Papers

We constrain the $z \approx 1$ HI distribution by jointly modeling two independent, existing observations of the 21-cm signal, the HI density parameter $\Omega_{\rm HI}$ measured using uGMRT by stacking the 21-cm emission from blue, star-forming galaxies, and the 21-cm autocorrelation power spectrum (PS) measured using CHIME. We assign HI to the dark matter halos in a cosmological simulation using an HI mass-halo mass (HIHM) relation with three free parameters whose values we estimate by performing a joint Bayesian inference comparing the simulated $\Omega_{\rm HI}$ and 21-cm PS with the measurements. We use the inferred HIHM posterior to simulate the HI distribution and predict the $z \approx 1$ HI mass function (HIMF). We find that the HIMF remains nearly constant at low HI masses $( \lesssim 3.6 \times 10^9 M_\odot)$, and it declines rapidly for larger HI masses. Around $\sim 90$ percent of the total HI gas is contained in the mass range $M_{\rm HI} \in [2 \times 10^9, \, 4 \times 10^{11}] \, M_\odot$. Our estimates predict a larger abundance of high mass HI galaxies than predicted by earlier observations and hydrodynamical simulations. We expect these results to be useful in understanding galaxy evolution and star formation.

The radio halo in the cool-core galaxy cluster, A1795, has recently been proposed to be of hadronic origin, because it extends on megaparsec scales, where no turbulence is expected to be injected into a relaxed cluster. In this paper we aim to constrain the properties of nonthermal protons and the cluster magnetic field strength under the hypothesis of a hadronic origin for the radio halo in the light of the available gamma-ray upper limits for this cluster. We assumed a radial profile and several central magnetic field intensity values, then derived the corresponding properties of the nonthermal protons necessary to reproduce the flux density and surface brightness profile of the radio halo. For the obtained results, we calculated the corresponding gamma-ray emission and compared it with the Fermi-LAT upper limit. We find that, for a magnetic field energy radial profile following that of the thermal gas, central magnetic field intensities $B_0<5\,\mu$G imply a gamma-ray emission at or above the Fermi-LAT upper limit. Therefore, larger values of the magnetic field are necessary in the hadronic scenario. For these values the radial profile of nonthermal protons must slightly decrease with radius, though more slowly than that of the thermal gas. For smaller values of the magnetic field, different mechanisms for producing or accelerating the nonthermal electrons are necessary.

Massive stars have a major impact on their environment in their host galaxy. Observational determinations of their physical parameters are required to better constrain evolutionary models. In this context, the binary system WR 25 whose dominant spectral type is that of a nitrogen sequence Wolf-Rayet star, is of particular interest. It exhibits the highest known hydrogen content among the Milky Way Wolf-Rayet stars, as well as additional absorption lines. It is most probably an object still on the main-sequence or close to leaving it. We acquired new high-resolution spectra of this extremely interesting object. We present an improved version of the SB1 orbital solution for the motion of the WN component. We confirm the detection of the previously reported probable O companion and definitively prove that it is indeed gravitationally bound to the WN star. A first SB2 solution is presented, and a mass-ratio WN/O of 2.02 +/- 0.36 is derived. Following a spectral disentangling procedure, we identify the companion as an O5(f^+) star belonging to either the main-sequence (V) or giant (III) luminosity classes. The spectral type of the companion, together with the above-mentioned mass ratio, points to a very massive primary WN star of at least 55 solar masses. This confirms that WR 25 belongs to the family of very massive WNLh objects, a very poorly populated class in the Milky Way. We demonstrate that the absorption component in the P-Cygni profile of the He II lambda 4859 line of WR 25 is mainly due to the O-type companion, and we propose to adopt a WN6ha spectral type for the WN component of the system. On the basis of the extracted disentangled spectra, we derive approximate physical parameters through a detailed CMFGEN analysis, given the difficulty in constraining both the extinction towards WR 25 and the definitive brightness ratio between the components.

Higher-order Laguerre-Gaussian (LG) modes have broader and more uniform transverse intensity distributions than the fundamental Gaussian mode, making them attractive for precision optical applications. In gravitational-wave detectors, their enhanced spatial averaging of thermally driven test-mass fluctuations can reduce thermal noise. Their implementation, however, requires efficient coupling of the injected beam to the target cavity eigenmode. Residual misalignment and mode mismatch couple power out of the desired mode, reducing intracavity power buildup and degrading detector sensitivity. Here, we analytically and numerically evaluate the coupling loss induced by misalignment and mode mismatch for a generic $\mathrm{LG}_{p,\ell}$ beam. We show that the leading-order loss due to angular or lateral misalignment scales as $2p+|\ell|+1$, whereas that due to waist size or waist position mismatch scales as $2p^2+2p+(2p+1)|\ell|+1$. Although sensitivity to imperfect coupling generally increases with mode order, the donut-shaped $\mathrm{LG}_{0,\ell}$ family exhibits favorable mode mismatch scaling: its loss factor reduces to $|\ell|+1$ and therefore increases only linearly with the azimuthal index. This robustness, together with their broad intensity profiles and central dark regions that permit selective mirror masking, provides additional practical motivation for using $\mathrm{LG}_{0,\ell}$ modes in precision interferometers, including gravitational-wave detectors.

The origin of black hole entropy remains one of the deepest mysteries in modern physics. Two recent developments offer complementary perspectives on this puzzle: the entropy release from regular Schwarzschild black holes with a de Sitter core (the OCK construction), and the local thermodynamics of the de Sitter vacuum (Volovik). In the OCK framework, the inner horizon carries positive Bekenstein-Hawking entropy $S_{\rm inner}=\pi h_c^2$ that is gradually released as the core shrinks, until a classical Minkowski breaking obstructs the evolution at $n=0$. In Volovik's framework, the total entropy of a homogeneous de Sitter region is $S_{\rm dS}= \operatorname{sgn}(H)\,\pi/H^{2} = \operatorname{sgn}(H)\,A/4$: expanding de Sitter ($H>0$) carries positive entropy, while contracting de Sitter ($H<0$) carries negative entropy. We show that the sign of the Hubble parameter is the unifying element linking the two pictures. The OCK core is de~Sitter only for $n>2$; the Minkowski breaking is a classical kinematic obstruction, not a dynamical transition to a contracting de Sitter phase. Any connection between the expanding and contracting regimes would require a quantum mechanism that remains speculative. Nevertheless, both frameworks embody the same thermodynamic principle, the shrinking of the interior drives the system toward increased total entropy, and together they provide a consistent picture of entropy flow during gravitational collapse. The integer nature of the OCK parameter suggests a quantized entropy spectrum and a statistical interpretation of black hole entropy, while the generalized second law is satisfied in both frameworks, and in the speculated quantum connection provided the environmental entropy is properly accounted for.

The Magnusian is a phase-space function that generates finite-time evolution through nested Poisson brackets. It is related to several familiar generators of classical dynamics, including the radial action, the eikonal phase and related quantities. In this work, we extend the Magnusian framework to systems with dissipation and nonlocal-in-time interactions using the in-in formalism, also known as the Schwinger-Keldysh or Galley formalism. This framework is particularly natural for binary dynamics, where integrating out the mediating gravitational field can produce both dissipative radiation-reaction effects and hereditary, nonlocal-in-time interactions. We derive the generalized Magnusian and show that it continues to generate finite-time evolution. As an application, we construct the Magnusian for Newtonian bound motion subject to the leading 2.5PN radiation-reaction force. The resulting generator defines a discrete evolution map from one cycle to the next and describes the evolution of the system in agreement with numerical solutions.

The blazar PKS 0346-27 at redshift z=0.991 is among the most distant extragalactic sources detected in very high energy gamma-rays. It underwent a major flare reaching TeV energies in November 2021. Recent modelling of its spectral energy distribution favoured a single-zone proton–synchrotron-dominated hadronic model with bulk Lorentz factor Gamma=10 over a single-zone leptonic jet model with much higher Gamma. Here we analyse archival radio data to give independent estimates of the jet bulk Lorentz factor. We present high-resolution radio imaging and brightness distribution modelling, as well as flare detection in long-term radio flux density monitoring data, and obtain Gamma<~10 values. This lends support to the hadronic model proposed for the PKS 0346-27 jet. Our results highlight the importance of long-term, very long baseline interferometry and total flux density monitoring in studying blazar jets.

Colliding winds in massive-star binaries generate non-thermal radio emission and an increased X-ray emission. We study the radio emission of the non-thermal emitter 9 Sgr, which is a long-period and highly eccentric binary. We conducted a monitoring campaign of 9 Sgr around its 2013 - 2014 periastron passage, obtaining radio, X-ray and optical spectroscopy data. In this paper, we analyse the radio data. The radio data at 3.6, 6 and 20 cm show a maximum near periastron. Other non-thermal radio emitters among O-type binaries have a minimum flux near periastron, because the synchrotron emission is absorbed by the free-free absorption in the two stellar winds. This is not the case for 9 Sgr, because even at periastron the orbital separation is sufficient to maintain the wind-wind collision and its associated synchrotron emission outside the effective free-free radius of both stars. Our standard modelling with a local magnetic field that decreases inversely proportional to the distance from the stars (1/r) fails to explain the observed fluxes. Instead, we need to adopt a local magnetic field that decreases faster than 1/r. While our model provides an acceptably good fit to the data, there is clearly still room for improvement. More advanced modelling should include magnetohydrodynamics and more detailed physics of the injection, acceleration and cooling of the relativistic electrons. Radio observations at orbital phases away from periastron can put further constraints on the models.

The Planck all-sky surveys at (sub)millimeter wavelengths enable us to accurately determine the corresponding local luminosity functions up to the highest luminosities. The detected galaxies are strictly local, so evolutionary effects, which are known to be particularly strong at these wavelengths, are not a problem. However, previous studies have so far relied only on the Planck Early Release Compact Source Catalog (ERCSC) for this purpose. Another important improvement over earlier estimates is the availability of complete all-sky catalogs of galaxies within hundreds of megaparsecs, with redshift-independent distances for nearby objects, for which redshifts are not reliable distance estimators. In this paper we re-estimate the (sub)millimeter local luminosity functions using data from the Second Planck Catalog of Compact Sources, which supersedes the previously used ERCSC and contains far more sources and more accurate photometry. We computed the luminosity functions using both the classical $1/V_{\rm max}$ and the nonparametric kernel density estimation (KDE) method, which overcomes limitations of binning techniques. Our implementation of the KDE uses the $1/V_{\max}$ weighting to account for survey selection effects. We obtain Planck-based local luminosity functions at 857, 545, 353, and 217 GHz, as well as the total IR luminosity function and the dust mass function. We find significant differences from earlier estimates and discuss their possible origins.

Young M-type stars exhibit frequent flares, which would seriously impact their habitable planets. Since stellar surfaces cannot be resolved, flare locations remain unknown. Here, by using the Mg I b emission line in LAMOST spectra, the location of a stellar flare from a young M dwarf is pinpointed at $ (-123.0^{+8.0}_{-5.8}, 80.5^{+2.9}_{-3.2})$ in degree in the polar region. Our method can be used to accurately locate stellar flares. This would enable us to assess the impact of stellar flares on planets more accurately and improve our understanding of stellar dynamo models.

Accurate measurements of interstellar dust mass are key to answering several astrophysical questions. A common method of obtaining the mass is to fit the far-infrared thermal emission of the dust with a modified blackbody model; however, this method is subject to several systematics. In particular, how temperature-dependent dust optical properties affect fit results has received little attention. We provide the first quantification of this effect based on experimental measurements of optical properties from the scientific literature. We created a grid of synthetic observations for variable-opacity dust and fitted it with a modified blackbody model; the difference between the input properties of synthetic observations and the values derived from the fit provides a measure of the bias induced by the temperature dependence. We find that fixing the value of the opacity power law index $\beta$ introduces a temperature-dependent bias on the fit, while keeping $\beta$ as a free parameter introduces a bias that depends mainly on the wavelength range used. For instance, depending on the properties of the observed object and on the choice of fit procedure, temperature dependence alone can induce an overestimate of 25-60% in dust masses at high redshift ($z \sim 8$). Our findings highlight the limitations of power laws as opacity models.

Relativistic particle beams propagating through dense ambient plasmas are susceptible to streaming instabilities that can govern the system dynamics in various astrophysical and laboratory settings. For an unmagnetized, collisionless plasma pervaded by a dilute, cold relativistic beam, the dominant instabilities are the quasielectrostatic, oblique two-stream (OTSI) and the essentially magnetic, current filamentation instability (CFI). While their linear and nonlinear properties have been researched for decades, most treatments assume unbounded, uniform systems and thus predict purely temporal instability growth. This assumption, however, is questionable for realistic configurations where a bounded beam continuously encounters fresh plasma. This feature causes instabilities to grow in a spatiotemporal manner. Whereas spatiotemporal perturbative treatments of streaming instabilities were derived as early as the 1960s, only recently have the spatiotemporal regimes of OTSI and CFI been addressed theoretically. Yet these models are restricted to a specific instability class, and hence cannot describe the competition between spatiotemporal OTSI and CFI. In this work, we present a unified, fully electromagnetic quasi-static model of all unstable modes arising throughout the beam. By not adopting the slowly varying envelope approximation (SVEA), we find that a previously unreported spatiotemporal CFI actually prevails near the front, precisely where the SVEA fails, and is only superseded by OTSI further back in the beam. Furthermore, we demonstrate that our model also captures the growth of the self-modulation and hosing instabilities excited by long, narrow beams. Comparisons with particle-in-cell simulations confirm the validity of the quasistatic approach for modeling streaming plasma instabilities triggered by relativistic dilute beams.

We present the first scientific results delivered by the upgraded THD2 high-contrast imaging testbed. We report two advances enabled by its improved stability and broadband performance. First, for the Roman Space Telescope, we demonstrate that Gaussian-shaped diversity probes outperform the baseline sinc probes by reducing non-linearities, supporting higher probe amplitudes, and improving electric field estimation efficiency. These results have led to their prioritization as an enhanced early observation for Roman. Second, within ESA's SUPPPPRESS project, we test new polarization-independent Vector Vortex Coronagraphs and design them to high-contrast performance approaching 1e-10 over a 20% bandwidth. We assess their behavior in narrow- and broadband light with active focal-plane wavefront control. Together, these results show how THD2 strengthens Europe's capability in high-contrast imaging, providing a unique platform reaching contrasts of 1e-8 to 1e-9 for developing next-generation coronagraphic technologies.

Plasma streaming instabilities excited by relativistic charged particle beams play a pivotal role in astrophysical and laboratory environments. Their numerical study, however, is challenged by the disparity in spatiotemporal scales between the background plasma and beam particles, which can differ by several orders of magnitude for tenuous, ultrarelativistic beams. Here, we exploit the quasistatic approximation (QSA) to develop a new theoretical framework capable of capturing the full unstable spectrum in the spatiotemporal regime relevant for beams that continuously encounter unperturbed plasma at their leading edge. Within this linear, fully electromagnetic model, we uncover a previously unreported spatiotemporal evolution of the current filamentation instability and elucidate its interplay with the oblique two-stream instability, predicting the dominance of filamentation in the vicinity of the beam front. The good agreement between theory, kinetic particle-in-cell (PIC) simulations, and QSA-based PIC simulations validates the robustness of the approach. By pushing QSA-based PIC simulations to extremely dilute electron-positron beams, such as those found in blazar jets, we demonstrate their unique ability to capture the rich nonlinear dynamics of streaming instabilities in parameter regimes previously inaccessible to kinetic simulations.

An intermediate-mass black hole (IMBH) hidden in our Galactic Center (GC) may explain the puzzling observations of the stellar distribution around Sagittarius A* (Sgr A*), the supermassive black hole (SMBH) in the GC. Future observations with the next-generation radio telescopes, such as the SKA, are promising to discover pulsars orbiting around Sgr A*, and thus provide the possibility of constraining the hidden IMBH with pulsar timing. We study the detectability of a third-body, the IMBH, in the pulsar-SMBH system based on radio timing observation. We find that the pulsar-SMBH system is very sensitive to such a third-body perturbation and can be used to put stringent constraints on the existence of the IMBH. Even under strong perturbations caused by the complex GC astrophysical environments, timing observation will still complement the existing observational constraints.

Modern stellar surveys measure millions of spectra, yet one self-consistent atmosphere and spectrum can require tens of minutes. This cost has motivated grids, spectral emulators, and data-driven models. We present Payne Zero, which reorganizes one-dimensional LTE Kurucz calculations for GPU-native synthesis and multicore atmosphere iteration, and validate it against the original Fortran programs. A 300-1000 nm solar spectrum sampled at a grid resolution of R = 300,000 takes about 14 s on an NVIDIA H100 GPU, while the APOGEE 1500-1700 nm interval takes about 1 s. Physical atmosphere iterations take 2-5 s on 16 AMD CPU threads, and learned initializers reduce the iterations required for convergence. Final spectra remain in practical parity across the tested dwarf and giant regimes. These speeds place direct synthesis inside an optimizer without a label-to-flux spectral emulator. We demonstrate direct many-element fitting of reduced APOGEE spectra and recover multi-element abundance trends broadly consistent with the survey catalog. GPU-resident velocity shifts, broadening, line-spread-function convolution, and detector sampling add negligible cost relative to synthesis. The direct-synthesis search takes less than one minute per star on an H100, while atmosphere verification runs independently on multicore CPUs. The same computational graph calibrates more than 100,000 oscillator-strength and damping corrections jointly against the Sun and Arcturus in about one minute on an H100. Payne Zero therefore brings direct physical fitting and atomic-data calibration to survey scale. The code is available at https://github.com/tingyuansen/payne-zero.

We combine the axiverse with a negative cosmological constant $\Lambda$, both originating from the string landscape, and apply an observation-time-weighted anthropic argument. Adopting a uniform prior on $\Lambda$ and a typical string-motivated axion decay constant comparable to the reduced Planck scale, this framework predicts a $\sim 40\%$ probability of observing $0.1 < \Omega_m < 0.9$, thereby naturally resolving the long-standing fine-tuning and coincidence problems of dark energy. Unlike many scalar-field dark energy models, the anthropic Lambda-axion universe (ALAverse) statistically disfavors slow-roll dynamics, as slow-roll requires fine-tuning of the initial field displacement. Moreover, the negative cosmological constant renders fast-roll scenarios anthropically unfavorable, since they typically yield only a very brief observational window with positive dark energy density. Having ruled out both extremes, the ALAverse characteristically predicts a moderate-roll dynamics. We derive a two-parameter parametrization in terms of $\delta_\Omega$ and $|\varepsilon_s|$ that covers ALAverse solutions as well as a broad class of canonical and phantom field models. Current observational data yield $\delta_\Omega = -0.0498 \pm 0.0186$, corresponding to a $2.7\sigma$ rejection of $\Lambda$CDM ($\delta_\Omega = 0$) and single-field thawing phantom models ($\delta_\Omega > 0$). The data also show a mild preference for the ALAverse over slow-roll quintessence, a trend that can be conclusively tested with future high-precision measurements of the Hubble diagram.

We use luminous red galaxies (LRGs) and background quasar spectra from DESI DR1 to measure the mean MgII equivalent width around massive quiescent galaxies as a function of projected radius and azimuth relative to the projected major axis. Our forced-measurement approach assigns a MgII doublet-window EW to every LRG-quasar pair, including spectra without individually detected absorbers, and subtracts a redshift-matched random-control signal measured from the same normalized quasar spectra. The all-angle profile declines smoothly over $r_p=0.01$-$1.0$ proper Mpc and shows stronger inner absorption at $0.4<z_{\rm LRG}<0.75$ than at $0.75<z_{\rm LRG}<1.1$. Superposed on this radial and redshift dependence, sightlines near the LRG major axis show enhanced absorption relative to the minor axis at $r_p\simeq30$-$80$ kpc. For the full $0.4<z_{\rm LRG}<1.1$ sample, the integrated fiducial major-minus-minor difference over $r_p=0.03$-$0.077$ Mpc is $0.184\pm0.075$ Angstrom, with a position-angle randomization probability $p=0.013$. The redshift split shows no significant evolution in the anisotropy amplitude, even though the inner EW profile itself evolves. Our results provide evidence for a localized major-axis enhancement of MgII-bearing cool/warm gas around LRGs, showing that azimuthal CGM structure is measurable in massive quiescent halos as well as in star-forming systems.

Low-thrust trajectory optimization is a core technology in deep-space mission design. Indirect methods based on Pontryagin's Minimum Principle (PMP) offer rigorous optimality guarantees, yet their practical application faces three bottlenecks: (1) transversality conditions must be derived case by case for each constraint type; (2) different dynamics models require repeated code rewrites; and (3) shooting equations are highly sensitive to initial guesses. This paper presents HELIOS (Heuristic Engine for Low-thrust Interplanetary Optimization System), a trajectory optimization agent built around a large language model (LLM). Given a physical problem described in natural language, the system autonomously performs PMP symbolic derivation, SymPy verification, C++ shooting-code generation, and numerical solution without human intervention. Key innovations include: (1) a constraint-adaptive derivation framework that unifies arbitrary constraints into psi(x,p)=0 form and automatically generates stationarity conditions for free parameters (e.g., gravity-assist turning angle); (2) dynamics-adaptive four-module code generation supporting non-standard dynamics (solar sail, J2 perturbation) without modifying the underlying template; and (3) a general derivation rule set covering critical error-prone points in PMP derivation. Experiments on 11 progressive test scenarios show that HELIOS correctly derives and solves problems from simple rendezvous (8 variables) to multi-leg stay transfers (48 variables), gravity-assist trajectories (17 variables), and solar-sail minimum-time transfers (8 variables). The best compilation success rate reaches 100% (11/11). A multi-model comparison (8 open-source LLM backends, total scores 250-905) verifies the model-agnostic architecture and reveals a positive correlation between model scale and derivation capability.

We present shock breakout (SBO) modeling of the recently discovered X-ray transient EP260321a detected by the Einstein Probe mission. Our semi-analytic model, based on our previous work, follows the interaction between a supernova ejecta with a mildly relativistic outer envelope and a dense, wind-like circumstellar medium (CSM) by using a thin-shell approximation that incorporates relativistic effects. We find that the observed properties of the X-ray emission are well explained by the breakout emission powered by a high-velocity envelope with a kinetic energy of $\sim3.5\times10^{49}\,\mathrm{erg}$ (excluding the supernova ejecta) and a dense wind characterized by a mass-loss rate of $\dot{M}\simeq1.2\times 10^{-3}(v_\mathrm{w}/10^3\,\mathrm{km\,s}^{-1})\,M_\odot\,\mathrm{yr}^{-1}$, where $v_\mathrm{w}$ is the wind velocity. The observed burst duration requires the dense CSM to extend up to $\sim350\,R_\odot$, corresponding to a CSM mass of $\sim 10^{-5}\,M_\odot$. These results demonstrate that SBO observations provide a sensitive probe of mass loss from stripped-envelope supernova progenitors shortly before core collapse.

As the nearest protoplanetary disk to Earth ($d = 60.14$ pc), TW Hya is one of the most studied protoplanetary disks and a critical benchmark for testing planet formation theories. We present high-contrast coronagraphic imaging of the TW Hya disk from JWST/NIRCam across four filters (F187N, F200W, F356W, and F444W). We detect the disk's scattered-light emission in F200W, F356W, and F444W. An elliptical fit to the disk image yields an average inclination of $i = 8.74^{+1.03}_{-0.94}$ degrees and a position angle of $\mathrm{PA} = 75.62^{+7.86}_{-6.56}$ degrees. We find tentative evidence for radial variations in these parameters, a trend consistent with a disk warp. Our companion search yields no new detections, placing the lowest mass limits yet on companions that might be responsible for carving out the dust gap. Assuming no local extinction and a system age of 10 Myr, the F444W data are sensitive to masses down to $\sim 0.4\,M_{\rm Jup}$ at separations of $1$ arcsec ($\sim 60$ AU). Accounting for local disk extinction analogous to the AS 209 system, our limits reach sub-Jupiter masses beyond $2$ arcsec. Furthermore, our analysis provides a detailed view of a previously detected feature in the outer disk at $\sim 120$ AU, confirming its morphology as a distinct bifurcation structure. This feature may indicate the presence of complex substructures arising from dynamical planet-disk interactions. These results demonstrate JWST's ability to characterize the architecture of protoplanetary disks and constrain the properties of forming worlds.

We consider how a class of morphological descriptors, the Minkowski Tensors (MTs), can be used to test the statistical isotropy of random fields on the sphere. The definition of the MTs involves an integral of a tensor, which is an ambiguous operation on a curved manifold. We find that existing estimators in the literature, when applied to fields on the two-sphere, either explicitly break covariance or artificially isotropize the MT due to a geometric rotation of tangent spaces. To evade these issues, we construct the MTs of individual connected components and use them to build correlation functions $\xi_{\pm}(\theta,\nu)$ of their relative orientations. These correlation functions are built from scalars and are therefore covariant, and can be used to search for alignment of structures as a function of scale (angular separation). We generate four sets of random fields on $S^{2}$ – isotropic, dipole modulated, globally-sheared and locally-sheared, and show how the connected component correlation functions can distinguish scale dependent alignments. For the sheared fields, the decay scale of $\xi_{+}$ measures the angular coherence of the alignment, and the amplitude of $\xi_{-}$ at large separations measures its globally coherent fraction, distinguishing the two shear models. In contrast, dipole modulation generates no significant signal in the orientation statistics. We show analytically that its effect on the traceless component of the Minkowski tensor is second order in the modulation amplitude $\lambda \ll 1$.

Cosmological stasis, a surprising phenomenon in which the abundances of different energy components in the universe with different equations of state remain constant despite cosmological expansion, has been a focus of recent attention. This behavior emerges as the consequence of an attractor that governs the dynamics of the corresponding cosmological system and pulls it towards stasis even if the system is not initially in this state. However, while some systems actually reach stasis in finite time, it is also possible for such systems to spend considerable time under the influence of this attractor, continually heading towards stasis without ever quite reaching it. This too represents behavior that is entirely unexpected within standard cosmological scenarios. In this paper, we present an explicit model which realizes both of these behaviors in a thermal context while satisfying all relevant phenomenological and cosmological constraints. Within this model, we then examine how the attractor influences the cosmological dynamics and explore the potential consequences for the early universe.

The hierarchical nature of galaxy formation in the Lambda cold dark matter ($\Lambda$CDM) cosmological framework model often leads to the presence of multiple supermassive black holes (SMBHs) in the galactic nuclei. The timescale over which galaxies merge plays a crucial role in shaping the dynamical evolution and the merger dynamics of their central SMBHs. While binary SMBH evolution has been extensively studied, the long-term dynamics of triple SMBH systems, especially in realistic, nonspherical galactic potentials, still remain less understood. In this work, we investigated the role of triaxiality in shaping the dynamical evolution of three SMBH triple systems taken from the ROMULUS25 cosmological simulation embedded in triaxial stellar backgrounds to find common dynamical evolution patterns and estimate typical coalescence times using high-resolution gravitodynamical $\textit{N}$-body simulations. We explored a range of orbital configurations and host galaxy shapes with initial conditions from the ROMULUS25 data and tracked the orbital evolution from the galactic inspiral to the formation of hard binaries at sub-parsec separations and used the observed hardening rates to estimate the time of coalescence. In all cases, the two heaviest black holes form an efficiently hardening binary, which merges within the Hubble time, while the third black hole (BH) either forms a stable hierarchical triple system with the heavier binary or remains on a wide galactic orbit. Finally, we analyzed the triaxiality of the galactic remnant from our simulations and conclude that the initial triaxial shape of the galaxies does not significantly change the final dynamical outcome of the triple systems.

On Aug. 5 at 06:34 UTC, a Falcon 9 upper stage (~3,900 kg) will strike the lunar surface at 2.43 km/s, yielding a potentially visible debris plume. We present a study of the expected impact dynamics and resulting possibly observable debris field. The debris plume should reach roughly 15 to 20 km in altitude for the ejecta curtain and 75 to 100 km for the central ejecta spike, extend 183 km laterally from the impact point near the sunlit limb, and yield a peak dust column density above 10 km altitude of 6.08*10^7 m^-2. Simulated I/F exceeds dark-sky background brightness by several orders of magnitude for the first few minutes after impact, reaching I/F = 1.27*10^-3 at the earliest resolved time (t = 5 s). Above 10 km, peak I/F reaches 1.33*10^-5, still several orders of magnitude brighter than the dark sky.

We obtain explicit formulas for the expected number and height distribution of critical points of smooth isotropic Gaussian random fields on $\mathbb{R}^d$. The expected number density formula is expressed in terms of at most one-dimensional integrals, regardless of the dimension $d$. To obtain the formulas, we provide a variant of de Bruijn's theorem, as well as Weierstrass' convolution formula with a Gaussian random variable and its inversion.

We constrain the Emergent Fractional Fractal (EFF) cosmological model through a joint likelihood analysis of recent cosmological observations at the background and perturbation levels. In this framework, an effective fractal dimension $d$ is introduced to parameterize possible fractional deviations from the standard cosmological model. We consider three combinations of datasets: (i) late-time (LT) observations including PantheonPlus Type Ia supernovae, $H(z)$ measurements, and growth-rate measurements $f\sigma_8$; (ii) LT combined with DESI DR2 BAO and Big Bang nucleosynthesis (BBN); and (iii) LT combined with DESI DR2 BAO and CMB distance priors. With the inclusion of CMB distance priors, the fractal dimension is constrained to $d = 2.0004^{+0.0006}_{-0.0003}$ at the $1\sigma$ confidence level. Model comparison using the Akaike Information Criterion (AIC) shows that the EFF and $\Lambda$CDM models fit the observational data equally well, while the Bayesian Information Criterion (BIC) favors the simpler $\Lambda$CDM model because of its smaller parameter space. These results show that current cosmological observations place strong constraints on fractal extensions of the standard cosmological framework and possible deviations from the $\Lambda$CDM model.

Primordial black hole (PBH) binaries in the stellar mass range may still contribute a fraction of the detectable compact object binaries by LIGO and future GW observatories. PBH binaries at formation typically have very high eccentricities. In this paper, we study the eccentricity of stellar mass range PBH binaries from all formation channels and account for all evolutionary pathways. We simulate large samples of PBH binaries, tracking their full orbital evolution up to their merger or to the present day. For those that merge, we compute their GW strain, detectability, and eccentricity distributions for LISA, DECIGO, ET, CE, and aLIGO. We find that PBH binaries that evolve in isolation completely circularize by the time their GWs enter any GW band except for LISA's, where residual eccentricities of order $O(10^{-2})$ can exist. Binaries that become part of dark matter halos can have multiple binary-single interactions with other PBHs, especially if they reside in the more dense environments among them and can have higher eccentricities even at their late inspiral phase, probed by the GW observatories. Considering the current limits on the abundance of stellar mass range PBHs, we predict that LISA and DECIGO together would be able to probe $O(10^2)$ such binaries with $e>0.01$. If these future GW observatories in space can exclude such eccentric binaries, then limits on the PBH abundance can be improved by an order of magnitude.

A comprehensive study of novae in the Large Magellanic Cloud (LMC) is presented. A total of 66 nova eruptions have been reported in the LMC over the past century ($1926 \unicode{x2013} 2025$). Of these, a total of 48 eruptions from 39 unique progenitor systems (nine eruptions are recurrences of four known recurrent novae) have sufficient photometric data to permit the maximum magnitudes and rates of decline to be reliably estimated. These data confirm earlier studies showing that LMC novae are, on average, slightly more luminous and faster evolving compared with novae in the Andromeda galaxy (M31) or the Milky Way. For the first time, the nova models of Yaron et al. have been used in conjunction with the light-curve data to estimate the fundamental properties of the LMC nova population. The models suggest that LMC novae are characterized by generally higher white dwarf (WD) masses and higher expansion velocities compared with M31 novae. The higher average WD masses have resulted in a higher percentage of recurrent nova eruptions in the LMC ($\sim$20.6%) compared with that seen in M31 ($\sim$6.40%). Future observations made possible by the Vera Rubin Observatory promise to revolutionize our understanding of nova populations in the LMC and in galaxies beyond the Local Group.

The formation, extension, and morphology of extra-tidal stars around globular clusters depend on the internal kinematics of the host cluster and the Galactic potential. Tracing the kinematics of faint tidal tails sheds light on their formation and contribution to the Milky Way halo. NGC 7492 is an outer halo globular cluster with conflicting evidence regarding the presence of tidal tails. If present, the tails are expected to be faint and overlap on the sky with the Sagittarius stream, located at a similar heliocentric distance but with distinct kinematics. We carried out a GIRAFFE spectroscopic follow-up of ten fields covering the expected tidal tails of NGC 7492. Gaia parallaxes were used to remove foreground contaminants, while only loose proper-motion constraints were applied in the target selection. Radial velocities and metallicities were derived for more than 700 stars, from the red giant branch to the upper main sequence. Cluster and extra-tidal stars were identified from their proper motions, radial velocities, and metallicities. This population extends at least 1.8 deg from the cluster center, confirming the tidal tails previously detected only photometrically, with positions consistent with particle-spray models of the cluster disruption. The Sagittarius stream is clearly identified through its distinct proper motions, radial velocities, and more metal-rich population. Despite the low spatial density of the extra-tidal stars, their kinematic signature is clearly detected, demonstrating that the tidal tails overlap on the sky with the Sagittarius stream but are physically unrelated. This spectroscopic dataset provides a robust basis for future studies of the tails at larger angular extents and fainter magnitudes.