Astrophysics of Galaxies
The DESIRED electron temperature relations in star-forming regions of the local Universe
M. Orte-García, C. Esteban, J. García-Rojas et al. (+7 more)
(Abridged) Aims. We present a homogeneous observational study of electron temperature ($T_{\rm e}$) relations between ionic species: $T_{\rm e}$([N II]), $T_{\rm e}$([O II]), $T_{\rm e}$([O III]), $T_{\rm e}$([S II]), $T_{\rm e}$([S III]) and $T_{\rm e}$([Ar III]), using 699 spectra of
Galactic and extragalactic H II regions and local
star-forming
galaxies (SFGs). Methods. We use the DEep Spectra of Ionised REgions Database Extended (DESIRED-E), comprising more than 3000 spectra with direct $T_{\rm e}$ determinations, selecting those with at least two $T_{\rm e}$ diagnostics. We recompute electron density ($n_{\rm e}$) and $T_{\rm e}$ using updated atomic data and a consistent methodology. The resulting $T_{\rm e}$–$T_{\rm e}$ relations are analysed using orthogonal distance regression, quantifying total and intrinsic dispersions and comparing slopes with previous works and photoionisation models. Results. Relations involving low-ionisation $T_{\rm e}$ diagnostics show large intrinsic dispersions, especially for $T_{\rm e}$([O II]) and $T_{\rm e}$([S II]), likely due to sensitivity to $n_{\rm e}$ inhomogeneities, recombination contributions, and uncertainties. In contrast, relations using $T_{\rm e}$([N II]) show lower dispersions, indicating that this diagnostic provides a more reliable estimate of the low-ionisation zone temperature when only higher-ionisation $T_{\rm e}$ diagnostics are available, despite observational difficulties at low
metallicity. Overall, slopes agree with model predictions, particularly for relations with low intrinsic dispersion, such as those involving $T_{\rm e}$([N II]) and $T_{\rm e}$([S III]). These results provide a robust empirical basis for estimating $T_{\rm e}$ when limited diagnostics are available.
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All authors M. Orte-García, C. Esteban, J. García-Rojas, J. E. Méndez-Delgado, K. Z. Arellano-Córdova, A. Z. Lugo-Aranda, L. Toribio San Cipriano, F. F. Rosales-Ortega, I. R. Martínez-Hernández, E. Reyes-Rodríguez
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Can a late-time cosmological model based on baby universe absorption explain the z-variation of w?
Jan Ambjorn and Yoshiyuki Watabiki
We point out that a simple late-time cosmological model where our Universe can absorb "baby universes" explains the exponential expansion of our universe without the need of a cosmological constant and leads to a z-dependence of the parameter w(z) in the equation of state. In this model w(z) is less than -1 for z sufficiently large.
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Earth and Planetary Astrophysics
Millimeter dust continuum and polarization in protoplanetary disks with scattering: A slab model
Naoya Kitade and Akimasa Kataoka
Millimeter continuum emission and self-scattering polarization from protoplanetary disks are widely used to constrain
dust properties. Interpreting these observations requires practical prescriptions for the disk emission. However, only approximate formulae are available for the continuum emission, and no widely applicable formula has yet been established for the polarized emission. We aim (i) to assess the validity of commonly used analytic approximations for the (sub)millimeter continuum emission from protoplanetary disks, and (ii) to derive realistic prescriptions for the disk emission for both the continuum and the polarization. We numerically solve the radiative transfer equation in an isothermal, constant-density plane-parallel slab, including
dust absorption, emission, and self-scattering with full Stokes parameters. We find that commonly used analytic approximations for the continuum emission are systematically about 10 to 15% lower than our numerical solutions. Consequently, SED analyses of (sub)millimeter observations that adopt these formulae are likely to overestimate the optical depth (and thus the disk mass) and the
dust temperature, and underestimate the albedo (and thus altering the inferred constraints on grain size). We also provide empirical fitting formulae that reproduce our numerical results for the continuum emission and polarization fraction. These formulae will enable observational data analyses to be carried out more accurately and efficiently than with the conventional approaches. For the analysis of (sub)millimeter observations, we recommend using our new empirical formulae or interpolation of our numerical results, rather than commonly used approximations.
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High Energy Astrophysical Phenomena
Imaging without visibilities: FAST-Effelsberg scintillometry of PSR B1508+55
Tim Sprenger, Xun Shi, Olaf Wucknitz et al. (+1 more)
Context. The spatially coherent multipath propagation of
pulsar radiation leads to a temporal and spectral interference patterns called scintillation. It is caused by density variations in the ionized interstellar medium, which often take the form of thin scattering screens filled with multiple subimages of the
pulsar. PSR B1508+55 is known to be scattered by one or two such screens. Aims. We investigate appropriate methods to achieve precise astrometry for a scattering screen from simultaneous observations of only two
telescopes on a very long baseline without forming visibilities. Methods. Two simultaneous observations of PSR B1508+55 were performed with the 100-m
telescope at Effelsberg and the Five-hundred-meter Aperture Spherical
Telescope (FAST). Using and improving existing scintillometry techniques, we leveraged the evolving, very long baseline to precisely measure the screen orientation, effective velocity, and scintillation arc
curvature. We inferred the one-screen and two-screen model parameters and we imaged the closer screen. Results. Each single epoch leads to much tighter angular constraints than long-term monitoring of scintillation arcs, revealing an ongoing
evolution of the orientation of the closer screen. Images of the scattered
pulsar were obtained with a resolution on the order of 0.1 mas. These results confirm the highly anisotropic
alignment of the scattered images, while also revealing small-scale deviations from a large-scale straight line. Conclusions. We demonstrate that simultaneous observations of scintillation can be used as a powerful substitute for very long baseline inferometry.
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All authors Tim Sprenger, Xun Shi, Olaf Wucknitz, Robert A. Main
Earth and Planetary Astrophysics
JWST COMPASS Program: The 3–5$\mu$m transmission spectrum of LTT 1445 A b
Natasha E. Batalha, Nicole Wallack, Tyler Gordon et al. (+16 more)
The search for an atmosphere on the closest rocky M
dwarf planet, LTT 1445 A b, has been the subject of intense investigation from both the ground and space. Here, we present the first JWST transmission spectrum of LTT 1445 A b using a single visit spanning 3-5~$\mu$m using NIRSpec/G395H. We conduct two independent reductions of the data using both the Eureka! and ExoTiC-JEDI pipelines. Overall, we measure the NRS1 transit depths to a median precision of $\sim23$~ppm in 41 spectroscopic channels with uniform widths of 30 pixels ($\sim$ 0.02 $\mu$m), and the NRS2 transit depths to $\sim36$~ppm precision in 65 spectroscopic channels, also with uniform widths of 30 pixels. We rule out any statistically significant spectral features at this precision and place limits on atmospheric
metallicity using a grid of chemical
equilibrium models with grey opaque clouds. Using NIRSpec/G395H alone, we can place limits on the atmospheric
metallicity of $\gtrsim350~\times$
Solar when the opaque pressure level is greater than 0.01~bars. We also conduct a combined analysis of JWST/NIRSpec and HST/WFC3 transmission data and find our atmospheric limits can be extended $\gtrsim500~\times$
Solar when considering both
datasets. Future analyses both in transit and emission will uncover whether there are detectable atmospheric features.
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All authors Natasha E. Batalha, Nicole Wallack, Tyler Gordon, Nicholas F. Wogan, Katherine A. Bennett, Jea Adams Redai, Mercedes López-Morales, Johanna Teske, Jeff Valenti, Munazza K. Alam, Lili Alderson, Artyom Aguichine, Natalie M. Batalha, Anna Gagnebin, Peter Gao, Annabella Meech, Sarah E. Moran, Hannah R. Wakeford, Angie Wolfgang
Earth and Planetary Astrophysics
A Climate-Constrained Bayesian Inverse Method for JWST Rocky Exoplanet Eclipse Spectra: A Case Study of LTT 1445A b
Nicholas Wogan, Natasha Batalha, Jegug Ih et al. (+2 more)
Determining whether temperate rocky
exoplanets orbiting M
stars retain atmospheres is currently a central goal of
exoplanet astronomy. To this end, the James Webb Space
Telescope has begun searching for atmospheres on these worlds with MIRI secondary eclipse spectroscopy and photometry. Here, we develop a novel
climate-constrained
Bayesian inference framework that yields atmospheric pressure and composition constraints from these
datasets, while accounting for planetary,
stellar, and model uncertainties. Our approach fits observations with model spectra derived from self-consistent pressure-temperature profiles at radiative-convective
equilibrium, thus maximizing the information extracted from the data and providing more robust inferences than
retrievals that use parameterized pressure-temperature profiles. We demonstrate the framework on the existing MIRI LRS eclipse spectrum of LTT 1445A b (1.34 $R_\oplus$ and $T_{\mathrm{eq}} \approx 431$ K). An atmosphere does not need to be invoked to explain the data, meaning a bare rock model produces an adequate fit. If the
planet has an atmosphere, the $2\sigma$ upper limits on surface partial pressures are $\lesssim 1$ bar for an optically thin gas like O$_2$, N$_2$ or CO, $\lesssim0.1$ bar for CO$_2$, $\lesssim 10^{-3}$ bar for H$_2$O, and $\lesssim 10^{-4}$ bar for SO$_2$. Scheduled MIRI F1500W observations could detect one of the thicker atmospheres permitted by the existing data (1 bar O$_2$ and 0.01 bar CO$_2$), if a precision of 20 ppm or better is achieved. This case study demonstrates that
climate-constrained
Bayesian inversion can turn rocky-
planet eclipse spectra into the quantitative constraints necessary to test population-level atmospheric retention hypothesis, like the
cosmic shoreline.
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All authors Nicholas Wogan, Natasha Batalha, Jegug Ih, Jacob Lustig-Yaeger, Kevin Stevenson
High Energy Astrophysical Phenomena
Pulsar scintillation arcs formed from correlated volume scattering
Tobias Kramer
Radio waves propagating through the interstellar medium are influenced by variations in
plasma density. For spatially localised
plasma structures along the line of sight, time-delay Doppler analyses of
pulsars often reveal scintillation arcs in the secondary spectrum, frequently exhibiting a
parabolic morphology. In the thin-screen approximation, the arc
curvature is commonly used to infer the distance to the
plasma concentration, which is modelled - via Kirchhoff-Fresnel diffraction theory - as an effective phase screen imposed by the column density of a localised disturbance. Here, we identify several limitations of this model that necessitate a fully three-dimensional treatment, without reducing the problem to a projected screen density. When volume propagation is considered, asymmetries and a richer variety of features emerge in the secondary spectrum compared to those predicted by the thin-screen approximation. For some cases the arc
curvature varies depending on the three-dimensional structure of the
plasma, rendering it a less reliable indicator of distance. We
conjecture that these phenomena are linked to the onset of branched flow produced by a sequence of weak but correlated scattering events.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Unified dark sector and Hubble-tension alleviation in scalar-vector-tensor gravity
Kimet Jusufi, Amir A. Khodahami, Ahmad Sheykhi et al. (+2 more)
We investigate a scalar-vector-tensor theory in which matter is minimally coupled to a Jordan-frame metric $\tilde g_{\mu\nu}=(1+\Xi)g_{\mu\nu}$, while a massive vector sector interacts with the baryonic current. We show that the conformal scalar coupling modifies the physical expansion rate measured by matter observers, leading to an enhancement of the Hubble constant inferred at low
redshift. We stress, however, that the Hubble rate is not a conformal invariant, whereas the acoustic angular scale $\theta_s$ is, and we derive the exact integral condition that the scalar field
evolution must satisfy. We show that a single-signed scalar velocity cannot satisfy it, and we construct instead a two-epoch phenomenological
evolution which matches $\theta_s$ exactly while retaining the late-time enhancement, at the cost of a small pre-recombination shift of the effective gravitational coupling. Importantly, the recombination temperature is unmodified, since particle masses are constant in the Jordan frame, only the expansion rate at that epoch being altered. The scalar potential naturally acts as a dynamical dark-energy sector, while the vector sector provides two distinct contributions. The temporal component, determined algebraically by the
baryon current, yields an apparent matter-like term in the background expansion that is not a true fluid but rather a manifestation of the interaction energy. The propagating spatial modes, on the other hand, form a vector condensate that behaves as a collisionless pressureless component and can play the cosmological role of cold dark matter. Hence, the framework connects scalar dynamics, effective dark-energy
evolution, and the $H_0$ tension within a single setup.
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All authors Kimet Jusufi, Amir A. Khodahami, Ahmad Sheykhi, Jackson Levi Said, Emmanuel N. Saridakis
Instrumentation and Methods for Astrophysics
Denoising Interferometric Observations Using Visibility-Informed Neural Networks
Jason P. Terry, Cassandra Hall and Sergei Gleyzer
The upcoming observations from the Square Kilometer Array Observatory will provide the astronomical community with a wealth of observations of important objects at long wavelengths. Full analysis of these outputs will necessitate specialized methods and software. Using synthetic observations of protoplanetary discs as an example, we present VIREO, a machine-learning-based visibility-informed method for denoising interferometric images. VIREO operates on image-plane observations, but it is informed by the interferometric measurement process through the UV-derived point spread function supplied as an additional input and used in the loss function. VIREO outperforms traditional cleaning methods and PSF-ignorant denoising models by producing data that is quantitatively cleaner and more conducive to analysis of the
planets within the disc. Applying VIREO to archival ALMA data creates images with significantly less background noise, while maintaining, and in some cases enhancing, the substructure. By demonstrating the general utility of visibility-informed models, our results suggest that VIREO can be applied across interferometric observatories when trained on appropriate
datasets.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Exploring the CMB in Anisotropic Universes
Robbert W. Scholtens, Marcello Seri, Holger Waalkens et al. (+1 more)
In recent years, there have been increasing challenges to the cosmological principle, based on new observations of e.g.
supernovae and the
cosmic bulk flow. As a result, the cosmological community is speaking their concern for the cosmological principle, and from which scales onwards it should apply. In this context, there is a desire to understand more fully the properties and signatures of cosmologies not obeying the cosmological principle. In this article, we let go of the demand of
cosmic isotropy, and instead assume only spatial homogeneity in our cosmological models. We follow the results of our previous works [see citations in the list of references], and here bring these together into one unified picture, with the goal of describing the signature(s) of anisotropy in anisotropic cosmological models. We first introduce the Bianchi models – a particular instance of spatially homogeneous cosmologies – and show that a metric can be constructed for them when an appropriate collection of desired Killing vector fields is supplied. Then, we give the perturbations of the Friedmann equations in such Bianchi models, in the Newtonian gauge, derived using much the same methodology as applicable to the FLRW models. We show these can be combined into one characteristic partial differential equation. Finally, we use this equation in order to simulate the CMB of a toy Bianchi V example and produce its power spectrum. We close with a discussion, and suggestions for further research.
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All authors Robbert W. Scholtens, Marcello Seri, Holger Waalkens, Rien van de Weygaert
Solar and Stellar Astrophysics · Cross-listed from gr-qc
Conservative and dissipative sectors in a nonlinear scalar model for the gravitational self-force problem
Francisco M. Blanco, Eanna E. Flanagan and Abraham I. Harte
When considering how self-interaction affects an object's motion, it can be convenient to decompose the self-force into conservative and dissipative pieces. As a toy model for understanding such decompositions of the gravitational self-force, we consider objects that do not affect the spacetime, but are instead coupled to a nonlinear scalar field. There is then a standard splitting of the first-order scalar self-force into conservative and dissipative components. Multiple criteria can be used to obtain this splitting, all of which imply the same result. However, the implications of these criteria generically differ at higher orders. Demanding that any reasonable conservative sector be
Hamiltonian, we identify multiple possible definitions of the conservative second-order self-force. Motivations for these possibilities and their properties are discussed and relevant
Hamiltonians are obtained. We assume the existence of a three-point function with certain properties that is a generalization of the Detweiler-Whiting two-point function. These results apply to the two-body problem but are restricted to unbound scattering trajectories, due to infrared divergences that arise for bound orbits.
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Astrophysics of Galaxies
Identifying group galaxies merging with massive clusters using machine learning
Rhys Jordan, Meghan E. Gray, Alfonso Aragón-Salamanca et al. (+3 more)
The environment plays a critical role in
galaxy evolution, with
galaxy clusters and their infall regions offering diverse conditions that shape
galaxies before they enter the dense cluster core, a process known as “pre-processing”. However, identifying environmental substructures, particularly
galaxy groups in these transitional zones, remains challenging due to projection effects and “fingers-of-god” distortions. In this work, we present a supervised machine learning framework for classifying
galaxies into three environmental categories: main cluster, group, and neither, using observable
galaxy properties such as positions, line-of-sight velocities, and
stellar mass. The model is trained on mock observations derived from cosmological simulations designed to replicate survey conditions and achieves an overall accuracy and class-size-weighted precision of 81%. The neither and main cluster populations are reliably recovered, whereas group
galaxies remain the most challenging to identify, achieving 30% completeness and 76% purity. Within $1\times R_{200}$, classification performance is suppressed, but it improves beyond this radius, reaching 40% completeness and 80% purity. Resampling and thresholding strategies allow the model to be tuned toward either higher purity or higher completeness; in this study, we adopt first-past-the-post thresholding to emphasise purity. Model performance is consistent across cluster masses and dynamical states, and it outperforms both Friends-of-Friends and Gaussian Mixture Modelling. This flexibility makes it well suited to upcoming spectroscopic surveys of cluster infall regions, providing a robust statistical tool for disentangling environmental influences on
galaxy evolution.
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All authors Rhys Jordan, Meghan E. Gray, Alfonso Aragón-Salamanca, Steven P. Bamford, Frazer R. Pearce, Roan Haggar
Astrophysics of Galaxies
DREAMS. JWST Spectroscopy of a $z=8.3$ Galaxy with an ALMA Dust Continuum Detection: Early Dust, Very High $T_{\rm dust}$, and a Multi-wavelength [OIII] Ratio Discrepancy
Kana Takechi, Masami Ouchi, Kimihiko Nakajima et al. (+10 more)
We present a deep DREAMS JWST/NIRSpec MSA medium-grating spectrum of MACS0416-Y1, a
galaxy at $z=8.312$ with the highest-
redshift ALMA
dust continuum detection to date, in order to characterize its properties together with archival IFU and ALMA data. The deep NIRSpec spectrum reveals a broad H$\beta$ line with a width of $\sim1100$ km s$^{-1}$. We interpret it as a broad-line AGN whose line diagnostics are consistent with AGN activity across its clumpy structure, given the absence of little red dot signatures. MACS0416-Y1 clearly shows [OIII]4363 emission, suggesting a moderately low
metallicity of $12+\log(\mathrm{O/H})=7.86^{+0.09}_{-0.08}$ ($0.15~Z_\odot$). The combination of [CII]158$\mu$m and
dust continuum emission indicates low
dust mass ratios of $\log (M_{\rm dust}/M_{\rm gas})=-3.60^{+0.29}_{-0.22}$ and $\log (M_{\rm dust}/M_{\rm metal})=-0.95^{+0.29}_{-0.20}$. Because the
metallicity of MACS0416-Y1 is around the critical
metallicity of $0.1\textrm{-}0.2~Z_\odot$, the system is expected to undergo
dust growth, explaining these low
dust mass ratios as well as its small
dust mass, $M_{\rm dust}\sim10^6~M_\odot$. The intense UV radiation from the AGN may contribute to a high
dust temperature of $T_{\rm dust}\simeq 91^{+62}_{-35}$ K, boosting the
dust-continuum emission above the ALMA detection limit despite the small $M_{\rm dust}$ at $z>8$. We find a very high total flux ratio of [OIII]88$\mu$m/[OIII]5007 = $0.26 \pm 0.06$ in MACS0416-Y1, above predictions from single ionized nebular models at any electron density. This discrepancy suggests that the [OIII]88$\mu$m and [OIII]5007 trace largely distinct regions, with the optical line suppressed in dusty nebulae, and thus requires careful interpretation when combining optical and infrared emission lines in JWST+ALMA studies.
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All authors Kana Takechi, Masami Ouchi, Kimihiko Nakajima, Tomokazu Kiyota, Yoichi Tamura, Yuichi Harikane, Yurina Nakazato, Tom J. L. C. Bakx, Akio K. Inoue, Hidenobu Yajima, Masato Hagimoto, Yoshiaki Ono, Yi Xu
Solar and Stellar Astrophysics
Self-Interacting Dark Matter in Brown Dwarfs
A. Pérez-Garrido
Brown
dwarfs, being transitional objects between
giant planets and low-mass
stars, possess dense, cool interiors that provide optimal conditions to explore non-standard physics. Capture and accumulation of dark-matter particles can alter the thermal, structural and dynamic of these substellar objects. We aim to apply a self-consistent two-fluid framework to model the internal structure of self-gravitating brown
dwarfs and to quantify how the presence of a dark-matter component modifies their mass–radius relations and dynamical properties. The brown
dwarf is modeled as a composite system of a baryonic fluid, described by a polytropic equation of state, and an independent dark-matter fluid. Both components are coupled through their shared gravitational potential in hydrostatic
equilibrium. We solve numerically the coupled Lane-Emden equations for a range of dark-matter mass fractions. We find that dark matter accumulating in the core reshapes the baryonic density profile, modifying both the radius and the second-order Love number. Radius and dynamical anomalies in brown
dwarfs can serve as diagnostic tools to constrain dark-matter properties. Future high-precision astrometric missions could identify these structural signatures, establishing brown
dwarfs as possible detectors of dark matter in the
Galaxy.
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High Energy Astrophysical Phenomena
Self-confinement of ultra-high-energy nuclei in cosmic filaments: implications for the UHECR spectrum and composition
Alessandro Cermenati, Roberto Aloisio and Carmelo Evoli
The spectrum and composition of ultra-high-energy
cosmic rays (UHECRs) suggest that the population dominating above the ankle releases particles with an unusual hard spectrum at low
rigidity, below the EV scale. In self-confinement scenarios, such an apparent hardening arises from transport: escaping UHECRs generate
magnetic turbulence that delays their own release from the magnetized environments surrounding their sources. We extend the self-confinement scenario based on the non-resonant streaming instability to a mixed
nuclear composition. We describe the confinement region with an effective leaky-box model including escape, photodisintegration, and secondary production. We then compare the resulting spectrum and composition with Auger measurements and compute the associated cosmogenic
neutrino and gamma-ray emission. We find that self-generated
turbulence can suppress the escaping flux below the EV scale for source luminosities and
magnetic-field coherence lengths compatible with UHECR sources hosted in
galaxy clusters and propagating through
cosmic filaments. During confinement, heavy
nuclei efficiently photodisintegrate, producing secondary
protons that contribute below the ankle and help account for the observed composition. The predicted
neutrino flux remains compatible with current limits, while the diffuse gamma-ray background provides a potentially strong constraint on the most extreme configurations.
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Earth and Planetary Astrophysics
Resonant Networks of Spin-Orbit Coupling in Ellipsoid-Ellipsoid Binary Asteroid Systems
Yuanzhe Zhang and Hanlun Lei
The dynamical
evolution of binary asteroid systems is deeply influenced by
spin-orbit resonances. However, their domains of influence and mutual interactions remain elusive, in particular in the space where multiple resonant modes coexist. In such regimes, the standard single-resonance approach is intrinsically limited and fails to capture the true coupled dynamics. To overcome this, we develop a global
Hamiltonian framework based on
elliptic expansions of the
spin-orbit coupling model, enabling the numerical construction of comprehensive resonant networks. Concentrating on a representative synchronous region that encompasses synchronous
spin-orbit,
spin-
spin,
spin-orbit-
spin, and doubly synchronous resonances, we study the dynamical boundaries of different resonant modes in a systematical manner. Crucially, we identify a secondary resonance structure arising from the strong nonlinear coupling between the synchronous resonances of the primary and secondary asteroids. Ultimately, this study provides a reliable parameter-space atlas, which is helpful for predicting the long-term evolutionary pathways of binary asteroid systems.
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Earth and Planetary Astrophysics
Tidal coplanarization of circumbinary planetary systems through stellar Cassini states
Hanlun Lei
Circumbinary
planets (CBPs) currently identified are in nearly coplanar configurations relative to their host binaries, yet the dynamical origin of this preference remains unclear. We investigate this question by simulating the secular
spin-orbit
evolution of CBP systems with
tidal decay. A representative case shows that the system evolves through three stages (coplanarization,
spin-orbit synchronization, and
spin-orbit
alignment) through the angular momentum exchange between
stellar spin and orbital motion. The
evolution of mutual inclination is strongly coupled to
stellar obliquity. Phase-space analysis and examination of
stellar Cassini states reveal that arbitrary initial inclinations are gradually damped to coplanarity by tides, while
stellar obliquity is adiabatically captured into Cassini states with diminishing oscillation amplitudes. This study provides a self-consistent analytical and numerical framework for determining
stellar Cassini states and understanding coupled
spin-orbit
evolution in CBP systems. It shows that
tidal dissipation, combined with adiabatic capture into Cassini states, drives the observed dynamical behavior.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
How Much Can Gravitons Be Squeezed?
Panagiotis Dorlis, Nick E. Mavromatos, Sarben Sarkar et al. (+1 more)
Quantum Gravity remains elusive, largely because its observable effects are suppressed by powers of the Planck scale. Direct detection of single gravitons is widely believed to be impossible. Here we propose a concrete astrophysical mechanism that may overcome this suppression. We show that superradiant
axion-like-particle clouds surrounding rotating black holes can generate multimode squeezed states of gravitons containing up to $10^6$ - $10^7$ correlated quanta. Such states exhibit distinctive polarization correlations and
quantum-noise signatures that could be detectable in future gravitational-wave interferometers. Observation of these signatures would constitute direct evidence for the
quantum nature of gravitational radiation. Conversely, their absence can place constraints on
axion-cloud lifetimes. Our approach also provides a test of General Relativity as an effective field theory.
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All authors Panagiotis Dorlis, Nick E. Mavromatos, Sarben Sarkar, Sotirios-Neilos Vlachos
Instrumentation and Methods for Astrophysics
Beyond AI as Assistants: Toward Autonomous Discovery in Cosmology
Licong Xu and Thomas Borrett
Recent advances in artificial intelligence (AI)
agents are pushing AI beyond tools toward autonomous scientific discovery. We discuss two complementary agentic systems for cosmology: CMBEvolve, which targets tasks with explicit quantitative objectives through LLM-guided code
evolution and tree search, and CosmoEvolve, which targets open-ended scientific workflows through a virtual multi-
agent research laboratory. As preliminary demonstrations, we apply CMBEvolve to out-of-distribution detection in weak-
lensing maps, where it iteratively improves the
benchmark score through code
evolution, and CosmoEvolve to autonomous ACT DR6 data analysis, where it identifies non-trivial pair- and scale-dependent behaviour and produces analysis-grade diagnostics. These examples show how cosmology can provide both controlled
benchmark tasks and realistic open-ended research problems for the development of AI scientist systems.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Wide parameter-space O3 search for continuous gravitational waves from unknown neutron stars in binary systems
P. B. Covas, M. A. Papa and R. Prix
Continuous gravitational waves, i.e., persistent and nearly-monochromatic signals emitted by asymmetric spinning
neutron stars, remain elusive. Searches for these signals from unknown binary systems are the most computationally challenging, but they are essential, given that binary
accretion provides a natural mechanism for creating the required asymmetry, and around half of the known
pulsars rotating above 25 Hz are part of a binary system. Here we report on a search of a large uncharted parameter-space region: for the first time we cover gravitational-wave frequencies above 520 Hz (from 50 to 1000 Hz), and, for the first time with advanced detectors, orbital periods lower than 3 days are explored. No signal is detected, and we set the most stringent constraints to date on the amplitude of signals of this kind. Our results exclude with $95\%$ confidence
neutron stars within 100 pc and rotating faster than $\sim$ 495 Hz from having ellipticities above $5.2 \times 10^{-8}$. Within the same distance our results also exclude r-mode amplitudes above $1.5 \times 10^{-6}$ for
stars rotating faster than $\sim$ 740 Hz.
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Astrophysics of Galaxies
Boundary-supported radial layering in Hoag-like ring galaxies
Yue Xu, Chenxi Sun and Jianwei Zhang
Clean Hoag-like ring
galaxies are often characterized by an old compact central component, a depleted gap, and a detached outer ring. We identify a boundary-supported radial-layering mechanism in a shell-deformed Kepler control model. A compact inner boundary supplies the core state, while a localized effective shell deformation, interpreted as the reduced imprint of externally supplied material settled near a finite circularization radius, needs to create only an internal maximum and a subsequent outer minimum. These act as the gap barrier and ring-supporting well. The onset of this structure is organized by a saddle-node threshold of the critical-point equation. In a 10^4-point Monte Carlo scan, shell-localized boundary-supported candidates occupy finite parameter volume under the adopted priors, and none of the localized candidates contains an ordered interior minimum–maximum–minimum subsequence. The same branch gives a scale-free gap-to-ring interval overlapping representative ratios for Hoag's Object, UGC 4599, and PGC 1000714, but not for the environmentally processed comparison object JO171.
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Solar and Stellar Astrophysics
Luminaries in the Sky: The TESS LEGACY sample of bright stars. II. In-depth seismic characterisation of 32 naked-eye stars in the PLATO LOP fields
E. Panetier, G. T. Hookway, E. Corsaro et al. (+13 more)
The NASA TESS mission is conducting a nearly full-sky survey, enabling the photometric characterisation of millions of
stars. The forthcoming ESA PLATO mission will provide long-duration, high-precision photometry of tens of thousands of bright
stars to be characterised through asteroseismology. The TESS Luminaries sample is a catalogue of 196 bright naked-eye (V < 6) main-sequence (MS) and sub-
giant (SG)
stars exhibiting
solar-like oscillations. Among them, the subset located within the PLATO long-duration observation phase (LOP) fields constitutes an exceptional set of targets that will be observable by PLATO from the earliest phases of the mission, making them ideal calibrators during commissioning and the first months of science operations. This paper aims to provide an in-depth asteroseismic characterisation of 32 Luminaries
stars that fall within the PLATO LOP fields of view. Individual mode parameters were extracted for the first time for 26 of them. We used three independent seismic pipelines, one of which is similar to the
algorithms used in the official PLATO pipeline. Statistical criterion were applied to identify the optimal combination of data calibration, observing cadence, and fitting pipeline for each
star. For all
stars, we derived large and small separations, the asymptotic phase term, radial mode amplitudes, and mean linewidths per order. Comparisons reveal consistent trends in the seismic parameters, confirming the robustness of our analysis. In SGs, mixed-mode identification differs in the three pipelines, revealing extraction inconsistencies requiring longer
datasets to improve our mode identifications. The Luminaries
stars located in the PLATO LOP fields constitute a unique sample that will play a crucial role in validating, calibrating, and optimising PLATO's seismic performance.
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All authors E. Panetier, G. T. Hookway, E. Corsaro, S. N. Breton, R. A. García, B. Liagre, M. N. Lund, M. B. Nielsen, D. B. Palakkatharappil, L. Debacker, J. Gosmain, M. Chaumard, A. Chontos, F. Grundahl, S. Mathur, A. R. G. Santos
Astrophysics of Galaxies
Discovery of a Compact Hub-Filament System in G286.21+0.17 with JWST and ALMA: Insights into Protocluster Formation and Competitive Accretion
L. K. Dewangan, N. K. Bhadari, Ram K. Yadav et al. (+17 more)
We present a multi-wavelength study of the massive protocluster G286.21+0.17 (G286) using JWST near-infrared (NIR) imaging and ALMA H$^{13}$CO$^{+}$(1–0) observations. The JWST images uncover a compact ($\sim$0.5 pc) hub-filament system (HFS), comprising a dense central hub connected by at least four converging filaments seen in absorption, along with multiple H$_2$ protostellar jets/
outflows. The hub hosts the dense core G286c1. H$^{13}$CO$^{+}$ emission confirms this HFS over [$-$19.2, $-$16.4]~km~s$^{-1}$, while the JWST images also trace prominent photodissociation regions surrounding H\,ii~region~A, powered by a B-type
star. The identified H$^{13}$CO$^{+}$ skeletons closely trace the major JWST absorption structures and show steep velocity gradients indicative of inflow. The radial distribution of ALMA 1.3 mm continuum cores (ALMAGAL and Cheng et al. 2020) exhibits power-law trends toward the hub center. The core number density, surface density, and core mass follow $Y \propto r^{\alpha}$ with $\alpha_\rho$ $\sim$$-$2.8 to $-$1.1, $\alpha_\Sigma$ $\sim$$-$0.4 to $-$0.6, and $\alpha_M$ $\sim$$-$0.7, whereas the core diameter remains nearly constant. Together with filament mass
accretion rates of 7.6–11$\times10^{-5}$ M$_\odot$ yr$^{-1}$, these results are consistent with competitive
accretion, highlighting preferential core growth toward the hub. Increasing filament linewidths toward the hub imply
gravity-driven inflow, but misaligned local velocity gradient and gravitational force directions along filaments point to a dynamically evolved system. The HFS likely formed through large-scale gas-layer interactions aided by compression from the adjacent H\,ii region. Overall,
star formation in G286 appears to be regulated by filamentary
accretion, competitive core growth in the hub, and
stellar feedback.
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All authors L. K. Dewangan, N. K. Bhadari, Ram K. Yadav, A. K. Maity, O. R. Jadhav, Kee-Tae Kim, Paul F. Goldsmith, A. Saha, Dana Alina, Chang Won Lee, Saurabh Sharma, Tie Liu, Patricio Sanhueza, Tapas Baug, E. Sharma, Fengwei Xu, Ariful Hoque, James O. Chibueze, Dana Makarova, Wenyu Jiao
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Parametrization of the primordial power spectrum in loop quantum cosmology
Almudena Guillén, Kai Langer, Guillermo A. Mena Marugán et al. (+2 more)
We investigate the imprints on the angular power spectra of cosmological perturbations of a pre-inflationary bounce phase, as described by the hybrid and dressed metric approaches to loop
quantum cosmology. For this purpose, we derive a new parametrization of the
primordial power spectrum at the end of the inflationary regime. Apart from slow-roll coefficients and cosmological parameters that are present in the standard cosmological scenario without
quantum modifications, this parametrization additionally depends only on pre-inflationary physics. More specifically, we find a dependence on the number of e-folds during the bounce epoch and on a characteristic suppression scale which, given the e-folds accumulated during
cosmic evolution, is determined by the energy density at the bounce. Recall that this density depends on the Immirzi parameter and the area gap known from LQG. This leads to a robust and accurate parametrization of the
primordial power spectrum. Since in pre-inflationary scenarios there is no preferred
vacuum state, we adopt the NO-AHD proposal, which selects a
vacuum that is optimally adapted to the background dynamics and yields a non-oscillatory
primordial power spectrum. With this choice, we show that the tensor-to-scalar ratio in both quantization approaches coincides with its expression in the standard $\Lambda$CDM model when the observed scales are not much smaller than the power-suppressed region. Computing also the angular power spectrum, we find that, for a total
cosmic expansion of about 140 e-folds, both the hybrid and the dressed metric approaches exhibit excellent agreement with Planck data at high multipoles, while apparently improving the fit with respect to $\Lambda$CDM for low multipole numbers.
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All authors Almudena Guillén, Kai Langer, Guillermo A. Mena Marugán, Niklas Rodenbücher, Antonio Vicente-Becerril
Astrophysics of Galaxies
A new hot core in the outer Galaxy: Impact of metallicity on the formation of complex organic molecules
Youxin Wang, Arnaud Belloche and Robin T. Garrod
Many complex organic molecules (COMs) in
star-forming regions are believed to form on
dust grains. We thus expect both the reduced
metallicity and
dust-to-gas ratio in the outer
Galaxy to have an impact on the chemical composition of these regions. We investigate if certain COMs are more sensitive than others to
metallicity by measuring the chemical composition of hot cores in the outer
Galaxy. We used NOEMA to perform an imaging spectral line survey of G135.27+2.79, located at a galactocentric distance of 13.1 kpc. We derived the rotational temperatures and column densities of the detected molecules while assuming local thermodynamic
equilibrium and compared the chemical composition of G135.27+2.79 to other sources and to the predictions of the three-phase astrochemical code MAGICKAL. G135.27+2.79 hosts three continuum cores, labeled MM1, MM2, and MM3. Most species in MM1 trace a hot, compact region, confirming MM1 as a hot core. The chemical composition of MM1 correlates rather well with that of the inner and outer
Galaxy hot cores G31.41+0.31 and WB89-789 SMM1, but its molecular abundances relative to methanol lie in between, which may reflect the influence of
metallicity on COM formation. The model results agree reasonably well, though with a few notable exceptions, with the COM abundances of MM1 relative to methanol and with the abundance ratios between MM1 and G31.41+0.31. Sensitivity to the reduced
metallicity and
dust-to-gas ratio varies between molecules, with carbon chains and nitriles most negatively affected. The lower
dust-to-gas ratio leads to slower adsorption under low-
metallicity conditions so that more carbon is locked up into CO in the gas. Slow adsorption means that CO is hydrogenated more efficiently on grains, enhancing CO-related COM abundances above expectations. These results demonstrate that
metallicity has a significant impact on the formation of COMs.
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High Energy Astrophysical Phenomena
GeV emission around SS 433 with 17 years Fermi-LAT observation
Qiwang Sun, Dmitry Khangulyan, Jiren Liu et al. (+1 more)
We present an analysis of 17 years of
Fermi-LAT observations of the microquasar SS~433. We detect four GeV sources in the region: a newly identified source, PS J1910+0550, located outside W50; the previously reported source J1913+0512; and two features, denoted as the East and West excesses, apparently associated with the X-ray lobes. We focus on the three sources located within W50. We do not confirm the previously reported periodic modulation from J1913+0512, as no significant periodicity is found in the full 17-year
dataset. The East and West excesses exhibit distinct morphological and spectral properties, suggesting different physical origins. The East excess shows a hard spectrum with
photon index $\sim1.7$, consistent with inverse Compton emission from relativistic electrons accelerated together with the particles responsible for the X-ray and TeV emission. In contrast, the West excess has a much softer spectrum with
photon index $\sim2.6$ and is spatially offset from the known X-ray and TeV emission regions in the western lobe. The spectral shape and offset position of the West excess make it strikingly similar to J1913+0512. The emission from these two regions can be explained by GeV particles accelerated in SS~433, distributed throughout the source volume, and interacting with localized dense gas targets. Under reasonable assumptions regarding particle transport and energetics, both
proton-
proton and bremsstrahlung scenarios are viable, although the hadronic scenario is more naturally accommodated. These findings may therefore represent the first observational evidence for the acceleration of
cosmic-ray
protons in large-scale
outflows from
Galactic microquasars.
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All authors Qiwang Sun, Dmitry Khangulyan, Jiren Liu, Siming Liu
Instrumentation and Methods for Astrophysics · Cross-listed from hep-ex
The simulation on neutron background reduction for InDEx at JUSL
Susmita Das, Maitreyee Nandy and Mala Das
Dark matter experiments are rare event search experiments that require zero background environment over very long exposures. To achieve this condition, a detailed simulation of detector geometry and experimental setup is required before the experiment is executed. Simulation plays a significant role in detector design and also provides a cost-effective and risk-free approach for predicting outcomes before real world experimentation. The present simulation work is focused on
neutron background reduction for a dark matter direct detection experiment in India, the Indian Dark matter search Experiment (InDEx). The FLUKA and FLAIR simulation tools have been used throughout the simulation process. The experimental and simulation results available in the literature are being reproduced using FLUKA for validation purposes. The calibration and InDEx experiment are simulated, and the results are compared against the experimental results. For
neutron background reduction in future experiments, the use of high density polyethylene (HDPE) is suggested and a shielding design using HDPE is presented. The results show that shielding reduces detector event rates by two orders of magnitude compared to the prior InDEx experiment without shielding.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Modifications of CMB Temperature and Polarization Quadrupole Signals in Thurston Spacetimes
Tanay Gupta, Sukanta Panda and Rajib Saha
Recent cosmological tests have discovered a fresh new set of anomalies in the large-scale isotropy of the universe. Motivated thus by the numerous pieces of evidence for large-scale
cosmic isotropy violation with the advent of the 'precision cosmology' era, we are led to explore the viability of anisotropic Thurston geometries, described in William Thurston's geometrization
conjecture. In this work, we examine the coherent temperature and polarization signals generated in the CMB sky by such geometries. We begin with introducing Thurston spacetimes as our background model and the formalism we use to obtain the patterns. We then construct a set of transfer equations relative to a given background and solve them for each spacetime geometry. We finally discuss the role of spatial
curvature in these FLRW limiting models along with their underlying geometry, and attempt to establish some general results on the
symmetries of the patterns produced by their time
evolution in terms of the Stokes parameters P, Q, U and V. We show the
evolution of temperature and polarization amplitudes in terms of such Stokes parameters at different timestamps and attempt to isolate individual Thurston geometries.
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High Energy Astrophysical Phenomena
Not All Who Wander Are Lost: Early Excess Demographics in the Volume-limited ZTF DR2 SN Ia Sample
César Rojas-Bravo, Ning-Chen Sun, Mathew Smith et al. (+7 more)
Early-time flux excesses in Type Ia
supernovae (SNe~Ia) offer a unique insight into their progenitor systems and explosion mechanisms. Although individual early-excess events and larger searches have been reported, demographic studies remain limited by sample size. We present a systematic search for early-time excess emission in a volume-limited sample ($z<0.06$) of SNe~Ia based on the Zwicky Transient Facility Data Release 2 (ZTF DR2). Using ZTF $g$- and $r$-band light curves, we identify candidates showing early-excesses shortly after the explosion time, and we apply conservative coverage and quality requirements to build reliable “excess” and “no-excess” bump and no-bump catalogs. From an initial sample of 1547 SNe~Ia, our final catalogs contain 42 early-excess and 110 no-excess events. We compare the two populations using SN and host environment parameters from ZTF DR2 and quantify the differences using two-sample statistical tests. We find the strongest differences are in SN light-curve properties: early-excess events have larger SALT2 stretch $x_1$ ($7.91\sigma$) and larger $r$-band secondary-maximum flux $\mathcal{F}_{r_2}$ ($6.25\sigma$), while differences in SALT2 color $c$ are weak ($0.57\sigma$). Early-excess events also favor bluer $(g-z)_{\rm local}$ ($3.41\sigma$) and lower $\log_{10} (M_*/M_\odot)_{\rm local}$ ($2.73\sigma$). Our results connect early excesses with SNe~Ia diversity, and motivate further analyses of upcoming larger samples.
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All authors César Rojas-Bravo, Ning-Chen Sun, Mathew Smith, Chun Chen, Xiaohan Chen, Zexi Niu, Anyu Wang, Zi-Yang Wang, Yi-Han Zhao, Jifeng Liu
Earth and Planetary Astrophysics
Where Do Hot Jupiters Come From? Revisiting Tidal Disruption and Ejection in High-Eccentricity Migration
Qianli Fan and Shang-Fei Liu
The origin of hot Jupiters remains a key open question. In the high-eccentricity migration scenario, traditional coreless models predict a strict
tidal exclusion zone within $\sim 2.7$
tidal radii $r_\textrm{t}$, in which
giant planets are either fully disrupted or ejected. We revisit this limit using three-dimensional hydrodynamic simulations of
giant planets with realistic dense cores (10 - 20 $M_\oplus$). We find that even a few-percent-mass core fundamentally changes the outcome: no total disruptions occur within the previously suggested destruction zone ($\lesssim 2.7 \, r_\textrm{t}$). For deep encounters ($\lesssim 1.7 \, r_\textrm{t}$)
planets suffer severe envelope stripping and are either progressively downsized to dense remnants or ejected after a few close encounters, possibly contributing to the free-floating
planet population. In the intermediate regime ($ \sim 1.7 $–$2.0, r_\mathrm{t}$),
planets experience significant partial mass loss over repeated encounters. For wider encounters ($ \gtrsim 2.0\, r_\mathrm{t} $), mass loss is minimal, allowing the
planets gradually circularize into hot Jupiters. Furthermore, we show that for highly eccentric orbits ($e\gtrsim 0.9$), the change in specific orbital energy $ \Delta E_{\mathrm{orb}} $ depends primarily on periastron distance $ r_\mathrm{p} $ rather than semi-major axis $ a $. This enables us to extrapolate our fixed-$ a $ results across a broad ($a$, $e$) parameter space and identify a well-defined
tidal ejection zone whose sharp boundaries converge asymptotically. Our results highlight the crucial role of planetary internal structure in high-eccentricity migration and suggest that the survival and transformation of core-bearing
giant planets are far more common than previously thought.
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