We investigate the expected uncertainties in recovering galaxy cluster mass profiles from upcoming spectroscopic survey data using The Three Hundred Project. Using the caustic technique, which leverages galaxy positions and line-of-sight velocities, we assess the systematic errors introduced by assumptions regarding velocity anisotropy and demonstrate how an iterative correction method can minimize these errors. We also assess the impact of survey magnitude limits on cluster mass estimates, highlighting potential biases across different observational strategies. We focus the analysis on our own CATARSIS survey, which aims at obtaining redshift measurements for all galaxies with magnitudes mAB,r < 22 within 2xR200c of 16 galaxy clusters with redshifts 0.14 < z < 0.27 using the future 8 arcmin^2 field-of-view TARSIS integral-field spectrograph of the Calar Alto 3.5-m telescope. Such data will enable us to mitigate systematic errors in the determination of density profiles. CATARSIS aims at enhancing the precision of mass profile estimates by deepening our understanding of the dynamical states and physical characteristics of galaxy clusters.

Sugars are essential biomolecules, serving as metabolic fuels, nucleic acid backbone components, and structural or energy-storage polymers. A central question in origin-of-life research is how monosaccharides formed on the primitive Earth, as laboratory experiments under prebiotic conditions yield insufficient concentrations. The detection of ribose, glucose and other monosaccharides in asteroids and meteorites suggests an exogenous origin, possibly in the interstellar medium (ISM) prior to meteoritic parent-body formation. However, no sugar has been observed in the ISM so far. We report the discovery of erythrulose, a chiral four-carbon ketose, in the ISM. The detection has been achieved thanks to ultrasensitive, broadband spectral surveys toward the Galactic Center molecular cloud G+0.693-0.027 obtained using the Yebes 40m and IRAM 30m telescopes. Erythrulose appears to be at least eight times more abundant than analogous three-carbon sugars, which remain undetected in our ultrasensitive observations. Quantum chemical and astrochemical models indicate that erythrulose forms efficiently on interstellar dust grains from simpler two-carbon aldehydes and alcohols. As ketoses readily isomerize into aldoses in aqueous conditions, interstellar erythrulose could have contributed to the sugar inventory available for early metabolic and replication processes.

We present the serendipitous discovery of a nine-member system comprised of protostellar and candidate prestellar sources in $\sim$350 au-resolution images from Complex Chemistry in hot Cores with ALMA (CoCCoA). The system is bound in a stability analysis, has a mean separation between pairs of 7930 au, and appears to have formed via the fragmentation of a single large-scale filamentary structure traced by 1.20\,mm continuum and H$^{13}$CO$^+$ J = 3-2 emission. Two multiples within the nine-member system, a triple and a binary, have properties consistent with formation by core fragmentation on $\sim$1500-1700 au scales. The hot core NGC 6334-43 is resolved into two components (ALMA2a/ALMA2b) separated by 618 au and driving a bipolar outflow traced by $^{12}$CO J = 2-1 and SiO J = 5-4 in $\sim$1250 au-resolution archival Atacama Large Millimeter/submillimeter Array (ALMA) data. Only one other source in the nine-member system is clearly protostellar: ALMA6a, which drives an outflow traced by $^{12}$CO. The outflow properties of ALMA2a/ALMA2b and ALMA6a are consistent with high-mass and low-mass Class 0 sources respectively. By fitting the CH$_{3}$CN J = 13-12 emission towards ALMA2a, ALMA2b and ALMA6a, we derive M$_{\rm vir}$ = 4.5, 5.4 and 2.6 M$_{\odot}$ respectively. The other six sources in the nine-member multiple have M$_{\rm gas}$ = 0.50-1.87 M$_{\odot}$ and appear young, as indicated by their sparse mm-wavelength line emission and non-detection in published cm continuum observations. Our results highlight the potential of serendipitous discoveries in ALMA surveys to add to the small observational sample of young high-mass protomultiple systems.

We present a fast, interpretable machine learning framework to classify early- and late-type galaxies in the COSMOS2025 catalog at $0 < z < 3$, without relying on image-based training labels or computationally expensive structural fitting. Using the Santa Cruz Semi-Analytic Model, we generate a training set with secure morphological labels defined by bulge-to-total mass ratio and specific star formation rate. We bridge the simulation-to-observation domain gap by injecting realistic photometric noise derived from COSMOS2025. A CatBoostClassifier trained on 66 broadband colors achieves excellent performance in the simulated domain, recovering late-types with 98\% precision/recall and early-types with 91\% precision and 88\% recall. Applied to 44,132 COSMOS2025 galaxies, the model reveals a striking bimodality: only about 6\% of galaxies receive intermediate probabilities ($0.3 < P(\text{Early type}) < 0.7$) -- nearly identical to the fraction observed in the simulation. This demonstrates that broadband colors are a decisive morphological discriminant, with the remaining 94\% classified at high confidence. Validation against independent bulge+disk decompositions yields 70\% overall accuracy, with late-types identified at 78\% purity and 74\% completeness. The most important color feature, F277W-F444W, reflects the expected optical/NIR contrast between old and young stellar populations. The full pipeline completes in under 30 minutes on standard hardware, demonstrating that simulation-trained color-based classifiers offer a scalable, physically interpretable route to approximate morphology for large next-generation surveys.

The primordial helium mass fraction, $Y_\mathrm{p}$, is a key observational pillar of Big Bang nucleosynthesis and a sensitive probe of early-Universe physics. Over the past several decades, numerous observational $Y_\mathrm{p}$ determinations have been published using a wide range of astrophysical tracers and cosmological techniques. Although recent measurements exhibit striking convergence and increasingly small uncertainties, the statistical and historical context of this consensus has not been examined systematically. Here, we compile and analyse a comprehensive dataset of observational $Y_\mathrm{p}$ determinations published between the late-1960s and 2022. The final sample comprises 143 reported values spanning multiple tracers. We find clear evidence for long-term convergence in published $Y_\mathrm{p}$ values, punctuated by statistically significant change points in the mid-2000s and early 2010s. Careful examination reveals that many extragalactic H{\sc ii}-region determinations are not fully independent, relying on re-analyses or partial reuse of a limited number of observational datasets. This reduces the effective number of independent constraints and provides important context for interpreting the precision of recent results. Our findings do not challenge the overall consistency of modern $Y_\mathrm{p}$ determinations with standard cosmology, but they underscore the importance of accounting for data dependence, methodological homogeneity and historical evolution when synthesising measurements.

This study conducts a comprehensive analysis of brightness and color variability in blazars, utilizing over six years of quasi-simultaneous g-band and r-band data from 1149 sources in the ZTF Data Release 22 (DR22), including 589 BL Lacs and 560 FSRQs. We quantify the amplitude of variability and the fractional root mean square (rms) variability for each source and statistically assess the overall and short-term color behaviors across different subclasses; examine the distribution of brightness variability characteristics across different blazar types and investigate how the extent of variability correlates with color trends. We found BL Lacs tend to exhibit a BWB (bluer when brighter) trend, while FSRQs display a RWB (redder when brighter) trend; BL Lacs with negligible host-galaxy contamination exhibit a BWB trend fraction of 14.7% (68/462) compared to 2.3% (11/462) for RWB trend, while FSRQs show 8.8% (49/560) BWB trend versus 14.1% (79/560) RWB trend. By statistically investigating how color behavior depends on brightness state across different timescales, we find that brighter states in both BL Lacs and FSRQs are more likely to exhibit BWB trend. Our results also show that BL Lacs with a BWB trend exhibit higher variability than those with a RWB trend, whereas FSRQs with a RWB trend display significantly greater variability than those with a BWB trend. These results suggest that blazar color variability depends jointly on source type, brightness state, and variability amplitude, highlighting the complexity of color evolution in blazars.

We report JWST/NIRSpec integral field unit (IFU) observations of the quasar J1512$+$4422 at $z \sim 6.2$ from the Aether survey. At $\sim$900 Myr after the Big Bang, this object already lies on the $M_{\rm BH}$-$σ_\ast$ relation found in the local universe, with an $M_{\rm BH} \simeq 8.9\times10^8\,M_\odot$ and a stellar velocity dispersion $σ_\ast \simeq 288$ km s$^{-1}$. We detect an outflow with a velocity of $\sim$478 km s$^{-1}$ in the nuclear region, which likely extends to $\sim$3.2 kpc in projection and has a median velocity of $\sim$352 km s$^{-1}$. The outflow dynamical time scale ($\sim$ 9 Myr) is consistent with the time scale of the current quenching process based on the star formation history as reported previously. The total mass outflow rate (92.6$^{+92.6}_{-74.1}$ M$_{\odot}$ yr$^{-1}$) is larger than the current star formation rate (0.9$^{+3.8}_{-0.8}$ or 4.3$^{+5.8}_{-3.7}$ M$_{\odot}$ yr$^{-1}$), and the total kinetic energy outflow rate (0.6$^{+0.6}_{-0.5}$\% of quasar luminosity) meets the threshold for negative quasar feedback as suggested by simulations. These results suggest that the outflow is capable of suppressing/quenching the star formation activity within the host galaxy. Furthermore, J1512$+$4422 exhibits $σ_\ast$, stellar mass and size similar to those of $z \gtrsim$ 3 quiescent/post-starburst galaxies, implying a link between the two. Overall, for objects like J1512$+$4422, the evolution of their SMBHs and host galaxies appears to be tightly coupled within the first billion years. The quasar feedback likely plays a critical role in both placing them on the $M_{\rm BH}$--$σ_\ast$ relation and quenching.

As the Centaurs of the Outer Solar System have become better studied, their relationship with the Jupiter Family Comets and their connection to the primordial protoplanetary disk has come under deeper scrutiny: which properties of the comets observed closer to the Sun are original, and which were modified significantly en route during their Centaur phase? The active Jupiter co-orbital comet P/2019 LD2 (ATLAS) attracted significant attention after its discovery when it was realized that the object would transition between a Centaur and JFC orbit in 2063, the first time this change can be observed and monitored in real time. In this study, we present new ground-based and Hubble Space Telescope imaging of the single other Jupiter co-orbital comet, P/2023 V6 (PANSTARRS), throughout late 2024 and early 2025. V6 was not detected in ground-based imaging after early October, and deep imaging with HST taken in early December is consistent with a $m_V = 28.06 \pm 0.03$ point source at its expected location. This both implies that the object ceased activity sometime in late 2024, and is thus in a different thermal state than LD2 despite both having large active fractions, and that V6's diameter is approximately $D\sim340$ meters. This is likely the smallest object directly observed by HST beyond the Main Belt, and certainly the smallest Centaur yet discovered, highlighting the ability to detect active sub-km objects beyond Jupiter with current surveys and potentially probing smaller sizes with LSST.

We examine how inferences of the neutron-star equation of state depend on mass and radius observations. We update previous results with recent measurements combined with theoretical input from chiral effective field theory and perturbative quantum chromodynamics. The revised constraints are consistent with, but tighter than, those obtained in earlier work. Isolating the effects of different classes of observations we find that the theoretical constraints, together with the requirement that the maximal neutron-star mass exceeds $2\,M_\odot$, dominate the equation-of-state inference over most densities. Radius measurements mainly refine the constraints at the low-density regime, $ρ\lesssim 2ρ_0$, whereas measurements of masses well above $2\,M_\odot$ improve the constraints over a wider density range. Finally, we explore the impact of possible future observations. The largest impact would arise from a measurement that refines the value of the maximal neutron star mass. It can be, e.g., a detection of an extremely massive neutron star or an improved upper limit. However, even a precise measurement a $2.5-2.6\,M_\odot$ NS will not alter our knowledge of the equation of state qualitatively. Conversely, observations lying well outside the present allowed region, would point to new physics in neutron-star cores and require a revision of the current framework.

Context: For the typical modeling of neutron stars cooling after an accretion episode in Low-Mass X-ray Binaries, an extra heating source of unknown physical origin, \textit{the shallow heating}, is invoked in order to account for the inferred high effective temperatures of the star up to hundreds of days after the end of accretion. The amount of the shallow heating generated in the crust is usually taken to be proportional to the accretion rate, although the proportionality constant may change from source to source. Aims: In this paper, we intend to model the effective temperature data of eight outburst episodes from seven different sources (\mxb, \xte, \exo, \igr, \swift, \rxs\ and \ks) without {\it ad hoc} shallow heating but accounting for the presence of thermonuclear heating due to the burning of the accreted H/He. Methods: We employ the fully relativistic code \texttt{nscool}, which simulates both the crust and core of a neutron star, equipped with a new boundary condition at the envelope/crust transition which considers thermonuclear heating leakage from the envelope into the crust and depends on the mass accretion rate. Results: We find that the neutron star cooling for seven out of eight of these outbursts can be well explained with this new boundary condition and without the requirement of {\it ad hoc} shallow heating. While the qualitative features of \exo\ cooling curve can be explained, a good fitting still requires additional physics.

Cosmic birefringence, a signature of parity-violating physics, rotates the cosmic microwave background (CMB) polarization plane, generating correlations between CMB $E$- and $B$-mode anisotropies. Measuring this effect remains challenging due to degeneracies with spurious rotations from instrumental polarization angle miscalibration and limited knowledge of Galactic foreground $EB$ correlations. We present a blind, map-based approach based on a multi-Stokes hybrid internal linear combination (ILC) that breaks this degeneracy and disentangles correlated and uncorrelated CMB polarization components. By jointly combining $E$- and $B$-mode frequency maps, the method preserves achromatic birefringence-induced CMB anisotropies while downweighting foregrounds and chromatic CMB anisotropies resulting from instrumental miscalibration. This enables a direct spatial linear-regression estimator of the birefringence angle. Applied to LiteBIRD simulations, the method yields competitive constraints on birefringence. Applied to Planck PR4 data, we measure a birefringence angle $β\simeq 0.32^\circ \pm 0.12^\circ$, consistent with previous independent analyses and stable across sky fractions.

We revisit the mass of the neutron star in the ultracompact binary 4U 1820--30 in light of a recently reported transient absorption feature at about 3.8 keV, interpreted as a gravitationally redshifted, highly ionized iron line and implying \(1+z\simeq1.72\), a very high stellar compactness. We examine whether the mass-radius locus implied by this interpretation can be made compatible with external EoS-informed benchmarks and timing-based estimates. We map the compactness implied by the redshift onto the mass-radius plane, including rotational effects, and compare the resulting region with an EoS-informed 95\% reference contour derived from NICER data of several neutron-star systems. While we do not perform a statistically self-consistent joint mass-radius inference for 4U 1820--30, we present a quantitative conditional consistency test in a common \(M-R\) framework, comparing published inputs under explicitly stated assumptions. We find that, if the maximum neutron-star mass is restricted to low values \((\leq 2.3\,M_{\odot})\), the redshift-implied locus shows at most marginal overlap with the EoS-informed contour, indicating substantial tension. Allowing a higher maximum mass enlarges the parameter space and can restore compatibility with that benchmark. However, such high masses remain in tension with previous touchdown-flux estimates, although they are not necessarily excluded by interpretations based on the highest detected quasi-periodic oscillation frequency. We conclude that the redshift interpretation of the 3.8 keV feature, the touchdown-flux estimates, and the QPO/ISCO interpretation do not naturally select the same mass-radius sector for this source under these assumptions. Reconciling them requires auxiliary assumptions with high leverage on the inferred compactness.

Wide-band correlators for radio astronomy interferometers demand accurate, scalable signal processing backends that sustain high aggregate throughput while preserving stable timing alignment across a large number of signal chains. Addressing these coupled constraints is challenging without a co-designed backplane architecture. We present a backplane system developed for the Control Readout System (CRS) Field Programmable Gate Array (FPGA) platform, extending its capabilities to support high channel count wideband radio correlators. The design and validation process are guided by the requirements of the Canadian Hydrogen Observatory and Radio-transient Detector (CHORD) telescope, which provides a representative use case for the system's performance evaluation. Each backplane hosts up to four CRS boards, and a single crate integrates four interconnected backplanes to accommodate sixteen CRS modules (for a total of 128 digitized inputs per crate) interconnected through 25 Gbps per-lane links and an on-backplane data shuffle network. Comprehensive validation demonstrates robust high-speed link performance, sub-sampling-level timing alignment stability, and stable thermal and power behavior across environmental variations. The architecture delivers observatory-scale scalability, providing a low-jitter and phase-consistent foundation for wideband digital correlators. By supporting expansion from single-crate to multi-crate configurations without firmware modification, the system offers a practical and flexible path toward next-generation interferometers requiring tightly synchronized, high-throughput digital backends.

Nereid, Neptune's third largest moon, is considered to be a captured irregular satellite due to its highly eccentric orbit. However, among irregular satellites, Nereid is an outlier: it is the largest, the closest to its host planet, and the most eccentric. We present James Webb Space Telescope near-infrared spectroscopy of Nereid that demonstrates that its composition is inconsistent with its suggested captured origin. We then simulate Nereid's early orbital history subsequent to Triton's capture to demonstrate a plausible dynamical pathway for a regular satellite formed in-situ around Neptune to evolve to Nereid's present-day orbit. Based upon the available spectroscopic and dynamical evidence, we propose that Nereid is not a body captured from the Kuiper belt, but rather the sole surviving intact regular satellite of Neptune.

Over the last decade of ALMA's operation the molecular inventory of protoplanetary disks has expanded rapidly, revealing a diverse set of nitrogen-bearing organics and carbon-chain molecules that trace both prebiotic chemistry and fundamental disk physics. Despite this progress, detections of larger species such as cyanopolyynes have remained limited, leaving larger carbon-chain chemistry in Class II disks largely unconstrained. Here, we report the first detection of HC5N toward the TW Hya protoplanetary disk, representing the largest cyanopolyyne identified to date in a Class II system. We derive a HC5N column density for two rotational transitions J = 41-40 and J = 37-36, N_T ~ 10^12 cm^-2 for assumed T_rot = 20-50 K and optically thin emission in LTE. We compare HC5N and HC3N formation mechanisms and analyze the HC3N/HC5N ratio. We use a chemical model to estimate the expected abundance and emitting layer of HC5N in a TW Hya-like disk. Although HC5N emission is spatially unresolved, measured column densities suggest an origin in the warm molecular layer where CN-based pathways are active. This detection extends the known carbon-chain chemistry in Class II disks and demonstrates that long cyanopolyynes can form and persist in planet-forming environments.

Molecular clouds are affected by dynamical processes such as cloud merging and stellar feedback that alter their topology. For this reason, the molecular clouds in the PHANGS-JWST catalogue are studied under the light of topological data analysis. This study shows correlations between physical characteristics of galaxies and topological summaries of molecular clouds.

A significant puzzle in extragalactic astronomy is the scarcity of Little Red Dots (LRDs) at $z < 3$, compared to their higher abundance at earlier epochs. To understand this transition, we investigate the cosmic evolution of LRD environments. We measure the overdensity for LRDs and the general galaxy population at $3<z<7$, and find that at $z > 4$, LRDs predominantly reside in under-dense regions relative to the general galaxy population. By $z \sim 3.5$, however, this environmental contrast roughly diminishes, and LRDs are found in regions of comparable density to typical galaxies. Simultaneously, the dark matter halo masses of LRDs, inferred from large-scale clustering, grow rapidly from $\lesssim 10^{10.1} \, M_{\odot}$ at $z \sim 7.5$ to $\sim 10^{11.3} \, M_{\odot}$ at $z \sim 3.5$, where the halo mass becomes close to that of normal galaxies at lower redshift. Applying an empirical stellar-to-halo mass scaling relation, we derive stellar masses for LRDs; these show that black hole masses remain over-massive relative to stellar mass at $z > 4$, but converge toward the local $M_* - M_{\rm BH}$ scaling relation by $z \sim 3.5$. The coherent evolution of LRDs' large-scale environments $-$ as expressed by their overdensity and halo mass $-$ points to a distinct evolutionary pathway from that of normal galaxies. The significantly increased halo masses of LRDs lead to larger galaxy sizes, driven primarily by the potential enhancement of halo spins. Consequently, these sources are no longer as compact as typical high-redshift LRDs. Meanwhile, the depletion of dense gas and/or elevated star formation in their host galaxies would also significantly alter the spectral energy distribution of LRDs.

The energy spectra for individual elements and/or for groups of elements in cosmic rays (CR) in the energy range between 100 $\times$ Z GeV and 10$^{3}$ $\times$ Z PeV (where Z is the charge number of the nucleus) have a number of features, including two steepenings ("knees") with the rigidity-dependent energies $E_{k1} \approx$ 15 $\times$ Z TeV and $E_{k2} \approx$ 3 $\times$ Z PeV and three hardenings ("ankles") at $E_{a1} \approx$ 500 $\times$ Z GeV; for protons $E_{a2-p} \approx$ 150 TeV and $E_{ a3-p} \approx$ 100 PeV. While the values of $E_{a1}$ for different nuclei are rigidity-dependent, the values of $E_{a2}$ (and probably of $E_{a3}$) are not: $E_{a2-He} \approx$ 1 PeV for Helium. The recent advances in precision measurements of the elemental CR spectra in the DAMPE and LHAASO experiments, and, to some extent, in IceTop and other experiments, make it possible, for the first time, to clarify the origin of the aforementioned spectral features. We show that the elemental CR spectra are reasonably well described with a sum of three components: 1) a low-energy Galactic component with a convex spectral shape reflecting the accelerated particle spectrum in the source; this component peters out after the TeV knee, 2) a high-energy Galactic component including the PeV knee, and 3) an extragalactic component. There is no need for any third, additional component of Galactic cosmic rays in the energy range between 10 PeV and 1 EeV.

As we enter the 2030s, the astronomical landscape will be dominated by large-scale infrared (IR) and optical surveys led by JWST, Euclid, and the Nancy Grace Roman Space Telescope. While these facilities provide unprecedented views of the dusty environments of nearby star-forming regions, they are fundamentally limited in their ability to probe the high-energy physics of accretion, magnetospheric activity, and disk photoevaporation. This white paper argues for the critical continued use of the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) and Cosmic Origins Spectrograph (COS) to bridge the "UV Gap." We demonstrate that UV spectroscopy is the only direct method for characterizing the feedback mechanisms that determine planet habitability and stellar maturation, serving as a mandatory scientific bridge toward the Habitable Worlds Observatory (HWO). The study of star formation stands at a critical intersection of multiple scientific disciplines, linking the high-energy physics of stellar birth to the chemical evolution of protoplanetary disks and the eventual habitability of exoplanets. As such, it represents one of the most compelling and essential science cases for the continued allocation of HST resources. Ensuring that HST provides high-resolution UV spectroscopic data now is a fundamental requirement for the success of future flagship missions, as these data provide the unique physical context that infrared observations alone cannot achieve.

Recent JWST observations reveal an unexpectedly slow evolution in ultraviolet luminosity functions (UV LFs) at redshifts $z > 10$. To investigate this phenomenon, we develop a semi-analytical model of the UV LF, calibrated against well-constrained measurements at $z \sim 2-10$. Our analysis identifies a transition in star formation modes across cosmic epochs: at $z \lesssim 5$, a longer characteristic star formation timescale with nearly constant star formation efficiency ($f_\star$) dominates, whereas at $6 \lesssim z \lesssim 10$, shorter timescales prevail without requiring an increase in $f_\star$. For $z > 10$, the slow UV LF evolution is best explained by a shift toward even shorter star formation timescales without changing the star formation efficiency. Dust-free conditions or a top-heavy initial mass function (IMF) alone cannot reproduce the observations at $z\sim 14$. By combining UV LF with stellar mass estimates from Prospector-based SED fitting, we try to break degeneracies between IMF variations and star formation histories. Our results indicate that evolving star formation timescales rather than IMF or dust changes are the primary drivers of the observed high-redshift UV LF evolution, reflecting changing physical conditions during the earliest phases of galaxy assembly. Additionally, we show that moderate AGN activity could further boost UV luminosities at $z \sim 14$, potentially explaining the observed UV LF without changes in stellar parameters.

Dust structures in protoplanetary discs have been widely observed and their creation remains an active field of research. Several possible origins have already been explored, including magneto-hydrodynamics, shadows and planets-disc interactions. The goal of this paper is to investigate whether a single migrating planet in a low-viscosity disc, including radiative processes, is capable of generating observable dust structures. We aim to examine both the lifetime of such structures and potential asymmetries within them. We perform a set of high-resolution, two-dimensional hydrodynamic simulations of migrating planets using three different equations of state: isothermal, constant $β$-cooling and an adaptive $β$ model. Dust is included in all simulations and the resulting dust density profiles are then post-processed to create radiative transfer images. For all equations of state considered, the planet undergoes one or several migration jumps, each producing dust rings and gaps. The lifetime of these structures depends on the phase of slow migration preceding and occurring between jumps, but in all cases they remain visible for at least 400 kyr. We find that cooling has a deciding effect on the migration behaviour and the number of jumps, but no measurable influence on the lifetime of the dust structures. The structures exhibit relatively few asymmetries, and large-scale vortices persist for an average of only 90 kyr. Our models highlight the capacity of planets to open multiple gaps while migrating, and stress the importance of a realistic cooling model. Care should be taken when interpreting and comparing such models directly to observations.

We present a Bayesian framework to constrain {mass ($M$), metallicity ($Z$), stellar age ($τ$), and the convective mixing length parameter ($α_{\rm MLT}$)} in main-sequence (MS) detached eclipsing binaries (DEBs). These systems provide precise values of stellar mass and radius, offering stringent tests of stellar evolution models. We combine these with broadband magnitudes in the $B$ and $V$ bands and Gaussian priors on spectroscopic mass and metallicity, and perform Markov Chain Monte Carlo inference using a fast machine-learning surrogate for one-dimensional stellar evolution models computed with Modules for Experiments in Stellar Astrophysics. To make this approach computationally feasible, we implement an active learning strategy that adaptively selects new stellar models to evaluate, concentrating training data in regions of parameter space where the surrogate is most uncertain. Applying this framework to 38 stars in DEB systems, we recover ages more precise than previous isochrone-based determinations and obtain bounds on $α_{\rm MLT}$ for a subset of lower-mass stars ($M \lesssim 1.5 M_\odot$), where convective envelopes provide sensitivity to the mixing length parameter. For several stars, the inferred $α_{\rm MLT}$ values lie below the Solar-calibrated value, supporting previous indications that a universal mixing length parameter may not adequately describe convection across the main sequence. The active learning methods developed here provide a scalable route to Bayesian inference with stellar evolution models, with clear applications to additional stellar physics parameters and other precisely characterized stellar systems.

Massive stars in binary systems that undergo mass transfer during their lifetime have a different evolution from that of single stars, possibly affecting their chemical yields. While massive stars produce most of the metals in the Universe, only few studies have investigated the effects of massive binary stars on the chemical evolution of the Milky Way. Following the most recent studies on massive binary-stripped star yields as functions of metallicity, we aim at improving previous results based on single-metallicity model grids. Here, by adopting a detailed model of chemical evolution for our Galaxy, we compute the evolution of 22 chemical species including C, N, O, $α$-elements and Fe-peak elements, adopting novel prescriptions for single and binary massive star yields. Our main results can be summarised as follows: (i) consistently with previous predictions, we observe very small differences in both the predicted solar abundances and [X/Fe] vs [Fe/H] relations even when including massive binary yields depending on metallicity; (ii) when adopting the new set of stellar yields for massive single stars, as computed by Farmer et al. (2023), we are able to reproduce both the K solar abundance as well as the [K/Fe] vs [Fe/H] relation, without invoking ad hoc assumptions on nucleosynthesis prescriptions; (iii) our model adopting Farmer's yields both for single and binary massive stars is able to better reproduce the [X/Fe] versus [Fe/H] relation for both Mg and Ca, as compared with standard nucleosynthetic yields adopted in chemical evolution models; iv) we find that no models can well reproduce the [C/Fe] and [Ti/Fe] vs [Fe/H] when adopting the new yields as functions of metallicity.

We study spherical accretion onto primordial black holes (PBHs) embedded in the core of a solar-type star. We compute the radiative efficiency self-consistently for the first time across the optically thin range ($10^{-16.5}$-$10^{-10}M_\odot$) with time-dependent simulations, and follow the growth up to $10^{-2}M_\odot$ using an analytical photon-trapping prescription above $5\times 10^{-13}M_\odot$. Near the Schwarzschild radius ($r_{\rm S}\sim 10^{-11}$cm for a $10^{-16}M_\odot$ PBH), gas compressed to $T\sim 10^{11}$K radiates through microphysical processes that fundamentally alter the classical adiabatic Bondi solution. We solve the time-dependent spherical Euler equations with an implicit cooling source term, determining $\dot M$, $η= L/\dot M c^2$, and the flow structure self-consistently. We identify three regimes for spherical accretion: a Hot Bondi regime ($M_{\rm BH}\lesssim 10^{-14}M_\odot$) in which bremsstrahlung cooling is dynamically negligible; a bremsstrahlung-cooling regime ($10^{-14}$-$5\times 10^{-13}M_\odot$) driving the flow toward isothermal with $η\approx 10^{-2}$; and a photon-trapping regime above $5\times 10^{-13}M_\odot$, in which the Bondi sphere is optically thick and the accretion rate remains close to the Bondi value. Cooling enhances $\dot M$ by a factor of $\sim$2-7, keeping growth super-exponential throughout the spherical regime. The radiative efficiency is an order of magnitude lower than previously assumed, and the critical initial PBH mass required to consume a solar-mass star within a Hubble time is $M_{\rm 0,crit}\sim 10^{-16}M_\odot$.

After four observational runs, the Ligo-Virgo-Kagra collaboration estimated a local binary black hole (BBH) merger rate density of $R_{0,\textrm{LVK}}\simeq 14-26\,\textrm{Gpc}^{-3}\,\textrm{yr}^{-1}$ within the 90% credible interval. Some previous studies already pointed out that, when a realistic evolution of the metallicity-dependent cosmic star formation rate density (SFRD) is adopted, theoretical models predict a local BBH merger rate density that exceeds the observed value by at least a factor of $\sim 10$ (Sgalletta et al. 2025). In this paper, we confirm and strengthen this claim by constructing an empirical model for the SFRD and metallicity evolution that includes a correction accounting for iron abundance. The adopted metallicity relation is flexible, enabling us to bracket the wide range of observational uncertainties. We show that, even under the most conservative assumptions regarding both the SFRD and the metallicity relation, the local BBH merger rate density is overestimated by a factor $> 10$. Attempts to reconcile the predicted and observed merger rates by modifying only the metallicity-dependent SFRD would require unrealistically high metallicities ($Z>Z_\odot$) even in low-mass galaxies at high redshift. This finding indicates that revisions to the treatment of stellar and binary evolution are necessary to achieve consistency between theoretical predictions and observations. We suggest that even a modest steepening of the delay-time distribution could help alleviate this tension.

The Cosmic Archipelago is an ensemble of galaxies, strongly lensed by the cluster MACSJ0416, showing extreme physical properties at $z\sim6.14$. We combine JWST/NIRCam with deep VLT/X-Shooter and JWST/NIRSpec IFU to perform a joint spectrophotometric analysis from the far ultraviolet to red optical rest-frame. We focus on CA4, a UV-faint ($M_{UV}=-17.7$), compact ($r_e=81\pm11$ pc) galaxy at $z=6.1446$, magnified by a factor $μ=3.73$. CA4 is a young, low-mass ($M_\star =4.3\times10^6$ M$\odot$), star-forming (${\rm SFR}=0.46$ M$\odot$/yr), and metal-poor ($Z\sim0.02$ Z$\odot$) galaxy, and an efficient producer of ionizing photons ($\log(ξ_{ion}/{\rm erg^{-1} Hz})\sim25.5$). Its properties place CA4 at the poorly explored interface between massive stellar clusters and dwarf galaxies during the epoch of reionization. Moreover, CA4 shows large Ly$α$ ($f_{esc}^{\rm Lyα}\sim43\%$) and Lyman-continuum ($f_{esc}\sim47\%$) escape fractions, consistent with its small Ly$α$ velocity offset ($Δv\sim100$ km/s) and extremely blue UV-continuum slope ($β=-3.10$). These characteristics suggest that such UV-faint, metal-poor galaxies may contribute significantly to cosmic reionization. We also confirm five additional systems at the redshift of the Cosmic Archipelago, magnified by factors up to 12.5. They are all young (mass-weighted ages $<11$ Myr) and metal-poor ($Z<0.05$ Z$_\odot$), spanning a wide range of stellar masses and SFRs. Given the large number of these bursty star-forming galaxies in a small cosmic volume, we estimate that the currently known members of the Cosmic Archipelago result in a significant overdensity at $z\sim6$ ($Δz\sim0.08$), with $δ_{gal}=12.3^{+6.6}_{-4.6}$. These results highlight the Cosmic Archipelago as an unprecedented laboratory for studying the earliest groups of low-mass, low-metallicity galaxies during the epoch of reionization.

Scaling relations hold among observed quantities that describe the thermodynamic properties of the gas in galaxy clusters and groups. However, observed data show systematic departures from the self-similar model's baseline predictions, particularly in lower-mass systems. I show that the observed departures from self-similar predictions can be efficiently described by two physical quantities modeled with power laws: the gas mass fraction ($f_g \sim T^{f_1} E_z^{f_z}$) and the temperature variation ($f_T \sim T^{t_1} E_z^{t_z}$). Using a large variety of published X-ray scaling relations, this study proceeds with an MCMC-based meta-analysis to constrain the temperature- and redshift-dependence of the meta-parameters $f_g$ and $f_T$ to calibrate the model. These calibrations indicate that, while the gas mass fraction ($f_g$) does not show significant evolution with cosmic time ($f_z = -0.11 \pm 0.03$), it decreases significantly with decreasing halo mass ($f_1 = 0.50 \pm 0.01$). On the other hand, the temperature variation shows a mild positive increase with both mass and redshift. Overall, modeling the departures from the self-similar model with $\{f_g, f_T\}$ drastically improves predictive accuracy, reducing the number of scaling relations in $>3σ$ ($>5 σ$) tension from 49 (36) percent under the self-similar scenario to just 11 (3) percent (four and one out of 39, respectively) that might be identified for their peculiarity. Moreover, the modelization through the generalized form allows me to present an extended discussion of the expected slopes and redshift evolution for several X-ray scaling laws, including the new quantity $Y_{LGT0} = L^{-1} M_g^2 T^{1/2}$, a proxy for the cluster's volume which does not depend on $f_g$ and $f_T$ by construction, and is predicted to relate directly to the mass without any redshift evolution: $M \sim Y_{LGT0} f_g^0 f_T^0 E_z^0$.

We constrain the difference in gravitational potential between our location and sources at $z \gtrsim 0.3$ using datasets at those redshifts. Our motivation is that the Hubble tension might be caused by a local void, as suggested by galaxy number counts. This would increase the redshift through outflow and gravitational redshift (GR). Only the latter is important at high redshift, where a void contributes a fixed additional GR contribution of $z_0$ due to our location on a potential hill. This $z_0$ model has various subtle effects that were not previously considered, including a hotter CMB and reduced BAO $r_{\rm d}$. We test whether $z_0$ can have the previously expected value of 0.84\%, which was based on fitting void parameters to galaxy number counts and local $H_0$ measurements. Combining BBN, CMB, BAO, and CC datasets at $z > 0.5$, we find that $z_0$ = $-0.4 \pm 0.9\%$, which rises to $0.0^{+0.6}_{-0.7}\%$ when extending our analysis down to $z > 0.29$. Although the results prefer the standard value of $z_0 = 0$, the best-fitting model with $z_0 = 0.84\%$ fits the data almost as well as $Λ$CDM, with $Δχ^2 < 2$. We find that $Λ$CDM faces a $2.81σ$ BAO anomaly in the standard $(H_0 r_{\rm d}, Ω_{\rm m})$ parameter space, where different regions are preferred by BAO and non-BAO datasets from $z > 0.29$. Fixing $z_0 = 0.84\%$ reduces this to $2.39σ$. This suggests that a local void large enough to solve the Hubble tension cannot be ruled out by higher-redshift datasets despite its novel impact on them.

The dynamical role of Lyman-$α$ (Ly$α$) radiation pressure feedback has been debated for nearly a century, with recent analytical and 1D numerical studies highlighting its potential dominance over other stellar feedback processes at Cosmic Dawn. Despite this, no multi-dimensional Ly$α$ radiation hydrodynamics (RHD) simulations have been performed to date. In this paper, we present the first 2D Ly$α$ RHD simulations using Lydion, an RHD code with a novel M1 moment method for Ly$α$ transfer, and self-consistent dust dynamics. Lydion yields a $\sim \mathcal{O}(100) \,\times$ speed-up compared to Monte Carlo radiative transfer in simple benchmarks, making 2D Ly$α$ RHD feasible. We perform simulations of star clusters and isolated stars embedded in dense, metal-poor ($Z/Z_\odot \leq 0.01$) clouds, and find that Ly$α$ feedback dramatically boosts outflows and dominates over feedback from direct and infrared radiation pressure. Ly$α$ leakage through lower-column density channels, Doppler shifts, and Ly$α$ photon destruction, while important, cannot prevent the build-up of strong Ly$α$ radiation pressure in H II regions, leading to radiative forces $\sim (2 - 16) \times L_{\rm bol}/c$, and Ly$α$ force multipliers $M_{\rm F} \sim 10-60$. Ly$α$ feedback may not preclude efficient star formation, but raises the threshold gas surface density for this to occur. We conclude that nearly all galaxy and star formation simulations are currently missing the strongest source of radiation pressure feedback in dense and metal-poor environments.

We report evidence for a brown-dwarf companion with mass $34^{+30}_{-11}~M_{\rm J}$ in the KELT-20 system, in which an ultra-hot Jupiter transits an A2-type star. The companion's properties are inferred from a joint analysis of astrometric accelerations and transit timing variations, and its present-day orbit imposes dynamical limits on where the hot Jupiter could have formed. Given the star's current luminosity, the water-ice line is expected at $\sim$8-15 au, but the companion's inferred pericenter distance of a few au would lead to orbit crossing or long-term instability for any planet formed at such distances. If the companion formed early and remained near its current orbit over the system's lifetime, the proto-hot Jupiter must have formed within $\sim$3.7 au to avoid orbit crossing, and within $\sim$1.5 au to remain dynamically stable over the system's lifetime. These results disfavor formation beyond the ice line and point instead to formation at smaller orbital distances followed by inward migration.