Papers

[Abridged] We aim to study the radial and vertical extents of 12CO gas, millimeter dust thermal emission and optical/NIR scattered light by dust in disks. We analyze a sample of 14 highly inclined protoplanetary disks. We present ALMA high angular resolution band 7 (0.9 mm) continuum images and 12CO (3-2) gas moment maps as well as HST and VLT/SPHERE scattered light images. The majority of disks in our sample (11 out of 14) follow Rgas > Rdust,micron > Rdust,mm. The other 3 disks appear more extended in millimeter continuum than in scattered light. Highly inclined disks tend to appear less radially extended in CO gas line emission than in millimeter dust continuum compared to less inclined disks. This results from optical depth effects and/or radial drift. The known correlation between disk size and millimeter continuum and line fluxes are confirmed in our sample with highly inclined disks significantly fainter than disks seen at lower inclination for a given disk radius. We found that this correlation is significantly tightened once fluxes are corrected for the disk inclination, consistent with the disks being optically thick at millimeter wavelengths. Regarding the vertical extent defined as the apparent emitting height, most disks in our sample follow Hgas > Hdust, mm. This strengthens our previous findings that the millimeter dust is highly decoupled from the gas and forms a layer in the disk midplane due to vertical settling. Most disks appear more vertically extended in gas than in scattered light, suggesting that the micron-sized dust is not fully coupled to the gas. We also estimated dynamical masses using PV diagrams for the first time for most of the objects in our sample. We found an anti-correlation between the dynamical mass and the aspect ratio, emphasizing the dominant role of gravity in setting the disk vertical extent, but no correlation with the disk radius.

Rotating space tethers have long been proposed as momentum-exchange devices capable of transporting payloads between orbital regimes without continuous propellant expenditure, offering a potential alternative to conventional propulsion for transfers from low Earth orbit to higher orbits. In this work, we numerically investigate a system of multiple rotating tethers distributed across different orbital radii and coupled through intermediate transfer platforms (elliptical nodes) moving along Keplerian trajectories. We identify families of dynamically consistent configurations in which neighboring tethers achieve near-phase synchronization, enabling coordinated payload exchange without impulsive maneuvers. Based on these results, we introduce the concept of a Space-Clock Elevator: a modular orbital transport architecture in which payloads are transferred sequentially between synchronized rotating tethers via intermediate elliptical nodes. Numerical experiments demonstrate that such synchronized tether networks can support outward payload transport while maintaining bounded tether tension and dynamically stable orbital motion.

Abridged : The fundamental parameters of rapidly rotating stars are key quantities to understand the impact of rotation on stellar evolution. A few nearby early-type stars offer the possibility of precise measurements of these parameters, which will help us constrain newly available two-dimensional models. We propose a method to retrieve the fundamental parameters of a fast rotating star (mass, rotation rate, and age), and also the inclination of its rotation axis on the line of sight, using five spectrophotometric observables along with a set of steady 2D-models. Using the temperature derived by the infrared flux method, the Vsini and the apparent luminosity, along with a grid of 2D steady state models, we select models that are compatible with all observational constraints, and derive the most probable mass, rotation rate, core hydrogen mass fraction relative to that of the envelope, and inclination of the rotation axis on the line of sight of the targetted star. We apply this method to two stars: Rasalhague (alpha Oph) and Alkaid (eta UMa). We confirm and improve the fundamental parameters of Rasalhague and provide a new determination of its rotation axis inclination on the line-of-sight, which we find to be $\sim69$ degrees. Concerning Alkaid, we infer a mass of $5.071\pm0.023 M_\odot$, a rotation rate corresponding to an equatorial rotation period of 14.6 hours. We also find an inclination of the rotation axis of $\sim42$ degrees. We show that Alkaid is a very young star, presumably between 2 and 8 Myrs off the Zero-Age Main Sequence. As a side result, using high resolution spectra and the Least Square Deconvolution method, we determined a precise value of the Vsini of Rasalhague, namely $224.3\pm2.6$ km/s. Similarly, we find $V\sin i=154.3\pm9.1$ km/s for Alkaid.

We investigate how resolving the inner few astronomical units of a massive protostellar disk affects the migration, disruption, and accretion signatures of an inward-moving fragment. In particular, we aim to determine whether the predicted burst strength and duration depend on the adopted sink cell size. We present a new three-dimensional radiation-hydrodynamic simulation of a $\sim$5$M_{\odot}$ protostar surrounded by a self-gravitating disk, comparing the original 30 AU sink model to a refined model with a 1 AU sink that resolves the inner disk. The resulting gas structures are post-processed with radiative transfer calculations to derive synthetic photometry and multi-band images. Both simulations produce a major accretion burst as a migrating fragment is tidally disrupted, but their detailed behavior differs markedly. The refined model shows faster migration, a complete tidal disruption of the fragment, and a shorter, sharper outburst (more consistent with observations) with nearly the same peak accretion rate as the 30 AU model, which yields a broader, smoother event. The refined run produces much stronger near- and mid-infrared emission, reflecting the formation of a compact, hot inner disk. Resolving the inner few AU qualitatively changes the dynamics and observable appearance of fragment-driven bursts. Diffuse fragment disruption can reproduce decade-long events, but the much shorter ($<$3 yr) bursts observed in some massive protostars likely require the tidal disruption of more compact objects such as second Larson cores. Our trajectory analysis indicates that second Larson cores can migrate sufficiently close to the star to be tidally destroyed, offering a plausible mechanism for the fastest FU-Ori-like bursts observed in massive protostars.

Infrared (IR) excess emission around white dwarfs (WDs) is commonly attributed to circumstellar debris disks and/or low-mass companions, providing a unique window into the evolution of planetary systems and binary evolution after the main-sequence stage. Based on a spectroscopically confirmed WD sample from the DESI Early Data Release, we performed a systematic search for IR excess by combining multi-band photometry from SDSS, Pan-STARRS, UKIDSS, 2MASS, and WISE. Using spectral energy distribution (SED) fitting, we initially identified 72 IR-excess candidates and conducted a stringent contamination assessment based on higher-resolution imaging within 6 arcseconds of each target. After removing sources affected by blending or source confusion, we obtained a final sample of 62 reliable IR excess candidates. Among them, we identify three candidate WD+M dwarf binaries (two new systems), five candidate WD+brown dwarf (BD) binaries (all new), 38 candidate WD+dust disks (28 new), and 16 ambiguous systems that could be either WD+BD or WD+dust (15 new). Compared with previous samples, our catalog extends the parameter space of known dusty WDs toward older cooling ages. Due to the limited spatial resolution of WISE, follow-up high-resolution imaging and/or infrared spectroscopy is required to confirm the physical nature of all candidate systems and to further expand the parameter space of dust disks in terms of cooling age and other properties.

We investigate the sensitivity of a torsion-bar gravitational-wave detector to Yukawa-type deviations from Newtonian gravity using a differential gravitational calibrator (GCal), where two rotating mass systems cancel the leading Newtonian torque. We derive an exact expression for the residual torque and map the Yukawa signal into a strain-equivalent response in the sub-Hz band. We evaluate the sensitivity in the $(\alpha_Y,\lambda)$ parameter space, finding optimal performance at scales comparable to the experimental geometry, reaching $|\alpha_Y| = 2.4\times10^{-5}$ at $\lambda = 8\mathrm{m}$. The sensitivity is limited by residual Newtonian torque from imperfect cancellation rather than statistical noise, with a systematic floor reached at $T_{\rm eq} \simeq 9.25\times10^{4}\mathrm{s}$ ($\sim 26$ hours). This limit is dominated by uncertainties in the source-mass geometry. The differential configuration retains sensitivity even at large interaction ranges, enabling constraints at meter-scale distances. These results establish torsion-bar detectors as a systematics-limited probe of non-Newtonian gravity in the sub-Hz band.

The Earth slowly decelerates in its rotation due to the energy dissipation caused by the interaction with the Moon. This leads to the continuous increasing in the length of the mean solar day (aka, length-of-day, or, LOD) relatively to 86,400 solar seconds at an average secular rate of +1.8 ms per century. But, on a shorter time scale the process is uneven. A positive leap second is used to be introduced on regular basis to support a consistency between the astronomical and atomic timescales. However, nowadays the LOD is steadily sparking a discussion about the timescale maintenance, in particular, from fears that a negative leap second will have to be introduced for the first time in the foreseeable future. The aim is to show that the LOD is currently dominated by the 18.6 yr lunar nutation signal whereas the long-term trends are essential for extrapolation after 2030. The LOD data since 1962 are used to estimate the long-term variations along the 18.6 yr and other harmonic signals in its spectrum. It is shown that the influence of the lunar nutation impact on the LOD variations was underestimated. At the moment, the LOD changes are completely determined by a signal with a period of 18.6 yrs. More detailed extrapolation reveals that LOD is likely to vary in a range between -1 ms to +1 ms until 2050 or may be longer.

The fiducial-independent angular/transverse BAO dataset, obtained from two-point angular correlation functions in thin redshift shells (hereafter BAOtr), systematically prefers smaller comoving distance ratios $D_{\rm M}/r_{\rm d}$ than the DESI DR2 three-dimensional BAO measurements at $z \lesssim 0.65$, driving dataset-dependent CPL dark-energy inferences and conflicting conclusions about the Hubble tension. We investigate whether this disagreement can be attributed to the $\Lambda$CDM fiducial assumed in the 3D BAO pipeline, or resolved within the CPL parametrisation. We show that the published 3D BAO distances are fiducial-independent by construction, with residual effects at $\lesssim 0.3\%$ – negligible against the 10–18% BAOtr uncertainties. We then scan the CPL parameter space with $\Omega_m$ and $H_0$ jointly determined at each $(w_0, w_a)$ by the Planck $\theta_*$ constraint and optimisation against the DESI data. Two complementary tests are performed: a direct comparison of each DESI-optimized model with the BAOtr data, and an $\alpha$-interpolation test that anchors the prediction to the DESI measurements. Both reveal an inescapable trade-off: models that fit DESI well ($\chi^2_{\rm DESI} \lesssim 5$) yield $\chi^2_{\rm BAOtr} \gtrsim 42$, while reducing the BAOtr tension to $\chi^2_{\rm BAOtr} \sim 37$ requires $\chi^2_{\rm DESI} \gtrsim 8$. No CMB-consistent CPL model fits both datasets simultaneously. The direct comparison at $z = 0.510$ – where BAOtr and DESI disagree by $3.7\sigma$ (data-versus-data) – sets an irreducible tension floor that no smooth modification of $D_{\rm M}(z)$ can remove. These conclusions are robust across analysis methods, extrapolation schemes, and substitution of SDSS for DESI. The remaining explanations are observational systematics – most plausibly in the BAOtr measurements – or new physics beyond CPL.

Pluto possesses a thin atmosphere primarily composed of N2, with minor constituents including CO and CH4. Photochemical processes generate distinct haze layers as observed by the New Horizons spacecraft. However, the mechanisms governing haze formation, as well as the composition and physical properties of the hazes, remain poorly constrained. Due to Pluto's highly eccentric orbit and obliquity, its surface temperature and atmospheric composition undergo substantial seasonal variations, but it is unclear how such seasonal variations impact the chemical pathways and efficiency of haze formation in Pluto's atmosphere. To address this, we conducted a laboratory simulation of Pluto's atmospheric photochemistry, in which N2/CH4/CO gas mixtures with CH4 concentrations varying from 0.1% to 5% were exposed to a glow discharge to initiate photochemical reactions. Gas-phase composition was monitored in situ using a residual gas analyzer (RGA), while the solid-phase products were characterized by atomic force microscopy (AFM), a gas pycnometer, infrared spectroscopy (IR), and very high-resolution mass spectrometry (VHRMS) to determine particle sizes, density, and composition, respectively. Our results show that increasing the CH4 mixing ratio significantly enhances the yield of gas and solid products. Under low CH4 conditions, nitrogen is primarily incorporated into solids as cyanide groups; whereas CH4-rich conditions favor the formation of amino groups, greatly promoting nitrogen incorporation into organic solids. These findings not only shed light on how seasonal variations into Pluto's atmosphere composition influence haze formation pathways, but also provide critical parameters to interpret observational data and to improve photochemical and microphysical models of planetary hazes.

GJ~486b is a close-in planet orbiting an M dwarf and is therefore expected to have undergone strong atmospheric escape. Motivated by theoretical and observational studies on the constraints of its water and atmosphere, we investigate which combinations of an primordial hydrogen-rich atmosphere and water inventory could fit the current water content implied by bulk density measurements. We model the atmosphere escape using VPLanet, following the loss of an initial hydrogen-rich atmosphere and the subsequent escape of a water-dominated atmosphere. By scanning a broad parameter space across different stellar ages, we invert for the initial hydrogen-rich atmospheric mass and water inventory consistent with the current constraints. Our results reveal a strong degeneracy between the water reservoir and the initial hydrogen-rich atmosphere. Even a modest hydrogen-rich atmosphere can significantly delay early escape of the water and reduce the water inventory required to reproduce the current water content. We also find that the inferred initial conditions are also strongly age dependent. Incorporating a planet formation dataset as a prior, we derive a probabilistic constraint on the host star age, yielding an expected age of $2.90^{+2.47}_{-2.27}$~Gyr, which is consistent with the results obtained from other methods to determine M dwarf ages.

We investigate a realistic non-supersymmetric hybrid inflation model incorporating right-handed neutrinos and assess its viability in light of recent cosmological observations. At tree level, the inflaton potential yields a blue-tilted scalar spectrum, which is disfavored by current data from Planck and ACT that instead support a red tilt. We show that including one-loop quantum corrections, arising from generic couplings required for reheating, significantly modifies the potential, flattening it at large field values. This leads to a red-tilted spectral index ($n_s < 1$) and a suppressed tensor-to-scalar ratio $r$, both consistent with observational constraints. To ensure theoretical control, we focus on sub-Planckian field values, where the effective field theory description remains valid. The coupling of the inflaton to right-handed neutrinos naturally facilitates efficient reheating and enables the generation of the baryon asymmetry via non-thermal leptogenesis. We further explore the model's parameter space using a multi-output random forest classifier, achieving prediction accuracies in the range of $87.5\%$ to $98.9\%$. Our analysis shows that approximately $15\%$ of the parameter space satisfies at least one current experimental constraint, underscoring the essential role of quantum corrections in reconciling particle physics models with precision cosmology, and highlighting the effectiveness of machine learning techniques in probing complex theoretical frameworks.

We investigate how the transition density \(\rho_{tr}\) affects hybrid constructions of the neutron-star equation of state (EoS) in which a nucleonic description at low densities is matched to a model-agnostic high-density extension based on a speed-of-sound parametrization. Using four representative nucleonic models–Taylor expansion, \(\frac{n}{3}\) expansion, Skyrme, and relativistic mean-field–built from identical nuclear matter parameters, we isolate the impact of the low-density EoS and the transition density on neutron star observables. We find that, within the present smooth-matching prescription, neutron star properties such as radii and tidal deformabilities retain significant sensitivity to the choice of low-density EoS for commonly adopted transition densities around \(\rho_{tr} \approx 2\rho_0\), even when the same high-density parametrization is employed. This residual dependence arises from differences in the matching conditions at \(\rho_{tr}\), which propagate into the high-density extension, so different low-density inputs lead to different effective high-density EoSs. These findings are robust across two distinct speed-of-sound parametrizations. Quantitatively, the model spread in radius and tidal deformability at $1.4\,M_\odot$ exceeds the current observational uncertainty by factors of $\sim 1.8$ and $\sim 1.4$ at $\rho_{\mathrm{tr}} \approx 2\rho_0$, whereas these factors reduce to $\sim 1.05$ and $\sim 0.4$ at $\rho_{\mathrm{tr}} = \rho_0$. Lowering the transition density, therefore, systematically diminishes the spread among models and leads to more consistent predictions. Our results demonstrate that the widely used choice \(\rho_{tr} \approx 2\rho_0\) does not guarantee model independence in hybrid EoS constructions, and should be treated as an explicit source of systematic uncertainty when inferring dense matter properties from neutron star observations.

Radio pulsars, as highly coherent point sources, serve as powerful probes of the ionized interstellar medium (IISM). Pulsar scintillation observations have revealed inverted arclets on the secondary spectrum, indicating quasilinearly aligned images created by substructures on a scintillation screen. The density profiles of these substructures remain unconstrained but are crucial to identifying their physical nature. This work employs a plasma lensing framework to study observable features of substructure phase screens. Using three lens models, we identify the substructure properties that can be constrained by observables. The outer caustic is the most prominent feature of a lensing substructure, measurable via multiepoch or ultrawideband observations. Its location constrains the maximum column density gradient of the substructure. The inner caustic, though difficult to observe except for substructures capable of producing extreme-scattering events, directly indicates the substructure size. Even when caustic locations are not observed, the minimum span where substructure images exist can be measured and used to place a lower limit on the column density amplitude. The logarithmic brightness of individual arclets forms a concave function of the pulsar-lens angular separation, contrasting with the convex brightness distribution of all substructure images–highlighting the complementarity of individual arclets to statistical studies. These findings reveal the potential of pulsar scintillation to uncover IISM substructure and underscore the need for multiepoch and/or ultrawideband measurements to constrain discrete lensing morphologies and help reveal the nature of interstellar plasma structures.

Extreme-mass-ratio inspirals (EMRIs) carry valuable information about their surrounding astrophysical environments. Over the course of their long-term evolution, interactions between the secondary object and the accretion disk can produce observable effects on both the orbital evolution and the emitted gravitational waveform. Based on the modifications to the companion's orbital evolution induced by the accretion disk environment, we investigate the feasibility of identifying the presence of accretion disk environmental effects in EMRI systems using gravitational wave signals. Within a Bayesian framework, we analyze the capability of EMRI systems with multiple parameter configurations to distinguish accretion disk environmental effects. Our results show that, under the $\alpha$-disk model, all injected events can successfully identify the environment in which the EMRIs reside. Furthermore, we examined the improvement in the precision of Hubble constant measurements using the dark siren method after correctly identifying the accretion disk environment and constraining the relevant disk parameters. Constraining these environmental parameters may further deepen our understanding of the host environment, thereby enabling a more reliable inference of the physical properties of the accretion disk and its associated luminosity and ultimately improving the measurement of cosmological parameters. We find that the measurement precision for a single event can improve by as much as $20\%$. This work highlights the necessity of incorporating environmental effects into future EMRI data analysis. Proper modeling of such effects not only helps identify EMRI systems embedded in accretion disk environments but also further improves the precision of gravitational wave cosmological parameter inference.

In 2021, Lei et al. claimed the equivalence between the two Lagrangians $\mathcal{L}_1 =-mc\sqrt{-g_{\mu\nu}{\dot{x}}^\mu{\dot{x}}^\nu}-V$ and $\mathcal{L}_2 = \frac{1}{2}mg_{\mu\nu} {\dot{x}}^\mu{\dot{x}}^\nu-V$ for describing particle dynamics in combined gravitational and matter fields. In the present work, we rigorously demonstrate that their equivalence depends critically on the external potential V. Both Lagrangians yield identical Hamiltonians that strictly satisfy the mass shell constraint, and are therefore equivalent when V vanishes or corresponds to an electromagnetic potential. However, they are generally not equivalent for generic external potentials excluding the electromagnetic ones. This discrepancy arises because L1 and L2 correspond to different Hamiltonian formulations. The Hamiltonian derived from L1 inherently enforces the mass shell constraint, whereas the Hamiltonian from L2 does not. When the Schwarzschild metric supplemented with an artificial mechanical potential is taken as a toy model, numerical investigations reveal that L1 leads to chaotic behavior, which signifies non-integrable dynamics. By contrast, L2 can be shown analytically to produce integrable dynamics free of chaos. In many scenarios, L1 is strongly recommended due to its theoretical superiority and universality. L2 is generally suitable for classical approximate problems involving low energy and weak gravity. Nevertheless, it is the preferred choice for strong field problems concerning the dynamics of charged (or neutral) particles near black holes with (or without) external electromagnetic fields, owing to its mathematical simplicity and computational efficiency. Moreover, it can still satisfy the mass shell constraint when an additional constraint is imposed on its corresponding Hamiltonian.

We study the geodesic motion and epicyclic oscillations of massive test particles around a static, spherically symmetric black hole (BH) solution of the Einstein–Skyrme (ES) theory in Anti-de Sitter (AdS) spacetime. The lapse function of this BH depends on the Skyrme coupling $\eta$, a charge-like parameter $Q$ inherited from the Skyrme term, and the cosmological constant $\Lambda<0$. We first map out the horizon structure and identify three regimes-non-extremal BH (NEBH), extremal BH (EBH), and naked BH (NBH)-showing that the NEBH $\to$ EBH $\to$ NBH transition is governed by $Q$ rather than $\eta$, which enters $f(r)$ only as a constant shift. We then derive the effective potential (EP), locate the innermost stable circular orbit (ISCO), and compute the radiative efficiency, finding that $\mathcal{E}_{\rm ISCO}>1$ in AdS renders the standard Novikov-Thorne formula negative. The corrected radial epicyclic frequency $\Omega_r$ reveals a distinctive AdS signature: $\nu_r$ grows at large $r$ and overtakes the orbital frequency $\nu_\phi$, causing the periastron precession frequency $\nu_p = \nu_\varphi - \nu_r$ to change sign-a feature absent in asymptotically flat geometries. Adopting the relativistic precession (RP) model for quasi-periodic oscillations (QPOs), we perform a Markov chain Monte Carlo (MCMC) analysis using twin-peak QPO data from XTE~J1550-564, GRO~J1655-40, Sgr~A$^*$, and M82~X-1. The posteriors converge to $Q\approx 0.6$ across all sources, with orbital radii near $r\approx 4.2\,M$ and masses consistent with independent estimates, demonstrating that the ES-AdS BH accommodates the observed frequency pairs within physically motivated parameter ranges.

We model the Seyfert II AGN NGC 1068 within a turbulence-induced magnetic reconnection framework to explain its high-energy emission. Observations reveal a neutrino flux excess higher than the observed GeV gamma-ray emission by orders of magnitude, with no detected TeV counterpart, suggesting efficient hadronic acceleration in the nuclear region with strong gamma-ray absorption. Assuming that proton acceleration occurs in a turbulent reconnection layer via a first-order Fermi process, we use a lepto-hadronic model based on a coronal-accretion disk configuration in which magnetic field lines anchored to the $2 \times 10^{7} M_{\odot}$ black hole horizon reconnect with field lines from the inner accretion disk corona. Our model matches the observed spectral energy distribution with a magnetic field $B_{c} \sim 10^{4}$ G and magnetic reconnection power $\dot{W_{B}} \sim 10^{43}$ erg s$^{-1}$, with $\sim 50\%$ efficiency in proton acceleration. Unlike previous studies, we find that both particle acceleration and emission take place in the inner region, where protons reach $\sim 10^{14}$ eV via first-order Fermi acceleration within the turbulent reconnection layer, rather than drift acceleration. These protons interact with disk photons, coronal X-rays, and coronal protons, producing neutrinos, predominantly via $pp$ interactions, at levels consistent with IceCube detections. The associated gamma-rays are attenuated by $\gamma\gamma$ annihilation, remaining below current upper limits. Turbulence-driven reconnection is thus a viable mechanism for neutrino production in the coronal region of NGC 1068 and similar sources.

Context. Nearly 150 tidal streams are known in the Milky Way, but full phase-space information exists for only a few. RR Lyrae stars (RRL), as standard candles, provide a powerful way to probe these structures, yet they have been identified in less than a dozen streams. Aims. We study the RRL population in all known stellar streams with reported proper motions in the galstreams library, performing the first systematic census of these stars. Our goals are to identify likely RRL members, map distances along streams, and compare RRL populations in streams and their progenitors. Method. We use a union of the largest RRL catalogs (Gaia DR3 SOS, PS1, and ASAS-SN-II) to construct a Bayesian probabilistic membership model and find 361 RRL in the 56 streams studied. Results. i) We find that 32 of the 56 streams have RRL in their tidal tails – 13 with progenitors and 19 without; 13 of these contain more than 3 RRL in their tails. ii) We report new RRL detections in 31 of these streams, anchoring distances and, in particular, inferring new distance gradients for 5 of them. iii) Our method provides intrinsic dispersion estimates in distance and proper motion for each track and statistically quantifies the expected contamination. iv) The census revealed some complex origin histories, such as the new plausible origin scenario we propose for M92 with multiple progenitors. v) We find that the presence of RRL in the tidal tails is linked to the late stages of progenitor dissolution. Conclusions. This census represents a first step toward identifying which of the studied stellar streams contain a significant number of RRL based on currently reported tracks while also providing a homogeneous and robust catalog of RRL members with precise empirical distances, crucial for a full phase-space analysis of these structures and their use as probes of the Galaxy's history and gravitational potential.

The Geostationary Operational Environmental Satellite (GOES) solar soft X-ray (SXR) irradiance in the 1-8Å wavelength range is a long-standing measure of solar activity, used to define the classification of flare strengths. As a result, the flare class, along with the SXR light curves, are routinely used as a primary input for forecasting properties of space weather drivers, from coronal mass ejection speed to energetic particle output. However, the GOES SXR irradiance lacks spatial information, leading to known classification errors, such as misattributed flare locations during periods of high activity. Moreover, GOES only provides observations from Earth's orbit, hindering forecasting for other places in the heliosphere. Motivated by these limitations, we introduce the Framework for Operational X-ray Emission Synthesis (FOXES), a Vision Transformer-based approach for translating Extreme Ultraviolet (EUV) spatially-resolved observations into SXR irradiance predictions. The model produces two outputs: (1) a global 1-8Å SXR flux prediction and (2) per-patch flux contributions, which offer a spatially-resolved interpretation of where the model attributes SXR emission. Trained, validated, and tested on over 3200 hours of observations, FOXES has demonstrated a translational mean absolute error of 0.051 dex for integrated SXR measurements. FOXES has also shown promise in dissecting the solar background SXR flux during flaring and non-flaring events. Overall, this model paves the way for EUV-based spatially-resolved flare detection to be extended beyond Earth's line of sight. Such capabilities could lead to a more comprehensive flare catalog and enable a true multiviewpoint monitoring of solar activity.

The colliding galaxy clusters system 1E 0657-56, the "Bullet Cluster", is often presented as a serious objection to modified gravity theories dispensing with dark matter in general, and in particular, to the MOND formalism. The argument centres on the fact that the baryonic matter distribution of this system is dominated by the X-ray emitting gas, while the projected surface density required under General Relativity to explain the observed lensing signal, centres on the observed galaxies. This spatial offset is interpreted as being in conflict with MOND, naively assuming that dark matter being absent, the gravitational potential should centre upon the largest mass distribution, the X-ray gas. However, as under General Relativity, under MOND, the gravitational potential of a system depends upon the volume density and not just the total mass. I here show that the surface density which QUMOND predicts will be inferred under General Relativity from the gravitational potential of the "Bullet Cluster", qualitatively matches the spatial distribution of what General Relativity inferences of lensing observations return. The close-to-point-like galaxies imply under QUMOND a relatively larger surface density signal than what is expected from the diffuse gas. As is common under MOND modeling of galaxy clusters, a mass deficit on the baryon content is obtained, in this case by a factor of 1.6. Beyond this, only small offsets on the details with respect to GR interpretations of lensing observations remain; MOND is hence shown to be no more discrepant with the "Bullet Cluster" than with any other galaxy cluster.

Modern radio and multi-instrument astrophysical datasets are increasingly assembled from surveys with different sensitivities and selection effects. In such heterogeneous datasets, published measurement uncertainties are often incomplete, non-uniform across subsets, or missing cross-correlation information altogether. This limits reliable statistical inference, since underestimated or inconsistently modeled uncertainties can distort fitted spectral shapes, bias parameter estimates, and obscure physically meaningful structure. We introduce the Fisher Information Metric Error Reconstruction (FIMER), an information-geometric framework for reconstructing effective measurement uncertainties directly from heterogeneous astrophysical data. FIMER combines weighted Fisher-information geometry, FBET and an adaptive discrete hyperparameter search, while incorporating prior statistical knowledge of detector behavior into the weighting procedure. The priors used are not chosen as arbitrary tuning prescriptions or uninformative regularizers; they are motivated by statistical properties of the underlying detection process. Poisson priors represent counting-statistics behavior, while extreme-value priors allow tail-dominated fluctuations to be incorporated when rare or asymmetric excursions are expected to influence the inferred uncertainty distribution. We apply FIMER to radio SEDs of RxAGN using COSMOS VLA data at 1.4 and 3 GHz together with GMRT data at 325 and 610 MHz. The results show that FIMER provides a practical route to uncertainty reconstruction in heterogeneous survey combinations, especially when reported uncertainties are unavailable, underestimated, or strongly correlated. The method is particularly relevant for archival and multi-survey astrophysical datasets, where full covariance information is rarely available but reliable statistical inference remains essential.

Mars' asymmetric figure with two opposing equatorial elevations stems from a frozen tidal bulge raised by a synchronous palaeo-moon Nerio. Nerio's emergence, via in situ accretion or by capture in the disk's remnants, and its synchronisation with Mars' rotation preceded or was coeval with crust formation. The submoon and antimoon regions hypothetically developed thinner crusts, intensifying the tectonics that further amplified Mars' triaxiality. We study Nerio's orbit stability and demise and its impact on Mars' rotation. Nerio may also have been the cause of the tidalites found in sediments. Stellar tides in the planet shrink the orbit of a planet-moon pair, so their synchronism is stable transiently. At some critical distance from the planet, the moon desynchronises and spirals down, spinning the planet up. Application to Mars and Nerio shows that Mars' spin rate at the desynchronisation moment matches the present rate to the first decimal. The coincidence should not be overinterpreted, as post-desynchronisation evolution included Mars' continued spin-up during Nerio's descent (till its destruction amid the LHB), followed by Mars' despinning by solar tides. Nerio's reaching the Roche limit intact is questionable. Beyond LHB hazards, it would imply Mars' larger spin-up, necessitating up to k2/Q ~ 18 to allow subsequent despinning to the present rate. This value may be high even for shallow oceans. Absent future evidence supporting such elevated k2/Q values, Nerio likely perished during the LHB. This verdict may be reconsidered should new data on Mars' ocean show up. The existence and subsequent demise of Nerio are indirectly confirmed by the presence of tidalites in Vastitas Borealis and Gale Crater. During its post-desynchronisation descent, Nerio was capable of producing tidalites in the ocean. After Nerio's demise, this work may have been continued by its massive remnant

The topology of cosmic reionization, the sizes, shapes, and connectivity of ionized bubbles is a primary observable of next-generation 21\,cm experiments. We show that this topology is sensitive to the microphysics of dark matter. Self-interacting dark matter (SIDM), with cross-sections $\sigma/m\sim 1$–$10\;\mathrm{cm^2/g}$ motivated by small-scale structure anomalies, reduces halo gas binding energies and increases the duty cycle of ionizing-photon escape. At fixed global neutral fraction $\bar{x}_{\rm HI}$, this reshapes the source population from rare, very bright emitters to more numerous, moderate emitters, producing qualitatively different ionization morphology. We decompose the effect into two scale-dependent levers: a $2$–$3\%$ emissivity-weighted bias shift at $k\lesssim 0.1\;h/\mathrm{Mpc}$, and a factor $2$–$4$ shot-noise suppression at $k\sim 0.1$–$1\;h/\mathrm{Mpc}$. A halo-by-halo semi-numerical simulation at $128^3$ resolution confirms a $\sim 60$–$70\%$ increase in the Euler characteristic of the ionization field for $\sigma/m \gtrsim 2\;\mathrm{cm^2/g}$, detected at $3.8\sigma$ across ten independent realizations. A blowout model connecting the binding-energy reduction to the duty cycle through the ISM column density distribution yields a detection threshold at $\sigma/m \sim 1$–$2\;\mathrm{cm^2/g}$. The signal exceeds the CDM baryonic uncertainty band and is robust to the functional form of the emissivity parametrization. The signal persists even if gravitational heating offsets $50$–$75\%$ of the blowout enhancement, and is not diluted by unresolved low-mass sources. Velocity-dependent SIDM produces a qualitatively distinct opposite-sign bias shift. These predictions are testable with SKA1-Low, establishing reionization as a new arena for probing dark matter models complementary to dwarf galaxies and galaxy clusters.

Europa's double ridges often display lower albedo and redder color than their surroundings. Their unique topography may cause sublimation-driven darkening due to illumination and self-heating, a process known as thermal segregation. We apply an advanced 3D thermophysical model, including shadowing and self-heating through mutual exchange of radiation, to digital elevation models of double ridges at a range of latitudes and orientations. Results show that self-heating in ridge troughs can markedly increase temperatures and sublimation rates, with a difference in maximum trough temperatures of up to 20 K, which may have implications for detection of endogenic heat. Incorporating a simple exosphere model and assuming an initial 10% concentration of 1 $\mu$m non-ice particles, we find thermal segregation can produce reddening in the form of dark lag layers from the equator to the middle latitudes, but is generally negligible at 60 degrees or higher. Lag formation timescales in ridge troughs are 10 - 100 yr to produce an optically thick layer. Modeling suggests that low-albedo lag layer formation provides positive feedback, further increasing surface heating. These effects may also darken Europa's surface in areas surrounding the ridges. However, the net mass balance controlling sublimation and lag formation is highly sensitive to the global water exosphere density: values $\sim 10^{16}$ molec/m$^{2}$ produce reddening in the trough and ablation of $\sim1~\mu\mathrm{m~yr^{-1}}$ of material, while values $\sim10^{18}$ molec/m$^{2}$ result in net deposition of $\sim 10~\mu\mathrm{m~yr^{-1}}$. Model predictions of resulting low albedo material in double ridge troughs are provided, which can be tested with eventual data from Europa Clipper.

Recent observations of hydrostatic structure and virial equilibrium in supersonically turbulent, self-gravitating molecular clouds imply a stability that contrasts with the transcience of turbulent structure. To investigate this contradiction, we model a molecular cloud as a turbulent eddy and study its evolution as a dynamical system. In a two-dimensional phase space of structure and energy, we find that the dynamical equilibrium is a saddle point, stable in the direction aligned with force balance, but unstable in the direction of energy balance because of the combination of the turbulent dissipation and the negative heat capacity of self-gravitation. Near the saddle point, evolutionary trajectories follow a characteristic pattern that first approaches the equilibrium before departing in the direction of instability. Since the phase-space speed is proportional to the virial and energy imbalance, trajectories slow near the equilibrium resulting in a local overdensity of clouds. Also, near equilibrium, the relaxation to force balance is faster than the growth rate of the instability in energy. Consequently, more clouds are observed in near equilibrium states with hydrostatic structure even though the equilibrium is metastable. This resolves the apparent contradiction of equilibrium structure observed in dynamically unstable, self-gravitating turbulence.

Quasi-biennial oscillations (QBOs) are shorter-term periodic signals that occur alongside the dominant 11-year solar cycle. In this study, we examine the spatial and temporal evolution of QBOs using helioseismic p-mode frequency shifts from the Global Oscillation Network Group (GONG) across solar Cycles 23 and 24 and the ascending phase of Cycle 25. By applying wavelet analysis to frequency shifts, we studied the changes in QBO periodicities to determine whether the QBO period and amplitude vary with latitude. Our results show that QBO periods exhibit a weak latitudinal dependence, with shorter and less persistent signals at low latitudes, while at higher latitudes the periods are nearly constant at $\sim$3 years. Cycle 24 tends to display slightly longer periods than Cycle 23, though within uncertainties. At all latitudes, QBO amplitudes increase with mode frequency, which is consistent with previous studies. Higher amplitude QBOs are found at low latitudes, reflecting the distribution of surface magnetic activity. The ratio of QBO to cycle amplitude is systematically higher in Cycle 24 than in Cycle 23, and above $20^\circ$ latitude the amplitude ratio is nearly uniform in Cycle 23 but shows modest variations in Cycle 24. A linear relation between QBO amplitude and cycle amplitude is found in both cycles, but with significantly different slopes, indicating that QBO amplitudes are not wholly governed by the solar cycle strength and are at least partially decoupled from it. Finally, we find no evidence that QBO period depends on QBO amplitude, consistent with a linear oscillation regime.

In this paper, we identify the magnetic reconnections at the hyperbolic flux tube (HFT), aided by slipping reconnection at quasi-separatrix layers (QSLs), which are pivotal to the occurrence of a confined M2.1 class flare in NOAA active region 12268. The magnetic field topology before the flare's onset is obtained through a non-force-free-field extrapolation scheme that accommodates a non-zero Lorentz force. A key aspect is the presence of an HFT in the computational domain above the flaring region, along with two QSLs at the lower boundary. To simulate the dynamics of the active region, we conduct a data-constrained magnetohydrodynamics (MHD) simulation initiated by the extrapolated field. The dynamics captured in the simulation document the formation of a current sheet within the HFT configuration, leading to magnetic reconnection at the HFT. Additionally, we observe the slipping motion of the footpoints of the magnetic field lines in the QSLs at the bottom boundary, which indicates the occurrence of slipping reconnection in the QSLs. Importantly, the magnetic reconnection at the HFT is suggested to be the primary driver in the development of the intricate flare brightenings and the flare ribbons.

The vertical structure of galactic disks is an important probe of disk assembly history. We investigate a sample of 79 local disk galaxies within 50 Mpc using data from the DESI Legacy Imaging Surveys. Vertical luminosity profiles as a function of radius in the g, r, and z bands are extracted and fitted with a single-component sech^2 model to determine the scale height and its radial variation (flaring). Our results show that local galactic disks are generally thin with negligible flaring. The median scale heights at one effective radius are 0.21, 0.22, and 0.22 kpc in the g, r, and z bands, respectively, while the corresponding median radial gradients are -0.006, 0.003, and 0.001. These values are consistent with those of the geometric thin disk of the Milky Way, represented by metal-rich, low-[alpha/Fe] populations, supporting the conclusion of weak flaring. We also find a clear positive correlation between scale height and stellar mass, extending down to 10^7 solar masses. These results provide a homogeneous benchmark for the vertical structure of nearby disk galaxies and support the cosmological representativeness of the Milky Way thin disk.

A method of determining ages and masses of asymptotic giant branch (AGB) stars between 0.8 and $\sim$6 M$_\odot$ is demonstrated, based on comparing the star's position in the period–absolute-magnitude diagram to theoretical evolutionary models. For samples of Milky Way stars, the method provides errors (statistical and systematic, respectively) of order of $^{+29}_{-35} \pm 15$ per cent in age, $^{+14}_{-7} \pm 7$ per cent in initial mass and $^{+17}_{-11} \pm 27$ per cent in current mass. However, its applicability to individual stars depends strongly on both their position in the $P-L$ diagram and the uncertainty of that position. This method is applied to published samples of AGB stars from the Gaia, NESS, DEATHSTAR and ATOMIUM surveys. These surveys' statistical ensembles are compared to expectations from stellar evolutionary models, finding that most AGB samples are biased towards stars of younger ages and higher masses. An average mass for Milky Way AGB stars is found to be $\sim$1.1 M$_\odot$, while mass returned to the interstellar medium by AGB stars typically comes from $\sim$1.2 M$_\odot$ stars with mass-loss rates of order $2-3 \times 10^{-6}$ M$_\odot$ yr$^{-1}$.

Fast radio bursts (FRBs) and gamma-ray bursts (GRBs) are both linked to compact-object activity, yet their possible connection remains unclear. Here we perform a systematic search for spatial and temporal associations between FRBs in the second CHIME/FRB catalog and Swift GRBs. Instead of using the positional ellipses reported in the catalog, the full CHIME localization probability maps are adopted for spatial cross-matching. This yields 130 candidate pairs and increases the number of spatially consistent matches by a factor of several. Applying a distance-consistency criterion based on DM-inferred FRB redshifts and GRB distances inferred via the Amati relation reduces the sample to 37 pairs, including 26 GRB-preceding-FRB candidates (24 LGRB–FRB and 2 SGRB–FRB). Monte Carlo simulations show that the overall excess of associations is not statistically significant, and the distribution of matches across localization confidence levels is consistent with random expectations. These pairs are therefore not claimed as secure associations, but are used to constrain a possible subdominant FRB–GRB connection. These results place constraints on any FRB–GRB connection and highlight the need for improved localization and larger samples.