Cosmology and Nongalactic Astrophysics
The magnetic mayhem in Abell 2199: discovery of synchrotron threads and homogeneous diffuse radio lobes
R. Timmerman, L. Rudnick, A. Botteon et al. (+2 more)
Sensitive low-frequency
radio observations have started uncovering examples of synchrotron-emitting threads, isolated from the rest of
radio emission in
galaxy clusters. As the bridge of
radio emission previously detected between the
radio lobes of 3C 338 in Abell 2199 is a candidate of such a structure, we observed this
galaxy cluster using the International LOFAR
Telescope. These observations revealed the presence of multiple narrow isolated synchrotron threads in 3C 338: east, west and north of the AGN and its
radio lobes. Chandra X-ray observations show that these structures most likely do not reside within cavities in the intracluster medium (ICM), and are therefore considered to be distinct structures from the
radio lobes. Non-detections in 1.5 GHz Very Large Array observations imply that the spectral index of these newly-discovered isolated threads is likely $\alpha_{1500}^{144} < -3.0$ or steeper. We consider these isolated synchrotron threads to most likely display examples of
magnetic threads within the ICM that have captured synchrotron-emitting
plasma, as has recently been proposed. Furthermore, our observations reveal the
radio lobes to show an almost perfectly uniform spectral index, unlike what would be expected if substantial age differences are present in the
radio lobes according to standard spectral ageing models. We find that the relativistic
plasma in 3C 338 is consistent with a homogeneous
cosmic ray electron population, with the spectral variations dependent on the local
magnetic field strength. Finally, we explore the various models that could explain this trend in the
radio lobes.
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All authors R. Timmerman, L. Rudnick, A. Botteon, G. Brunetti, R. Kale
Cosmology and Nongalactic Astrophysics
Galaxy Power Spectrum at Two-Loop Order: Implications for Weak Lensing Surveys and New Physics
Mikhail M. Ivanov
We compute the
galaxy power spectrum at two-loop order in cosmological perturbation theory (effective field theory, EFT). We derive
galaxy bias operators through the fifth order and obtain two-loop renormalization conditions for their bias coefficients. We also derive the relevant higher-derivative and
stochastic contributions, and implement IR resummation using time-sliced perturbation theory. We obtain the complete dark-matter and
galaxy renormalization conditions for the higher-derivative operators at the power spectrum, bispectrum, and trispectrum level. Having identified the redundant operators, we find that the two-loop
galaxy power spectrum requires 21 additional bias, higher derivative and
stochastic parameters per
galaxy sample relative to the one-loop model. We compare our computation with the
galaxy-
galaxy and
galaxy-matter power spectra from the PT Challenge N-body simulation at $z=0.61$ and find a per mille-level agreement up to $k=0.85~h$Mpc$^{-1}$. We show that even with conservative priors on all EFT parameters, the two-loop model produces an unbiased measurement of the mass fluctuation amplitude $\sigma_8$ with three times narrower error-bars than the linear theory model. The improvement over the one-loop model is $\simeq 40\%$. This suggests significant gains in the two-loop EFT analyses of
galaxy clustering and
galaxy–
lensing two-point functions (“$2\times2$ pt”) from CMB
lensing maps and imaging surveys like Euclid, LSST, and Roman. In addition, our two-loop computation offers a probe of new physics scenarios that modify the shape of the matter power spectrum at wavenumbers $(0.4-0.8)~h$Mpc$^{-1}$ such as the presence of ultra-light
axion dark matter sub-components with masses $m_a\sim 10^{-24}$ eV.
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Astrophysics of Galaxies
Little Red Dots as Intermediate Mass, Super-Eddington Engines: Insights from Type IIn Supernovae and The 1837-1856 Great Eruption of $\eta$ Carinae
Rohan P. Naidu, Jorryt Matthee, Anna de Graaff et al. (+20 more)
JWST's Little Red Dots (LRDs) display a unique constellation of features that do not occur simultaneously in any other class of
galaxies or AGN. Here we observe that many of these features find parallels in the 19th century Great Eruption (GE) of $\eta$ Carinae and a sub-class of
supernovae (Type IIn). Drawing on these
stellar phenomena –
outflows trapped by dense circumstellar gas envelopes – we sketch a possible scenario for LRDs.
Outflows from the central engine produce an enshrouding envelope of gas that may be thought of as a slow wind. This dense wind and its enormous extent produce an opacity so high that a pseudo-photosphere forms within the wind, obscuring the central engine and manifesting as a blackbody-like continuum. Radiation from the buried engine powers the system. The engine may also launch fast winds that crash into the existing envelope to generate shocks. Lines form within the wind above the photosphere – electron scattering and absorption in the clumpy (ionized + neutral) medium account for broad wings and P-Cygni cores. A key implication is that inferences of “overmassive black holes" may be interpreting this wind-like physics as a virial broad-line region. We propose an escape velocity argument to constrain the mass of the engine, which yields $M<10^{5} M_\odot$ for the typical LRD. The lack of variability and low surface
gravity of the photosphere provide further support for intermediate mass ($M\approx10^{3-6} M_\odot$), but very luminous super-Eddington ($L_{\rm{bol}}/L_{\rm{edd}}\gtrsim5$) systems harboring a supermassive
star or intermediate mass black hole. Paralleling the
evolution of IIn SNe,
dust production in the envelope may mark the beginnings of classical AGN. This paper explores a possible self-consistent explanation for the entire life-cycle of LRDs, from their enshrouding in dense gas to their fates as seeds of massive black holes.
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All authors Rohan P. Naidu, Jorryt Matthee, Anna de Graaff, Alberto Torralba, Chris Ashall, Harley Katz, John Chisholm, Gabriel Brammer, Luc Dessart, Anna-Christina Eilers, Raphael E. Hviding, David O. Jones, Vasily Kokorev, Joel Leja, Hanpu Liu, Zhaoran Liu, Devesh Nandal, Pascal A. Oesch, Conor L. Ransome, Robert A. Simcoe, Wendy Q. Sun, Andrea Weibel, Mengyuan Xiao
Astrophysics of Galaxies
Morpho-kinematic of galaxies at cosmic noon
F. Rigamonti and F. R. Ditrani
Recent studies of local
galaxies highlight the need for high-resolution photometry and kinematics to accurately characterize
galactic structures. From this, limitations emerged in the standard two-phase evolutionary scenario, where
galaxies first form dispersion-supported bulges followed by secular disk growth. IFS surveys, combining photometry and kinematics, demonstrated that morphology and dynamics correlate weakly, with bulges and disks forming a continuum in their kinematic properties. This scenario is further supported by JWST observations. From analyses based on visual morphology emerged that mature
galaxies with distinct morphological features exist at earlier times than expected. This, however, needs to be confirmed with high-resolution
stellar kinematics observations. We, therefore, propose to measure
stellar kinematics at high spatial resolution for massive
galaxies at
cosmic noon to probe the build-up of central regions and to disentangle the true nature of structures inferred from visual morphology (e.g., disks and bulges with different degrees of rotation). This will enable studying how
galaxy mass, kinematics, and
star formation co-evolve, providing a complete census of
galactic structures and their formation pathways. In this regard, the VESPER-SHARP instrument on the E-ELT is uniquely suited for this program, offering, within reasonable exposure times, rest-frame optical coverage at $z\sim2$, high spatial resolution, a suitable field of view, and multiplexing for simultaneous observations.
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Instrumentation and Methods for Astrophysics
Mapping Stellar Heterogeneities with the Nautilus Space Observatory
Adina D. Feinstein, Jeff Valenti, Julien de Wit et al. (+9 more)
Stellar photospheric heterogeneities, such as starspots and faculae, are a fundamental limitation for
exoplanet transmission spectroscopy. Inhomogeneous surfaces can imprint wavelength-dependent signals during transits that may mimic or mask atmospheric absorption features, especially for
planets orbiting cool low-mass
stars. Recent work has shown that the information content of transmission spectroscopy observations can be sufficient to correct for
stellar contamination, but only if
stellar photosphere and active-region models have adequate fidelity. This requires empirical benchmarking with observations that validate next-generation
stellar models and identify which spectral diagnostics best encode heterogeneity properties as a function of spectral type, activity level, and time. We propose a two-generation Nautilus program that leverages the scalable architecture of the observatory concept. Generation 1 would use broad-wavelength time-series observations of transiting
exoplanet systems to connect starspot-crossing events and out-of-transit variability to localized and disk-integrated heterogeneity properties. Generation 2 would use the optimized spectral diagnostics identified in Generation 1 to conduct slitless spectroscopic monitoring of large samples of GKM
stars on different timescales. Generation 2 instrumentation would include activity tracers of both the photosphere and chromosphere. This program would provide the
benchmark data and population-level framework needed to turn
stellar contamination into a calibrated input for
exoplanet atmospheric
retrievals.
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All authors Adina D. Feinstein, Jeff Valenti, Julien de Wit, Valeriy Vasilyev, Chia-Lung Lin, Daniel Apai, Ana Glidden, Prajwal Niraula, Peter Plavchan, Benjamin V. Rackham, Noah Tuchow, Luis Welbanks
Earth and Planetary Astrophysics
Testing the prevalence of hydrogen-silicate miscibility in young sub-Neptunes
James G. Rogers and Hilke E. Schlichting
Hydrogen-silicate miscibility can significantly alter the interior structure and thermal
evolution of sub-Neptunes. We consider the interplay between this miscibility and
stellar-driven atmospheric escape. We find that, for the first $\sim 100$ Myr, sub-Neptunes store most of their hydrogen content within their miscible interiors, protecting it from escape. As hydrogen is removed from the top of the atmosphere, more hydrogen is exsolved from the miscible interior, resupplying the envelope mass and delaying the
planet's contraction when compared with models that do not account for miscibility. We construct a population-level
Bayesian hierarchical inference model which tests for the prevalence of fully miscible sub-Neptunes. With conservative measurement uncertainty and no completeness corrections, we predict that $\sim 100-200$ observed young sub-Neptunes with measured radii, masses and ages $\lesssim 1$ Gyr are required to differentiate between fully miscible and immiscible models. This survey size requirement decreases with improved measurement uncertainty. Furthermore, one can reliably infer the underlying distributions of planetary initial conditions if completeness corrections are included in the analysis.
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High Energy Astrophysical Phenomena
Expansion rate of the young, oxygen-rich supernova remnant G292.0+1.8
Maria Aslanidou, Manan Agarwal and Jacco Vink
Core-collapse
supernova remnants (CCSNRs) are ideal targets for studying ejecta–interstellar-medium interactions, shock dynamics, and explosion characteristics. G292.0+1.8 is a classic CCSNR featuring oxygen-rich ejecta, circumstellar material, a rapidly moving
pulsar, and a
pulsar wind nebula (PWN). We examine its expansion rate using deep Chandra ACIS-I observations over two nearly independent $\sim$10 yr baselines (2006–2016). After applying astrometric corrections based on
Gaia DR3 sources, we extracted radial profiles in 19 sectors around the forward shock. The weighted-mean expansion rate is $0.016\% \pm 0.001\%\,\mathrm{yr^{-1}}$ in the broadband, implying an expansion age of ${\sim}2500$ yr for a uniform ambient medium, consistent with previous estimates of 2000–3700 yr. For a $1/r^2$ circumstellar density profile (Wolf-Rayet progenitor wind), the inferred age is ${\sim}4100$ yr. Narrow-band analysis of $\alpha$ elements (O-Ne, Mg, Si-S) shows that lighter elements follow the broadband behaviour, while heavier elements expand more slowly, consistent with their origin in deeper
stellar layers. We discuss the pronounced azimuthal asymmetry of the expansion, the apparent paradox that some sectors expand (with $\sim$2500 km/s) preferentially in the direction of the
neutron-
star kick, and the role of reflected shocks from the reverse-shock–PWN interaction.
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Cosmology and Nongalactic Astrophysics
Primordial Black Holes in a Radiation-Dominated Universe
Thomas W. Baumgarte, Katy Clough, Mary Gerhardinger et al. (+2 more)
Primordial fluctuations frozen out during inflation re-enter the cosmological horizon and can collapse, leading to the formation of
primordial black holes. We perform simulations of the direct collapse of over-dense regions re-entering the horizon during a radiation-dominated epoch, using full 3+1 general relativistic simulations with the BSSN formalism. Building on previous studies, we impose periodic boundary conditions and allow the matter content of the Universe to self-consistently drive its dynamics. We analyze the
evolution of over-densities in both the collapse and dispersal regimes and find a threshold, $0.77<\delta_c<0.83$, above which over-densities collapse and form
primordial black holes. Our findings are consistent with previous analytic predictions as well as numerical studies that use different formalisms and computational approaches, and hence provide independent validation of those results.
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All authors Thomas W. Baumgarte, Katy Clough, Mary Gerhardinger, John T. Giblin Jr., Amanda Miller
Cosmology and Nongalactic Astrophysics
GIGA-Lens 2.0: Strong-Lens Modeling on Multiple GPU Nodes
Xiaosheng Huang, Linus Upson, Nicolas Ratier-Werbin et al. (+12 more)
We present GIGA-Lens 2.0: a major upgrade to the GPU-accelerated
Bayesian framework for modeling strong
lensing systems that allows it to be run across multiple GPU nodes. We have succeeded in running GIGA-Lens 2.0 on 128 nodes or 512 A100 GPUs. We demonstrate the speed benefits of this new version, and apply them to modeling 100 simulated systems and a real system, DESI J238.5690+04.7276. We also present other changes to the framework that have yielded further improvement on performance.
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All authors Xiaosheng Huang, Linus Upson, Nicolas Ratier-Werbin, Harry Lu, Sean Xu, Elden Yap, Evan Odell, Ansel Parke, Harsh Ambardekar, Saul Baltasar, Nestor Demeure, Bradley Richardson, Andi Gu, Yuan-Ming Hsu, Junyi Liu
Astrophysics of Galaxies
Prescriptions for the stochasticity effect on the integrated X-ray luminosity of star-forming galaxies:Implications for selecting star-forming galaxies and AGN in X-ray surveys
Elias Kyritsis, Andreas Zezas and Konstantinos Kovlakas
(abridged) The integrated X-ray luminosity (Lx) of
star-forming
galaxies is dominated by high-mass X-ray binary (HMXB) populations. The discrete nature of these populations introduces
stochastic sampling effects that distort the X-ray Luminosity Function (XLF) and bias observed scaling relations. We investigate how
stochastic sampling of the HMXB XLF affects the predicted integrated Lx across a wide range of
star-formation and
metallicity conditions, quantifying the scatter to provide a statistical framework for interpreting X-ray observations. Using Monte Carlo simulations, we derive Lx distributions over a broad grid of
star-formation rate (SFR) and
metallicity values. By measuring statistical quantities describing these distributions, we parametrize the luminosity scatter by fitting surfaces to the upper and lower Lx bounds as functions of SFR and
metallicity. We provide practical prescriptions to compute the expected Lx for given SFR and
metallicity, fully accounting for
stochastic effects without rerunning costly XLF sampling. Applying these to local and high-
redshift samples shows stochasticity must be considered before attributing Lx differences to intrinsic properties. A simulation study across z=0.5-5 reveals mild
redshift evolution of
stochastic scatter, with minimum scatter at z~2.5. Our prescriptions quantify biases in scaling relations introduced by flux-limited surveys. At low
redshifts,
stochastic effects can raise Lx by up to 1 dex, overlapping with the low-luminosity AGN regime and biasing source classification in deep surveys. These prescriptions offer a framework for constraining scatter, quantifying extreme outliers, and refining X-ray source classification in current and future surveys.
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Instrumentation and Methods for Astrophysics
Gaussian processes on ray-guided transformed uniform grids for fast, flexible, and auto-differentiable adaptive source reconstruction in lens modelling
Wolfgang J. R. Enzi, Coleman M. Krawczyk, Tian Li et al. (+1 more)
Strong gravitational
lensing constrains cosmology and dark matter, but robust inference requires accurate source reconstruction. The achievable source resolution is highly position-dependent. Adaptive meshes can place resolution where needed, but typically rely on discontinuous operations, such as Delaunay tessellations or Voronoi binning, which can restrict regularization choices and break differentiability. In this paper, we present a novel approach for modelling the source on a ray-guided transformed uniform grid (RTU grid), that is adaptive to the lens mass model, auto-differentiable and flexible with respect to the regularization by allowing for an arbitrary choice of power spectrum. We achieve this by defining the source as a Gaussian process on a uniform grid, which is then transformed based on the cumulative distributions of rays traced back to the source plane. This approach ensures that source pixels contain a more uniform number of rays. The approach is fast by leveraging the fast
Fourier transform to describe the Gaussian process in
Fourier space. We apply this new approach to mock data and show that it achieves comparable fit quality with fewer source pixels, typically corresponding to about a factor of two fewer pixels per dimension, and increases Evidence Lower Bounds (ELBOs) for the same number of pixels. Using the RTU grid only mildly affects the difference in ELBO for models with and without substructures within lens
galaxies. A fast, flexible, and auto-differentiable source reconstruction can greatly benefit the analysis of large samples of lens systems, e.g. those found within the Euclid survey
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All authors Wolfgang J. R. Enzi, Coleman M. Krawczyk, Tian Li, Thomas E. Collett
Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
Efficient Eccentric Effective-One-Body Dynamics via Near-Identity Averaging Transformations
Philip Lynch, Alessandra Buonanno, Aldo Gamboa et al. (+1 more)
Next-generation gravitational-wave detectors, such as LISA, the Einstein
Telescope, and
Cosmic Explorer, will require accurate and efficient models of long-lived black hole binary signals, including those with significant eccentricity. A challenge for eccentric effective-one-body models is the cost of resolving rapidly oscillating orbital dynamics over the inspiral, particularly for low-mass and large-mass-ratio systems. We address this by recasting the nonspinning eccentric effective-one-body equations of motion in terms of osculating orbital elements and then applying near-identity averaging transformations to eliminate the fast orbital-timescale structure during the inspiral. Each order in this procedure suppresses the oscillatory behavior by one factor of the ratio of orbital to radiation-reaction timescales. The resulting averaged dynamics are evolved on the radiation-reaction timescale, and then the system is mapped back to the full EOB dynamics for the final transition to plunge. This reduces the cost of the inspiral dynamics by up to two orders of magnitude, eliminating this as the primary bottleneck for long waveforms. The overall waveform-generation speedup spans $1.5 - 8 \times$, motivating the development of more efficient waveform-generation methods. We also validate the accuracy of the method by comparing waveforms generated from the averaged and full effective-one-body dynamics across a broad region of parameter space for moderate to large eccentricities. Carrying out this averaging procedure to next-to-next-to-leading order is needed to accurately model comparable-mass binaries, yielding mismatches $\leq 8.05 \times 10^{-5}$. These results establish near-identity averaging as a practical route to efficient eccentric effective-one-body inspirals, and provide a foundation for further extensions to low-eccentricity and spinning waveform models.
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All authors Philip Lynch, Alessandra Buonanno, Aldo Gamboa, Maarten van de Meent
Solar and Stellar Astrophysics
Wave-Driven Mixing Enhanced by Rotation in Red Giant Branch Stars
Simon Blouin, Paul R. Woodward, Pavel A. Denissenkov et al. (+2 more)
Stars like our Sun expand as they exhaust their core hydrogen fuel, becoming red
giants that eventually reach sizes up to 100 times their original radius. These
giants have long presented a puzzle: they show systematic changes in their surface chemical composition that can only be explained by the transport of material from their
nuclear-burning interior to their surface. The challenge is that this transport must somehow cross a stable layer that acts as a barrier between the
star's outer convective envelope and its
nuclear-burning interior. The convective motions in the envelope create internal waves that propagate through this barrier layer, but on their own these waves produce very little material transport. Here we show through high-resolution three-dimensional hydrodynamical simulations that
stellar rotation dramatically amplifies how effectively these waves can mix material across this barrier. We find that the mixing rates can exceed those in non-rotating
stars by over 100 times, increasing with faster rotation rates. This enhanced mixing provides a natural explanation for the observed chemical signatures in typical red
giants. The amplification of wave-driven mixing by rotation may have implications beyond red
giants to other types of
stars.
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All authors Simon Blouin, Paul R. Woodward, Pavel A. Denissenkov, Praneet Pathak, Falk Herwig
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Evaluating the Fourier Approximation in Pulsar Timing Array Analysis
Yongqi Zhang, Hayden Scholz, Ken D. Olum et al. (+53 more)
Pulsar timing arrays search for
stochastic processes such as gravitational waves by comparing pulse time of arrival data for millisecond
pulsars to expectations from a background with a given power spectral density (PSD). To make the analysis computationally tractable, the
Bayesian likelihood is usually computed using an approximation in which the signal is taken to be a sum of
Fourier modes appropriate to the total time of observation, even though the true signal is not periodic. We study the difference between likelihoods computed with this
Fourier approximation method for power law spectra and those computed exactly (or using more-closely spaced frequencies as a proxy for the exact result) in the NANOGrav 15-year
dataset. We find that the true marginal likelihoods for power-law PSDs are on average about half as large as the likelihoods computed using the
Fourier approximation. This could lead to an error of a factor of two in model comparison. However, in the important comparison of uncorrelated vs. Hellings-Downs correlated models, a very similar correction appears in both, so the model comparison is essentially unaffected. We also compare parameter estimation results for power law PSDs, finding little difference between the methods. We briefly discuss spectra with sharper features, for which the approximation could be much worse.
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All authors Yongqi Zhang, Hayden Scholz, Ken D. Olum, Lucas Steinberger, Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Paul T. Baker, Paul R. Brook, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Paul B. Demorest, Timothy Dolch, Justin A. Ellis, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Jeffrey S. Hazboun, Ross J. Jennings, Megan L. Jones, David L. Kaplan, Matthew Kerr, Michael T. Lam, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Alexander McEwen, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Cherry Ng, David J. Nice, Timothy T. Pennucci, Benetge B. P. Perera, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Ann Schmiedekamp, Carl Schmiedekamp, Brent J. Shapiro-Albert, Ingrid H. Stairs, Kevin Stovall, Abhimanyu Susobhanan, Joseph K. Swiggum, Stephen R. Taylor, Michele Vallisneri, Rutger van Haasteren, Haley M. Wahl
Cosmology and Nongalactic Astrophysics
Universal distance modes from DESI BAO and Type Ia supernovae: what do cosmological rulers actually measure?
Matias Zaldarriaga
We use an SVD decomposition of the low-
redshift distance measurements from DESI BAO and three Type Ia
supernova compilations to identify the leading linear directions probed by the data and to localize the tension with the LCDM CMB-anchored predictions. The leading direction V_0 – whose data amplitude we denote c_0 – is, to high accuracy, a measurement of Omega_m h^2: the projection of the data on V_0 probes essentially this one CMB-derived parameter combination. BAO constrains this parameter more tightly than the CMB itself; the three SN compilations do not. In every extension of LCDM we consider, the leading measurable direction remains V_0, and it is where most of the tension with the CMB resides. In the w0-wa extension a second direction V_1 becomes measurable and provides an independent test of dynamical dark energy; the data show no significant tension in this direction. The only other beyond-LCDM extension that opens a genuinely new measurable direction is spatial
curvature, and only marginally and only for BAO; both measurable directions then independently prefer positive spatial
curvature, though the second direction is poorly constrained.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Nonequilibrium Andreev transport at the QGP-2SC interface
Tingyu Zhang, Honoka Hoshino, Hiroyuki Tajima et al. (+2 more)
We discuss a nonequilibrium Andreev reflection at an interface between
quark-
gluon plasma (QGP) and two-
flavor color superconducting (2SC)
quark matter. Based on the Schwinger-Keldysh framework and a relativistic tunneling model, we evaluate the momentum-resolved tunneling current generated by a chemical-potential bias between the QGP and 2SC phases. We find that the Andreev reflection appears as at the fourth order of the tunneling strength, in which an incident
quark in QGP is converted into a reflected hole, while a Cooper pair is injected into the 2SC condensate. We show that the Andreev reflection is enhanced when the bias becomes comparable to the gap and is suppressed in the supergap region, which is similar to that in superconducting materials. The present formulation provides a field-theoretical pathway to strongly-correlated transport across dense-matter interfaces relevant to nonequilibrium dynamics in compact
stars.
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All authors Tingyu Zhang, Honoka Hoshino, Hiroyuki Tajima, Motoi Tachibana, Mariusz Sadzikowski
Cosmology and Nongalactic Astrophysics
Rapid Hubble constant inference from GW170817 using GPU-accelerated nested sampling: prior sensitivity and the limits of post-hoc reweighting
Ming Han Yang, Metha Prathaban, David Yallup et al. (+1 more)
The bright-siren measurement of the Hubble constant from GW170817 (Abbott et al. 2017) assumes that switching from a volumetric to a uniform-in-$d_L$ luminosity-distance prior can be implemented by post-hoc reweighting of the baseline samples, rather than by re-running the inference under the target prior. Using a GPU-native heterodyned nested sampling pipeline that completes the full $n_{\rm live}=5000$ analysis in about 13 min on a single A100, we recompute the GW170817 $H_0$ posterior under four prior variants for the modern aligned-
spin tidal waveform IMRPhenomXAS_NRTidalv3. Switching from the volumetric to a uniform-in-$d_L$ distance prior raises the high-tail probability $P(H_0>120\,\mathrm{km/s/Mpc})$ from 0.017 to 0.159 when imposed during sampling and shifts the weighted-median $H_0$ from 77.6 to 87.6 km/s/Mpc, while the binned MAP stays at 70.5 km/s/Mpc: both the tail and the bulk move under a change of prior that leaves the mode in place. Post-hoc reweighting of the baseline samples to the same target prior recovers only $P=0.041$ in the tail, approximately 17% of the directly sampled shift. The three prior variants that carry an independent nested sampling evidence agree to $\Delta\ln Z\lesssim 1.8$, so the data show at most a weak preference among the distance priors; the tail and bulk shifts are therefore properties of the prior, not a data update. Targeted mode-isolated runs reveal a $(d_L,\iota)$ bimodality whose high-$H_0$, low-$d_L$ branch (Mode B; $|\ln\mathcal{B}_{\rm B/A}|<1$) the volumetric prior assigns negligible mass: this is the mechanism behind the reweighting deficit. The reweighted posterior has a lower effective sample size than the baseline, independently flagging the coverage failure. The runtime budget makes full-sample prior-sensitivity reruns the default robustness tool for bright-siren cosmology, replacing post-hoc reweighting.
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All authors Ming Han Yang, Metha Prathaban, David Yallup, Will Handley
Solar and Stellar Astrophysics
High-Resolution Spectroscopy of Raman-scattered He II Lines in the Symbiotic Nova RR Telescopii
Jaejin Shin, Seok-Jun Chang, Hee-Won Lee et al. (+1 more)
Raman-scattered emission features in symbiotic
stars provide a powerful diagnostic of mass-loss and transfer processes, as they uniquely probe both ionized and neutral regions within interacting binaries. When resolved with high-resolution spectroscopy, these features encode detailed information on the physical properties of the neutral hydrogen medium. In this work, we present high-resolution spectroscopic observations of the symbiotic nova RR Telescopii obtained with FEROS in 2004 and GHOST in 2024, providing a $\sim$ 20 yr baseline. We report the clear detection of all three Raman-scattered He II lines at 6545 Å, 4851 Å, and 4332 Å, and constrain the distribution and kinematics of H I through line profile analysis. The three Raman lines exhibit distinct relative velocities, indicating that they trace different depths within the H I region. The Raman conversion efficiencies of the three Raman He II lines in 2024 are significantly lower than those in 2004, indicating substantial changes in the physical properties of the neutral hydrogen region. In addition, radiative transfer modeling implies a larger covering factor (opening angle) of the neutral region in 2004 than in 2024. These results indicate that the neutral hydrogen region cannot be characterized by a single H I column density, emphasizing the need for advanced radiative transfer modeling that accounts for the complex kinematics and geometry of the H I region. Overall, these results establish Raman-scattered He II lines as a powerful tool for spectroscopic
tomography, allowing for direct constraints on the structure and kinematics of neutral hydrogen in symbiotic binaries.
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All authors Jaejin Shin, Seok-Jun Chang, Hee-Won Lee, Sam Kim
Cosmology and Nongalactic Astrophysics
Cosmology-dependent covariance in galaxy cluster number counts: consequences for parameter inference
Henrique C. N. Lettieri, Mariana Penna-Lima and Sandro D. P. Vitenti
Galaxy clusters provide constraints on cosmology through their abundance as a function of mass and
redshift. Parameter inference from cluster counts requires modelling the covariance entering the likelihood, including contributions from Poisson shot noise and super-sample covariance (SSC) induced by long-wavelength density fluctuations. Since evaluating the full covariance during parameter inference can be computationally expensive, many analyses compute it at a fiducial cosmology and keep it fixed. In this work, we investigate the impact of covariance misspecification on the estimation of $\Omega_c$, $\sigma_8$, and $w$. We perform a systematic analysis in which the covariance is either varied consistently with the sampled cosmology or fixed at displaced cosmological models, including intermediate strategies where only selected components, such as SSC, are held fixed. Our analysis incorporates observational effects relevant for LSST-like optical surveys, including mass-proxy scatter and photometric
redshift uncertainties. We find that the
estimators of $\Omega_c$, $\sigma_8$, and $w$ remain unbiased even when the covariance is evaluated at an incorrect cosmology. However, fixing the covariance can significantly over- or underestimate confidence regions. The magnitude and sign of this effect are primarily driven by parameters controlling the amplitude of matter fluctuations. For LSST-like surveys, an inconsistent covariance specification can artificially modify the apparent $S_8$ tension inferred from cluster counts. We further show that a single covariance update evaluated at the recovered best-fit cosmology is sufficient to restore the correct uncertainty normalization. These results indicate that fixed-covariance approximations may be adequate for some single-probe analyses, but a fully cosmology-dependent treatment is required for consistent multi-probe studies. ABRIDGED
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Earth and Planetary Astrophysics
CARMApy: An Open-Source Python Framework for Simulating Microphysical Clouds in Planetary Atmospheres
Wolf Cukier, Diana Powell, Xi Zhang et al. (+3 more)
CARMApy is a new open-source python code that performs bin-scheme microphysical modeling of clouds in
exoplanet atmospheres. It models key cloud properties such as particle size distributions and microphysical rates from first principles. The code is a wrapper of ExoCARMA, a well tested Fortran code with an almost half century long heritage. CARMApy includes the microphysical processes of homogeneous and heterogeneous nucleation, condensational growth, evaporation, coagulation, and vertical transport. CARMApy has 10 built-in default condensates and allows the user to specify additional condensates. In this work we describe CARMApy and the data products that it can generate, along with the history of its code heritage. We additionally compile a complete description of the theory and methods used in CARMA. Lastly we
benchmark CARMApy and show that its results are consistent with previous versions of CARMA, while executing the code ~1.9 times faster single threaded ~3.8 times faster multithreaded.
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All authors Wolf Cukier, Diana Powell, Xi Zhang, Peter Gao, Dominic Samra, Vighnesh Nagpal
High Energy Astrophysical Phenomena
Sloshing Motions in Abell 3571 Revealed by XRISM/Resolve Velocity Mapping
Itsuki Aihara, Congyao Zhang, Sora Nakajima et al. (+12 more)
Minor mergers can induce sloshing motions in the intracluster medium, leaving characteristic signatures in the thermodynamic structure and gas kinematics of cluster cores. Abell 3571 is an X-ray-bright, apparently relaxed cluster at $z \sim 0.04$. We observed the central $\sim 300$ kpc region of Abell 3571 with four partially overlapping XRISM Resolve pointings, covering three contiguous Resolve fields to the north, south and east with a total exposure time of approximately 575 ks. The velocity dispersions are subsonic and are at the level of $\sim 100$–$150 \, \mathrm{km~ \, s^{-1}}$ across most regions. The cooler region associated with the northern surface-brightness excess is blueshifted by up to $\sim -60 \, \mathrm{km \, s^{-1}}$ relative to the brightest cluster
galaxy (BCG), while the hotter region in the southern and eastern surface-brightness deficit regions is redshifted by up to $\sim 170 \, \mathrm{km \, s^{-1}}$. Numerical simulations suggest that this large-scale thermodynamic and kinematic asymmetry is broadly consistent with early-phase sloshing induced by an off-axis minor merger. Abell 3572, an X-ray-faint gas-poor cluster located 1.6 Mpc to the south, is a promising candidate for the perturber. Given the lack of clear signatures of prominent AGN feedback in Abell 3571, these results suggest that sloshing-driven gas redistribution may contribute to delaying the re-establishment of a strong cool core in Abell 3571.
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All authors Itsuki Aihara, Congyao Zhang, Sora Nakajima, Kyoko Matsushita, Hannah McCall, Irina Zhuravleva, Shogo B. Kobayashi, Kotaro Fukushima, William R. Forman, Christine Jones, Annie Heinrich, Daniele Rogantini, Kosuke Sato, Kazunori Suda, Ildar Khabibullin
Solar and Stellar Astrophysics
SN 2019vxm: A luminous and long-lived Type IIn supernova with early flash-ionisation features
Y.-Z. Cai, A. Pastorello, T. J. Moriya et al. (+38 more)
We present the photometric and spectroscopic analysis of the luminous and long-lasting Type IIn
supernova (SN) 2019vxm. The SN reaches a peak V-band absolute magnitude of MV = -20.01 +/- 0.13 mag in 35.0 days, and displays slow
evolution in both the light curves and spectra, resembling that of long-lived SNe IIn. A mid-infrared (MIR) excess is detected starting from seven months after maximum brightness, suggesting a few 10^-3
solar masses of
dust are newly formed at >= 210 days (and up to 0.01
solar masses at +4.5 yr). The spectra are dominated by a blue continuum at early stages, with narrow, symmetric Balmer lines and flash-ionisation emission lines of C III, N III, and He II. Comparing our flash-ionised spectrum with early interacting SN spectral models, we estimate a lower limit for the mass-loss rate of the progenitor of >= 0.01
solar masses per year. A weak P Cygni absorption feature is detected in the H-beta profile of the high-resolution Echelle spectrum at +19.7 d, suggesting the presence of slow-moving (60 +/- 10 km/s), unshocked circumstellar material (CSM) arising from the pre-SN wind of the progenitor. The H-alpha and H-beta profiles gradually evolve and become broader and asymmetric, showing a progressively increasing blueshift, with a clear flux deficit in the red wings of the broad velocity component after +102 days. Our observed bolometric light curve before about 100 days can be well fitted by a power-law function (L(t) = 2 x 10^44 (t/day)^-0.49 erg/s), which is very similar to SN 2010jl.
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All authors Y.-Z. Cai, A. Pastorello, T. J. Moriya, X.-F. Wang, A. Reguitti, A. V. Filippenko, L. Tomasella, K. Čotar, A. Siviero, N. Elias-Rosa, T. G. Brink, G. Valerin, S. Benetti, J.-W. Zhao, Z.-H. Peng, Z.-Y. Wang, I. Altunin, R. Baer-Way, E. Baron, V. Chander, M. Chu, A. deGraw, J. M. DerKacy, J. Isern, C. Jennings, R. Kotak, L.-P. Li, P. Marziani, M. May, P. A. Mazzali, A. Morales-Garoffolo, S. Moran, P. Ochner, I. Salmaso, L. Tartaglia, M. Turatto, H.-Y. Wu, D.-F. Xiang, S.-Y. Yan, J.-J. Zhang, W. Zheng
Earth and Planetary Astrophysics
The impact of numerical derivatives on radial velocity extraction
A. M. Silva and K. Al Moulla
The radial velocity (RV) method is a widely used technique to infer planetary masses and orbital parameters. One of the most widely used methods to compute RVs is based on the
alignment of a high-SNR, data driven,
stellar model with individual observations, commonly referred to as template matching. Typically, the
alignment is performed through a $\chi^2$ minimization, but some approaches rely on the derivative of the
stellar template to do so, which is often the case in line-by-line methods. In this paper we aim to explore the limitation of derivative-based methods for RV extraction in the case of using low-SNR
stellar models. We use simulated Gaussian profiles to investigate the effect of computing a numerical derivative of the
stellar template, in comparison with the usage of an analytical profile. The impact on RV and associated uncertainty is then analyzed as a function of the signal-to-noise ratio (SNR) of the line. Then, using real observations we compare the residuals between a derivative-based RV extraction and a classical template matching implementation, as function of the SNR of the
stellar template. We find that on simulated Gaussian profiles the usage of the numerical approach leads to a RV residual at the level of the meter per second, at a per-pixel SNR regime of 100. An increase of the SNR leads to a decrease of this impact, falling under the current noise-floor of state-of-the-art spectrographs at SNR>1000 for a single spectral line. The inclusion of multiple spectral lines in the simulations lead to an overall decrease of the contamination, across all SNR regimes. The application to a real
dataset presents a decrease of the RV impact with the increase of the template's SNR, albeit still presenting a 12.5 cm/s difference when including 78 observations in the
stellar template.
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High Energy Astrophysical Phenomena
Enabling population studies on wind-driven Galactic binary systems
B. Marcote, P. Benaglia, V. Bosch-Ramon et al. (+8 more)
Galactic binaries driven by
stellar wind shocks, such as colliding wind binaries (CWBs) and gamma-ray binaries (gBs), harbor one of the most efficient particle acceleration engines known in the Universe. Despite their potential, these sources remain relatively unexplored, particularly in the domains of low
radio frequencies and very high resolution. As a result, we lack comprehensive population studies and well-characterized individual systems. Only a few of these binaries, such as the iconic gB PSR B1259$-$63 or the massive CWB WR 140, have been studied in enough detail to probe their wind dynamics and shock physics. Current observations lack the sensitivity to detect weak non-thermal synchrotron emission from low-energy particle populations and the angular resolution to resolve shock structures on sub-au scales. The Square Kilometre Array Observatory (SKAO) will mark a significant improvement in both sensitivity and resolution with its SKA-low and SKA-mid
telescopes, solving these challenges. This will enable systematic studies of the winds and shock interactions in these binary systems. Additionally, SKA-VLBI will facilitate the observation of changes in shock geometry at different orbital phases, linking particle acceleration processes to the binary's orbital characteristics and
stellar wind properties. SKAO will pave the way for comprehensive population studies of these energetic binary systems.
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All authors B. Marcote, P. Benaglia, V. Bosch-Ramon, M. De Becker, S. del Palacio, P. Atri, J. Moldón, J. M. Paredes, M. Ribó, G. E. Romero, A. Tej
Astrophysics of Galaxies
The SKA-VLBI Perspective on Radio-Quiet AGN
Francesca Panessa, Tao An, James Petley et al. (+21 more)
The
accretion-ejection mechanism in Active
Galactic Nuclei (AGN) remains a central open problem in astrophysics, tied to the role of AGN feedback in
galaxy formation and
evolution.
Radio-quiet AGN dominate the observed AGN population. Lacking luminous jets, their
radio emission traces a rich set of processes spanning the host
galaxy kpc scales down to the vicinity of the supermassive black hole:
star formation, AGN-driven winds and shocks, free-free emission from photo-ionized gas, low-power jets, and coronal activity close to the inner
accretion disk. The Square Kilometre Array (SKA) will probe these processes across a wide frequency range with unprecedented sensitivity, wide-field survey capability, and, critically, high-resolution VLBI imaging. Flux, spectral, and polarization monitoring will constrain dynamics and environmental coupling, while mapping
nuclear regions on sub-pc to kpc scales will disentangle compact cores from host emission, resolving the diversity of
radio activity across
accretion regimes and jet powers from the local Universe to the
cosmic dawn. At the full AA4 deployment, the SKA-MID phased into global VLBI arrays will deliver sub-milliarcsecond imaging and $\mu$Jy sensitivity over 0.35–15\,GHz, enabling the first population-level census of
radio-quiet AGN
nuclei. Earlier AA$\ast$ operations will support pilot studies of the brightest nearby systems.
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All authors Francesca Panessa, Tao An, James Petley, Ailing Wang, Ranieri Diego Baldi, Ehud Behar, Emmanuel Bempong-Manful, Gabriele Bruni, Ning Chang, Sina Chen, Lang Cui, Filippo D'Ammando, Marcello Giroletti, Magdalena Kunert-Bajraszewska, Sibasish Laha, Ari Laor, Ian McHardy, Eileen Meyer, Monica Orienti, Miguel Pérez-Torres, Isabella Prandoni, Claudio Ricci, David R. A. Williams-Baldwin, Zsolt Paragi
Solar and Stellar Astrophysics
The role of mass transfer efficiency in stability criteria: Implementation in SEVN and a test on blue stragglers and binary compact objects
M. Echeveste, G. J. Escobar, G. Iorio et al. (+12 more)
Context: The stability of mass transfer through Roche-lobe overflow plays a key role in shaping the outcome of binary interactions. However, the criterion for mass transfer stability remains one of the main open questions in the theory of binary
evolution. Aims: We develop a mass transfer stability prescription that accounts for mass and angular momentum loss, and implement it in the population synthesis code SEVN. We assess its impact relative to the standard formalism used in SEVN, using blue stragglers and binary compact objects as illustrative cases. Methods: We derive an expression for the response of the Roche-lobe radius to mass loss in the general case where the mass and angular momentum of the system are not conserved. On the basis of this formulation, we construct a new mass transfer stability criterion that modifies the standard approach only through the Roche-lobe response term. Results: Population synthesis simulations with SEVN show that the new criterion allows stable mass transfer in binaries with higher donor-to-accretor mass ratios, leading to an overall increase in the predicted number of blue stragglers and promoting their formation in wider orbits. This contributes to reconciling the differences between theory and observations. For binary compact objects, the impact of the new stability criterion varies across system types, with the strongest effects occurring in binaries containing at least one
neutron star. In particular, for low mass transfer efficiency, the new criterion enhances the contribution of channels involving stable mass transfer and leads to a larger number of systems, including gravitational wave progenitors. Conclusion: The inclusion of a new, simple, yet more consistent prescription for mass transfer stability has proven that refining this criterion can significantly improve our understanding of the formation channels of specific
stellar populations.
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All authors M. Echeveste, G. J. Escobar, G. Iorio, E. Pancino, M. Mapelli, D. Alvarez Garay, A. Avdeeva, E. Leitinger, S. Nedhath, S. Rani, E. Reggiani, N. Sanna, S. Saracino, L. Steinbauer, A. Turchi
Solar and Stellar Astrophysics
Spatially Coherent and Intermittent Alfvénic Fluctuations in Solar Polar Spicules
Edris Tajfirouze, Christopher H. K. Chen, Richard J. Morton et al. (+1 more)
Alfvénic fluctuations are considered a key mechanism for transporting energy from the lower
solar atmosphere into the corona, with spicules acting as dynamic conduits for this transfer. We investigate transverse and Doppler velocity fluctuations in quiet-Sun polar spicules observed in the Si IV 1394\,Å\ line by the Interface Region Imaging Spectrograph.
Fourier analysis in time and space is used to characterize power across frequency and spatial scales. The temporal power spectra show broadband fluctuations with enhanced power in the 3–7~mHz range and a peak near 4–6~mHz. Spatial
Fourier analysis of Doppler velocities reveals a perpendicular power spectrum scaling as $\sim k_{\perp}^{-1.43}$, slightly shallower than the canonical $-5/3$ and $-3/2$ slopes of strong MHD
turbulence, but consistent with reflection-driven
turbulence simulations. Velocity increment PDFs show non-Gaussian behavior, with kurtosis increasing toward smaller scales, consistent with intermittency. Spatial coherence analysis using cross-correlation and spectral diagnostics indicates an outer scale of a few hundred to about a thousand kilometres, with cross-correlation yielding smaller values. These results provide observational evidence that polar spicules host multiscale Alfvénic fluctuations consistent with a developing turbulent cascade and intermittency, suggesting a role in energy transport into the
solar corona.
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All authors Edris Tajfirouze, Christopher H. K. Chen, Richard J. Morton, Peter R. Young
Instrumentation and Methods for Astrophysics
Streak detection in the VST/OmegaCAM archive using deep learning
Elisabeth Rachith, Stephan Hellmich, Vincent Fiszbin et al. (+3 more)
Ground-based astronomical surveys inadvertently capture streaks from satellites and space debris crossing their fields of view. These incidental observations from wide-field instruments such as OmegaCAM on the VST offer valuable opportunities to characterise resident space objects without the need for dedicated observing time. We developed an automated deep-learning pipeline to detect and classify streaks in the OmegaCAM archive, enabling large-scale analyses of space object populations and their impact on astronomical data. The pipeline combines an adapted Hough transform lookup-based convolutional neural network (HT-LCNN) for initial streak detection on raw images with a VGG6-based CNN classifier to reject false positives. We augmented a manually annotated
dataset of 384 000 patches from archive images with physically simulated streaks. Following a detection, we applied astrometric calibration and cross-matched the results with the space-track catalogue. We find the detector achieves F1-scores of 0.966 (validation) and 0.958 (test) on the augmented
dataset, detecting > 95% of artificial streaks with a signal-to-noise ratio of S/N > 4. On real 2023 data, the precision drops to 0.783 due to image variability, but the classifier boosts it to 0.990, while retaining 97% of true positives and rejecting > 96% of false positives. Applied to one year of VST observations (1 246 048 OmegaCAM CCD frames), the pipeline identified 25 335 streaks, including more than 20% uncorrelated with catalogue entries; finally, 16.9% of images revealed some level of contamination. The pipeline demonstrates robust performance on real archival data and successfully uncovers faint uncatalogued objects, highlighting the potential of survey archives for debris monitoring.
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All authors Elisabeth Rachith, Stephan Hellmich, Vincent Fiszbin, Belén Yu Irureta-Goyena, Andrew Price, Jean-Paul Kneib
Earth and Planetary Astrophysics
Multi-year Ground-Based Survey Photometry of Active Comet 103P/Hartley 2 and Centaur (2060) Chiron: A Tale of Two Comets in the Pre-LSST Era
Joseph Murtagh, Megan E. Schwamb, Michael S. P. Kelley et al. (+22 more)
Comets and Centaurs trace the
evolution of trans-Neptunian objects (TNOs) into the inner
solar system. Their activity reflects the interplay between volatile sublimation,
dust dynamics, and ring scattering. Yet the long-term behavior of individual objects is less constrained. To probe this evolutionary transition, we use wide-field survey photometry from the Asteroid Terrestrial-impact Last Alert System, Zwicky Transient Facility, and Las Cumbres Observatory observations of the Jupiter-family comet (JFC) 103P/Hartley 2 during its 2023/24 apparition, and the Centaur (2060) Chiron across 2020-2025, including its 2021 outburst. For 103P, heliocentric activity slopes are asymmetric about perihelion, with a steep inbound index ($n_{r,\rm pre}=-3.48\pm0.08$) and flatter outbound value ($n_{r,\rm post}=-1.16\pm0.04$), consistent with enhanced relative
dust contribution post-perihelion. Reduced brightness versus prior apparitions matches reported secular fading trends.
Dust mass-loss rates are $\sim4$-16 kg s$^{-1}$ for assumed grain properties. Colors exhibit a blueward trend near perihelion, consistent with enhanced gas contamination of the $g$-band, with possible phase-dependent scattering. A periodogram recovers a $\sim18.7$ hr activity-linked period near perihelion. For Chiron, subtracting a quiescent baseline reveals exponential decay from the 2021 outburst on a $\sim1.4$ yr timescale. Seasonal phase curves flatten from $\beta_o=0.150\pm0.034$ mag deg$^{-1}$ in 2021 to $\lesssim0.09$ mag deg$^{-1}$ by 2023-2025, converging with quiescent behavior. Broad-band colors remain unchanged at ATLAS ($c-o$)=0.22$\pm$0.09 mag. This extended activity suggests a new epoch of persistent, low-level activity and/or evolving ring-scattering. These objects bracket the TNO-to-JFC evolutionary sequence, with 103P near the volatile-depleted end, and Chiron still volatile-rich and capable of episodic activity.
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All authors Joseph Murtagh, Megan E. Schwamb, Michael S. P. Kelley, Matthew M. Knight, Thomas Lehmann, Giannantonio Milani, A. Fraser Gillan, Alan Fitzsimmons, Ryan R. Lyttle, Matthew M. Dobson, Carrie E. Holt, Tim Lister, Joseph P. Chatelain, Sarah Greenstreet, Quanzhi Ye, Henry H. Hsieh, Denis Bodewits, Tracy X. Chen, Richard G. Dekany, Matthew J. Graham, Steven L. Groom, George Helou, Mansi M. Kasliwal, Ashish A. Mahabal, Reed Riddle
High Energy Astrophysical Phenomena
Systematic study of the morphology and length of slow stable hybrid star branches
Mauro Mariani, Milva G. Orsaria, Germán Lugones et al. (+1 more)
We introduce and systematically study the length of the slow stable hybrid
star branch as a quantitative measure of the extended stability region that arises in hybrid
neutron stars when the
hadron-
quark phase conversion is slow compared to the radial oscillation timescale. Combining generalized piecewise-polytropic hadronic equations of state of varying stiffness with a constant-speed-of-sound
quark-matter model, we construct a large set of hybrid equations of state spanning a broad range of transition pressures, energy-density jumps, and
quark-matter speeds of sound. We identify four morphological types for the slow stable branch in the mass-radius plane: waterfall branches that descend monotonically from the hadronic maximum mass, bridges that connect the hadronic branch to a second unconditionally stable hybrid branch, tails that extend briefly beyond the maximum mass of an unconditionally stable hybrid branch, and tail-bridges that combine features of the latter two. Their prevalence is governed primarily by the transition pressure and the energy-density jump, while the branch length is also significantly influenced by the stiffness of the hadronic sector and the
quark-matter speed of sound. Imposing current astrophysical and microphysical constraints shows that viable long branches are predominantly of waterfall type, and that stiff hadronic equations of state – strongly disfavored under the rapid-conversion assumption – remain compatible with all current constraints within the slow-conversion framework. In the plane of transition
baryon density versus density jump, slow stable configurations open a new region of viable parameter space inaccessible under rapid conversions.
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All authors Mauro Mariani, Milva G. Orsaria, Germán Lugones, Ignacio F. Ranea-Sandoval