Galaxy's oldest surviving
stars with upcoming surveys.
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All authors Thiago Ferreira, Earl P. Bellinger, Ebraheem Farag, Christopher J. Lindsay
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
All-Loop Renormalization and the Phase of the de Sitter Wavefunction
Alexander Farren, Ciaran McCulloch, Enrico Pajer et al. (+1 more)
Cosmological observables of the
primordial universe are encoded in the late-time field-theoretic wavefunction. For shift-symmetric scalars in de Sitter, a good approximation for many inflationary models, the wavefunction must be purely real at tree-level. This property is violated by a
quantum anomaly in the process of renormalization. As a result, we show that the imaginary part of the wavefunction is fixed by its dependence on the renormalization scale to all loop orders in perturbation theory. This follows from unitarity, locality, dilation isometry and a Bunch-Davies state. The compact relation we uncover for the wavefunction implies an infinite set of relations among correlators of massless fields and their conjugate momenta, which we exemplify at one-loop order.
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All authors Alexander Farren, Ciaran McCulloch, Enrico Pajer, Xi Tong
High Energy Astrophysical Phenomena
Gamma-ray Signatures of r-Process Radioactivity from the Collapse of Magnetized White Dwarfs
Tetyana Pitik, Yong-Zhong Qian, David Radice et al. (+1 more)
We predict the gamma-ray line emission from $r$-process
nuclei synthesized in the ejecta of the
accretion-induced collapse (AIC) of a magnetized, rapidly rotating white
dwarf. Using ejecta from a two-dimensional general-relativistic
neutrino-magnetohydrodynamic simulation, further evolved with a radiation-hydrodynamics code coupled to an in-situ
nuclear reaction network, we construct angle-dependent gamma-ray spectra in the $0.01$-$10\,\mathrm{MeV}$ band via composition-dependent ray-tracing through the ejecta. The emission between $\sim$1 and $10\,$d is dominated by $^{132}$I ($t_{1/2} = 2.3\,$h), continuously replenished by the decay of its parent $^{132}$Te ($t_{1/2} = 3.2\,$d), with additional contributions from $^{131}$I, $^{133}$Xe, and $^{132}$Te. At $t\gtrsim 20$ d, $^{56}$Co (from $^{56}$Ni decay) becomes the primary emitter. The simultaneous presence of $r$-process and iron-peak gamma-ray lines is distinctive of AIC ejecta and absent in binary
neutron star mergers, where iron-peak
nuclei are generally not synthesized. Comparing with the $3\sigma$ continuum sensitivities of planned MeV gamma-ray
telescopes (COSI, AMEGO-X, e-ASTROGAM, GRAMS, GammaTPC), we find the brightest $r$-process lines detectable to $\sim 10\,\mathrm{Mpc}$ by GammaTPC and GRAMS, with the signal approaching their sensitivity threshold at $30\,\mathrm{Mpc}$. The $r$-process spectral features survive time integration over $\sim 30$ d exposures, demonstrating robustness against the long observation times required by gamma-ray detectors.
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All authors Tetyana Pitik, Yong-Zhong Qian, David Radice, Daniel Kasen
Astrophysics of Galaxies
Quantifying the Milky Way, LMC and their interaction using all-sky kinematics of outer halo stars
Richard A. N. Brooks, Jason L. Sanders, Adam M. Dillamore et al. (+4 more)
The recent pericentric passage of the Large Magellanic Cloud (LMC) has dislodged the Milky Way's (MW) centre of mass, inducing dynamical disequilibrium, the reflex motion, in the kinematics of outer
stellar halo stars. Using data out to $160 \, \rm kpc$ from the combined H3+SEGUE+MagE outer
halo survey, we constrain the mass of the MW and LMC, as well as the resulting reflex motion and the
stellar halo velocity anisotropy. Using a suite of 32,000 rigid MW–LMC simulations, each with a MW
stellar halo evolved to the present day in the combined MW–LMC potential, we perform Simulation Based Inference by training a neural posterior
estimator on the means and dispersions of the radial and tangential velocities of
stars from the combined H3+SEGUE+MagE outer
halo sample. Relative to
halo stars at $100 \, \rm kpc$, we find the magnitude of the reflex velocity to be $v_{\rm travel} = 38.6^{+8.3}_{-7.8}\,\rm km \, s^{-1}$. Simultaneously, we determine the enclosed MW mass, $M_{\rm MW}(< 50 \, \rm kpc) = 3.36 \pm 0.15 \times 10^{11}\, \rm M_{\odot}$ and the enclosed LMC mass, $M_{\rm LMC}(< 50 \, \rm kpc) = 8.76^{+1.94}_{-1.77} \times 10^{10}\, \rm M_{\odot}$. Our results suggest that the total LMC mass must be at least $\sim20\%$ that of the MW. The velocity anisotropy prior to the LMC's infall is constrained to be $\beta_0 = 0.68 \pm 0.02$. Finally, we demonstrate that neglecting the LMC in models biases the estimated MW mass to prefer more massive values.
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All authors Richard A. N. Brooks, Jason L. Sanders, Adam M. Dillamore, Nicolás Garavito-Camargo, Vedant Chandra, Adrian M. Price-Whelan, Phillip Cargile
Earth and Planetary Astrophysics
Worlds Next Door. IV. Mapping the Late Stages of Giant Planet Evolution with a Precise Dynamical Mass and Luminosity for $\epsilon$ Ind Ab
Aniket Sanghi, William Thompson, James Mang et al. (+21 more)
We present new JWST/NIRCam 4-5 $\mu$m (F410M, F430M) and JWST/MIRI 18-25 $\mu$m (F1800W, F2100W, F2550W) imaging detections of the nearby (3.6 pc) cold (275 K) gas
giant exoplanet $\epsilon$ Ind Ab. The F2550W detection of $\epsilon$ Ind Ab constitutes the longest wavelength image of an
exoplanet acquired to date. Combining three decades of radial velocity monitoring,
Gaia-Hipparcos absolute astrometry, and relative astrometry from direct imaging (including the new NIRCam astrometry), we conduct a comprehensive re-analysis of $\epsilon$ Ind Ab's orbit and obtain a dynamical mass $M_{\rm Ab} = 6.5^{+0.7}_{-0.6}\;M_{\rm Jup}$. Using $\epsilon$ Ind Ab's NIRCam and MIRI photometry, we assemble the first 4-25 $\mu$m spectral energy distribution (SED) of a cold gas
giant outside the
Solar System. The NIRCam photometry supports a metal-enriched atmosphere for $\epsilon$ Ind Ab based on analysis with atmospheric model grids, consistent with predictions from the
giant planet mass-
metallicity relation. While the current data do not provide definitive evidence for or against the presence of water ice clouds, we tentatively find that the H$_2$O vapor absorption-dominated F2550W photometry is systematically brighter ($>1\sigma$, but $<2\sigma$) than predictions from cloud-free/rainout chemistry models and better explained by a cloudy model. We calculate a bolometric luminosity of $\log L_{\rm bol}/L_\odot = -7.23 \pm 0.03$ dex by directly integrating $\epsilon$ Ind Ab's SED. Combining this with the
planet's dynamical mass and age ($3.5 \pm 1.0$ Gyr), we demonstrate excellent agreement with evolutionary model predictions in a new regime of low luminosities, low masses, and old ages. Our results establish $\epsilon$ Ind Ab as a
benchmark system for planetary
evolution studies and set the stage for the detailed atmospheric characterization of this temperate extrasolar world.
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All authors Aniket Sanghi, William Thompson, James Mang, Jerry Xuan, Dimitri Mawet, Jean-Baptiste Ruffio, Yapeng Zhang, Jason Wang, Caroline Morley, Eric Nielsen, William Roberson, Elisabeth Matthews, Aarynn Carter, Ian Crossfield, Mathilde Mâlin, Björn Benneke, Alexis Bidot, András Gáspár, Carrie He, Katelyn Horstman, Alexander Madurowicz, Christian Marois, Rebecca Oppenheimer, Marshall Perrin
Cosmology and Nongalactic Astrophysics
Binary Black Holes population synthesis based on the current LVK observations
Mehdi El Bouhaddouti, Ilias Cholis and Muhsin Aljaf
The ongoing observations from ground based gravitational-wave observatories have led to the detection of more than a hundred merger events between black holes. We use the LIGO-Virgo-KAGRA (LVK) observations from 2015 to early 2024, to test the population synthesis of these merging binaries; which will allow us to probe the formation mechanisms and environments of these black holes. We test if the current sample of binary black holes can be explained only by the merger of black holes coming from the collapse of the cores of massive
stars, i.e. as just first generation black holes merging with each other. Those black holes' masses will roughly follow a power-law distribution. We also test if in addition to the merger between first generation black holes, there is evidence for a second population of black hole binaries in which at least one the binaries' members is the product of an earlier merger between black holes. These binaries are typically referred to as signals of hierarchical mergers. Such a population can possibly explain the observation of very massive black hole binaries by the LVK collaboration. We find that the LVK observations give a statistical preference in log-likelihood of up to $- 2 \Delta ln\mathcal{L} = -150$ or in log-Bayes factor of up to $ln\textrm{BF} = 71$, for the full sample of black hole binaries originating from a combination of black holes following a power-law distribution and black holes from hierarchical mergers. The ratio of black holes following a power-law mass-distribution to a mass-distribution expected from hierarchical mergers is found to be as high as one-to-one. We also consider that some of the LVK black hole merging binaries are the result of
primordial black holes (PBHs), merging inside dark matter
halos and in the intergalactic medium. Adding a third population is preferred. [abridged]
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Scalar shortcut to beyond-Kerr ringdown tests and their complementarity with black-hole shadow observations
Paolo Pani and Andrea P. Sanna
The quasinormal modes of black holes (BHs) in the large-angular-momentum limit can be computed within the eikonal approximation. This approximation is often extrapolated to low angular momentum to obtain a rough estimate of the dominant ringdown modes. Although approximate, this approach is particularly convenient in theories beyond general relativity with intricate dynamics, or for phenomenological metrics that lack an underlying fundamental theory. Here we explore a complementary approximate strategy: we compute exactly the quasinormal modes of a test scalar field propagating on the BH background and use their deviations from the general-relativity predictions as a proxy for the corresponding corrections to the gravitational quasinormal modes. For Kerr-Newman and Einstein-scalar-Gauss-Bonnet BHs, we show that this method reproduces the exact corrections (including the coupling among different degrees of freedom) within tens of percent, an accuracy that is adequate as long as ringdown measurements remain at the percent level. Furthermore, this method is typically comparable to, or more accurate than, the eikonal approximation. We then apply the same strategy to phenomenological metrics commonly employed in tests of
gravity using BH imaging. By computing scalar quasinormal modes in a large family of these metrics for the first time, we find that current ringdown constraints are comparable to, and in some cases more stringent than, those derived from BH shadow observations, while also providing complementary bounds on sectors that would otherwise be inaccessible.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Binary-boosted Dark Matter
Javier F. Acevedo and Adam Ritz
We explore the aggregate effect of binary systems on the Milky Way's dark matter (DM) velocity distribution with Monte Carlo simulations. Through gravitational interactions with binaries, transiting DM particles can gain substantial energy. We analyze this mechanism across a range of
galactic binaries, and find it to be most effective for double black holes, where ejection speeds can reach $\sim 2000 \ \rm km/s$ while attaining a large ejection rate. We assess the expected binary-boosted DM flux from synthetic populations of black hole binaries in the
galaxy, and show direct detection experiments can be sensitive to it. In particular, we demonstrate that large noble
liquid detectors such as Lux-Zeplin and PandaX-4T can extend their mass sensitivity down to the sub-GeV scale, and potentially become competitive with other lower-threshold experiments when the full
galactic black hole binary population is taken into account. This boosting mechanism, being gravitational in nature, is largely model- and mass-independent.
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Earth and Planetary Astrophysics
A second visit to Eps Ind Ab with JWST: new photometry confirms ammonia and suggests thick clouds in the exoplanet atmosphere of the closest super-Jupiter
Elisabeth C. Matthews, James Mang, Aarynn L. Carter et al. (+9 more)
With JWST, we are directly imaging cold (~200-300K),
solar-age
giant exoplanets for the first time. At these temperatures many molecular features appear and water-ice clouds may condense and affect the emission spectrum; early photometric measurements of cold
giant planets are already showing some tension with the predictions of cloud-free,
solar-
metallicity atmosphere models. Here we present new JWST/MIRI coronagraphic observations of the cold
giant exoplanet Eps Ind Ab at 11.3um. Together with archival data, we use these new observations to study the atmosphere of this cold
exoplanet, and we also re-fit its orbit, finding an updated mass of $7.6\pm0.7$ Mj and an eccentricity of $0.24^{+0.11}_{-0.08}$. The
planet is significantly brighter (by $0.88\pm0.08$ mag) at 11.3um than at 10.6um, indicating the presence of ammonia. However, this ammonia feature is shallower than expected. This could indicate a low-
metallicity or nitrogen-depleted atmosphere, but our preferred explanation is the presence of thick water-ice clouds that suppress the ammonia feature and the near-IR emission of Eps Ind Ab. Photometry of the small but growing sample of cold,
giant exoplanets demonstrates that they are consistently fainter than expected between 3 to 5um, consistent with the water-ice cloud hypothesis. 10.6um and 11.3um photometry of this cold
exoplanet sample would be valuable to determine whether the suppressed ammonia feature is universal, and to frame a new open question about the underlying physical cause.
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All authors Elisabeth C. Matthews, James Mang, Aarynn L. Carter, Mathlide Mâlin, Caroline V. Morley, Bhavesh Rajpoot, Leindert A. Boogaard, Jennifer A. Burt, Ian J. M. Crossfield, Fabo Feng, Anne-Marie Lagrange, Mark W Phillips
Instrumentation and Methods for Astrophysics
unxt: A Python package for unit-aware computing with JAX
Nathaniel Starkman, Adrian Price-Whelan and Jake Nibauer
unxt is a Python package for unit-aware computing with JAX. unxt is built on top of quax, which provides a framework for building array-like objects that can be used with JAX. unxt extends quax to provide support for unit-aware computing using the astropy.units package as a units backend. unxt provides seamless integration of physical units into high performance numerical computations, significantly enhancing the capabilities of JAX for scientific applications.
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High Energy Astrophysical Phenomena
Very High Energy Gamma Rays from Ultra Fast Outflows
B. Le Nagat Neher, E. Peretti, P. Cristofari et al. (+1 more)
Context. Ultra fast
outflows (UFOs) from active
galactic nuclei (AGN) are expected to lead to the formation of sub-relativistic strong shocks expanding in a dense circumnuclear medium, and thus have the potential for being efficient particle accelerators, and to be proficient sources of gamma rays and
neutrinos. Aims. We investigate the detectability of a sample of nearby identified UFOs in gamma rays and
neutrinos with current and next- generation instruments. Methods. We model the acceleration of particles at the strong shocks of UFOs, and estimate the associated gamma-ray and
neutrino signal. We adopt our model to investigate the prospects for detection with current and next-generation observatories. Results. We find that several UFOs could be detectable in the very-high-energy (VHE) domain - for example, by the Cherenkov
Telescope Array Observatory (CTAO)- even if they remain undetected by
Fermi-LAT in the high-energy range. Detectability is favored for hard
proton spectra (spectral index {\alpha} \lessim 3.9), high acceleration efficiencies, and amplified
magnetic fields. Our results suggest that next-generation VHE observatories could detect the first gamma-ray signatures of AGN UFOs, providing a new probe of particle acceleration in sub-relativistic shocks
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All authors B. Le Nagat Neher, E. Peretti, P. Cristofari, A. Zech
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Flash from the Past: New Gamma-Ray Constraints on Light CP-even Scalar from SN1987A
Yue Yu, Writasree Maitra, P. S. Bhupal Dev et al. (+4 more)
We derive new constraints on light CP-even scalars using old gamma-ray observations in the direction of SN1987A by the
Solar Maximum Mission (SMM) satellite. Light scalars can be abundantly produced in the
supernova core via the nucleon bremsstrahlung process, can stream out of the
supernova-environment and decay into
photons – either primary
photons or secondary
photons from
lepton-antilepton pairs – thus leading to a gamma-ray signal. From the non-observation of excess
photon flux by SMM after the detection of the
neutrino burst from SN1987A, we set new constraints on the mixing angle of the CP-even scalar with the Standard Model
Higgs boson.
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All authors Yue Yu, Writasree Maitra, P. S. Bhupal Dev, Jean-Franccois Fortin, Steven P. Harris, Kuver Sinha, Yongchao Zhang
High Energy Astrophysical Phenomena
Multimessenger Characterization of High-Energy Neutrino Emission from the Brightest Neutrino-Active Galactic Nuclei
Jose Alonso Carpio, Ali Kheirandish and Kohta Murase
The observation of high-energy
neutrinos from the direction of the nearby active
galaxy, NGC 1068, was a major step in identifying the origin of high-energy
cosmic neutrinos. The multimessenger data imply that high-energy
neutrinos originate from the hearts of active
galaxies which are opaque to GeV-TeV $\gamma$-rays. This realization is reinforced by the excess of
neutrinos in the direction of NGC 4151 and Circinus
Galaxy, other nearby active
galactic nuclei (AGNs). Understanding the vicinity of supermassive black holes with electromagnetic radiation is often challenging due to uncertainties associated with the absorption of emission in these dense environments, and
neutrinos can be used as a powerful probe of the inner parts of the active
galaxies. Considering the five brightest
neutrino-active
galaxies, NGC 1068, NGC 4151, CGCG 420-15, Circinus
Galaxy, and NGC 7469, we employ the measured
neutrino spectra together with the sub-GeV $\gamma$-ray emission measured by the
Fermi satellite to break the degeneracy and narrow in on the parameter space of
neutrino emission from turbulent coronae of AGNs. We also study contributions of jet-quiet AGNs, whose properties are similar to NGC 1068 and NGC 7469, to the isotropic
neutrino background flux, through exploring possibilities that the
neutrino luminosity function may deviate from the X-ray luminosity function. Our results will help estimate the prospects for identifying additional
neutrino-active
galaxies and guide future targeted analyses.
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Astrophysics of Galaxies
An Alternate Pathway for H$_2$ Formation in the Early Universe: A physical process to account for the presence and coevolution of the luminous galaxies and supermassive black holes at the high redshifts
Amrendra Pandey, Olivier Dulieu and Nadia Bouloufa-Maafa
Molecular hydrogen (H$_2$) and hydrogen deuteride (HD) are key coolants in
primordial gas and regulate the formation of the first
stars and proto-
galaxies. Recent results from the James Webb Space
Telescope provide striking insights into
galaxies detected at high
redshifts, which are found to be significantly more abundant and luminous than expected from
galaxy formation models, thus suggesting a gap in our understanding of the early Universe. Standard pathways for H$_2$ formation in the early Universe proceed through the H$^-$ and H$_2^+$ intermediates, both of which are strongly suppressed at high
redshift by the
cosmic microwave background. We propose an additional pathway for H2 and HD formation that could be active as early as the end of the epoch of recombination and could enable the formation of the first
stars earlier than the current prediction at
redshift z ~ 30 - 20. The proposed pathway relies on the manifestation of Jahn-Teller dynamical coupling between electronic states of H$_3^+$. This coupling induces transient three-body recombination in H$^+$, H and H, and charge exchange within the charged atom-dimer complex that directly creates ground-state H$_2$ (and HD), bypassing the fragile intermediates that limit the standard
primordial pathways. Our analysis shows that this mechanism could occur under the thermodynamic conditions of the post-recombination epoch, also suggesting that it might be playing a role in the active
galactic nuclei feedback processes, regulating the formation rates of the first
stars and the
accretion rates of the first black holes. Though the global impact on
galaxy formation and black-hole growth is not yet determined and will require quantitative assessment in future modeling, the mechanism offers an additional chemical route for H$_2$ and HD formation, with substantial cosmological relevance for
primordial chemistry and early structure formation.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Black Hole Mergers as the Fastest Photon Ring Scramblers
D. Giataganas, G.F. Giudice, A. Ianniccari et al. (+5 more)
Black holes are the most efficient scramblers in nature. By mapping the instantaneous mass and angular momentum of two spinless black holes in a quasi-circular binary onto those of an effective Kerr black hole, we demonstrate that the final state of the merger remnant corresponds with remarkable accuracy to the configuration that renders null geodesics unstable at the highest possible rate. This suggests a deep connection between the properties of black holes resulting from binary mergers and their unstable null orbits.
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All authors D. Giataganas, G.F. Giudice, A. Ianniccari, A.J. Iovino, A. Kehagias, F. Quevedo, D. Perrone, A. Riotto
Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
A Deep Learning Framework for Amplitude Generation of Generic EMRIs
Yan-bo Zeng, Jian-dong Zhang, Yi-Ming Hu et al. (+1 more)
One of the main targets for space-borne gravitational wave detectors is the detection of Extreme Mass Ratio Inspirals(EMRIs). Data analysis of EMRIs requires waveform models that are both accurate and fast. The major challenge for the fast generation of such waveforms is the generation of the Teukolsky amplitudes for generic (eccentric and inclined) Kerr orbits. The requirement for modeling ${\sim 10^5}$ harmonic modes in a four-dimensional parameter space makes traditional approaches, including direct computation or dense interpolation, computationally prohibitive. To overcome this issue, we introduce a convolutional encoder-decoder architecture for a fast and end-to-end global fitting of the Teukolsky amplitudes. We also adopt a transfer learning strategy to reduce the size of the training
dataset, and the model is gradually trained from the simplest Schwarzschild circular orbits to generic Kerr orbits step by step. Within this framework, we obtain a surrogate model based on a semi-analytical Post-Newtonian
dataset, and the full harmonic amplitudes can be generated within milliseconds, while the median mode-distribution error for generic orbits is $\sim 10^{-3}$. This result indicates that the framework is viable for the construction of efficient waveform models for EMRIs.
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All authors Yan-bo Zeng, Jian-dong Zhang, Yi-Ming Hu, Jianwei Mei
Instrumentation and Methods for Astrophysics
A GPU-Accelerated Transient Detection Pipeline for DECam Time-Domain Surveys
Lei Hu, Tomás Cabrera, Antonella Palmese et al. (+8 more)
We present a GPU-accelerated transient detection pipeline developed for time-domain surveys with the Dark Energy Camera (DECam). It enables real-time-capable image processing, incorporating science-driven candidate filtering to support rapid transient identification in time-critical observing programs. The pipeline serves as the core transient discovery engine for multiple long-term DECam programs, including the GW-MMADS gravitational-wave follow-up campaign and the DESIRT survey for intermediate-
redshift transients with DESI synergy. The pipeline ingests calibrated imaging products from the DECam Community Pipeline and performs image differencing using the SFFT
algorithm, coupled with CNN-based real-bogus classification, to produce science-ready transient alerts and light curves that are delivered to community brokers. We validate the pipeline using archival DECam data from the DESIRT survey. The real-bogus classifier achieves a completeness of $\sim$ 99% of real transients while rejecting $\sim$ 96% of subtraction artifacts, and the workflow typically reduces the candidate load to a manageable level for survey operations. With GPU acceleration, the typical processing time per DECam exposure is $\sim$ 50 s from calibrated image processing to alert generation using a modest allocation of computing resources.
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All authors Lei Hu, Tomás Cabrera, Antonella Palmese, Lifan Wang, Igor Andreoni, Xander J. Hall, Xingzhuo Chen, Jiawen Yang, Frank Valdes, Brendan O'Connor, Yuhan Chen
Solar and Stellar Astrophysics
Evolution and formation of ultramassive white dwarf stars: The case for a 9Msun progenitor
Ana S.R. Antonini, Alejandra D. Romero and S.O. Kepler
We study the full
evolution of a 1.313 Msun white
dwarf star that descended from a 9 Msun main-sequence progenitor with an initial
metallicity of Z=0.02. Using MESA r24.08.01, we calculate its entire
evolution from pre-ZAMS to the WD cooling curve, including both the
evolution through 139 thermal pulses and the post-AGB phase. The resulting remnant is an ultramassive H-deficient WD, for which the composition, in mass fraction, is 47.7% O16, 39.7% Ne20, 4.2% Mg24, 3.3% Na23 and 0.386% C12 – corresponding to a total mass of 5 x 10^-3 Msun of C –, surrounded by a 1.5 x 10^-5 Msun He layer. We also investigate the effects of fully suppressing the TP-SAGB stage by adopting a high mass-loss rate only after the second dredge-up, and find only minor differences in the final mass and composition. In addition, we calculate models with and without phase separation during the WD stage, estimating a cooling delay of only 16 Myr. This is the first ultramassive white
dwarf sequence for which both the TP-SAGB and post-AGB stages are calculated and, to our knowledge, the most massive WD model from complete
evolution for which cooling times and detailed abundance profiles are published
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Astrophysics of Galaxies
Systematic selection of surrogate models for nonequilibrium chemistry
Robin Janssen, Lorenzo Branca and Tobias Buck
Nonequilibrium chemistry is central to many astrophysical environments but remains a major computational bottleneck in simulations because solving the associated stiff ODE systems is expensive. Neural surrogates promise large speedups, yet existing studies rarely provide systematic comparisons of architectures or rigorous optimization toward both accuracy and efficiency. We introduce CODES, a principled framework for optimizing and benchmarking astrochemical surrogate models. Using CODES, we compare four neural surrogate architectures across four KROME-generated
datasets spanning
primordial and molecular-cloud chemistry with up to 287 reactions across 37 species. Dual-objective optimization reveals pronounced accuracy-efficiency trade-offs across architectures. Fully connected models achieve the highest accuracy and most reliable uncertainty estimates, while latent-
evolution models show improved robustness under iterative prediction. Our results highlight the importance of systematic optimization and architectural comparison. The
datasets, metrics, and benchmarking procedure are publicly released within CODES to enable reproducible surrogate benchmarking.
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