Papers

We review the creation mechanism of primordial black holes from first order phase transitions. We discuss various model-dependent and independent mechanisms and relate the properties of these mechanisms to the properties of primordial black holes. For each of these mechanisms, we provide model-specific examples.

Intense magnetic fields in the atmospheres of neutron stars render non-trivial angular dependence of intensity and polarization of soft X-ray emission originating from their surfaces. By tracking the complex electric field vector for each photon during its atmospheric transport and propagation in general relativistic and birefringent magnetospheres, our Monte Carlo simulation, named MAGTHOMSCATT, allows for capturing the complete polarization properties, including the intricate interplay between linearity and circularity. The new inclusion in MAGTHOMSCATT of quantum electrodynamical influences on polarization in the magnetosphere is presented. We simulate the pulsed and polarized X-ray emission from the outer layers of optically thick, fully ionized atmospheres of neutron stars, with a focus on the radiation emitted from extended polar caps of magnetars, which are the most highly magnetized neutron stars. Using the recent intensity pulse profile data for the magnetar 1RXS J11708-4009, we constrain the geometric parameters, namely the angles between the magnetic axis and the observer's viewing direction relative to the spin axis, as well as the sizes of emission regions. The distributions of these parameters and the best-fit configuration are provided. In addition, we discuss the important impacts of vacuum birefringence in the magnetosphere on increasing the linear polarization degree. A comparison with the case of a weakly magnetized neutron star, RX J0822.0-4300, is also discussed. Our simulation still needs further development, particularly to incorporate the vacuum resonance effect. Nevertheless, the formalism presented here can be employed to constrain geometric parameters for various types of neutron stars.

The current tension between early- and late-Universe measurements of the Hubble constant ($H_0$), along with the still elusive nature of dark matter and dark energy, calls for model-independent probes of the Universe's expansion history. The cosmic chronometers (CC) method offers a unique opportunity to directly measure the Hubble parameter $H(z)$ without relying on any cosmological model assumptions or integrated distance measurements. Despite its potential, this technique remains statistics-limited: no current survey is optimized to detect large samples of CC, restricting the precision on $H(z)$ to $\sim$20% at intermediate redshifts. Here, we investigate the opportunities that a next-generation spectroscopic facility could offer to CC studies, providing an estimate of the accuracy achievable on the reconstruction of the Hubble parameter in redshift. We demonstrate that with such a facility, it will be possible to derive constraints on key cosmological parameters, assessing the impact that such improvements would have on our understanding of the expansion history of the Universe and on current cosmological tensions.

We first present a systematic investigation into the effect of the $^{16}$O($^{16}$O, n)$^{31}$S reaction rate on the evolution and nucleosynthesis of Population III (Pop III) stars. We simulate the evolution of a 15 M$_\odot$ Pop III star from the zero-age main sequence through to core collapse, while varying the $^{16}$O($^{16}$O, n)$^{31}$S reaction rate by factors of 0.1, 1, and 10. Our results demonstrate that increasing this reaction rate prompts earlier onset and extended duration of core oxygen burning at lower temperatures and densities. A higher reaction rate also increases neutron excess in OSi-rich layers, thereby promoting the synthesis of neutron-rich isotopes, particularly $^{31}$P and $^{39}$K. Most notably, the K yield is enhanced by a factor of 6.4. For a tenfold enhancement of the $^{16}$O($^{16}$O, n)$^{31}$S rate, the predicted [K/Ca] and [K/Fe] values from presupernova models reach 0.29 and 0.22 dex, respectively-values that are consistent with the most recent observational data for extremely metal-poor stars. These findings hold promise as a potential new solution to the problem of potassium underproduction and offer a valuable theoretical reference and motivation for subsequent measurements of oxygen fusion reaction rate.

We consider the gravitational Noether-Ward identities for the evolution of general metric perturbations on quantum matter backgrounds. In this work we consider Einstein's gravity covariantly coupled to a massive, non-minimally coupled, quantum scalar field in general curved backgrounds. We find that each term in the equation of motion for gravitational perturbations satisfies its own Noether-Ward identity. Even though each term is non-transverse, the whole equation of motion maintains transversality. In particular, each counterterm needed to renormalize the graviton self-energy satisfies its own Noether identity, and we derive the explicit form for each. Finally, in order to understand how the Noether-Ward identities are affected by the definition of the metric perturbation, we consider two inequivalent definitions of metric perturbations and derive the Noether-Ward identities for both definitions. This implies that there are Noether-Ward identities for every definition of the metric perturbation.

Continuous gravitational waves from rapidly rotating neutron stars are on the new frontiers of gravitational wave astrophysics and have strong connections to electromagnetic astronomy, nuclear astrophysics, and condensed matter physics. In this Colloquium I survey prospects for detection of continuous gravitational waves from various neutron star populations, especially aided by electromagnetic observations. Although there are caveats, current theories and observations suggest that the first detections are likely within a few years, and that many are likely in the era of next generation detectors such as Cosmic Explorer and the Einstein Telescope. I also survey what can be learned from these signals, each one of which will contain more cycles than all the compact binary mergers ever detected. Since continuous gravitational wave emission mechanisms depend on aspects of neutron star physics, such as crustal elasticity, which are not well constrained by current astronomical observations and physical experiments, their detection can tell us a great deal that is new about extreme matter. Even more can be learned by combining gravitational wave observations with data from the Square Kilometre Array, the Next Generation Very Large Array, FAST, and other electromagnetic detectors operating in the next generation era.

Continuous gravitational waves have the potential to transform gravitational wave astronomy and yield fresh insights into astrophysics, nuclear and particle physics, and condensed matter physics. We evaluate their detectability by combining various theoretical and observational arguments from the literature and systematically applying those arguments to known astronomical objects and future gravitational wave detectors. We detail and update previous estimates made in support of Cosmic Explorer [M. Evans et al., arXiv:2306.13745; I. Gupta et al., Class. Quantum Grav. 41, 245001 (2024)]. It is commonly argued that the spins of accreting neutron stars are regulated by gravitational wave emission and that millisecond pulsars contain a young pulsar's magnetic field buried under accreted material. If either of these arguments holds, the first detection of continuous gravitational waves is likely with near future upgrades of current detectors, and many detections are likely with next generation detectors such as Cosmic Explorer and the Einstein Telescope. A lack of detections in the next several years would begin to raise serious doubts about current theories of millisecond pulsar formation.

In this paper, we investigate the production of primordial black holes (PBHs) during the radiation-dominated era. The collapse of significant density perturbations originating from large primordial scalar fluctuations generated during inflation can lead to the formation of primordial black holes. In our study, we adopt the Higgs hybrid metric-Palatini model as our framework, in which the inflaton field and the Palatini curvature are non-minimally coupled. To achieve our objective, we analyze the behavior of the primordial curvature power spectrum, which exhibits a large enhancement at small scales corresponding to large wavenumbers $k$. Furthermore, we examine the probability of PBHs formation by studying the mass variance, $\sigma(M_{PBH})$, and the mass fraction of the total energy density collapsing into PBHs, $\beta(M_{PBH})$. The evolution of both functions is consistent with current observational constraints. Finally, we investigate the abundance of primordial black holes as a dark matter candidate. We found that they can account for the totality or a fraction of the current dark matter content, depending primarily on the values of the coupling constant and the e-folds number.

Gamma-ray bursts (GRBs) are among the most potent probes of Lorentz invariance violation (LIV), offering direct constraints on the quantum gravity energy scale ($E_{\rm QG}$) based on observations of energy-dependent time lags. Individual GRBs with well-defined positive-to-negative lag transitions have been used to set lower limits on $E_{\rm QG}$, but they suffer from uncertainties of spectral-lag measurements and systematics due to theoretical modeling of each burst. Here, we combine observations of 32 GRBs with positive-to-negative lag transitions to derive a statistically robust constraint on $E_{\rm QG}$ through hierarchical Bayesian inference. We find that the dominant systematic uncertainty in LIV constraints arises from the intrinsic lag modeling. Accounting for this uncertainty with cubic spline interpolation, we derive robust limits of $E_{\rm QG,1} \ge 4.37 \times 10^{16}$~GeV for linear LIV and $E_{\rm QG,2} \ge 3.02 \times 10^{8}$~GeV for quadratic LIV. We find that the probability for LIV, i.e., $E_{\rm QG,1}$ being below the Planck scale, is estimated to be around 90%, which we conclude as no significant evidence for LIV signatures in current GRB spectral lag observations. Our hierarchical approach provides a rigorous statistical framework for future LIV searches and can be extended to incorporate multi-messenger observations.

In this work, we investigate the effective parameter space associated with the axion mass and the axion decay constant in both the light and heavy QCD axion scenarios. We initiate our discussion by considering the simplest case of two axions, quantitatively analyzing the parameter space in these two distinct scenarios. We find that the axion mass ratios exhibit a high degree of similarity in these two situations. In contrast, the ratios of axion decay constants display a complete opposition. Furthermore, we generalize our conclusions to encompass the case of multiple axions.

We investigated the gravitational potential and mass distribution in the Galactic Center by examining the morphology and kinematics of the circumnuclear gaseous disk revealed by the molecular line data from the ALMA CMZ Exploration Survey (ACES). We obtain an estimate of the shape of the potential {within the central $\sim 20$ pc} to reproduce the observed properties of the circumnuclear gas disk (CND) by simulating the motion of test particles for various axial ratios and show that the potential is approximately spherical. We construct a rotation curve by applying the terminal velocity method to the position-velocity diagrams, and calculate the mass distribution in the Galactic Center. The distribution of mass density is found to be of cusp type, approximated by $\rho_{\rm mass} \sim 1.56\times 10^5(R/1 {\rm pc})^{-1.9}~M_{\odot} {\rm pc}^{-3}$, where $R$ is the distance from the nucleus. We discuss the tidal effect caused by the gravitational potential that produces the rotation curve and show that the gas disk is stable against self-gravitational contraction within a critical radius of $ R_{\rm T}\sim 14 ~(\rho_{\rm gas}/10^5 {\rm H_2~cm^{-3}})^{-1/2}~{\rm pc}$. This suggests suppression of star formation and a top-heavy IMF in the circmunuclear region.

We study the impact of heavy dark matter (DM) captured in massive stars via scattering(s) with the star constituents. We focus on the first stars and use stellar evolution simulations to track down how DM capture evolves over time from the zero-age main sequence to the late metal-rich stages of stellar evolution. During the early hydrogen-helium-dominated phase, the capture process is well described by scattering with two targets. As a star evolves, metal production leads to the formation of a dense core surrounded by a lighter envelope. The core significantly enhances the capture of ultra-heavy DM; in this case, three distinct nuclear species are required to accurately describe multiple-scattering capture. We use the Eddington inversion method to obtain a realistic DM velocity distribution, better suited when the star is near the center of a halo, than the widely used Maxwell-Boltzmann distribution. We find that heavy DM would be able to thermalize and achieve capture-annihilation equilibrium within a massive star's lifetime for regions of the parameter space not excluded by direct detection. For non-annihilating DM, because of the high amount of targets available for capture and despite massive stars being short-lived, it would even be possible for DM to achieve self-gravitation and collapse to a black hole, which eventually could swallow the star from within before the expected end of the star's life, for non-excluded regions of the parameter space. Our results highlight the dependence of DM capture on the stellar evolutionary stage, composition, and halo location, demonstrating that accurate modeling of massive stars is essential for constraining heavy DM with primordial stellar populations.

We present a catalogue of 453 molecular clouds in M31 extracted from CO J=1-0 data observed with CARMA using a dendrogram. Our clouds have the mean values of 2.8 km s$^{-1}$, 22.1 pc and 10$^{5.2}$ M$_\odot$ for the velocity dispersion, radius and mass, respectively. The velocity dispersion shows a weak anti-correlation with the galactocentric radius. The clouds in M31 show mean and median values of 2.0 and 1.4, respectively, for their virial parameters, indicating that most of them are gravitationally bound. Our dendrogram analysis identifies 35 sources with multiple velocity components, which we classify as molecular cloud complexes. We study the size-velocity dispersion and size-mass relationships for the clouds in M31, finding the slopes of 0.43$\pm$0.05 and 1.36$\pm$0.06 for the former and the latter, respectively. Our size-velocity dispersion relationship agrees with those of Milky Way (MW) and M31 clouds. The slope of our size-mass relationship is shallower than those in clouds and cloud complexes of the MW. We find offsets between the isosurfaces of the clouds and star formation rate (SFR) peaks in M31, supporting the scenario where the evolutionary state of individual sources plays a role in the Kennicutt-Schmidt (KS) law at parsec scales. We find a slope of 0.66$\pm$0.07 for the KS law, which is slightly lower than the values of $\sim$0.8 for MW clouds.

The stellar evolution of lithium-rich (Li-rich) giant stars at very low metallicities remains largely unexplored to date. Using two recent large LAMOST catalogues of field, low-mass giant stars (both Li-rich and Li-poor) with metallicities from -4.0 to -1.0, we studied the conditions for Li enrichment and the distribution of stellar rotations in the Galactic halo and thick disc. Due to the scarcity of stars with [Fe/H] < -3.0, only three Li-rich RGB stars are known in this regime. The observational appearance of giants across the horizontal branch (HB) and asymptotic giant branch (AGB) stages (with Li abundances up to 6.15 dex) has been detected for metallicities > -2.5. Among these stars, we detected IR excesses indicative of giant stars losing mass, showing a recent episodic Li-enrichment process related to the Cameron-Fowler mechanism for the formation of new 7Li. Because stars with IR excesses are distributed across most metallicity values, we suggest this mechanism is at work throughout an important part of the Galaxy's evolutionary history. Based on these IR excesses, we identified three Li thresholds: about 1.5 dex for RGB stars, about 0.5 dex for HB stars, and about -0.5 dex for AGB stars, establishing a new criterion to characterise Li-rich giants. We carried out a study of stellar rotations in metal-poor giant stars, revealing that a plateau appears for velocities greater than 40 km/s up to near 90 km/s, with Li abundances from 1.02 to 1.82 dex. Among Li-rich giants with v sin i > 40 km/s, increasing rotation is observed as metallicity decreases from -1.0 to -2.5. The presence of RGB and HB Li-rich giants with rotations up to 90 km/s suggests that stellar models must account for extended 3He reservoir lifetimes as a source of 7Li. The velocity around 40 km/s appears to be a new critical value.

Detecting primordial B-mode polarization of the Cosmic Microwave Background (CMB) provides a direct probe of inflationary gravitational waves. However, the signal is extremely faint and contaminated by gravitational lensing, instrumental noise, and astrophysical foregrounds. Here we present a score-based diffusion approach, formulated using variance-exploding stochastic differential equations (VE-SDEs), to reconstruct the primordial B-mode angular power spectrum from contaminated observations. The method employs a reverse SDE guided by a score model trained exclusively on random realizations of the primordial low $\ell$ B-mode angular power spectrum corresponding to a fixed tensor-to-scalar ratio $r=0.001$. During inference, the reverse SDE iteratively drives the observed angular power spectrum toward the learned primordial manifold, effectively denoising and delensing the input. The model is tested on simulated observational spectra that include gravitational lensing, complex polarized foreground combinations, and instrumental noise characteristics representative of the proposed ECHO mission. The trained score model learns the underlying statistical distribution of the primordial B-mode field for the given $r$, which acts as a physics-guided prior that can generate new, consistent realizations of the signal. This approach provides a robust framework for primordial signal recovery in future CMB polarization missions.

This article presents a comprehensive analysis of the physics of gravitational waves, exploring both the theoretical foundations and the most recent experimental advances. After a general introduction to the theory of general relativity and its major implications, the article discusses the history of gravitational waves, from their prediction by Einstein to their actual detection. It then explains what gravitational waves are and how they interact with appropriate detectors. The main mechanisms of gravitational radiation emission are analyzed, with a focus on compact binary systems of compact objects, whose orbits typically evolve in three phases: inspiral, merger, and the final ringdown phase, each of these phases leaving distinct signatures in the emitted waves. The article highlights the fundamental role of the giant interferometers LIGO, Virgo, and KAGRA, true cathedrals of modern science, and revisits the historic event GW150914, the first direct detection of gravitational waves, which confirmed the predictions of general relativity and opened a new era for astronomy. This achievement was recognized with the 2017 Nobel Prize in Physics. Other observed events are also discussed, along with their astrophysical sources, and the possibility of detecting gravitational waves of cosmological origin, originating from the Big Bang itself. Finally, current and future projects are analyzed, including observatories based on increasingly sophisticated interferometers, as well as proposals for alternative detection methods, illustrating how gravitational-wave astronomy is shaping the present and future of our exploration of the universe. In concluding, the detection of gravitational waves is set in a broader context by examining the discoveries across the electromagnetic spectrum, thereby illustrating the complementary perspectives these different observational channels provide.

This study re-evaluates the previously assumed interaction between the galaxy pair UGC 694 and IC 412 through a combined kinematical and photometric approach. While morphological features such as tidal bridges have been visually identified in past surveys, our quantitative analysis using SDSS DR16 kinematical data reveals a significant radial velocity offset of approximately 8372 km/s. UGC 694 exhibits a heliocentric velocity of 12683 +/- 34 km/s, placing it at a distance of approximately 188 Mpc, whereas IC 412 is located in the foreground at approximately 62 Mpc with a velocity of 4311 +/- 46 km/s. This vast spatial separation of approximately 123.5 Mpc confirms that the perceived proximity is a line-of-sight projection effect rather than a physical gravitational encounter. Furthermore, we utilize differential photometry to analyze the structural asymmetry and color distribution of UGC 694. Our photometric findings suggest that the galaxy's disturbed morphology is not a result of a tidal encounter with IC 412, but likely originates from internal evolutionary processes or minor mergers with undetected companions. This work emphasizes the critical role of multi-wavelength validation in classifying interacting systems to avoid misinterpretation due to projection effects.

In this work, we study the realisation of unitarity-based cutting rules for primordial cosmological correlators computed within the Schwinger-Keldysh path integral formalism. While cutting rules have been previously derived for wavefunction coefficients, here we examine them directly at the level of cosmological observables expressed diagrammatically. The resulting rules closely resemble those familiar from flat-space scattering amplitudes, but with an additional subtlety: in order to express the discontinuity of a correlator as the product of lower-order correlators, one must introduce a specific combinations of diagrams which do not appear in the computation of observables themselves. We explicitly verify these rules for several classes of correlators, both at tree level and with loop corrections, arising from theories involving different types of interactions.

We present observational evidence supporting the presence of a stratified accretion disk wind in active galactic nuclei (AGN), based on multi-wavelength spectroscopic analysis of broad and narrow emission lines. The diversity in emission line profiles, ionization potentials, and kinematic signatures suggests a structured outflow emerging from the accretion disk, with different zones contributing to specific spectral features. High-ionization lines (e.g., Civ {\lambda}1549) exhibit strong blueshifts and asymmetric profiles indicative of fast, inner winds, while low-ionization lines (e.g., He̱ta}, Mgii {\lambda} 2800) show more symmetric profiles consistent with predominant emission from slower, denser regions farther out, although exhibiting systematic blueshifts in quasars radiating at high Eddington ratios. The intermediate ionization lines (e.g., Aliii {\lambda}1860) present a situation that is intermediate in terms of shift amplitudes, although in several super-Eddington candidates radial outflow velocity may reach values comparable to the ones of the high ionization lines. These results are consistent with radiatively driven wind models featuring radial stratification. We made preliminary photoionization modeling assuming unabsorbed radiation emitted from the corona and the hotter disk regions emission or absorbed by a layer of gas. Our findings provide new constraints on the geometry and physical conditions of AGN winds, providing clear evidence in favor of stratified wind emission.

In the outer core of neutron stars, $^3$P$_2$ superfluid neutrons and $^1$S$_0$ superconducting protons are deemed to exist, forming quantum vortices and magnetic fluxtubes, respectively. Those quantum vortices and fluxtubes play an important role in explaining observed sudden changes of rotational frequency, known as pulsar “glitches.” While the most of conventional glitch models rely on pinning/unpinning dynamics of neutron $^1\text{S}_0$ superfluid vortices in the inner crust, contributions of the outer core have not been ruled out. However, the latter possibility has been less explored so far and further thorough investigations are desired. In this study, we are thus developing a microscopic model based on spin-2 Gross-Pitaevskii equation (GPE) for neutron $^3$P$_2$ superfluid vortices coupled with Ginzburg-Landau equation (GLE) for fluxtubes associated with superconducting $^1\text{S}_0$ protons. In this contribution, we outline our theoretical framework and report tentative results showing how shape of quantum vortices could be affected by the presence of a proton fluxtube.

Using the photon-ion merged-beams technique at the PETRA\,III synchrotron light source, we have measured cross sections for double and up to tenfold photoionization of La$^{+}$ ions by a single photon in the energy range 820–1400~eV, where resonances and thresholds occur that are associated with the excitation or ionization of one $M$-shell electron. These cross sections represent experimental benchmark data for the further development of quantum theoretical methods, which will have to provide the bulk of the atomic data required for the modeling of nonequilibrium plasmas such as kilonovae. In the present work, we have upgraded the Jena Atomic Calculator (JAC) and pushed the state-of-the-art of quantum calculations for heavy many-electron systems to new limits. In particular, we have performed large-scale calculations of the La$^+$ photoabsorption cross section and of the deexcitation cascades, which set in after the initial creation of a $3d$ hole. Our theoretical results largely agree with our experimental findings. However, our theoretical product-ion charge state distributions are somewhat narrower than the experimental ones, which is most probably due to the simplifications necessary to keep the cascade calculations tractable.

Photometric Redshift is critical for analyzing astronomical objects, but existing ML methods often overlook the aleatoric uncertainties inherent in observed data. We introduce Starkindler, a novel training objective that explicitly incorporates observational errors into the model's objective function, thereby directly accounting for aleatoric uncertainty. Unlike traditional probabilistic models that focus solely on epistemic uncertainty, Starkindler provides uncertainty estimates that are regularised by aleatoric uncertainty, and is designed to be more interpretable. We train a simple convolutional neural network (CNN) using data from Sloan Digital Sky Survey (SDSS) and compare against the Photometric redshift estimates provided by SDSS. We show improvements in accuracy, calibration and reduction in predicted outlier rate. We also conduct an ablation study which confirms that excluding observational errors significantly degrades model performance, underscoring the importance of accounting for aleatoric uncertainty. Our results suggest that Starkindler not only enhances predictive performance but also provides interpretable uncertainty estimates, making it a robust tool for astronomical data analysis.

We develop a formulation of nonlinear cosmological perturbations on superhorizon scales in multi-fluid systems. It is based on the Arnowitt-Deser-Misner formalism combined with a spatial gradient expansion characterized by a small expansion parameter defined as the ratio of the comoving wavenumber to the Hubble scale. The background spacetime is assumed to be a flat Friedmann-Lemaitre-Robertson-Walker universe. Within this framework, we explicitly construct nonlinear long-wavelength solutions for cosmological perturbations. Since multi-fluid systems are inherently non-adiabatic, these solutions admit both adiabatic and entropy modes already at leading nonlinear order. We define adiabatic and entropy perturbations and discuss the non-uniqueness in defining pure entropy perturbations. Using different choices of pure entropy initial conditions, we analyze the time evolution of physical quantities such as the curvature perturbation and density perturbations in the geodesic slicing for two-fluid systems.

The exponential increase in artificial satellites, growing from 852 in 2004 to over 9,000 in 2023, has intensified the risk of the Kessler Syndrome: a cascading chain reaction of orbital collisions. This paper analyzes the dynamics of space debris accumulation to identify the primary orbital features contributing to this systemic risk. We compiled and analyzed Two-Line Element (TLE) datasets from Space-Track.org and historical collision data using a Python-based data mining approach. Specifically, we derived satellite velocities using the Vis-Viva equation and evaluated the correlation of five key features, launch piece count, orbital period, apogee, perigee, and Radar Cross Section (RCS) size, with debris density. Our evaluation reveals that apogee and orbital period exhibit the strongest correlation with the risk of the Kessler Syndrome, indicating that satellites in higher orbits pose a disproportionately greater threat to long-term sustainability due to navigational constraints. Contrary to common assumptions, our data suggests that velocity and object size (RCS) show negligible direct correlation with collision incidence in the current dataset. Based on these findings, we propose mitigation strategies focusing on integrating AI-driven autonomous navigation systems and deploying advanced radiation-resistant shielding materials to enhance the resilience of high-orbit assets.

Double-double radio galaxies (DDRGs) display inner and outer jets or lobes thought to result from intermittent accretion. Due to randomly triggered accretion events, the lifetime of the retriggered jet is not expected to have any connection to the time of quiescence between jets, yet we show that a correlation between the two quantities may exist, which we interpret as resulting from continued accretion through the quiescent jet phase. Despite continuous accretion, a jet is absent because its presence depends on a non-zero value of black hole spin, but accretion transitions the system from counter-rotation to corotation, and therefore through zero black hole spin where a jet cannot form. The time of jet quiescence depends on how long it takes to spin the black hole up again in corotation, which is longer for lower accretion rates. Once the black hole spin is large enough for a renewed jet, this inner jet will last longer the lower the accretion rate is. Hence, in a continuous accretion scenario, longer quiescent times tend to associate to longer inner jet times. In addition, DDRG jets are of FRII morphology which we show to result from the absence of a tilt in the accretion disk in the transition through zero black hole spin, ensuring the absence of an FRI jet in a way that connects with our understanding of X-shaped radio galaxies. Both correlated timescales as well as sameness in jet morphology offers evidence in favor of our picture.

Artificial Intelligence (AI) is transforming domains from healthcare and agriculture to finance and industry. As progress on Earth meets growing constraints, the next frontier is outer space, where AI can enable autonomous, resilient operations under extreme uncertainty and limited human oversight. This paper introduces Space AI as a unified interdisciplinary field at the intersection of artificial intelligence and space science and technology. We consolidate historical developments and contemporary progress, and propose a systematic framework that organises Space AI into four mission contexts: 1 AI on Earth, covering intelligent mission planning, spacecraft design optimisation, simulation, and ground-based data analytics; 2 AI in Orbit, focusing on satellite and station autonomy, space robotics, on-board/near-real-time data processing, communication optimisation, and orbital safety; 3 AI in Deep Space, enabling autonomous navigation, adaptive scientific discovery, resource mapping, and long-duration human-AI collaboration under communication constraints; and 4 AI for Multi-Planetary Life, supporting in-situ resource utilisation, habitat and infrastructure construction, life-support and ecological management, and resilient interplanetary networks. Ultimately, Space AI can accelerate humanity's capability to explore and operate in space, while translating advances in sensing, robotics, optimisation, and trustworthy AI into broad societal impact on Earth.

Stellar convection in the presence of magnetic field affects the emergent intensity, as well as the structure and evolution of cool main-sequence dwarfs. We aim to understand the effect of faculae-like field strengths on near-surface stellar convection using 3D radiative MHD simulations of near-surface magneto-convection. We compare simulations of F, G, K and M main-sequence stars with a small-scale dynamo (SSD) to faculae-like spatially averaged field strengths (from 100 to 500 G). We focus on the effect of imposed magnetic field on the thermodynamic stratification and velocities, along with the bolometric intensity and surface field strength. Imposed magnetic fields result in reduced average density and gas pressure near the surface compared to the SSD simulations. The temperature stratification also shows a dip at and just below the stellar surface. The changes in average bolometric intensity are within a percent, with different trends with field strength for different stellar types. In addition, the convective velocities are reduced. The magnitude of changes in thermodynamic quantities are related to field strength as well as the stellar $T_{\rm eff}$. Faculae-strength magnetic fields modify the near surface convection by reducing gas pressure and density as well as suppressing convection in regions with strong field concentrations. The strength of these effects depends on the stellar type.

The proposed multi-impact model explains the formation of the Moon, Charon, and binary asteroids without invoking catastrophic cosmic events. The main elements of the new model are as follows: a. A primordial, low-mass proto-satellite disk with prograde rotation existed around the proto-Earth. b. Most of the lunar material was ejected from Earth mantle by numerous impacts of large asteroids. This naturally explains the lunar iron deficiency. c. Collisions between ejecta and particles of the prograde proto-satellite disk stabilize the fragments on satellite orbits. We demonstrate the high efficiency of the multi-impact mechanism: ejecta on prograde orbits readily merges with the prograde proto-satellite disk, whereas retrograde ejecta falls back onto Earth.

Interstellar comet 3I/ATLAS (C/2025 N1) exhibits an unusual, tightly collimated dust feature in the sunward hemisphere which has been widely described as an anti-tail. At the same time, precise constraints on the nucleus size have been derived from a combination of high-resolution imaging and non-gravitational dynamics. In this work I present a unified analysis that combines existing constraints on the nucleus radius with new ground-based RGB imaging of the dust anti-tail obtained with a 0.25 m telescope at the Toni Scarmato Astronomical Observatory (MPC L92).

Line-intensity mapping (LIM) is an emerging observational technique that is used to observe the universe on large scales at low resolution through spectral line emission. Stacking analyses coadd cutouts of LIM data on positions of known signal emitters, robustly detecting signal otherwise hidden in a noisy map. In this article, we present two augmentations of a stacking pipeline, both aiming to refine the sensitivity of the stack by assuming a specific observed signal shape in 2D spatial axes or 3D spatial and spectral axes, as well as stacking on source coordinates more precise than the resolution of the LIM data cube. We test these methods on a series of simplistic and complex simulations mimicking observations with the CO Mapping Array Project (COMAP) Pathfinder. We find that these fitting methods provide up to a 25% advantage in detection significance over the original stack method in realistic COMAP-like simulations. We also find that the optimal fitting profile, given our CO line model and galaxy model, is larger than the 5' width of the COMAP beam and takes on a Lorentzian shape in the spectral dimension. Our findings suggest a nuanced dependence of the optimal profile size and shape on the LIM signal itself, including redshift-space clustering and fingers-of-God effects that depend on the tracer luminosity function and bias.