Papers for Wednesday, May 06 2026

Planned and ongoing searches for life, both biological and technological, confront an epistemic barrier concerning false positives - namely, that we don't know what we don't know. The most defensible and agnostic approach is to adopt diffuse (uninformative) priors, not only for the prevalence of life, but also for the prevalence of confounders. We evaluate the resulting Bayes factors between the null and life hypotheses for an idealized experiment with $N_{pos}$ positive labels (biosignature detections) among $N_{tot}$ targets with various priors. Using diffuse priors, the consequences are catastrophic for life detection, requiring at least ${\sim}10^4$ (for some priors ${\sim}10^{13}$) surveyed targets to ever obtain "strong evidence" for life. Accordingly, an HWO-scale survey with $N_{tot}{\sim}25$ would have no prospect of achieving this goal. A previously suggested workaround is to forgo the agnostic confounder prior, by asserting some upper limit on it for example, but we find that the results can be highly sensitive to this choice - as well as difficult to justify. Instead, we suggest a novel solution that retains agnosticism: by dividing the sample into two groups for which the prevalence of life differs, but the confounder rate is global. We show that a $N_{tot}=24$ survey could expect 24% of possible outcomes to produce strong life detections with this strategy, rising to $\geq50$% for $N_{tot}\geq76$. However, AB-testing introduces its own unique challenges to survey design, requiring two groups with differing life prevalence rates (ideally greatly so) but a global confounder rate.

The star-forming main sequence of galaxies has now been observed out to redshifts of $z\sim6$ and beyond. However, it remains unclear how long typical galaxies remain on or near it as they evolve, and how frequently they return after departing from it. To determine the expected star formation histories, we construct an analytical model to evolve galaxy properties along the star-forming main sequence over time. Our modeled star formation histories and mean ages agree remarkably well with those reconstructed from observational data. Older and more peaked star formation histories arise naturally for more massive galaxies. Simultaneously, we demonstrate that low-mass ($M_*\geq10^{8}\mathrm{M}_\odot$), early-forming ($z>3$) progenitors that remain on the star-forming main sequence must evolve into very massive ($M_*\approx10^{11}\mathrm{M}_\odot$) galaxies today. Consequently, the progenitors of intermediate mass galaxies ($M_*=10^{10}\mathrm{M}_\odot$) must have either formed late ($z<2$) or underwent significant phases ($T>1$Gyr) with suppressed star formation rates ($0.3$dex below the star-forming main sequence). We provide tracks to connect galaxies from $z=6$ to $z=0$ by their star-forming behavior above or below the main sequence. By applying number density arguments to construct evolutionary histories for Milky Way-mass galaxies, we find that they must undergo a significant phase of suppressed star formation, nearing quiescence, or otherwise become too massive. This is particularly true for the Milky Way itself, where we show that the observed presence of a large amount of old stars directly implies a departure from the star-forming main sequence over the majority of its history.

Direct observational constraints on how galaxies acquire their gas remain remarkably limited, hindering our understanding of the baryon cycle. We present a search for down-the-barrel \ion{Na}{i} D absorption towards 15.6 million galaxies at $z < 0.6$ in DESI Data Release 2. We use Bayesian evidence ratios to assess whether the absorption requires additional components tracing interstellar gas distinct from the systemic component of the galaxy. We construct a catalogue of 50 088 (27 420) galaxies with moderate (strong) evidence for down-the-barrel absorption. The inferred absorption components are broadly distributed in velocity, with approximately 50% at $v_{\rm flow} < -50$ km/s, 30% within 50 km/s of the systemic velocity and the remaining 20% at $v_{\rm flow} > 50$ km/s. We find strong evidence for a large population of low-velocity, infalling absorbers with velocities $\sim$20 km/s in edge-on galaxies, consistent with radial inflows predicted in simulations. The stronger correlation in early-type galaxies between inflow velocity and stellar velocity dispersion, compared to that with stellar mass, suggests that a portion of these inflows may be associated with accreting satellites. These results reveal the multiple pathways in which galaxies accrete gas at redshift $z < 0.6$ for the first time in a statistically significant sample.

The detailed abundance patterns of quiescent galaxies offer powerful constraints on their formation and evolution. Yet physical insight remains elusive, as nucleosynthetic yields are notoriously uncertain. We introduce a framework that circumvents this problem by using Milky Way abundance trends as empirical proxies for the yields. Applied to quiescent galaxies spanning three redshifts, SDSS ($z\sim0$), LEGA-C ($z\sim0.7$), and JWST/SUSPENSE ($z\sim2$), our approach recovers the $\alpha$- and Fe-peak abundances with a median offset of ~0.05 dex across 14 elements, compared to ~0.23 dex for theoretical yields. The largest discrepancies arise in N, Sr, Ba, and (at $z\sim2$) C, all of which depend on AGB enrichment, a channel we do not explicitly model. We explore the impact of a top-heavy IMF on our predictions and find that it can shift the IMF-averaged core-collapse supernova yields by ~0.05-0.2 dex in a direction that reduces the overall residuals. Surprisingly, the predictions succeed even without modeling the full chemical-evolution history of a galaxy; just Mg and Fe, which trace the relative contributions of core-collapse and Type Ia supernovae, suffice to predict $\alpha$- and Fe-peak elements. The success of the empirical yields, previously demonstrated in dwarf galaxies and the Milky Way disk, and now extended to massive quiescent galaxies, suggests that $\alpha$- and Fe-peak nucleosynthetic yields are largely universal. This lack of complexity makes galaxy abundance patterns highly predictable. Embedding these empirical yields in SPS models will improve inferences on stellar population properties and star formation histories. Moreover, incorporating them into cosmological simulations will produce more observationally motivated predictions.

We present a hemispherical comparison analysis of the deceleration parameter $q_0$ using the Pantheon+ sample of Type Ia supernovae to test the isotropy of cosmic acceleration and the robustness of redshift corrections. We detect directional variations in $q_0$ across redshift frames. Even in the $z_{\mathrm{HD}}$ frame, where corrections for the CMB dipole and peculiar velocities are applied, a residual dipolar anisotropy persists with $\Delta q_0 = 0.112$ and a maximum signal to noise $S/N = 2.155$, aligned with the CMB dipole direction and decreasing with increasing minimum redshift cut. The anisotropy is stronger in the $z_{\mathrm{hel}}$ and $z_{\mathrm{CMB}}$ frames, where kinematic corrections are incomplete, while the transition to $z_{\mathrm{HD}}$ reduces but does not remove the signal. Inferring the dipole from the supernovae data yields $v_{\odot} = 307.26^{+32.00}_{-22.28},\mathrm{km \, s^{-1}}$ toward $(\mathrm{RA},\mathrm{DEC}) = (156.40^{+4.72}_{-4.71}, -3.38^{+5.54}_{-8.23})^\circ$, mildly discrepant with the Planck CMB dipole at the $\sim 1.9\sigma$ level. When this SNe inferred dipole is incorporated into the redshift correction pipeline, the hemispherical anisotropy is suppressed, with the dipolar pattern disappearing and the maximum signal reduced to $S/N \lesssim 1.75$, while the remaining fluctuations become consistent with statistical noise, suggesting that part of the signal arises from residual mismatches in the modeling of the local velocity field. Since current redshift corrections rely on peculiar velocity reconstructions based on the density field, our results suggest a residual bulk flow not fully captured by these models, highlighting a source of systematic uncertainty in low redshift supernova cosmology.

We develop a formalism to characterize the imprints of late-time sources of cosmological fluctuations under the sole assumption that the injection occurs on timescales short compared to the horizon. For post-recombination injections, we derive the general modification of photon geodesics in the presence of scalar, vector, and tensor perturbations, and compute the resulting impact on the Cosmic Microwave Background through the integrated Sachs-Wolfe effect. We show that the signal is generically dominated by instantaneous injections of anisotropic stress. As an application, we consider first-order phase transitions in a sequestered dark sector and show that current observations constrain fractional energy injections at the permille level.

Recent observations of the high-redshift Universe, particularly with JWST, have revealed a population of quenched galaxies that challenges current galaxy formation models, which systematically underpredict their abundance. This discrepancy has been extensively studied for massive systems, motivating revisions to internal quenching mechanisms such as AGN feedback. However, the origin of quenching in lower-mass galaxies at high-z has received far less attention, largely due to previous observational limitations. JWST has now identified low-mass quenched galaxies (${M_{\star}}<10^{10}{\rm M_{\odot}}$). Given this emerging observational evidence, we investigate the viability of environmental quenching as the primary mechanism suppressing star formation in low-mass galaxies at $z>3$. We analyze several simulations, including L-GALAXIES, IllustrisTNG, SIMBA, and TNG-Cluster, jointly comprising more than half a million galaxies at z=5. Across all simulations, quenched systems are overwhelmingly satellites, despite representing less than 10\% of the total galaxy population. Satellite quenching increases with host halo mass and decreases with both stellar mass and halocentric distance, showing strong correlations with enhanced ram-pressure exposure and gas depletion. The simulations, particularly L-GALAXIES, produce low-mass quenched galaxies broadly consistent with those observed by JWST. Our results suggest that the recently discovered high-redshift quenched low-mass galaxies are possibly environmentally quenched systems residing in the vicinity of massive halos. According to the simulations, these galaxies are often only temporarily quenched: nearly 90\% of them merge within a few hundred megayears, and a small fraction rejuvenate and resume star formation. Extended samples from future observations will enable robust tests of the environmental origin of galaxy quenching in the early Universe.

The dust observed in debris disks is the result of a collisional cascade initiated from $\sim$ km-sized parent bodies. Using near-infrared to sub-millimeter observations, we can probe particle sizes spanning 2-3 orders of magnitude, and with sufficient angular resolution we can follow the dynamics of these dust particles. Observations taken as part of the ALMA ARKS program allowed for a detailed comparison with near-infrared scattered light observations, at unprecedented resolution. The comparison between the two wavelength regimes reveals that for most gas-bearing debris disks, the distribution of small dust grains peaks outward of the distribution of large dust grains. In this paper we investigate whether gas-dust interactions can explain such radial offsets. We perform numerical simulations and compute surface brightness profiles at several wavelengths to assess which parameters drive these radial offsets. We find that while larger gas masses lead to more efficient outward radial drift, the resulting radial offset strongly depends on the optical depth of the disk, as the drift efficiency directly competes with the particles' collisional lifetime. We also find that increasing the relative number of $\mu$m-sized dust grains usually yields a larger radial offset between scattered light and millimeter observations. Finally, we show that mid-infrared observations can complement near-infrared and sub-millimeter images, and we discuss the formation of secondary rings at near-infrared wavelengths. The angular resolution achieved by the ARKS program has opened a new avenue to study the dynamics of dust particles in debris disks, revealing unexpected differences between the appearance of the disks scattered light and thermal emission. We showed that gas-dust interactions can explain the observed radial offsets and provide pointers as to which parameters have the most significant impact.

Hot subdwarf binaries with white dwarf companions with orbital periods of less than two hours are progenitor candidates for massive single white dwarfs as well as a variety of thermonuclear explosions. Our aim is to determine the binary properties of the hot subdwarf -- white dwarf system ZTF J000742.62+480414.51, model its future evolution, and characterize the brightening events seen in TESS photometry. Using data from ZTF and TESS, we performed a Lomb Scargle analysis to find the orbital period and the period of the brightening events. Analysis of time-resolved spectroscopy was combined with light curve modeling to determine the effective temperature, surface gravity, and radius of the primary star, the masses of both stars, and to confirm the presence of an accretion disk. X-ray observations were performed with Swift, and MESA modeling was used to find the future evolution of the system. The kinematics of the system were also calculated. ZTF J000742.62+480414.51 consists of an accreting $0.48\pm0.01\,M_\odot$ white dwarf with a $0.42\pm0.01\,M_\odot$ B-type hot subdwarf acting as a donor. The system exhibits SU UMa type dwarf nova outbursts with a recurrence time of $P_{\mathrm{out}} \approx 9$ days. No X-rays were detected, with an upper limit on the X-ray luminosity of about $3\times10^{31}$ erg/sec. The system lies in the Galactic thin disk, and has an orbital period of $P_{\mathrm{orb}} = 108.72\pm0.01$ minutes. The system has likely formed from a main sequence binary with component masses $\gtrsim2\,\mathrm{M_{\odot}}$ and will likely merge into a single white dwarf, but a thermonuclear explosion cannot be ruled out. ZTF J000742.62+480414.51 consists of a low mass white dwarf actively accreting hydrogen rich material from a B-type hot subdwarf, and is the first hot subdwarf -- white dwarf system discovered that produces dwarf nova outbursts.

We present new James Webb Space Telescope Mid-Infrared Instrument (MIRI) Medium-Resolution Spectrometer (MRS) observations of the nearby ultra-luminous infrared galaxy F10565+2448. These integral field spectroscopic data reveal an unresolved nuclear outflow in both warm-ionized and warm-molecular gas phases as well as a resolved blueshifted kpc-scale warm-molecular outflow. The unresolved warm-ionized outflow has a mean projected velocity up to $-520$ km/s, while the unresolved warm-molecular outflow is slower at $-150$ km/s. For the resolved warm-molecular outflow, the projected mean velocity ($-280 < v_{50} < -110$ km/s) is only slightly faster than the velocity of the disk ($-70 < v_{50} < 120$ km/s) and as such likely does not exceed the estimated escape velocity of $\gtrsim 300$ km/s. The warm-molecular outflow is slightly hotter ($507 \pm 25$K) than the disk ($329 \pm 5$K), and displays areas of higher temperature and lower column density that may indicate a shock front, which we explore using the [Fe II] 5.34 $\mu$m/Pf$\alpha$ shock diagnostic. Analysis of the polycyclic aromatic hydrocarbon features reveal trends of ionization and grain size that first decrease with radius up to 1 kpc before increasing up to 3 kpc. These results bolster the picture of F10565+2448 being an AGN-starburst composite where both star formation and AGN-powered phenomena are required to explain the outflow energetics.

Coupling between the photosphere, chromosphere and corona in the quiet Sun (QS) is governed by a complex interplay between magnetic structuring, heating, mass loading, and radiative cooling. Constraining how this balance responds to variations in small-scale magnetic flux remains limited. We investigate how chromospheric heating and its thermodynamic coupling to higher atmospheric layers vary as a function of small-scale magnetic flux emergence. We performed a parametric set of 3D radiative-MHD simulations with the Bifrost code, starting from a weakly magnetised QS reference model and injecting horizontal magnetic flux of increasing amplitude into the sub-surface convection zone. The resulting chromospheric dynamics, heating, mass loading, and coronal response were analysed. Chromospheric temperatures and mechanical heating rise monotonically with increasing magnetic-field strength. Although the fractional contribution of shocks decreases, reconnecting current sheets keeps maintaining about 50%. In contrast, the temperature at the base of the corona exhibits a non-monotonic response, reaching a maximum at intermediate magnetic amplitudes and decreasing for the strongest-field case. We show that stronger magnetic-field strength increases chromospheric heating, which increases the coronal-base density through efficient mass loading, and amplifies radiative losses. These density-driven radiative losses dominate the coronal energy balance and thus lead to reduced coronal-base temperatures despite increased heating. Our results demonstrate the sensitivity of chromospheric structure and dynamics to small-scale flux emergence, and its key role in regulating coronal thermodynamics. This result illustrates the chromosphere-s role as a thermodynamic gatekeeper, and further warrants future investigations of atmospheric models relevant to global solar-wind models and space-weather forecasts.

High-resolution JWST-MIRI images now allow us to resolve in great detail the multi-scale nature of the emission in nearby star-forming galaxies, from compact star-forming regions to large-scale diffuse emission, giving new insights into dust emission, its composition, and the surrounding interstellar medium (ISM). We aim to understand at which scale the different processes driving dust emission in mid-infrared (7.7-21 um) wavelengths take place and if we can disentangle dense regions' emission from emission linked to a more diffuse component. We use and enhance the constrained diffusion decomposition (CDD) algorithm, an alternative to the wavelet transform decomposition, to disentangle the emission coming from compact regions from the emission originating from diffuse sources. This allows us to cleanly quantify the mid-IR spectral properties of the ISM at intervals within a continuum of physical scales. We find a transition scale of PAH emission around 300 pc, with weaker PAH fraction at smaller scales, highlighting the destruction of PAHs in HII regions. We also show variations in the PAH fraction in different morphological environments, with a smaller fraction in bright and star-forming environments. Studying and comparing the probability distribution functions (PDFs) of HII regions and diffuse ISM with the PDFs at different scales, we find a similar separation scale around 200 pc at which we observe a transition from a power-law PDF for dense structures to a log-normal one for the diffuse ISM.

Reconnection-driven nanoflares are widely considered a leading mechanism for coronal-loop heating, but their direct fingerprints in the tenuous coronal plasma remain elusive. The recently discovered coronal nanojets offer a potential probe of reconnection dynamics, but their extreme collimation, directionality and multi-wavelength visibility are not fully understood. Here we present a 3D rMHD simulation that unprecedentedly reproduces the key properties of nanojets, offering a viable model to explain their nature. These results provide a unified picture in which nanojet morphology, dynamics and detectability are contingent on the thermodynamic environment of reconnection. Together, our results point to a cool origin of coronal nanojets, where cool and dense material permits narrow, multi-band jet signatures to emerge from reconnection.

High resolution spectral observations of transition region spectral lines capture the signatures of energy deposition and redistribution at the boundary between the lower and upper atmosphere, and have significant relevance for investigating the physical processes responsible for heating the solar atmosphere. Spectroscopic observations of the solar transition region have long revealed excess line broadening and non-Gaussian profiles, but their physical origin remains debated, and their spatial distribution and prevalence not well established. Here we analyze Si IV line profiles in full-disk mosaics of observations with Interface Region Imaging Spectrograph (IRIS), and show that the non-Gaussian profiles comprise ~60% of the observed profiles, significantly more than previously reported. The IRIS observations, together with magnetic field extrapolations, indicate that the degree of non-Gaussianity systematically depends on the viewing angle between the line of sight and the magnetic field. We find that k-like profiles, indicative of suprathermal velocity distributions, are significantly more prevalent when the magnetic field is oriented at a large angle with respect to the line of sight, at all intensity levels. k-like profiles on average correspond to more limited line width and reduced redshift, compared with Gaussian profiles, particularly in bright regions, such as plage and moss. The results provide observational evidence of the importance of anisotropic kinetic processes in the solar transition region that are not captured by the magnetohydrodynamic approaches that are typically invoked to study the low solar atmosphere. Our observations indicate that more advanced multi-fluid and/or kinetic modeling should be developed.

We present the Milky Way Globular Cluster Corpus v1.3.1, a unified machinereadable database of fundamental parameters for 174 Milky Way globular clusters assembled from four independent published surveys. Each cluster record integrates photometric and structural parameters from Harris [1996] (2010 revision), Gaia EDR3 proper motions from Vasiliev and Baumgardt [2021], N-body dynamical masses and orbital parameters from Baumgardt et al. [2023],, and mean chemical abundances from the APOGEE DR17 globular cluster Value Added Catalog of Schiavon et al. [2024]. The corpus contains 17,438 non-null data points across 174 clusters stored in JSONL, JSON, and flat CSV formats with consistent native-typed fields (float, int, bool, null), embedded provenance blocks, and fully documented schema. Survey coverage is 157/174 clusters for Harris photometry, 170/174 for Gaia EDR3 proper motions, 154/174 for Baumgardt N-body dynamics, and 72/174 for APOGEE DR17 chemistry. The corpus was designed as a Retrieval-Augmented Generation (RAG) knowledge base for large language model applications in astrophysics research, following the same multi-survey integration methodology as the Unified Galaxy HI Rotation Curve Corpus [Flynn, 2026b], and has been validated for structured context injection with instruction-following language models. It is equally suitable for traditional quantitative analyses including orbit modeling, cluster classification, chemical tagging, and multi-survey cross-validation. The dataset is available at Zenodo DOI: https://doi.org/10.5281/zenodo.19907766

The Antennae galaxies merger produces the brightest infrared emission of any galaxy within ~20 Mpc, mostly from intense star formation taking place in supergiant molecular cloud complexes in the overlap region. Here, we present new, high-resolution NIRCam and MIRI images of the Antennae galaxies taken with the F150W, F187N, F335M, F360M, F410M, and F770W filters on JWST to search for the predicted but as-yet-undiscovered population of deeply embedded, optically obscured star clusters. We identify a population of 45 sources, 40 previously unknown, with high Bralpha/Halpha and Paalpha/Halpha flux ratios which are likely very young clusters still embedded or just emerging from their natal cocoons, and estimate their age, extinction (A_V), and mass. We find that all are extremely young (< 2.5 Myr), have A_V between 2 and 10 mag, and masses between ~ 10^4 and several x 10^6~Msun. We believe we have now uncovered all clusters with M > 3 x 10^4 Msun and A_V > 2 mag in the Antennae. While our sample represents a small fraction(~15%) of clusters younger than 3~Myr by number, it dominates the ionizing photon luminosity across the galaxy pair (~60%). We find elevated H_2/PAH ratios of the ISM surrounding the most massive pair of embedded clusters, supporting the idea that merger-induced shock-heated gas play an important role in the formation of extremely massive clusters.

Metallicity can play a significant role in massive binary evolution through its impact on the opacity within stellar interiors and wind-driven mass loss. In this work, we investigate how the double neutron star (DNS) delay time distribution (DTD) is shaped by the metallicity-dependent evolution of the helium star$-$NS progenitor system. Drawing from insights rooted in single and binary star physics, we argue that at a given metallicity, the stellar radius during the helium main-sequence sets a lower limit on the size of the DNS orbit at birth. We then perform population synthesis with the detailed binary evolution code POSYDON to illustrate the resulting DTD across a range of metallicities. Our results indicate that, independent of binary physics assumptions, the majority of DNS mergers across metallicities occur typically no earlier than $\simeq 40\,\rm{Myr}$ after star formation and peaks strongly between $80-250\,\rm{Myr}$. Roughly $15\%$ of DNSs merge within 80 Myr, which may explain $r$-process enrichment in environments with brief star formation histories, while $\gtrsim 20\%$ merge on delay times $>1$Gyr, providing an explanation for short gamma-ray bursts in old, metal-poor galaxies. The shape of the DTD can be complex, with a metallicity-dependent split in the dominant formation channel imprinting a characteristic double-peaked structure. Although ideally oriented natal kicks can produce very short merging DNS, we find that the required kick magnitudes are inconsistent with observations. Our work has implications for assessing the contribution of DNS mergers to $r$-process enrichment and gamma-ray bursts/kilonovae transients across cosmic time.

AGN feedback is a key piece of galaxy evolution but is difficult to model due to its high specific energies, multiphase nature, and limited simulation resolutions. Arkenstone is a subgrid framework for representing multiphase flows in coarse resolution simulations that has been used to model stellar feedback driven galactic winds. It ensures the correct treatment of high specific energy feedback that would otherwise be challenging to model accurately in Lagrangian simulations. We introduce the new Arkenstone BH model, which extends the Arkenstone framework to model black hole feedback. We focus on describing the first piece of this framework, which follows the hot, high specific energy phase of these outflows. The second piece, which treats their multiphase structure with a scheme for modeling unresolved cold clouds, will be implemented and described in a later paper. We present Arkenstone BH in simulations of an isolated galaxy to demonstrate the framework and its ability to capture high specific energy feedback that interacts only weakly with cold, dense gas. We show how these energetic outflows suppress star formation in our isolated galaxy by counteracting the inflow of gas from the circumgalactic medium into the interstellar medium. This work is part of the "Learning the Universe" collaboration, which aims to understand the Universe's underlying physics and initial conditions.

The amplitude of the detected stochastic gravitational wave background (SGWB) measured by pulsar timing arrays (PTAs) and the discovery of early and over-massive central black holes at high redshift by the James Webb Space Telescope (JWST) challenge current models of supermassive black hole (SMBH) formation. We study if halos containing a significant population of primordial black holes (PBHs) would increase the amplitude of the PTA signal. PBHs add an iso-curvature component to the matter power spectrum, accelerating the formation and merger of dark matter halos at all redshifts. We propose that black holes in the halo sink to the center via dynamical friction. The central black hole grows through hierarchical merging in addition to the gas accretion channel. We computed the resulting GW amplitude and performed a Bayesian inference analysis using the NANOGrav 15-year dataset. We show that the predicted amplitude of the gravitational wave background agrees with the observations. Our model only requires $0.09\%-0.12\%$ of the total mass of the halo to fall to the center, compatible with a fraction $f_{\rm pbh}\sim 0.1$ of PBHs as dark matter, if the in-falling PBHs in the stellar mass range are about a $1\%$ of the total population, as found in our previous estimation of the formation of SMBHs at $z\sim 6-10$. The PBH model that explains the JWST new found populations of SMBHs also explain the amplitude of the stochastic background of gravitational waves.

Extragalactic fast radio bursts (FRBs) have emerged as powerful probes of turbulence within the intergalactic medium (IGM), a phenomenon that plays a crucial role in various cosmological and astrophysical processes. In this study, we employ the structure function (SF) analysis on the dispersion measures (DMs) of over 3,000 FRBs, leveraging the recently released CHIME/FRB Catalog 2 alongside previously observed sources. By comparing our results with mock datasets generated from cosmological simulations, we find excellent agreement at large angular separations. At small angular scales, our findings reveal a potential scaling behavior consistent with a two-dimensional (2D) Kolmogorov power spectrum. From this scaling, we constrain the turbulence outer scale to be on the order of several Mpc, which aligns with theoretical expectations, independent observations of the low-redshift IGM, and cosmological simulations. Ultimately, to conclusively confirm this Kolmogorov-like turbulent cascade and overcome current small-sample statistical limitations, a larger sample of FRBs with sub-arcsecond localization is required.

High-quality, short-cadence photometry from TESS enables the detection of rapid oscillators with unprecedented sensitivity. In this work, we conduct a homogeneous search for high-frequency variability using 20-second cadence light curves from TESS Cycle 7 (Sectors 84--96). From $\sim 3.9\times10^{4}$ light curves, we compute Lomb-Scargle periodograms and select candidates exhibiting at least one significant signal with $\mathrm{FAP}\le 10^{-4}$ at frequencies $f\ge 50~\mathrm{d^{-1}}$. After excluding previously reported objects and performing pixel-level and light-curve vetting to mitigate contamination, we identify 73 rapid oscillators, including 24 pulsating white dwarfs, 31 hot subdwarfs, and 18 A-F stars. Using an iterative prewhitening procedure, we carry out a detailed frequency analysis for each target and derive the oscillation frequencies and amplitudes. We further investigate the physical origins of the detected frequency content and present statistical characterizations of the rapid-oscillator sample. We highlight one white dwarf and one subdwarf that exhibit clear frequency multiplets consistent with rotational splitting. This work enlarges the sample of rapid oscillators accessible with TESS data and provides a uniformly measured frequency-amplitude catalog, establishing a consistent basis for future asteroseismic and population studies.

Due to computational efficiency and numerical stability limitations, coronal simulations constrained by static magnetograms are typically performed first and then used to drive inner-heliosphere (IH) models. In this paper, we calculate the Sun-to-Earth coronal and wind evolutions using a single time-evolving MHD model, showing that implicit MHD models have the potential to meaningfully simplify and improve the overall Sun-to-Earth modelling pipeline. We extend the implicit time-evolving coronal MHD model COCONUT out to 1 AU, and utilise it to investigate solar coronal and wind evolutions around a solar maximum Carrington rotation (CR). We compare quasi-steady-state and time-evolving Sun-to-Earth simulations to evaluate the impact of the inner-boundary magnetic field evolution, which is neglected in steady-state simulations, on background plasma parameters. Comparisons with commonly used coupled Sun-to-Earth simulations are also conducted to further validate and assess the Sun-to-Earth model COCONUT. The results show that the time-evolving implicit MHD modelling approach yields noticeable differences compared to oversimplified steady-state simulations, and is efficient enough for practical applications. Modelling the solar corona and wind using a single MHD model simplifies the modelling pipeline and avoids uncertainties associated with coupling different coronal and IH models. The noticeable differences in the temporal evolution of plasma parameters at the L1 and L5 points highlight the need to use continuously evolving, synchronised magnetic field observations to improve global coronal and solar wind simulations, whereas the overall consistent evolutionary trend reveals the reliability of using L5 observations to forecast solar wind conditions near Earth about four days in advance.

Energetic electrons accelerated at coronal reconnection sites during solar flares precipitate into the lower solar atmosphere, generating nonthermal emissions and regulating energy deposition. However, how their transport and precipitation are jointly governed by the three-dimensional (3D) magnetic topology, turbulent scattering, and Coulomb collisions remains unclear. Here, we aim to disentangle these physical processes by using a data-constrained 3D particle transport model for the 2011 August 4 flare. The simulated distribution of precipitated electrons aligns closely with photospheric quasi-separatrix layers and reproduces the observed two-ribbon morphology in 1700~Å. We reveal a strong polarity asymmetry, with the 10~s precipitation fraction about six times higher in the weak positive polarity. This arises primarily from distinct mirror ratios of different polarities under the 3D magnetic configuration and can be understood via a modified escape probability for an asymmetric magnetic bottle. Varying strengths of turbulent scattering lead to a rise-then-fall trend and a pronounced energy dependence in the precipitation fraction. Coulomb collisions globally suppress precipitation, especially at low energies, and further amplify the polarity asymmetry. This integrated modeling framework bridges detailed transport physics to observable flare emissions and advances the development of quantitative models for realistic solar flare events.

Artificial satellites and space debris increasingly contaminate astronomical images, affecting scientific surveys and producing large volumes of streaked exposures. Manual inspection is no longer feasible at scale, and reliable detection and characterisation of streaks has become essential for both data-quality control and the monitoring of objects in Earth orbit. We present StreakMind, an automated pipeline designed to detect Near-Earth Objects and satellite streaks in astronomical images, characterise their geometry, and cross-identify them with known orbital objects. The system integrates all inference results into a structured database suitable for large surveys. A YOLO OBB model was trained on a hybrid dataset of 2335 images and applied to processed FITS frames. Geometric refinement, inter-frame association, satellite cross-identification, and Gaussian-based confidence scoring were then used to produce final identifications stored in a relational database. Observations from La Sagra Observatory were used to develop and test the method. On the test set, the model achieved a precision of 94 percent and a recall of 97 percent. It reliably detected faint streaks, delivered consistent geometric reconstructions, and performed robust satellite cross-identification. StreakMind demonstrates strong potential for large-scale automated analysis of linear streaks produced by both Near-Earth Objects and artificial satellites, contributing to space situational awareness.

Context. Strong gravitational lenses provide a unique tool to probe cosmology and astrophysics at high redshift, offering constraints on the mass distribution of background source populations. Despite their scientific value, their rarity and subtle visual features make them challenging to identify in the wealth of data delivered by facilities such as the James Webb Space Telescope (JWST), whose unmatched resolution and near-infrared coverage make it particularly well-suited to detecting lensing systems in this regime. Aims. We make use of the specialised open-source software AnomalyMatch, a semi-supervised learning method to trawl the ASTRODEEP and COSMOS-Web surveys for gravitational lenses. Methods. Building on a training dataset of eleven previously identified gravitational lenses, we use AnomalyMatch and its iterative human-in-the-loop method to train a neural network to identify gravitational lenses in JWST Level 3 products using ESA Datalabs. Results. In total we identify 58 unique gravitational lenses. These are graded by four experts into 16 Grade A, 16 Grade B, and 26 Grade C lenses. Of all lenses identified, 37 were previously uncatalogued. We analyse their properties such as photometric redshift measurements and spectroscopic redshift, when the latter is available. The lenses previously identified span spectroscopic redshifts to zspec < 1.39 and photometric redshifts to zphot < 2.21. The uncatalogued lens system with the highest redshift is at zphot = 2.1. Conclusions. Overall, we demonstrate the potential of AnomalyMatch for large-scale searches for gravitational lenses and other rare high-redshift objects in JWST archives.

Instabilities in telescope pointing, commonly referred to as jitter, introduce image degradation that can compromise the accuracy of critical scientific observables. This work presents a differentiable forward-modeling approach to both understand and mitigate the impact of jitter. We apply dLux -- a differentiable optical simulation framework built in the JAX numerical simulation framework -- to model the blurring effects of jitter on the final image. We categorize jitter into low-, medium-, and high-frequency regimes with respect to the camera frame rate and build simple jitter models based on its manifestation on the detector. The forward-model approach proves effective for low- and high-frequency regimes, but the inherent unpredictability of medium-frequency jitter may lead to model misspecification. As a test case we apply these models to the TOLIMAN mission, a forthcoming CubeSat telescope dedicated to detecting nearby Earth-analogue exoplanets through high-precision astrometry. Using Fisher information analysis, we quantify the effect of jitter on TOLIMAN's primary science observable -- the angular binary separation of the Alpha Centauri AB binary components. We find model misspecification does not introduce a systematic bias on the recovered binary separation except when fitting a one-dimensional jitter model to a two-dimensional motion, hence we recommend the use of a two-dimensional model. The forward-model approach offers a generalized method applicable to other telescope systems, including ongoing work with JWST's NIRISS instrument. This approach represents a significant step toward delivering higher accuracy measurements at modern observatories as demands on precision continue to rise.

Galaxy formation and evolution is one of the most active areas of research in astronomy. In recent times there have been several developments on the observational fronts particularly with the discovery of several relations between galaxy physical properties. The exact details of how they come about still remains to be understood. Such a development has been primarily possible due to a deluge of multi-wavelength data ranging from the ultra-violet (UV) to the radio, mainly due to wide field surveys e.g., the Sloan Digital Sky Survey (SDSS) in the optical. Meanwhile, simultaneous theoretical developments like a better understanding of dust attenuation and emission led to the development of techniques to extract information from the SEDs of galaxies, exploiting information from the far-ultraviolet (FUV) to the far-infrared (FIR). The substantial progress made in stellar evolution theory in the 1980s and 1990s paved the way for the latter approach to become the de facto standard in modeling the SEDs of galaxies. It became possible to synthesise a population of stars with a certain distribution and evolve it in time, keeping track of the emission from the stars, new star formation activity, gas enrichment with elements heavier than hydrogen and helium, and the absorption and re-emission from the interstellar dust. This technique, known as the stellar population synthesis (SPS), makes use of these multi-wavelength (UV to IR) data to generate a library of model SEDs. The observed SEDs can then be compared with such a library using statistical fitting techniques like the Bayesian statistics to infer the physical properties of galaxies. The main focus of this thesis is on the reliability of stellar population synthesis modelling when only limited photometry of a small number of wavelength bands is available. It is divided in two parts: elaborate understanding of SPS modelling (Part I) and...

The frequency of pressure (p) mode in $\delta$~Scuti stars can exceed the Nyquist limit of \textit{Kepler} long-cadence photometry. {These 'super-Nyquist frequencies' (SNFs) are observed as 'reflected' peaks at lower frequencies, i.e., they are Nyquist aliases that pose} a threat to asteroseismic diagnostics. Their impact on $\delta$~Scuti p modes has yet to be comprehensively explored. We performed a systematic survey to search for SNFs in 1,838 \textit{Kepler} $\delta$~Scuti stars through a novel technique based on sliding Lomb-Scargle periodogram, identifying 15,265 confirmed SNFs in 1,309 stars, from a total of 259,883 frequencies. We observe that the total number of detected frequencies per star remains featureless across the $\delta$~Scuti instability strip; however, young stars pulsate in higher frequencies and so have significantly more SNFs on average. Both the number and the rate of SNFs diminishes accordingly as $\delta$~Scuti stars become more evolved, which is consistent with both observation and stellar models. Furthermore, our method detects a greater fraction of modes as SNFs at higher frequencies, rising from approximately 1\% at 20 \(\mu \)Hz to 23\% at the Nyquist limit. The rate of underdetection is highest amongst low-amplitude modes. The SNF modulation patterns can be well distinguished from phase modulations induced by binarity or nonlinear mode interactions. We provide a frequency catalog for future asteroseismic studies of $\delta$~Scuti stars, wherein we identify each peak as being real or an alias, enabling further investigations into regular patterns of pulsation modes, linear combination frequencies, and theoretical modeling.

Polarised dust emission observations are a valuable tool to infer the structure of the magnetic field and the dispersion of polarisation position angles may be used to estimate magnetic field strengths. A natural consequence of magneto-dynamic turbulence is for the angular dispersion to have a length-scale dependence, making the measurement of angular dispersion non-trivial. In this paper, we present a study of parametrised, scale dependent maps, focusing on the effect of pixel size and beam convolution on the measured angular dispersion when using the commonly employed unsharp-masking and structure function methods. We find that in all cases the measured angular dispersion is underestimated compared to the true value. The degree to which the measured angular dispersion is underestimated varies by factors of 1-10 when measured on scales of 1-3x the beam size, and depends on the underlying structure of the polarisation angle field. This suggests that currently derived magnetic field strengths using angular dispersions are chronically overestimated, potentially leading to an overly magnetically-dominated view of star formation. We present a method to estimate a correction factor to account for this and apply it to JCMT Orion A OMC-1 observations. We find that the magnetic field in OMC-1 is predominately found to vary on scales much larger than the JCMT's 14'' beam and has a rather low degree of unresolved dispersion, leading to a correction factor of only $\sim$1.6 for angular dispersion measured at a scale of 14''/0.028 pc.

Be/X-ray binary pulsars show transient outbursts and complex timing behaviour, including millihertz quasi-periodic oscillations (QPOs), whose physical origin and energy dependence remain poorly understood. We aim to characterise the temporal evolution and energy-dependent properties of the mHz QPO during the 2020 giant outburst of 1A 0535+262. We use the multi-Lorentzian fitting framework to jointly model the power spectra and the real and imaginary parts of the cross-spectrum, incorporating simultaneous broadband X-ray observations from NICER and Insight-HXMT (0.2-120 keV). We report the first detection of weak, but significant, mHz QPOs at low X-ray energies (below 27 keV), extending their detection to a new energy regime. The centroid frequency evolves from 41 to 93 mHz, with the peak root-mean-square (rms) amplitude detected in the 50-65 keV. Throughout the outburst, the QPOs generally exhibit a hard lag between 0.12 pi rad and 0.9 pi rad. However, at the outburst peak, the higher-energy bands (above 35 keV) display a soft lag of up to -0.93 pi rad. We propose that interactions between soft seed photons and an extended outflow located outside the magnetosphere can account for the observed hard lags. Furthermore, we detect a double-peaked mHz QPO only at high energies (E above 35 keV) near peak luminosity. The two peaks maintain an approximately constant separation of 2*nu_spin and exhibit anti-correlated phase evolution. Our results indicate that the mHz QPOs in 1A 0535+262 are closely linked to the coupled evolution of a soft-photon source and a Comptonizing outflow or corona. The joint cross-spectral framework provides a complementary probe of mHz QPOs beyond traditional power-spectral analyses.

Our initial impressions of astronomical objects was that they are inherently "static" over the course of any reasonably long observation. However, with the discovery of quasars and their scintillation in 1963-64, we learnt that there are transient phenomena even at the astronomical scales. The world of known transients has been expanding ever since then. Objects and phenomena like quasars, gamma ray bursts (GRBs), pulsars, rotating radio transients (RRATs), fast radio bursts (FRBs) and ultra long period transients (ULPTs) have answered several unanswered questions about the end states of stellar collapse, i.e, the formation and properties of back holes, neutron stars and white dwarfs. Even more interestingly, they have made us better realise how little we know about the universe. Even after more than 5 decades of research, many lurking questions about neutron stars await answers. In the current work, I explored the arena of FRB and radio pulsar astronomy by joining and contributing to the efforts of the SPOTLIGHT collaboration. The recent decades have witnessed huge leaps in radio instrumentation and high performance computing (HPC) technologies driven by the development of high throughput Graphics Processing Units (GPUs). These major technological advancements are conducive to probing extremely small time scales (up to microseconds) of astronomical events. Modern and next generation radio transients surveys at existing and upcoming radio telescopes worldwide are designed to make optimal use of the available resources to push the research frontiers with the sheer volume of data they produce (hence the terminology, data-driven astronomy). There is an urgent need to upgrade the existing time-domain radio astronomy software to keep up with the pace of the technological revolution on the hardware side. Although pulsar phenomena has been studied in great detail...

G7.7$-$3.7 is a possible historical SNR, with the origin of its cocoon-like morphology and its supernova type remaining unclear. We performed L-band radio polarization observations of G7.7$-$3.7 using the Very Large Array in C and B-configurations. The high-resolution 1.4 GHz continuum image reveals a cocoon-like morphology with multiple shells and faint blowout structures. The total flux density is 9.6$\pm$0.5 Jy and the spectral index map shows predominantly nonthermal emission, with an integrated spectral index of $-$0.38$\pm$0.04. Polarization images of G7.7$-$3.7 show high linear polarization fraction (30%-40%) in the northwestern filaments and moderate polarization (10%-20%) in the northeast and south. The magnetic fields aligned with the filamentary structures, consistent with shock compression. Large rotation measure (RM) variations across the SNR likely originate from magnetized massive progenitor winds. We suggest that the cocoon-like morphology results from the interaction between the SNR and pre-existing circumstellar shells, demonstrating that the radio polarization provides useful constraints on the environments and even the progenitor mass-loss.

We present the development and benchmarking of Poisson solvers for graphics processing units (GPUs). Implemented in the Astaroth platform, the solvers feature high computational efficiency. We present novel combinations of discretizations and smoothers and document practical and performance-focused implementations aimed at reducing time-to-solution for self-gravitating systems. We describe the solver architectures and validate their accuracy against known analytic solutions. We measure convergence and timing per iteration for various solver algorithms, including conjugate gradient, successive overrelaxation, and multigrid in Cartesian coordinates, along with biconjugate gradient stabilized in spherical coordinates. We also couple the solvers to the Astaroth hydrodynamics to simulate a classic time-dependent problem in star formation, measuring accuracy and time-to-solution, for self-gravity on three-dimensional structured grids. Our results demonstrate that the solvers achieve performance similar to other algorithms implemented in Astaroth, and provide a solid foundation for integration into production-scale astrophysical simulations.

Cosmic dust is mainly formed in the atmospheres of evolved stars. In carbon rich stars, amorphous carbon along with silicon carbide are the main constituents of dust grains yet the mechanisms involved in the formation of these grains are still poorly understood. Several molecular precursors have been proposed to form silicon carbide grains. Here, we have simulated in the laboratory the formation of silicon carbide dust starting from atomic C, atomic Si and H$_2$ and we have clearly identified SiC$_2$ as a key molecular precursor of nanodust analogues. We show that the interaction of molecular hydrogen with atomic carbon initiates the formation of hydrocarbons, which then react with atomic silicon to produce gas-phase SiC$_2$. In our experiments, the silicon carbide nanodust analogues are partially hydrogenated. Chemical routes for the formation of SiC$_2$ and organosilicon species are discussed on the basis of thermochemical calculations and chemical kinetics modelling. Our findings reveal the central role of molecular hydrogen in the formation of SiC$_2$ and contribute to a deeper understanding of silicon carbide dust formation processes in evolved stars, from atoms to molecules, clusters, and ultimately dust grains.

The origin of the optical flux variability in active galactic nuclei (AGN) is largely unknown. Previous studies have correlated features of the variability structure function (SF) with AGN properties, though they mostly involved high-luminosity AGN to avoid biases from host galaxy flux. In this work, we characterise optical variability in a sample of 246 low-luminosity AGN at $z < 0.1$ from the Six-degree Field Galaxy Survey (6dFGS) through the ensemble variability SF. We use lightcurves from the Asteroid Terrestrial-impact Last Alert System (ATLAS) with a cadence of $\sim$2 days over eight years, and perform host-AGN decomposition on recent spectra to obtain the host fraction. We find that the slope of the SF depends on black hole mass, increasing from $\sim 0.1$ at $\log M_{\mathrm{BH}}/M_\odot \sim 6.5$ to $\sim 0.3$ at $\log M_{\mathrm{BH}}/M_\odot \sim 8$. Contrary to some earlier work, We do not find breaks in the SF, and two-epoch spectra taken 20 years apart suggest that the SF keeps rising into decadal timescales. In addition, we measure an anticorrelation of the amplitude with the luminosity and a positive correlation with the black hole mass. The variability behaviour also suggests that extinction is not the main driver of the variety in Seyfert subtypes.

Robust reddening maps of the Large and Small Magellanic Clouds (LMC/SMC) are crucial for a wide range of astrophysical studies, including the calibration of the cosmic distance ladder, investigations of stellar populations in low-metallicity environments, and the characterization of interstellar dust properties. We aim to construct reddening maps of the Magellanic Clouds using spectral energy distribution (SED) fitting, and to investigate the impact of different stellar atmosphere models on the resulting maps. We combined optical ($ugriz$) photometry from the SMASH survey with near-infrared ($YJK_{\rm s}$) photometry from the VMC survey for red giant branch (RGB) stars. Observed SEDs were matched to synthetic photometry derived from three atmosphere model grids. Our maps cover 34.5 deg$^2$ of the LMC and 24.5 deg$^2$ of the SMC at 4 arcmin resolution. We find mean reddening values of $E(B-V)=0.076 \pm 0.022$ mag for the LMC and $0.058 \pm 0.024$ mag for the SMC. We found that employing different atmospheric models results in differences up to 0.03 mag in the mean reddening. Canonical $R_V$ values for the Magellanic Clouds (3.41 for LMC and 2.74 for SMC, Gordon et al. 2003) provide results consistent with previous studies. We confirm higher and more structured reddening in the LMC compared to the SMC, with 30 Doradus standing out as the dominant high-reddening region. Our results show that the absolute reddening scale depends on the choice of stellar atmosphere models, while the relative spatial structure of the reddening maps remains stable.

Among the few ways to probe the early Universe, neutrinos offer a particular window on high energy phenomena occurring before recombination. We discuss the opportunities of observing primordial high energy neutrinos (Phenus): neutrinos produced before or around recombination from the decay or annihilation of long-lived relics, arriving at detectors today with energies in the GeV-PeV range. We summarise the results of a general study of this scenario, covering the sharp spectral features such fluxes would display, the theoretical (BBN and CMB) and experimental constraints on the source particle parameter space, and the regions that could realistically be probed by current and future neutrino telescopes. We also present a dedicated Monte Carlo code for computing the distortion of the Phenu spectrum by final state radiation and interactions with the cosmic neutrino background during propagation, and apply it to assess the primordial origin hypothesis for the KM3-230213A ultrahigh energy neutrino event.

JWST's discovery of unexpectedly bright $z>10$ galaxies has triggered claims that standard $\Lambda$CDM cannot reproduce their abundances, while estimates of the ionizing escape fraction $f_{\rm esc}$ at $z>6$ have spanned a factor of four for over a decade. Here we show that both tensions arise from a structural degeneracy in reionization equations: global observables constrain only the product $f_{\rm esc}\times f_{\star,0}$ (peak star formation efficiency), not individual parameters. We demonstrate that this degeneracy, previously considered a limitation, provides a precise diagnostic framework. By leveraging JWST UV luminosity function shapes to independently constrain $f_{\star,0}$, we derive robust bounds on $f_{\rm esc}$. Joint profile-likelihood analysis across Gaussian, log-normal, and duty-cycle burst scatter models excludes the proposed crisis threshold ($\varepsilon > 3.5\%$) at $4.5\sigma$ confidence, with stochastic star formation histories strengthening rather than weakening the result. Combining these constraints with constant and evolving $f_{\star,0}$ measurements yields the first empirical reconstruction of $f_{\rm esc}(z)$ across $z=7$--$12$. A constant-efficiency scenario ($f_{\rm esc}\approx 10$--$16\%$) connects smoothly to low-redshift direct detections, whereas an evolving scenario ($f_{\rm esc} \approx 6\%$ at $z=12$) conflicts with low-metallicity ISM porosity expectations. JWST Cycle 3--4 will distinguish these pathways at $>2\sigma$, transforming a long-standing fundamental inference barrier into a powerful quantitative probe of early-universe physics.

Context. Green Pea galaxies (GPs) are local starburst galaxies serving as analogues for high-redshift star-forming galaxies, particularly Lyman continuum leakers. It remains debated whether their starbursts are driven by internal secular processes or external triggers. Aims. We aim to constrain the role of environment in this triggering, testing whether external influence comes from close interactions or diffuse processes like gas accretion. Methods. We analyse VLT/MUSE observations of 24 GPs at $z \sim 0.2$ to identify companions via spectral line features. We derive key physical properties (extinction, SFR, stellar mass, age, metallicity) for GPs and companions, and estimate group dynamical masses. Results. We identify 22 emission-line galaxies, 11 being companions ($|\Delta v| \leq 500$ km s$^{-1}$). We find a high companion fraction ($33^{+11}_{-8}$%) and a $\sim$1 dex number density excess compared to the field, confirming GPs reside in overdense environments. Companions typically lie at projected separations of $\sim$100 kpc with no evidence of ongoing interactions. Physically, GPs form a homogeneous class of young (mass-weighted age $\sim$230 Myr), metal-poor, high-sSFR starbursts with elevated velocity dispersions. In contrast, companions are more evolved ($\sim$1.6 Gyr) and heterogeneous in stellar mass, metallicity, and dust attenuation. Inferred group dynamical masses are $\sim$3 dex higher than total stellar masses, suggesting significant dark matter and neutral gas. Conclusions. GPs do not appear triggered by ongoing major mergers with close (10-30 kpc) companions. Results favor a scenario where GPs are transient starbursts in overdense regions, plausibly sustained by gas accretion. Limited spatial resolution prevents ruling out very close mergers ($\lesssim 10$ kpc). High dynamical-to-stellar mass ratios imply substantial non-stellar mass in these systems.

Detecting and characterising exoplanet atmospheres remains challenging because atmospheric signals can be comparable to residual noise and instrumental/astrophysical systematics. Spectral features span from a few ppm for small planets up to $\sim 10^3$ ppm for warm/hot giants, while high-quality JWST time-series spectroscopy typically reaches $\sim 10$--$50$ ppm (occasionally $\sim 100$--$200$ ppm in the presence of stellar variability or stronger systematics), making correlated noise across temporal and spectral dimensions a key limitation. With JWST delivering an increasing volume of high-precision transmission spectra, and Ariel set to extend this to a homogeneous survey of $\sim 10^3$ exoplanet atmospheres, robust benchmarking resources with known ground truth are essential to develop and validate data-driven (including ML-based) detrending approaches. As a major step towards this goal, we use ExoSim2 and TauREx to generate one of the most comprehensive public datasets based on the current payload design of the ESA Ariel mission, specifically intended to benchmark detrending algorithms. We also provide a deep neural network baseline for time-series reduction, and use it to highlight the limitations of ML based detrendng methods, i.e. the risks posed by dataset shift when observed distributions diverge from those of the training set, a scenario likely to arise in real observations. This dataset is featured in the Ariel Data Challenge 2024 on Kaggle and has been field-tested for robustness and simulation fidelity. By making these resources publicly available, we aim to support the community in developing, comparing, and stress-testing scalable and reliable methods for exoplanet transmission spectroscopy.

The ESA Gaia mission is a 10+ year astrometric whole-sky scan, demanding consistent data quality over the whole timespan of operations Aims. The Gaia First Look (FL) is a system whose aim is monitoring the data quality to identify problems, which includes early warning capabilities for potential upcoming issues. Methods. In order to achieve its goals, the Gaia FL implemented its own limited astrometric solution, and used the daily calibrations from other segments of the Data Processing and Analysis Consortium (DPAC), as well as the diagnostic data from the satellite itself, in order to obtain a complete picture of the situation of the Gaia satellite on a daily basis. This led to a short-term health and data quality check, but also to a broader overview of the longer-term trends and evolutions within the payload. Potential issues that were encountered were reported to other groups within DPAC for further analysis purposes. When required, ways to mitigate the problems were discussed, and implemented. Results. We show a number of findings by the Gaia FL concerning longer-term evolution, individual but common effects, as well as detrimental impacts, all of which occurred over the operational phase of the Gaia mission

Observations indicate that the total abundance of S-bearing species in dense clouds is orders of magnitude lower than the cosmic sulfur abundance. Addressing this "missing sulfur problem" requires a combination of astronomical observations, laboratory experiments, and theoretical models. In this work, we use the pyRate astrochemical model to simulate the VUV photon irradiation of a CO$_2$:CS$_2$ ice mixture at 10 K in the laboratory, with the goal of supporting the interpretation of the experimental results and testing our current understanding of the sulfur evolution in interstellar ices. For this purpose, the astrochemical model was adapted to the experimental conditions, and the chemical network was compiled from several sources to ensure that all known reactions involving sulfur species were included. The results indicate that nondiffusive chemistry is necessary to reproduce the formation of S-bearing species observed in the experiment. However, some discrepancies were found in the major S-bearing ice chemistry products predicted by the model and the experiment. The compounds OCS, CS, and SO are overpredicted by the model, while it falls short in accounting for $\rm SO_2$ and sulfur allotropes. These discrepancies are likely due to a combination of an incomplete knowledge of the chemical reactions at play (either because of missing reactions and/or because of unconstrained reaction barriers), and uncertainties in the experimental analysis. This work represents the first effort to model the chemistry of a multicomponent ice analog with a rate-equation based code, and highlights the complementary nature of theoretical and experimental astrochemistry to disentangle the chemical evolution of sulfur in the interstellar medium.

Modeling the interior of a rocky or water-rich exoplanet is a thermodynamic closure problem: every layer's density, temperature gradient, and phase must follow from an equation of state (EoS) that remains self-consistent across the pressure-temperature range from surface to core. Existing EoS span disciplines, use different formalisms, and rarely supply the full thermodynamic quantities needed by evolutionary models of interior phase transitions. We present PALEOS (Planetary Assemblage Layers: Equations of State), an open-source toolkit consolidating EoS for iron, magnesium silicate (MgSiO$_3$), and water (H$_2$O) into a unified, phase-aware, thermally responsive framework spanning 17 phases. PALEOS derives density, energy, entropy, heat capacities, thermal expansion, and the adiabatic gradient analytically via Maxwell relations, and is released as lookup tables on regular P-T grids. We validate it against the Preliminary Reference Earth Model, recovering Earth's radius to 0.3% and lower-mantle densities to 3%, and compute 17,900 mass-radius relations from 0.1 to 100 $M_\oplus$ for rocky (Fe + MgSiO$_3$) and water-rich (Earth-like core + H$_2$O envelope) compositions at 300-4000 K. Continuous solid-to-melt EoS let thermal expansion span the fully-solid to magma-ocean regime: the radius offset exceeds 1% above 1500 K and reaches 16% at 4000 K for low-mass silicate planets, comparable to composition degeneracy and transit-radius uncertainties. We demonstrate this on two ultrashort-period super-Earths, WASP-47 e and TOI-1807 b: each admits two purely rocky solutions indistinguishable in mass and radius but in radically different states, one fully solid with no dynamo, the other hosting a deep magma ocean and a liquid iron core capable of sustaining a magnetic field. Phase-aware, thermally resolved EoS are essential for translating astronomical observations into exoplanetary geophysics.

We compute the thermal activation rate of metastable self-gravitating Bose-Einstein condensates with attractive self-interaction (e.g., dilute axion stars) by using the instanton theory. Explicit analytical results are given close to the maximum mass $M_{\rm max}$ [P.H. Chavanis, Phys. Rev. D 84, 043531 (2011)] by using the normal form of the saddle-node bifurcation close to that point. We show that the lifetime of metastable states is extremely long, scaling as $t_{\rm life}\sim e^N\, t_D$, where $N$ is the number of bosons in the system and $t_D$ is the dynamical time ($N\sim 10^{57}$ and $t_D\sim 10\, {\rm hrs}$ for typical QCD axion stars; $N\sim 10^{96}$ and $t_D\sim 100\, {\rm Myrs}$ for the quantum core of a dark matter halo made of ultralight axions). Therefore, metastable equilibrium states can be considered as stable equilibrium states in practice. We compare our results with similar results obtained for Bose-Einstein condensates in laboratory, globular clusters and self-gravitating Brownian particles in astrophysics, the Brownian mean field model (BMF) in statistical mechanics, and bacterial populations in biology. Our presentation parallels the calculation of the quantum tunneling rate of dilute axion stars given in a previous paper [P.H. Chavanis, Phys. Rev. D 102, 083531 (2020)]. These calculations can find application in various domains of physics and astrophysics.

We present VERSUS, a publicly available, fast void-finding algorithm designed to identify spherical underdensities in the density field that can be accurately described by excursion set predictions of the void size function. We validate the algorithm against both a synthetic distribution of particles designed to trace a known input void population, and mock galaxy sample built from a $(2\ h^{-1}\text{Gpc})^3$ AbacusSummit simulation populated with a realistic galaxy-halo connection, including systematic effects designed to mimic real survey data. In all cases, VERSUS demonstrates excellent performance, achieving strong agreement with theoretical predictions for the void size function across the range $25 < R \,[\ h^{-1}\text{Mpc}] < 61$ without requiring any post-processing of the void catalogue. The code is user-friendly, modular, and readily applicable to observational survey data. Its computational efficiency further enables the use of simulation-based modelling approaches, facilitating robust and consistent cosmic void analyses with Stage-IV surveys.

We present new constraints on the local-type primordial non-Gaussianity parameter, $f_\mathrm{NL}^\mathrm{local}$, through analysis of the scale-dependent bias effect on the cosmic infrared background (CIB). To avoid biases from galactic dust contamination on large scales, we use cross-correlations between the CIB and Planck cosmic microwave background (CMB) lensing maps to constrain non-Gaussianity. Our measurement employs new dust-cleaned CIB maps that have been designed to be unbiased on large scales, which allows us to improve our constraining power on $f_\mathrm{NL}^\mathrm{local}$ by a factor of $\sim 2$ over previous CIB analyses. We derive a constraint of $f_\mathrm{NL}^\mathrm{local}=43 \pm 23$, matching the precision of the tightest existing constraints from cross-correlation methods. Consistency- and null-tests demonstrate that our results are robust to modeling assumptions and residual dust contamination.

Thermohaline convection is a standard chemical mixing process in stellar interiors, yet its mixing efficiency is not fully settled. Competing theories predict turbulent diffusion coefficients, $D_\mu$, that can differ by orders of magnitude, leading to uncertainties in stellar models and interpretations of observations. This paper explores a potential resolution to existing discrepancies. We first complete the linear stability theory and identify two types of unstable modes: slow growing modes at large length scales and fast growing modes at small length scales. We then reevaluate $D_\mu$ considering the full spectrum of unstable modes and find that it can self-consistently interpolate between previously proposed theoretical scalings across the instability parameter space. The question of thermohaline mixing efficiency in stars may be settled by future simulations that quantify the scale-dependent contributions of fast and slow modes to $D_\mu$ and determine how the modes dominating the transport change across parameter space.

Context. Ellerman bombs (EBs) are observational signatures of small-scale magnetic reconnection, key to understanding the lower solar atmosphere. While their role in active regions has been widely studied using the H$\alpha$ line, near-ultraviolet (NUV) spectra routinely observed by the Interface Region Imaging Spectrograph (IRIS) offer a promising alternative for EB identification, enabling large-scale studies. Aims. We aim to identify the most important spectral signatures of EBs in the IRIS NUV spectra. With this, we seek to develop a robust criterion for their detection solely using the IRIS NUV spectra. In parallel, we determine the typical atmospheric stratification associated with EBs. Methods. We used four coordinated observations between the Swedish 1-m Solar Telescope (SST) and IRIS. Using the H$\alpha$ line as a reference, we detected 18 different EBs and studied their associated IRIS NUV spectra. In addition, we used the IRIS$^{2+}$ inversion tool to infer the temperature, line-of-sight velocity, and non-thermal broadening from the EB spectra. Results. The defining feature of EBs in the IRIS NUV is the enhancement of the wings of the subordinated Mg II triplet in between the Mg II h&k lines. Inversions reveal that these signatures are produced by localized temperature increase of $\Delta$ T~1650 K around log$\tau$=-3.8. Using only the Mg II triplet signatures, we found a detection criterion that successfully recovered 14 of 18 H$\alpha$-detected EBs. In addition, the shape of the Mg II h&k lines in relation to the Mg II triplet can serve as a proxy for the EB formation height. Conclusions. The NUV spectrum observed by IRIS is a good candidate for detecting EBs, opening the doors to large-scale studies across the extensive IRIS database, removing the dependence on H$\alpha$ observations.

New basis functions for 2 dimensional (2D) image analysis with a circular boundary (referred to as multipole analysis) are derived which are equal-area weighted. We present open access Python code hosted by GitHub, with which users can apply the multipole analysis to images. The new multipole analysis is applied to a set of 28 supernova remnants (SNRs) which are selected to have both radio and X-ray images, and have been identified as Type Ia or Type CC. Each pair of SNR images (radio and X-ray) was convolved to the same spatial resolution prior to analysis. The resulting multipole radial powers and angular powers, from order 0 to 5, for a given SNR are different for different multipoles and for a given multipole are different between X-ray and radio images. The X-ray radial powers (for orders >0) are larger on average than the radio radial powers (more radial structure in X-rays than radio). The angular powers are smaller than the radial powers on average (more radial structure than angular structure). Comparing Type Ia and Type CC populations, the radial powers (for orders >0) are on average larger for Type CC than Type Ia for X-ray and radio images, with larger difference for X-ray images. The angular powers (for orders >0) are similar between Type Ia and Type CC for both radio and X-ray images.

Quasar microlensing is both a very useful tool in cosmology and astrophysics, and a source of uncertainty in some studies like the determination of the Hubble constant from lensed quasars. Microlensing probability and time-scales have been statistically studied using as a reference scale the Einstein ring crossing time of an isolated mass. Our goal is to extend the statistical analysis of microlensing to all currently known lensed quasars with available data, considering realistic optical depths and the gravitational effect of the lens galaxy. We take into account new observational results about quasar sizes and peculiar velocities of lens galaxies. We apply automatic lens modeling to the 204 systems available. For each image, we compute microlensing magnification maps and histograms. Using thin disk source sizes scaled to take into account recent measurements of accretion disk sizes, we find a mean source crossing time of $2.59\pm 0.07$ years. The mean Einstein radius crossing time is $ 11.29 \pm 0.05$ years. When a fraction of mass in microlenses $\alpha=0.2$ is adopted, we find a good matching between the modeled histogram of mean microlensing magnifications for the images in our sample and the experimental histogram of microlensing magnifications. From the modeling of microlensing magnification histograms, we estimate the average half-light radius of the quasar source, $R_{1/2}=5.4\pm 2.7$ light-days, and a lower limit to the mass fraction in microlenses, $\alpha\ge 0.15$. From the microlensing magnification maps, we find that a lensed quasar image has a mean probability of approximately 9% of being involved in a high-magnification event ($\Delta m \le -0.32$). We select a group of images with the largest probabilities and the smallest crossing times.

The power spectrum (PS) of the density field in supersonic turbulence is a fundamental quantity that characterizes the statistical properties of the structures formed in compressible flows. It is also widely used to estimate the Mach number in the interstellar medium from simulation-derived relations. We provide here a first quantitative explanation for the evolution of the slope of the PS of the density field with the Mach number in homogeneous isotropic isothermal turbulence using a time-invariant quantity derived by Chandrasekhar (1951). For simulated turbulent flows, the model reproduces very well the measured slopes for different widths of the inertial range and density variances. Our model also provides a comprehensive interpretation of the characteristic slopes of the PS of the density field measured in the interstellar medium. Based on these results, we stress that the Mach number cannot be reliably deduced from the slope of the PS of the density field. We finally discuss a resolution criterion that must be fulfilled to correctly simulate a turbulent flow with a given density PS slope.

We investigate the plausible history of the XUV luminosity evolution of the planet-hosting M4 star GJ 1132 (~0.2 solar masses) to infer the cumulative incident XUV flux intercepted by the short-period (~1.6 d) Earth-sized transiting planet GJ 1132 b. We include the dominant observational uncertainties, compare two quiescent XUV luminosity evolution models, and simulate the XUV luminosity evolution from flares based on TESS data and a re-analysis of Kepler stars. We find only 4 flares in GJ 1132's TESS 123 day lightcurve, which is relatively few for M dwarfs and, in conjunction with the ~125 day period, suggests that this star is many Gyr old. We find that all model permutations predict that the planet has at least a 95% chance of receiving more than 50 times as much XUV flux as modern Earth, confirming that this planet is a good candidate for permanent atmospheric loss. We also find that an empirical XUV model for M dwarfs predicts 2-3 times more total XUV flux than a commonly used solar twin model and that the empirical model's distribution is 2-3 times narrower. Flares contribute about 20% of the cumulative XUV flux on planet b, which, while modest, ensures the planet lies firmly on the atmosphere-free side of the "cosmic shoreline."

Neutron-star mergers can launch mildly relativistic to moderately relativistic outflows whose interaction with the ejecta can reshape kilonova emission. We parametrically study magnetically powered outbursts from long-lived merger remnants, such as flare-like eruptions and collapse-driven shocks, and quantify their impact on ejecta dynamics, composition, and observables. Using two-dimensional special-relativistic magnetohydrodynamic simulations, we follow magnetized blast waves injected into expanding merger ejecta for early- and late-launch scenarios across a range of shock strengths. We then post-process Lagrangian tracer histories with the nuclear reaction network WinNet and the radiative-transfer code SuperNu with realistic opacities, to connect shock heating directly to nucleosynthesis and kilonova light curves. We find that sufficiently strong shocks can reheat portions of the ejecta to nuclear statistical equilibrium, increase the electron fraction in the shocked material, and deposit entropy, leading to systematic changes in $r$-process yields. These thermodynamic and compositional changes can leave observable imprints on kilonova emission -- especially in color evolution and late-time light-curve behavior -- indicating that magnetically driven remnant variability can potentially contribute to kilonova diversity.

We compare images of core-collapse supernova (CCSN) remnants (CCSNRs) and jet-shaped planetary nebulae (PNe) that have a narrow, faint zone extending from side to side, termed a pipe, with a hydrodynamical numerical simulation exploding a massive star with three pairs of jets in the framework of the jittering jets explosion mechanism (JJEM), and conclude that jets shaped the pipes in these CCSNRs and PNe. We present two jet-shaped PNe with a pipe and three PNe with two opposite narrow jet-shaped lobes, and argue that in some cases the two opposite narrow lobes might merge to form one long, faint zone extending from side to side of the PN, namely, a pipe. From the qualitative similarity of the pipe morphology of the two CCSNRs we analyze with the pipe of the PNe, we suggest that jets also shaped the pipe of these CCSNRs. We strengthen this conclusion with a three-dimensional hydrodynamic simulation that reproduces two opposite narrow lobes, similar to those observed in PNe with lobes. These lobes can merge later to form a pipe. This paper is another in a series that strengthen the case for the JJEM as the primary explosion mechanism of CCSNe by comparing CCSNR morphologies with those of jet-shaped PNe.

Past work has shown that ocean salinity and planetary obliquity both influence the climates of Earth-like exoplanets throughout the habitable zone of Sun-like stars. The effects of salinity and obliquity can be profound, with low vs. high salinity or obliquity resulting in distinct climate states in some scenarios. However, past work has considered salinity or obliquity in isolation and has not explored how each may modulate the effects of the other. We investigate how ocean salinity and planetary obliquity jointly impact climate and habitability using the ROCKE-3D coupled ocean-atmosphere general circulation model. We find that salinity and obliquity have a greater combined impact on planetary climate than the sum of their effects in isolation. This synergy between salinity and obliquity arises due to the ice-albedo feedback, producing distinct climate states that range from ice-free to globally glaciated while having same initial atmospheric conditions and receiving the same instellation. Consequently, ocean salinity and planetary obliquity can together lead to divergent habitability outcomes for otherwise identical planetary scenarios and initial conditions. Salinity and obliquity can jointly increase the planetary fractional habitability across oceans and continents, especially for cold exoplanets. Although neither ocean salinity nor planetary obliquity can be reliably predicted or observationally constrained, their synergistic effects must be considered in future studies of planetary climate and exoplanet observations, especially when characterizing planetary habitability.

Stellar abundance analysis relies on flexible, high-performance spectral synthesis. To meet these needs, we present PySME v1.0, an updated Python implementation of Spectroscopy Made Easy (SME) designed for precise and survey-scale modelling of stellar spectra.A central challenge in SME based synthesis is the efficient treatment of very large line lists, including both the preselection of negligible lines and the subsequent formal synthesis. PySME v1.0 introduces a revised line-selection framework based on opacity ratio and line depth, together with dynamic line list construction and control of the effective wavelength span over which each line contributes to the synthetic spectrum. These workflows support parallel preprocessing of weak-line selection and reduce the line list passed to the synthesis core, thereby improving scalability while preserving synthetic accuracy. PySME v1.0 also incorporates an updated equation-of-state treatment that improves the modelling of hydrogen lines, particularly Balmer features, while maintaining close agreement with previous SME results for metal lines. The Python interface has further been extended to support parameter-dependent derived quantities updated during optimisation, and PySME provides non-local thermodynamic equilibrium (NLTE) departure-coefficient grids for 17 elements. Together, these developments establish PySME v1.0 as a robust and efficient framework for high-precision stellar abundance analyses in large spectroscopic surveys.

The largest known molecule in space, C60 , has been detected in its neutral and cationic form through its vibrational, UV-driven fluorescence emission spectrum and its electronic absorption spectrum, respectively. The detection of several polycyclic aromatic hydrocarbon molecules through their pure rotation spectrum in cold, dense, molecular cloud cores suggests that C60 might be present in these environments as well. The low flux of UV pumping photons in molecular cloud cores and the absence of suitably bright background stars, make detection of C60 and its cation through the commonly used methods impractical. As C60 has no permanent dipole moment, its pure rotational transitions are forbidden and its presence must be inferred from the rotational transitions of C60 derivatives with permanent dipole moments. Here, we present a study of the predicted rotational spectrum of protonated C60 that has a sizeable permanent dipole moment. Protonation of C60 reduces the icosahedral symmetry to Cs and results in a dipole moment of about 3.8 Debye. The resulting C60H+ is a closed shell system

We present a data-driven fuzzy set framework for classifying galaxies into the red sequence, blue cloud, and green-valley populations using multiple observables from the Sloan Digital Sky Survey (SDSS DR18). Unlike traditional methods based on hard boundaries in colour or stellar mass, our approach assigns continuous membership degrees using sigmoidal functions derived from bimodal galaxy properties, including $(u-r)$ colour, specific star formation rate (sSFR), and $D4000$. Membership functions are constructed via Gaussian mixture modeling and combined using a conservative fuzzy minimum operator. Applying this method to a volume-limited sample of 88,579 galaxies, we compare with the empirical classification of \citet{schawinski14}. The fuzzy approach reduces contamination in the red and green-valley populations and yields more physically consistent distributions of star formation and morphology. Red galaxies show a unimodal low-sSFR distribution, while green-valley galaxies exhibit clearer signatures of morphological evolution. We also examine the dependence of active galactic nucleus (AGN) fraction on stellar mass and find no significant differences between methods, indicating robust global AGN trends. However, clustering analysis reveals subtle differences: fuzzy-classified red galaxies show enhanced large-scale clustering, suggesting a stronger association with highly biased dark matter halos. These results demonstrate that fuzzy classification provides a flexible, physically motivated alternative to hard-cut methods, enabling a more accurate and interpretable view of galaxy populations and their evolution.

Timing analyses of accreting black holes often package nodal information in ways that depend on benign choices of time and azimuthal convention. We identify the corresponding pipeline-invariant content for slightly tilted circular rings and express it as an orbital nodal phase, $\Delta\psi_{\rm orb}$. In Kerr, this quantity gives the clean geodesic baseline for nodal timing: it equals the nodal precession per orbit, is invariant under the benign remappings considered here, and, for prograde Kerr spin, decreases monotonically with radius outside the innermost stable circular orbit. A fixed-$\Omega_\phi$ transport framework then isolates genuine metric sensitivity from trivial radius drift and provides the natural framework for far-field quadrupolar and higher-multipolar timing-response calculations. Two small analysis-level effects are also identified, namely a second-order bias from coherent radial breathing and the absence of an intrinsic geometric offset from exact slow fixed-$\Omega_\phi$ loops. A limited published-data illustration for GRO J1655$-$40 shows that the observational proxy for $\Delta\psi_{\rm orb}$ can be reconstructed directly from standard reported quasi-periodic oscillation frequencies once an orbital-frequency anchor and an identification convention are specified. Within the thin-ring limit, $\Delta\psi_{\rm orb}$ therefore provides a pipeline-robust reporting quantity and a Kerr-baseline diagnostic for source-level, simulation-level, and strong-gravity comparison applications.

Metastable strings can arise from a two-step symmetry breaking chain of the type $SU(2) \to U(1) \to 1$.They can decay through quantum tunneling by nucleating a monopole-antimonopole pair, and are prominent candidates for explaining the gravitational wave background detected at Pulsar Timing Arrays (PTAs).We investigate the classical stability of the strings arising in this commonly-considered setup, which serves as a fundamental input for discussing their possible decay channels. We identify the regions of parameter space in which the strings are either classically stable or unstable. Our results show that classical instabilities can impact the parameter space relevant for PTAs. We also discuss the possible fate of the string network in the regions of classical instability.

Particles that decouple relativistically from the Standard Model bath during reheating represent a versatile class of well-motivated cold dark matter candidates. In fact, ultrarelativistic decoupling ($T_{\rm FO}\gg m_\chi$) is quite generic for beyond the Standard Model (BSM) heavy portal interactions with strong couplings and relatively low reheating temperatures. In this work, we study the direct detection prospects for ultrarelativistically frozen-out (UFO) candidates, using $Z'$-portal dark matter as a case study. Although typical UFO cross sections are suppressed by a heavy mediator mass scale, we find that experiments such as LZ, XENONnT, PandaX, and DarkSide-50 have already excluded a large portion of the UFO parameter space and there remains viable space above the neutrino fog for $0.4 \text{ GeV} \lesssim m_{\rm DM}\lesssim 1$ TeV. Moreover, SuperCDMS SNOLAB, which is expected to begin collecting data in 2026, should access a large region of UFO parameter space in the 0.5-10 GeV mass range. For heavy BSM portal interactions ($M\gtrsim 1$ TeV), UFOs are typically more accessible to detection than freeze-in candidates due to the comparatively larger cross sections. We also carefully delineate regions of parameter space with degeneracy between UFO and non-relativistic freeze-out. In sum, UFOs are attractive candidates for ongoing and next-generation dark matter detection experiments in a looming post-WIMP era.

Wormholes are fascinating alternatives to black hole geometries. In this paper, we have studied a special case of wormhole solution in the context of $R=0$ spacetime. Our approximate analytical calculations show that under a strictly static axial gravitational perturbation of this spacetime, the magnetic-type tidal Love number (for $\ell=2$) vanishes if we keep the solution of the master equation up to linear order in the regularisation parameter of the geometry.

In this work we generalize the entropy transfer from electron-positron annihilation to photons in the early Universe. The generalization is implemented within the Tsallis formalism by using generalized distribution functions derived from Curado-Tsallis constraints. Through this deformation, the entropy density of the electromagnetic sector is modified, while the photon component is kept extensive. Therefore, the nonextensive correction is introduced only in the $e^-e^+$ pairs. This affects the entropic degrees of freedom before electron-positron annihilation and consequently modifies the temperature ratio $T_\nu/T_\gamma$. The resulting correction is then mapped into the effective number of relativistic species, $N_{\rm eff}$. Finally, by performing a combined $\chi^2$ analysis using CMB$+$BAO and BBN data, we obtain the $2\sigma$ bound $|q-1|\leq 1.3\times10^{-2}$ for the nonextensive parameter. This result implies that any departure or correction from Boltzmann-Gibbs extensivity must remain small during the MeV era.

Non-radial oscillations of neutron stars provide a powerful probe of stellar structure and relativistic gravity, but a fully general relativistic treatment for gravitationally coupled two-fluid stars with independently conserved currents has so far been lacking. In this work, we develop a fully relativistic framework for polar perturbations of gravitationally coupled two-fluid neutron stars, assuming that the two fluids interact only through the common spacetime and are not coupled by entrainment or direct microphysical interactions. We derive the coupled linear perturbation equations governing the metric and both fluid components, and complete the formulation by establishing the regularity, surface, and exterior matching conditions required for a well-posed oscillation eigenvalue problem. We then implement the resulting system numerically and compute representative polar mode spectra for gravitationally coupled two-fluid stellar models. This implementation provides a practical way to address mode identification in gravitationally coupled two-fluid stars, allowing the fundamental ($\mathsf{f}$) and pressure ($\mathsf{p}$) mode branches of the spectrum to be classified according to their dominant inner- or outer-fluid character through the associated eigenfunctions and their node structure. The formalism developed here provides a foundation for extending relativistic asteroseismology to multi-fluid compact stars and for exploring their potential gravitational-wave signatures in a fully general relativistic setting.

Ultralight dark matter (ULDM) couplings to matter fields and ULDM self-interactions are typically treated as independent probes. However, since the ULDM-matter couplings unavoidably induce self-interactions through quantum loop corrections, bounds on self-interacting ULDM from astrophysical and cosmological observations will also limit the coupling strength to matter. Applying this argument, we find that self-interaction bounds can impose strong constraints on the linear ULDM couplings to neutrinos, excluding a large portion of parameter space that is widely considered for probing ULDM via neutrino oscillation experiments. In addition, the self-interaction bounds also limit the quadratic ULDM couplings to electrons and light quarks, which can become stronger than from the stringent test of equivalence-principle violation. Our results demonstrate that the extreme observational sensitivity of cosmic microwave background and structure formations to repulsive self-interactions can robustly translate into powerful constraints on the ULDM interactions with fundamental particles.

We study eccentric extreme-mass-ratio inspirals (EMRIs) into scalar clouds formed through superradiant instabilities, within a fully relativistic perturbative framework. While previous relativistic analyses were limited to circular motion, we consider eccentric equatorial orbits around a Schwarzschild black hole and show that eccentricity induces a dense sequence of potentially detectable resonances in the scalar fluxes near the last stable orbit. The resonances we uncover only appear in a fully relativistic calculation, as they are intrinsically tied to the split between azimuthal and radial frequencies in the strong-field regime. By evolving the orbit adiabatically, we show that these resonances can induce detectable dephasing in the gravitational waveform. Our results demonstrate that eccentricity could play a decisive role in confidently detecting EMRIs embedded in scalar clouds with future space-based detectors.

We derive bounds on the lifetime of an evaporating black hole. The bound follows from energy conservation and purification, within the framework of `asymptotically semiclassical spacetimes'. We use the recently derived expression for the Bondi flux of Hawking radiation, together with the expression for the entanglement entropy of Hawking radiation at null infinity, to investigate the purification phase after the last semiclassical ray. We discuss the energy-cost of entanglement purification and we find a lower bound on the purification time of the black hole, which scales as $M_0^4/\hbar^{3/2}$, where $M_0$ is the initial black hole mass. Additionally, motivated by quantum gravity considerations, we include the additional assumption that a Planck mass black hole is metastable. With this assumption, we find that the the purification time is extended to be exponential in the square of the initial black hole mass, i.e. in its initial area. We find that the redshift exponent is negative in this purification phase, which indicates the existence of a white-hole remnant which releases information slowly. We comment on phenomenological implications for primordial black hole remnants.