Papers for Wednesday, Nov 12 2025

In the field of deep space radiation shielding design, traditional high-Z metals are being progressively replaced by novel low-Z materials such as hydrogenated graphene foam, polyethylene-carbon nanotube composite fibers, and boron-rich hydrogen-containing metal-organic frameworks. This transition stems from the constraints of the "gram-scale weight reduction" bottleneck. However, the mechanisms behind these materials' outstanding "lightweight performance" remain at the purely phenomenological level. To address this issue, this paper innovatively proposes a ternary coupled semi-empirical model, with "proton density" (rho_p) as the core independent variable (equivalent to electron density), establishing correlations with full absorption threshold (Eth) and proton utilization rate (eta_p). To validate the model's practicality in complex system design, we embedded it into the NSGA-II genetic algorithm (POP=20, MAXGEN=10). Under constraints of 2-5 layer structures with total thickness <=1 cm, the model's predicted optimal solutions showed an average design error of only 6.2%-8.2% compared to Geant4 heavy simulation dose results. This study provides the first quantitative physical explanation of the inherent trade-off between low-Z materials' "mass savings" and high-Z materials' "space savings." When rho_p<1 mol cm^-3, materials demonstrate extremely high proton utilization rates (eta_p reaching 60-100 MeV cm^-2 mol^-1), achieving 35%-55% mass savings. Conversely, when rho_p>1 mol cm^-3, although eta_p drops below 30 MeV cm^-2 mol^-1, its exceptionally high full absorption threshold (Eth) enables ultra-thin shielding technology. This work offers a robust, physically interpretable, and scalable design tool for multi-objective optimization of area density, thickness, and dose in deep space missions.

The Roman Galactic Plane Survey (RGPS) is a 700-hour program approved for early definition as a community-designed General Astrophysics Survey. It was selected following a proposal call for science programs that would benefit from an early community-based definition (Sanderson et al 2024). The community was invited to submit white papers and science pitches with a deadline of May 20, 2024; the Roman Galactic Plane Survey Definition Committee (RGPS-DC) first met on Sep 11, 2024. Based on the input provided, the RGPS-DC recommends a survey consisting of three elements: (1) a wide-field science element (691 sq deg, 541 hrs) covering the Galactic plane, Galactic latitude |b|<2 deg and Galactic longitude l=+50.1 deg to -79 deg (281 deg), in four filters (F129, F159, F184, and F213) with higher latitude extensions for the bulge, the Serpens South/W40 star formation region, and Carina, (2) a time-domain science element (19 sq deg , 130 hrs) of six fields, including the full Nuclear Stellar Disk (NSD) and Central Molecular Zone (CMZ), with coverage in seven filters and repeat observations in one or more filters with cadences from 11 minutes to weeks, and (3) a deep-field/spectroscopic science element (4 sq deg , 30 hrs) consisting of fifteen Roman pointings (with a wide range of extinction, diffuse emission, stellar density and population) using longer exposure times in seven filters in addition to grism and prism observations. This document summarizes the science that can be done with this survey, the process of survey definition, and details on all of the program elements.

We present a measurement of the free-streaming length of dark matter (DM) and subhalo abundance around 28 quadruple image strong lenses using observations from JWST MIRI presented in Paper III of this series. We improve on previous inferences on DM properties from lensed quasars by simultaneously reconstructing extended lensed arcs with image positions and relative magnifications (flux ratios). Our forward modeling framework generates full populations of subhalos, line-of-sight halos, and globular clusters, uses an accurate model for subhalo tidal evolution, and accounts for free-streaming effects on halo abundance and concentration. Modeling lensed arcs leads to more-precise model-predicted flux ratios, breaking covariance between subhalo abundance and the free-streaming scale parameterized by the half-mode mass $m_{\rm{hm}}$. Assuming subhalo abundance predicted by the semi-analytic model {\tt{galacticus}} (N-body simulations), we infer (Bayes factor of 10:1) $m_{\rm{hm}} < 10^{7.4} \mathrm{M}_{\odot}$ ($m_{\rm{hm}} < 10^{7.2} \mathrm{M}_{\odot}$), a 0.4 dex (0.3 dex) improvement relative to omitting lensed arcs. These bounds correspond to lower limits on thermal relic DM particle masses of $7.4$ and $8.4$ keV, respectively. Conversely, assuming DM is cold, we infer a projected mass in subhalos ($10^6 < m/M_{\odot}<10^{10.7}$) of $1.6_{-1.1}^{+2.4} \times 10^7 \ \mathrm{M}_{\odot} \ \rm{kpc^{-2}}$ at $95 \%$ confidence. This is consistent with {\tt{galacticus}} predictions ($0.6 \times 10^7 \mathrm{M}_{\odot} \ \rm{kpc^{-2}}$), but in tension with recent N-body simulations ($0.3 \times 10^7 \mathrm{M}_{\odot} \ \rm{kpc^{-2}}$). Our results are the strongest limits on WDM, and the most precise measurement of subhalo abundance around strong lenses. Further improvements will follow from the large sample of lenses to be discovered by Euclid, Rubin, and Roman.

The detection of strong Balmer breaks and absorption features in Little Red Dots (LRDs) suggests they host AGN embedded within dense gas envelopes, potentially powered by super-Eddington accretion. We present GLIMPSE-17775, a luminous ($L_{\rm bol}\sim10^{45}$ erg s$^{-1}$) LRD at $z=3.501$ behind Abell S1063 ($\mu\sim2$), observed with deep JWST/NIRCam and a $\sim$20 hr (80 hr de-lensed) NIRSpec/G395M spectrum. The data reveal 40+ emission and absorption features, including a rich forest of low-ionization FeII lines and numerous broad hydrogen recombination transitions. We use this depth to test the dense-gas interpretation through five independent diagnostics. Nearly all permitted lines show exponential wings with consistent FWHM, the signature of Thomson scattering requiring $n_e\gtrsim10^8$ cm$^{-3}$. Adopting this width yields $M_{\rm BH}\sim10^{6.7}M_\odot$, a factor of ten lower than Gaussian fits, and $\lambda_{\rm Edd}\sim1.8$. Additional diagnostics support the same picture: a pronounced Balmer break ($f_{\nu,4050}/f_{\nu,3670}=2.0\pm0.1$), enhanced HeI $\lambda7065$ and $\lambda10830$ with P-Cygni absorption, Bowen-fluorescent OI $\lambda8446$-$\lambda11290$ emission requiring Ly$\beta$ pumping, and 16 FeII lines matching fluorescence models. These features indicate a dense ($n\sim10^8$ cm$^{-3}$), partially ionized cocoon where scattering and fluorescence dominate line formation, providing strong evidence that at least some LRDs are powered by super-Eddington black-hole growth in the early Universe.

The spatial extent of the environment's impact on galaxies marks a transitional region between cluster and field galaxies. We present a data-driven method to identify this region in galaxy clusters with masses $M_{200\rm ,mean}>10^{13} M_{\odot}$ at $z = 0$. Using resolved galaxy samples from the largest simulation volume of IllustrisTNG (TNG300-1), we examine how galaxy properties vary as a function of distance to the closest cluster. We train neural networks to classify galaxies into cluster and field galaxies based on their intrinsic properties. Using this classifier, we present the first quantitative and probabilistic map of the transition region. It is represented as a broad and intrinsically scattered region near cluster outskirts, rather than a sharp physical boundary. This is the physical detection of a mixed population. In order to determine transition regions of different physical processes by training property-specific models, we categorise galaxy properties based on their underlying physics, i.e. gas, stellar, and dynamical. Changes to the dynamical properties dominate the innermost regions of the clusters of all masses. Stellar properties and gas properties, on the other hand, exhibit transitions at similar locations for low mass clusters, yet gas properties have transitions in the outermost regions for high mass clusters. These results have implications for cluster environmental studies in both simulations and observations, particularly in refining the definition of cluster boundaries while considering environmental preprocessing and how galaxies evolve under the effect of the cluster environment.

A method of obtaining bolometric corrections ($BC_{\rm V}$) from observed high-resolution, high-$S/N$ spectra is described. The method is applied to spectra of 128 stars collected from the literature with well-determined effective temperatures ($T_{\rm eff}$) with $S_\lambda(V)$ transparency profiles of Bessell and Landolt. Computed $BC_{\rm V}$ are found accurate within several milimagnitudes and the effect of different $S_\lambda(V)$ is found to be no more than 0.015 mag. Measured visual to bolometric ratio ($L_{\rm V}/L$) from the sample spectra and classically determined $BC_{\rm V}$ from bolometric ($M_{\rm Bol}$) and visual ($M_{\rm V}$) absolute magnitudes helped us to determine the zero-point constant ($C_{\rm 2}$) of the $BC_{\rm V}$ scale. Determined $C_{\rm 2}$ for each star for each $S_\lambda(V)$ profile revealed $C_{\rm 2} = 2.3653\pm0.0067$ mag if $S_\lambda(V)$ profile of Bessell is used, and $C_{\rm 2} = 2.3826\pm0.0076$ mag if $S_\lambda(V)$ profile of Landolt is used. Expanding $C_{\rm Bol} = 71.197425 ...$ mag and $c_{\rm Bol} = -18.997351 ...$ mag announced by IAU2015GARB2, and using definition of $C_{\rm 2} = C_{\rm Bol}-C_{\rm V} = c_{\rm Bol}-c_{\rm V}$, where capital $C$ is for the absolute and small $c$ is for the apparent, subscripts indicating bolometric and visual, the zero-point constants: $C_{\rm V} = 68.8321\pm0.0067$ mag and $c_{\rm V} = -21.3627\pm0.0067$ mag, if $L_{\rm V}$ and are in SI units, were determined corresponding to $S_\lambda(V)$ of Bessell. The zero-point constants corresponding to $S_\lambda(V)$ of Landolt are smaller, but the difference is not more than 0.02 mag. Typical and limiting accuracies for predicting a stellar luminosity from an apparent magnitude and a distance are analyzed.

We clarify the role of the oft-misunderstood Null Energy Condition (NEC) in the context of the current cosmological data. In particular, the NEC implies the sum of the total energy density and pressure satisfies $\rho_{tot}+P_{tot} \ge 0$; the energy conditions do not apply separately to individual components of the cosmological fluid. Consequently, we show that under the current best-fit cosmological model no violation of the NEC takes place, past or future. Further, growth in the energy density of an individual component cannot be used to signal violation of the NEC. We illustrate these points with a worked example whereby misestimation of the matter density leads to a phase during which $\rho_{de} + P_{de} < 0$ for the effective dark energy, followed by a phantom crossing and subsequent $\rho_{de} + P_{de} > 0$. At no time is the NEC violated. We also introduce ``elephant'' and ``chimera'' classes of physics for crossing $w_{de}=-1$.

We report observations of Type Ia SN 2021hem, discovered <48 hours of last non-detection, and located in an apparently hostless environment. With a peak absolute B-band magnitude of -19.96 mag, and a lack of secondary maximum in near-infrared and i-band light curves make it resemble 2003fg-like events. The slowly evolving light curves, and the earliest spectrum showing CII absorption lines, further support this classification. Fireball model fit to early light curves yields a time of first light of -16.43 days relative to B-band maximum. The first detection occurs 1.51 days before the onset of the fireball-like flux rise. This early emission, and $(g - r)_0$ color, is inconsistent with circumstellar or companion interaction. Instead, shallow $^{56}$Ni mixing or an asymmetric $^{56}$Ni distribution offers a plausible explanation. SN2021hem is the fifth known 2003fg-like SN with early-time excess flux emission. The estimated mass of radioactive $^{56}$Ni in SN2021hem is $1.00\pm0.09 M_\odot$. Deep GTC imaging obtained 2.5 yr after the explosion (with $m_{lim,r}=24.4$ mag and $\mu_{lim,r} = 26.3\rm~mag~arsec^{-2}$), reveals no coincident host, thereby ruling out most faint dwarf and UDGs. Alternatively, assuming the nearest plausible host galaxy, at a distance of 102 kpc, implies a hyper-velocity progenitor ejected at $\sim$2200 km/s. A faint diffuse feature ~6 kpc from the SN site has also been detected in the image, with its surface brightness of a UDGs. However, it is unclear whether it is a galaxy and is associated with SN2021hem. Considering its large normalized directional light distance ($d_{DLR}\sim3-4$) from SN, and its unusual elongation, it is a candidate of low probability to be the host galaxy of SN2021hem. These results identify SN2021hem as one of the strongest candidates for a hostless SN Ia, underscoring the diversity of luminous, slowly evolving, 2003fg-like explosions.

Changing-look active galactic nuclei (CL-AGNs) exhibit dramatic spectral variability on unexpectedly short timescales, challenging standard accretion flow models. Despite growing samples, the physical drivers of this extreme variability, and the potential link to host-galaxy properties, remain unknown. Regardless of the underlying mechanism, the transition between AGN-dominated and host-dominated spectra offers a unique opportunity to study relations between AGNs and their hosts within the same objects. We present intermediate-resolution spectroscopy of 23 CL-AGNs identified by the Sloan Digital Sky Survey V (SDSS-V), obtained with VLT/X-shooter and Gemini-N/GMOS. An analysis of the Mgii emission line observed in the spectra demonstrates that the majority of these sources cannot be driven by variable obscuration. Our CL-AGNs roughly follow the M_BH-sigma_* and M_BH-M_* relations of inactive galaxies, with a median black hole-to-stellar mass ratio of 0.38%, although they show hints of a shallower slope. We find no evidence that the stellar population properties of our CL-AGNs, including stellar mass, age, young stellar fraction, and star-formation rate differ from those of Type 2 AGNs in SDSS. These results suggest that CL-AGNs reside in typical AGN host galaxies and that their extreme variability is likely unrelated to host-galaxy environment, supporting the idea that CL-AGNs are not a distinct population, but rather represent a phase of normal AGN activity. This result, in turn, implies that CL-AGNs can serve as useful probes of the AGN-host connection, providing access to both AGN-dominated and host-dominated spectra of the same systems.

Most star clusters dissolve into the Galaxy over tens to hundreds of millions of years after they form. While recent Gaia studies have honed our view of cluster dispersal, the exact chronology of which star formation events begat which star cluster remnants remains unclear. This problem is acute after 100 Myr, when cluster remnants have spread over hundreds of parsecs and most age estimates for main sequence stars are too imprecise to link the stars to their birth events. Here we develop a Bayesian framework that combines TESS stellar rotation rates with Gaia kinematics to identify diffuse remnants of open clusters. We apply our method to the Pleiades, which previous studies have noted shows kinematic similarities to other nearby young stellar groups. We find that the Pleiades constitutes the bound core of a much larger, coeval structure that contains multiple known clusters distributed over 600 pc. We refer to this structure as the Greater Pleiades Complex. On the basis of uniform ages, coherent space velocities, detailed elemental abundances, and traceback histories, we conclude that most stars in this complex originated from the same giant molecular cloud. This work establishes a scalable approach for tracing the genealogies of nearby clusters and further cements the Pleiades as a cornerstone of stellar astrophysics. We aim to apply this methodology to other associations as part of the upcoming TESS All-Sky Rotation Survey.

Early helioseismic results have shown that the tachocline has a prolate shape. However, the models used in those studies constrained the tachocline to be either prolate or oblate. We use helioseismic data obtained from long time series (2304 and 4608 days) to determine the shape of the solar tachocline. Like previous work, we use forward modeling methods for this work; however, we allow more flexibility for the shape of the tachocline. We find that the tachocline does indeed deviate from a simple prolate structure and bulges out at mid latitudes. The center of the tachocline lies in the radiative zone at low latitudes, in the convection zone at intermediate latitudes, and back in the radiative zone at high latitudes. The high-latitude ($ > 60^\circ$) behavior is, however, uncertain and model dependent. Models that allow more variation of the shape indicate that the tachocline at high latitudes is almost coincident with the base of the convection zone.

The physical mechanisms driving neutrino and electromagnetic flares in blazars remain poorly understood. We investigate a prominent multi-messenger flare in the quasar PKS 0446+11 to identify the processes responsible for its high-energy emission. We analyze the IceCube-240105A high-energy neutrino event together with contemporaneous observations in the gamma-ray, X-ray, optical, and radio bands. The on- and off-flare spectral energy distributions (SEDs) are modeled within a single-zone leptohadronic framework. Multi-epoch VLBA observations from the MOJAVE program provide parsec-scale polarization data that complement the multi-wavelength light curves. No significant time delay is detected between the neutrino arrival and the flares in different energy bands. This is consistent with an extremely small jet viewing angle below 1 deg, inferred from the parsec-scale polarization structure. The flare can be reproduced by the injection of a proton population and an increase of the Doppler factor from 18 to 24. We also detect an approximately 90 deg rotation of the EVPA in the parsec-scale core during the initial phase of the flare, indicating the emergence of a shock formed by the change in the bulk plasma speed. Our comprehensive multi-messenger analysis demonstrates that the extreme beaming and sub-degree viewing angle of this distant blazar can account for the observed neutrino and electromagnetic activity. These findings strengthen the case for blazars as efficient accelerators of hadrons and as significant contributors to the observed high-energy neutrino flux.

The ability to make accurate determinations of planetary parameters is inextricably linked to measuring physical parameters of the host star, in particular the stellar radius. In this paper we fit the stellar spectral energy distributions of exoplanet hosts to measure their radii, making use of only archival photometry, the $Gaia$ parallaxes and $Gaia$ extinction maps. Using the extinction maps frees us of the degeneracy between temperature and extinction which has plagued this method in the past. The resulting radii have typical random uncertainties of about 2 per cent. We perform a quantitative study of systematic uncertainties affecting the methodology and find they are similar to, or smaller than, the random ones. We discuss how the stellar parameters can be used to derive the properties of both transiting exoplanets, and those where only a radial-velocity curve is available. We then explore in detail the improvements the method makes possible for the parameters of the PanCET sample of transiting planets. For this sample we find the best literature measurements of the planetary radii have mean uncertainties about 40 per cent larger than those presented here, with the new measurements achieving precisions of 2 per cent in radius and 10 per cent in mass. In contrast to much recent work, these transiting exoplanets parameters are derived without using theoretical models of stellar interiors, freeing them of the assumptions those models contain, and any priors for stellar age. As the data used are available for the whole sky, the method can be used for self-consistent measurements of the planetary parameters of a very large fraction of known exoplanets.

We present a Python code for calculating and displaying magnetic field extrapolations from given two-dimensional boundary conditions, specifically from solar surface magnetograms. The code implements analytical magnetohydrostatic models that incorporate the transition from non-force-free to force-free magnetic fields in the solar atmosphere. It allows for different parameterisations of this transition and includes functions to compute magnetic fields, plasma pressure, and density. Fast Fourier methods ensure efficient computation, and the output includes three-dimensional visualisations of field lines and plasma structures. The implementation is optimised for accessibility and speed, making it suitable for both research and educational purposes. The only prerequisite for running the code is a Python compiler. All source code, examples, input files, solutions, and instructions are available for download from GitHub.

In the nebular phase, supernovae are powered by radioactive decay and continuously fade, while their densities have decreased enough such that the expanding nebula becomes (largely) optically thin and the entire structure can be studied. Models for the nebular phase need to take Non-Local Thermodynamic Equilibrium (NLTE) effects into account, while at the same time radiative transfer effects often cannot be ignored. To account for the asymmetric morphologies of SNe, 3D input ejecta models must be used. In this work, we present the \texttt{ExTraSS} (EXplosive TRAnsient Spectral Simulator) code, which has been upgraded to be fully capable of 3D NLTE radiative transfer calculations in order to generate synthetic spectra for explosive transients in the nebular phase, with a focus on supernovae. We solve the long-standing difficulty of 3D NLTE radiative transfer -- to manage generation and storage of millions of photoexcitation rates over $\sim10^{5}$ of cells -- by developing a new Domain Decomposition algorithm. We describe this new methodology and general code operations in detail, and verify convergence and accuracy.

The nebular phase of a supernova (SN) occurs several months to years after the explosion, when the ejecta become mostly optically thin yet there still is sufficient radioactive material to keep the supernova bright. The asymmetries created by the explosion are encoded into the line profiles of the emission lines which appear in the nebular phase. In order to make accurate predictions for these line profiles, Non-Local Thermodynamic Equilibrium (NLTE) radiative transfer calculations need to be carried out. In this work, we use \texttt{ExTraSS} (EXplosive TRAnsient Spectral Simulator) -- which was recently upgraded into a full 3D NLTE radiative transfer code (including photoionization and line-by-line transfer effects) -- to carry out such calculations. \texttt{ExTraSS} is applied to a 3D explosion model of a $9.0\,M_\odot$ H-rich progenitor which is evolved into the homologous phase. Synthetic spectra are computed and the lines from different elements are studied for varying viewing angles. The model spectra are also compared against observations of SN 1997D and SN 2016bkv. The model is capable of creating good line profile matches for both SNe, and reasonable luminosity matches for He, C, O, and Mg lines for SN 1997D -- however H$\alpha$ and Fe I lines are too strong.

We present an overview of the JWST GLIMPSE program, highlighting its survey design, primary science goals, gravitational lensing models, and first results. GLIMPSE provides ultra-deep JWST/NIRCam imaging across seven broadband filters (F090W, F115W, F200W, F277W, F356W, F444W) and two medium-band filters (F410M, F480M), with exposure times ranging from 20 to 40 hours per filter. This yields a 5$\sigma$ limiting magnitude of 30.9 AB (measured in a 0.2 arcsec diameter aperture). The field is supported by extensive ancillary data, including deep HST imaging from the Hubble Frontier Fields program, VLT/MUSE spectroscopy, and deep JWST/NIRSpec medium-resolution multi-object spectroscopy. Exploiting the strong gravitational lensing of the galaxy cluster Abell S1063, GLIMPSE probes intrinsic depths beyond 33 AB magnitudes and covers an effective source-plane area of approximately 4.4 arcmin$^2$ at $z \sim 6$. The program's central aim is to constrain the abundance of the faintest galaxies from $z \sim 6$ up to the highest redshifts, providing crucial benchmarks for galaxy formation models, which have so far been tested primarily on relatively bright systems. We present an initial sample of $\sim 540$ galaxy candidates identified at $6 < z < 16$, with intrinsic UV magnitudes spanning $M_{\mathrm UV}$ = $-$20 to $-$12. This enables unprecedented constraints on the extreme faint end of the UV luminosity function at these epochs. In addition, GLIMPSE opens new windows for spatially resolved studies of star clusters in early galaxies and the detection and characterization of faint high-$z$ active galactic nuclei. This paper accompanies the first public data release, which includes reduced JWST and HST mosaics, photometric catalogs, and gravitational lensing models.

We present model calculations of the reionization history of hydrogen using star formation histories, computed with a galaxy formation model which reproduces properties of local dwarf galaxies and UV luminosity functions of galaxies at $z=5-16$. We use the ionizing photon density functions predicted by the model along with different models for the escape fraction of ionizing photons, $f_{\rm esc}$, to study the effects of ionizing photons from faint galaxies and different assumptions about $f_{\rm esc}$ on the evolution of hydrogen ionized fraction with redshift, $Q_{\rm HII}(z)$. We show that accounting for the contribution of faint galaxies with UV luminosities $M_{1500}>-13$, and with a constant ionizing photon escape fraction of $f_{\rm esc}=0.1$ results in the hydrogen reionization history consistent with all current observational constraints. Comparing results of the $f_{\rm esc}=0.1$ model and two alternative models shows that the model with a strong luminosity dependence of $f_{\rm esc}$, which assigns high $f_{\rm esc}$ to faint galaxies, results in early reionization inconsistent with observational constraints. However, the model in which $f_{\rm esc}$ follows a universal redshift-independent correlation with the recent maximum specific star formation rate, motivated by the results of the SPHINX galaxy formation simulation, results in the reionization history in good agreement with existing observational constraints, even though this model produces a sizeable ionized hydrogen fraction of $Q_{\rm HII}\approx 0.15-0.2$ at redshifts $z=8-12$. Our results show that the relative contribution of faint dwarf galaxies to reionization depends sensitively on assumptions about the escape fraction for galaxies of different luminosities, and that this is the main source of uncertainty in modeling hydrogen reionization.

We perform one of the first spatially resolved studies of warm ($>$100 K) and cold (10-100 K) molecular gas in the circumgalactic medium (CGM), focusing on the brightest cluster galaxy (BCG) of a cool-core galaxy cluster, MACS1931-26 at z=0.35. This galaxy has a massive H$_2$ reservoir and a radio-loud active galactic nucleus (AGN) and is undergoing a starburst event. We present new JWST observations of this system, revealing warm H$_2$ gas that is co-spatial with the cold molecular gas traced by CO, extending over 30 kpc around the BCG in a tail-like structure reaching into the circumgalactic medium of this galaxy. Analysis of the mid-infrared pure H$_2$ rotational lines H$_2$S(1), H$_2$S(5), and H$_2$S(9) indicate warm gas temperatures of $515.6 \pm 0.8$ K and $535.2\pm 1.9$ K in the BCG and tail regions, respectively. We compare cold gas, traced by the CO(3-2) observed with ALMA, to the warm gas traced by JWST. The warm-to-cold molecular gas fraction is comparable in the BCG ($1.4\%\pm0.2\%$) and the CGM tail ($1.9\%\pm0.3\%$). Our analysis suggests that the dissipation of the kinetic energy of the H$_2$-emitting gas is sufficient to lead to the formation of the CO gas. This observation provides new insights into the molecular gas distribution and its potential role in the interplay between the central galaxy and its circumgalactic environment.

Sub-Neptunes represent the current frontier of exoplanet atmospheric characterisation. A proposed subset, Hycean planets, would have liquid water oceans and be potentially habitable, but there are many unanswered questions about their atmospheric dynamics and 3D climate states. To explore such climates in detail, we report a General Circulation Model (GCM) for Hycean worlds, building on a modified version of the ExoCAM GCM. Considering the temperate sub-Neptune K2-18 b as a Hycean candidate, we implement GCMs with different surface pressures and albedos. We find dynamical structures similar to those of tidally-locked terrestrial planets as `slow rotators' with either one equatorial or twin mid-latitude zonal jets. We see moist convective inhibition that matches high resolution models, although in hotter cases the inhibited zone is subsaturated. When imposing a top-of-the-atmosphere (TOA) Bond albedo ($A_b$) by modifying the incident stellar flux, we find that the threshold for K2-18~b to not enter a runaway greenhouse state is $A_b \geq 0.55$ for a 1 bar atmosphere, consistent with previous studies, and $A_b \geq 0.8$ for a 5 bar atmosphere. However, a more realistic treatment of the albedo, by modelling scattering within the atmosphere using an enhanced Rayleigh parametrisation, leads to lower lapse rates and stronger thermal inversions. We find that 1 bar atmospheres are stable for an albedo of $A_b \geq 0.27$, 5 bar atmospheres for $A_b \geq 0.35$, and 10 bar atmospheres for $A_b \geq 0.48$. Moderate albedos such as these are typical of the solar system planets and the required scattering is consistent with observational constraints for K2-18~b, supporting its plausibility as a Hycean world.

The single-epoch virial method is a fundamental tool for estimating supermassive black hole (SMBH) masses in large samples of AGNs and has been extensively employed in studies of SMBH-galaxy co-evolution across cosmic time. However, since this method is calibrated using reverberation-mapped AGNs, its validity across the entire AGN population remains uncertain. We aim to examine the breathing effect-the variability of emission line widths with continuum luminosity-beyond reverberation-mapped AGNs, to assess the validity and estimate potential systematic uncertainties of single-epoch virial black hole mass estimates. We construct an unprecedentedly large multi-epoch spectroscopic dataset of quasars from SDSS DR16, focusing on four key broad emission lines (Ha, Hb, MgII, and CIV). We assess how breathing behavior evolves with the rest-frame time interval between observations. We detect no significant breathing signal in Ha, Hb, or MgII at any observed timescale. In contrast, CIV exhibits a statistically significant anti-breathing trend, most prominent at intermediate timescales. Notably, for Hb, which has shown breathing in previous reverberation-mapped samples, we recover the effect only in the small subset of quasars with clearly detected BLR lags and only during the epochs when such lags are measurable-suggesting that both the lag and breathing signals are intermittent, possibly due to a weak correlation between optical and ionizing continua. These results highlight the complex, variable, and timescale-dependent nature of line profile variability and underscore its implications for single-epoch black hole mass estimates.

The Milky Way harbours a prominent m=1 lopsided distortion in both stellar and neutral gas distributions. On the other hand, chemo-dynamical studies have been proven to be effective in grasping the overall evolution of galaxies. Here, we investigate systematically the excitation and evolution of a merger-driven $m=1$ lopsidedness in a Milky Way (MW)-like host galaxy, as a function of chemical distribution of stars. Using seven dissipationless, high-resolution $N$-body simulations of minor mergers (between a MW-like host and a satellite) under varying orbital configurations (prograde/retrograde and different orientation of the satellite orbital plane), we first show that a tidal interaction excites a prominent $m=1$ lopsidedness in the stellar density and velocity distribution of the MW-like host. Assigning, a posteriori, metallicities to stellar particles of the MW-like host based on the current observational constraints, we sub-divide the stars into metal-rich ([Fe/H] > 0), metal-intermediate (-0.5 < [Fe/H] <0), and metal-poor (- 0.5 < [Fe/H]) populations. We demonstrate that metal-rich population always show a much stronger $m=1$ lopsidedness in both density and velocity distributions when compared to other two populations. This trend holds true for all minor merger model considered here, regardless of their orbital configurations. Furthermore, minor merger also triggers a transient off-centred stellar disc-dark matter halo configuration, with metal-rich population showing the highest degree of disc-halo offset. We show that the metal-rich population which is kinematically colder (i.e. lower velocity dispersion) by construction, is more susceptible to external perturbations. Lastly, using a catalogue of photometry and metalicity for the LMC, we show that the strength of the $m=1$ distortion (predominantly in the form of an one-arm spiral) in stars increases with metallicity as well.

Gravitational-wave astronomy presents an exciting opportunity to provide an independent measurement of the expansion rate of the Universe. By combining inferences for the binary component masses and luminosity distances from individual observations, it is possible to infer $H_0$ without direct electromagnetic counterparts or galaxy catalogs. However, this relies on theoretical gravitational-wave models, which are known to be incomplete descriptions of the full predictions of general relativity. Although the accuracy of our models are improving, they are also becoming increasingly expensive as additional phenomena are incorporated. In this work, we demonstrate that there is no significant advantage in including spin-precession and higher-order multipole moments when inferring $H_0$ via the mass spectrum method for current and near-future gravitational-wave event numbers. Even when simulating a population of highly precessing and preferentially asymmetric-mass-ratio binaries, we show that the inferred $H_0$ posterior changes minimally. Using a simpler, less accurate model, achieves comparable $H_0$ estimates with six times less computational cost (on average). Using computationally cheaper models for single event inference may become crucial as thousands of gravitational-wave observations are expected to be detected in the near future.

NASA's TESS mission has unveiled a plethora of eclipsing binaries (EBs), among them hundreds of triples and higher order, hierarchical systems. These complex targets require follow-up observations to enable full characterization of system architectures and identify the most compact multiples expected to undergo the most dramatic dynamical evolution. We report first results from a long-term effort to perform such follow-up, focusing here on multi-band speckle imaging of a majority, 57, of the sample of 97 quadruple and higher order eclipsing binaries (Q+EBs) identified via TESS light curves by V. B. Kostov et al. (2022). Diffraction-limited imaging with the Differential Speckle Survey Instrument (DSSI) on the ARC 3.5-meter telescope and HRCam on the SOAR 4.1-m telescope reveals nearly 60% of the 57 to resolve into two sources separated by $\geq$ 0.03 arcseconds. For these partly resolved systems, we report derived characteristics (e.g., relative position angle, angular separation, and magnitude differences in multiple passbands) from the speckle imaging. We find those Q+EBs partly resolved with 4-m class telescopes to have significantly inflated Gaia parallax errors and large Gaia RUWE, particularly for systems with separations comparable to Gaia's resolution limit (~0.6 arcseconds). For unresolved systems we report upper limits on angular and linear projected separations. We find two partly resolved Q+EBs with wide linear separations having eclipse timing variations that are therefore candidates of higher than quadruple multiplicity. Finally, we demonstrate how speckle imaging of resolved Q+EBs during an eclipse can clarify which speckle-resolved Q+EB subsystem is associated with a particular set of TESS eclipses.

We present the first observations of the HD92945 debris disk obtained with JWST, targeting this nearby K0V star located at 21.54 pc from the Sun. High-contrast coronagraphic imaging was performed using JWST/NIRCam in the F200W and F444W filters. After subtracting the disk contribution through forward modeling by means of synthetic PSFs and MCMC optimizations, the residuals were analyzed to identify candidate point sources. From these, we derived contrast curves and constructed detection probability maps for substellar companions. The disk is clearly detected in both NIRCam filters and reveals a broad, inclined structure with a gap, consistent with previous scattered-light and ALMA observations. The modeling confirms the presence of a gap at ~80 au and shows a scale height and scattering properties compatible with a dynamically active disk. A significant brightness asymmetry is observed in the southwestern inner ring at both 2 and 4.4 {\mu}m, consistent with previous ALMA results. Observing this feature across different wavelengths and epochs strongly supports a scenario where one or more unseen planetary companions are perturbing the disk. No comoving sources are detected, and all candidate objects in the field are consistent with background stars or galaxies. The derived detection limits exclude planets more massive than ~0.4-0.5 MJ beyond 100 au and more massive than ~1 MJ beyond 20-40 au. This, in turn, rules out the possibility of a single planet placed beyond ~20 au as responsible for the astrometric signal observed by Gaia. These results, combined with the observed disk features, support a scenario in which a single or multiple sub-Jupiter planets dynamically shape the system through mechanisms such as secular apsidal resonances, providing a coherent explanation for the gap, the asymmetric brightness distribution and the astrometric signal.

The integration of aerodynamic drag is a fundamental step in simulating dust dynamics in hydrodynamical simulations. We propose a novel integration scheme, designed to be compatible with Strang splitting techniques, which allows for the straightforward integration of external forces and hydrodynamic fluxes in general-purpose hydrodynamic simulation codes. Moreover, this solver leverages an analytical solution to the problem of drag acceleration, ensuring linear complexity even in cases with multiple dust grain sizes, as opposed to the cubic scaling of methods that require a matrix inversion step. This new General Implicit Runge-Kutta integrator (GIRK) is evaluated using standard benchmarks for dust dynamics such as DUSTYBOX, DUSTYWAVE, and DUSTYSHOCK. The results demonstrate not only the accuracy of the method but also the expected scalings in terms of accuracy, convergence to equilibrium, and execution time. GIRK can be easily implemented in hydrodynamical simulations alongside hydrodynamical steps and external forces, and is especially useful in simulations with a large number of dust grain sizes.

Accurately modeling molecular hydrogen ($\text{H}_{2}$) is an important task in cosmological simulations because it regulates star formation. One fundamental property of $\text{H}_{2}$ is the ability to self-shield, a phenomenon in which the $\text{H}_{2}$ in the outer layer of a molecular cloud absorbs the photodissociating Lyman-Werner UV radiation and shields the inner $\text{H}_{2}$. Historically, numerical approximations have been utilized to avoid intensive ray-tracing calculations. This paper evaluates the use of the Sobolev-like density-gradient approximation in $\text{H}_{2}$ self-shielding modeling and tests its agreement with a more rigorous adaptive ray-tracing method in cosmological simulations. We ran four high-resolution zoom-in cosmological simulations to investigate the models' effects in the early Reionization Era ($z \geq 12$). We find that the approximation model returns a higher $\text{H}_{2}$ photodissociation rate in low gas density environments but lower the rate when gas density is high, resulting in low-mass halos having less $\text{H}_{2}$ while high-mass halos having more $\text{H}_{2}$. The approximation also hinders star formation in small halos, but it less affects the stellar mass of larger halos. Inside a halo, the discrepancies between the two models regarding $\text{H}_{2}$ fraction, temperature, and stellar mass are radially dependent. On a large scale, the simulations using the approximation have less $\text{H}_{2}$ in the intergalactic medium and may experience a slower reionization process. These results show that the Sobolev-like approximation alters properties of galaxies and the large-scale universe when compared to the ray-tracing treatment, emphasizing a need for caution when interpreting results from these two techniques in cosmological simulations.

Neutron stars (NSs) provide a unique laboratory to probe dark matter (DM) through its gravitational imprint on stellar evolution. We use a two-fluid framework with non-annihilating, asymmetric DM, both fermionic and bosonic, that interacts with ordinary matter (OM) solely through gravity. Within this framework, we track proto-neutron stars (PNSs) across their thermal and compositional evolution via quasi-static modeling over the Kelvin--Helmholtz cooling timescale. We uncover a distinct thermal signature: DM cores deepen the gravitational potential, compressing and heating the baryonic matter, while extended DM halos provide external support, leading to cooling of the stellar matter. In contrast, hyperons and other exotic baryons soften the equation of state similarly to DM cores but reduce, rather than increase, the temperature. DM thus alters both temperature and particle distribution profiles in ways that provide a clear diagnostic of its presence. DM cores also enhance compactness and shift hyperon onset, with the strongest effects during deleptonization and neutrino-transparent phases due to reduced neutrino pressure contributions. Consequently, this early thermal evolution, observable through supernova neutrino light curves and young pulsar cooling curves, offers a direct, testable probe of DM in NSs.

Intermediate-mass stars (1-3 Msun) host some of the brightest and best-studied debris discs. This stellar class is also the most frequent host of molecular gas in systems older than typical protoplanetary disc lifetimes, and the most likely to host detected giant planets in radial-velocity surveys. The debris discs of intermediate-mass stars have therefore become fertile ground for studying disc-planet interactions. In this work, we present the first ALMA observations toward the A-type star HD 126062, located in Upper Centaurus Lupus / Lower Centaurus Crux, with the aim of characterising its debris disc. We probed the thermal continuum emission using observations at 1.3 mm, analysed through image reconstruction under different visibility-weighting regimes and parametric model fitting to the observed visibilities. The setup also covered the frequency of the 12CO(2-1) line, allowing imaging of gas near the system. We detected dust continuum emission from an exo-Kuiper belt around HD 126062. Modelled as a Gaussian ring, the visibilities are consistent with a radial separation R = 2.01'' (+0.04, -0.05), equivalent to ~270 (+5, -4) au, and a full width at half maximum DeltaR = 0.71'' +- 0.09 (95 +- 12 au). The continuum emission appears nearly face-on, with inclination <=17 deg. 12CO(2-1) emission is detected in the vicinity of the debris disc, with most of it located external to the exo-Kuiper belt. The exo-Kuiper belt characterised here is among the largest yet detected and agrees with previous predictions of the dust distribution based on spectral energy distribution fitting. The morphology and velocity offset relative to the systemic velocity suggest that the gas is not associated with the star or disc, but likely originates from a diffuse cloud in the nearby galaxy.

Giant planet atmospheres are thought to reflect the gas phase composition of the disk when and where they formed. However, these atmospheres may also be polluted via solid accretion or ice sublimation in the disk. Here, we propose a novel mechanism for enriching the atmospheres of these giant planets with volatiles via pebble drift, fragmentation, and ice sublimation. We use a combination of 3D hydrodynamic simulations, radiative transfer, and particle tracking to follow the trajectories and resulting temperatures of solids in a disk containing an embedded planet forming outside the CO snowline. We show that small dust can become entrained in the meridional flows created by the giant planet and advected above the disk midplane where temperatures are well above the sublimation temperature of CO. This transport of small grains occurs over 10 kyr timescales, with individual micron-sized grains cycling between the midplane and surface of the disk multiple times throughout the planetary accretion stage. We find that this stirring of dust results in sublimation of CO gas above the snow surface in the dust trap created exterior to the giant planet, leading to super-solar CO abundances in the pressure bump. This mechanism of Dust Recycling and Icy Volatile Enrichment in cold giant planets, which we call the DRIVE effect, may explain enhanced metallicities of both wide separation exoplanets as well as Jupiter in our own Solar System.

Wide-field, multi-filter photometric surveys enable the reconstruction of the Milky Way's star formation history (SFH) on Galactic scales and offer new insights into disc assembly. The twelve-filter system of the Javalambre Photometric Local Universe Survey (J-PLUS) is particularly suitable, as its colours trace stellar chemical abundances and help alleviate the age-metallicity degeneracy in colour-magnitude diagram fitting. We aim to recover the SFH of the Galactic disc and separate its chemically distinct components by combining J-PLUS DR3 photometry with Gaia astrometry. We also evaluate the potential of isochrone fitting to estimate stellar ages and metallicities as proxies for evolutionary trends. We fit magnitudes and parallaxes of $1.38\times10^{6}$ stars using a Bayesian multiple isochrone method. The bright region of the colour-absolute-magnitude diagram ($M_{r}\leq4.2$ mag) constrains ages, while the faint region provides an empirical metallicity prior mitigating the age-metallicity degeneracy. Both PARSEC and BaSTI isochrones, in solar-scaled and $\alpha$-enhanced forms, are adopted. The recovered SFH reveals two sequences: an $\alpha$-enhanced population forming rapidly between $12.5$ and $8$ Gyr ago, enriching from [M/H]$\sim-0.6$ to $0.1$ dex; and a solar-scaled sequence emerging $\sim8$ Gyr ago, dominating after $\sim7$ Gyr with slower enrichment reaching solar metallicity by $3$ Gyr. Metal-rich ([M/H]$\gtrsim0$) stars are confined to $\vert z_{GC}\vert\lesssim1$ kpc, whereas metal-poor ([M/H]$\lesssim-0.5$) stars reach $\vert z_{GC}\vert\sim2$ kpc. Simultaneous fitting of both isochrone families reveals distinct formation epochs for the thin and thick discs. J-PLUS multi-filter photometry, combined with Gaia parallaxes, mitigates age-metallicity degeneracies and enables detailed mapping of the Milky Way's temporal and chemical evolution.

Accurate stellar dating provides crucial information about the formation and development of planetary systems. Existing age-dating techniques are limited in terms of both the spectral type and age range they can accurately probe, and many are unreliable for stars older than 1 Gyr. Recent studies have suggested that a star's X-ray luminosity correlates strongly with stellar age and shows a steep fall-off at ages older than 1 Gyr. In this work, we present X-ray luminosity relationship values from eROSITA for four previously unassessed stars. Additionally, we reassess the X-ray luminosity/age relationship present in 24 main-sequence stars older than a gigayear. We confirm that a correlation does appear to exist between stellar age and X-ray luminosity at ages older than 1 Gyr. However, we measure a shallower slope with age than previous research for older stars, similar to what was found for younger stars. We also find evidence for significant astrophysical variability in a star's X-ray luminosity, which will likely limit the precision with which X-ray measurements can yield age estimates. We also find weak evidence for mass dependence in the X-ray luminosity/age relationship. These results suggest that although X-ray luminosity correlates with stellar age, it may not serve as a reliable standalone age indicator and is better used as part of a broader suite of age-dating methods.

Observations over the past few decades have found that planets are common around nearby stars in our Galaxy, but little is known about planets that formed outside the Milky Way. We describe the design and early implementation of a survey to test whether planets also exist orbiting the remnant stars of ancient dwarf galaxies that merged with the Milky Way, and if so, how they differ from their Milky Way counterparts. VOYAGERS (Views Of Yore - Ancient Gaia-enceladus Exoplanet Revealing Survey) is a radial velocity (RV) search using precision spectrographs to discover exoplanets orbiting very low metallicity ($-2.8 < [\mathrm{Fe/H}] \leq -0.8$) stars born in the dwarf galaxy Enceladus, which merged with the Milky Way galaxy about 10 Gyr ago. A sample of 22 candidates have been screened from a catalog of Gaia-Enceladus-Sausage (GES) members using a combination of stellar properties and reconnaissance observations from the TRES spectrograph. Precision RV measurements have been initiated using the NEID, HARPS-N, and CARMENES spectrographs. We plan to focus most upcoming observations on 10 main sequence targets. Data collection is well underway, with 778 observations on 22 candidates (385 of which are 10 focus targets), but far from complete. This survey is designed to be sensitive to sub-Neptune mass planets with periods up to hundreds of days. We note that the RV analysis gives mass multiplied by $\sin (inclination)$ or the minimum mass for exoplanets. The expected survey yield is three planets, assuming that occurrence rates are similar to those in the Milky Way and taking into account the degeneracy with inclination in our yield models. Our survey is designed to detect at least one exoplanet if occurrence rates are similar to known Milky Way exoplanets or, if no exoplanets are discovered, to rule out a Milky Way-like planet population in GES with 95% confidence level.

We present a multi-wavelength study of a blazar PKS 0446+11, motivated by its spatial association with the neutrino event IC240105A detected by the IceCube Neutrino Observatory on 2024 January 5. The source is located 0.4 degrees from the best-fit neutrino direction and satisfies selection criteria for VLBI-selected, radio-bright AGN that have been identified as highly probable neutrino associations. PKS 0446+11 exhibited a major gamma-ray flare in November 2023, reaching approximately 18x its 4FGL-DR4 catalog average. Around the neutrino epoch, PKS 0446+11 remained in an elevated state, with the gamma-ray flux more than six times above its catalog level, the X-ray flux an order of magnitude above the archival measurements, and the optical-UV emission also enhanced. We used Fermi-LAT, Swift-XRT/UVOT, and archival multi-wavelength data to construct multi-wavelength light curves and spectral energy distributions (SEDs). SED modeling shows that the emission is best described by a leptonic scenario, with synchrotron emission at low energies and external Compton scattering of broad-line region and dusty torus photons dominating the X-ray - gamma-ray output. A lepto-hadronic model fails to adequately reproduce the observed SED, although hadronic cascades can broadly account for the X-ray and gamma-ray spectral coverage at lower flux levels. We compute the expected neutrino flux for the hadronic scenario and compare it to the IceCube 90% upper limit. Our results highlight the importance of continued multi-wavelength and neutrino monitoring to better understand the physical conditions under which this blazar may serve as neutrino source.

We introduce the PanRadio Gamma-ray Burst (GRB) program carried out on the Australia Telescope Compact Array: a systematic, multi-year, radio survey of all southern \textit{Swift} GRB events, comprehensively following the multi-frequency evolution of their afterglows from within an hour to years post-burst. We present the results of the 400-day observing campaign following the afterglow of long-duration (collapsar) GRB~230815A, the first one detected through this program. Typically, GRB~230815A would not otherwise receive traditional radio follow-up, given it has no known redshift and lacks comprehensive multi-wavelength follow-up due to its high line-of-sight extinction with $A_V = 2.3$. We found its early X-ray jet break at ${\sim}0.1$ days post-burst to be at odds with the evolution of the multi-frequency radio light curves that were traced over an unusually long duration of $400$ days. The radio light curves approximately evolved (with minor deviations) according to the standard self-similar expansion for a relativistic blast wave in a homogeneous environment prior to jet break, showing no evidence for evolution in the microphysical parameters describing the electron acceleration processes. We reconcile these features by proposing a two-component jet: the early X-ray break originates from a narrow component with a half-opening angle ${\sim}2.1^{\circ}$, while the evolution of the radio afterglow stems from a wider component with a half-opening angle $\gtrapprox 35^{\circ}$. The PanRadio GRB program will establish a sample of comprehensively followed GRBs, where a rigorous inspection of their microphysical and dynamical parameters can be performed, thereby revealing the diversity of features in their outflows and environments.

Analytical models are essential for building physical intuition and guiding the interpretation of exoplanet observations by clarifying the dependencies that shape atmospheric signatures. We present a generalization of the classical isothermal, isobaric transmission model by allowing the opacity to vary with pressure as a power law, $\kappa \propto P^{n}$, and explicitly defining the reference opacity $\kappa_{0}$ at a chosen pressure $P_{0}$. By treating the slant optical depth as an Abel transform of the radial absorption coefficient, we derive a closed-form expression for the effective transit radius in a hydrostatic, isothermal atmosphere with pressure-dependent opacity. The solution provides a compact framework for exploring non-isobaric effects and explicitly links the vertical opacity gradient to observable spectral features. We benchmark the model against empirical transmission spectra of Earth and the hot Jupiter WASP-39b, finding a significantly improved fit relative to the isobaric formula. This generalized expression offers a physically interpretable foundation for analyzing high-precision spectra from JWST and upcoming ARIEL observations, and can serve as a basis for semi-analytical retrieval approaches optimized for computational efficiency.

Spaceborne gravitational wave observatories, exemplified by the Laser Interferometer Space Antenna (LISA) mission, are designed to remove laser noise and clock noise from interferometric phase measurements in postprocessing. The planned observatories will utilize electro-optic modulators (EOMs) to encode the onboard clock timing onto the beam phase. Recent research has demonstrated the advantage of introducing an optical frequency comb (OFC) in the metrology system with the modified framework of time-delay interferometry (TDI): the removal of the EOM and the simultaneous suppression of the stochastic jitter of the laser and the clock in the observation band. In this paper, we explore an alternative approach with the OFC-based metrology system. We report that after proper treatment, it is possible to use the measured carrier-carrier heterodyne frequencies to monitor the time derivative of the pseudoranges, which represent the physical light travel time and the clock difference. This approach does not require changing the existing TDI framework, as previous OFC based efforts did. We also present the experimental demonstration of our scheme using two separate systems to model two spacecraft. Using this novel approach, we synchronize the two independent phase measurement systems with an accuracy better than 0.47 ns, while the stochastic jitter in the observation band is suppressed down to the setup sensitivity around the LISA performance levels at 15 pm/sqrt(Hz).

The use of galaxy clusters to constrain cosmology is limited in part due to uncertainties in derived cluster masses, which often depend on the gas temperature. Unfortunately, there exists a longstanding discrepancy in temperature measurements of the same galaxy clusters made by the two most sensitive X-ray observatories, Chandra and XMM-Newton. The NuSTAR X-ray Observatory's greater sensitivity to the exponential turnover in the bremsstrahlung continuum allows for more precise and potentially more accurate galaxy cluster temperature estimates, especially given its unique ability to independently calibrate its optics in orbit. We present new NuSTAR spectra of 10 relaxed clusters ($5~\mathrm{keV} < kT < 10~\mathrm{keV}$), extracted from identical regions as previous spectra from Chandra and XMM-Newton. The 3--20~keV spectra are well fit by single temperature models, and fits done in narrower bandpasses provide no clear evidence in support of the existence of multi temperature gas. We find NuSTAR temperatures are typically $\sim 15\%$ higher than XMM-Newton temperatures. In contrast, good agreement is found between NuSTAR and Chandra temperatures for clusters with $kT \lesssim 7~\mathrm{keV}$, with Chandra measurements exceeding NuSTAR's in hotter systems. When more clusters are included, the trend is reinforced and can be extended to higher temperatures. A generic increase to Chandra's $E > 2~\mathrm{keV}$ effective area ($\sim 5\%$ at 5~keV) is found to explain the trend reasonably well. These results demonstrate the potential for NuSTAR data to address the two-decade-old temperature discrepancy between Chandra and XMM-Newton.

Astrometry measures shifts in a star's photocentre and can be used to detect reflex motion due to orbiting exoplanets. Brightness asymmetries (e.g. starspots) rotating in and out of view can also cause apparent motion of the photocenter, termed astrometric jitter, that has previously been considered a source of noise. Here, we explore whether it can be used to map stellar surfaces. We derive a Cramer-Rao bound on the minimum variance for which a stellar surface can theoretically be estimated, quantifying the information content in rotational astrometric jitter. To regularize and break singularities in the Fisher information, we impose a spatial-smoothness Gaussian-Markov random field prior. A key challenge in mapping surfaces arises for stars with unknown rotational axis inclinations, requiring joint estimation of the inclination and the stellar surface. We characterize the coupling between them and quantify the precision gain when inclination is known versus unknown.

To investigate the physical origin of the Balmer decrement in the broad-line region of active galactic nuclei (AGNs), we measure the temporal variability of the fluxes of the broad H$\beta$ and H$\alpha$ emission lines using multi-epoch spectroscopic data of low-redshift AGNs from the Sloan Digital Sky Survey. The analysis of the mean spectra reveals that the Balmer decrement shows no correlation with AGN luminosity, while it is inversely correlated with the Eddington ratio. However, the temporal variation of the Balmer decrement in individual objects exhibits an even stronger anti-correlation with AGN luminosity, suggesting that the change in AGN luminosity plays a dominant role in determining the Balmer decrement. By comparing the temporal evolution of the Balmer decrement with the continuum color, we find that reddening due to the AGN itself may not be the primary factor. Instead, radiative transfer effects and excitation mechanisms, which deviate from the Case B recombination, appear to be critical for the variation of the Balmer decrement. These results provide useful insights into the underlying physics of changing-look AGNs and high-$z$ AGNs, such as the ``little red dots'', which exhibit extreme values of the Balmer decrement that can be misinterpreted as evidence for dust.

Delayed reverberations of broad emission lines in response to optical continuum variations have been widely observed in active galactic nuclei (AGNs). They serve as a powerful tool for probing inner structures of AGNs and estimating the masses of supermassive black holes (SMBHs). The delays exhibit a strong correlation with approximately the square root of the optical luminosity - a relationship known as the "standard structure" of AGN broad-line regions (BLRs). Here, we report the discovery of leading delays in H{\beta} line reverberations (LDRs) in the quasar PHL 1092 preceding variations of the 5100 Å continuum by 17-57 days, based on our eight-year continuous campaign of reverberation mapping of super Eddington AGNs. The LDRs suggest that the 5100 Å continuum regions are so extensive that they are larger than the BLRs. This phenomenon not only fundamentally disrupts the well-established BLR size-luminosity relation but also violates the principle of causality. This unprecedented LDRs challenge the conventional methods for estimating SMBH mass as well as the standard model of AGNs. A preferred scenario to explain the LDRs is that the SMBH-disk contains a population of accreting stellar-mass black holes (sMBHs) as extra heating sources of the disk. Consequently, continuum regions of the disk are efficiently stretched so that the 5100 Å regions exceed the BLRs, yielding the observed LDRs. Generally, sMBH activities there could provide new physics of AGN phenomena, which can be tested by LIGO, LISA/Tianqin and ET detections of gravitational waves from sMBH mergers.

Impact ejecta with velocities exceeding the escape velocity of planetary bodies become meteorites and dust particles in interplanetary space. We present a new method that allows simultaneous measurement of the size and velocity of the largest high-velocity ejecta. High-speed camera images revealed the time required for the ejecta to reach the secondary target, and ejecta size was determined after the experiment by analyzing the craters formed upon their impact on the secondary target. We defined the size-velocity relationships of sub-millimeter ejecta with velocities exceeding 1 km^{-1}, focusing on the largest detectable ejecta in our experiments. The results show that millimeter-sized meteoroids impacting the rocky surfaces of planetary bodies at 7 km^{-1} eject particles up to a few tens of micrometers in size toward interplanetary space at velocities exceeding the escape velocity of the body, even when it is greater than 1 km^{-1}.

Recent discoveries have revealed a population of "popcorn planets" that have masses similar to that of Neptune but radii comparable to Jupiter, leading to exceptionally low bulk densities $\rho_p \lesssim 0.3\,\mathrm{g}\,\mathrm{cm}^{-3}$. Their anomalously-inflated radii, along with recent JWST atmospheric observations, suggest a source of internal heating. Because these planets are nominally too cool to be affected by the hot Jupiter inflation mechanism, dissipation of eccentricity tides within the planet has been proposed as a leading explanation for the source of this heat flux. Using the MAROON-X spectrograph on Gemini-North, we conducted a high-precision radial-velocity campaign to precisely measure the eccentricities of three of these popcorn planets: WASP-107 b, TOI-1173 b, and HAT-P-18 b. We constrained their eccentricities below $e < 0.03$--$0.05$ to 95% confidence, decisively ruling out active heating from eccentricity tides as the cause of these planets' inflated radii (except for the unlikely scenario in which their tidal quality factors are less than the Earth's). An alternative heating mechanism is likely responsible for inflating these planets. Our measurements also provide new constraints on $e\cos\omega$, significantly shrinking the eclipse timing uncertainties to better than $\pm2.5$ hr and allowing for confident scheduling of thermal emission measurements for these enigmatic planets.

We present a compact and reproducible method for general relativistic polarization transport in the Kerr metric that achieves median electric vector position angle (EVPA) residuals of $\langle \Delta \mathrm{PA} \rangle \approx 0.09^\circ$, a 95th percentile of $0.31^\circ$, and a worst case $\Delta \mathrm{PA} \lesssim 0.32^\circ$ for spins up to $|a/M|=0.9$, while maintaining a fivefold or greater speedup relative to a strict reference integrator. Across the benchmark grid, typical residuals remain at the sub-tenth-degree level, with only modest degradation ($\Delta \mathrm{PA} \lesssim 2^\circ$) near the Thorne spin limit. Photon four-momenta $k^\mu$ and polarization four-vectors $f^\mu$ are advanced using a fourth order Runge-Kutta scheme with cached Christoffel symbols, maintaining the constraints $u\cdot f=0$ and $n\cdot f=0$, where $u^\mu$ is the ZAMO four-velocity and $n^\mu$ is the disk normal, while keeping $k\cdot f \simeq 0$. A physically motivated gauge is enforced by projecting the polarization into the local zero-angular-momentum observer (ZAMO) screen at every substep, ensuring numerical stability of the orthogonality constraints. Accuracy and performance are benchmarked over a representative grid in spin, inclination, image-plane azimuth, and radius. The method comfortably meets IXPE and NICER polarization tolerances and approaches EHT requirements. The approach provides a practical foundation for future general relativistic polarimetry and simulation pipelines.

Metal-rich asteroids and iron meteorites are considered core remnants of differentiated planetesimals and or products of oxygen-depleted accretion. Investigating the origins of iron-rich planetesimals could provide key insights into planet formation mechanisms. Using differentiation models, we evaluate the interior structure and composition of representative-sized planetesimals (approx. 200 km diameter) while varying oxygen fugacity and initial bulk meteoritic composition. Under the oxygen-poor conditions that likely existed early in the inner regions of the Solar System and other protoplanetary disks, core fractions remain relatively consistent across a range of bulk compositions (CI, H, EH, and CBa). Some of these cores could incorporate significant amounts of silicon (10-30 wt percent) and explain the metal fractions of Fe-rich bodies in the absence of mantle stripping. Conversely, planetesimals forming under more oxidizing conditions, such as beyond snow lines, could exhibit smaller cores enriched in carbon, sulfur (more than 1 wt percent), and oxides. Sulfur-rich cores, like those formed from EH and H bulk compositions, could remain partly molten, sustain dynamos, and even drive sulfur-rich volcanism. Additionally, bodies with high carbon contents, such as CI compositions, can form graphitic outer layers. These variations highlight the importance of initial formation conditions in shaping planetesimal structures. Future missions, such as NASA's Psyche mission, offer an opportunity to measure the relative abundances of key elements (Fe, Ni, Si, and S) necessary to distinguish among formation scenarios and structure models for Fe-rich and reduced planetesimals.

We present the full sample of measurements of the warm dust emission of 31 strongly-lensed, multiply imaged quasars, observed with JWST MIRI multiband imaging, which we use to constrain the particle properties of dark matter. The strongly lensed warm dust region of quasars is compact and statistically sensitive to a population of dark matter halos down to masses of $10^6$ M$_\odot$. The high spatial resolution and infrared sensitivity of MIRI make it uniquely suited to measure multiply imaged warm dust emission from quasars and thus to infer the properties of low-mass dark halos. We use the measured flux ratios to test for a warm dark matter turnover in the halo mass function. To infer the dark matter parameters, we use a forward modeling pipeline which explores dark matter parameters while also accounting for tidal stripping effects on subhalos, globular clusters, and complex deflector macromodels with $m=1, m=3, \text{ and } m=4$ elliptical multipole moments. Adopting a comparable prior on the projected density of substructure to our previous analyses, the data presented here provide a factor of 2 improvement in sensitivity to a turnover in the halo mass function. Assuming subhalo abundance predicted by the semi-analytic model galacticus we infer with a Bayes factor of 10:1, a half-mode mass $m_{\rm{hm}} < 10^{7.8} M_{\odot}$ (m>5.6 keV for a thermally produced dark matter particle). If instead we use a prior from N-body simulations, we infer $m_{\rm{hm}} < 10^{7.5} M_{\odot}$ (m>6.9 keV). This is one of the strongest constraints to date on a turnover on the halo mass function, and the flux ratios and inference methodology presented here can be used to test a broad range of dark matter physics.

Newborn magnetars are important gravitational wave sources due to their ultra-strong magnetic fields and fast spins, and the entire population in the Universe may significantly contribute to the stochastic gravitational wave background (SGWB). In this work, we investigate the SGWB from newborn magnetars and assess its detectability by the advanced LIGO (aLIGO) and Einstein Telescope (ET) based on three typical formation mechanisms of magnetars, i.e., the $\alpha-\Omega$ dynamo, convective dynamo, and magnetic flux conservation. For the two dynamo scenarios, when calculating the SGWB, we creatively incorporate the anti-correlations between the magnetic fields and initial spin periods $P_{\rm i}$ with the initial dipole-field distribution of newborn magnetars. For the flux-conservation scenario, a bimodal lognormal form is adopted to describe the distribution of initial dipole fields, and all magnetars are assumed to have the same $P_{\rm i}$. Our results show that the SGWB from newborn magnetars may be undetectable by the aLIGO and ET if the magnetars are formed due to these mechanisms since the signal-to-noise ratio of the SGWB with respect to the ET for an observation time of one year is only 0.37 for the $\alpha-\Omega$ dynamo, $3\times10^{-4}$ for the convective dynamo, and at most 0.21 for the flux conservation.

To validate key technologies for wide field-of-view (FOV) X-ray polarization measurements, the Cosmic X-ray Polarization Detector (CXPD) CubeSat series has been developed as a prototype platform for the Low-Energy Xray Polarization Detector (LPD) onboard the POLAR-2 mission. The wide-FOV design significantly increases the complexity of the background environment, posing notable challenges for real-time gamma-ray burst (GRB) identification. In this work, we propose an in-orbit GRB identification method based on machine learning, using simulated spectral data as input. A training dataset was constructed using a Geant4-based simulator, incorporating in-orbit background and GRB events modeled within the 2-10 keV energy range. To meet the computational constraints of onboard processing, we employ a multimodal large language model (MLLM), which is fine-tuned using low-rank adaptation (LoRA) based on miniCPM-V2.6 and quantized to 4-bit precision. The model achieves perfect classification accuracy on validation data and demonstrates strong regression performance in estimating GRB spectral indices, with an RMSE of 0.118. Furthermore, we validate the feasibility of onboard deployment through a simulated satellite data processing pipeline, highlighting the potential of our approach to enable future real-time GRB detection and spectral analysis in orbit.

We study the QCD--DM scenario by analyzing the imprint of energy injection from decaying dark-sector particles on the spectral distortions (SDs) of the Cosmic Microwave Background (CMB). We adopt a unified framework capable of describing both relativistic and non-relativistic particles, as well as fast and slow decay regimes. Within this approach, we model exponential, power-law, oscillatory, and two-step decays, computing the resulting $\mu$- and $y$-type distortions across the parameter space spanned by the confinement scale $a_c$, decay rate $\Gamma_\chi$, energy-transfer efficiency $\Sigma_\chi$, and velocity $v_{\chi c}$. We find that power-law, oscillatory, and cascade decays can be effectively mapped onto exponential models with appropriate rescaling. The dominant factors controlling SDs are the decay epoch and lifetime, with $v_{\chi c}$ becoming relevant only in the ultra-relativistic limit. FIRAS observations impose tight constraints on early energy injection, with $\mu$-type distortions placing the strongest bounds on $\Sigma_\chi$. Simultaneous matching of both $\mu_{\rm firas}$ and $y_{\rm firas}$ breaks the degeneracy between $\Gamma_\chi$ and $\Sigma_\chi$, localizing preferred decay rates around $\Gamma_\chi \lesssim (3.3-4.4)\times10^{-3}~{\rm yr}^{-1}$ and $\Sigma_\chi \lesssim 8.5\times10^{-4}$ for relativistic particles, while fast decays with $\Gamma_\chi \gtrsim 6.5~{\rm yr}^{-1}$ become observationally negligible. Our results show that CMB spectral distortions are a powerful probe of dark-sector dynamics. Future missions such as PIXIE or PRISM could extend current limits by several orders of magnitude and test previously inaccessible regions of parameter space.

Direct electromagnetic observation of the orbital motion of a sub-parsec, supermassive black hole binary (SMBHB) would provide the first conclusive proof of such systems existing. Widely considered to be the sources of gravitational waves, binaries are expected to form as a natural consequence of galactic mergers and determining the processes that drive their evolution is essential for understanding cosmological evolution. In this work, we evaluate the prospects of using ground and spaceborne Very Long Baseline Interferometry (VLBI) to observe supermassive black hole binaries and estimate their orbital parameters. The Black Hole Explorer (BHEX) is considered as the primary case study. Achieving unprecedented resolution, BHEX will provide access to a new volume of binary parameter space, potentially enabling the first, confident detection of an SMBHB. A binary toy model using a post-Newtonian orbit propagation is developed and simulated observations by BHEX and a ground array of telescopes are performed. An orbit fitting approach using Bayesian dynamic nested sampling is presented and its efficacy is demonstrated on the simulated observational data for a set of example binary systems. It is found that for BHEX, binary detection requires a total flux density of 0.04 Jy with a minimum separation of ~2 microarcseconds and an observable mass ratio dependent on the total flux. With three annual observations, BHEX could constrain semi-major axis and eccentricity of binaries with orbital periods <10 years to within 13% of the true values. A curved trajectory could confidently be detected in binaries with period <23 years. Proposals for how candidate sources could be identified in time for the BHEX mission are also provided. Finally, we constrain the requirements of a future spaceborne VLBI system, capable of performing a statistically significant survey of supermassive black hole binaries.

We study an entropy-based framework to analyze gravitational-wave signals from core-collapse supernovae. We use waveforms generated by numerical simulations and analyze them in both the time domain and the time-frequency domain using short-time Fourier and continuous wavelet transforms. From each representation, we compute four entropy measures -- Shannon, exponential, Rényi, and Tsallis -- and apply three feature selection methods to identify the most informative features. We then train machine-learning classifiers on these features to compare the performance of different methodological combinations. We find that the combination of Rényi entropy from the wavelet domain and the Relief-F selection method yields the most effective discrimination among different gravitational-wave signals.

Strong gravitational lensing by galaxies is a powerful tool for studying cosmology and galaxy structure. The China Space Station Telescope (CSST) will revolutionize this field by discovering up to $\sim$100,000 galaxy-scale strong lenses, a huge increase over current samples. To harness the statistical power of this vast dataset, we forecast its cosmological constraining power using the gravitational-dynamical mass combination method. We create a realistic simulated lens sample and test how uncertainties in redshift and velocity dispersion measurements affect results under ideal, optimistic, and pessimistic scenarios. We find that increasing the sample size from 100 to 10,000 systems dramatically improves precision: in the $\Lambda$CDM model, the uncertainty on the matter density parameter, $\Omega_m$, drops from 0.2 to 0.01; in the $w$CDM model, the uncertainty on the dark energy equation of state, $w$, decreases from 0.3 to 0.04. With 10,000 lenses, our constraints on dark energy are twice as tight as those from the latest DESI BAO measurements. We also compare two parameter estimation techniques -- MultiNest sampling and Bayesian Hierarchical Modeling (BHM). While both achieve similar precision, BHM provides more robust estimates of intrinsic lens parameters, whereas MultiNest is about twice as fast. This work establishes an efficient and scalable framework for cosmological analysis with next-generation strong lensing surveys.

The HyperScout-H (HS-H) instrument is one of the payloads aboard ESA's Hera spacecraft. Hera is a planetary defence mission that aims to provide a detailed characterization of the near-Earth binary asteroid (65803) Didymos-Dimorphos after the NASA/DART mission impact. HS-H is a versatile dual-use payload, functioning as a hyperspectral imager that captures both images and spectral data within the 0.65--0.95 $\mu$m wavelength range. The observations from this instrument will offer key insights regarding the composition of the two bodies Didymos and Dimorphos, space weathering effects, and the potential presence of exogenous material on these asteroids. Thanks to its wide field of view ($\approx 15.5^\circ \times 8.3^\circ$ in paraxial approximation), HS-H will be able to monitor the system's orbital dynamic and dust environment. At the same time, both components of this binary asteroid remain in the field of view for most of the asteroid phase of the mission. These results also complement the data obtained from other instruments in characterizing the geomorphological units. The data that will be obtained by HS-H will enable the creation of maps highlighting key spectral features, such as taxonomic classification, spectral slope, and band parameters. This article presents the pre-flight calibration of the instrument, outlines the science objectives, and discusses the expected investigations. The instrument's capabilities are demonstrated through laboratory observations of two meteorite samples and a dedicated software toolbox was developed specifically for processing the instrument's data.

The angular momentum evolution of stars is crucial for understanding the formation and evolution of stars and star clusters. Using high-resolution magnetohydrodynamical (MHD) simulations of star formation in clouds with different physical properties, we study the initial distribution of stellar rotation periods in young clusters. We compare these results with observations of young Galactic clusters. Simulations qualitatively reproduce the observed trend of increasing rotation period with stellar mass. Additionally, simulations with lower virial parameter (ratio of turbulence to gravity) or solenoidal turbulence driving produce period-mass distributions that more closely match the observed ones. These simulations also recover the break in the mass-period relation. However, the break appears at higher masses than in observations and is absent in the youngest simulated clusters. This suggests that the emergence of the break is an important diagnostic of angular momentum evolution during the earliest stages of cluster formation. The simulations yield stars that rotate about an order of magnitude faster than those observed. This discrepancy mainly reflects the earlier evolutionary stage of the simulations, while unresolved physical interactions between stars and discs might also contribute. This conclusion is supported by simulations showing a significant period increase within 0.1-1 Myr. We quantify the required angular-momentum loss by rescaling simulated rotation periods to match observations, finding that 80-95% of the initial angular momentum must be removed within the first Myr. Our results highlight that understanding the earliest stages of star cluster formation is fundamental to addressing the angular momentum problem.

We examine whether Flat Spectrum Radio Quasars (FSRQs) and BL Lacertae objects (BL Lacs) can act as plausible astrophysical sources of diffuse ultra-high-energy cosmic rays (UHECRs). Using realistic luminosity-dependent density evolution (LDDE) functions derived from observed gamma-ray luminosity functions for FSRQs and BL Lacs, we calculate the redshift evolution of the cosmic ray source population through integrated luminosity functions. The diffuse UHECRs flux from these sources is modelled by propagating nuclei through extragalactic space, including energy losses from interactions with cosmic photon backgrounds. The resulting UHECRs spectra are compared with observational data from the Pierre Auger Observatory and the Telescope Array, with fluxes normalised at reference energies. In addition to spectral comparisons, we generate HEALPix-based sky maps and identify potential hotspots. Near these hotspots, several galaxies and extragalactic sources are found, suggesting possible associations with the enhanced flux regions. Our results indicate that LDDE-modelled AGNs could contribute significantly to the observed diffuse UHECRs flux and provide constraints on their role as dominant sources.

We investigated the distributions of classified young stellar object (YSO) in nine star-forming regions associated with Hii regions, namely Sh2-22, Sh2-19, Sh2-17, M16, M8, IC5070, Sh2-252, NGC2467 and M42, as a means of exploring the star formation scenarios (triggered or spontaneous) in the various regions. The YSO distributions of nine regions along the galactic longitudes and across different spiral arms were explored. It is noted that Sh2-22 and Sh2-19 may have evidence of localized triggered star formation, whereas Sh2-17 may be a spontaneous star forming region. The results showed that the location within the Milky Way may influence localized triggered star formation within individual regions. There is strong evidence that there are fewer older stars (Transition Disks) within the Outer regions of the Galaxy (2.91 +- 1.74%), accompanied by a higher number of Class I (32.49 +- 10.77%). This is different from the Inner Galactic regions where the Transition Disks are higher (32.93 +- 13.78%) as compared to low Class I sources (11.01 +- 4.81%). The number of Class II stars is relatively high and increases from the Inner regions (52.64 +- 10.07%) to Outer regions (64.54 +- 11.09%). These nine star-forming regions are not an accurate representation of locations throughout the Galaxy and the results may be biased.

Galaxy clusters can be used as powerful cosmological probes, provided one can obtain accurate mass estimates, which requires a precise knowledge of the underlying astrophysics of galaxy clusters. For these purposes, spatially resolved measurements of the thermodynamic properties of intra-cluster medium (ICM), such as density and temperature, are necessary. In particular, temperature estimates are traditionally obtained through spatially resolved X-ray spectroscopy. Such measurements suffer from their sensitivity to the chosen energy calibration, may exhibit inherent biases, and are especially hard to perform at high redshift as they require deep observations. In recent years however, millimetre wavelength data with high spatial resolution, comparable to the one of current X-ray telescopes, have begun to be available. This has enabled the implementation of new methods to infer and map the cluster temperature in individual clusters, using the combination of density maps from X-ray data and pressure maps from millimetre data. In this paper, we present the first systematic validation of this approach on a large sample of synthetic clusters generated in The Three Hundred hydrodynamical simulations. We show that we are able to recover theoretical estimates of the temperature, namely the mass-weighted and spectroscopic-like temperatures, within biases of the order of $\lesssim 1\%$ in the best cases, up to $\sim 10\%$ in average, with scatters of the order of $10\%$. To prepare the application of this approach to observed data, we discuss the modelling of the effective length $l_\mathrm{eff}$, a key quantity necessary for the combination of X-ray and SZ projected data. In particular we provide templates calibrated on simulations for this quantity, and investigate their impact in the recovery of the temperature map, compared to other standard models.

Radiative transfer is a fundamental process in astrophysics, essential for both interpreting observations and modeling thermal and dynamical feedback in simulations via ionizing radiation and photon pressure. However, numerically solving the underlying radiative transfer equation is computationally intensive due to the complex interaction of light with matter and the disparity between the speed of light and the typical gas velocities in astrophysical environments, making it particularly expensive to include the effects of on-the-fly radiation in hydrodynamic simulations. This motivates the development of surrogate models that can significantly accelerate radiative transfer calculations while preserving high accuracy. We present a surrogate model based on a Fourier Neural Operator architecture combined with U-Nets. Our model approximates three-dimensional, monochromatic radiative transfer in time-dependent regimes, in absorption-emission approximation, achieving speedups of more than 2 orders of magnitude while maintaining an average relative error below 3%, demonstrating our approach's potential to be integrated into state-of-the-art hydrodynamic simulations.

We investigate the non-Gaussian features in the distribution of the matter power spectrum multipoles. Using the COVMOS method, we generate 100\,000 mock realisations of dark matter density fields in both real and redshift space across multiple redshifts and cosmological models. We derive an analytical framework linking the non-Gaussianity of the power spectrum distribution to higher-order statistics of the density field, including the trispectrum and pentaspectrum. We explore the effect of redshift-space distortions, the geometry of the survey, the Fourier binning, the integral constraint, and the shot noise on the skewness of the distribution of the power spectrum measurements. Our results demonstrate that the likelihood of the estimated matter power spectrum deviates significantly from a Gaussian assumption on nonlinear scales, particularly at low redshift. This departure is primarily driven by the pentaspectrum contribution, which dominates over the trispectrum at intermediate scales. We also examine the impact of the finiteness of the survey geometry in the context of the Euclid mission and find that both the shape of the survey and the integral constraint amplify the skewness.

We give a general overview of what the scientific community refers to as "exocomets". The general definition of exocomets, as presented in this work, is discussed and compared with Solar System comets and interstellar objects, addressing their detection around main-sequence stars as well as orbiting white dwarfs. We introduce the different types of exocomet observations, highlighting the difference between exocometary 'bodies' and exocometary 'material'. We provide a census of all exocometary system candidates detected so far, both via spectroscopy and photometry, including detections around white dwarfs.

We present the first strong gravitational lensing model for the cluster PSZ2 G118.46+39.32 (z = 0.3967) using new NIRCam imaging from the Strong LensIng and Cluster Evolution (SLICE) JWST program. We leverage the broad coverage of the SLICE ultrawide JWST filters to identify new lensed galaxies, some of which are not visible in HST, to model the cluster's mass distribution. The model was constructed with a total of 11 multiply imaged systems, decomposed into 30 images with 60 clumps used as strong lensing constraints. PSZ2 G118.46+39.32 shows a clear bimodal structure, indicating that it may be undergoing a merger. The predicted mass distribution of the model aligns with the X-ray gas in the cluster, suggesting it is in a pre-merger state.

The T-Tauri type young stellar object RY Tau exhibits a dust depleted inner cavity characteristic of a transition disk. We constrain the spatial distribution and mineralogy of dust in the RY Tau protoplanetary disk in the inner few astronomical units using spectrally resolved interferometric observations in the L, M, and N bands obtained with VLTI/MATISSE. Employing a 2D temperature gradient model we estimate the orientation of the inner disk finding no evidence of significant misalignment between the inner and outer disk of RY Tau. Successively, we analyze the chemical composition of silicates depending on spatial region in the disk and identify several silicate species commonly found in protoplanetary disks. Additionally, a depletion of amorphous dust grains toward the central protostar is observed. Monte Carlo radiative transfer simulations show that hot dust close to the protostar and in the line of sight to the observer, either in the uppermost disk layers of a strongly flared disk or in a dusty envelope, is necessary to model the observations. The shadow cast by a dense innermost disk midplane on the dust further out explains the observed closure phases in the L band and to some extent in the M band. However, the closure phases in the N band are underestimated by our model, hinting at an additional asymmetry in the flux density distribution not visible at shorter wavelengths.

Multiplicity in pre-main-sequence (PMS) systems shapes circumstellar and circumbinary disks, often producing features such as inner cavities, spiral arms, and gas streamers that facilitate mass transfer between the disk and stars. Consequently, accretion in eccentric close binaries is highly variable and synchronized with their orbits, producing bursts near periastron passages. In this study, we examine the orbital and accretion properties of the eccentric Classical T-Tauri binary DQ Tau using medium- to high-resolution spectroscopy from the Very Large Telescope (VLT) X-Shooter and UVES instruments. The data were taken during a monitoring of inner disk chemistry with JWST, and our analysis is needed for correct interpretation of JWST data. We refine the orbital parameters and report an increment in the argument of periastron of 30 degrees. This apsidal motion may be caused by the massive disk acting as a third body. We also explore the possibility that it is due to a still undetected additional (sub-)stellar companion, estimating a lower limit of 15 MJ for its mass at the cavity edge (a=3 abin). We investigate accretion of the primary and secondary using the Ca II 849.8 nm emission line. The primary accretes more at periastron than in previous quiescent phases, while the secondary dominates post-periastron. Additionally, we report elevated Lacc at apastron, possibly due to interaction with irregularly shaped structures near the closest approach to the circumbinary disk. Finally, we derive each star's accretion luminosity across disentangled epochs and compare it to UV-excess-based results, finding good agreement. The individual Lacc values can be used as input for chemical models.

We present a multiscale microstructural analysis of olivine from the non-poikilitic lithology of the poikilitic shergottite NWA 7721, using dark-field X-ray microscopy (DFXM), electron backscatter diffraction (EBSD), and context in situ 2D micro-XRD. A single olivine crystal contains two distinct subgrain populations. Type 1 subgrains are fine (1-5 micrometers), randomly oriented, and nearly strain-free, whereas Type 2 subgrains are coarse (greater than 30 micrometers), aligned, and strongly strained. Layered DFXM data reveal slip-band features in Type 2 that are absent in Type 1. We interpret Type 1 as products of shock-induced recrystallization, whereas Type 2 preserves remnants of a highly deformed parent grain. This bimodal microstructure, not observed in other Martian meteorites including the paired NWA 1950 and ALH A77005, points to a heterogeneous response to impact influenced by pre-existing strain in the olivine grain. We propose that NWA 7721 olivine experienced substantial crustal or magmatic stress before impact. The subsequent shock wave imposed a rapid load-release cycle that mobilized dislocations and produced low-angle boundaries in Type 2, while driving recrystallization of Type 1. Grain-growth constraints limit the post-shock heating duration to approximately 2.3 s, consistent with rapid quenching. These results provide the first evidence that non-poikilitic olivine in NWA 7721 preserves dynamic crustal deformation on Mars in the Late Amazonian.

Building upon a thermodynamic formalism, we show that self-gravitating systems in hydrostatic equilibrium with a uniform density are maximal entropy states when submitted to perturbations which are slow on dynamical timescale. We coin this phenomenon "thermodynamic blocking", given its similarity with the more general "kinetic blocking". This result underlines the importance of the thermodynamic formalism which proves useful when kinetic equations break down.

We present an Atacama Large Millimeter/submillimeter Array (ALMA) Band 9 continuum detection ($3.3 \sigma$) of MACS0416_Y1 that confirms the suspected warm dust (91$^{+62}_{-35}$ K) of this Lyman-Break Galaxy (LBG) at $z = 8.3$ with $\log_{10} M_{\ast}/$M$_{\odot} = 9.0 \pm 0.1$. A modified black-body fit to the ALMA Bands 3 through 9 data of MACS0416_Y1 finds an intrinsic infrared luminosity of 1.0$^{+1.8}_{-0.6} \times{} 10^{12}\ \mathrm{L_{\odot}}$, placing this UV-selected LBG in the regime of Ultra Luminous Infrared Galaxies (ULIRGs). Its luminous but modest dust reservoir (1.4$^{+1.3}_{-0.5} \times{} 10^{6}\ \mathrm{M_{\odot}}$) is co-spatial to regions with a UV-continuum slope $\beta_{\rm UV} \approx -1.5$ as seen by James Webb Space Telescope (JWST) imaging. Although this implies some dust obscuration, the JWST photometry implies less obscured star formation than seen in the complete characterization by ALMA, implying some spatial separation of dust and stars on scales below 200 pc, i.e., smaller than those probed by JWST and ALMA. This source is an extreme example of dust-obscured star formation contributing strongly to the cosmic build-up of stellar mass, which can only be revealed through direct and comprehensive observations in the (sub)mm regime.

Context. Rapid rotation in massive stars leads to gravity darkening and oblateness, significantly affecting their radiation-driven winds. These effects can alter wind dynamics and play a role in forming slowly equatorial outflowing winds. Aims. This work investigates the transition region where the fast solution (i.e. high terminal velocities) of radiation-driven winds in a massive rotating star, in the frame of the modified-CAK theory, switches to the Omega-slow solutions (a denser and slower wind) when the effects of gravity darkening and oblateness are considered. This Omega-slow solution appears when the rotational speed is higher and equal to 75% of the critical rotation speed. Methods. To explore the transition region for various equatorial models of B-type stars, we focus on the co-existence interval where both solutions simultaneously exist and the transition point where fast solutions switch to Omega-slow solutions. Results. Using our stationary numerical code Hydwind, we first analyse the individual effects of gravity darkening and stellar oblateness caused by high rotational speeds and then examine their combined impact on the wind solutions. Conclusions. We find that for a certain range of rotational speeds, both the fast and Omega-slow solutions can co-exist, and the co-existence range strongly depends on the initial conditions. When only gravity darkening is considered, the co-existing interval shifts towards higher rotational speeds. While in the presence of the oblateness, the co-existing interval also occurs at higher rotational speeds; however, it is less than the gravity darkening effect. We also explored how line-force parameters affect the critical point, the location of the co-existing interval, and where the solution switches.

First-order phase transitions (FOPTs) in cold neutron stars (NSs) have been extensively studied and have provided valuable insights into the behavior of the densest matter visible in our Universe, although a strong consensus has yet to emerge. Revisiting the possibility of a hadron-quark FOPT from a new perspective, we examine the interplay between the coupled nature of gravity and microscopic interactions in Tolman--Oppenheimer--Volkoff (TOV) equations and the fundamental requirements of thermodynamic consistency in NSs. We demonstrate that a sharp FOPT manifested as a plateau in the equation of state (EOS) $P(\varepsilon)$, i.e., pressure $P$ versus energy density $\varepsilon$, is intrinsically incompatible with the regularity conditions of the TOV solutions. Although numerical integrations of the TOV equations with EOSs incorporating FOPTs may yield seemingly reasonable mass-radius relations consistent with current observations, such results can mask underlying inconsistencies. Our analysis thus establishes a structural consistency criterion for constraining dense-matter EOSs using NS observables, complementing existing studies of possible phase transitions in NS interiors.

In this starter guide, we provide a high-level overview of analysis of WFC3/IR data available from the Mikulski Archive for Space Telescopes (MAST). We intend this guide as a starting point for users examining WFC3/IR data for the first time, or for those refreshing their memory on WFC3/IR data analysis. Therefore, we focus on the analysis of archival data, not preparing new observations. Three appendices include A) a summary of the instrument and an optical schematic, B) examples from the Exposure Time Calculator, and C) a glossary of uncommon acronyms. This report addresses only data from WFC3's IR channel; not the UVIS channel.

Connecting the formation and evolution of galaxies to the large-scale structure is crucial for interpreting cosmological observations. While hydrodynamical simulations accurately model the correlated properties of galaxies, they are computationally prohibitive to run over volumes that match modern surveys. We address this by developing a framework to rapidly generate mock galaxy catalogs conditioned on inexpensive dark-matter-only simulations. We present a multi-modal, transformer-based model that takes 3D dark matter density and velocity fields as input, and outputs a corresponding point cloud of galaxies with their physical properties. We demonstrate that our trained model faithfully reproduces a variety of galaxy summary statistics and correctly captures their variation with changes in the underlying cosmological and astrophysical parameters, making it the first accelerated forward model to capture all the relevant galaxy properties, their full spatial distribution, and their conditional dependencies in hydrosimulations.

$\textit{Context.}$ There is considerable debate on how massive stars form, including whether a high-mass star must always form with a population of low-mass stars or whether it can also form in isolation. Massive stars found in the field are often considered to be runaways from star clusters or OB associations. However, there is evidence in the Milky Way and the Small Magellanic Cloud of high-mass stars that appear isolated in the field and cannot be related to any known star cluster or OB association. Studies of more distant galaxies have been lacking so far. $\textit{Aims.}$ In this work, we identified massive star candidates that appear isolated in the field of the nearby spiral galaxy NGC 4242 (distance: 5.3 Mpc), to explore how many candidates for isolated star formation we find in a galaxy outside the Local Group. $\textit{Methods.}$ We identified 234 massive ($M_{ini}\geq15M_{\odot}$) and young ($\leq 10$ Myr) field stars in NGC 4242 using the Hubble Space Telescope's Solar Blind Channel of the Advanced Camera for Surveys, the UVIS channel of the Wide Field Camera 3 from the Galaxy UV Legacy Project (GULP) and optical data from the Legacy ExtraGalactic UV Survey (LEGUS). We investigated the surroundings of our targets within the range of projected distances expected for runaway stars, $74$ pc and $204$ pc. $\textit{Results.}$ We find that between $9.8\%$ and $34.6\%$ of our targets have no young stellar groups or massive stars within the threshold radii, making them appear isolated. This fraction reduces to $3.2\%-11.5\%$ when we consider the total number of massive stars expected from the observed UV star formation rate. $\textit{Conclusions.}$ Our results show that there is a small population of young and massive, potentially isolated field stars in NGC 4242.

We provide a detailed characterisation of the planetary system orbiting HD 85426 (TOI-1774). This bright G-type star ($M_{\ast}$: 0.99 $\text{M}_{\odot}$; $R_{\ast}$: 1.13 $\text{R}_{\odot}$; age: 7.4 Gyr; V mag: 8.25) hosts a transiting sub-Neptune, HD 85426 b, with an orbital period of 16.71 days and a blackbody equilibrium temperature of $824^{+11}_{-11}$ K. By jointly analysing HARPS-N RVs, TESS, and CHEOPS photometric data and using two different stellar activity mitigation techniques, we constrain planet b's mass to $6.0^{+1.5}_{-1.6}$ $\text{M}_{\oplus}$ and $8.5^{+1.3}_{-1.4} $ $\text{M}_{\oplus}$, depending on the mitigation technique. We investigate the dependence of these results on the priors, data selection, and inclusion of other Keplerians in the modelling. Using this approach, we identify the presence of two non-transiting planetary companions with minimum masses near 10 $\text{M}_{\oplus}$ and orbital periods of 35.7 and 89 days. Additionally, we reject the initial hypothesis that the 35.7-day periodic signal was due to stellar activity. We also determine HD 85426 b's radius to be $2.78^{+0.05}_{-0.04}$ $\text{R}_{\oplus}$ and compute a transmission spectroscopy metric in the range of 82 to 115, making this planet a highly valuable target for atmospheric characterisation.

The James Webb Space Telescope (JWST) begun to revolutionize our view of the Cosmos. The discovery of Blue Monsters (i.e. ultracompact yet very bright high-z galaxies) and the Little Red Dots (i.e. very compact dustless strong Balmer break cosmic dawn sources) pose significant challenges to pre-JWST era models of the assembly of first stars and galaxies. In addition, JWST data further strengthen the problem posed by the origin of the supermassive black holes that power the most distant quasars observed. Stars powered by Dark Matter annihilation (i.e. Dark Stars) can form out of primordial gas clouds during the cosmic dawn era and subsequently might grow via accretion and become supermassive. In this paper we argue that Supermassive Dark Stars (SMDSs) offer natural solutions to the three puzzles mentioned above. Moreover, we present the best evidence so far, for the existence of SMDSs: the identification of a He~II$\lambda$2511~Å absorption feature at $S/N\sim4$ in the spectrum of JADES-GS-z13-0.

Similar to the solar cycle, the magnetic cycles of other solar-type stars are also variable. How the variability of the stellar cycle changes with the rotation rate or the dynamo number is a valuable information for understanding the stellar dynamo process. We examine the variability in the stellar magnetic cycles by studying 81 stars from the data of the Mount Wilson Observatory, which started observations in 1966. For 28 stars, we have time series data available till 2003, while for others, the data are limited till 1995. We specifically explore how the variability changes with respect to three rotation-related parameters. We find a modest positive correlation between the variability and the stellar rotation period. In addition, we find suggestive negative correlations between the variability and the inverse squared Rossby number ($Ro^{-2}$), and the ratio of the mean cycle duration and rotation period ($\log \, (\langle P_{\rm cyc} \rangle / P_{\rm rot})^2$). Variability computed from the magnetic field of stellar dynamo models also show similar trends. Finally, inspired by previous studies, we examine dynamo number scaling in our model data and find that $Ro^{-0.6}$ (instead of $Ro^{-2}$ as suggested in the linear $\alpha \Omega$ dynamo theory) and $(\langle P_{\rm cyc} \rangle /P_{\rm rot})^{0.6}$ (instead of $\log \, (\langle P_{\rm cyc} \rangle / P_{\rm rot})^2$ as predicted in previous observations) are a good measure of the dynamo number. In conclusion, our results demonstrate that the stellar magnetic cycle variability decreases with the increase of the rotation rate or the dynamo number.

Gravitational waves (GWs) propagating through the universe can be microlensed by stellar and intermediate-mass objects. Lensing induces frequency-dependent amplification of GWs, which can be computed using \texttt{GLoW}, an accurate code suitable for evaluating this factor for generic lens models and arbitrary impact parameters depending on the lens configuration. For parameter inference, we employ the DINGO algorithm, a machine learning framework based on neural posterior estimation, a simulation-based inference method that uses normalizing flows to efficiently approximate posterior distributions of the physical parameters. As a proof-of-principle, we demonstrate that it enables efficient parameter estimation of diffracted GW signals using an isolated point mass lens model. This method can be useful for rapidly identifying microlensed events within large GW catalogs and for conducting population studies of compact binaries. Compared to traditional parameter estimation techniques, we find that combining DINGO with importance sampling can provide efficient estimation of the background Bayes-factor distribution, which is required in evaluating the significance of candidate lensed events. However, for foreground (lensed) events, care must be taken, as sampling efficiency can decrease when the lensed data lie outside the distribution learned by the unlensed DINGO network. Our framework can be naturally extended to more complex and realistic lens models, allowing detailed analyses of the microlensed GWs.

We present a novel ray acceleration structure for radiative transfer outside of local thermodynamic equilibrium (non-LTE), leveraging techniques from computer graphics to improve computational efficiency. By applying mipmapping (local recursive spatial averaging) and sparse voxel grids, we exploit spatial coherence and sparsity in astrophysical models to accelerate the formal solution of the radiative transfer equation. We introduce a variance-limited mipmapping (VLM) scheme with tunable error control, and extend it to handle anisotropic emission via two methods: velocity interpolation, and so-called "Core and Voigt". Our approach integrates a hierarchical digital differential analyzer (HDDA) for efficient ray traversal, which, combined with the mipmapping scheme achieves an order of magnitude speedup with less than 0.5 % error in the 99.9th percentile of the level populations. These methods are implemented in the DexRT code and demonstrate significant performance gains in realistic solar atmospheric models.

Lunar dust -- the sub-millimeter fraction of the regolith -- controls the optical, thermophysical, electrical, mechanical, and environmental behavior of the Moon's surface. These properties set the performance envelopes of remote-sensing retrievals, regolith geotechnics, volatile cycles, and exploration systems, while also posing operational and biomedical risks. We synthesize Apollo sample analyses and in-situ observations (Surveyor, Lunokhod, Apollo) with contemporary datasets from the LRO Diviner Lunar Radiometer, the LADEE/LDEX exospheric dust measurements, and Chang'e-4 Lunar Penetrating Radar (LPR). We also incorporate 2024-2025 results: Chandrayaan-3 ChaSTE thermophysics at the Vikram lander's site, SCALPSS plume-surface diagnostics from Intuitive Machines Mission 1 (IM-1), and Negative Ions at the Lunar Surface (NILS) detections of a dayside near-surface H$^{-}$ population on Chang'e-6. The review links (i) production and modification processes to (ii) grain-scale physical/chemical/electrical/optical/mechanical properties, then to (iii) mobilization pathways (meteoroid ejecta, electrostatic hopping, rocket-plume entrainment), and finally to (iv) region-specific design ranges across maria, highlands, pyroclastic units, magnetic swirls, and permanently shadowed regions (PSRs). We quantify temperature-illumination dependence across day/night and PSR-equator regimes through a two-channel $k(T,\rho)$ model and charge-relaxation scaling. We provide closed-form expressions for adhesion-aware lift thresholds and for near-surface (0-3~m) dust transport at apex/hover heights as functions of sheath structure. The result is a design-ready set of relations, figures, and tables that propagate microphysics and composition into engineering parameters for upcoming landed and rover operations.

Supermassive stars (SMSs) may explain both the early emergence of supermassive black holes and the unusual abundance patterns observed in young galaxies and globular clusters. They are traditionally associated with primordial ``direct collapse'' at very low metallicity, but recent studies indicate that SMSs can also form in metal-enriched environments alongside numerous low-mass stars. We present detailed evolutionary models of SMSs with metallicities \(Z/Z_\odot = 10^{-5}\)--\(10^{-2}\), computed using \textsc{GENEC} and consistent with protostellar growth rates derived from cluster-collapse simulations. The final masses reach \(\sim7.2\times10^{4}\,M_\odot\) at \(10^{-5}\,Z_\odot\) and \(\sim2.3\times10^{3}\,M_\odot\) at \(10^{-2}\,Z_\odot\) through gas accretion and stellar collisions. Each model is evolved through the pre-main-sequence and core-hydrogen-burning phases, terminating either at the onset of general-relativistic instability \(Z\lesssim10^{-4}\,Z\) or at core-helium exhaustion for \(Z\gtrsim10^{-3}\,Z\). The dominant growth mode transitions from collision-dominated to accretion-limited between \(Z = 10^{-4}\) and \(10^{-3}\), while stellar lifetimes remain nearly constant at \(1.8\)--\(2.0\) Myr. We find that even in extreme cases, when additional hydrogen supplied by collisions amounts to \(\sim4.7\times10^{4}\,M_\odot\), the lifetime is only extended by \(\sim0.6\) Myr. During core-hydrogen burning, the critical accretion rate required to maintain the supergiant phase along the Hayashi line (\(\dot{M}_{\mathrm{crit}}\)) decreases as nuclear fuel is consumed, reducing UV emissivity and feedback efficiency. This facilitates SMS formation in a broader range of environments than previously expected, including those with metallicities up to \(Z \simeq 0.01\,Z_\odot\), typical of globular clusters.

We systematically study how cooling creates structural changes in supernova remnants as they evolve. Inspired by the peculiar morphology of the Pa 30 nebula, we adopt a framework in which to characterize supernova remnants under different degrees of cooling. Our cooling framework characterizes remnants with a singular parameter called $\beta$ that sets how rapidly the system's thermal energy is radiated or emitted away. A continuum of morphologies is created by the implementation of different cooling timescales. For $\beta \gtrsim 400$, or when the cooling timescale is shorter than $\approx \frac{1}{400}$ of the Sedov time, the ejecta is shaped into a filamentary structure similar to Pa 30. We explain the filament creation by the formation of Rayleigh-Taylor Instability fingers where cooling has prevented the Kelvin-Helmholtz Instability from overturning and mixing out the tips. The ejecta in these filaments have not decelerated and are moving almost completely ballistically at $\approx 95-100\%$ their free expansion speed. In this rapid cooling regime, an explosion energy $\approx 3.5 \times 10^{47}$ erg is inferred. We also propose the cooling mechanism required to create these structures necessitates removing energy at a rate of $2\%$ of $E_{\rm ej}/t$, which implies a cooling luminosity of $\approx 10^{36}$ erg/s.

We explore the cosmological signatures of neutrino and Hot Dark Matter (HDM) wakes, which refers to the preferential accumulation of neutrinos (or, more broadly, HDM particles) downstream of moving cold dark matter structures. We improve on existing theoretical models, and provide forecasts for the detectability of the effect in future surveys under more realistic conditions than previously considered in the literature. We show that neutrino and HDM wakes are unlikely to be ever observed with the most natural tracer of a hot subcomponent of the total dark matter on cosmological scales, i.e. 2D weak lensing surveys. However, the effect can be detected at a high significance with idealistic 3D maps of a tracer of HDM, for sufficiently small values of the effective free-streaming length (e.g. present-day values of $k_{\textrm{fs},0} \gtrsim 0.1\textrm{Mpc}^{-1}$ to reach $\textrm{SNR} \gtrsim 1$, for a HDM species accounting for a percent of the total dark matter). HDM wakes are a smoking gun of the effects of free-streaming, which cannot be mimicked by changes to the background expansion history (such as allowing for the dark energy to be dynamical), and hence offer another avenue to search for massive neutrinos, and hot subcomponents of the total dark matter more broadly, in a way that complements traditional observables.

We show that dark stars, which are dark-matter-powered stars in the early universe, can grow by accretion to masses in the range $\mathscr{O}\left ({10}^4\right )-\mathscr{O}\left ({10}^7\right)\,{M_\odot}$ before the general-relativistic Feynman-Chandrasekhar instability causes their dynamical collapse to black holes. These accreting dark star configurations avoid standard stellar nuclear- and weak-interaction evolution that would lead to their demise long before they reached this supermassive size. Remarkably, this mechanism for supermassive black hole (SMBH) genesis is relatively robust to initial dark star mass, formation epoch, accretion rate and its history. The SMBHs produced this way can serve as seeds for even larger SMBHs $({\gtrsim}10^9\,M_\odot)$ that have been discovered at high redshift.

We investigate the impact of instrumental and astrophysical systematics on dark energy constraints derived from Type~Ia supernova (SN-Ia) observations. Using simulated datasets consistent with current SN-Ia measurements, we explore how uncertainties in photometric calibration, intergalactic dust, progenitor evolution in luminosity and light-curve stretch, and intrinsic color scatter affect the inferred dark energy equation of state parameters (w0, wa). We test the Generalised Scale Factor (GEN) evolution and benchmark it against three time-evolving dark energy models; namely Chevallier Polarski Linder (CPL), Jassal Bagla Padmanabhan (JBP) and Logarithmic (LOG) parametrizations; comparing their sensitivity to these systematic effects. Calibration biases and progenitor evolution emerge as the dominant sources of uncertainty, while simpler parametrisations, viz. GEN, which directly describes the expansion rate, remains relatively stable under all systematic injections, unlike CPL, JBP and LOG that rely on the dark energy equation of state. These findings underscore the need for sub-per cent calibration precision and enhanced astrophysical modelling to ensure the robustness of dark energy inferences from current and future SN-Ia cosmology experiments.

The James Webb Space Telescope (JWST) has discovered numerous bright galaxies at high redshifts ($z\approx$ 10 -- 14). Many astrophysical models and beyond the Standard Model physics scenarios have been proposed to explain these observations. We investigate, for the first time, the implications of dark matter (DM) scattering with baryons (protons and electrons) in light of the JWST UV luminosity function (UVLF) observations. These interactions suppress structure formation on galactic scales, which may have an observable effect on the UVLF measurements at high redshifts. Using a recent galaxy formation model designed to explain high-redshift observations, we obtain strong upper limits on DM-baryon scattering cross-sections and explore new regions of the parameter space. For DM-proton scattering with cross-section $\propto v^{-2}$ velocity dependence, we obtain the strongest limit for DM masses of $\sim$ 1 -- 500 MeV. For other cases that we study (DM-proton scattering cross-section $\propto v^{0},\,v^{-4}$, and DM-electron scattering cross-section $\propto v^{0},\,v^{-2},\,v^{-4}$), our limits are competitive with those obtained from other cosmological observables. Our study highlights the potential of JWST observations as a novel and powerful probe of non-gravitational interactions of DM.

The horizon-scale images of supermassive black holes (BHs) by the Event Horizon Telescope Collaboration (EHT) have provided new opportunities to test general relativity and other theories of gravity. In view of future projects, such as the next-generation Event Horizon Telescope (ngEHT) and the Black-Hole Explorer (BHEX), having the potential of enhancing our ability to probe extreme gravity, it is natural to ask: \textit{how much can two black-hole images differ?} To address this question and assess the ability of these projects to test theories of gravity with black-hole shadows, we use general-relativistic magnetohydrodynamic and radiative-transfer simulations to investigate the images of a wide class of accreting BHs deviating from the Kerr solution. By measuring the mismatch between images of different BHs we show that future missions will be able to distinguish a large class of BHs solutions from the Kerr solution when the mismatch in the images exceeds values between $2\%$ and $5\%$ depending on the image-comparison metric considered. These results indicate future horizon-scale imaging with percent-level image fidelity can place meaningful observational constraints on deviations from the Kerr metric and thereby test strong-field predictions of general relativity.

In this work, we show that ultralight dark photons, which couple to the Standard Model photon through kinetic mixing, can potentially source galactic scale magnetic fields. Although these magnetic fields would be too weak to detect at present in galaxies due to plasma screening effects, we show that dark photons can provide the seed magnetic field strength ($10^{-20}$ G) required for dynamo amplification in galaxies. Such dynamo-amplified magnetic fields are consistent with observations of $\mu$G strength galactic magnetic fields.

Gravitational wave signals from compact binary coalescences offer a powerful and reliable probe of General Relativity. To date, the LIGO-Virgo-KAGRA collaboration has provided stringent consistency tests of General Relativity predictions. In this work, we present forecasts for the accuracy with which General Relativity can be tested using third-generation ground-based interferometers, focusing on Einstein Telescope (ET) and binary black hole mergers. Given the expected high detection rate, performing full Bayesian analyses for each event becomes computationally challenging. To overcome this, we adopt a Fisher matrix approach, simulating parameter estimation in an idealized observation scenario, which allows us to study large populations of compact binary coalescences with feasible computational efforts. Within this framework, we investigate the constraints that ET, in its different configurations, can impose on inspiral post-Newtonian coefficients, by jointly analyzing events using a Bayesian hierarchical methodology. Our results indicate that ET could in principle achieve an accuracy of $\mathcal{O}(10^{-7})$ on the dipole radiation term and $\mathcal{O}(10^{-3})$ on higher-order post-Newtonian coefficients, for both the triangular and the two L-shaped designs, with $10^4$ catalog events. We also assess the number of detections required to confidently identify deviations from General Relativity at various post-Newtonian orders and for different detector configurations.

The search for neutrinoless double beta decay (0$\nu\beta\beta$) is fundamental for investigating lepton-number violation, probing new physics beyond the Standard Model, and determining whether neutrinos are Majorana particles. CUORE (Cryogenic Underground Observatory of Rare Events), a cryogenic bolometric experiment at LNGS, studies 0$\nu\beta\beta$ in $^{130}$Te using 988 TeO$_2$ crystals. It is a milestone of cryogenic detector arrays with a tonne-scale detector operated for more than 7~years below 15~mK. Since 2017, CUORE has accumulated over 2.9~tonne-years of exposure, achieving one of the leading 0$\nu\beta\beta$ limits and one of the most precise two-neutrino double beta decay (2$\nu\beta\beta$) half-life measurements thanks to a detailed background reconstruction across a broad energy range. Building on CUORE's success, CUPID (CUORE Upgrade with Particle ID) aims to significantly enhance its 0$\nu\beta\beta$ discovery sensitivity to $10^{27}$ yr in $^{100}$Mo, covering the Inverted Hierarchy of neutrino masses. It will employ 1596 lithium molybdate (Li$_2$MoO$_4$) crystals enriched in $^{100}$Mo, alongside 1710 light detectors with Neganov-Trofimov-Luke amplification, enabling simultaneous heat and light readout for enhanced background rejection, particularly against alpha contamination and 2$\nu\beta\beta$ pileup. CUPID will reuse CUORE's cryostat and infrastructure. Current efforts focus on detector performance validation, sensitivity studies, and finalizing the experimental design to maximize physics reach. This work presents the latest CUORE results and outlines the key milestones toward CUPID's realization.

Pulsar timing arrays probe isotropic stochastic gravitational wave (GW) backgrounds in the nanohertz band but are insensitive to its parity-violating component. Motivated by recent progress in pulsar polarization arrays, we study the response of pulsar polarimetry to GWs and evaluate its potential to detect circular polarization in isotropic stochastic GW backgrounds, which characterizes parity violation. Based on geometric optics, we derive the rotation of the polarization of electromagnetic waves induced by propagation through a GW background. We show that the cross-correlation between pulsar timing and polarimetry signals isolates the circular polarization component from the GW intensity, sharing the same Hellings-Downs angular pattern. With future facilities such as the SKA, timing-polarimetry correlations could reach sensitivities to the circular polarization of GWs comparable to those of the current astrometric methods.

Gravitational waves (GWs) are direct probes of cosmological gravity, sensitive to space-time inhomogeneities along their propagation. The presence of massive objects breaks homogeneity and isotropy, allowing for new interactions between different GW polarizations, and opening up the intriguing opportunity to test modified gravity theories. This setup generalizes the notion of gravitational deflection and lensing, revealing novel phenomena in modified theories. Any non-minimal theory introduces effective mass terms for GWs, causing \textit{lens-induced dispersion} (LID), a frequency-dependent phase shift on the waveform. We compute GW dispersion in Einstein's general relativity (GR) for a spherical matter distribution, finding a small but non-zero phasing that is potentially accessible to next-generation detectors. We then extend our analysis to scalar-tensor theories, focusing on symmetron gravity as an example of screened theory, combining cosmological deviations and consistency with local gravity tests. We find enhanced GW dispersion in a large region of the symmetron parameter space, compared to both GR and Brans-Dicke theory. We argue that dispersion, associated to an effective mass for the metric fluctuations, can in some cases prevent the propagation of GWs through some astrophysical bodies, turning them into reflectors. Our analysis shows that the Earth becomes an efficient GW shield for a hitherto unconstrained region of the symmetron parameter space, leading to a $\sim 50\%$ fraction of events becoming unobservable or at least displaying a dramatic modification of the detector antenna response. The richness and universality of dispersive phenomena in non-minimal theories open a new avenue to test theories of dynamical dark-energy, relevant in light of recent observational results challenging the $\Lambda$CDM paradigm.

This paper presents a method for determining spacecraft angular rates using event-based camera sensing. This is achieved by analyzing the temporal distribution of brightness events triggered by the apparent motion of stars. The location and polarity of the events are used to infer the apparent motion field of the stars, which is, in turn, employed to estimate the observer angular velocity in the camera frame. This can be converted to the spacecraft angular rates provided an attitude reference. The method is validated through numerical simulation for a synthetic dataset of event streams generated on random spacecraft pointing and rates conditions. The accuracy of the method is assessed, demonstrating its potential to complement or replace conventional rate sensors in spacecraft systems using event camera sensing.

The forthcoming space-based gravitational-wave observatory Laser Interferometer Space Antenna (LISA) should enable the detection of Extreme Mass Ratio Inspirals (EMRIs), in which a stellar-mass compact object gradually inspirals into a supermassive black hole while emitting gravitational waves. Modeling the waveforms of such systems is a challenging task, requiring precise computation of energy and angular momentum fluxes as well as proper treatment of orbital resonances, during which two fundamental orbital frequencies become commensurate. In this work, we perform a systematic comparison of fluxes derived from three approaches: the quadrupole formula, post-Newtonian approximations, and time-domain solutions of the Teukolsky equation. We show that quadrupole-based fluxes remain in good agreement with Teukolsky results across a broad range of orbital configurations, including perturbed orbits. Building on these insights, we explore the dynamical impact of resonance crossings within the adiabatic approximation. By introducing novel numerical methods, we reduce computational costs and uncover diverse resonance-crossing behaviors. These results contribute to the effort to understand theoretically and model adequately resonance crossings during an EMRI.

Extremely large mass-ratio inspirals (XMRIs), formed by brown dwarfs inspiraling into a massive black hole, emit gravitational waves (GWs) that fall within the detection band of future space-borne detectors such as LISA, TianQin, and Taiji. Their detection will measure the astrophysical properties of the MBH in the center of our galaxy (SgrA$^\ast$) with unprecedented accuracy and provide a unique probe of gravity in the strong field regime. Here, we estimate the benefit of using the GWs from XMRIs to constrain the Chern-Simons theory. Our results show that XMRI signals radiated from the late stages of the evolution are particularly sensitive to differences between Chern-Simons theory and general relativity. For low-eccentricity sources, XMRIs can put bounds on the Chern-Simons parameter $\zeta$ at the level of $10^{-1}$ to an accuracy of $10^{-3}$. For high-eccentricity sources, XMRIs can put bounds on the parameter $\zeta$ at the level of $10^{-1}$ to an accuracy of $10^{-6}$. Furthermore, using the time-frequency MCMC method, we obtain the posterior distribution of XMRIs in the Chern-Simons theory. Our results show that almost all the parameters can be recovered within $1\sigma$ confidence interval. For most of the intrinsic parameters, the estimation accuracy reaches $10^{-3}$. For the brown dwarf mass, the estimation accuracy reaches $10^{-1}$, while for $\zeta$, the estimation accuracy reaches $\Delta\log_{10}\zeta=0.08$ for high eccentricity sources and 1.27 for low eccentricity sources.

RF pulse modulation techniques are widely applied to shape RF pulses for various types of RF stations of particle accelerators. The amplitude and phase modulations are typically implemented with additional RF components that require drive or control electronics. For the RF system-on-chip (RFSoC) based next generation LLRF (NG-LLRF) platform, which we have developed in the last several years, RF modulation and demodulation are fully implemented in the digital domain. Therefore, arbitrary RF pulse shaping can be realized without any additional analogue components. We performed a range of high-power experiments with the NG-LLRF and a prototype Cool Copper Collider (C\(^3\)) structure. In this paper, the RF field measured at different stages with different pulse shapes and peak power levels up to 16.45 MW will be demonstrated and analyzed. The high precision pulse shaping schemes of the NG-LLRF can be applied to realize the phase modulation for a linear accelerator injector, the phase reversal for a pulse compressor, or the modulation required to compensate for the beam loading effect.

We test dark-energy-motivated screening mechanisms with near-Earth space-based measurements. Within a post-Newtonian treatment, we compute leading corrections to three observables, namely geodetic precession (Gravity Probe B), pericenter advance of LAGEOS-2, and Sagnac time delay in a prospective orbital configuration. We then map these corrections to bounds on chameleon, symmetron, and dilaton models. LAGEOS-2 data yield the strongest Earth-orbit limits for symmetron and dilaton models, while a prospective Sagnac setup provides the tightest constraint for chameleons. These results highlight the relevance of low-density, space-based experiments as sensitive probes of screened dark energy and exclude previously allowed regions of parameter space.

Space weather predictions of the solar wind impacting Earth are usually first based on remote-sensing observations of the solar disc and corona, and eventually validated and/or refined with in-situ measurements taken at the Sun$-$Earth Lagrange L1 point, where real-time monitoring probes are located. However, this pipeline provides, on average, only a few tens of minutes of lead time, which decreases to $\sim$30 minutes or less for large solar wind speeds of $\sim$800 km/s and above. The G5 geomagnetic storm of 2024 May provided an opportunity to test predictions generated employing real-time data from the STEREO-A spacecraft, placed 13° west of Earth and 0.04 au closer to the Sun than L1 at the time of the event, as shown recently by Weiler et al. (2025). In this Commentary, we contextualise these results to reflect upon the advantages of measuring the solar wind in situ upstream of L1, leading to improvements in both fundamental research of interplanetary physics and space weather predictions of the near-Earth environment.

A universal contribution exists in the infrared (low frequency) regime of all gravitational waves, which results from nonlinear memory. Nonlinear memory is sourced by linear order gravitational waves and exists for any gravitational-wave background. We calculate the stochastic nonlinear memory signal of various stochastic backgrounds of cosmological (scalar induced, reheating, phase transition, topological defect, turbulence) and astrophysical (binary mergers of stellar-mass, intermediate mass, supermassive, and primordial black holes) origins. These results allow us to derive the complete frequency spectrum of cosmological and astrophysical SGWB. We calculate how to probe the thermal state of the universe, i.e. the equation of the state, via the memory spectrum's slope and also discuss the detection prospects at various frequency bands with future experiments.

Metastable cosmic strings provide a minimal and predictive origin for the stochastic gravitational-wave background reported by Pulsar Timing Array experiments. We analyse this possibility in electroweak-like dark sectors with a single-stage breaking $SU(2)\times U(1)\!\to\!U(1)$ driven by one Higgs field. In the regime with dark sector Higgs mass below the $Z'$ mass, and for sufficiently small $W'$ mass, the resulting $Z$-string is classically stable but undergoes quantum decay via nucleation of monopole-antimonopole pairs along the string. We compute the corresponding semiclassical bounce action in a thin-defect approximation, treating both the string core and the monopole endpoints as localised defects whose sizes are small relative to their separation in the tunnelling configuration. This yields a decay rate per unit length that depends on the gauge couplings and the mass hierarchy. We delineate the parameter space in which single-scale dark-sector models reproduce the PTA signal, and verify that the thin-defect approximation remains valid throughout the phenomenologically favoured region, without invoking extended Higgs sectors or multi-stage symmetry breaking.