Papers for Thursday, Feb 19 2026

Event horizons are a defining feature of black holes. Consequently, there have been many efforts to probe their existence in astrophysical black hole candidates, spanning ten orders of magnitude in mass. Nevertheless, horizons remain an obstacle to unifying general relativity and quantum mechanics, most sharply presented by the information paradox. This has motivated a proliferation of horizonless alternatives (black hole foils) that avoid event horizons and are therefore benign. We show that for typical accreting astronomical targets, largely independent of a foil's underlying microphysics, a horizonless compact surface will generically be ensconced within an optically thick, scattering dominated baryonic settling layer that efficiently reprocesses the kinetic energy of infalling matter into observable thermal emission. The emergent photosphere luminosity is driven toward the accretion-powered equilibrium value and is only weakly sensitive to the foil redshift. These atmospheres are convectively stable and naturally imply that the emitting photosphere forms at modest redshift even when the surface redshift is extreme. Moreover, local gas-surface interaction provides a microphysical lower bound on the effective base temperature, insulating the atmosphere from arbitrarily cold foils. The unknown properties of the foil enter only through local boundary conditions controlling baryon processing and thermal coupling at the surface, making the solutions broadly applicable to horizonless alternatives that do not invoke significant additional nonlocal interactions. Thus, under minimal assumptions (GR exterior and local surface interactions), horizonless foils are generically observationally exposed: the absence of a thermal photosphere directly constrains or rules out broad classes of such models.

Supermassive black hole growth plausibly occurs via runaway astrophysical black hole mergers in nuclear star clusters that form intermediate mass black hole seeds at high redshifts. Such a model of Little Red Dots yields an order-of-magnitude higher rate of tidal disruption events than that of black hole captures. Our prediction, normalised to our proposed resolution of SMBH seeding, yields detectable TDE rates at high redshift. The resulting dense gas cocoons generate the nuclei of LRDs, each incorporating a central massive black-hole-star, with comparable masses in gas, stars, and massive black hole within a scale of around a parsec as inferred from the various spectral signatures.

Diffuse radio emission in galaxy clusters, such as radio halos, relics, and mini halos, is a key tracer of non-thermal processes, turbulence, and magnetic fields within the intra-cluster medium. However, their low surface brightness, as well as contamination from compact sources and imaging artefacts, makes their detection challenging. The sheer volume of data from instruments such as the Square Kilometre Array will render traditional manual-inspection based detection methods infeasible. This paper introduces a novel machine learning approach that uses active learning to rapidly identify diffuse emission candidates from a small, optimally-selected subset of data. We apply the self-supervised deep learning algorithm Bootstrap Your Own Latent to extract features from source cutouts in the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). We then pass these features through the Astronomaly: Protege anomaly detection framework to identify the final candidates. Using a human-labelled set, we evaluate our pipeline on high-resolution (~7''), convolved (15''), and combined-feature MGCLS datasets. Interestingly, the high-resolution features identify diffuse sources more efficiently than the convolved resolution, which are in turn outperformed by the combined features. Of the top 100 sources ranked by Protege, 99% exhibit diffuse characteristics, with 55% confirmed as cluster-related emission. Our work shows that Protege can identify diffuse emission with minimal human labelling effort, offering a powerful, scalable tool capable of detecting both known and novel diffuse radio sources.

In interstellar medium studies, separating ordered and random velocity or magnetic fields is essential for interpreting turbulence in both simulations and observations. We investigate how the choice of averaging scale affects the measurement and characterization of magnetic and kinetic turbulence in Milky Way-sized disk galaxies with different initial magnetic morphologies. We analyze two magnetohydrodynamic simulations of isolated disk galaxies, one initialized with a toroidal magnetic field (Model T) and the other with a random field (Model R). Using spherical filtering, we decompose the magnetic and velocity fields into mean and fluctuating components while varying the averaging scale, and examine their energy ratios and power spectra as functions of time and averaging radius. Both models develop ordered and turbulent magnetic structures, whose relative strengths vary strongly with the averaging radius. The power spectra of the velocity and magnetic mean fields steepen with increasing smoothing scale, tracing the transition from coherent to turbulent regimes. The turbulent kinetic energy dominates over the magnetic counterpart, though the latter remains dynamically significant. Very importantly, we find that these ratios depend more strongly on the averaging radius than on the initial conditions of the magnetic field. The characterization of turbulence as strong or weak, meaning whether or not fluctuations dominate over the mean depends sensitively on the chosen averaging scale, rather than being an intrinsic property of the system. The strong dependence of the turbulence fractions on the averaging scale has direct implications for magnetic field estimates obtained from observational methods such as the Davis-Chandrasekhar-Fermi technique emphasizing the need for careful scale selection when interpreting magnetic and kinetic turbulence in galaxies.

We measure the velocity anisotropy profile $\beta(r)$ of different galaxy cluster member populations by analysing the stacked projected phase space of nine massive ($M_\mathrm{200c}>7\times10^{14}$ M$_\odot$) galaxy clusters at intermediate redshifts ($0.18 < z < 0.45$). We select our sample of galaxy clusters by choosing the most round and virialised objects among the targets of the CLASH-VLT spectroscopic program, which offers a large spectral database. Complementary MUSE observations on most of these clusters allowed us to identify an unprecedented number of cluster members, strongly enhancing the precision of our measurement with respect to previous studies. Our sample of cluster members is divided in four classes: red and blue by colour, and high- and low-mass by stellar mass. We employ two parallel techniques, namely the MAMPOSSt method (parametric in $\beta(r)$) and the Jeans equation inversion (non parametric in $\beta(r)$). The results from both techniques are found in agreement for any given cluster member population, and suggest that the orbital anisotropy in galaxy clusters grows from the centre (where $\beta\approx 0.2-0.4$) to the virial radius ($\beta\gtrsim 0.8$), and it is similar for the different cluster member populations. We also find an interesting dynamical feature in the Jeans inversion results, that is a drop in $\beta(r)$ at a distance of $\sim 250$ kpc from the cluster centre. We provide robust anisotropy estimates by exploring a highly significant number of model combinations: 72 with MAMPOSSt (varying the mass, surface number density, $\beta(r)$ model, and galaxy population) and 18 (varying total mass model and galaxy population) in the Jeans inversion. Such an extensive investigation of the $\beta(r)$ profile in galaxy clusters is a wide basis for future studies on cluster dynamical masses and cluster cosmology in the era of large spectroscopic surveys

Little Red Dots (LRDs), among the most enigmatic high-redshift discoveries by JWST, are commonly believed to be powered by accreting supermassive black holes. Here, we explore the possibility that these sources are globular clusters in formation, with rest-frame UV arising from a very young stellar population and rest-frame optical from a short-lived supermassive ($>10^4$ M$_\odot$) star. The spectral profiles of LRDs are broadly consistent with this scenario, though the observed temperatures and bolometric luminosities favor emission reprocessed by optically thick, continuum-driven winds not fully captured by current models. The LRD $z\sim5-7$ UV luminosity function naturally evolves, under standard evolutionary and mass-loss prescriptions, into a present-day mass function with a turnover at $\log_{10}(M_\ast$/$M_\odot)=5.3$ and an exponential cutoff at high masses, consistent with local globular-cluster populations. We estimate the total present-day number density of LRDs formed across all redshifts to be $\approx0.3$ Mpc$^{-3}$, similar to local globular clusters. The observed LRD redshift range matches the age distribution of metal-poor globular clusters, without current LRD counterparts to the metal-rich population. If LRDs are globular clusters in formation, we predict chemical abundance patterns characteristic of multiple stellar populations, including enhanced He and N, and potential Na-O and Al-Mg anti-correlations. These results offer a local perspective to explore this surprisingly abundant population of distant sources, and a potential new window into extreme stellar astrophysics in the early Universe.

We present a comprehensive photometric and kinematic study of the open clusters HSC 25, HSC 37, and HSC 2878, located in the innermost regions of the Galactic disc. Utilizing data from Gaia DR3 and the UPMASK membership algorithm, we identify 44, 55, and 112 most probable members for HSC 25, HSC 37, and HSC 2878, respectively. The mean proper-motion components are obtained as (-5.901 +/- 0.41, -6.213 +/- 0.40), (-3.231 +/- 0.56, -4.564 +/- 0.47), and (-3.830 +/- 0.51, -5.198 +/- 0.44) mas yr^-1 for HSC 25, HSC 37, and HSC 2878, respectively. The open clusters span a broad range of evolutionary stages, with estimated ages of log(t/yr) = 8.38 +/- 0.08, 7.04 +/- 0.09, and 9.04 +/- 0.09, and corresponding heliocentric distances of 7.36 +/- 0.37, 6.79 +/- 0.18, and 6.17 +/- 0.22 kpc. The obtained metallicities are 0.0388 +/- 0.0039, 0.0259 +/- 0.0028, and 0.0209 +/- 0.0023, respectively. Total mass estimates are 135, 755, and 204 solar masses, respectively, highlighting notable differences in stellar content across the clusters. An analysis of dynamical relaxation times suggests that HSC 25 and HSC 2878 are dynamically evolved, whereas the much younger HSC 37 is still in an early phase of dynamical evolution. The high space velocities and orbital parameters of these clusters reveal significant deviations from typical disc kinematics. HSC 25 and HSC 37 exhibit eccentric orbits and small perigalactic distances, consistent with dynamically heated or accreted origins within the Galactic bulge. In contrast, HSC 2878's relaxed, planar orbit suggests in situ bulge membership despite its age. These findings point toward a heterogeneous dynamical origin for the clusters, with implications for star formation and evolution in the inner Milky Way.

We investigate how pulsar timing array (PTA) measurements of the nanoHertz gravitational-wave background (GWB) can constrain models for the growth history of supermassive black holes (SMBHs) and how active galactic nucleus (AGN) and stellar feedback models can affect GWB predictions. Feedback regulates supermassive black hole (SMBH) growth, altering the black hole mass function (BHMF). Using BHMFs drawn from multiple cosmological simulation suites including IllustrisTNG, MillenniumTNG, Simba, and CAMELS, and combining these with a quasar-based SMBH binary population framework, we predict the resulting GWB amplitude under a range of different stellar and AGN feedback prescriptions. We find that the choice of both stellar and AGN feedback models alters the high-mass end of the BHMF and changes the predicted GWB amplitude by up to a factor of 2 for the fiducial simulations and a factor 10 for extreme feedback variations in CAMELS. Models with inefficient or absent AGN feedback produce abundant SMBHs and yield GWB amplitudes consistent with PTA data, yet fail in producing realistic galaxies. Fiducial models of AGN and stellar feedback suppress SMBH growth too much and under-predict the expected signal, an effect which could possibly be mitigated by more realistic black hole seeding and growth prescriptions. The mismatch between the GWB amplitudes predicted by cosmological simulations and those observed by PTAs suggests that SMBH growth is more efficient or occurs earlier than captured by current models. This demonstrates that PTA measurements provide a powerful new probe of feedback physics and the SMBH population.

Deep JWST images of AS1063 reveals tens of thousands of globular clusters in the galaxy cluster AS1063. When compared with the lensing model based on the same JWST data, the distribution of globular clusters traces closely the distribution of lensing mass (mostly composed of dark matter). Interestingly, both the distributions of dark matter and globular clusters have large central cores. However the size of the core in the distribution of globular clusters is about half the size the core of the dark matter distribution. We argue that the standard cold dark matter and fuzzy dark matter models struggle to explain these large cores. Meanwhile, the self interacting dark matter with a velocity dependent cross section, combined with core stalling, offers a natural explanation to the existence of these cores if $\sigma_{\rm SI}\approx 0.3$ cm$^2$ g$^{-1}$ for galaxy cluster halos. But we also discuss how the lack of hydrodynamical N-body simulations capable of resolving globular clusters in galaxy cluster scale halos, hinders the possibility of ruling out the standard non-collisional dark matter scenario. Future high-resolution hydrodynamical simulations of galaxy clusters, with several trillion particles, and containing over a hundred thousand globular clusters, can provide the insight needed to transform the epistemic nature of dark matter into an ontological one

We present the third data release of the LOFAR Two-metre Sky Survey (LoTSS-DR3). The survey images cover 88% of the northern sky and were created from 12,950 hrs of data (18.6 PB) accumulated over 10.5 years. The images were produced through direction-independent and direction-dependent calibration pipelines that correct for instrumental effects as well as spatially and temporally varying ionospheric distortions. In our 120-168 MHz continuum mosaic images with an angular resolution of 6 arcsec (9 arcsec below declination 10$^\circ$) we catalogue 13,667,877 sources, formed from 16,943,656 Gaussian components. The scatter in the astrometric precision approximately follows the expected noise-like behaviour but with an additional systematic component of at least 0.24 arcsec that is likely due to calibration imperfections. The random flux density scale error is 6%, while the systematic offset was previously shown to be within 2%. The median sensitivity of our mosaics is 92$\mu$Jy beam$^{-1}$. Completeness simulations, accounting for realistic source models, time- and bandwidth-smearing effects, and astrometric errors, indicate that we detect more than 95% of compact sources with integrated flux densities exceeding 9 times the local root mean square (RMS) noise. However, the recovered source counts in a particular integrated flux density bin do not match the injected counts until flux densities exceed 45 times the local RMS noise. The Euclidean-normalised differential source counts derived from the survey constrain the radio source population over five orders of magnitude and are in good agreement with previous deep and wide-area surveys. All data products are publicly available, including catalogues, individual-field Stokes I, Q, U, and V images, mosaicked Stokes I images, and $uv$ data with associated direction-dependent calibration solutions.

We develop a general framework to discover scientific algorithms and apply it to three problems in computational cosmology. Our code, MadEvolve, is similar to Google's AlphaEvolve, but places a stronger emphasis on free parameters and their optimization. Our code starts with a baseline human algorithm implementation, and then optimizes its performance metrics by making iterative changes to its code. As a further convenient feature, MadEvolve automatically generates a report that compares the input algorithm with the evolved algorithm, describes the algorithmic innovations and lists the free parameters and their function. Our code supports both auto-differentiable, gradient-based parameter optimization and gradient-free optimization methods. We apply MadEvolve to the reconstruction of cosmological initial conditions, 21cm foreground contamination reconstruction and effective baryonic physics in N-body simulations. In all cases, we find substantial improvements over the base algorithm. We make MadEvolve and our three tasks publicly available at this http URL.

We investigate the growth of central supermassive black holes in galaxies, aiming to distinguish between gas accretion versus BH merger-driven growth modes. By performing and analysing cosmological hydrodynamical simulations of $(50 ~ {\rm Mpc})^3$ comoving boxes, we also study how the BH feedback parameters affect the coevolution between SMBHs and their host galaxies. Starting as $10^5 M_{\odot}$ seeds, we find that the BHs grow initially via BH mergers to $\sim 10^7 M_{\odot}$. Gas accretion onto the BHs is initially low, then increases with time, and reaches the Eddington rate after $7-9$ Gyrs. The BHs then undergo very fast growth via efficient gas accretion over a period of $600 - 700$ Myr, when the BH mass increases $10^2 - 10^3$ times, causing their predominant growth from $10^7 M_{\odot}$ to $(10^9 - 10^{10}) M_{\odot}$. Taking into account the cosmological gas inflows and outflows, SMBHs do not grow to more than $10^{10} M_{\odot}$ by $z=0$, because of gas depletion from galaxy centers driven by AGN feedback. In terms of SMBH - host galaxy coevolution along the $M_{\rm BH} - M_{\star}$ relation, we find that they initially lie below and thereby move upward toward the relation. We make some physical implications of the growth of high-$z$ Little Red Dots recently observed by JWST: the normal-mass SMBHs had predominantly undergone BH merger driven evolution, whereas the overmassive BHs underwent periods of Eddington-limited or super-Eddington bursts of gas accretion.

Recent observations indicate that in some Milky Way globular clusters (GCs) pristine red giant branch (RGB) stars appear more centrally concentrated than enriched ones. This contradicts most multiple stellar population (MSP) formation scenarios, which predict that the enriched (second) population (2P) should initially be more concentrated than the pristine (first) population (1P). Previous MOCCA Monte Carlo simulations suggested that this apparent overconcentration is a transient effect arising in clusters that have lost a large fraction of their initial mass and host an active black hole subsystem (BHS), and is visible only when RGB stars are used as tracers. In this letter, we test this interpretation using tailored NBODY6++GPU models evolved with direct N-body simulations, providing an independent validation that does not rely on a statistical treatment of relaxation. We performed direct N-body simulations with the NBODY6++GPU code, adopting initial conditions designed to reproduce the dynamical regime relevant to the proposed mechanism. The simulations include updated stellar and binary evolution, dynamical interactions, and the Galactic tidal field, enabling a direct comparison with MOCCA results. The simulations confirm that the spatial distributions and kinematics inferred from RGB stars can be strongly affected by stochastic fluctuations and interactions with the BHS. Preferential ejection of 2P RGB and their progenitors from the cluster center leads to a transient apparent overconcentration of 1P RGB stars, in agreement with earlier MOCCA predictions.

Stellar microlensing is a powerful tool for probing dark matter in the form of planetary and stellar mass compact objects (COs), in particular primordial black holes (PBHs). Under standard assumptions, current observations exclude COs in the mass range $10^{-11} \lesssim M/M_{\odot} \lesssim 10^{4}$ making up all of the dark matter. We provide an overview, aimed at theorists working on PBHs, of the history, theory, observational status, and future prospects of the field.

Jellyfish galaxies, which exhibit tails of gas opposite to their direction of motion, are a galaxy population showcasing the most extreme effects of ram pressure stripping (RPS). We present the emission line properties of a preliminary sample of five jellyfish galaxies in the Coma cluster, observed with the WEAVE Large-IFU as part of the Coma Legacy IFU Survey (CLIFS). When complete, CLIFS will form a sample of 29 jellyfish galaxies in Coma, selected based on the presence of one-sided tails in the radio continuum, enabling a comprehensive picture of the effects of ram pressure on galaxies in the Coma cluster. We extract emission line properties and confirm consistency between disk fluxes measured from WEAVE and MaNGA for galaxies with overlapping disk coverage between surveys. Comparing resolved radio and H$\alpha$-based star formation rates, we find that, in contrast to the disk, the dominant source of tail emission is not star formation. We find evidence for diffuse ionized gas excited by RPS-driven shocks in the tails, as indicated by: (1) LINER-like tail emission with the [OI]/H$\alpha$ BPT diagnostic; (2) enhanced [OII]/H$\alpha$ ratios in the tails relative to the disks; and (3) similarly elevated emission line velocities and velocity dispersions in the tails with respect to the disks. These results demonstrate that ram-pressure-driven shocks dominate the ionized emission in jellyfish galaxy tails.

Rapid inward migration driven by Type I torques threatens the survival of low-mass planets in their nascent protoplanetary disks (PPDs). Positive co-rotation torques offer a potential solution, but require viscous diffusion to remain unsaturated. However, it is unclear if (magneto)-hydrodynamic turbulence provides the necessary diffusion, and disk profiles supporting such torques are often also susceptible to the Convective Overstability (COS) for suitable gas cooling timescales. To this end, we investigate torques on low-mass planets through radially global 2D (razor-thin) and vertically unstratified 3D hydrodynamic simulations of PPDs with thermal diffusion and optically thin cooling. Our 3D models with thermal diffusion, which allows COS development, show systematically different torque behavior compared to 2D models, wherein COS is absent. In 3D, the COS saturates into large-scale, long-lived vortices that migrate radially and interact gravitationally with the embedded planet. When these vortices encounter the planet, they typically provide positive torque "kicks" counteracting inward migration, as the less-massive vortices are scattered onto horseshoe orbits by the more-massive planet. We validate our simulation methods against the theoretical framework of Paardekooper et al. (2011) and demonstrate that COS-induced torque modifications can extend migration timescales by factors of approximately 10. For plausible disk models, our results suggest that COS activity can lengthen migration timescales sufficiently to overlap with, or even exceed Super-Earth formation windows (0.1-5 Myr). In contrast, simulations with optically thin cooling do not show significant torque modifications, as COS saturates in near-axisymmetric structures without producing large-scale vortices for the disk models considered here.

Recent simultaneous multiwavelength observations of a nearby young solar-type star EK Dra in the optical, H$\alpha$ spectrum, and X-ray, have provided evidence for stellar prominence eruptions associated with superflares. The large prominence eruption is suggested to have been caused by a large mid-latitude spot on the polarity inversion lines near the stellar limb from the concurrent Zeeman Doppler Imaging (ZDI) and optical photometry by the TESS. In this study, we perform starspot mapping for the TESS data of EK Dra to investigate the relation of starspots and magnetic fields from the photometry and ZDI. We also explore the multiwavelength rotational variability ascribed to starspots and active regions for the TESS, B-band, H$\alpha$, and X-ray light curves. As a result, we find that (i) spot locations deduced from the TESS light curve are mostly consistent with the intensity map from the ZDI except for a polar spot, and (ii) the H$\alpha$ light curve exhibits clear periodicity with respect to the TESS light curve because the H$\alpha$ line is radiated around spots in the chromosphere. The X-ray light curve does not show such association probably because of multiple spots on high activity level and extended spatial structure of coronal active regions. The results provide clues to explore their association with stellar flares at different heights of active regions in chromospheric and coronal lines. Our study also enables us to quantify the stellar XUV radiation from the magnetic fields of active stars toward understanding atmospheric evolution of exoplanets.

Long baseline optical and infrared interferometric arrays achieve high angular resolution and enable detailed astrophysical measurements. Interferometers have enabled observations of stars at various stages of evolution, as well as studies of binary stars, circumstellar disks, and active galactic nuclei. The CHARA Array is a long-baseline interferometric array at the Mount Wilson Observatory, USA. At the core of CHARA operations are the delay lines, which equalize the optical path length for all telescopes as the Earth rotates and compensate for optical path variations induced by atmospheric turbulence. We report recent upgrades and performance of the CHARA Array optical delay lines for high-precision interferometric observations. The legacy system had been operational for over two decades, and it was increasingly difficult to acquire replacement parts. Beginning in mid-2021, the control system underwent a major upgrade, replacing the aging VME-based architecture with a modern hybrid FPGA and Linux-based system; this modernization continued through the end of 2024. We describe hardware/software changes, the servo architecture, and lab/on-sky performance. The upgraded system achieves residual delay line cart tracking errors of $\sim12$~nm, the same level as the legacy system, and a control bandwidth of 100-130~Hz, allowing fringe tracking across the R, H, and K bands. Initial commissioning revealed key issues such as metrology time-tick jitter and vibration-induced visibility loss, which were diagnosed and resolved. We note ongoing and future efforts to extend baselines up to 1~km and support advanced observing modes such as dual-field interferometry and nulling. This paper is a reference for current and future use of the CHARA Array and for next-generation instrument design.

Mid-infrared observations of planet-forming disks reveal a wide diversity in molecular spectra. Carbon and oxygen abundances play a central role in setting the chemical environment of the inner disk and the spectral appearance. We aim to systematically explore how variations in elemental carbon and oxygen abundances affect the mid-infrared spectra of planet-forming disks, and to identify robust mid-infrared molecular diagnostics of C/H, O/H, and the C/O ratio. Using the thermochemical disk code ProDiMo and the line radiative transfer code FLiTs, we construct a grid of 25 models with varying carbon and oxygen abundances, covering a broad range of C/O ratios. We analyze the resulting mid-infrared molecular emission, including species such as $\rm H_2O$, $\rm CO$, $\rm CO_2$, $\rm C_2H_2$, $\rm OH$. We find that the mid-infrared molecular spectra are highly sensitive not only to the C/O ratio, but also to the absolute abundances of carbon and oxygen. Despite the same disk structure and C/O ratios, molecular fluxes (e.g., $\rm C_2H_2$, $\rm CO_2$) vary by more than an order of magnitude. This variation stems from the differences in excitation conditions and emitting regions caused by the elemental abundances of oxygen and carbon. We identify diagnostic molecular flux ratios - such as $\rm CO_2$/$\rm H_2O$ and $\rm H_2O$/$\rm C_2H_2$ - that can serve as tracers of C/H and O/H respectively. By combining these diagnostics, we demonstrate a method to infer the underlying C/O ratio. Our model grid provides a framework for interpreting mid-infrared molecular emission from disks, allowing estimates of elemental abundances if the disk properties and structure are known. Comparisons with recent JWST observations suggest that a variety in C and O abundances is seen in a sample of T Tauri disks, possibly shaped by disk transport processes and the presence of gaps.

We revisit the diffusive instability in dusty disks that arises when the dust mass diffusivity and/or viscosity decreases sufficiently steeply with increasing dust density. Our updated model includes an incompressible, viscous gas that responds azimuthally and couples to the dust through drag. We show that the basic criterion for diffusion-slope-driven instability remains approximately $\beta_\mathrm{diff}\lesssim -2$ for small dust stopping times, with gas feedback providing only modest quantitative changes for parameters motivated by streaming-instability turbulence. We perform nonlinear numerical calculations and confirm linear growth and mode selection toward the fastest-growing wavenumber. However, for power-law closures $D\propto\Sigma^{\beta_\mathrm{diff}}$ with $\beta_\mathrm{diff}<0$, the nonlinear evolution does not saturate. Instead, steepening gradients amplify the nonlinear dust-pressure term and drive finite-time collapse into increasingly sharp spikes. Motivated by the absence of multidimensional saturation channels in our 1D framework, we test a simple piecewise closure in which the negative diffusion slope operates only over a finite density interval. This modification eliminates blowup and produces peak densities controlled by the imposed saturation scale. Our results support diffusive instabilities as a linear organizing mechanism in dusty turbulence, while highlighting that realistic nonlinear saturation requires additional physics beyond the present closure.

Bilobate contact binaries comprise a significant fraction of the relict Kuiper Belt, which includes the exemplary contact binary (486958) Arrokoth. The surfaces of its lobes contain similar amounts of highly volatile chemical species and few craters, indicating formation in a homogeneous and gentle environment. Arrokoth's bilobate shape was initially hypothesized to have formed via the direct gravitational collapse of a pebble cloud in the solar system's protoplanetary disk. However, alternative hypotheses have proposed that Arrokoth may be the result of binary planetesimal formation and the subsequent dynamical evolution of the binary components into contact through external perturbations over long timescales. Here, we show that contact binary planetesimals like Arrokoth can form directly from the gravitational collapse of pebble clouds. We used a soft-sphere discrete element method (SSDEM) to discover that planetesimals form a wide variety of shapes, including bilobate contact binaries. This method creates planetesimals as particle-aggregates with particles resting upon each other's surfaces via mutual surface penetration. The formation of contact binaries in our simulations strengthens the hypothesis that Arrokoth, and perhaps many other contact binaries in the Kuiper Belt, formed directly as bilobate objects from gravitational collapse, and so their shapes and surfaces record the era of planet formation.

The nature of dark matter and dark energy are among the central questions in cosmology. Strong gravitational lenses with multiple source planes provide a geometric probe of cosmology: the ratio of deflection angles at different redshifts depends only on angular-diameter distances, constraining the matter density $\Omega_m$ and the dark energy equation of state $w$. However, constraints from this technique have historically lagged behind those from the CMB, SNe Ia, and BAO. In this work, we present new cosmological constraints from the Carousel Lens, a cluster-scale lens with more than 40 extended images from 11 spectroscopically confirmed sources. Its relaxed core and rich set of extended images behind the main halo make it particularly suitable for cosmological inference. Using the GIGA-Lens pipeline, we construct a pixel-level lens model including six HST-detected sources and four mass components. From this model, we obtain $w$CDM constraints of $\Omega_m = 0.34^{+0.16}_{-0.13}$ and $w = -1.31^{+0.35}_{-0.32}$ from the Carousel Lens alone, accounting for both statistical and systematic uncertainties. We further project that including four additional known higher-redshift sources, assuming similar fractional uncertainties, could improve the constraining power by ~80%, bringing the precision close to that of the CMB and SNe Ia. For an evolving dark energy model ($w_0w_a$CDM), the Carousel Lens alone yields constraints comparable to the CMB, providing an independent and complementary probe alongside SN Ia and BAO. While currently systematic uncertainties dominate, which we quantify through simulations, our results demonstrate that relaxed multi-source-plane cluster lenses can deliver competitive cosmological constraints. Further improvements are expected from reductions in systematics and from incorporating higher-redshift sources (known and new) with high-resolution imaging.

The first stars likely formed from pristine clouds, marking a transformative epoch after the dark ages by initiating reionisation and synthesising the first heavy elements. Among these, low-mass Population III stars are of particular interest, as their long lifespans raise the possibility that some may survive to the present day in the Milky Way's stellar halo or satellite dwarfs. As the first paper in a series, we present hydrodynamic evolutionary models for 0.7 - 1 MSun stars evolved up to the white dwarf phase, utilising the MESA software instrument. We systematically vary mass-loss efficiencies, convective transport, and overshooting prescriptions, thereby mapping how uncertain physics influences nucleosynthetic yields; surface enrichment, including nitrogen-rich post-main sequence stars arising from convective shell mergers; remnant properties, such as low-mass helium or carbon-oxygen white dwarfs (M_WD ~ 0.45-0.55 MSun) and transient UV-bright phases; and potential observational signatures, including neutrino emission during shell mergers and helium flashes. These models establish a predictive framework for identifying surviving Pop III stars and their descendants, providing both evolutionary and observational constraints that were previously unexplored.

We present the discovery and analysis of three microlensing planets identified through brief positive anomalies on the wings of their light curves. The events, KMT-2021-BLG-0852, KMT-2024-BLG-2005, and KMT-2025-BLG-0481, were detected in high-cadence survey data from the KMTNet, OGLE, MOA, and PRIME collaborations. The anomaly morphologies are consistent with major-image perturbations induced by planetary-mass companions located near the peripheral caustic. A systematic exploration of model degeneracies, including binary-source scenarios, higher mass-ratio binary lenses, and the inner--outer caustic degeneracy, firmly establishes the planetary origin of each signal. Measurements of the angular Einstein radius and event timescale, combined with Bayesian priors from a Galactic model, yield the physical parameters of each system. The hosts are low-mass stars (0.12--0.75~$M_\odot$), while the companions are Saturn-mass planets (0.16--0.59 $M_{\rm J}$) projected at separations of 1.1--7.8 au, placing them beyond the snowline of their hosts. These results demonstrate the capability of microlensing to detect and characterize cold giant planets around low-mass stars at kpc distances, populating the critical transition region between ice giants and gas giants.

In this work, we investigate the effects of the growth rate scale dependence in the Symmetron modified gravity (MG) model on cosmic structure formation and we analyze the redshift-space distortion (RSD) multipoles, comparing with the Hu-Sawicki $f(R)$ model (specifically the F6) and the standard $\Lambda$CDM model. The analysis employs a scale-dependent growth equation and utilizes the fk-PT perturbation theory approach, implemented in the FOLPS-nu code, to compute the full 1-loop power spectrum multipoles, in particular, the monopole and quadrupole ($\ell=0,2$, respectively). The results show that at redshift $z=0$, the monopole of both MG models is suppressed compared to $\Lambda$CDM, with the Symmetron being closer to the standard model, while the quadrupole presents the opposite behavior. To validate the pipeline, we use General Relativity (GR) mock catalogs (EZMocks), since suitable Symmetron simulations are not available. The main result is that the Markov Chain Monte Carlo (MCMC) analysis successfully recovers the expected GR limit (i.e., $\beta_0 \approx 0$) from the Symmetron model when applied to this mock data, confirming the viability of our methodology for cosmological inference. Then, we conclude that the pipeline is prepared to test MG models against current and near-future galaxy surveys.

Forbush decreases (FDs) are transient depressions in the galactic cosmic-ray flux observed by global neutron-monitor networks and are commonly associated with interplanetary disturbances driven by coronal mass ejections and related shocks. Despite extensive observational work, quantitatively comparing FD morphology across events and linking it to storm severity remains challenging due to heterogeneous station responses, coverage gaps, and the multivariate nature of the network. This work introduces a graph-based event representation in which each FD is mapped to an event network constructed from pairwise dissimilarities between station response time series. A controlled sparse backbone is obtained via the minimum spanning tree, enabling comparable event graphs across cases. From each graph, a compact set of geometric/topological fingerprints is computed, including global integration measures, spectral summaries, mesoscopic structure, centrality aggregates, and complexity descriptors. Predictive skill is assessed using strict leave-one-event-out validation over a pre-defined grid of distance metrics and distance-domain transformations, with selection criteria fixed \emph{a priori}. The proposed fingerprints exhibit measurable signal for three tasks: (i) multi-class classification of geomagnetic storm intensity (G3/G4/G5) with moderate but consistent performance and errors dominated by adjacent categories; (ii) stronger binary severity screening ($\ge$G4 vs.\ G3) with high sensitivity to severe events; and (iii) drop regression with partial least squares achieving positive explained variance relative to a fold-wise mean baseline.

We present the first detection of the 3-Point Correlation Function (3PCF) Baryon Acoustic Oscillation (BAO) signal from the DESI Data Release 1 (DR1) sample of Luminous Red Galaxies (LRGs), which contains over 2.1 million galaxies. Our analysis is based on a tree-level redshift-space bispectrum template, which is then transformed to position space using the Fast Fourier Transform on Logarithmic scales (FFTLog) algorithm. We detect the BAO feature with a significance of approximately $8.1\sigma$ using the EZmock covariance matrix and $8.5\sigma$ using the analytical covariance matrix, for the full LRG redshift range ($0.4<z<1.1$), denoted as the $z_{\rm full}$ sample. We use the Abacus altMTL mocks, the most precise DESI DR1 mock catalogs currently available, to validate our model. We find that our model fits the mocks well, with a small offset of $0.6\%$ in the recovered BAO scale, which we treat as a systematic error due to modeling. We measure the angle-averaged distance, $D_{\rm V}(z = 0.68)/r_{\rm d} = 15.88 \pm 0.27$ ($1.72\%$ precision) when using the covariance matrix estimated from EZmocks and $D_{\rm V}(z = 0.68)/r_{\rm d} = 15.72 \pm 0.18$ ($1.12\%$ precision) when using the analytical Gaussian covariance matrix. Our results show excellent agreement with the DESI DR1 2PCF BAO measurements as well. We also explore several other ways to estimate the error and find between $1.7$--$2.2\%$ precision on the BAO scale from the EZmock covariance matrix and between $1.1$--$1.5\%$ precision from the analytical covariance matrix. This work represents the first detection of the BAO feature in the DESI 3PCF, establishing its ability to probe the expansion history of the Universe with future DESI 3PCF measurements.

This study examines the variability of ionospheric total electron content (VTEC) in response to solar and geomagnetic drivers across solar cycles 23 to 25. While the dominant effect of solar radiation on VTEC is well-known, a comprehensive understanding of how these relationships and their time-lags vary across distinct solar cycle phases and across cycles of differing intensity has been lacking. Using global VTEC data from the Chinese Academy of Sciences Global Ionospheric Maps (CASG) and solar-geophysical indices from NASA's OMNI dataset spanning from 1998 to 2025, this study bridges that gap by quantifying correlation strengths and time-lag relationships between VTEC and parameters such as $F_{10.7}$ solar flux, R sunspot number, Kp, Ap, and Dst indices, and solar wind properties. Results show that solar proxies, particularly $F_{10.7}$ and R sunspot number, exhibit the strongest, most consistent correlations with VTEC, especially during the ascending and descending phases of the solar cycle, with a characteristic $\sim2$-day lag attributed to thermospheric oxygen dynamics and ionospheric recombination processes. In contrast, geomagnetic indices exhibit weaker and phase-dependent correlations, while direct correlations between solar wind parameters and global VTEC are weak, as their influence is primarily mediated by geomagnetic activity and exhibits strong regional and temporal heterogeneity. Phase-resolved analyses further reveal that geomagnetic activity plays a more prominent role during transitional phases, while maximum and minimum periods are dominated by EUV variability and non-solar drivers, respectively. These findings highlight the necessity of incorporating solar phase and time-lag dependencies in ionospheric modelling and forecasting efforts.

We study the advection effect of the Galactic wind on the local cosmic ray spectra. The spectral hardening from a few hundred GV and softening from a few TV are reproduced by a velocity profile with a maximum velocity of $\sim 700~\mbox{km}~ \mbox{s}^{-1}$ without introducing a break in the power-law dependence of the diffusion coefficient. Additionally, we find that a hard CR spectrum below $\sim$ TV with an index of $\sim 2$ at an altitude $\sim 3$-$5$ kpc from the Galactic disk. This hard spectrum is favorable for the gamma-ray spectrum of the Fermi bubbles. With the obtained CR fluxes, we discuss the matter circulation in our Galaxy with the wind. While the wind has an essential role in maintaining the metal abundance in the disk, the production rate of Beryllium, which originates from CR spallation, is so low that the ratio Be/O in the halo should be larger than that in the disk gas.

This paper re-evaluates the relationship between the observed sunward electron cutoff energy and the depth of the Sun's global electrostatic potential. It investigates whether taking into account the effects of local traps formed by magnetic fluctuations provides an alternative explanation for the observed electron deficit. The fluctuations of the highly variable interplanetary magnetic field form a series of shallow magnetic mirror traps that move at approximately the speed of the solar wind. The study investigates the dynamics of electrons as they move outward against an attractive solar electrostatic potential and interact with these traps. By following the motion of the electrons using first-principles calculations, we assess the effect of the traps on the velocity distribution of the particles. Electrons that escape the local trap continue to lose energy as they move outward until they are eventually captured by subsequent traps, preventing them from returning to the observer as sunward-moving particles. We derive a mathematical expression for the cutoff velocity, defined as the limit beyond which particles can no longer overtake the outer endpoint of a local trap. It turns out that the observed cutoff energy characterizes only the local potential drop within a trap, rather than the total depth of the Sun's potential well. The true potential well can be significantly deeper, scaled by the ratio of the radial distance from the Sun to the trap size. Furthermore, electrons captured by these moving traps contribute to the formation of the solar wind core population. The Sun's electrostatic potential is a more significant factor in solar wind acceleration than previously interpreted from cutoff data. The interaction between electrostatic deceleration and moving magnetic traps provides a new framework for understanding the origin and behavior of the solar wind core electrons.

We report multiwavelength observations of the highly offset (~22.4 kpc) SN 2024abvb, the sixth Type Icn supernova to date. With a peak magnitude of Mr = -19.55 +/- 0.11 mag, it is among the most luminous in the existing sample and shows similar colours and decline rates to other SNe Icn. The early optical spectra show a blue continuum with narrow C II features (vFWHM ~ 2000 km s^-1), consistent with a typical wind velocity of a Wolf-Rayet star. The absence of C III lambda 5696 emission at the time of explosion is consistent with a Type Ibn supernova; however, the lack of narrow He lines in both the optical and near-infrared spectra supports a SNe Icn classification. Unlike the majority of SNe Icn, we do not detect broad features in the late-time (7-21 days relative to o-band peak) spectral phase of SN 2024abvb. Semi-analytical modelling of the light curves shows that it can be reproduced by ~2.6 Msun of SN ejecta interacting with ~0.3 Msun of circumstellar material (CSM), both larger than other SNe Icn but consistent with rapidly evolving SNe Ibn. The metallicity at the SN location is significantly lower than the global metallicity of its host galaxy, suggesting that line-driven mass loss required to strip the progenitor of its H and He envelopes was likely inefficient. We estimate the star-formation-rate history at the location of SN 2024abvb and find that it lies at the bottom ~5th percentile among SESNe hosts, inconsistent with a Wolf-Rayet progenitor. Based on its spectral features, local and host environment properties, and host-galaxy offset, we favour an 8-10 Msun star stripped by a compact companion as the progenitor, with a sufficient runaway velocity to reach the observed offset.

Accurate estimation of propagation characteristics of coronal mass ejections (CMEs) is crucial for predicting their geoeffectiveness. Stereoscopic techniques to study the kinematics of CMEs generally have been carried out using remote sensing observations from three viewpoints, i.e. STEREO-A, STEREO-B, and SOHO. Since the loss of STEREO-B in 2014, stereoscopic reconstruction of CMEs has been restricted to the observations from only two viewpoints, i.e., STEREO-A and SOHO. When the angle of separation between STEREO-A and SOHO is small, it leads to larger uncertainties in the CME kinematics derived using stereoscopic techniques. In this paper, we demonstrate how this limitation can be addressed and how uncertainties in the estimation of CME kinematics and propagation direction can be reduced. For this purpose, we selected the CME of April 21, 2023, which was observed by two spacecraft, i.e. STEREO-A and SOHO, separated by a small 10 degree angle. Using the Graduated Cylindrical Shell (GCS) model on the remote-sensing observations near the Sun and the Advanced Drag-Based Model (ADBM) in the heliosphere, we estimated the arrival time of the CME at different locations in the heliosphere and compared it with the actual arrival time obtained from the in-situ measurements taken by three spacecraft, BepiColombo, STEREO-A and Wind. Our analysis reveals a directional uncertainty of approx 20 degree from observations from two viewpoints. These uncertainties significantly affect the arrival-time prediction of the CME. We consider the actual chronology of CME arrival times at STEREO-A and Wind as critical parameters to constrain the direction of propagation, which serves as a key input in the ADBM. The chronology of arrival of the CME ejecta at STEREO-A, which is 4.5 hrs earlier than at Wind, proved essential for resolving directional ambiguities in the GCS reconstruction model

We analyze an XRISM/Resolve observation of NGC1068, focusing on the Fe K$\alpha$ and Fe K$\beta$ fluorescent lines and on the Fe XXV and Fe XXVI emission complexes. Line centroid energies, intrinsic widths, flux ratios, and constraints on the Compton shoulder are derived through local spectral fitting, and compared with atomic calculations and theoretical predictions. The centroid energies of the Fe K$\alpha$ and Fe K$\beta$ lines tightly constrain the emitting material to be neutral or near-neutral. The observed Fe K$\beta$/K$\alpha$ ratio, together with the stringent upper limit on the Compton shoulder ($\lesssim$8--11% of the core flux), disfavour reflection dominated by a homogeneous, classical Compton-thick medium, indicating that most of the neutral Fe K$\alpha$ emission arises in optically thin or moderately Compton-thick gas. The Fe XXV and Fe XXVI emission lines exhibit remarkably large velocity widths, of several thousand km~s$^{-1}$. These broad profiles closely resemble the integrated optical and infrared [O III] and [O IV] lines associated with the large-scale biconical outflow, and are naturally interpreted as the X-ray signature of a more highly ionized, faster, and more spatially confined phase of the same outflow. The iron-K emission of NGC1068 reveals a stratified circumnuclear environment in which neutral and highly ionized components arise in physically distinct regions. The neutral Fe K fluorescence originates predominantly in optically thin or mildly Compton-thick material, despite the persistently Compton-thick line-of-sight obscuration, indicating a geometrically complex cold reprocessor. The highly ionized iron emission lines trace a fast component consistent with a warm bipolar outflow on parsec scales, whose large velocities and inferred energetics suggest that it may represent an efficient channel for feedback in a heavily obscured Seyfert galaxy.

The Orion Nebula Cluster (ONC) provides the closest example of star and planet formation in highly irradiated environments. It is a key region to study how UV radiation from massive stars drive mass-loss in protoplanetary disks through photoevaporation. Far-UV photons (6<E<13.6 eV) heat up the gas of the disk, forming a photodissociation region (PDRs). We use the NIRCam images from the PDRs4All program combined with those of the GTO program 1256 to extract key information on ONC disks. Specifically, the radii of the disks observed in silhouette against the bright background , the presence and positions of the dissociation fronts (DFs), the presence and positions of ionization fronts (IFs), intensities of Pa $\alpha$ lines, and their near IR SEDs. From those, we construct a typology for ONC disks: Type I show an IF and DF nearly merged at the disk surface; Type II have their DFs at the disk surface and IFs at a distance of several 10s of astronomical units from the disk; and Type III also have their DF at the disk surface, but show no IF. For all disks, we find that PAH emission traces the PDR. We establish that the SEDs of candidate JuMBOs observed as part of the PDRs4All program are similar to the SEDs of Type III ONC disks except for JuMBO24, which is of Type I or II. A detailed look at this SED shows it is compatible with a young low mass binary star with an unresolved ionized disk : a microproplyd binary. We observe that the disk radius of ONC disks increases with increasing projected distance to the ionizing source interpreted as evidence of the truncation of the disks by the photoevaporation. The disk radii measured at IR wavelengths appear larger than at millimeter wavelengths, interpreted as evidence of the dust radial segregation within the disks. The thermal pressure within the PDRs of ONC disk increases with the FUV radiation field, but with a flatter slope.

We present an in-depth Chandra X-ray analysis of the galaxy cluster SPT-CL J0417$-$4748 (hereafter SPT J0417), at z = 0.58, with a focus on its thermodynamic properties and the apparent absence of central star formation. Utilizing a total Chandra exposure of 103 ks, we find that the large-scale X-ray morphology is consistent with a dynamically relaxed, cool-core system. The intracluster medium (ICM) shows a central density of 0.08+/-0.01 cm^{-3}, a central pseudo-entropy of 26^{+6}_{-5} keVcm^{2} and a central cooling time of 515^{+96}_{-75} Myr, values typical of massive cool-core clusters. Despite these conditions, no evidence of recent or ongoing star formation is detected in the brightest cluster galaxy (BCG). Spectral energy distribution (SED) fitting of DES photometry indicates that the bulk of the stellar population formed at z~1.25, with no significant star formation over the past ~3 Gyr, while optical spectra from Magellan show no [O II] emission. Complementary ASKAP radio and Spitzer infrared data indicate a lack of strong current AGN activity in the BCG. SPT J0417 exemplifies massive, relaxed, cool-core clusters in which cooling and star formation appear almost completely quenched, providing valuable insights into how AGN feedback regulates the long-term thermal balance of the intracluster medium.

We computed Lyapunov times ($T_L$) for a sample of trans-Neptunian objects (TNOs) and outer main-belt asteroids (MBAs) using three numerical approaches: the variational method and two implementations of the renormalization technique. For each object, $T_L$ was derived both from the nominal orbit and from ensembles of 1001 orbital clones, enabling direct comparison between single-orbit and ensemble-based estimates. Across the sample, the methods generally produced consistent results, though larger discrepancies were observed for some MBAs. TNOs, in contrast, displayed greater consistency across methods, likely due to fewer overlapping resonances. Importantly, clone ensembles provided more robust and reliable stability indicators than nominal-orbit computations. Median values from clone populations reduced method-dependent biases and revealed dynamical behaviors that would remain hidden in single-orbit analyses, especially for objects with poorly constrained orbits or evolving in resonant regions. While our study focused on a limited but diverse set of objects, the methodology can be directly extended to larger populations, offering a systematic framework for exploring the long-term stability and dynamical evolution of main-belt asteroids, trans-Neptunian objects or other classes of objects in the Solar System.

We present the results of observations of the radio halo in the Coma galaxy cluster at 4.8 GHz performed with the Sardinia Radio Telescope. The radio halo in this cluster is detected for the first time at this frequency with a statistical significance higher than $3\sigma$. After the removal of the Radio Frequency Interference and of the discrete sources contribution, and after the correction for the Sunyaev-Zel'dovich effect, we estimate a flux density of $61\pm11$ mJy, higher than the value previously reported in literature at this frequency. By using the value we obtained, it is possible to estimate an integrated spectral index between 4.8 and 6.6 GHz of $\alpha\sim1.17$, where $F(\nu)\propto \nu^{-\alpha}$, indicating a possible higher-frequency slowdown of the spectral steepening observed between 1.4 and 4.8 GHz. Such a spectral behavior is compatible with turbulent re-acceleration if the seed electrons have a spectrum extending up to high energies, as in the case of continuous injection by hadronic interactions or dark matter annihilation. We also report the detection at 4.8 GHz of a polarized spot inside the halo, without an evident counterpart, already detected at 6.6 GHz.

The merger of a He white dwarf (WD) and a CO WD is the favored formation channel for R Coronae Borealis (RCB) stars. These stars exhibit ${^{16}}\mathrm{O}/{^{18}}\mathrm{O}$ ratios that are orders of magnitude lower than the solar value. However, it is not fully understood whether such low ${^{16}}\mathrm{O}/{^{18}}\mathrm{O}$ ratios can be achieved in WD merger remnants for the predicted lifetime of RCB stars of around $10^4\,\mathrm{years}$. In this work, we perform detailed nucleosynthesis calculations of a 3D magnetohydrodynamical simulation of a merger of a $0.3\,M_\odot$ He WD and a $0.6\,M_\odot$ CO WD for $4000\,\mathrm{s}$ at which point a steady state in temperature and density is reached. From this point, we follow several radial zones to study the long-term production of ${^{18}}\mathrm{O}$ and its variability throughout the burning region. We find that the asymmetric merger process leaves an imprint on the distribution of the abundances at the end of our hydrodynamic simulation. During the long-term evolution up to $100\,\mathrm{years}$, we observe ${^{16}}\mathrm{O}/{^{18}}\mathrm{O}$ ratios of order of unity, although the timescale on which ${^{18}}\mathrm{O}$ is destroyed again is highly location dependent. Importantly, our calculations suggest that in the outer layers of the burning shell, the dominant production channel is $^{14}\mathrm{C}(\alpha,\gamma)^{18}\mathrm{O}$ instead of the commonly considered $^{14}\mathrm{N}(\alpha,\gamma)^{18}\mathrm{F}(\beta^+)^{18}\mathrm{O}$ reaction, whereby the former can be sustained for longer periods of time. Furthermore, these outer regions do not reach the conditions necessary for fast $\alpha$-captures in ${^{18}}\mathrm{O}$ to ${^{22}}\mathrm{Ne}$, thus being favorable to maintaining a low ${^{16}}\mathrm{O}/{^{18}}\mathrm{O}$ ratio.

A protostellar disk is threaded by a static magnetic field that is perpendicular to the disk-surface. The magnetic field acts to brake the protostellar disk and cause the disk material to move towards the protostar. General analytic equations are derived for the accretion speed, and mass accretion rate. Simplified analytic equations are also obtained for the disk energy dissipation, accretion timescale and the disk radial position plus disk surface density, as a function of time. In addition to providing physical insight, such equations might be useful as a check on computational models for protostar and protostellar disk formation.

We report an instrumental observation of the very exceptional Geminid fireball which was observed in scope of the Czech part of the European Fireball Network (EN) on 13 December 2012 at 4h12m59.4s UT. The uniqueness of this Geminid fireball consists of the record depth of its penetration in the atmosphere (to the height of 32.5 km) and in the fact that most likely a very small fraction of its initial mass survived severe deceleration in the atmosphere and landed on the ground. Such deeply penetrating Geminid with so precise and reliable data has not yet been observed. From a comparison with a large number of Geminids observed by the European Fireball Network and all brightest Geminids from the Prairie Fireball Network in USA and the Canadian MORP Network, we have shown that for Geminids with an entry mass greater than approximately 10 grams, the terminal altitude limit does not decrease further as it does for smaller Geminids, but remains constant at around 38 km. In this comparison, we have shown that there is only one exception, and that is the Geminid presented here. This one penetrated nearly 6 km deeper with very low terminal speed for Geminids. During the atmospheric flight this Geminid meteoroid slowed down from its original speed of 35.75 km/s to 6.8 km/s. This small meteoroid with initial mass of only 0.25 kg is probably the fastest candidate for a meteorite dropping event ever observed. This solid meteoroid belonging to the meteor shower survived a significant dynamic pressure of almost 2 MPa and thus ranks among the interplanetary bodies of asteroidal origin that caused the observed meteorite fall. Although a similar Geminid event has been previously presented in the literature, we demonstrate here that this claim was flawed.

Fast radio bursts (FRBs) are bright, energetic, radio pulses of extragalactic origin. A dichotomy has emerged in the population: some produce repeat bursts, while the majority do not. Most repeating sources only show rare repetitions, and none have been studied extensively over the wide bandwidths necessary to disentangle the physical processes that produce emission from distortions to bursts caused by intervening ionised gas. Here we present radio observations of the most active repeating source, FRB 20240114A. Using an ultrawideband receiving system, we have detected 5526 repetitions, revealing an extreme spectral and temporal variability in the burst emission. The bursts exhibit longer-term broadband variations in central emission frequency over multiple months, and narrowband bursts that have correlations in central frequencies on time scales of milliseconds to minutes. The spectral and temporal properties are consistent with the source undergoing magnification by foreground plasma lenses, potentially embedded in a turbulent circumsource medium. This extreme example highlights the role of plasma lenses in the observed properties of burst emission and can explain the diversity in activity and energetics of the entire FRB population.

ATUS, the Astronomical Telescope of the University of Stuttgart, is a fully remote-controlled 0.6 m f/8.17 Ritchey-Chrétien telescope optimized for high-cadence, high-fidelity photometry of transient sources. Observations are time-referenced with very high accuracy and precision, making it an ideal platform for time-domain astronomy and space situational awareness. Initially conceived to support instrument developments and operations of SOFIA, the Stratospheric Observatory for Infrared Astronomy, it evolved into a scientific instrument for various use cases in instrument development, astronomical research, and teaching. This paper presents an overview of its development and optimization to achieve diffraction-limited images and highly accurate pointing and tracking, even at high speeds. The findings and lessons learned are universally applicable to other telescopes that are currently at the planning stage, or where similar issues might be encountered.

Using the Socrates photolysis scheme, we present newly calculated photolysis rates under modern Earth atmospheric conditions for species directly relevant to Earth and species relevant to different atmospheric compositions. We compare to a previous photolysis comparison exercise, namely PhotoComp 2011. Overall, we find good agreement between our results and previous work, with discrepancies usually caused by the implementation of temperature or pressure dependent quantum yields and updated cross-section data. We provide a new set of benchmark photolysis rates for additional species both for Solar irradiance and when irradiated by an M dwarf host star. In general, the higher actinic flux at far-UV and shorter wavelengths of the M dwarf compared to the Sun drives increased photolysis rates for reactions with high threshold energies. This work provides an updated set of benchmark results for further studies of photolysis in the Earth's atmosphere and that of other planets.

The nearby quasar, PG 1211+143, has one of the prototype examples of an ultra fast outflow (UFO), as seen in several past XMM-Newton and Chandra observations. In December 2024, PG 1211+143 was observed simultaneously with XRISM Resolve and XMM-Newton, allowing both the Fe K and soft X-ray outflows to be examined at high resolution simultaneously. The Resolve spectrum revealed a forest of Fe K band absorption lines from the UFO (Mizumoto et al. 2026), comprising of up to six discrete velocity components ranging from $v/c=-0.074$ to $v/c=-0.40$. Here we present the simultaneous XMM-Newton RGS (Reflection Grating Spectrometer) spectrum, where three lower ionization counterparts of the Fe K velocity zones are observed; at $v/c=-0.074, -0.12$ and $-0.33$. The soft X-ray absorbers tend to be somewhat less ionized than their Fe K counterparts, with their opacity mainly arising from Fe L shell lines and highly ionized Oxygen. From comparing the Resolve and RGS absorbers, we show that the outflow can be parameterized with a density profile varying with radius as $r^{-5/3}$, while the lower ionization zones likely originate from denser clumps of gas. Pure electron scattering appears insufficient to provide enough thrust to power the wind, unless sufficient low ionization gas capable of radiative line driving exists outside of the line of sight. Overall, PG 1211+143 provides further evidence for the clumpy nature of accretion disk winds, as was recently revealed in the quasar PDS 456 with XRISM.

Polarized emission from interstellar dust grains is commonly used to infer information about the underlying magnetic field from the diffuse interstellar medium to molecular cloud cores. Therefore, the ability to accurately determine properties of the magnetic field requires a thorough understanding of the dust alignment mechanism. We investigate the influence of anisotropic radiation fields on the alignment of dust particles by magnetic fields, known as radiative torque (RAT) alignment. Specifically, we take advantage of the unique spatial configuration of the molecular cloud core L43, which contains an embedded yet optically visible star acting as a local source of anisotropic illumination. Based on polarization maps obtained at wavelengths of $154 \mu\mathrm{m}$ (SOFIA/HAWC+), as well as $450 \mu\mathrm{m}$ and $850 \mu\mathrm{m}$ (JCMT/SCUBA-2), which show variations in the degree and angle of polarized emission across all wavelengths, we applied the differential measure analysis method to infer magnetic field strengths and analyze the global polarization spectrum of this source. We derived plane-of-sky magnetic field strengths ranging from approximately 13 to 60 $\mu\mathrm{G}$, varying with wavelength, and find a negative slope of the polarization spectrum. Compared to 3D radiative transfer simulations, this finding can be attributed, at least partially, to variations in dust properties and temperatures along the line of sight. However, the additional influence of variations in the magnetic field orientation along the line of sight cannot be ruled out. Our results favor radiative torques as the primary alignment mechanism, as they indicate that the degree of polarization is dependent on temperature and hence the strength of the local radiation field.

Massive O-type stars lose a significant fraction of their mass through radiation-driven winds, a process that critically shapes their evolution and feedback into the interstellar medium. Accurate predictions of mass-loss rates are essential for models of stellar structure and population synthesis. We computed wind parameters for O-type stars using a self-consistent approach that couples the hydrodynamics of the wind with detailed calculations of the line acceleration. This approach follows the theory of radiation-driven stellar winds and allows us to derive mass-loss rate distributions for different atomic configurations of the stellar flux. We used the TLUSTY code for stellar atmosphere models to compute non-local thermodynamic equilibrium models; these models served as input radiation fields for the calculation of the line-force parameters, for which we used the LOCUS code. These line-force parameters were then iteratively coupled with the HYDWIND code to solve the wind hydrodynamics. The procedure was applied across a grid of stellar parameters for three chemical configurations. We obtain self-consistent wind parameters for a broad set of O-type stellar models. The results show a systematic decrease in mass-loss rates with the inclusion of more elements in the radiation field, which is attributed to a strong effect on the UV region of the spectral energy distribution. As more elements are included, resulting in a larger number of spectral lines, the contribution from the UV diminishes, leading to lower mass-loss rates. We fitted three theoretical prescriptions for $\dot{M}$ using a Bayesian approach; this yielded Pearson correlation values greater than 0.92 for all three model grids. It also allowed for the estimation of the wind momentum-luminosity relationships for each of the grids, yielding results similar to those based on observations of O-type stars.

Cosmological vector fields are central to many early-Universe phenomena, including inflationary dynamics, primordial magnetogenesis, and dark-matter scenarios. However, constructing models able to generate cosmological magnetic fields while avoiding strong coupling, backreaction, and cosmic microwave background constraints remains challenging. We study a novel mechanism in which brief non--slow-roll phases during inflation amplify primordial magnetic fields at small scales, while maintaining theoretical consistency and observational viability. We incorporate parity-violating interactions in the vector sector and demonstrate, for the first time in a non--slow-roll framework, that chirality can significantly boost magnetic-field amplitudes and imprint distinctive polarization-dependent spectral features. We complement detailed numerical computations with an analytical treatment yielding compact expressions for chiral vector mode functions that reproduce the main spectral properties. We then develop a systematic formalism to evaluate the stochastic gravitational-wave background naturally induced at second order by these amplified fields, identifying both an intensity component and a circularly polarized contribution with characteristic frequency profiles. We discuss detection prospects with future multiband gravitational-wave observatories, showing that chiral signatures could provide a distinctive observational probe. Our results introduce new avenues for enhancing primordial magnetic fields and their associated gravitational-wave signals, opening promising possibilities for their future detection and interpretation, both with cosmological and gravitational wave probes.

The distribution of meteor magnitudes is known to follow an exponential distribution, where the base of this distribution is called the population index. The distribution of observed magnitudes preserves this behavior, but is truncated by the detection threshold. If both the population index and detection threshold can be determined, observed meteor rates can be converted to fluxes and extrapolated to any desired brightness or size. We argue that the distribution of observed or instrumental meteor magnitudes is best modeled as an exponentially modified Gaussian (exGaussian) distribution. This is for three reasons: first, an exGaussian distribution is the natural result of random variations in detection threshold and/or post-detection measurement errors in magnitude. Second, an exGaussian distribution provides a better fit to the magnitude distribution than all other competing distributions in the literature; we demonstrate this using both a set of faint optical meteor magnitudes and a set of radar meteor echo amplitudes. Finally, the population index, mean detection threshold, and random variation/error terms are easily extracted from the best-fit parameters of an exGaussian distribution.

Strongly lensed supernovae (SNe) provide a powerful way to study cosmology, SNe and galaxies. Modelling the lens system is key to extracting astrophysical and cosmological information. We present adaptive-optics-assisted high-resolution images of SN Winny (SN 2025wny) in the J and K filters obtained with the Large Binocular Telescope (LBT). The LBT imaging confirms the presence of a fifth point source, whose colour is consistent with that of the other SN images at similar phases, while lens modelling robustly supports its interpretation as an additional image of SN~Winny. We measure the positions of the five SN images with uncertainties varying between 1 and 14 milliarcseconds. We build the first mass models using lenstronomy and GLEE, and explore three classes of mass models for the two lens galaxies G1 and G2. The optimal model class of the three is a singular isothermal ellipsoid for G1, a singular isothermal sphere for G2, and an external shear. We infer the enclosed masses within the Einstein radius as 4.61^{+0.06}_{-0.04} \times 10^{11}\,M_\odot for G1 and 1.01\pm0.02 \times 10^{11}\,M_\odot for G2. The lensing configuration by the two lens galaxies can produce two additional magnified SN images beyond the five observed ones; the exclusion of such model configurations further constrains the lens model parameters. Our model fits to the observed image positions with an RMS of ~0.0012" - 0.0025", within the observed positional uncertainties. The predicted magnifications of the multiple images vary between ~1.6 (for the faintest fifth image E) to ~10 (for the brightest image A). The predicted relative lensing magnifications of the multiple images do not match that of the observed within 2\sigma uncertainties. The differences in the relative magnifications could be due to millilensing/microlensing. Our mass models form the basis for future analyses of this unique system. (abridged)

The redshifted 21-cm signal emitted by neutral Hydrogen (HI) is a promising probe to understand the evolution of the topology of ionized regions during the Epoch of Reionization (EoR). The topology of ionized regions allows us to infer the nature and properties of ionizing sources, i.e., early galaxies and AGNs. Traditional Fourier statistics, such as the power spectrum, help us quantify the strength of fluctuations in this field at different length scales but do not preserve its phase information. Analyzing the 21-cm brightness temperature field in the image domain retains its non-Gaussian characteristics and morphological information. One such approach is to track the coalescence of multiple ionized regions to form one contiguous ionized region spanning the universe. This is referred to as percolation, and its onset is quantified by a sharp rise in the value of the Largest Cluster Statistic (LCS) approaching unity. In this work, we carry out a percolation analysis of 21-cm brightness temperature fields by studying the redshift evolution of the LCS along a lightcone to distinguish between several simulated reionization scenarios. We have extended previous results on reionization model comparison from the analysis of coeval 21-cm maps to understand how the lightcone effect biases the observed percolation behavior and affects the distinguishability of the source models. We estimate the LCS of subvolumes of different sizes in the 21-cm lightcone maps and study their redshift evolution for different reionization scenarios using a moving volume approach. We find that the percolation transition inferred from a lightcone approaches that from the coeval box as we increase the bandwidth of the moving volume in all but one reionization scenario.

The solar dynamo relies on the regeneration of the poloidal magnetic field through processes strongly modulated by nonlinear feedbacks such as tilt quenching (TQ) and latitude quenching (LQ). These mechanisms play a decisive role in regulating the buildup of the Sun's polar field and, in turn, the amplitude of future solar cycles. In this work, we employ Physics-Informed Neural Networks (PINN) to solve the surface flux transport (SFT) equation, embedding physical constraints directly into the neural network framework. By systematically varying transport parameters, we isolate the relative contributions of TQ and LQ to polar dipole buildup. We use the residual dipole moment as a diagnostic for cycle-to-cycle amplification and show that TQ suppression strengthens with increasing diffusivity, while LQ dominates in advection-dominated regimes. The ratio $\Delta D_{\mathrm{LQ}}/\Delta D_{\mathrm{TQ}}$ exhibits a smooth inverse-square dependence on the dynamo effectivity range, refining previous empirical fits with improved accuracy and reduced scatter. The results further reveal that the need for a decay term is not essential for PINN set-up due to the training process. Compared with the traditional 1D SFT model, the PINN framework achieves significantly lower error metrics and more robust recovery of nonlinear trends. Our results suggest that the nonlinear interplay between LQ and TQ can naturally produce alternations between weak and strong cycles, providing a physical explanation for the observed even-odd cycle modulation. These findings demonstrate the potential of PINN as an accurate, efficient, and physically consistent tool for solar cycle prediction.

The nearly scale-invariant primordial power spectrum provides the standard initial conditions for cosmological perturbations. However, the largest scales remain only weakly constrained by CMB observations, leaving room for deviations such as an infrared (IR) cut-off. This possibility is further motivated by the persistence of large-scale CMB anomalies, most notably the low quadrupole power. In this work, we revisit several broad classes of phenomenologically motivated IR cut-off scenarios using parametrised functional forms of the primordial power spectrum. We confront these models with the latest CMB, BAO, and supernova data and derive updated constraints on the cut-off scale and associated features. Our results remain consistent with earlier studies, showing that although such models suppress power at low multipoles, the improvement in fit is marginal and does not overcome the associated parameter penalties. We therefore find no statistically significant evidence favouring IR cut-off models over the standard power-law spectrum with current data. We further explore the interplay between IR cut-off features and a possible increase in the reionisation optical depth, motivated by the recent CMB-BAO tension highlighted by DESI DR2 within the $\Lambda$CDM framework. We show that the additional freedom introduced by large-scale suppression is generally insufficient to support a substantial increase in optical depth, owing to the weak statistical preference for suppressed large-scale temperature power. Finally, we examine the implications of IR cut-off models for large-scale CMB anomalies by analysing the corresponding anomaly statistics within a Bayesian framework.

We present high-angular resolution ($\simeq 0\rlap.{''}06$) VLA and ALMA observations of Orion South separated by 15.52 years. The purpose of this study was to search for orbital motions in three close ($\simeq 0\rlap.{''}1$) binary systems in the region. We do not detect changes in the position angle of the binaries but in two of the cases we detect significant changes in their separation in the plane of the sky. We use these changes to estimate that the total mass of the binaries is in the $\simeq$1-2 $M_\odot$ range. We also estimate the disk masses from the mm emission. The dust-to-stellar mass ratio is in the range of 0.04 to 0.18, values consistent with those expected for very early stellar evolution (Class 0) protostars.

Motivated by observational evidence from JWST and theoretical results from cosmological simulations, we use a simple parametric, phenomenological model to test to what extent bursty star formation with standard Initial Mass Function, no continuous star formation, no mergers, \mr{and no dust} can account for the observed properties in the $M_{UV}$ vs $M_*$ plane of galaxies at redshifts $z>5$. We find that the simplest model that fits the data has a quiescence period between bursts $\Delta t \sim 100$~Myrs and the stellar mass in each galaxy grows linearly as a function of time from $z=12$ to $z=5$ (i.e., repeated bursts in each galaxy produce approximately equal mass in stars). The distribution of burst masses across different galaxies follows a power-law $dN/dM_* \propto M_*^\alpha$ with slope $\alpha \sim -2$. At $z>9-10$ the observed galaxy population typically had only one or two bursts of stars formation, hence the observed stellar masses at these redshifts (reaching $M_* \sim 10^{10}$~M$_\odot$), roughly represent the distribution of masses formed in one burst.

Particle-in-Cell (PIC) methods have achieved widespread recognition as simple and flexible approaches to model collisionless plasma physics in fully kinetic simulations of astrophysical environments. However, in many situations the standard PIC algorithm must be extended to include macroscopic effects in microscale simulations. For plasmas subjected to shearing or expansion, shearing-box and expanding-box methods can be incorporated into PIC to account for these global effects. For plasmas subjected to local acceleration in confined regions of space, a leaky-box method can allow closed-box PIC simulations to account for particle escape from the accelerator region. In this work, we review and improve methods to include shearing, expansion, and escape in PIC simulations. We provide the numerical details of how Maxwell's equations and the particle equations of motion are solved in each case, and introduce generalized Boris-like particle pushers to solve the momentum equation in the presence of extra forces. This work is intended to serve as a comprehensive reference for the implementation of shearing-box, expanding-box, and leaky-box algorithms in PIC.

Synchrotron radiation plays a central role in astrophysical and high-energy processes. Its spectral description involves the synchrotron function, defined by a non-trivial integral of modified Bessel functions and commonly evaluated through numerical methods or dedicated approximations. In this work, we obtain a compact analytical representation of the synchrotron function using the Method of Brackets, which yields systematically controllable asymptotic expansions in both the small- and large-argument regimes. The resulting expressions accurately reproduce numerical integration and make the analytic structure of the function explicit. Our results provide an efficient alternative to repeated numerical evaluations and facilitate applications requiring fast and controlled approximations.

The time-dependent modulation of the event rate in dark matter direct detection experiments, arising from the motion of the Earth with respect to the Galactic rest frame, is a distinctive signature whose observation is crucial for claiming a discovery of dark matter. While annual modulation has been well studied for decades, daily modulation due to the Earth's rotation has attracted increased attention recently due to the identification of anisotropic solid-state detector materials that yield a direction-dependent scattering rate without sacrificing the overall rate. We perform a statistical analysis of daily modulation in dark matter scattering experiments, with the goal of maximizing the statistical significance of a modulating signal in the presence of an unknown background rate, which may be either flat (non-modulating), or modulating over a 24-hour period with a known or unknown phase. In the background-dominated regime, we find that the discovery significance scales as $f_\text{RMS} \sqrt{T}$, where $T$ is the total exposure time and $f_\text{RMS}$ is the root-mean-square modulation amplitude; in particular, the significance continues to improve with exposure rather than saturating due to systematic uncertainties in the background rate. Using anisotropic trans-stilbene detectors for sub-GeV dark matter as a benchmark example, we provide prescriptions for optimizing the significance for a given total detector mass and location. In an example analysis using three detectors, optimizing the detector orientations can reduce the required exposure by a factor of $\sim 5$ for a desired discovery or exclusion significance, even after profiling over an unknown modulating background phase.

In this work, we reformulate the relativistic BDNK (Bemfica-Disconzi-Noronha-Kovtun) diffusion equation in flux-conservative form, and solve the resulting equations in $(1+1)$D using both a second-order Kurganov-Tadmor finite volume scheme and physics-informed neural networks (PINNs). In particular, we introduce the SA-PINN-ACTO framework, which combines the self-adaptive PINN technique with an exact enforcement of initial and periodic boundary conditions through an algebraic transform of the network's raw output, allowing the network to focus solely on minimizing the PDE residual. We test both approaches on smooth and discontinuous initial data, for both trivial and dynamically evolving velocity and temperature BDNK backgrounds, and for two characteristic speeds. The SA-PINN-ACTO method matches the converged Kurganov-Tadmor solutions for smooth profiles, while for discontinuous profiles the errors increase, reflecting an expected limitation of PINNs near sharp gradients.

The Event Horizon Telescope (EHT) image of M87* provides a direct test of strong-field gravity, measuring an angular shadow diameter $\theta_d = 42 \pm 3~\mu\mathrm{as}$ and a circularity deviation $\Delta C \leq 0.1$. Such observations allow quantitative tests of the Kerr paradigm and of possible deviations from the no-hair theorem. In scalar-tensor extensions of gravity, black holes may possess primary scalar hair, introducing an additional independent parameter beyond mass and spin. In this work, we construct rotating black hole solutions with primary scalar hair in beyond Horndeski gravity and analyze their photon regions and shadow formation. We show that the scalar hair parameter $Q$ induces characteristic modifications of the shadow, and in particular negative $Q$ enlarges the shadow and reduces its oblateness, while positive $Q$ shrinks and enhances its distortion. Modeling M87* within this framework and imposing the EHT bounds on $\theta_d$ and $\Delta C$, we determine the viable $(a,Q)$ parameter space. We find that current observations do not exclude rotating black holes with primary scalar hair, although the allowed region is significantly restricted for $Q>0$. Finally, the scalar-hair-induced deviations are of order $\mathcal{O}(\mu\mathrm{as})$, placing them near the sensitivity threshold of present instruments and within reach of next-generation horizon-scale imaging.

A transient violation of the null energy condition (NEC) during inflation provides a novel mechanism for producing primordial black holes (PBHs) and stochastic gravitational wave (GW) backgrounds. In this work, we extend previous studies by computing the GW contributions from both the ringdown phase of PBH formation and subsequent binary mergers. Our results show that this scenario produces a rich, multi-component GW spectrum consisting of primordial GWs, scalar-induced GWs, and GW emissions from PBH ringdown and binary mergers. We demonstrate that these correlated signatures across different frequency bands provide a novel and powerful avenue to probe or constrain NEC violation during inflation through future multi-band GW observations.

Comet-type periodic orbits of the circular restricted three-body problem (CR3BP) are periodic solutions that are generated from very large retrograde and direct circular Keplerian motions around the common center of mass of the primaries. In this paper we first provide an analytical proof of the existence of comet-type periodic orbits by using the classical Poincaré continuation method. Within this analytical approach, we also determine their Conley-Zehnder index, defined as a Maslov index using a crossing form. Then, by applying a standard corrector-predictor technique, we explore numerically the two families of comet orbits within the Earth-Moon CR3BP. We compute their stability indices, identify vertical self-resonant orbits up to multiplicity six, investigate the vertically bifurcated periodic solutions and discuss their orbital characteristics. Our main results we illustrate in form of bifurcation graphs, based on symplectic invariants, which provide a topological overview of the connections of the bifurcated branches, including bridge families.