Papers for Friday, Apr 25 2025

Free space optical (FSO) communication using lasers is a rapidly developing field in telecommunications that can offer advantages over traditional radio frequency technology. For example, optical laser links may allow transmissions at far higher data rates, require less operating power and smaller systems and have a smaller risk of interception. In recent years, FSO laser links have been demonstrated, tested or integrated in a range of environments and scenarios. These include FSO links for terrestrial communication, between ground stations and cube-sats in low Earth orbit, between ground and satellite in lunar orbit, as part of scientific or commercial space relay networks, and deep space communications beyond the moon. The possibility of FSO links from and to the surface of Mars could be a natural extension of these developments. In this paper we evaluate some effects of the Martian atmosphere on the propagation of optical communication links, with an emphasis on the impact of dust on the total link budget. We use the output of the Mars Climate Database to generate maps of the dust optical depth for a standard Mars climatology, as well as for a warm (dusty) atmosphere. These dust optical depths are then extrapolated to a wavelength of 1.55 um, and translated into total slant path optical depths to calculate link budgets and availability statistics for a link between the surface and a satellite in a sun-synchronous orbit. The outcomes of this study are relevant to potential future missions to Mars that may require laser communications to or from its surface. For example, the results could be used to constrain the design of communication terminals suitable to the Mars environment, or to assess the link performance as a function of ground station location.

It is demonstrated that estimators of the angular power spectrum commonly used for the stochastic gravitational-wave background (SGWB) lack a closed-form analytical expression for the likelihood function and, typically, cannot be accurately approximated by a Gaussian likelihood. Nevertheless, a robust statistical analysis can be performed by extending the framework outlined in \cite{PRL} to enable the estimation and testing of angular power spectral models for the SGWB without specifying distributional assumptions. Here, the technical aspects of the method are discussed in detail. Moreover, a new, consistent estimator for the covariance of the angular power spectrum is derived. The proposed approach is applied to data from the third observing run (O3) of Advanced LIGO and Advanced Virgo.

We present nuclear (100-150 pc) spectral energy distributions (SEDs) for a sample of 23 nearby luminous infrared galaxies hosting a total of 28 nuclei. We gather aperture photometry from high-resolution X-ray to submillimeter data for each nuclear region localized by ALMA observations of the dust continuum. We model the broadband SEDs using X-CIGALE. Binning the merging systems by interaction class, we find that the AGN fraction (fraction of AGN infrared luminosity to total infrared luminosity) appears enhanced in the late- and post-merger stages compared to early-stage mergers. Examining the relationship between X-ray emission and infrared emission of the nuclear regions, we find that the infrared emission in the nucleus is dominated by dust and AGN, with minimal contribution from stars. We also find that nuclear regions have higher X-ray hardness ratios than the host galaxies globally among both the AGN and non-AGN population. We highlight the similarities and differences in the SEDs of dual nuclei in five closely separated late-stage merging systems: Arp 220 ($d_\mathrm{nuc} \sim$ 0.5 kpc), NGC 6240 ($d_\mathrm{nuc} \sim$ 1 kpc), IRAS 07251-0248 ($d_\mathrm{nuc} \sim$ 2 kpc), IRAS F12112+0305 ($d_\mathrm{nuc} \sim$ 4 kpc), and IRAS F14348+1447 ($d_\mathrm{nuc} \sim$ 6 kpc). The SEDs for these resolved pairs are distinct, suggesting that the AGN state is much more susceptible to the stellar and dust content within the immediate circumnuclear ($<$150 pc) environment than to the host's global infrared luminosity or merger stage.

We report the detection of thermal emission from and confirm the planetary nature of WD 1856+534b, the first transiting planet known to orbit a white dwarf star. Observations with JWST's Mid-Infrared Instrument (MIRI) reveal excess mid-infrared emission from the white dwarf, consistent with a closely-orbiting Jupiter-sized planet with a temperature of $186^{+6}_{-7}$ K. We attribute this excess flux to the known giant planet in the system, making it the coldest exoplanet from which light has ever been directly observed. These measurements constrain the planet's mass to no more than six times that of Jupiter, confirming its planetary nature and ruling out previously unexcluded low-mass brown dwarf scenarios. WD 1856+534b is now the first intact exoplanet confirmed within a white dwarf's "forbidden zone", a region where planets would have been engulfed during the star's red giant phase. Its presence provides direct evidence that planetary migration into close orbits, including the habitable zone, around white dwarfs is possible. With an age nearly twice that of the Solar System and a temperature akin to our own gas giants, WD 1856+534b demonstrates JWST's unprecedented ability to detect and characterize cold, mature exoplanets, opening new possibilities for imaging and characterizing these worlds in the solar neighborhood.

The mass of the Local Group (LG), comprising the Milky Way (MW), Andromeda (M31), and their satellites, is crucial for validating galaxy formation and cosmological models. Traditional virial mass estimates, which rely on line-of-sight (LoS) velocities and simplified infall assumptions, are prone to systematic biases due to unobserved velocity components and anisotropic kinematics. Using the TNG cosmological simulation, we examine two limiting cases: the \underline{minor infall} model -- ignoring perpendicular velocities to the LoS directions) and the \underline{major infall} model -- assuming purely radial motion towards the Center of Mass (CoM). Our simulations demonstrate that geometric corrections are vital: the minor-infall model underestimates the true mass, while the major-infall model overestimates it. By applying these calibrated corrections to observed dwarf galaxy kinematics within 1 Mpc of the LG's CoM, we derive a refined LG mass of $M_{\mathrm{LG}} = (2.99 \pm 0.60) \times 10^{12}\, M_\odot$. This finding aligns with predictions from the $\Lambda$CDM model, timing arguments, and independent mass estimates, resolving previous discrepancies. Our analysis highlights the importance of correcting for velocity anisotropy and offers a robust framework for dynamical mass estimation in galaxy groups.

Theoretical arguments and observations suggest that in massive halos ($>10^{12}\,M_\odot$), the circumgalactic medium (CGM) is dominated by a 'hot' phase with gas temperature near the virial temperature ($T \approx T_{\rm vir}$) and a quasi-hydrostatic pressure profile. Lower-mass halos are however unlikely to be filled with a similar quasi-static hot phase, due to rapid radiative cooling. Using the FIRE cosmological zoom simulations, we demonstrate that the hot phase is indeed sub-dominant at inner radii ($\lesssim 0.3\,R_{\rm vir}$) of $\lesssim 10^{12}\,M_\odot$ halos, and the inner CGM is instead filled with $T \ll T_{\rm vir}$ gas originating in outflows and inflows, with a turbulent velocity comparable to the halo virial velocity. The turbulent velocity thus exceeds the mass-weighted sound speed in the inner CGM, and the turbulence is supersonic. UV absorption features from such CGM trace the wide lognormal density distributions of the predominantly cool and turbulent volume-filling phase, in contrast with tracing localized cool 'clouds' embedded in a hot medium. We predict equivalent widths of $W_\lambda \sim 2\lambda v_c/c \sim 1A$ for a broad range of strong UV and EUV transitions (Mg II, C II, C IV, Si II-IV, O III-V) in sightlines through inner CGM dominated by turbulent pressure of $\lesssim L^*$ galaxies at redshifts $0 \leq z \lesssim 2$, where $\lambda$ is the transition wavelength, $v_{\rm c}$ is the halo circular velocity and $c$ is the speed of light. Comparison of our predictions with observational constraints suggests that star-forming dwarf and $\lesssim L^*$ galaxies are generally dominated by turbulent pressure in their inner CGM, rather than by thermal pressure. The inner CGM surrounding these galaxies is thus qualitatively distinct from that around quenched galaxies and massive disks such as the Milky-Way, in which thermal pressure likely dominates.

The Radial Acceleration Relation (RAR) follows from Milgromian gravitation (MoND). Velocity dispersion data of many dwarf spheroidal galaxies (dSphs) and galaxy clusters have been reported to be in tension with it. We consider the Generalized Poisson Equation (GPE), expressed in terms of the p-Laplacian, which has been applied in electrodynamics. We investigate whether it can address these tensions. From the GPE we derive a generalized RAR characterized by the $p$-parameter from the p-Laplacian and a velocity dispersion formula for a Plummer model. We apply these models to Milky Way and Andromeda dSphs and HIFLUGS galaxy clusters and derive a $p$-parameter for each dSph and galaxy cluster. We explore a relation of $p$ to the mass density of the bound system, and alternatively a relation of $p$ to the external field predicted from Newtonian gravity. This ansatz allows the deviations of dSphs and galaxy clusters from the RAR without introducing dark matter. Data points deviate from the Milgromian case, $p=3$, with up to $5\sigma$-confidence. Also, we find the model predicts velocity dispersions, each of which lies in the 1$\sigma$-range of their corresponding data point allowing the velocity dispersion to be predicted for dSphs from their baryonic density. The functional relation between the mass density of the bound system and $p$ suggests $p$ to increase with decreasing density. We find for the critical cosmological density $p(\rho_{\text{crit}}) = 12.27 \pm 0.39$. This implies significantly different behaviour of gravitation on cosmological scales. Alternatively, the functional relation between $p$ and the external Newtonian gravitational field suggests $p$ to decrease with increasing field strength.

Using high-resolution general relativistic magnetohydrodynamic (GRMHD) simulations, we investigate accretion flows around spinning black holes and identify three distinct accretion states. Our results naturally explain some of the complex phenomenology observed across the black hole mass spectrum. The magnetically arrested disk (MAD) state, characterized by strong magnetic fields (plasma-$\beta << 1$), exhibits powerful jets (of power $\sim10^{39}$ erg s$^{-1}$), highly variable accretion, and significant sub-Keplerian motion. On the other hand, weakly magnetized disks (plasma-$\beta >> 1$), known as the standard and normal evolution (SANE) state, show steady accretion with primarily thermal winds. An intermediate state bridges the gap between MAD and SANE regimes, with moderate magnetic support (plasma-$\beta \sim 1$) producing mixed outflow morphologies and complex variability. This unified framework explains the extreme variability of GRS 1915+105, the steady jets of Cyg X-1, and the unusually high luminosities (even super-Eddington based on stellar mass black hole) of HLX-1 without requiring super-Eddington mass accretion rates. Our simulations reveal a hierarchy of timescales that explain the rich variety of variability patterns, with magnetic processes driving transitions between states. Comparing two with three dimensional simulations demonstrates that while quantitative details differ, the qualitative features distinguishing different accretion states remain robust. The outflow power and variability follow a fundamental scaling relation with mass determined by the magnetic field configuration, demonstrating how similar accretion physics operates from stellar-mass X-ray binaries (XRBs) to intermediate mass black hole sources. This could be extrapolated further to supermassive black holes.

The James Webb Space Telescope (JWST) discovered 79 transients out to $z$$\sim$4.8 through the JADES Transient Survey (JTS), but the JTS did not find any $z$$>$5 transients. Here, we present the first photometric evidence of a $z$$>$5 transient/variable source with JWST. The source, AT 2023adya, resides in a $z_{\mathrm{spec}}$$=$5.274 galaxy in GOODS-N, which dimmed from $m_{\rm F356W}$$=$26.05$\pm$0.02 mag to 26.24$\pm$0.02 mag in the rest-frame optical over approximately two rest-frame months, producing a clear residual signal in the difference image ($m_{\rm F356W}$$=$28.01$\pm$0.17 mag; SN$_\mathrm{var}$$=$6.09) at the galaxy center. Shorter-wavelength bands (F090W/F115W) show no rest-frame ultraviolet brightness change. Based on its rest-frame V-band absolute magnitude of M$_\mathrm{V}$$=$$-$18.48 mag, AT 2023adya could be any core-collapse supernova (SN) subtype or an SN Ia. However, due to low SN Ia rates at high redshift, the SN Ia scenario is unlikely. Alternatively, AT 2023adya may be a variable active galactic nucleus (AGN). However, the JWST NIRCam/Grism spectrum shows no broad H$\alpha$ emission line (FWHM$=$130$\pm$26 km s$^{-1}$), disfavoring the variable AGN scenario. It is also unlikely that AT 2023adya is a tidal disruption event (TDE) because the TDE models matching the observed brightness changes have low event rates. Although it is not possible to determine AT 2023adya's nature based on the two-epoch single-band photometry alone, this discovery indicates that JWST can push the frontier of transient/variable science past $z$$=$5 and towards the epoch of reionization.

The Pair Instability (PI) boundary is crucial for understanding heavy merging Black Holes (BHs) and the second mass gap's role in galactic chemical evolution. So far, no works have critically and systematically examined how rotation and mass loss affect the PI boundary or BH masses below it. Rapid rotation significantly alters stellar structure and mass loss, which is expected to have significant effects on the evolution of stellar models. We have previously derived a critical core mass independent of stellar evolution parameters, finding the BH (Pulsational) PI boundary at $M_{ CO, crit} = 36.3 M_\odot$ for a carbon-oxygen (CO) core. Using MESA, we model massive stars around the PI boundary for varying rotation rates and metallicities. We implement mechanical mass loss in MESA, studying its effects on massive stars in low-metallicity environments. Below $1/100$th $Z_\odot$, mechanical mass loss dominates over radiative winds. We check the BH-PI boundary for rapid rotators to confirm our critical core mass criterion and derive model fits describing rotation's impact on core and final masses. Fast rotators reach a point (typically $\Omega / \Omega_{crit} \approx 0.6$) where the entire star becomes chemically homogeneous, evolving like a stripped star. This lowers the maximum BH mass before PI to its critical core mass of $M_{CO, crit} = 36.3 M_\odot$, aligning with the bump feature in the BH mass distribution observed by LIGO/VIRGO.

Granulation in the photospheres of FGK-type stars induces variability in absorption lines, complicating exoplanet detection via radial velocities and characterisation via transmission spectroscopy. We aim to quantify the impact of granulation on the radial velocity and bisector asymmetry of stellar absorption lines of varying strengths and at different limb angles. We use 3D radiation-hydrodynamic simulations from MURaM paired with MPS-ATLAS radiative transfer calculations to synthesise time series' for four Fe I lines at different limb angles for a solar-type star. Our line profiles are synthesised at an extremely high resolution (R = 2,000,000), exceeding what is possible observationally and allowing us to capture intricate line shape variations. We introduce a new method of classifying the stellar surface into three components and use this to parameterise the line profiles. Our parameterisation method allows us to disentangle the contributions from p-modes and granulation, providing the unique opportunity to study the effects of granulation without contamination from p-mode effects. We validate our method by comparing radial velocity power spectra of our granulation time series to observations from the LARS spectrograph. We find that we are able to replicate the granulation component extracted from observations of the Fe I 617 nm line at the solar disk centre. We use our granulation-isolated results to show variations in convective blueshift and bisector asymmetry at different limb angles, finding good agreement with empirical results. We show that weaker lines have higher velocity contrast between granules and lanes, resulting in higher granulation-induced velocity fluctuations. Our parameterisation provides a computationally efficient strategy to construct new line profiles, laying the groundwork for future improvements in mitigating stellar noise in exoplanet studies.

Motivated by recent discoveries of X-ray quasi-periodic eruptions, we revisit the collision of a black hole and an accretion disk. Assuming that they are orbiting a supermassive black hole in orthogonal orbits, we perform a general relativistic simulation of the collision, varying the relative velocity $V_0$ from $0.032c$ to $0.2c$ (where $c$ is the speed of light) with a variety of disk thickness and a realistic local density profile for the disk. Our findings indicate that the mass of the outflow matter from the disk, $m_{\rm ej}$, is slightly less than the expected value. Meanwhile, the typical energy associated with this outflow $E_{\rm ej}$ is $\sim m_{\rm ej}V_0^2$. Thus, the predicted peak luminosity from disk flares is approximately equal to the Eddington luminosity of the black hole, whereas the peak time and duration of the flares, which are $\propto m_{\rm ej}^{1/2}$, are shorter than that previously believed. We also demonstrate that the property of the outflow matter induced by the incoming and outgoing stages of the black hole collision is appreciably different. We find that a high mass accretion rate onto the black hole from the disk persists for a timescale of $\sim 10^6$ Schwarzschild time of the black hole after the collision for $V_0/c \lesssim 0.1$, making this long-term accretion onto the black hole the dominant emission process for black hole-disk collision events. Implications of these results are discussed.

Context. Star-forming galaxies emit {\gamma}rays with relatively low luminosity, but the study of their emission is no less captivating. While it is known that their {\gamma}-ray luminosity in the GeV band is strongly linked to their star formation, the origin of their emission at higher energies remains uncertain due to limited observations. Aims. Our aim is to assemble the largest possible sample of star-forming galaxies with potential detectability by the new-generation of Cherenkov telescopes. Methods. To achieve this, we compile a comprehensive sample of galaxies, including those previously detected by Fermi-LAT in the GeV energy range as well as a larger sample of star-forming galaxies in the Local Volume that have been cataloged in the near-infrared band. We estimate their {\gamma}-ray flux assuming a proportional relationship with their star formation rate, and then select the brightest candidates. The predicted spectra in the TeV band are derived using a simple empirical model normalized to the star formation rate and a model based on extrapolating the latest Fermi-LAT data to higher energies. The ground-based detectability of {\gamma}-ray emission from these sources is assessed through a comparison to the most recent instrument response functions. Results. Our investigation reveals that almost a dozen star-forming galaxies may be detectable by upcoming {\gamma}-ray telescopes. Conclusions. The observation of numerous star-forming galaxies in the TeV band is a fundamental piece of the panchromatic puzzle for understanding the physics inside these galaxies. The significant increase in the number of galaxies that can be studied in detail in the near future, particularly with the Cherenkov Telescope Array Observatory, promises a major step forward in the study of the conditions of acceleration and transport of cosmic rays in nearby extragalactic environments.

Atmospheric turbulence degrades the quality of astronomical observations in ground-based telescopes, leading to distorted and blurry images. Adaptive Optics (AO) systems are designed to counteract these effects, using atmospheric measurements captured by a wavefront sensor to make real-time corrections to the incoming wavefront. The Fried parameter, r0, characterises the strength of atmospheric turbulence and is an essential control parameter for optimising the performance of AO systems and more recently sky profiling for Free Space Optical (FSO) communication channels. In this paper, we develop a novel data-driven approach, adapting machine learning methods from computer vision for Fried parameter estimation from a single Shack-Hartmann or pyramid wavefront sensor image. Using these data-driven methods, we present a detailed simulation-based evaluation of our approach using the open-source COMPASS AO simulation tool to evaluate both the Shack-Hartmann and pyramid wavefront sensors. Our evaluation is over a range of guide star magnitudes, and realistic noise, atmospheric and instrument conditions. Remarkably, we are able to develop a single network-based estimator that is accurate in both open and closed-loop AO configurations. Our method accurately estimates the Fried parameter from a single WFS image directly from AO telemetry to a few millimetres. Our approach is suitable for real time control, exhibiting 0.83ms r0 inference times on retail NVIDIA RTX 3090 GPU hardware, and thereby demonstrating a compelling economic solution for use in real-time instrument control.

The COronal DEnsity and Temperature (CODET) model is a physics-based model (Rodríguez-Gómez et al. 2018; Rodríguez-Gómez 2017) . This model uses the relationship between the magnetic field, density, temperature, and EUV emission. This model provides mean daily Solar Spectral Irradiance time series in EUV wavelengths in long time scales from days to solar cycles. The current manuscript presents the updated/new CODET model version 1.1. It uses observational datasets from SDO/EVE MEGS-A at $28.4 \ \mathrm{nm}$ and $21.1 \ \mathrm{nm}$ wavelengths to obtain the goodness-of-fit between them and the modeled SSI from April 30, 2010, to May 26, 2014. The model described well observational data during that period, with less than $20\%$ error in both wavelengths. Additionally, SSI predictions are provided using the new model parameters from July 1996 to October 2024, where SOHO/MDI and SDO/HMI photospheric magnetic field data are available. These predictions were compared with GOES/EUVS at $28.4 \ \mathrm{nm}$ and mean daily values of SDO/AIA at $21.1 \ \mathrm{nm}$ data, with errors of $\sim 26\%$ and $42\%$ for $28.4 \ \mathrm{nm}$ and $21.1 \ \mathrm{nm}$, respectively. The error analysis for model fitting and predictions shows how accurate the model predictions are. Thus, the CODET model provides a reliable estimate of the Solar Spectral Irradiance time series in EUV wavelengths where no observational data is available, e.g., after the SDO/EVE MEGS-A era.

We present X-ray spectra ($0.7-20$ keV) of two high synchrotron-peaked blazars Mrk 421 and 1ES 1959+650 from simultaneous observations by the SXT and LAXPC instruments onboard \textit{AstroSat} and the \textit{Swift}-XRT during multiple intervals in 2016-19. The spectra of individual epochs are satisfactorily fitted by the log-parabola model. We carry out time-resolved X-ray spectroscopy using the \textit{AstroSat} data with a time resolution of $\sim$10 ks at all epochs, and study the temporal evolution of the best-fit spectral parameters of the log-parabola model. The energy light curves, with duration ranging from $0.5-5$ days, show intra-day variability and change in brightness states from one epoch to another. We find that the variation of the spectral index ($\alpha$) at hours to days timescale has an inverse relation with the energy flux and the peak energy of the spectrum, which indicates a harder-when-brighter trend in the blazars. The variation of curvature ($\beta$) does not follows a clear trend with the flux and has an anti-correlation with $\alpha$. Comparison with spectral variation simulated using a theoretical model of time variable nonthermal emission from blazar jets shows that radiative cooling and gradual acceleration of emitting particles belonging to an initial simple power-law energy distribution can reproduce most of the variability patterns of the spectral parameters at sub-day timescales.

Despite a wealth of multi-wavelength, spatially resolved, time-domain solar activity data, an accurate and complete temporo-spatial solar flare census is unavailable, which impedes our understanding of the physics of flare production. We present an Automatically Labeled EUV and X-ray Incident SolarFlares (ALEXIS) pipeline, designed to decompose the X-Ray flux of the full solar disk into a minimum set of discrete regions on the Solar surface. ALEXIS returns an average RMSE between the XRS time series and the discrete EUV signals of 0.066 $\pm$ 0.036 for a randomly selected test bed sample of 1000 hour-long data segments from May 2010 - March 2020. Flare emission that requires multiple regions was found to be synchronous: flares occurring at the same time, sympathetic: flares separated by minutes, or needed to capture the background emission before and/or after the main flare. ALEXIS uses the original full resolution and cadence of both the Atmospheric Imaging Assembly Instrument and the GOES13-15 Solar X-Ray Imager. Comparison of the ALEXIS catalog with those produced by SWPC and SolarSoft show that these canonical databases need revisiting for 62$\%$ and 15$\%$ of the sub-sample, respectively. Additionally, we increased the number of flares reported by SWPC and SolarSoft by 15$\%$. Our pipeline misses 6.7$\%$ of the 1057 flare sub-sample and returns 5$\%$ of false positives from 1211 flares reported by ALEXIS. The ALEXIS catalog returns flare peak times, coordinates, the corrected scaled XRay magnitude, and the associated NOAA active region with a HARP identifier number independently from any external data products.

Many post-AGB star binaries are observed to have relatively high orbital eccentricities (up to 0.6). Recently, AC Her was observed to have a polar-aligned circumbinary disk. We perform hydrodynamic simulations to explore the impact of a polar-aligned disk on the eccentricity of a binary. For a binary system with central masses of 0.73 M_sun and 1.4 M_sun, we find that a disk with a total mass of 0.1 M_sun can enhance the binary eccentricity from 0.2 to 0.7 within 5000 years, or from 0.01 to 0.65 within 15000 years. Even if the disk mass is as low as 0.01 M_sun, the binary eccentricity grows within our simulation time while the system remains stable. These eccentricity variations are associated with the variations of the inclination between the disk and the binary orbit due to von Zeipel-Kozai-Lidov oscillations. The oscillations eventually damp and leave the binary eccentricity at a high value. The numerical results are in good agreement with analytical estimates. In addition, we examine the AC-Her system and find that the disk mass should be on the order of 10^(-3)M_sun for the disk to remain polar.

Producing stable $^{58}$Ni in Type Ia supernovae (SNe Ia) requires sufficiently high density conditions that are not predicted for all origin scenarios, so examining the distribution of $^{58}$Ni using the NIR [Ni II] 1.939 $\mu$m line may observationally distinguish between possible progenitors and explosion mechanisms. We present 79 telluric-corrected NIR spectra of 22 low-redshift SNe Ia from the Carnegie Supernova Project-II ranging from +50 to +505 days, including 31 previously unpublished spectra. We introduce the Gaussian Peak Ratio, a detection parameter that confirms the presence of the NIR [Ni II] 1.939 $\mu$m line in 8 SNe in our sample. Non-detections occur at earlier phases when the NIR Ni line has not emerged yet or in low signal-to-noise spectra yielding inconclusive results. Subluminous 86G-like SNe Ia show the earliest NIR Ni features around ~+50 days, whereas normal-bright SNe Ia do not exhibit NIR Ni until ~+150 days. NIR Ni features detected in our sample have low peak velocities ($v$~1200 km/s) and narrow line widths ($\leq$ 3500 km/s), indicating stable $^{58}$Ni is centrally located. This implies high density burning conditions in the innermost regions of SNe Ia and could be due to higher mass progenitors (i.e. near-$M_{ch}$). NIR spectra of the nearly two dozen SNe Ia in our sample are compared to various model predictions and paired with early-time properties to identify ideal observation windows for future SNe Ia discovered by upcoming surveys with Rubin-LSST or the Roman Space Telescope.

The article describes observations of the crescent of Venus and other bright planets using a large camera obscura. The goal of the article is to demonstrate that these observations can be successfully performed. Achieving positive results depends on solving several key problems. The most significant of these is the difficulty of perceiving the extremely faint light of a planet on the camera obscura screen. This issue is resolved through the use of special directional screens. Two main types (translucent and reflective) are described in the article. The construction of a so-called ``artificial Venus'', designed to test directional screens and determine the average sensitivity of human vision, is also presented. \\ Other serious challenges include aiming the camera obscura at the celestial object and compensating for Earth's rotation. One of the methods discussed involves the use of a flat intermediate mirror and a special mount for its guidance.\\ The objective of the paper is fulfilled through the presentation of both visual and photographic observation results. In addition to Venus's crescent, observations of the Saturn's rings are also presented. The proposed design of the camera obscura, which incorporates a specialized projection system, enables the separation of its two functions: directing light from objects and focusing its energy. The elements performing these tasks are fully scalable. This can be used in the construction of modern telescopes. The article also comments on the possibility of observing the phases of Venus in the distant past and the important consequences resulting from this.

JWST galaxy deep spectral surveys provide a unique opportunity to trace a broad range of evolutionary features of galaxies and the intergalactic medium given the huge distance the photons are propagating. We have analyzed the spectral data of JWST galaxies up to a redshift of around 7 using the Kolmogorov technique, which is an efficient tool for testing the tiny comparative randomness properties of cumulative signals, that is, for distinguishing the contributions of regular and stochastic sub-signals. Our aim is to determine if certain identical spectral features of galaxies have undergone any distortions or systematic evolution across a broad range of redshifts. Our results indicate a change in the spectral properties of the sample galaxies at around z \simeq 2.7 at over a 99% confidence level.

The formation of Saturn is modeled by detailed numerical simulations according to the core-nucleated accretion scenario. Previous models are enhanced to include the dissolution of accreting planetesimals, composed of water ice, rock, and iron, in the gaseous envelope of the planet, leading to a non-uniform composition with depth. The immiscibility of helium in metallic hydrogen layers is also considered. The calculations start at a mass $0.5$ Earth masses and are extended to the present day. At 4.57 Gyr, the model, proceeding outwards, has the following structure: (i) a central core composed of $100$% heavy elements and molecules, (ii) a region with decreasing heavy element mass fraction, down to a value of $0.1$, (iii) a layer of uniform composition with the helium mass fraction $Y$ enhanced over the primordial value, (iv) a helium rain region with a gradient in $Y$, (v) an outer convective, adiabatic region with uniform composition in which $Y$ is reduced from the primordial value, and (vi) the very outer layers where cloud condensation of the heavy elements occurs. Models of the distribution of heavy elements as a function of radius are compared with those derived to fit the observations of the Cassini mission, with rough qualitative agreement. The helium mass fraction in Saturn's outer layers is estimated to be around $20$%. Models are found which provide good agreement with Saturn's intrinsic luminosity and radius.

The spectral variability of changing-look active galactic nuclei (CL-AGNs) occurred on timescales of years to tens of years, posing a significant challenge to the standard thin disk model. In this work, we propose a sandwich model, including an optically thick disk in the mid-plane (Disk 1) and two disks of low effective optical depth on both sides (Disk 2). These two types of disks are coupled with magnetic fields, which allow viscous torque interaction between them. As a consequence, the radial velocity of Disk 1 can increase by up to three orders of magnitude compared to the standard thin disk, leading to an equivalent decrease in the accretion timescale. Therefore, such a sandwich model can account for the rapid variability in CL-AGNs. In addition, we also discuss the influence of the magnetic pressure on Disk 2. When Disk 2 is dominated by the magnetic pressure, it resembles a "warm corona", which is responsible for the soft X-ray excess.

Understanding the epochs of cosmic dawn and reionisation requires us to leverage multi-wavelength and multi-tracer observations, with each dataset providing a complimentary piece of the puzzle. To interpret such data, we update the public simulation code, 21cmFASTv4, to include a discrete source model based on stochastic sampling of conditional mass functions and semi-empirical galaxy relations. We demonstrate that our new galaxy model, which parametrizes the means and scatters of well-established scaling relations, is flexible enough to characterize very different predictions from hydrodynamic cosmological simulations of high-redshift galaxies. Combining a discrete galaxy population with approximate, efficient radiative transfer allows us to self-consistently forward-model galaxy surveys, line intensity maps (LIMs), and observations of the intergalactic medium (IGM). Not only does each observable probe different scales and physical processes, but cross-correlation will maximise the information gained from each measurement by probing the galaxy-IGM connection at high-redshift. We find that a stochastic source field produces significant shot-noise in 21cm and LIM power spectra. Scatter in galaxy properties can be constrained using UV luminosity functions and/or 21cm power spectra, especially if astrophysical scatter is higher than expected (as might be needed to explain recent JWST observations). Our modelling pipeline is both flexible and computationally efficient, facilitating high-dimensional, multi-tracer, field-level Bayesian inference of cosmology and astrophysics during the first billion years.

The outer solar system is theoretically predicted to harbour an undiscovered planet, often referred to as P9. Simulations suggest that its gravitational influence could explain the unusual clustering of minor bodies in the Kuiper Belt. However, no observational evidence for P9 has been found so far, as its predicted orbit lies far beyond Neptune, where it reflects only a faint amount of Sunlight. This work aims to find P9 candidates by taking advantage of two far-infrared all-sky surveys, which are IRAS and AKARI. The epochs of these two surveys were separated by 23 years, which is large enough to detect the ~3'/year orbital motion of P9. We use a dedicated AKARI Far-Infrared point source list for our P9 search - AKARI Monthly Unconfirmed Source List, which includes sources detected repeatedly only in hours timescale, but not after months. We search for objects that moved slowly between IRAS and AKARI detections given in the catalogues. First, we estimated the expected flux and orbital motion of P9 by assuming its mass, distance, and effective temperature to ensure it can be detected by IRAS and AKARI, then applied the positional and flux selection criteria to narrow down the number of sources from the catalogues. Next, we produced all possible candidate pairs whose angular separations were limited between 42' and 69.6', corresponding to the heliocentric distance range of 500 - 700 AU and the mass range of 7 - 17 Earth masses. There are 13 pairs obtained after the selection criteria. After image inspection, we found one good candidate, of which the IRAS source is absent from the same coordinate in the AKARI image after 23 years and vice versa. However, AKARI and IRAS detections are not enough to determine the full orbit of this candidate. This issue leads to the need for follow-up observations, which will determine the Keplerian motion of our candidate.

We formulate an effective field theory (EFT) of coupled dark energy (DE) and dark matter (DM) interacting through energy and momentum transfers. In the DE sector, we exploit the EFT of vector-tensor theories with the presence of a preferred time direction on the cosmological background. This prescription allows one to accommodate shift-symmetric and non-shift-symmetric scalar-tensor theories by taking a particular weak coupling limit, with and without consistency conditions respectively. We deal with the DM sector as a non-relativistic perfect fluid, which can be described by a system of three scalar fields. By choosing a unitary gauge in which the perturbations in the DE and DM sectors are eaten by the metric, we incorporate the leading-order operators that characterize the energy and momentum transfers besides those present in the conventional EFT of vector-tensor and scalar-tensor theories and the non-relativistic perfect fluid. We express the second-order action of scalar perturbations in real space in terms of time- and scale-dependent dimensionless EFT parameters and derive the linear perturbation equations of motion by taking into account additional matter (baryons, radiation). In the small-scale limit, we obtain conditions for the absence of both ghosts and Laplacian instabilities and discuss how they are affected by the DE-DM interactions. We also compute the effective DM gravitational coupling $G_{\rm eff}$ by using a quasi-static approximation for perturbations deep inside the DE sound horizon and show that the existence of momentum and energy transfers allow a possibility to realize $G_{\rm eff}$ smaller than in the uncoupled case at low redshift.

We present a unique discovery of three new detected systems showing two different phenomena together. These are 2+2 quadruple stellar systems showing two eclipsing binaries as the inner pairs. And besides that, these systems were also found to exhibit the precession of the inner orbits causing the inclination changes manifesting themselves through the eclipse depth variations. We are not aware of any similar known system on the sky nowadays, hence our discovery is really unique. In particular these systems are: CzeV4315 = HD 228777 (periods 6.7391 d and 0.91932 d, inclination change of pair B of about 1.4deg/yr); ASASSN-V J075203.23-323102.7 = GDS_J0752031-323102 (8.86916 d + 2.6817 d, inclination change of pair B of about 1.03deg/yr, now only ellipsoidal variations); ASASSN-V J105824.33-611347.6 = TIC 465899856 (2.3304 d + 13.0033 d, inclination change of pair B, now undetectable). These systems provide us unique insight into the quadruple-star dynamics, including the orbit-orbit interaction, Kozai-Lidov cycles, and testing the stellar formation theories of these higher order multiples.

Gaia Data Release 3 (GDR3) contains a wealth of information to advance our knowledge of stellar physics. In these lecture notes we introduce the data products from GDR3 that can be exploited by the stellar physics community. Then we visit different regions of the HR diagram, discuss the open scientific questions, and describe how GDR3 can help advance this particular topic. Specific regions include hot OB and A type stars, FGK main sequence, giants, and variable sources, low mass stars, and ultra-cool dwarfs. Examples of scientific exploitation are also provided. These lecture notes are accompanied by a 3-hour lecture presentation and a 3-hour practical session that are publicly available on the website of the Ecole Evry Schatzman 2023: Stellar physics with Gaia, this https URL, see Lectures and Hands-on Work.

Syn-glycolamide, a glycine isomer, has recently been detected in the G+0.693-0.027 molecular cloud. Investigations on its formation in the interstellar medium could offer insights into synthetic routes leading to glycine in prebiotic environments. Quantum chemical simulations on glycolamide (NH$_2$C(O)CH$_2$OH) formation on interstellar ice mantles, mimicked by a water ice cluster model, are presented. Glycolamide synthesis has been here modeled considering a stepwise process: the coupling between formaldehyde (H$_2$CO) and the radical of formamide (NH$_2$CO$^{\bullet}$) occurs first, forming the glycolamide precursor NH$_2$C(O)CH$_2$O$^{\bullet}$, which is then hydrogenated to give anti-glycolamide. We hypothesize that anti-to-syn interconversion will occur in conjunction with glycolamide desorption from the ice surface. The reaction barrier for NH$_2$C(O)CH$_2$O$^{\bullet}$ formation varies from 9 to 26 kJ mol$^{-1}$, depending on surface binding sites. Kinetic studies indicate that this reaction step is feasible in environments with a $T > 35~\text{K}$, until desorption of the reactants. The hydrogenation step leading to anti-glycolamide presents almost no energy barrier due to the easy H atom diffusion towards the NH$_2$C(O)CH$_2$O$^{\bullet}$ intermediate. However, it competes with the extraction of an H atom from the formyl group of NH$_2$C(O)CH$_2$O$^{\bullet}$, which leads to formyl formamide, NH$_2$C(O)CHO, and H$_2$. Nonetheless, according to our results, anti-glycolamide formation is predicted to be the most favored reactive channel.

We study the asymptotic behaviour of the free, cold-dark matter density fluctuation bispectrum in the limit of small scales. From an initially Gaussian random field, we draw phase-space positions of test particles which then propagate along Zel'dovich trajectories. A suitable expansion of the initial momentum auto-correlations of these particles leads to an asymptotic series whose lower-order power-law exponents we calculate. The dominant contribution has an exponent of $-11/2$. For triangle configurations with zero surface area, this exponent is even enhanced to $-9/2$. These power laws can only be revealed by a non-perturbative calculation with respect to the initial power spectrum. They are valid for a general class of initial power spectra with a cut-off function, required to enforce convergence of its moments. We then confirm our analytic results numerically. Finally, we use this asymptotic behaviour to investigate the shape dependence of the bispectrum in the small-scale limit, and to show how different shapes grow over cosmic time. These confirm the usual model of gravitational collapse within the Zel'dovich picture.

Black holes, both supermassive and stellar-mass, impact the evolution of their surroundings on a large range of scales. While the role of supermassive black holes is well studied, the effects of stellar-mass black holes on their surroundings, particularly in inducing structures in the interstellar medium (ISM), remain under explored. This study focuses on the black hole X-ray binary GRS 1915+105, renowned for its active jets, and the primary aim is to unveil and characterise the impact of GRS 1915+105 on its environment by identifying structures induced by jet-ISM interaction. Methods: We observed GRS 1915+105 with MeerKAT for a total exposure time of 14~hr, and we obtained the deepest image of GRS 1915+105 to date. Using a previously proposed self-similar model for large-scale jets, we inferred the properties of both the jets and the ISM, providing insights into the jet-ISM interaction site. Our observations revealed a bow shock structure near GRS 1915+105, likely induced by a jet interacting with the ISM and blowing an overpressured cavity in the medium. We constrained the ISM density to 100--160 particles\,cm$^{-3}$ while assuming a temperature range of 10$^4$--10$^6$\,K, which implies a bow shock expansion velocity of $20\,{\rm km\,s}^{-1}<\dot{L} <\,360\,{\rm km\,s}^{-1}$. We estimate that the jet responsible for the formation of the bow shock has an age between 0.09 and 0.22 Myr, and the time-averaged energy rate Conclusions: Our results confirm that in stellar-mass black holes, the energy dissipated through jets can be comparable to the accretion energy, and through the interaction of the jet with the ISM, such energy is transferred back to the environment. This feedback mechanism mirrors the powerful influence of supermassive black holes on their environments, underscoring the significant role a black hole's activity has in shaping its surroundings.

This study aims to detect and characterize quasi-periodic oscillations (QPOs) signals in X-ray observations of NGC 4151. We employed the Weighted Wavelet Z-transform (WWZ) and Lomb-Scargle periodogram (LSP) methods for our analysis. QPO signals with frequencies of 5.91 $\times 10^{-4}$ Hz and 5.68 $\times 10^{-4}$ Hz were detected in observations conducted by Chandra (ObsID 7830) in 2007 and XMM-Newton (ObsID 0761670301) in 2015, with confidence levels of 3.7 $\sigma$ and 3.3 $\sigma$, respectively. These signals are the first to be independently observed by two different telescopes over an eight-year period with closely matched frequencies. Most notably, the combined confidence level of the QPO signals from these two independent observations reaches an exceptional 5.2 $\sigma$, which is rare in astrophysical research and significantly strengthens our conviction in the authenticity of these signals. A detailed analysis of the observational data suggests that these QPO signals may be correlated with the properties of the central supermassive black hole. Additionally, spectral analysis of the observational data revealed no significant spectral differences between the QPO and non-QPO segments. These findings provide new insights into the X-ray variability mechanisms of the central black hole in NGC 4151 and offer a novel perspective for black hole mass estimation.

Solar active regions (ARs) are crucial for understanding the long-term evolution of solar activities and predicting eruptive phenomena, including solar flares and coronal mass ejections. However, the cycle-dependent properties in the north-south asymmetry of ARs have not been fully understood. In this study, we investigate the hemispheric distribution of ARs from Carrington Rotation 1909 to 2278 (between 1996 May and 2023 November) by using three parameters that describe the magnetic field distribution of ARs: number, area, and flux. The main findings are as follows: (1) The three AR parameters show significant hemispheric asymmetry in cycles 23-25. The strong correlation between AR area and flux indicates that they can better reflect the intrinsic properties of solar magnetic field. (2) The correlation between sunspot activity and AR parameters varies in the two hemispheres across the different cycles. The AR parameters provide additional information for the variations in sunspot activity, which can better predict the intensity and cyclical changes of solar activity. (3) The variation in the fitting slope sign of the asymmetry index for AR parameters reflects periodic changes in hemispheric ARs, providing valuable insights into the activity of other stars. (4) Both the dominant hemisphere and the cumulative trend of AR parameters display a cycle-dependent behavior. Moreover, the trend variations of AR area and flux are similar, reflecting the long-term evolutionary characteristics of solar magnetic field. Our analysis results are relevant for understanding the hemispheric coupling of solar magnetic activity and its cyclic evolutionary patterns.

As the lifetime of a black hole decreases, the energy of the Hawking radiation it emits increases, ultimately culminating in its disappearance through a powerful burst of gamma rays. For primordial black holes (PBHs) with an initial mass of $\sim 5\times10^{14}$ g, their lifespans are expected to end in the present epoch. Detecting such PBH bursts would provide compelling evidence of their existence. The Cherenkov Telescope Array (CTA) has the potential to observe these bursts at the high-energy end of the gamma-ray spectrum. To investigate this possibility, we conduct a study to evaluate the sensitivity of CTA to the local burst rate density of PBHs. Our results suggest that during a 5-year observational campaign, CTA could exclude a local burst rate density exceeding $\sim 36\ \mathrm{pc}^{-3}\ \mathrm{yr}^{-1}$, which represents an improvement of one order of magnitude over the upper limit set by the Large High Altitude Air Shower Observatory (LHAASO). In addition, we propose an observation strategy optimized for detecting PBH bursts.

Determining stellar ages is challenging, particularly for cooler main-sequence stars. Magnetic evolution offers an observational alternative for age estimation via the age-chromospheric activity (AC) relation. We evaluate the impact of metallicity on this relation using near one-solar-mass stars across a wide metallicity range. We analyze a sample of 358 solar-type stars with precise spectroscopic parameters determined through a line-by-line differential technique and with ages derived using Yonsei-Yale isochrones. We measured chromospheric activity (S-index) using high-quality HARPS spectra, calibrated to the Mount Wilson system, and converted to the $R^{\prime}_{\mathrm HK}(T_{\mathrm{eff}})$ index with a temperature-based photospheric correction. Our findings show that the AC relation for $R^{\prime}_{\mathrm HK}(T_{\mathrm{eff}})$ is strongly influenced by metallicity. We propose a new age-activity-metallicity relation for solar-type main-sequence (MS) stars ($\log{g} \gtrsim 4.2 $) with temperatures 5370 $\lesssim$ $T_{\mathrm{eff}}$ $\lesssim$ 6530 K and metallicities from -0.7 to +0.3 dex. We show that taking metallicity into account significantly enhances chromospheric ages' reliability, reducing the residuals' root mean square (RMS) relative to isochronal ages from 2.6 Gyr to 0.92 Gyr. This reflects a considerable improvement in the errors of chromospheric ages, from 53\% to 15\%. The precision level achieved in this work is also consistent with previous age-activity calibration from our group using solar twins.

The nearby (d=3.6 Mpc) starburst galaxy M82 has been studied for several decades by very long baseline interferometry (VLBI) networks such as e-MERLIN and the European VLBI Network (EVN). The numerous supernova remnants (SNRs), HII regions and other exotic transients make it a perfect laboratory for studying stellar evolution and the interstellar medium (ISM). Its proximity provides a linear resolution of 17 pc/arcsec, enabling decadal-time-scale variability and morphology studies of the tens of compact radio sources. In this proceedings, we describe new techniques developed in the last ten years that provide deeper, more robust imaging, enable in-band spectral index mapping, and allow wider fields of view to be imaged to find new radio sources.

Recent observations have revealed the spectral feature of carbonaceous grains even in a very distant galaxy. We develop a state-of-the-art dust synthesis code by self-consistently solving molecule and dust formation in supernova (SN) ejecta that contain various elements in different layers. With a progenitor mass 25 Msun and explosion energy 10^{52} erg, we run the following four test calculations to investigate the impact of input physics. (i) With molecule formation solved, our SN model produces 8.45x10^{-2} Msun carbonaceous grains. (ii) If all available C and Si were initially depleted into CO and SiO molecules, respectively, the C grain mass could be underestimated by ~40%. In these two models producing 0.07 Msun 56Ni without mixing fallback, a large amount of silicates (0.260 Msun) created in O-rich layers are also ejected and likely to hide the spectral feature of carbonaceous grains. We then consider mixing-fallback that can reproduce the observed elemental abundance ratios of C-normal and C-enhanced extremely metal-poor stars in the Milky Way. (iii) In the former, the mass ratio of carbonaceous to silicate grains is still small (~0.3). However, (iv) in the latter (known as a ``faint SN'), while the C grain mass is unchanged (6.78x10^{-2} Msun), the silicate mass is reduced (9.98x10^{-3} Msun). Therefore, we conclude that faint SNe can be a significant carbonaceous dust factory in the early Universe.

Baryonic cycling is reflected in the spatial distribution of metallicity within galaxies, yet gas-phase metallicity distribution and its connection with other properties of dwarf galaxies are largely unexplored. We present the first systematic study of radial gradients of gas-phase metallicities for a sample of 55 normal nearby star-forming dwarf galaxies (stellar mass $M_\star$ ranging from $10^7$ to $10^{9.5}\ M_\odot$), based on MUSE spectroscopic observations. We find that metallicity gradient shows a significant negative correlation (correlation coefficient $r \approx -0.56$) with $\log M_\star$, in contrast to the flat or even positive correlation observed for higher-mass galaxies. This negative correlation is accompanied by a stronger central suppression of metallicity compared to the outskirts in lower-mass galaxies. Among the other explored galaxy properties-including baryonic mass, star formation distribution, galaxy environment, regularity of the gaseous velocity field, and effective yield of metals $y_{\rm eff}$-only the velocity field regularity and $y_{\rm eff}$ show residual correlation with the metallicity gradient after controlling for $M_\star$, in the sense that galaxies with irregular velocity fields or lower $y_{\rm eff}$ tend to have less negative or more positive gradients. Particularly, a linear combination of $\log M_\star$ and $\log y_{\rm eff}$ significantly improves the correlation with metallicity gradient ($r \approx -0.68$) compared to $\log M_\star$ alone. The lack of correlation with environment disfavors gas accretion as a dominant factor. Our findings imply that metal mixing and transport processes, including but not limited to feedback-driven outflows, are more important than in-situ metal production in shaping the metallicity distribution of dwarf galaxies.

The co-evolution of massive black holes (BHs) and their host galaxies is well-established within the hierarchical galaxy formation paradigm. Large-scale cosmological simulations are an ideal tool to study the repeated BH mergers, accretion and feedback that conspire to regulate this process. While such simulations are of fundamental importance for understanding the complex and intertwined relationship between BHs and their hosts, they are plagued with numerical inaccuracies at the scale of individual BH orbits. To quantify this issue, taking advantage of the $(100 \, h^{-1}\,\text{cMpc})^3$ FABLE simulation box, we track all individual BH mergers and the corresponding host galaxy mergers as a function of cosmic time. We demonstrate that BH mergers frequently occur prematurely, well before the corresponding merger of the host galaxies is complete, and that BHs are sometimes erroneously displaced from their hosts during close galaxy encounters. Correcting for these artefacts results in substantial macrophysical delays, spanning over several Gyrs, which are additional to any microphysical delays arising from unresolved BH binary hardening processes. We find that once the macrophysical delays are accounted for, high-mass BH merger events are suppressed, affecting the predictions for the BH population that may be observable with LISA and pulsar timing arrays. Furthermore, including these macrophysical delays leads to an increase in the number of observable dual active galactic nuclei, especially at lower redshifts, with respect to FABLE. Our results highlight the pressing need for more accurate modelling of BH dynamics in cosmological simulations of galaxy formation as we prepare for the multi-messenger era.

The population of high-redshift radio galaxies (HzRGs) is still poorly studied because only a few of these objects are currently known. We here present the results of a pilot project of spectroscopic identification of HzRG candidates. The candidates are selected by combining low-frequency radio and optical surveys that cover a total of ~2,000 squared degrees using the dropout technique, that is, the presence of a redshifted Lyman break in their photometric data. We focused on 39 g-dropout sources, which is about one-third of the selected sources, that are expected to be at 3.0 < z < 4.5. We considered single and double radio sources separately and searched for g-dropout sources at the location of the midpoint of the radio structure for the latter. The host galaxy is expected to be located there. We confirm only one out of 29 candidate HzRG associated with an extended radio source. For the compact radio sources, we instead reach a success rate of 30% by confirming 3 out of 10 HzRG targets. The four newly discovered HzRGs show a wide range of spectral radio slopes. This supports the idea that not all HzRGs are ultrasteep radio sources (USSs). The criterion for USSs is most commonly used to find HzRGs, but this method only selects a subpopulation. We discuss various contamination sources for the objects that are selected with the Lyman-break method and conclude that they are likely mainly HzRGs, but with a Ly$\alpha$ line that is underluminous with respect to expectations.

The chemical enrichment of X-ray-emitting hot halos has primarily been studied in closed-box galaxy clusters. Investigating the metal content of lower-mass, open systems can serve as a valuable tracer for understanding their dynamical history and the extent of chemical enrichment mechanisms in the Universe. In this context, we use an 85.6 ks XMM-Newton observation to study the spatial distribution of the abundance ratios of Mg, Si, and S with respect to Fe in the hot gas of the ram-pressure-stripped M86, which has undergone morphological transformations. We report that the chemical composition in the M86 galaxy core is more similar to the rest of the hot gaseous content of the Universe than to its stellar population. This result indicate that even extreme supersonic ram-pressure is insufficient to strip the inner part of a galaxy of its hot atmosphere. Comparison with other galaxies undergoing ram-pressure stripping suggests that stripping the "primordial" atmosphere of a galaxy requires a combination of ram-pressure stripping and strong radio-mechanical AGN activity. The X-ray emission structures within M86, the plume and the tail, are found to be relatively isothermal. We observe that the Mg/Fe ratio in the plume is $3.3\sigma$ higher than in the M86 galaxy core and is consistent with that in the M86 group outskirts and the Virgo ICM, suggesting that the plume might originate from the low-entropy group gas due to a galaxy-galaxy collision rather than from the ram-pressure stripping of the dense galaxy core.

Context. Observations with warm Spitzer and JWST revealed high and variable brightness in the planet 55 Cnc e. Aims. Inventory of the tidal effects on the rotational and orbital evolution of the planet 55 Cnc e enhanced by the nonzero orbital eccentricity. Methods. The creep-tide theory is used in simulations and dynamical analyses that explore the difficult trapping of the planet rotation in a 3:2 spin-orbit resonance and the most probable synchronization of the rotation. Results. The strong tidal dissipation of energy, enhanced by the non-zero orbital eccentricity, may explain the observed brightness anomalies. However, the strong dissipation should also circularize the orbit. The observed non-zero eccentricity, if true, would indicate that an unknown planet in a close orbital resonance with 55 Cnc e perturbing the motion of this planet should exist.

Stellar activity can be observed at different wavelengths in a variety of different activity indicators. We investigated the correlation between coronal and chromospheric emissions by combining X-ray data from stars detected in the eROSITA all-sky surveys (eRASS1 and eRASS:5) with Ca II infrared triplet (IRT) activity indices as published in the third Gaia data release (Gaia DR3). We specifically studied 24 300 and 43 200 stellar sources with reliable Ca II IRT measurement and X-ray detection in eRASS1 and eRASS:5, which is by far the largest stellar sample available so far. The largest detection fraction is obtained for highly active sources and stars of a late spectral type, while F-type and less active stars (as measured in the Ca II IRT) remain mostly undetected in X-rays. Also, the correlation is the strongest for late-type sources, while F-type stars show a rather weak correlation between the X-ray to bolometric flux ratio and the Ca II IRT activity index. The relation between the X-ray and Ca II IRT surface fluxes changes with the fractional X-ray flux without showing two separated branches as described in previous studies. For fast rotators, both activity indicators saturate at a similar Rossby number and the X-ray to bolometric flux ratio decreases faster than the IRT index for slower rotating stars. As a consequence, the ratio between X-ray and IRT fluxes is constant in the saturation regime and decreases for slow rotators.

Analyses of stellar spectra, stellar populations, and transit light curves rely on grids of synthetic spectra and center-to-limb variations (limb darkening) from model stellar atmospheres. Extensive model grids from PHOENIX, a generalized non-LTE 1D and 3D stellar atmosphere code, have found widespread use in the astronomical community, however current PHOENIX/1D models have been substantially improved over the last decade. To make these improvements available to the community, we have constructed the NewEra LTE model grid consisting of 37438 models with $2300K \leq T_{eff} \leq 12000K$, $0.0\le log{(g)} \le 6.0$ metallicities [M/H] from $-4.0$ to $+0.5$, and for metallicities $-2.0 \le [M/H] \le 0.0$ additional $\alpha$ element variations from $-0.2 \le [\alpha/{\rm Fe}] \le +1.2$ are included. The models use databases of 851 million atomic lines and 834 billion molecular lines and employ the Astrophysical Chemical Equilibrium Solver for the equation of state. All models in the NewEra grid have been calculated in spherical symmetry because center-to-limb variation differences from plane-parallel models are quite large for giants and not insignificant for dwarfs. All model data are provided in the Hierarchical Data Format 5 (HDF5) format, including low and high sampling rate spectra. These files also include a variety of details about the models, such as the exact abundances and isotopic patterns used and results of the atomic and molecular line selection. Although the model structures have small differences with the previous grid generation, the spectra show significant differences, mostly due to the updates of the molecular line lists.

Galactic archaeology relies on accurate stellar parameters to reconstruct the galaxy's history, including information on stellar ages. While the precision of data has improved significantly in recent years, stellar models used for age inference have not improved at a similar rate. In fact, different models yield notably different age predictions for the same observational data. In this paper, we assess the difference in age predictions of various widely used model grids for stars along the red giant branch. Using open source software, we conduct a comparison of four different evolution grids and we find that age estimations become less reliable if stellar mass is not known, with differences occasionally exceeding $80\%$. Additionally, we note significant disagreements in the models' age estimations at non-solar metallicity. Finally, we present a method for including theoretical uncertainties from stellar evolutionary tracks in age inferences of red giants, aimed at improving the accuracy of age estimation techniques used in the galactic archaeology community.

After the inflationary phase, the universe enters the preheating phase, during which the inflaton field rolls down its potential and oscillates. When the potential significantly deviates from a parabolic shape at its minimum, these oscillations trigger an instability in the scalar perturbations, leading to their amplification. This phenomenon, known as self-resonance, has important implications in cosmology. Notably, since scalar perturbations couple to tensor perturbations at second order in the equations of motion, this amplification results in the production of Gravitational Waves (GWs), referred to as Scalar-Induced Gravitational Waves (SIGWs). In this study, we investigate the production of SIGWs during the preheating phase for a class of inflationary models known as $\alpha$-attractors, characterized by a single parameter $\alpha$. We focus on small values of this parameter, specifically $\alpha \sim O(10^{-1} - 10^{-4})$, where the self-resonance effect is particularly pronounced. We obtain lower bounds on this parameter, $\log_{10}(\alpha)>-3.54$ for the T-model and $\log_{10}(\alpha)>-3.17$ for the E-model, based on the energy density of SIGWs constrained by Big Bang nucleosynthesis, which ultimately translates into lower bounds on the tensor-to-scalar ratio, $r>9.61\times10^{-7}$ for the T-model and $r>2.25\times10^{-6}$ for the E-model.

Accretion and outflows are astrophysical phenomena observed across a wide range of objects, from white dwarfs to supermassive black holes. Developing a complete picture of these processes requires complementary studies across this full spectrum of jet-launching sources. Jet-interstellar medium (ISM) interaction sites near black hole X-ray binaries provide unique laboratories to study jet energetics. This work aims to detect and characterise the bow shock near one black hole X-ray binary, Cyg X-1, and then use this bow shock structure to parametrise the properties of the jet launched by Cyg X-1 over its lifetime. We used the MeerKAT radio telescope to investigate the bow shock structure formed by the interaction between the jets of Cyg X-1 and the ISM. We successfully detect the bow shock north of Cyg X-1 in the L and S bands and report its size and brightness. We present the spectral index distribution across the bow shock, which is in the range -0.9 to 0.4, with an error distribution (0.6 to 1.5) that peaks at unity. We determine that the unshocked ISM density is 6-7 cm^-3 for a temperature range of 10^4 to 3*10^6 K. This temperature range suggests that the velocity of the bow shock is 21 km/s to 364 km/s. The age of the Cyg X-1 jet responsible for the bow shock is 0.04 to 0.3 Myr, and the power of the jet is constrained to 2*10^31 ergs/s to 10^35 ergs/s. We also detect new morphological features of the bow shock in the S-band image. The comparison of archival H_alpha maps with the new radio observations hints at different regions of emission, different temperature ranges, and different ISM densities. The spectral index suggests a consistent emission origin across the structure. The ISM density around Cyg X-1 is on the higher end for Galactic environments, and our results indicate a lower jet energy transport rate than prior estimates.

We investigate a quintessence axion model for dynamical dark energy, motivated in part by recent results from the Baryon Acoustic Oscillation (BAO) measurements of the Dark Energy Spectroscopic Instrument (DESI) and the Cosmic Microwave Background (CMB) observations from the Atacama Cosmology Telescope (ACT). By carefully treating the initial conditions and parameter sampling, we identify a preferred parameter space featuring a sub-Planckian axion decay constant and a relatively large axion mass, which naturally avoids the quality problem and remains consistent with the perturbative string conjecture. Our parameter scan also uncovers a trans-Planckian regime of theoretical interest, which is only mildly disfavored by observations. The results remain robust when DESI BAO data are combined with CMB and supernova observations. Finally, we discuss the possible connection between this model and the recently reported non-zero rotation of the CMB linear polarization angle, emphasizing the broader cosmological implications and the promising prospects for testing this scenario. We show that an $\mathcal{O}(1)$ electromagnetic anomaly coefficient is preferred by the strongest constraint, which is in full agreement with the minimal quintessence axion model.

Hot dust-obscured galaxies (Hot DOGs), the most infrared (IR) luminous objects selected by the WISE all-sky mid-IR survey, have yielded a sample of intrinsically luminous quasars (QSOs) with obscured nuclear activity and hot dust temperatures. The molecular gas excitation properties have yet to be examined in detail under such extreme conditions. Here we study the most far-IR luminous WISE Hot DOG W2246-0526, focusing on the central host galaxy. Multi-J CO transition measurements at J=2-1, 5-4, 7-6, 12-11, and 17-16 provide the most well-sampled CO excitation ladder of any WISE Hot DOG to date, providing the first self-consistent modeling constraints on the molecular gas and dust properties. We implement a state-of-the-art TUrbulent Non-Equilibrium Radiative transfer model (TUNER) that simultaneously models both the line and dust continuum measurements. Due to a combination of high molecular gas densities and high kinetic temperatures, this extreme CO spectral line energy distribution peaks at J = 10 to 12, likely making this the most highly excited galaxy ever reported. We derive the alpha_CO conversion factors and conclude that (J=3-7) CO line luminosities trace the bulk of the molecular gas mass. W2246-0526 is a rapidly evolving system, with a high value of the molecular gas kinetic temperature versus dust temperature T_k / T_d ~ 3.9, reflecting previously reported shocks and outflows injecting kinetic energy within the central kpc of this host. This first comprehensive simultaneous modeling of both the molecular gas and dust in any object within the WISE-selected Hot DOG sample motivates obtaining well-sampled dust and line spectral energy distributions to better understand the conditions within these short-lived episodes in galaxy evolution that are associated with the most obscured supermassive black hole activity.

Eccentric cavities in circumbinary disks precess on timescales much longer than the binary orbital period. These long-lived steady states can be understood as trapped modes in an effective potential primarily determined by the binary quadrupole and the inner-disk pressure support, with associated frequencies $\omega_Q$ and $\omega_P$. Within this framework, we show that the ratio $\omega_P/\omega_Q$ is the main parameter determining the mode spectrum, and obtain a thorough understanding of it by systematically solving this problem with various degrees of sophistication. We first find analytical solutions for truncated power-law disks and use this insight in disks with smooth central cavities. Our main findings are: (i) The number of modes increases for thinner disks and more-equal-mass binaries. (ii) For 2D disks, the normalized ground-mode frequency, $\omega_0/(\omega_Q+\omega_P)$, decreases monotonically with the ratio $\omega_P/\omega_Q$. (iii) For thin disks, $\omega_P\ll\omega_Q$, the ground-mode frequency coincides with the maximum of the effective potential, which tracks the gravitational quadrupole frequency inside the inner-disk cavity, and is thus rather sensitive to the density profile of the cavity, where these modes are localized. (iv) For thick disks, $\omega_P\gg\omega_Q$, increasing pressure support anchors the peak of the effective potential at the inner cavity radius as the ground-mode extends farther out and its frequency decreases. (v) In agreement with numerical simulations, with $\omega_P/\omega_Q \simeq 0.1$, we find that disk precession is rather insensitive to the density profile and ground-mode frequencies for 3D disks are about half the value for 2D disks.

The Lyman-alpha (Ly{\alpha};1216 Å) line is the brightest emission line in the quiescent solar spectrum and radiates a significant fraction of the available nonthermal energy during flares. Despite its importance, there is a lack of detailed studies of Ly{\alpha} spectral variability during flares. Recently, spectrally resolved Ly{\alpha} flare observations from the SORCE/SOLSTICE instrument have become available. This study examines Ly{\alpha} spectral variability and its relationship with HXR emission from nonthermal electrons, using observations of two M-class flares from SORCE/SOLSTICE and RHESSI. Imaging observations from STEREO/SECCHI EUVI and SDO/AIA provide further context. Enhancements across the Ly{\alpha} line profile were found to closely correlate with bursts of HXR emission, suggesting a primarily nonthermal origin. Red enhancement asymmetries at the peak of each flare were attributed to chromospheric evaporation, while blue wing enhancement and blue asymmetry were linked to a bright filament-eruption seen in SDO/AIA 1600 Å images. These findings contribute to the understanding of spectral Ly{\alpha} variability during flares and highlight the need for future studies using a higher quality and quantity of spectral Ly{\alpha} flare observations. Such studies will further characterise the physical mechanisms driving Ly{\alpha} flare variability.

Cosmic inflation may exhibit stochastic periods during which quantum fluctuations dominate over the semi-classical evolution. Extracting observables in these regimes is a notoriously difficult program as quantum randomness makes them fully probabilistic. However, among all the possible quantum histories, the ones which are relevant for Cosmology are conditioned by the requirement that stochastic inflation ended. From an observational point of view, it would be more convenient to model stochastic periods as starting from the time at which they ended and evolving backwards in times. We present a time-reversed approach to stochastic inflation, based on a reverse Fokker-Planck equation, which allows us to derive non-perturbatively the probability distribution of the field values at a given time before the end of the quantum regime. As a motivated example, we solve the flat semi-infinite potential and derive a new and exact formula for the probability distribution of the quantum-generated curvature fluctuations. It is normalisable while exhibiting tails slowly decaying as a Levy distribution. Our reverse-time stochastic formalism could be applied to any inflationary potentials and quantum diffusion eras, including the ones that can lead to the formation of primordial black holes.

We have created a large database of similarity information between sub-regions of Hubble Space Telescope images. These data can be used to assess the accuracy of image search algorithms based on computer vision methods. The images were compared by humans in a citizen science project, where they were asked to select similar images from a comparison sample. We utilized the Amazon Mechanical Turk system to pay our reviewers a fair wage for their work. Nearly 850,000 comparison measurements have been analyzed to construct a similarity distance matrix between all the pairs of images. We describe the algorithm used to extract a robust distance matrix from the (sometimes noisy) user reviews. The results are very impressive: the data capture similarity between images based on morphology, texture, and other details that are sometimes difficult even to describe in words (e.g., dusty absorption bands with sharp edges). The collective visual wisdom of our citizen scientists matches the accuracy of the trained eye, with even subtle differences among images faithfully reflected in the distances.

We present the first extensive seismic modelling of SX Phe stars in the stellar system $\omega$ Cen. First, using the new values of reddening $E(B-V)$ and distance modulus $(m-M)_V$, and bolometric corrections from Kurucz model atmospheres, we determine the effective temperatures and luminosities of all SX Phe variables in $\omega$ Cen with available $(B-V)$ colours. Next, we carefully select SX Phe stars that have a frequency ratio strongly suggesting excitation of two radial modes, and, in addition, their preliminary pulsational models have the values of $(T_{\rm eff},~ L)$ consistent with observational determinations. For five double-mode radial pulsators, we perform an extensive seismic modeling using the Bayesian analysis based on Monte Carlo simulations. We study the effect of opacity tables and helium abundance. With the OPAL data and $Y=0.30$, we obtained masses in the range (1.0,~1.2) M$_{\odot}$, metallicity $Z\in(0.0007,~0.0029)$ and the age of about (1.9,~3.8) Gyr. The OP and OPLIB seismic models have always higher metallicites, sometimes outside the allowed range for $\omega$ Cen. In the case of three stars, we find seismic models within the observed range of $(T_{\rm eff},~L)$ with all three opacity tables. In the case of two stars, with the highest metallicity, seismic models computed with the OP and OPLIB tables are located far outside the observed error box. The OPAL seismic models follow the age$-$metallicity relation known for $\omega$ Cen from the literature.

In the third-generation (3G) gravitational-wave (GW) detector era, GW multi-messenger observations for binary neutron star merger events can exert great impacts on exploring the cosmic expansion history. Extending the previous work, we explore the potential of 3G GW standard siren observations in cosmological parameter estimation by considering their associated electromagnetic (EM) counterparts, including $\gamma$-ray burst (GRB) coincidence observations by the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor and GW-triggered target-of-opportunity observations of kilonovae by different optical survey projects. During an assumed 10-year observation, we predict that the number of detectable GW-kilonova events is $\sim 4900$ with redshifts below $\sim 0.4$ under GW network and Large Synoptic Survey Telescope in the $i$ band, which is three times more than that of GW-GRB detections. For the cosmological analysis, we find that with the inclusion of GW-kilonova detections, the constraints on cosmological parameters from GW-EM detections are significantly improved compared to those from GW-GRB detections. In particular, GW-EM detections can tightly constrain the Hubble constant with a precision ranging from $0.076\%$ to $0.034\%$. Moreover, GW multi-messenger observations could effectively break the cosmological parameter degeneracies generated by the mainstream EM observations, CMB+BAO+SN (CBS). The combination of CBS and GW-EM can tightly constrain the equation of state parameters of dark energy $w$ in the $w$CDM model and $w_0$ in the $w_0w_a$CDM model with precisions of $0.72\%$ and $0.99\%$, respectively, meeting the standard of precision cosmology. In conclusion, GW multi-messenger observations could play a crucial role in helping solve the Hubble tension and probing the fundamental nature of dark energy.

Adjacent type-I and -II proton superconductors in a rotation-powered pulsar are predicted to exist in a metastable state containing macroscopic and quantized flux tubes, respectively. Previous studies show that the type-I and -II regions are coupled magnetically, when macroscopic flux tubes divide dendritically into quantized flux tubes near the type-I-II interface, through a process known as flux branching. The studies assume that the normal-superconducting boundary is sharp, and the quantized flux tubes do not repel mutually. Here the sharp-interface approximation is refined by accounting for magnetic repulsion. It is found that flux tubes in the same flux tree cluster with a minimum-energy separation two to seven times less than that of isolated flux tubes. Neutron vortices pin and cluster about flux trees. We find that the maximum characteristic wave strain $h_0$ of the current quadrupole gravitational radiation emitted by a rectilinear array of clustered vortices exceeds by $(1+N_{\rm v,t})^{1/2}$ the strain $h_0 \sim 10^{-32}(f/30 {\rm Hz})^{5/2} (D/1 {\rm kpc})^{-1}$ emitted by uniformly distributed vortices, where $N_{\rm v,t}$ is the mean number of pinned vortices per flux tree, $f$ is the star's spin frequency, and $D$ is the star's distance from Earth. The factor $(1 + N_{\rm v,t})^{1/2}$ brings $h_0$ close to the sensitivity limit of the current generation of interferometric gravitational wave detectors under certain circumstances, specifically when flux branching forms relatively few (and hence relatively large) flux trees.

We consider, in the context of axion-inflation, the \textit{Pure Natural Inflation} (PNI) model coupled with an SU(2) gauge sector via a Chern-Simons term. As the axion rolls down its potential, it dissipates energy in the gauge sector thus sourcing fluctuations of scalar and tensor degrees of freedom therein. Gauge field fluctuations will, in turn, feed primordial gravitational waves as well as curvature perturbations. Remarkably, we can use upcoming cosmological probes to test this mechanism across a vast range of scales, from the CMB to laser interferometers. Due to their flat plateau at large field values, we find that PNI potentials fare better vis-á-vis CMB observations than the conventional sinusoidal potential of chromo-natural inflation (CNI). We show that, even when the dynamics begin in the weak backreaction regime, the rolling of the axion leads to a build-up of the gauge-quanta production, invariably triggering the strong backreaction of the gauge sector tensors on the background dynamics. This transition results in the copious production of both scalar and tensor perturbations, which we study in detail. The gravitational wave signatures include a rich peak structure with a characteristic scale-dependent chirality, a compelling target for future gravitational wave detectors. Additionally, the peak in scalar perturbations may lead to the formation of primordial black holes, potentially accounting for a significant fraction of the observed dark matter abundance.

We present WI2easy, a Mathematica package for high-precision analysis of warm inflation (WI) dynamics, enabling efficient computation of both background evolution and curvature perturbations. Designed with a user-friendly interface, the tool supports a broad spectrum of inflaton potentials--including large-field, small-field, and hybrid models--and accommodates arbitrary dissipation coefficients dependent on temperature, field amplitude, or both, encompassing canonical forms prevalent in WI studies. Users can define custom models through intuitive commands, generating full dynamical trajectories and perturbation spectra in a streamlined workflow. This facilitates rapid confrontation of theoretical predictions with observational constraints, empowering systematic exploration of WI parameter spaces. WI2easy bridges the gap between theoretical models and observational cosmology, offering a robust, adaptable framework for next-generation inflationary analyses.

We introduce a new 1D stellar spectral synthesis Python code called \stardis. \stardis\ is a modular, open-source radiative transfer code that is capable of spectral synthesis from near-UV to IR for FGK stars. We describe the structure, inputs, features, underlying physics, and assumptions of \stardis\ as well as the radiative transfer scheme implemented. To validate our code, we show spectral comparisons between \stardis\ and \textsc{korg} with the same input atmospheric structure models, and also compare qualitatively to \textsc{phoenix} for solar models. We find that \stardis\ generally agrees well with \textsc{korg} for solar models on the few percent level or better, that the codes can diverge in the ultraviolet, with more extreme differences in cooler stars. \stardis\ can be found at \href{this https URL}{this https URL}, and documentation can be found at \href{this https URL}{this https URL}.

Mass loss through stellar winds governs the evolution of stars on the asymptotic giant branch (AGB). In the case of carbon-rich AGB stars, the wind is believed to be driven by radiation pressure on amorphous carbon (amC) dust forming in the atmosphere. The choice of dust optical data will have a significant impact on atmosphere and wind models of AGB stars. We compare two commonly used optical data sets of amC and investigate how the wind characteristics and photometric properties resulting from dynamical models of carbon-rich AGB stars are influenced by the micro-physical properties of dust grains. We computed two extensive grids of carbon star atmosphere and wind models with the DARWIN 1D radiation-hydrodynamical code. Each of the two grids uses a different amC optical data set. The stellar parameters of the models were varied to cover a wide range of possible combinations. A posteriori radiative transfer calculations were performed for a sub-set of the models, resulting in photometric fluxes and colours. We find small, but systematic differences in the predicted mass-loss rates for the two grids. The grain sizes and photometric properties are affected by the different dust optical data sets. Higher absorption efficiency leads to the formation of a greater number of grains, which are smaller. Models that are obscured by dust exhibit differences in terms of the covered colour range compared to observations, depending on the dust optical data used. An important motivation for this study was to investigate how strongly the predicted mass-loss rates depend on the choice of dust optical data, as these mass-loss values are more frequently used in stellar evolution models. Based on the current results, we conclude that mass-loss rates may typically differ by about a factor of two for DARWIN models of C-type AGB stars for commonly used dust optical data sets.

Quasar pair, a special subclass of galaxy pair, is valuable in the investigation of quasar interaction, co-evolution, merger, and clustering, as well as the formation and evolution of galaxies and supermassive black holes. However, quasar pairs at kpc-scale are rare in the universe. The scarcity of available samples hindered the deeper exploration and statistics of these objects. In this work, we apply an astrometric method to systematically search for quasar candidates within a transverse distance of 100 kpc to known quasars in the Million Quasar Catalog. These candidates are ${\it Gaia}$ sources with zero proper motion and zero parallax, which are the kinematic characteristics of extragalactic sources. Visual inspection of the sample was performed to remove the contamination of dense stellar fields and nearby galaxies. A total of 4,062 quasar pair candidates were isolated, with the median member separation, ${\it Gaia}$ G-band magnitude, and redshift of 8.81$^{\prime\prime}$, 20.49, and 1.59, respectively. Our catalog was compared with three major candidate quasar pair catalogs and identified 3,964 new quasar pair candidates previously uncataloged in the three catalogs. Extensive spectroscopic follow-up campaigns are being carried out to validate their astrophysical nature. Several interesting quasar pair candidates are highlighted and discussed. We also briefly discussed several techniques for improving the success rate of quasar pair selection.

Precision observations of orbital systems have recently emerged as a promising new means of detecting gravitational waves and ultra-light dark matter, offering sensitivity in new regimes with significant discovery potential. These searches rely critically on precise modeling of the dynamical effects of these signals on the observed system; however, previous analyses have mainly only relied on the secularly-averaged part of the response. We introduce here a fundamentally different approach that allows for a fully time-resolved description of the effects of oscillatory metric perturbations on orbital dynamics. We find that gravitational waves and ultra-light dark matter can induce large oscillations in the orbital parameters of realistic binaries, enhancing the sensitivity to such signals by orders of magnitude compared to previous estimates.

Dark matter (DM) candidates with very small masses, and correspondingly large number densities, have gained significant interest in recent years. These DM candidates are typically said to behave "classically". More specifically, they are often assumed to reside in an ensemble of coherent states. One notable exception to this scenario is when isocurvature fluctuations of the DM are produced during inflation (or more generally by any Bogoliubov transformation). In such contexts, the ultralight DM instead resides in a squeezed state. In this work, we demonstrate that these two scenarios can be distinguished via the statistics of the DM density fluctuations, such as the matter power spectrum and bispectrum. This provides a probe of the DM state which persists in the limit of large particle number and does not rely on any non-gravitational interactions of the DM. Importantly, the statistics of these two states differ when the modes of the squeezed state are all in-phase, as is the case at the end of inflation. Later cosmological dynamics may affect this configuration. Our work motivates future numerical studies of how cosmological dynamics may impact the initial squeezed state and the statistics of its density fluctuations.

Detection of sub-GeV dark matter (DM) particles in direct detection experiments is inherently difficult, as their low kinetic energies in the galactic halo are insufficient to produce observable recoils of the heavy nuclei in the detectors. On the other hand, whenever DM particles interact with nucleons, they can be accelerated by scattering with galactic cosmic rays. These cosmic-ray-boosted DM particles can then interact not only through coherent elastic scattering with nuclei, but also through scattering with individual nucleons in the detectors and produce outgoing particles at MeV to GeV kinetic energies. The resulting signal spectrum overlaps with the detection capabilities of modern neutrino experiments. One future experiment is the Deep Underground Neutrino Experiment (DUNE) at the Sanford Underground Research Facility. Our study shows that DUNE has a unique ability to search for cosmic-ray boosted DM with sensitivity comparable to dedicated direct detection experiments in the case of spin-independent interactions. Importantly, DUNE's sensitivity reaches similar values of DM-nucleon cross sections also in the case of spin-dependent interactions, offering a key advantage over traditional direct detection experiments.

The ringdown phase of a binary black-hole merger encodes key information about the remnant properties and provides a direct probe of the strong-field regime of General Relativity. While quasi-normal mode frequencies and damping times are well understood within black-hole perturbation theory, their excitation amplitudes remain challenging to model, as they depend on the merger phase. The complexity increases for precessing black-hole binaries, where multiple emission modes can contribute comparably to the ringdown. In this paper, we investigate the phenomenology of precessing binary black hole ringdowns using the SXS numerical relativity simulations catalog. Precession significantly impacts the ringdown excitation amplitudes and the related mode hierarchy. Using Gaussian process regression, we construct the first fits for the ringdown amplitudes of the most relevant modes in precessing systems.

Searches for neutrino isocurvature usually constrain a specific linear combination of isocurvature perturbations. In this work, we discuss realistic cosmological scenarios giving rise to neutrino isocurvature. We show that in general both, neutrino and matter isocurvature perturbations are generated, whose ratio we parameterize by a newly introduced mixing angle. We obtain the first limits on this new mixing angle from PLANCK data, and discuss novel insights into the early Universe that could be provided by future measurements.

Satellite-based estimates of greenhouse gas (GHG) properties from observations of reflected solar spectra are integral for understanding and monitoring complex terrestrial systems and their impact on the carbon cycle due to their near global coverage. Known as retrieval, making GHG concentration estimations from these observations is a non-linear Bayesian inverse problem, which is operationally solved using a computationally expensive algorithm called Optimal Estimation (OE), providing a Gaussian approximation to a non-Gaussian posterior. This leads to issues in solver algorithm convergence, and to unrealistically confident uncertainty estimates for the retrieved quantities. Upcoming satellite missions will provide orders of magnitude more data than the current constellation of GHG observers. Development of fast and accurate retrieval algorithms with robust uncertainty quantification is critical. Doing so stands to provide substantial climate impact of moving towards the goal of near continuous real-time global monitoring of carbon sources and sinks which is essential for policy making. To achieve this goal, we propose a diffusion-based approach to flexibly retrieve a Gaussian or non-Gaussian posterior, for NASA's Orbiting Carbon Observatory-2 spectrometer, while providing a substantial computational speed-up over the current operational state-of-the-art.

It is well known that the event horizon of the de Sitter universe can produce particles, and one can get sizable Hawking radiation by considering inflationary phases as de Sitter spacetimes with large Hubble rates. In this compact paper, we consider the graviton emission part of these radiations and assume that these graviton signals can exist in the current universe in the form of gravitational waves. We predict an energy density parameter of $\log_{10}(\Omega_{\rm GW} h^2) \sim \mathscr{O}(-25) - \mathscr{O}(-30)$ and its associated peak frequency $\log_{10}(f_{\rm peak}^0) \sim \mathscr{O}(6)-\mathscr{O}(5)$, depending on the reheating temperature. These signals occupy a frequency band below the ultrahigh-frequency regime and possess a detectable energy density, offering a promising target for future gravitational wave observatories. We believe that the detection of such signals would provide a compelling test of Hawking's radiation theory in a cosmological context.

Recent results have shown that singularities can be avoided from the general relativistic standpoint in Lorentzian-Euclidean black holes by means of the transition from a Lorentzian to an Euclidean region where time loses its physical meaning and becomes imaginary. This dynamical mechanism, dubbed ``atemporality'', prevents the emergence of black hole singularities and the violation of conservation laws. In this paper, the notion of atemporality together with a detailed discussion of its implications is presented from a philosophical perspective. The main result consists in showing that atemporality is naturally related to conservation laws.

Gravitational-wave data from advanced-era interferometric detectors consists of background Gaussian noise, frequent transient artefacts, and rare astrophysical signals. Multiple search algorithms exist to detect the signals from compact binary coalescences, but their varying performance complicates interpretation. We present a machine learning-driven approach that combines results from individual pipelines and utilises conformal prediction to provide robust, calibrated uncertainty quantification. Using simulations, we demonstrate improved detection efficiency and apply our model to GWTC-3, enhancing confidence in multi-pipeline detections, such as the sub-threshold binary neutron star candidate GW200311_103121.

As part of the collaboration building a set of detectors for the new collider, our group was tasked with designing and building a large-scale cosmic ray detector, which was to complement the capabilities of the MPD (Dubna) detec-tor set. The detector was planned as a trigger for cosmic ray particles and to be used to calibrate and test other systems. Additional functions were to be the detection of pairs of high-energy muons originating from some parti-cle decay processes generated during collisions and con-tinuous observation of the cosmic muon stream in order to detect multi muons events. From the very beginning, the detector was designed as a scalable and universal device for many applications. The following work will present the basic features and parameters of the Modular COsmic Ray Detector (MCORD) and examples of its possible use in high energy physics, astrophysics and geology. Thanks to its universal nature, MCORD can be potential used as a fast trigger, neutron veto detector, muon detector and as a tool in muon tomography.