Papers for Friday, May 22 2026

Gravitational-wave detectors operate in inherently non-stationary environments, requiring robust detector characterization (DetChar) to distinguish instrumental transients from astrophysical signals. Traditional DetChar frameworks typically rely on morphological classifiers or energy-based projections, such as band-limited root-mean-square (BLRMS) metrics, which can conflate global amplitude scaling with physical reconfigurations of the spectrum. In this work, we introduce Fisher information velocity, a novel geometric channel that models the detector's power spectral density (PSD) as a point on a Riemannian manifold. By tracking the kinematic drift of the noise floor and utilizing exterior algebra to calculate tangent divergence ($\sin \theta$), we mathematically decouple simple energy surges from spectral warps, or differential redistributions of power across frequency bands. Applying this framework via the sgn-drift streaming pipeline to ~40 hours of high-cadence Advanced LIGO O4a data, we evaluate N=282,080 independent manifold velocity samples. High-resolution phase space mapping reveals a bimodal taxonomy of severe instrumental non-stationarity, classifying events into structural pivots (87.2%) and isotropic surges (12.8%). Among co-detected events, the geometric channel achieves higher significance than standard BLRMS monitors in 74% of cases with a median sensitivity ratio of $\Gamma = 1.65$. The two channels detect largely non-overlapping populations, increasing the total anomaly catalog by 87% over BLRMS alone. Systematic validation on 10 confirmed GWTC-4.0 events and ~5,000 simulated injections demonstrates robust insensitivity to astrophysical signals, establishing this geometric channel as a sensitive, complementary, and veto-safe diagnostic for current and next-generation detector networks.

We present an information-theoretic analysis of the Cosmic Web that goes beyond the scalar density contrast and exploits the full structure of the tidal deformation tensor. The three eigenvalues (lambda1, lambda2, lambda3) of the tidal Hessian furnish a natural morphological classifier: clusters, filaments, walls, and voids correspond to (+,+,+), (+,+,-), (+,-,-), and (-,-,-) sign patterns, and their joint probability distribution function (PDF), known analytically in the linear regime from Doroshkevich (1970), defines a continuous Shannon entropy that quantifies the information encoded in the geometry of large-scale structure. Additional information resides in the shear invariants Q = Trace(T2) and A = Trace(T3), which are algebraically independent of the density contrast delta and capture anisotropic deformation invisible to the density alone. The information dimension of each morphological component is related to its Hausdorff (fractal) dimension through the multifractal formalism: clusters (DH = 1.2), filaments (DH = 1.8), walls (DH = 2.5), and voids (DH = 3) define a spectrum of generalized Renyi dimensions Dq, whose q = 1 limit recovers the Shannon information dimension. The resulting entropy budget identifies filaments as the dominant information carriers of the mater distribution, while the tidal eigenvalue entropy is maximized in wall-like configurations near the saddle points of the gravitational potential. We also compute the redshift evolution of the multifractal entropy and derive its relation to the linear growth rate f(z), providing an independent constraint complementary to redshift-space-distortion measurements of f*sigma8.

Type Ia supernovae (SNe Ia) play an important role throughout astrophysics, most notably as standardizable cosmological candles. Yet, their stellar progenitors and explosion mechanism remain areas of active investigation. For decades, the canonical model for normal brightness SNe Ia used in cosmology was a carbon-oxygen white dwarf (WD) accreting from a non-degenerate stellar companion, approaching the Chandrasekhar mass (M_Ch). Previously, all models of near-M_Ch SNe Ia invoked an ad hoc assumption on the critical process of detonation initiation, and could therefore be tuned to a variety of outcomes. Here, we present global 3D hydrodynamical simulations of near-M_Ch progenitors, which incorporate, for the first time, a laboratory-validated ab initio mechanism for the turbulence-driven deflagration-to-detonation transition (tDDT). The tDDT detonation mechanism is highly efficient, leading to detonation initiation which is prompt in comparison to most prior work. Despite spanning a factor of six in central ignition density and qualitatively distinct ignition topologies, all models converge on nearly identical synthetic spectra at peak luminosity, spectroscopically matched to the overluminous SN 1999aa. The turbulence-driven Chapman-Jouguet criterion drives each progenitor to a common detonation configuration from diverse initial conditions, providing a physical foundation for the ignition-insensitive detonation outcomes implicit in the empirical standardizability of SNe Ia. This provides the first physically motivated, self-consistent pathway for delayed detonation in SNe Ia simulations. Further work is necessary to understand how this mechanism might produce more delayed detonation initiation and potentially fail, thereby yielding SNe Iax.

A rapid estimate of gravitational-wave (GW) detectability associated with astronomical transients is crucial for optimizing multi-messenger follow-up strategies and for constraining the physical origin of the transient itself. We introduce here the Targeted Detectability Range (TDR), designed to evaluate with minimal computational effort the detectability of compact binary coalescences under the hypothesis of association with an external messenger, such as an electromagnetic or neutrino signal. Unlike the standard GW range, which is based on averaged source parameters, the TDR incorporates prior information from observations of the external messenger, including sky localization, inclination constraints, and physically motivated bounds on component masses. We report the detectability range of all gamma-ray bursts, short and long duration, observed during the first three observing runs of the LIGO-Virgo-KAGRA collaboration. The method is validated by performing a systematic comparison with the 90$\%$ exclusion distances provided by modeled targeted GW searches.

We investigate the role of mass ratio reversal (MRR), in which the initially less massive star in a binary forms the more massive compact object, in shaping the astrophysical binary black hole (BBH) merger rate and mass distribution inferred by LIGO-Virgo-KAGRA, comparing simulation outcomes from population synthesis frameworks COMPAS and SEVN. We find that the observational imprint of MRR differs qualitatively between the two models. In COMPAS, MRR systems dominate the merger rate density at high primary masses ( $\gtrsim$ 12 M$_\odot$), high secondary masses ( $\gtrsim$ 20 M$_\odot$), and high mass ratios ($q>0.6$), whereas in SEVN, MRR systems remain subdominant across the BBH mass distribution. This implies that the initially less massive star can massquerade as the observed primary black hole, such that the primary-mass distribution is not a direct tracer of the initially more massive stars, but instead a superposition of physically distinct evolutionary populations. We identify in the simulations three distinct evolutionary pathways leading to MRR systems: core-growth, in which stable mass transfer increases the helium-core mass of the secondary; PPISN-shrinking, where pulsational pair-instability episodes reduce the primary remnant mass; and asymmetric-CCSN, where differential supernova mass loss drives the reversal. When weighted by the local BBH merger-rate density, the core-growth channel dominates almost exclusively. MRR systems predominantly originate from massive ($\gtrsim$ 50 M$_\odot$), low-metallicity progenitors, with most of the systems forming below 0.1 $Z_\odot$. Our results demonstrate that MRR is a physically distinct and potentially observable feature of isolated binary evolution. Accounting for MRR will be important for robustly connecting future gravitational-wave observations to the physics of massive binary evolution and compact-object formation.

We re-examine the claim by Wiseman et al. (2026) that progenitor-age bias has a negligible impact on cosmological inferences from Type Ia supernovae (SNe Ia). We show that their inferred host-age-Hubble residual (HR) slope is severely underestimated because their combined SN Ia sample spans an unusually wide redshift range ($0.04 < z < 0.42$), over which the mean host age evolves by $\sim$\,3 Gyr. As a result, SNe Ia spanning substantial host-age differences are effectively assigned similar HR values prior to regression, artificially flattening the inferred age-HR relation. In addition, their application of the Pantheon+ host-mass correction further suppresses the slope, but the underlying dust model is highly incompatible with the measured dust attenuation curves of galaxies. We also demonstrate that our age bias correction is robust to uncertainties in host-progenitor age mapping arising from different choices of the SN Ia delay-time distribution. The reduced progenitor-age evolution argued by Wiseman et al. (2026) must, by the same logic, be accompanied by a steeper inferred progenitor-age-HR slope. When these two effects are consistently combined in computing the redshift-dependent magnitude correction, the final correction, and hence the resulting cosmological impact, remain largely unchanged from Son et al. (2025).

We analyse new H-band integral-field unit observations of two galaxies at ~4 Mpc, using a principal components analysis of pixel spectra to probe their giant star content. In both galaxies, the signals arise in near-resolved point-like sources without large-scale variation, consistent with each pixel sampling stars randomly from a common underlying population. In the (mostly) old bulge of NGC 5128, the observed pixel-to-pixel variation is dominated by a component with a mid-M giant spectrum with prominent CO bandheads. We also recover a smoother second spectral component, apparently driven by contributions from later spectral types. This component is not present in predictions from Poisson-sampled models of old stellar populations; we suggest that it arises from the cool phases of long-period variable stars. (An appendix provides direct evidence for such variables in complementary two-epoch MUSE observations.) In the contrasting galaxy NGC 5102, where a post-starburst stellar population is known to be present, we again find two distinct components. As before, the first component carries the CO bands typical of M-giants. The second eigenspectrum in this younger galaxy shows a strong 1.77 micron C2 bandhead, a feature which is characteristic of carbon stars. Our results highlight the ability of integral field data to access information beyond the total spectrum, even when individual stars cannot be classically resolved.

Recent observations have revealed a unique class of active galactic nuclei (AGNs), termed little red dots (LRDs). These objects are hypothesized to be powered by massive black holes rapidly accreting in dense gaseous environments. Theoretical studies suggest that the circum-nuclear gas can form an optically thick black hole envelope (BHE), whose structure resembles the atmospheres of convective stars near the Hayashi limit. Given that such cool stars typically generate magnetic fields, we propose a dynamical and spectral model for an LRD enshrouded by a magnetized BHE. Assuming spherical free-fall accretion onto a rotating, magnetized BHE, our model accounts for key observational properties of LRDs. We propose that the Doppler component of broad emission lines originates from plasma clumps co-rotating within the BHE magnetosphere. Including additional broadening due to electron scattering allows the resulting line profile to be fitted by a combination of a Gaussian core and an exponential tail. This model can reproduce Doppler components up to a few thousand ${\rm km~s^{-1}}$. We suggest that conventional black hole mass estimation methods based on the virial relation may yield erroneous results. Furthermore, our model is consistent with X-ray non-detections in LRDs. We evaluate the X-ray luminosities of two potential sources: the post-shock region of accretion shocks and a magnetically heated corona. We find that these X-ray luminosities are constrained to $\lesssim 10^{41}~{\rm erg~s^{-1}}$ across a wide range of black hole masses ($10^5 M_\odot \lesssim M_{\rm BH}\lesssim 10^7M_\odot$) and accretion rates, consistent with current upper limits on X-ray emission.

Recent efforts to characterise the molecular gas content of brightest cluster galaxies (BCGs) at intermediate redshift have revealed a sub-population of gas-rich systems, whose star formation activity is likely influenced by environmental processing. In this study, we aim to investigate the molecular gas reservoirs and star formation fuelling of central galaxies in groups, also known as brightest group galaxies (BGGs), at intermediate redshifts. We present targeted carbon monoxide (CO) line observations of three BGGs in the COSMOS field at $z \sim 0.3$, obtained with the IRAM 30m telescope. The galaxies exhibit disturbed morphologies, extended blue substructures, and interaction signatures. Furthermore, they exhibit significant star formation rates derived from multiwavelength diagnostics. We detect CO(1$\rightarrow$0) emission in one system, revealing a substantial molecular gas mass of $M_{H_2} \sim 3 \times 10^{10}$ M$_\odot$, while for the other two BGGs, CO emission lines remain undetected, yielding stringent upper limits of $M_{H_2} \lesssim 10^{10}$ M$_\odot$. By combining molecular gas constraints with fiducial star formation rates derived from total infrared emission, we infer gas depletion timescales in the range of $\lesssim 0.5-1.5$ Gyr. These results may indicate that, despite their active star formation and interaction signatures, some BGGs could already experience efficient gas exhaustion or suppressed gas replenishment, suggesting that gas depletion precedes star formation quenching. Our findings hint that environmental processes in galaxy groups could strongly regulate the availability of cold gas and drive rapid evolutionary phases in central galaxies, possibly bridging the gap between gas-rich BCGs and passively evolving systems.

Whether intermediate-mass black holes reside in nearby star clusters has remained contested for decades. We address this question by training neural network and random forest regressors on synthetic catalogs generated with the {\sc Rapster} cluster evolution code, mapping observable cluster properties such as total mass and half-mass radius onto the mass of the heaviest black hole built up through repeated mergers. Applying these models to nearby globular and nuclear star clusters, we forecast the intermediate-mass black hole population that each system may host. Globular clusters are unlikely to contain black holes more massive than $\sim 100\,M_\odot$, with an occupation fraction near 0.02, although they can produce remnants within the upper mass gap with masses approaching $100\,M_\odot$. Among nuclear star clusters, a handful of cases, including NGC 5102 and NGC 5206, yield predicted central black hole masses above $100\,M_\odot$, which we contrast with kinematically inferred estimates. Where the observationally claimed masses exceed our predictions, the implication is that the assembly history involved processes beyond hierarchical mergers, most plausibly accretion of gas and stars. Finally, we employ a normalizing flow to quantify, for individual globular clusters, the likelihood that their initial conditions were favorable to a collisional runaway during the first few million years after formation.

We present the galaxy stellar population catalogue from the JWST Advanced Deep Extragalactic Survey (JADES) Data Release 5 (DR5), providing homogeneous Bayesian inference of physical galaxy properties in GOODS-N and GOODS-S. Using deep JWST/NIRCam and MIRI imaging combined with ancillary multi-wavelength data, we model the spectral energy distributions of ~500,000 sources with the Prospector framework. Our modelling incorporates flexible non-parametric star-formation histories (SFHs), nebular emission, dust attenuation, metallicities, and mid-infrared AGN and dust emission. We adopt an evolving star-forming main sequence (SFMS) prior for modelling the SFHs, which provides a physically-motivated long-term shape of SFHs while retaining non-parametric flexibility. The prior links stellar mass growth and SFR through the observed redshift-dependent SFMS, shaping the global behaviour of the inferred SFHs but allowing substantial deviations and scatters wherever supported by the data. We derive posterior distributions for stellar masses, SFRs, SFHs, dust attenuation, metallicities, and AGN contributions. The depth and wavelength coverage of JADES enable robust stellar mass measurements down to low-mass limits, as well as improved constraints on recent star-formation activity for ~350,000 galaxies at z = 1 - 9. The adoption of a physically motivated prior mitigates unphysical solutions and reduces degeneracies between redshift, age, dust, and metallicity, particularly for faint sources. We validate the catalogue through consistency checks and comparison to spectroscopic redshifts where available. The resulting value-added catalogue provides a uniform set of stellar population parameters suitable for statistical studies of galaxy growth, quenching, and the build-up of stellar mass across cosmic time. The full catalogue and posterior summaries are publicly released as part of JADES DR5.

J=1--0 SiO masers at 43 GHz have a well-established distinctive signature in asymptotic giant branch (AGB) stars. 28SiO transitions typically dominate these spectra with the v=1 and v=2 emission being especially prominent and ubiquitous. Several predictions about enhanced 29SiO abundances in exotic stars prompt us to catalog the cases where 29SiO maser emission is enhanced compared to 28SiO. Our purpose is to catalog the known cases of 43 GHz spectra dominated by emission from isotopologue transitions (iso-dom spectra), to explore the commonalities in these sources, and to explain the cause of such maser signatures. Our catalog is drawn from SiO maser line ratios in the infrared-color-selected BAaDE survey and supplemented with a literature detection. The BAaDE catalog has cemented the typical signature of 43 GHz SiO masers, showing it is dominated by the v=1 and v=2 lines. Thirty-five iso-dom spectra are identified, meaning that this signature is seen in about 0.2% of our SiO maser-bearing stars. Their infrared colors are blue compared to other sources of the same period, similar to all sources displaying isotopologue masers. It is clear that the iso-dom nature of sources is variable, but unclear whether this is tied to stellar phase. A large abundance abnormality among the iso-dom sources is disfavored as the iso-dom sources do not appear significantly different from other stars which host isotopologue masers. Maser pumping, affecting the population inversions of specific transitions, can instead explain the enhanced signatures. We posit that iso-dom spectra appear in AGB stars which have undergone third-dredge up (enhancing the 29SiO and 30SiO abundance slightly) and which, in addition, are experiencing very low turbulence velocity (<1 km/s), creating a line overlap which pumps the maser transitions very efficiently.

We present a new absolute age determination for NGC 6791, one of the Milky Way's oldest and most metal-rich open clusters. Its unusual properties make it an important probe of inner-disk evolution and asteroseismic calibration, but its age has remained difficult to determine because of coupled uncertainties in reddening, distance, photometry, and stellar-model physics. Gaia DR3 photometry together with detached eclipsing binaries (DEBs) in NGC 6791 are combined with 10,000 Monte Carlo isochrone sets (marginalizing over uncertainties in composition, convective mixing processes, opacities, diffusion, nuclear reaction-rates, distance modulus, and reddening) to determine the age of NGC 6791. For each isochrone we build a synthetic color-magnitude diagram (CMD) that matches the observed star count in the MSTO and subgiant-branch window and injects empirical photometric scatter perpendicular to the ridgeline, enabling CMD comparisons without artificial-star tests. We assess CMD morphology using a bootstrap-calibrated two-dimensional Kolmogorov-Smirnov statistic, and add an external check based on the nearest-point metric: a coeval DEB statistic in $(M,L)$ space. These statistics are mapped to probability-density weights via bootstrap-resampling and combined into a single isochrone weight. NGC 6791 is determined to have an age of $8.46\pm0.66$ Gyr, $[\mathrm{Fe/H}]=+0.280\pm0.079$, $Y=0.2968\pm0.0158$, $(m{-}M)_V=13.333\pm0.058$, and $E(B{-}V)=0.183\pm0.024$. Our error budget shows no single dominant contributor, and highlights differences between open-cluster and globular-cluster age errors. Combined with its super-solar metallicity, our age estimate favors an inner-Galaxy origin for NGC 6791 and subsequent outward migration, provides a benchmark for asteroseismic calibration at high metallicity, and extends the absolute cluster age--metallicity relation to an old, metal-rich open cluster.

We present a uniform, epoch-resolved analysis of soft X-ray observations of eight comets obtained with NICER, using Bayesian statistics to identify charge-exchange line components, measure relative ion fluxes, and infer nominal solar-wind freeze-in temperatures. The sample exhibits recurring spectral morphologies that fall into distinct families: carbon-dominated, intermediate, and nitrogen-/oxygen-dominated. Epoch-resolved flux ratios yield a robust separation between diagnostics: carbon-derived freeze-in temperatures cluster near T_freeze(C) about 1.4-1.7 MK, while nitrogen- and oxygen-derived diagnostics are systematically higher, typically T_freeze(N,O) about 2.0-2.3 MK. Short-timescale variability in inferred freeze-in conditions is common, indicating that instantaneous solar-wind charge-state fluctuations, rather than large changes in coma composition, dominate the spectral differences. We discuss instrumental and modeling limitations, demonstrate how our Bayesian fitting method mitigates degeneracies via physically motivated priors and Bayesian model selection, and recommend laboratory measurements and coordinated high-resolution X-ray observations to refine charge-exchange diagnostics and validate low-resolution inferences.

We investigate thermosphere responses to non-orographic gravity waves (GWs) using wind measurements from the Neutral Gas and Ion Mass Spectrometer onboard the Mars Atmosphere and Volatile EvolutioN mission, alongside simulations from the Mars Planetary Climate Model. We focus on zonal jets in high-latitude regions of the upper atmosphere. Jet acceleration and deceleration (280 m/s ) arise from momentum divergence (1,300 m/s/sol ) driven by wave saturation and wind filtering. Simulations and observations indicate that GWs modulate these jets in the hemisphere associated with the descending branches of the Hadley Cell, due to the absence of wave critical layers in the middle atmosphere. Interactions between GWs and the mean flow can shape the circulation and dynamics of the upper atmosphere of Mars.

The element abundances of Milky Way disc stars encode entangled imprints of multiple enrichment processes, making it difficult to uncover the underlying chemical evolution. Here we re-project 16 stellar abundances for 199,290 red giant stars ([Fe/H]$ > -1$) into a set of (4) shared enrichment patterns, providing a generative framework for learning the organising structure of the Milky Way disc. The relative contributions of these patterns vary systematically across the disc, revealing a low-dimensional enrichment basis that responds coherently to global drivers of disc evolution. By grouping stars according to their pattern contributions, we identify coherent enrichment pathways that exhibit strong chemo-spatial correlations and are stratified in both age and height above the plane, linking radial growth to vertical disc structure. Stars occupying similar positions along these enrichment pathways also show coherent vertical deviations across radius, indicating that the low-dimensional chemical structure captures the disc's response to dynamical perturbations. We identify a transition in enrichment behaviour at approximately 6 Gyr, marking the onset of a more chemically mixed regime with increasing contributions from delayed sources. Within this connected system, the observed $\alpha$-bimodality arises within a shared, low-dimensional abundance structure, with stars populating continuous sequences of changing enrichment fractions that are tightly coupled to spatial, temporal, and orbital coordinates across the Milky Way disc.

Pulsar timing is a valuable source of high-precision astrophysical measurements which can be used to probe gravitational physics, including by detecting gravitational waves. An important factor limiting the precision of these measurements is pulse jitter; i.e., intrinsic, short-timescale variation in the amplitude and shape of pulses from a given pulsar. Because conventional pulse time-of-arrival (TOA) measurement relies on template matching, which assumes the average pulse shape is stable, such variation gives rise to jitter noise in TOA measurements. Here we introduce a generalization of the template matching technique, making use of principal component analysis, which can account for variations in pulse shape. We compare this technique to other proposals for mitigating jitter noise in pulsar timing, paying particular attention to the possibility of corrections absorbing other astrophysical signals of interest, and demonstrate its effectiveness using simulated data.

Most hot subdwarfs (sdO/B) are low-mass core-helium-burning stars formed through binary interaction. A subgroup of intermediate He-rich sdOBs shows extreme heavy-metal (Z>30) enrichments exceeding $10^4$ times solar, especially in Zr or Pb. We analyse the first ultraviolet spectra of the "heavy metal" subdwarfs LSIV-14 116 (Zr-rich) and EC22536-5304 (Pb-rich) to determine their abundance patterns and test nucleosynthesis models. Both stars show exceptionally rich heavy-element spectra dominated by ions in stages III-VI, many absent from standard line lists. We compiled literature energy levels, wavelengths, and oscillator strengths and implemented them in the SYNSPEC code. In addition, we computed new oscillator strengths for As III, Se III, Hf IV, and Tl IV. New photoionisation cross-sections for Pb III-VI enabled the first non-LTE models of multiply ionised Pb. In LSIV-14 116 we detect 16 light and 24 heavy metals (Ga-Bi); Br, Nb, Mo, Pd, In, Sb, Te, and Xe are measured in an sdO/B star for the first time. In EC22536-5304 13 light and 26 heavy metals are detected, including first detections of La, Ce, Pr, Nd, Er, Yb, Lu, Hf, Ta, W, Os, Pt, Hg, Tl, and Bi. LSIV-14 116 peaks at ~4.3 dex for Sr-Sn relative to solar, declining to 3.1 dex at Pb and 2.3 dex at Bi, whereas EC22536-5304 reaches 6.2 dex for Pb and 5.4 dex for Bi. Both stars are Fe-poor. The abundance patterns cannot be explained by atomic diffusion alone and retain a clear nucleosynthetic signature. EC22536-5304 closely matches predictions of i-process nucleosynthesis, providing strong evidence for i-process self-enrichment in hot subdwarfs. EC22536-5304 likely formed via Roche-lobe overflow, whereas LSIV-14 116 likely originated from the merger of two low-mass white dwarfs, which may explain differences in its enrichment pattern. These results suggest that heavy metals in other He-sdO/Bs may also be self-synthesised.

In the 2021 outburst of RS Ophiuchi, the gamma- and the X-ray flux were measured quasi-simultaneously from day 1 after the optical peak, offering the first comprehensive view of shocks in a nova occurring in a symbiotic system. We present a previously unpublished observation done with NuSTAR in the 3-79 keV range, 9 days after maximum, and we review the complex history of the evidence of shocks in the previous outbursts of this nova in the light of the intensive X-ray monitoring of 2021. We find evidence that the shock causing the particle acceleration measured with the Cherenkov telescopes produced also the thermal flux detected in the 0.2-30 keV X-ray range, while the large gamma-ray flux observed with Fermi after about a day, is not consistent with the X-ray observations. We conclude that an initial, strong shock, with particle-particle loss timescale shorter than the timescale of particle acceleration at energy higher than a few GeV, occurred close to the red giant atmosphere,where either the X-rays' emitting volume was reduced by turbulence, or - perhaps less likely - the X-rays were completely absorbed by large column density near the giant and by the accretion wake along the line of sight. We compare RS Oph with other novae in long period systems with evolved companions,discussing how the shocks' phenomenology is a powerful tool to derive other physical parameters. Finally, we discuss predictions that in T CrB, expected to have a new outburst within the next few years, the shocks may not be as energetic as in RS Oph.

A recent 2023 paper by Massaro et al. introduced the G4Jy-3CRE, a new catalog of the brightest radio sources in the southern hemisphere that serve as a southern equivalent to the Third Cambridge Catalog Revised (3CR). The G4Jy-3CRE catalog selected 264 sources from the GLEAM-4Jy survey based on the same criteria used to select the sources in the 3CR. In this paper, we present new Australian Square Kilometre Array Pathfinder (ASKAP) continuuum imaging of the G4Jy-3CRE catalog. We use the three most recent data releases from the Rapid ASKAP Continuum Survey (RACS), covering the sky south of +30°decl.: RACS-low1, RACS-mid, and RACS-high. Together, these data releases cover a range of frequencies from 600 to 1800 MHz. The RACS surveys have improved spatial resolution and sensitivity over archival surveys at the same frequency, enabling us to classify 173 sources (66% of the sample) with morphologies indicative of the presence of jets, 37 of which did not show jet activity on archival radio maps. We were able to effectively classify FRI/FRII galaxies up to a redshift of z = 1.35. Moreover, we identified six optical counterparts for sources that were either previously unidentified or ambiguous.

Time variability is a strong probe of energetic phenomena which occur at small spatial scales, like Active Galactic Nuclei (AGN). We use ALMA observations at 100 GHz executed over a period of 2.5 months to look for time variability in the Antennae galaxies, a prototypical early stage merger galaxy pair, for which there are no previous signatures of an AGN in the optical, infrared or X-ray. Most 100 GHz detections in the Antennae are spatially extended and associated with star forming regions, but two sources in the southern galaxy NGC 4039 are compact. One of these compact sources, S3, is offset by 1 arcsecond in the northeast direction from the stellar peak of NGC 4039, and marginally resolved at 10 parsec resolution. The other source, S4, is co-spatial with the stellar peak of NGC 4039 and unresolved even at a resolution of 4 parsec. We examine the time variability of these two sources using their power spectrum. We find that S4 varies with a characteristic timescale of 13+/-3 days, indicating that the phenomena responsible for the 100 GHz emission is smaller than 0.01 parsecs. By comparing the observed flux of the two sources with various candidate origins, we show that while S3 can be explained either by a young massive stellar cluster or an AGN, S4 is likely to be an AGN that is possibly Compton-thick.

Altair is an A-type star known to have an appreciably oblate shape owing to its very fast rotation (~300 km/s). Despite of numerous publications on this star, its chemical abundances have been scarcely investigated so far, presumably because of the practical difficulty that spectral lines are considerably broadened by rapid rotation and badly blended with each other. Motivated by this situation, a spectroscopic analysis was conducted to study the photospheric abundances of Altair by using the synthetic spectrum-fitting technique, in order to clarify whether or not any chemical peculiarities exist. The microturbulent velocity was determined to be 2.9 (+/-0.9) km/s by requiring that the metallicity does not show any systematic region-dependence. Then, the abundances of 17 elements (C, N, O, Mg, Al, Si, S, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn, Sr, Ba) were derived, where the non-LTE effect was taken into consideration as much as possible. The results revealed considerable region-by-region dispersion (several tenths dex or even more), reflecting the difficulty of reliable abundance determination for such a very rapid rotator. Nevertheless, the differential mean abundances relative to the Sun turned out to fall within -0.5 < [X/H] < +0.3 for all elements without any dependence upon the atomic number. Accordingly, we may conclude that (1) no appreciable anomalies of chemical abundance patterns exist in the atmosphere of Altair, (2) but its global metallicity is likely to be slightly subsolar (~-0.2 dex on the average).

We report the discovery of tidal disruption event (TDE) WFST250820mmsw/AT2025wet by the 2.5-meter Wide Field Survey Telescope (WFST). It exhibits a blue nuclear flare throughout the observed evolution with a g-band peak magnitude ~22, which is about 3 magnitudes brighter than its host galaxy. A Keck/LRIS spectrum taken near the optical peak reveals a featureless blue continuum, with no discernible emission lines. However, its redshift can be accurately determined to be 1.037 by its host galaxy absorption lines. Blackbody fits to the multiband spectral energy distribution (SED) of AT2025wet yield a constant temperature of ~19,000K and a peak luminosity of (8.27 +0.92 -0.71)*10^44 erg s^-1 while actually the SED likely peaks at a much shorter wavelength than a 19,000K blackbody. The SED modeling of the host galaxy implies a stellar mass of ~10^11.2 M_odot and an estimated central black hole mass of ~10^8 M_odot, with no evidence of significant active galactic nucleus activity prior to the flare. All of these observations are well consistent with a featureless TDE scenario, making it the highest-redshift non-jetted TDE known to date. TDEs at such high redshift provide us a unique opportunity to explore the intrinsic SEDs of TDEs, particularly to test whether they peak in the extreme-UV regime, thereby addressing the missing energy puzzle and the origin of optical emission in TDEs. Ongoing surveys represented by WFST and the Legacy Survey of Space and Time (LSST) are expected to discover an increasing number of TDEs at higher redshifts, which will extend our census of SMBHs across redshift space and help unravel the mysteries of optical TDEs through direct probes of their UV emission.

This chapter reviews the application of Artificial Intelligence (AI) techniques to the study of galaxy clusters, covering both theoretical developments and their use as tools to infer cluster properties from a variety of observational tracers. We discuss recent advances in mass estimation from SZ, X-ray, optical, and dynamical data, highlighting the ability of AI methods to capture non-linear features, projection effects, and complex cluster morphologies beyond more classical approaches. In addition, we present other emerging applications, including the emulation of baryonic physics from N-body simulations, the characterization of dynamical states and mergers, and the analysis of the diffuse components such as the intracluster light. Particular emphasis is placed on the role of simulations in training these models, the impact of baryonic modelling, and the need for a robust uncertainty quantification and interpretability. Finally, we outline current limitations and future prospects, stressing the importance of combining flexible simulation strategies with AI techniques to fully exploit next-generation surveys for precision cosmology.

We present a framework for detecting transient gamma-ray phenomena in a controlled environment by combining end-to-end simulations of the Fermi-LAT sky with self-supervised spatio-temporal deep learning. We generate a ten-year synthetic Universe with gtobssim and process the simulated events into daily all-sky maps of counts and exposure, obtaining a time-ordered sequence that mirrors the structure of Fermi-LAT observations. To model the nominal evolution of the sky, we employ a Convolutional Long Short-Term Memory (ConvLSTM) network that operates directly on map sequences, preserving spatial locality while learning temporal dependencies. The model is trained to reconstruct expected emission, and departures from the learned baseline are quantified through pixel-wise mean-squared residual maps. We then define statistically motivated anomaly criteria by estimating per-pixel thresholds from the residual distribution on the training set, and we enforce spatial coherence via local filtering to suppress isolated fluctuations. The ConvLSTM is then deployed as trained predictor on Fermi-LAT daily maps, where the sky can depart from the nominal behavior because of genuine astrophysical variability and instrumental non-stationarities. The resulting pipeline flags localized, time-dependent excesses consistent with high-variable sources or transient events (e.g., flares or GRBs) and provides a benchmark for evaluating anomaly-detection strategies on long-duration, Fermi-LAT-like datasets.

Neutron stars in close binary systems have the potential to spin up to millisecond periods due to the accretion of matter and angular momentum from their low-mass companions. In later stages of this process, they sometimes start to swing between the accretion-powered and rotation-powered regimes, manifesting themselves as low-mass X-ray binaries and millisecond radio pulsars, respectively. Such systems are known as transitional millisecond pulsars. PSR J1023+0038 was the first one of this kind to be discovered and the first to show optical pulsations at the rotation frequency of the neutron star during a peculiar low accretion state. The optical pulse profile is characterized by a smooth double-peaked shape resembling thermal light curves of X-ray pulsars, but more likely emerging from re-emission of the pulsar wind energy by charged particles in the surrounding medium. Although the amplitudes of the peaks show strong variability, the overall structure of the pulse profile was observed to be fixed, with the optical pulsed fraction less than 1 percent. Here, we report time-resolved observation of a dramatic violation of this permanence during our high temporal resolution observations of PSR J1023+0038 with the 6-m BTA telescope of the Special Astrophysical Observatory. On a timescale of a few seconds the pulse profile took a single-peaked, nearly sinusoidal shape, with synchronous magnification of the pulsed fraction up to about 5 percent. After spending about 220 seconds in this new regime, accompanied by flaring activity, the system returned to its normal state. We discuss a number of possible explanations of this peculiar behavior in the context of the physics and geometry of interactions between the pulsar wind and surrounding matter. However, a complete picture is yet to be revealed.

The recent James Webb Space Telescope (JWST) observations reported the unexpectedly large abundance of massive galaxies with stellar masses of $\sim 10^{10}~M_{\odot}$ at high redshifts $z \simeq 6.5 - 9$ compared with the prediction of the standard $\Lambda$CDM model. As a possible solution to the tension, we consider a blue-tilted spectrum of density perturbations with a positive running. We find that, for $\alpha_s \simeq 0.2$ and $\beta_s \simeq 0.2$, a joint analysis with CMB observations shows that the tension can be resolved at the 1$\sigma$ confidence level. Such a blue-tilted spectrum is also plausible from the perspective of primordial black hole formation on much smaller scales in the early Universe.

Stellar spectra encode key information on the physical properties and chemical compositions of stars. Accurate stellar parameter determination is essential for addressing major questions such as galaxy and stellar evolution. Large-scale spectroscopic surveys have accumulated unprecedented spectral data. Traditional feature extraction or model-fitting approaches struggle with high-dimensional, massive datasets, limited generalization, and computational inefficiency. Recent advances in large language models demonstrate strong generalization and feature-learning in tasks like natural language processing, DNA/RNA sequence analysis, and protein/chemical parsing. Stellar spectra are continuous sequential signals, enabling the transfer of language models to stellar spectroscopy. Here, we propose a two-stage large language model framework for stellar parameter inference, achieving accurate estimation of effective temperature, surface gravity, metallicity, and abundances of ~20 chemical elements. Scaling-law analyses show systematic performance improvements with increasing data, providing a scalable framework for forthcoming large-scale surveys.

We present a unified H i rotation curve database for 129 dwarf and irregular galaxies drawn from four Local Volume surveys: the Local Volume H i Survey (LVHIS; 33 galaxies), VLA-ANGST (29), LITTLE THINGS (26), and WALLABY DR2 (41). The database provides standardised kinematic parameters, distance estimates, morphological classifications, and rotation curve data in machine-readable JSON, JSONL, and CSV formats with a documented 27-field schema, supporting retrieval-augmented generation (RAG) applications and cross-survey kinematic analysis. Quality tiers distinguish 26 galaxies with full multi-point tilted-ring rotation curves from 103 with single-ring or profile-width estimates. Three worked examples demonstrate corpus queries, including application of the {\omega} correction to DDO 154 (LITTLE THINGS). This work is presented as a data resource; no new dynamical model is proposed. The database and all computation scripts are available at Zenodo (this https URL).

Magnetic fields observed across cosmic scales are difficult to explain within conventional physics. A primordial origin is, thus, often assumed. While a nonminimal coupling of the inflaton with the electromagnetic field could theoretically generate magnetic fields of about $10^{-13}$ G, this approach faces significant issues, including strong-coupling and backreaction problems. ``Dark photons", arising naturally in hidden-sector extensions of the Standard Model, provide a well-motivated framework for addressing various cosmic as well as particle physics issues. We demonstrate that coupling dark photons with standard ones can result in adequate magnetogenesis without the limitations of existing models. This minimal mechanism may also provide insights into unresolved cosmic mysteries.

Blazars' non-thermal emission shows rapid variability across all wavelengths, so spectral energy distributions (SEDs) built from quasi-simultaneous data are crucial for revealing the jets physical properties. In this work, we construct quasi-simultaneous broadband SEDs for 93 Fermi blazars (56 FSRQs, 35 BL Lacs, and 2 blazar candidates of uncertain type), fit both peaks with cubic functions to allow for potential asymmetries, and examine correlations among key parameters. Our main results are summarized as follows: (1) We find that synchrotron peak frequency and curvature are only weakly related, suggesting that charged particles are accelerated by mixed acceleration mechanism. (2) The blazar sequence is confirmed in the observer's frame through negative correlations of both the bolometic luminosity $\log L_{\rm bol}$ and the Compton dominance $\log Y$ with the synchrotron peak frequency $\log \nu_{\rm syn}^{\rm peak}$. After correcting for Doppler boosting, a weak positive correlation emerges between $\log L_{\rm bol}$ and $\log \nu_{\rm syn}^{\rm peak}$. FSRQs and BL Lacs exhibit distinct correlation patterns within the blazar sequence, indicating differences in cooling mechanisms. (3) Using variability time lags between 0.1-1 GeV and 1-300 GeV light curves, we estimate lower limits of Doppler factors for 4 sources, providing a jet-speed diagnostic anchored directly to the $\gamma$-ray emission zone.

(abridged) We aim to predict the most important parameters for grain-grain collision outcomes for models of interstellar grain population evolution on astrophysical scales: the threshold velocity above which colliding grains shatter, the threshold for vaporization, and resulting distributions of grain sizes. We use molecular dynamics simulations which evolve the dynamics of each atom in a dust grain to explore the outcomes of collisions between silicate grains of radii $a \in [5,50]~Å$ at velocities $0.1-20$ km/s. We run simulations of grains with two materials: amorphous SiO$_2$ and an amorphous silicate of composition suggested by Draine \& Hensley (2021). With these simulations, we quantify the collision velocity dependence of shattered and vaporized mass fractions, and the resulting size distributions of shattering products. We find grain shattering thresholds are $\sim$6 km/s for both amorphous SiO$_2$ and astrodust material, which is a factor of $\sim$2 higher than the canonical value for silicates of 2.7 km/s from Jones et al. (1996). This discrepancy is mostly alleviated by correcting an error in the expression for these velocity thresholds derived in Tielens et al. (1994). We find that the size distributions of shattered products are generally not consistent with the power law distributions predicted by this previous model. We also find that their expression fails to predict the fraction of shattered or vaporized material observed in our numerical simulations. The model of Hirashita \& Kobayashi (2013) for the same quantities similarly fails to match the simulations. We provide updated shattering velocity thresholds for standard candidate grain materials to the astrophysics community. Broadly, our updated threshold velocities that astrophysical dust grains may be more robust to shattering in the interstellar medium than previously assumed.

Solar prominences are dynamic structures suspended within the solar corona and are manifestation of solar activity. Their evolution includes eruptions linked to coronal mass ejections, making their detection critical for space weather monitoring and forecasting. The vast amounts of high-cadence data provided by missions such as SDO/AIA motivate the application of deep learning frameworks capable of assimilating large-scale datasets. However, previous studies have reported poor model performance caused by contamination from hot coronal emission from the EUV HeII 304 Å channel. Using an existing labeled prominence dataset, we find that trained YOLOv5 object detection models exhibit a strong bias towards the 304 Å colormap, rather than physically meaningful prominence features. We develop a further two models comprising three-channel images constructed through an original dataset preprocessing pipeline: (i) full-disk grayscale, full-disk enhanced corona, and disk-removed, (ii) same as (i) with all disk-removed images. Our pipeline corrects instrument degradation to maintain more consistent feature representations across the solar cycle. The composite model (i) achieves a mAP@50 of 0.749 and a recall of $78\%$ on the test set, outperforming previous bounding box methods. Visual analysis of the composite models reveals that many apparent false positives are valid unlabeled prominences. We additionally demonstrate cross-instrument generalization by testing the composite model on SUVI image data. By examining dataset biases that propagate into model predictions, we provide recommendations for robust dataset construction. We present a reliable, physically-motivated, and versatile deep learning model to automatically detect prominences in EUV images, providing a framework beneficial for space weather applications.

We report the identification of the likely X-ray and optical counterpart to the unassociated Fermi source 4FGL J2249.4+6229. To clarify its nature, we investigate the X-ray data from Swift/XRT and SRG/eROSITA as well as photometric data from optical catalogues and archival spectroscopic data from the Gemini-North telescope. Using Zwicky Transient Facility data spanning over 6.6 yr, we confirmed a period of $\approx$5.6 h likely associated with the orbital motion in a binary system. The folded light curves have a smooth sinusoidal shape with two peaks per period and the amplitude of $\approx$0.2 mag. The X-ray spectra of the source are well fitted by an absorbed power law with the photon index of $\approx$2.0 and unabsorbed flux of $\approx$1.4$\times10^{-13}$ erg s$^{-1}$ cm$^{-2}$. All these together with the X-ray to optical flux ratio of $\sim$0.2 implies that 4FGL J2249.4+6229 is a promising redback candidate. Fitting the optical light curves with the direct heating model, we obtained the companion mass of $\approx$0.5 M$_\odot$ and temperature of $\approx$3600 K implying an M-type star. This places it among the coldest and most massive companions known in redback this http URL spectra confirms the M-type star and shows the broad asymmetric H$\alpha$ emission line. For the distance of 500--550 pc derived from the optical data, the source can be the redback with the lowest X-ray and $\gamma$-ray luminosities.

Context: Trans-Neptunian objects are distant bodies that retain valuable information about the origin and evolution of the Solar System. Many of these objects constitute binary systems. Studying binaries allows us to further characterise this primitive population and is critical for determining mass densities, a key but elusive physical property. Nevertheless, satellite detection can be challenging. Aims: This study aims to constrain the presence of close-in satellites around a selection of ten trans-Neptunian objects, including four known binary systems used for methodology validation. Methods: We developed a methodology independent of primary-secondary separation. We exploit the combination of occultation-derived sizes and thermal emission data from the "TNOs are Cool" Herschel Space Observatory key project. We model the thermal emission from a binary system to explain the thermal excess that cannot be reproduced by a single body of the occultation-derived size. Results: We obtain satisfactory constraints for the validation targets (208996) Achlys, (229762) G!kún{"hòmdímà, (38628) Huya and (174567) Varda. We find that (84522) 2002 TC302, (119951) 2002 KX14, and (307261) Máni are likely binary systems, which was previously unknown. We report size estimates for their putative satellites. For (84922) 2003 VS2, (28978) Ixion, and (470316) 2007 OC10 we find that no sizable satellite is needed to reconcile thermal and occultation data.

Cosmological data from the cosmic microwave background (CMB), baryon acoustic oscillations, and Type Ia supernovae suggest that the component driving the accelerated expansion of the Universe may be dynamical at the $\sim 2.5$-$3\sigma$ CL. The best-fit CPL model produces a level of cosmic structure similar to that of $\Lambda$CDM, with both models exhibiting mild tension with redshift-space distortion data. In this {\it Letter}, we parametrize possible departures of the effective gravitational coupling from Newton's constant in the late Universe, below a comoving scale $\lambda_c$, using two redshift bins, $0 \leq z < 1$ and $1 \leq z \leq 3$. We then determine the optimal values of $\lambda_c$ and the amplitude of these deviations from General Relativity, assuming a background with dynamical dark energy in CPL form. We find that, in order to achieve the required suppression of structure growth at low redshifts while remaining consistent with CMB constraints -- primarily from the late-time ISW effect at low $\ell$ and lensing at high $\ell$ -- modified gravity effects must appear on scales smaller than $\lambda_c \sim \mathcal{O}(10)\,\mathrm{Mpc}$. Using Planck PR4, DESI DR2, Pantheon+ (or DES-Dovekie) and redshift-space distortions data we confirm that a CPL background with standard gravity is moderately preferred over $\Lambda$CDM; this preference strengthens to a mildly strong level when modified gravity effects are included. This enhancement leaves the CPL parameters largely unchanged, but shifts them slightly further into the quintom region.

Magnetar short bursts (SBs) are hard X-ray transients of durations $0.01-1$ s peaking at $\sim 10-100$ keV, and are prime targets for new high-energy missions and polarimeters. The recent association of SBs with bright radio bursts in SGR 1935+2154 has broadened interest in SB physics. We present new advanced fireball models combining general relativistic light bending, polarized transport in magnetized photospheres, magnetic photon splitting attenuation, and magnetospheric vacuum birefringence. These models also have relevance to trapped fireballs in magnetar giant flare pulsating tails. We adopt confined flux tube geometries consistent with adiabatic fireballs, and anisotropic/polarized emergent intensities to produce spectra and polarizations, and energy-time Stokes impulse responses. We predict that most fireballs are highly linearly polarized, especially when vacuum birefringence is important. There is rich potential for diagnostics: coexisting direct and lensed delayed images, gaps by occultation of the neutron star surface, and Shapiro+Rømer delay with temporal caustics. These effects can imprint spin phase dependence of the spectral and polarization character of bursts. Predicted signatures depend strongly on viewing geometry, fireball configuration, and photon splitting assumptions, yielding large variance in model high-energy spectral shapes and cutoffs, and energy-dependent polarization. The models can reproduce established double-blackbody SB spectral phenomenology, and we find that the unusual April 2020 radio-associated SB from SGR 1935+2154 is broadly consistent with a footpoint close to the magnetic pole, and possibly near pole-on viewing geometry. Our models motivate reverberation-style analyses for SBs and suggest that high-quality data might constrain source geometry, burst crustal footpoints, and, potentially, neutron star masses and radii.

Neutrino signal from a population of Seyfert galaxies has been detected by IceCube neutrino telescope in the muon neutrino channel that has sensitivity mostly to the Northern Hemisphere sources. This detection can be verified by KM3NeT telescope that has sensitivity also in the Southern Hemisphere. We define a catalog of Seyfert galaxies that are expected to be detectable with KM3NeT, assuming that the neutrino luminosity scales with the intrinsic hard X-ray luminosity of the sources. We find that four sources: NGC 1068, NGC 4151, NGC 4945 and Circinus galaxy, are detectable by KM3NeT, if their spectra follow either NGC 1068 or NGC 4151 spectral template based on IceCube data. We discuss uncertainties of the neutrino flux estimate, considering the Compton-thick nature of three of the four detectable sources: NGC 1068, NGC 4945 and Circinus. The limited catalog of the four sources can be used in KM3NeT source search to reduce the trial factor of analysis aimed at independent verification of the neutrino signal from Seyfert galaxies.

Automated sky surveys frequently report sparse-in-time multiband photometric observations of asteroids passing through their fields of view. Photometric data are currently available for tens of thousands of asteroids, and new data collection is ongoing. We aim to describe and characterize the performance of a statistical test for identifying asteroids that display surface color heterogeneity based on sparse-in-time multiband photometric survey data. Using simulated photometry for a set of synthetic asteroids with predetermined physical properties, we estimated the sensitivity of the statistical test for surface color heterogeneity to errors in assumed model properties using a Monte Carlo approach. We evaluated the detection and false positive rates as a function of the number of observations, measurement noise, error in assumed period, pole orientation, shape, and phase function. We examined the required accuracy in various parameters of the photometric model needed to obtain reliable results to evaluate the feasibility of applying the test to realistic datasets. Regional-scale surface color heterogeneity can be detected by examining differences in the shape of an asteroid's light curve as a function of viewing geometry across multiple bandpasses. Differences in light curve shapes as a function of wavelength are highlighted in this work through comparison of the observed photometric measurements to the predictions of a well-fitting, uniformly colored photometric model. Statistically significant deviations from the prediction of the uniformly colored model are taken as evidence of surface color heterogeneity. The performance of this test depends on the accuracy of model assumptions, with the detection rate being most sensitive to errors in the assumed rotational period, while the false positive rate is most sensitive to errors in the assumed band-dependent phase functions.

We study a string-motivated theoretical prior on the quintessential dark energy model with exponential potential, \( V(\phi) = V_0 e^{-\lambda \phi} \), allowing for non-zero spatial curvature. First, we formulate the corresponding dynamical system and investigate its cosmological evolution numerically, illustrating the phase-space behaviour and the influence of curvature on the background dynamics. In open universes (\( \Omega_k > 0 \)), it has been suggested that a curvature-related fixed point may support accelerated expansion even for relatively steep potentials compatible with swampland considerations. Next, we explicitly impose swampland-motivated priors on the slope parameter $\lambda$, restricting it to values consistent with the de Sitter conjecture that excludes the (curved) $\Lambda$CDM limit. Furthermore, we restrict our considerations to the range of field excursion that is consistent with the swampland distance conjecture. Our primary interest is the possibility that such theoretically-motivated priors may shift values of cosmological parameters inferred by observational data, compared with the standard analysis based on theory-agnostic priors such as a sufficiently wide flat prior. We examine this possibility using a combination of Planck CMB data, DESI BAO measurements, and recent Type Ia supernova samples, performing a Bayesian inference of the model parameters. Our analysis indicates that the swampland-motivated prior mildly shifts the values of $\Omega_k$.

We present the results of an observation of the broad-line radio galaxy 3C 111 with the X-Ray Imaging and Spectroscopy Mission (XRISM). The unprecedentedly high spectral resolution of XRISM/Resolve revealed that the Fe K$\beta$ emission line is significantly weaker than expected from the Fe K$\alpha$ line. This feature may be explained by a blueshifted absorption line from an ionized wind overlapping the Fe K$\beta$ energy. The inferred outflow velocity is 4600 km s$^{-1}$ or 17200 km s$^{-1}$, depending on whether the absorption feature is identified as Fe XXVI or Fe XXV, with the current data unable to distinguish between the two interpretations. Based on spectral modeling, the kinetic power of the wind is estimated to lie in the range 10$^{41}$-10$^{44}$ erg s$^{-1}$, although this estimate is subject to large uncertainties primarily due to the poorly constrained location of the absorber. The inferred wind power is smaller than the jet power of 3C 111 ($\sim 3\times 10^{44}$ erg s$^{-1}$), and is broadly consistent with theoretical expectations that the jet power exceeds that of disk winds.

Solar irradiance measurements are limited to the last few decades, requiring reconstructions to assess solar variability on longer timescales and its impact on Earth's climate. We present the first physics-based reconstruction of total solar irradiance (TSI) at annual resolution over the last three millennia. The reconstruction is obtained by extending the SATIRE-T model beyond the telescopic era using recently published, annually resolved sunspot number series derived from cosmogenic isotope records. This yields a continuous, physics-based TSI record extending from the satellite era back over the last three millennia, with annual resolution throughout the pre-telescopic period. Over the full three-millennia interval, the reconstructed TSI exhibits a maximum difference of $1.04_{-0.2}^{+0.14}\,\mathrm{W\,m^{-2}}$, defined as the difference between the maximum and minimum of the 50-yr running mean values.

Detecting the redshifted global 21-cm signal from the cosmic dawn (CD) remains a major challenge due to strong terrestrial Radio Frequency Interference (RFI), particularly dominated by Frequency Modulation (FM) transmissions in the 88-110 MHz range. While observations from the radio-quiet lunar farside are ideal, Earth orbit offers an intermediate and simpler alternative that may mitigate several limitations of ground-based experiments. We assess the feasibility of detecting the global 21-cm signal from Earth orbit by quantifying FM-based RFI at different altitudes and orbital configurations. We present STARFIRE-2 (Simulation of TerrestriAl Radio Frequency Interference in oRbits around Earth -- 2), an algorithm that estimates FM transmitter-based RFI intercepted by radiometers in orbit. The model constructs a global FM transmitter database and compensates for incomplete data using statistical methods. Using PRATUSH as the reference experiment, we simulate a range of orbital scenarios to identify configurations that minimize RFI and optimize sensitivity for global 21-cm detection. The algorithm can also be adapted for other experiments. Simulations indicate that conducting such an experiment from Earth orbit is feasible for a thermal noise limited instrument placed in a low-Earth, near-polar orbit. Mock sky observations further demonstrate that most theoretically plausible cosmic dawn 21-cm signals can be recovered with high confidence under these optimized orbital conditions.

We use a three-dimensional model to calculate steady-state climates at various intervals in Earth's future, across a parameter space of increasing insolation and decreasing CO$_2$ mixing ratio. Comparison with prior results shows an overestimation of warming by one-dimensional models when solar constant is increased and CO$_2$ mixing ratio is fixed. We consider two future trajectories as limiting cases: strong weathering, in which surface temperature remains constant but CO$_2$ is drawn down; and weak weathering, in which CO$_2$ remains constant and surface temperature increases. Under strong weathering, we find the conventional 10 ppm CO$_2$ starvation limit for C4 photosynthesis occurs at 1.35 Gyr; however, we suggest that crassulacean acid metabolism (CAM) photosynthesis could persist below this limit and note that aquatic macrophytes can utilize dissolved bicarbonate if atmospheric CO$_2$ is low. If we take the CO$_2$ starvation limit at 1 ppm instead, then the vegetative biosphere could continue until 1.84 Gyr. Thermal limits apply instead under weak weathering, in which Earth would be too hot for most land plants at 1.68 Gyr (>323 K) and too hot for all land plants (>338 K) at 1.87 Gyr. These lifetimes approach the moist and runaway greenhouse limits for Earth. We discuss other possible mechanisms for extending the lifetime of Earth's biosphere, noting that both technological intervention and evolutionary processes could enable life to adapt to a brightening sun.

The ExtragaLactic alErt Pipeline for Hostless AstroNomical Transients (ELEPHANT), has been developed as a framework for filtering hostless candidates, in real time alert systems, and implemented as a filter in the Fink broker. ELEPHANT works on stamps and requires minimal information, thus allowing for fast identification of extragalactic transient events. In this work we evaluate the performance of the ELEPHANT pipeline by systematically analyzing flagged hostless candidates identified between 1 September 2023 and 31 December 2025. Our goal is to quantifying its accuracy and identify dominant sources of contamination. For each flagged candidate we collected additional information from multiple catalogues and archival repositories. We further examined their light-curve evolution and astrometric consistency (coordinate dispersion over time) to refine source classification. Results. Out of 877 flagged events, 67 are confidently confirmed as genuinely hostless candidates, with no detectable host galaxy in either existing catalogues or archival imaging, representing a high-purity sample of intrinsically faint or absent hosts. Additional 51 events are linked to visually identifiable hosts that are entirely absent from both catalogues and ZTF stamps. For the confirmed hostless subset, the inferred upper limits on host-galaxy absolute magnitudes extend well below the luminosity range of typical dwarf galaxies. The pipeline showed an overall accuracy of 0.84, with the majority of the classified flagged events being Type Ia supernovae, and the second most detected class being Type I superluminous supernova. ELEPHANT has been adapted to deal with the Rubin alert stream and has been processing its alerts since February 2026.

The Lyman-$\alpha$ forest refers to the series of absorption features observed in the spectra of distant quasars that are produced by neutral hydrogen in the intergalactic medium. Observed over a wide range of redshifts with both ground- and space-based facilities, the Lyman-$\alpha$ forest provides a powerful probe of numerous physical processes, including the thermal state of intergalactic gas, the timing and topology of cosmic reionization, the expansion history of the Universe, the growth of cosmic structure, massive neutrinos, and the nature of dark matter. This chapter reviews the transformative impact of machine-learning techniques on Lyman-$\alpha$ forest analyses, particularly in overcoming the computational and methodological limitations of traditional approaches. We discuss a broad range of machine-learning applications, including the automated characterization of individual absorption systems, improved reconstruction of the intrinsic quasar continuum, accelerated emulation of hydrodynamical simulations, and the development of simulation-based analyses, field-level inference methods, and three-dimensional reconstruction techniques for the underlying matter density field. As current and upcoming surveys continue to increase both the volume and precision of Lyman-$\alpha$ forest observations, ML-driven pipelines are becoming an essential component of next-generation astrophysical and cosmological analyses.

Supermassive black holes power Active Galactic Nuclei (AGN), injecting energy that regulates accretion and shapes host galaxies. We investigate the morphology, excitation, and kinematics of molecular hydrogen (H2) in the inner circumnuclear disk of Centaurus A, the nearest radio galaxy. We present JWST/MIRI MRS integral-field spectroscopy of the central 170x100 pc2 at 0.3"-0.7" (5-12 pc) resolution, focusing on pure rotational H2 lines. The spectra show strong nuclear continuum and bright H2 emission from S(1) to S(8), including the first S(8) detection in Centaurus A. Optically thin nuclear lines enable maps of temperature, column density, and ortho-to-para ratio from spaxel-level excitation-diagram fitting. Warm H2 shows a complex morphology, dominating the central region where CO emission is weak or undetected. Low-excitation H2 lines trace an inhomogeneous ring with a 20-pc-radius cavity aligned with the jet's near side, suggesting that the jet affects the morphology of the molecular disk. Higher-excitation lines form filamentary structures around the AGN. Kinematics are rotational with an S-shaped distortion, indicating non-circular motions or a warped disk. A coherent, low-dispersion (70 km/s) streamer spirals inward. A power-law temperature distribution yields a warm (100-2000 K) H2 mass of (5.6+/-1.4)e5 Msun and a dynamical mass of 5e8 Msun within 100 pc. Shock excitation is supported by enhanced H2/continuum and H2/PAH ratios, elevated [Ne III]/[Ne II], and sub-equilibrium ortho-to-para ratios (1.6-2.4). Turbulent dissipation can balance H2 cooling and likely dominates heating beyond 30 pc. In the inner 100 pc of Centaurus A, AGN feeding and feedback are linked: shocks excite H2, regulate the gas temperature, and prevent cooling below 100 K, explaining the weak CO emission and lack of a massive outflow. These shocks may drive angular momentum loss and help fuel the nucleus.

Massive galaxies experience complex evolutionary processes, including mergers and gas accretion, which can disrupt the chemical equilibrium between their stellar and gaseous components. Using the IllustrisTNG (TNG100) simulation at $z=0$, we investigated the prevalence and physical properties of such chemically decoupled systems within the massive star-forming galaxy population. We identify a substantial subpopulation ($\sim 31.5\%$ of the sample) that exhibits systematic stellar-gas decoupling, characterised by a metal-rich stellar component coexisting with a diluted gas reservoir. These non-equilibrium galaxies are closely linked to recent merger activity and partial quenching, and display systematically suppressed star-formation rates and reduced gas fractions, consistent with a transitional evolutionary phase. We then examined the implications of this phase for galaxy-scale habitability prescriptions by applying a terrestrial planet abundance proxy that combines stellar mass, gas-phase metallicity, and the rate of sterilising events. Despite their diluted gas reservoirs, non-equilibrium galaxies dominate the high end of the inferred present-day habitability proxy distribution, exceeding equilibrium systems by more than an order of magnitude. We interpret this as a habitability trade-off: the same gas dilution and quenching processes that reduce the efficiency of future terrestrial planet formation simultaneously create a transient phase of suppressed radiation hazards for existing planets. The Andromeda galaxy (M31) shows qualitative similarities to this chemically decoupled population, suggesting that galaxies exiting their peak star-forming phase represent a distinct and highly relevant demographic for galaxy-scale habitability. Galactic habitability is therefore intrinsically time-dependent.

Pulsar timing is a foundational part of pulsar research to triage the most interesting systems and to characterise properties (rotational or otherwise) of the population of these extreme objects. Due to the efficiency of a number of sensitive and/or wide-field surveys in recent years, the number of new pulsars discoveries is growing year-on-year, and most of these lack even basic timing parameter measurements. This work aims to demonstrate the capabilities of international Low Frequency Array (LOAFR) stations operating as single telescopes to follow-up, time and characterise these sources, offering new insight into the emission properties of these neutron stars, and support efforts to build timing models for these sources. Between 2020 and 2023 we used the local-mode allocation of the Irish LOFAR station to follow-up 33 pulsar candidates announced from various surveys at different observing frequencies to determine if an international LOFAR station has sufficient sensitivity to detect and time these sources. From the 33 pulsars selected, 22 pulsars were detected and 17 were selected for long-term monitoring across 590 hours of observing time. This has resulted in coherent timing solutions for all of these sources at 150 MHz -- 7 of these have never had any reported timing solutions, the remaining 10 solutions agree well with announcements from others since the beginning of our project. For a fraction of sources announced by surveys each year, the 14 international LOFAR stations are well placed to follow-up survey candidates for long-term pulsar monitoring beyond the standard timing campaigns performed at these telescopes to date, reducing the pressure on observing time availability at these observatories, and enabling the full scientific potential of these pulsars to be realised.

Internal magnetic fields have recently been detected and measured in the radiative core of red giant stars using asteroseismology. Being one of red giant stars progenitors and exhibiting high radial order gravity modes, $\gamma$ Doradus stars are also good candidates to hold detectable magnetic fields in their radiative envelope. We aim to detect internal magnetic field in a rapidly rotating $\gamma$ Doradus star for the first time, through its influence on the propagation of Kelvin gravito-inertial modes. We used the seismic variable $\delta K_a$, defined as a combination of Kelvin modes frequencies, which is sensible to the presence of a magnetic field. Following the detection, we carried out a modelling of the star oscillation spectrum considering a magnetic component following a Bayesian approach. We found a magnetic signature into the radiative envelope of KIC 2309579. If located just above the core, in the layers that were previously convective, the magnetic field would reach $\sim$ 4 kG.

The dynamical role of the magnetic field in the star formation process is tightly linked to the coupling between matter and the field. This coupling is due to the interaction between ions and neutrals in the partially ionized interstellar medium. When the ionization degree drops in the dense environment of prestellar cores, the magnetic field and the matter may decouple, leading to differences in the infalling velocities of ions and neutrals known as ambipolar diffusion. The onset of gravitational collapse resulting from ion-neutral decoupling has never been observed. The aim of this work is to search for signatures of ambipolar diffusion within a prestellar core. We observed the deuterated N$_2$D$^+$ ion and the neutral para-NH$_2$D species towards the prototypical prestellar core L1544. These two species are ideal tracers of prestellar cores sampling the same high densities in the core interior. We compared the velocity centroid and linewidth maps of the ion-neutral pair. We find a mean ion-neutral velocity difference of $\sim$0.05 km/s towards the core. By comparing with predictions from self-consistent calculations of the ambipolar resistivity including dust grain growth, we interpret the observed ion-neutral velocity difference in L1544 as a signature of ambipolar diffusion. We do not detect a significant ion-neutral linewidth difference that may be attributed to the subsonic infall motions of the gas in L1544 and geometrical effects in the presence of inclination. These results emphasize the role of dust grain growth at the prestellar core stage in setting the ambipolar resistivity and regulating the dynamical evolution of dense cores towards their collapse into protostars. We propose that measurements of ion-neutral drift velocities provide new constraints on the total magnetic field strength and the dust size distribution within prestellar cores.

$\xi$ Tau is one of the most compact multiple stellar systems, which is sufficiently close (67 pc) to be constrained by all kinds of observations. To better constrain its current configuration, we utilized new observational data: (i) photometry from TESS and astrometry from WDS, and (ii) our own photometry from the MOST spacecraft and spectroscopy from the CTIO observatory. [...] Given the hierarchical architecture of $\xi$ Tau, ((Aa+Ab)+B)+C, we detected the orbital evolution on all time scales. Oscillations of periods $P$ occur on the shortest, orbital time scales ($P_1$, $P_2$); the variation of eccentricity $e_1$ is from 0 to 0.008, and of $e_2$ from 0.202 to 0.207, respectively. Oscillations of projected $i$, $\Omega$ are coupled, and occur on the secular time scale of about 7000 d. The inclination $i_1$ of the inner, eclipsing pair (Aa+Ab) changes from $86.1^\circ$ to $87.1^\circ$, which is clearly manifested in eclipse depths. There is also a long-term trend due to the outer orbit ($P_3 \doteq 18900\,{\rm d}$), with a perihelion passage (a `bump') of component C, which is manifested in radial velocities. The mutual inclinations between the three orbital planes, ${\simeq}\,0.5^\circ$ and $71^\circ$, are very different. Long-term stability is ensured by suppressing Kozai oscillations due to the fast precession rate $\dot\omega_2$. The best model requires tidal dissipation in the inner binary (with the time lag of ${\sim}100\,{\rm s}$) and five components, where component C is a binary (Ca+Cb). Although the masses of the three components ($2.27$, $2.15$, $3.78\,M_\odot$) are now constrained to within 1%, the suspected binary (Ca+Cb), offset by $600\,{\rm mas}$, should be better characterized. A key question remains whether this bright stellar system contains additional dwarf or exoplanetary components with low masses. Continuing monitoring of $\xi$ Tau is highly desirable.

Iron fluorescence is produced by the irradiation of the solar photosphere by coronal X-rays during flares. This study presents the first comprehensive analysis of iron K$\alpha$ fluorescence characteristics in 47 X-class flares observed during the inaugural year of the Solar Low Energy X-ray Spectrometer (SoLEXS) on board India's Aditya-L1 mission. Leveraging the capability of modern silicon drift detectors (SDDs) for simultaneous broadband continuum and line measurements, the Fe K$\alpha$ flux and the exciting flux ($F_{>7.11 \text{ keV}}$) are quantified for each event, establishing a well-determined relationship between them across the sample. The derived fluorescence efficiencies exhibit a center-to-limb dependence consistent with theoretical models, offering a potential diagnostic to probe coronal source heights and viewing geometries. While statistical uncertainties currently limit the ability to track rapid height variations on short timescales, the mean fluorescence efficiency during the flare peak provides a potential constraint on the effective coronal source height. However, this derivation remains subject to a fundamental degeneracy, as the estimated source height cannot be uniquely determined without assuming a specific value for the photospheric iron abundance. These findings demonstrate that SDDs, despite having lower spectral resolution than traditional crystal spectrometers, provide a new diagnostic for the solar iron fluorescence observations.

We show that the morphology of the core-collapse supernova (CCSN) remnant RCW 103 is very similar to the morphology of the brightest regions in the recently released JWST IR images of the jet-shaped planetary nebula (PN) PMR 1, and conclude that two energetic pairs of jets shaped RCW 103, compatible with the jittering-jets explosion mechanism (JJEM). The PN PMR 1 IR image exhibits two opposite, large, and prominent ears with a narrow, faint region connecting them through the center, a pipe. Observations and simulations have shown that a pair of jets inflates such a pair of ears in PNe. The brightest regions of PN PMR 1 form two clumpy sectors, each shaped like a wide pizza slice, with a faint region between them; the CCSN remnant RCW 103 has a very similar morphology. We identify two shells in the X-ray image of RCW 103 and suggest that two close pairs of energetic jets shaped this CCSN remnant. We find only traces of two of the four expected ears in RCW 103. The ears in RCW 103 were already dispersed and are very faint. Deeper X-ray observations might detect them. Such energetically misaligned pairs of jets are compatible with the JJEM, which predicts that a few to about 20 pairs of jets are responsible for most CCSN explosions.

We explore the observational signatures of flybys in scattered light images of protostellar discs. The warps are modelled using 1D warp propagation theory coupled to a fast radiative transfer code that simulates the shadows induced. We consider two scenarios, namely a flyby in a plane orthogonal to, and at an angle with, the disc plane. In both models the outer disc becomes warped (leading to a broad shadow in the outer disc) and the warp wave propagates back and forth (causing the shadow to oscillate). We find that the inner disc, although tilted, is not warped and is therefore not shadowed. For a low viscosity disc ($\alpha=10^{-4}$) the warp lasts for most of the disc's lifetime ($\tau \sim 10^6\,$years), and for $50\%$ of the time the azimuthal variance of the surface brightness from the scattered light images, $\sigma^2$, is above $0.01$, meaning that the shadow in the disc is significant. We find that a significant fraction of discs in nearby star forming regions should have undergone a flyby sufficient to induce an observable warp, and that surveys of shadowed discs could provide a valuable probe of disc viscosity.

Measurements from the Dark Energy Survey (DES) Year 3 data have shown that the Weyl potential -- the sum of the spatial and temporal distortions of the geometry -- evolves more slowly than predicted by General Relativity, assuming a $\Lambda$CDM background evolution. An evolving dark energy with a phantom crossing, as preferred by the Dark Energy Spectroscopic Instrument (DESI), is expected to decrease the depth of the gravitational potentials through a stronger acceleration than in $\Lambda$CDM, potentially solving the tension with General Relativity. In this paper, we show that $w_0w_a$CDM models indeed reduce the tension with respect to $\Lambda$CDM, down to a level of $1.6-2.2\sigma$, depending on the treatment of CMB lensing. This reduction is not due to an increase in the Weyl potential's uncertainties, but truly to the impact of the evolving background on the theoretical predictions in General Relativity. More data are needed to robustly determine if evolving dark energy fully explains the low value of the Weyl potential at intermediate redshifts, or if modifications of gravity or interactions in the dark sector are needed, which could simultaneously stabilize the phantom crossing indicated by DESI.

We model the solar radial velocity (RV) signal induced by faculae, the dominant contributor to RV variability in Sun-like stars. We use a representative case of a facular patch transiting the visible solar disk as the Sun rotates to disentangle various physical effects contributing to the RV signal. Our approach is based on 3D radiative magnetohydrodynamic (MHD) simulations of the solar photosphere and upper convection zone with the MURaM code and spectral synthesis with the MPS-ATLAS code. We show that the faculae-induced RV strongly depends on the facular position on the solar disk. Near disk centre, facular magnetic fields inhibit the convective blueshift and thus produce a relative redshift of the solar spectrum. Surprisingly, when located closer to the limb, namely at heliocentric angles greater than about $60^\circ$, faculae produce a relative blueshift. This transition from redshift to blueshift is caused by the effect of magnetic fields on horizontal flows, which dominate the signal near the limb, and on the visibility of these flows. In combination with solar rotation, this centre-to-limb dependence of the facular effect leads to a complex RV profile during the facular transit and, in particular, to a phase lag between the maximum of the RV signal and the facular crossing of the central meridian. We further show that, in contrast to stellar reflex motion, the facular signal strongly depends on the spectral line in which it is measured.

Particle-accelerating colliding-wind binaries (PACWBs) are multiple systems of massive stars in which strong stellar winds collide, accelerating particles to relativistic energies. This population of relativistic particles emits NT radiation, including synchrotron radiation in the radio domain. This emission is expected to be linearly polarized, but the polarization signature has not yet been detected for a PACWB. Our objective is to quantify the linear polarization of synchrotron radiation in two well-known PACWBs and to interpret our measurements within the framework of the physics of these specific NT emitters. We observed the PACWBs WR 147 and HD 167971 with the Very Large Array (VLA) radio interferometer in the frequency bands L and C (1-2 and 4-8 GHz, respectively), where synchrotron emission is expected to be more prominent. We performed polarization calibration and analyzed the resulting Stokes maps. We did not detect any polarization signature for either of the two targets in either of the two bands, even when considering narrower bands to mitigate the effect of bandpass depolarization. The most conservative upper limit on the polarization degree is on the order of 1% for both targets. The lack of linear polarization for the two targets is likely attributable to a combination of effects, including the turbulent nature of the magnetic field in the synchrotron-emitting region, and depolarization processes based on Faraday rotation that are certainly active in these sources. Their complex geometry, unresolved by the VLA at these frequencies, is most likely to lead to beam depolarization. We emphasize that, in contrast to other canonical synchrotron sources, PACWBs are also subject to thermal dilution. This is especially relevant for systems with stars whose winds are strong enough to contribute copiously to thermal emission, such as those harboring a Wolf-Rayet component.

Statistical assessment of stellar parameters enables validation and improvements in theoretical models. We compiled a sample of 85 transiting stellar and substellar companions, with masses ranging from $\sim$13-100 $M_\mathrm{Jup}$. We focus on analyzing 50 transiting companions with robust ages and model constraints, and evaluate the degree of radius inflation versus mass, separation, equilibrium temperature, and metallicity. Our evaluation of the differences between measured and model radii indicates an $8.7\pm1.9$% radius inflation for the full sample, at $4.6\sigma$ discrepancy, validating the existence of radius inflation at a population level in transiting brown dwarfs. For brown dwarfs at separations $\leq 0.05$ au, we find an even higher radius inflation, with a median inflation of $16\pm6$% at $2.7\sigma$, and the inflation decreases toward wider separations, likely due to reduced stellar irradiation. Finally, we provide our compilation for the community to use.

We assess the dynamical feasibility of redirecting small volatile-bearing trans-Neptunian objects (TNOs) onto Mars-impacting orbits using continuous low-thrust propulsion and a single gravity-assist encounter. The study considers two representative dynamical classes: classical Kuiper Belt--like and Scattered Disk--like initial orbits, and determines the minimum characteristic velocity increment $\Delta V$ required to drive the objects onto a Mars-impacting trajectory within a specified transfer time $\Delta T$. The dynamics is modelled in the two-body problem with a fixed maximum low thrust included, allowing the computed $\Delta V$ to represent a dynamical lower bound independent of specific propulsion-technical implementation. Three trajectory classes are investigated: (i) inward spiral transfer, (ii) time-dependent thrust-direction steering optimized via global evolutionary algorithms, and (iii) hybrid transfers combining low thrust with a single Neptune flyby. Pure spiral trajectories yield very high velocity expenditures ($\Delta V \gtrsim 22~\mathrm{km~s^{-1}}$) and millennia durations, confirming that monotonic inward migration is dynamically inefficient for TNO redirection. In contrast, optimized steering strategies systematically increase orbital eccentricity and achieve Mars-impacting geometries with $\Delta V \approx 2.5$--$3.2~\mathrm{km~s^{-1}}$ over 380--540 yr timescales. A single Neptune encounter further reduces the total $\Delta V$ in favourable cases, with minimum values falling below those of direct optimized transfers. These results establish a quantitative lower bound on the energy cost of importing volatiles from the outer Solar System to Mars, showing that controlled redirection is feasible under modest $\Delta V$ budgets when target bodies are chosen from favourable regions of orbital phase space.

Dwarf galaxies in the Local Group offer a way to test dark matter (DM) models against stellar kinematic data. In this work, we study degenerate fermionic DM in two cases: the standard non-interacting Fermi gas, and an interacting degenerate DM fluid described by a phenomenological equation of state motivated by interacting Fermi systems. These interactions modify the compressibility of the DM fluid and, in some regions of parameter space, lead to mechanically unstable branches that must be treated through a Maxwell construction. We solve the corresponding non-relativistic hydrostatic equations consistently and compute the line-of-sight velocity-dispersion profiles using the spherical Jeans equation. We then perform MCMC fits to eight classical Milky Way dwarf spheroidal galaxies. The data favor DM fermion masses in the range $100$--$300\,{\rm eV}$. We find that the interacting and non-interacting equations of state give broadly similar posterior distributions for the fermion mass, central density, and stellar anisotropy. Current data therefore do not strongly prefer an interacting equation of state over the free degenerate Fermi-gas, thereby excluding large deviations from the non-interacting limit.

In a previous article, we obtained the first-ever list of astrometric binary asteroid candidates. Some of these candidates have now been confirmed. In that previous work, however, the details of the statistical methods were not provided. Our first aim is to provide methodological details and performance evaluation of the approach used for detecting binaries. Our second aim is to establish an updated list of binary asteroid candidates from Gaia FPR astrometric residuals exploration, where we account for the statistical properties of FPR data. We account for the astrometric uncertainties from FPR and we refine the statistical model of the data, which we use in MC simulation to evaluate the strength of the individual detections; we set up a trend detection method in the residuals and apply a dedicated period search algorithm; we update the statistical selection process to build the list of candidates; we set up a method for detecting objects in multiple windows of consecutive observation; we refine the method for confidence interval estimation of these parameters and we better constrain the physical parameter selection. We detect 343 binary asteroid candidates corresponding to 410 windows of consecutive observations in the astrometric data. We show that in noise-only control simulations, the typical number of detections is 88% lower than in the FPR data. We also detect 9 known binaries, 25 candidates overlapping with the Pan-STARSS survey and 99 overlapping with our previous binary search in DR3. Finally, we report the detection of 45 objects with trends in residuals suggestive of wide binary systems. Our results and analyses demonstrate that although detecting binary asteroids is a difficult problem due to their low signal level, the proposed method is likely to provide a reliable list of detections, including systems poorly accessible to conventional techniques.

The behavior of magnetic field lines in a turbulent plasma is a key property of the medium, with important consequences for plasma dynamics and charged-particle transport. We study the diffusion properties of magnetic field lines in synthetic turbulence featuring different polarization configurations for the magnetic perturbations, as prescribed by the existing magnetohydrodynamic modes (namely, Alfvénic and magnetosonic). These turbulent field realizations are then compared with the isotropic (or, random) polarization case, which is the one typically adopted in the literature. We construct polarized synthetic turbulence simulations and study the properties of field lines through the running diffusion coefficient. Our key findings can be summarized as follow: (i) field line wandering is strongly dependent on polarization configurations, (ii) we unveil that the sub-diffusive phase of field line is highly dependent on the polarization and is well reproduced by theoretical predictions based on Corrsin's hypothesis in the low turbulence level regime, (iii) in particular the scaling of the asymptotic diffusion coefficient in magnetosonic-like polarization is $(\delta B/B)^4$ at odd with the $(\delta B/B)^2$ scaling found in the quasi-linear regime for random polarization, (iv) interestingly we note that the subdiffusive phase of field line transport in the magnetosonic-like polarization follows closely the one observed in recent high resolution MHD turbulence simulations, we end giving a word of caution when FL transport is investigated in such simulations.

Cosmic rays (CRs) are a ubiquitous non-thermal component of the interstellar medium (ISM). A data-driven three-dimensional (3D) map of their distribution is essential for understanding CR transport and constraining the spatial distribution of their sources. In this work, we reconstructed the 3D spatial distribution of the Galactic cosmic-ray proton (CRp) density. We model the diffuse gamma-ray emission arising from inelastic hadronic interactions between CRps and interstellar gas. Using a map of dust-correlated diffuse gamma-ray emission based on ten years of Fermi-LAT observations together with a three-dimensional gas density model, we infer the spatial CRp distribution through a morphological matching approach. The logarithmic CRp density field is described by a Gaussian process defined on a spherical-times-radial grid, while both the field and its correlation structure are inferred simultaneously using Iterative Charted Refinement. The posterior distribution of the reconstructed 3D CRp density field is approximated using geometric variational inference. The reconstructed CRp density exhibits a smooth but spatially structured distribution with a limited dynamical range across the Galactic disk. We find a moderate enhancement of the CRp density toward the inner Galaxy. The inferred normalization at the Solar position is consistent with local CR measurements by the AMS-02 instrument.

We employ a Minimum Spanning Tree (MST) approach to characterize the spatial distribution and mass segregation of compact millimeter continuum sources within the Central Molecular Zone (CMZ) of the Milky Way. We use a modified form of the complete version of the 1.3 mm dust continuum catalog from the CMZoom survey, which identifies 685 compact sources with typical effective radii of $\sim0.1$ pc. For 22 of 35 CMZ clouds, we calculate the thermal and turbulent Jeans lengths and masses, and determine that compact source separations, as well as compact source masses, are more consistent with thermal fragmentation at $\sim0.1$ pc size scales. We construct the mass segregation ratios for compact sources in 17 CMZ clouds and determine that 5 of the analyzed clouds display some form of mass segregation ($\Lambda_{MSR} > 1.5$), while the remaining clouds show either inverse mass segregation ($\Lambda_{MSR} < 0.75$), or no evidence of true mass segregation ($0.75 < \Lambda_{MSR} < 1.5$). Finally, we find that although some actively star-forming clouds do exhibit mass segregation, other similarly active clouds do not, indicating an unclear correlation with evolutionary stage for star forming clouds in the CMZ, given the current available data.

The interior crust and much of the liquid core of neutron stars is believed to be a quantum liquid mixture of neutron and proton superfluids and a relativistic electron liquid. Quantized vortices in the neutron superfluid and quantized flux lines in the proton superconductor are topological defects of these hadronic condensates. I consider the formation of the superfluid state in young neutron stars under non-equilibrium conditions imposed by the neutrino cooling rate. The nonequilibrium phase transition implies that the onset of superfluidity is accompanied by the generation of quantized vortices based on the mechanism envisioned by Kibble in the context cosmic string formation in an evolutionary models of an expanding universe, and further developed by Zurek for nonequilibrium phase transitions in quantum liquids such as \Hefour. I discuss the Kibble-Zurek mechanism (KZM) and scaling relations for topological defect formation starting from the Cooper pair fluctuation propagator for temperatures approaching $T_c$. I then calculate the predicted vortex densities based on Urca and modified Urca cooling mechanisms in the cores of neutron stars for several models of the superfluid gap and transition temperature of the interior neutron superfluid. In all cases studied the KZM leads to a large density of topological defects in the condensate phase, which in 3D form a random network of vortex lines and loops, i.e. the generation of quantum turbulence.

We study the mass function of primordial black holes (PBHs) within the excursion-set theory, in which the response of the stochastic density contrast to the variation of the coarse-graining scale is described by colored noises. For several window functions often used in the literature, we investigate how this choice affects the formation probability as well as the resultant mass function of PBHs. It is found that the low-mass tail of the mass function differs from the one predicted from Carr's formula. The difference comes from the prevalence of correlated noises, by which degeneracy of the formation probabilities ceases to exist. Nevertheless, Carr's formula still provides a practical estimation in the vicinity of the characteristic mass scale, as long as a smooth window function in Fourier space is used.

Using temperature retrievals from Akatsuki radio occultation measurements, we characterize gravity wave activity as a function of vertical wavenumber and altitude and, for the first time, estimate the absolute horizontal momentum fluxes and the magnitude of the associated gravity wave drag (i.e., wave acceleration), which quantify the potential effects of these waves in the Venusian middle atmosphere between 40--95 km. Observed temperature perturbations, which are indicative of atmospheric gravity wave activity, reach amplitudes of approximately $\pm$10 K, and significant momentum flux (10--30 m$^2$ s$^{-2}$) and wave drag (0.003--0.03 m s$^{-2}$) are detected across all analyzed profiles. The inferred wave drag represents a lower bound on the total gravity wave-induced drag in the Venusian atmosphere. Momentum flux tends to increase exponentially with altitude below approximately 50--60 km, then peaks and attenuates at higher altitudes. Wave drag becomes prominent where momentum flux begins to decrease, which is a consequence of wave dissipation. Both quantities exhibit multiple altitude-localized maxima, which is consistent with upward wave propagation followed by dissipation at different altitudes for different vertical wavelengths. Damping due to gravity wave nonlinear interactions is likely to play the major role in limiting the growth of wave amplitudes and fluxes with height. These features are observed across a range of latitudes and local times. Overall, the results provide observational constraints on gravity wave momentum transport and dissipation in the Venusian middle atmosphere and could guide numerical models in their effort to quantify wave-mean flow interactions in Venus's atmosphere.

YZ Ret (Nova Reticuli 2020) is the first VY Scl-type nova-like variable observed to undergo a classical nova eruption. Following the outburst, timing analysis of 20-s cadence TESS data revealed a periodicity at approximately 42 s, suggesting a possible classification as a fast-spinning Intermediate Polar. To definitively identify the nature of this modulation, we performed a multi-instrument timing analysis using high-speed ground-based photometry Zorro/Gemini South (1 s cadence) and the South African Astronomical Observatory (5 s cadence) alongside TESS Sector 97 observations. Our ground-based data reveal a highly coherent period of 37.69131 +- 0.00001 s, which we identify as the true rotation period of the white dwarf. We demonstrate that the apparent 42.61 s signal in the TESS data is a Nyquist alias of this fundamental frequency. Furthermore, the signal amplitude in the TESS data is suppressed by a factor of ~0.6 relative to the Gemini observations, a result consistent with the theoretical sinc-function damping expected for a 20-s integration time. The extreme coherence and long-term stability of the 37.69131 s signal rule out transient phenomena such as dwarf nova oscillations or non-radial pulsations. We conclude that YZ Ret hosts a fast-spinning magnetic white dwarf in an Intermediate Polar configuration. This discovery implies that mass loss during the nova eruption was likely driven by a fast magnetic rotator wind and provides a physical explanation for the missing supersoft X-ray phase, suggesting that nearly the entire accreted envelope was exhausted, promptly quenching the nuclear burning.

APOGEE and Gaia data have revealed that the Milky Way's structure appears to have evolved through three distinct kinematic phases. First, at early cosmic times, the Milky Way was a disordered protogalaxy, which subsequently "spun up" to a second kinematic phase marked by star formation occurring in a rotating, thick stellar disk. The thick disk phase later transitioned to a third (and final) phase with star formation occurring in a cold, thin stellar disk. In this paper, we use a suite of FIRE-2 simulations of Milky Way-mass galaxies to demonstrate that the same three phases arise in our cosmological zoom-in simulations, and study their physical origin. In all of our galaxies, the early disordered phase occurs when the rate of cool gas ($T \leq 10^4$ K) converting into stars is low, the star formation rate is bursty, and the baryonic mass "sloshes" within the host potential with respect to the center of mass motion. The gas in the galaxy begins to spin coherently after the sloshing phase ends, followed by the spin-up of young stars. The central potential of the galaxy is least concentrated just prior to gas spin-up. This second, thick disk phase coincides with a period when the rate of cool gas converting into stars is highest, even though the star formation rate remains bursty in this phase. The final transition to the thin disk phase occurs when the inner circumgalactic medium virializes. The thin disk phase is associated with a time of steady star formation and intermediate rates of cool gas converting into stars. Mergers do not appear to play a defining role in driving transitions between the three phases. The condition for the formation of a thick disk appears to be fairly minimal: a stable center of mass motion. The formation of a thin disk requires more: gas must accrete slowly enough for its angular momentum to mix and become coherent prior to joining the galaxy.

We initiate the study of gravitational-wave lensing in the wave-optics regime within modified gravity. We consider a phenomenological setup in which the gravitational-wave amplitude obeys a curvature-coupled propagation equation. This framework reproduces the standard GR behaviour in the geometric-optics regime, while leading to qualitatively different infrared dynamics. In particular, the usual argument implying that the amplification factor approaches unity in the zero-frequency limit no longer applies. This is due to the persistence of curvature-induced interactions in the infrared, which modify the natural propagation basis itself. As a result, the standard Fresnel treatment ceases to be valid at sufficiently low frequency. The correct infrared regime is instead controlled by an interacting static Green function, with a finite-frequency completion provided by a partial-wave formulation. We show that this structure admits an equivalent distorted-wave interpretation, in which the curvature interaction is absorbed into a dressed reference propagation basis, while the residual lensing effect is encoded in finite-frequency phase shifts. We further demonstrate that these phenomena admit a natural interpretation in the language of scattering amplitudes. Wave-optics lensing can therefore probe propagation-level departures from GR that remain entirely invisible in geometric optics.

A method for measuring the altitude and particle size of noctilucent clouds, based on positioning and photometry from wide-angle three-color cameras, has been developed to determine the three velocity components, particle radius, and its derivative with respect to time for different cloud fragments. The updated method is applied to observational data of bright clouds during the summers of 2023-2025. Meridional motion of the cloud is found to be the principal factor driving the change in particle size. The effect of particle size evolution in the presence of a strong latitudinal temperature gradient is also studied.

Gravitational waves from merging compact binaries are sensitive to line-of-sight acceleration (LOSA) induced by a massive companion in their vicinity. Interestingly, the leading-order contributions of LOSA and residual orbital eccentricity to the Fourier phase of the inspiral waveform exhibit similar frequency dependence, raising the possibility that a small eccentricity could mimic LOSA effects in transient GW events such as GW190814. We perform Bayesian inference using the IMRPhenomXPHM waveform family as the baseline LIGO-Virgo-KAGRA waveform model, augmented with leading-order LOSA and residual eccentricity corrections while using 32 seconds of data associated with GW190814. For a LOSA-only analysis, we find no evidence for a non-zero LOSA effect in GW190814, with a Bayes factor relative to the baseline model of approximately 0.22, consistent with the findings of Hendriks et al. and in tension with the claim by Yang et al., who employed only 4 seconds of GW190814 data. In a joint analysis that includes both leading-order LOSA and eccentricity effects, we obtain informative posteriors for both parameters, with representative values a/c approximately -2.8 x 10^{-3} s^{-1} and e_0 approximately 0.11. However, the corresponding Bayes factor relative to the baseline model is approximately 0.64, suggesting that the 32-second data do not provide significant evidence for either LOSA or residual eccentricity in GW190814. Further, our Bayesian runs reveal a strong correlation between the LOSA and eccentricity parameters, indicating a significant degeneracy in their imprint on the inspiral phase. This finding is consistent with our theoretical arguments and most likely explains the non-zero parameter estimates obtained in the joint analysis.

Collisionless shocks are common in astrophysical systems and stand as sites of particle acceleration. While particles at perpendicular shocks may not return to the upstream region, at oblique shocks a fraction of energetic electrons manage to escape the shock and travel upstream. An extended region known as the electron foreshock is formed, where these reflected particles drive various instabilities that may promote electron acceleration. Here we present the first 2D3V particle-in-cell (PIC) simulations of electron-ion non-relativistic oblique shocks that explore the interaction of the foreshock with pre-existing compressive turbulence with relative amplitude of 15% based on interstellar medium estimates. We find that pre-existing turbulence influences the emergence and behavior of the whistler-wave instability, as it enhances the amplitudes of the magnetic-field fluctuations and leads to larger nonlinear structures. This impacts the dynamics of the reflected electrons, resulting in a shorter and hotter electron foreshock. At the end of our simulations, with pre-existing upstream turbulence we observe non-thermal electrons that are more numerous, reach higher energies, and carry a larger portion of the total energy.

Neutron star (NS) is one of the most promising astrophysical targets to probe non-gravitational interaction of dark matter (DM) with visible matter. Their compactness makes them an ideal object which can capture particle DM efficiently over its lifetime using the DM-nucleon scattering cross-section. If DM particles are bosonic, then the captured DM population may form a Bose-Einstein condensate at the center of the NS, increasing the DM density significantly. In this work, we study the phenomenology of such scenario with enhanced DM annihilation rate due to the increased density in a condensate. The enhanced DM annihilation makes the NS surface `hotter' than in the standard cooling scenario. We show that the annihilation rate is enhanced by a factor of $\mathcal{O}(10^{15}-10^{20})$ if DM forms a condensate, and DM with freeze-in value annihilation cross-section can heat up the NS to higher temperatures, bringing it within the reach of James Webb Space Telescope. It also allows us to probe DM-nucleon scattering cross section within the neutrino fog regime which will complement the terrestrial direct detection searches. Moreover, the enhanced annihilation from the condensate changes the lower limits on s-wave DM annihilation cross-section for capture-annihilation equilibrium and the formation of a black hole inside the NS. Finally, we show an example of a scalar DM model where such small annihilation and DM-nucleon scattering cross sections can generically arise.

Ghost-free non-local gravity is investigated with regards to its late-time dynamics. Viable solutions in this model are confronted with the observational data including the Pantheon+ catalogue of Type Ia supernovae, the Dark Energy Spectroscopic Instrument, the measurements of baryon acoustic oscillations and the Hubble parameter estimations $H(z)$. The ghost-free non-local gravity is found to be successful in these tests in comparison to the $\Lambda$CDM model and can be also comparable with the generalized exponential $F(R)$ gravity scenario. However the model encounters difficulties when the data from the above observations and the cosmic microwave background radiation data are combined. In tests with the whole set of Pantheon+, DESI, $H(z)$ and CMB data, the generalized exponential $F(R)$ model is essentially more successful. This success is related with the dynamical behavior of its effective dark energy equation of state evolving from a phantom to a quintessence phase during the late-time epoch, whereas the ghost-free non-local model demonstrates only a quintessence behavior. Hence the ghost-free non-local gravity scenario is successful only when the Pantheon+, DESI and $H(z)$ data are considered. The generalized exponential $F(R)$ model satisfies the viability conditions and in tests with all observational data including CMB surpasses the $\Lambda$CDM model in $\chi^2$ statistics and also with information criteria.

We study the dynamics of a binary orbiting a supermassive black hole (SMBH), focusing on both binary scattering in unbound orbits and eccentric von Zeipel-Lidov-Kozai (vZLK) oscillations in bound orbits. The motion is described in a local inertial frame in Kerr spacetime, where tidal effects are encoded in the Riemann curvature. For unbound (parabolic and hyperbolic) orbits, we identify four scattering regimes-adiabatic, tidally affected, chaotic, and disruptive-depending on the binary semi-major axis. As the binary becomes softer, tidal interactions near periapsis lead to strong eccentricity excitation, large changes in the orbital parameters, and eventually chaotic behavior or tidal disruption, with a sensitive dependence on the argument of periapsis. For eccentric bound (elliptic) orbits, the vZLK mechanism differs qualitatively from the standard one, although the $z$-component of the angular momentum in the local inertial frame remains approximately conserved. The evolution proceeds on a dynamical timescale and exhibits step-like changes driven by repeated periapsis passages, which can be interpreted as a sequence of scattering events. We refer to this behavior as scattering-type vZLK oscillations. The rotation of the SMBH also modifies the oscillation profiles, although its effect is less significant than the dependence on the initial orbital parameters. These results suggest a unified picture of periapsis-driven tidal dynamics in galactic nuclei.

We present measurements of K-shell x-ray emission following charge exchange of fully ionized argon with various neutral gaseous targets at small collision energies inside an electron beam ion trap. We also resolve the principal quantum number of electron capture in extreme-ultraviolet spectra from initially bare and hydrogen-like oxygen ions held in the same trap. We analyze discrepancies between these as well as previous measurements with theoretical models based on the multichannel Landau-Zener approach.

We investigate photon-axion conversion in the vicinity of rotating Kerr black holes where strong gravity traps photons on near-circular trajectories, effectively enhancing the path length. We explore the observable signatures of such a conversion near the photon region. The process, driven by ambient magnetic fields, is significantly more efficient around supermassive black holes such as M87*, since the luminosity of photons increases with the mass of the BH. By numerically evaluating photon path lengths (on which the conversion depends), we analyze how key parameters-photon frequency, axion mass, photon-axion coupling, magnetic field strength, plasma density, and black hole spin-affect the conversion probability and the resultant dimming of photon spectral luminosity. We find that the conversion is most efficient at high frequencies (X-rays and gamma rays), while the frequency window associated with efficient conversion widens with an increase in the photon-axion coupling and a decrease in the electron density and the axion mass. The magnitude of dimming of the photon spectral luminosity depends primarily on the magnetic field, the photon-axion coupling and the BH spin. Our study reveals that rotating black holes generally exhibit enhanced dimming compared to static ones. Thus, if future telescopes achieving a resolution $\sim 10^{-5}$ arcsec in the X-ray/gamma-ray band detect a dimming of the photon spectral luminosity, then they can provide interesting constraints on the axion mass and its coupling with photons.