The Astronomy and Astrophysics Review最新文献

Galaxy clusters are among the most powerful laboratories to probe fundamental physics, from the formation of cosmic structures to the nature of dark matter, dark energy, and gravity. Realizing their full potential requires accurate and unbiased determinations of their mass profiles, a longstanding challenge in cluster cosmology. In this context, the kinematics of member galaxies in clusters has become a key tool to reconstruct the mass distribution and investigate the dynamical properties of clusters. The advent of large spectroscopic datasets has enabled the application of increasingly sophisticated models and robust techniques, which make kinematic analyses competitive with other probes of cluster dynamics. In this review, we provide a comprehensive overview of cluster kinematics, covering the main methods to infer dynamical masses and mass profiles, their physical assumptions, and the impact of systematics, such as deviation from dynamical equilibrium, triaxiality, and substructures. We discuss the complementarity with other techniques to investigate the structure of clusters and highlight recent applications to tests cosmological models. We focus in particular on the role of kinematical studies in constraining the dark sector (dark matter and dark energy) and in providing novel insights into the behavior of gravity at Mpc scales. Finally, we outline current limitations and future prospects, emphasizing that the combination of improved modeling and forthcoming spectroscopic surveys will establish cluster kinematics as a fundamental probe in the era of precision cosmology.

Red novae or luminous red novae are a class of optical transients that have emerged over the past two decades. They occupy an intermediate-luminosity regime between classical novae and supernovae and are characterized by cool, slowly expanding ejecta and a pronounced evolution toward red, dust-enshrouded remnants. These events are now widely interpreted as the outcome of binary coalescence involving non-compact stars, providing a rare opportunity to directly observe the dynamical phases of stellar mergers and their immediate aftermath. Observational studies of red novae provide a glimpse into the still poorly understood physics of unstable mass transfer and common-envelope evolution in binary stars, responsible for the formation of high-energy astrophysical phenomena, compact binary systems, and gravitational-wave sources. In this review, we synthesize current observational knowledge of red novae, including their outburst properties, population characteristics, and long-term remnants. Observations of light curves, spectra, and circumstellar environments reveal a complex interplay between mass ejection, collisions, radiative processes, and dust formation. Archival detections of red novae progenitors show a diversity of systems, ranging from low-mass contact binaries to massive evolved stars, with a notable representation of post-main-sequence stars. We also examine current efforts to predict red nova outbursts and establish robust event rates in the Local Universe, both of which remain challenging. Finally, we outline future prospects, including the impact of large-scale time-domain surveys and the potential connection between stellar mergers and gravitational-wave sources.

The goal of this review article series is to provide a comprehensive overview of galactic star formation and quenching from both an observational and theoretical perspective. Drawing on a vast quantity of literature, we attempt to answer a deceptively simple question: why do galaxies cease forming stars? In Part II, we concentrate primarily on results from theory and simulations, in addition to direct observational tests of theoretically proposed quenching routes. Over the past two decades, N-body simulations, semi-analytic models, idealized hydrodynamical simulations, cosmological hydrodynamical simulations, and zoom-in hydrodynamical simulations have all provided crucial insights into the fundamental causes and specific mechanisms of galaxy quenching. Throughout this part of the review, we discuss intrinsic routes to massive galaxy quenching from strong baryonic feedback—including supernovae and active galactic nuclei (in both the ejective and preventative modes). Additionally, we discuss dynamical stabilization and the role of mergers. We go on to consider environmental routes to quenching via both ram pressure and dynamical stripping, and as a consequence of the location of satellite galaxies within the cosmic web. We review observational tests of the fundamental causes, specific mechanisms, and triggering of quenching from various techniques. Finally, we conclude with tentative answers to the major outstanding issues in this field.

This review summarizes the changing observational and theoretical landscape that has led to rapid developments in our understanding of the orbital history of the Milky Way’s most massive satellite galaxies, the LMC and SMC. The determination of high precision center-of-mass proper motions for the Clouds and their environs, coupled with new insights into the structure of dark matter halos from cosmological simulations, indicates that the Clouds are recent additions to the Milky Way’s satellite system, where the LMC was sufficiently massive at infall to induce distortions in the Milky Way’s dark matter halo, and bring in satellites of its own. To gain insights into the orbital history of the Clouds it is, therefore, necessary to integrate orbits in a time-evolving Milky Way + LMC potential. The proper motion measurements further indicate that the LMC and SMC have had a recent strong encounter with each other. This leaves open the impact of this encounter on their internal structures, and the degree of correspondence between their stellar, HI and dark matter centers. The choice of kinematic center in turn affects the center of mass proper motions; this is the biggest observational unknown, even in the high precision Gaia era. Given the expected mass loss of the SMC, the distortions it induces in the LMC halo, and the recent LMC–SMC close encounter, understanding the orbits of objects about the LMC (including the SMC) and interpreting observational data of the Clouds requires full N-body simulations that are constrained by their present-day structure and kinematics.

The Sun is one of the fundamental benchmarks in astronomy, and there is ever growing interest in precise and accurate determinations of its chemical composition. We present the current state-of-the-art in spectroscopic determinations of the solar elemental abundances, that now routinely employ three-dimensional (3D) radiative-hydrodynamic simulations of the solar photosphere and post-processing in non-local thermodynamic equilibrium (non-LTE). We critically review the recent literature and present recommended present-day and protosolar abundances of the 83 long-lived elements, and discuss their implications vis-à-vis primitive meteorites, helioseismology, neutrino fluxes, and the Solar Modelling Problem.

The goal of this review article series is to provide a comprehensive overview of galactic star formation and quenching from both an observational and theoretical perspective. Drawing on a vast quantity of literature, we attempt to answer a deceptively simple question: why do galaxies cease forming stars? In Part I, we concentrate on observational results, especially from the past two decades, where there have been enormous advances made toward answering this fundamental question. In Part II, we focus on theory and simulations, including discussion of direct observational tests thereof. Observationally, the advent of wide-field spectroscopic galaxy surveys, spatially resolved spectroscopy, high-resolution sub-mm and radio observations, X-ray observations, the Hubble Space Telescope (HST), and most recently the James Webb Space Telescope (JWST) have all contributed significantly to our empirical knowledge of star formation and its demise in galaxy quenching. We discuss the fundamental problems which quenching aims to solve, various routes to identifying quiescent galaxies in observations, observational constraints on quenching from studies of galaxy populations, and the spatially resolved view of quenching. We end this part of the review with a detailed discussion of the latest results on galaxy quenching at the high-redshift frontier from JWST observations.

About 15 years ago, a new type of extreme (with kinetic energies of (textrm{E}_k sim 10^{47-49}) erg) molecular outflows associated with very luminous ((ge ) (10^5) (textrm{L}_odot )) and massive ((10^3) (textrm{M}_odot )) young clusters was confirmed, the Explosive Molecular Outflows. This new class of outflows is largely different from the classical bipolar protostellar flows, with spatial distributions made of numerous narrow straight filament- or streamer-like ejections in an almost isotropic arrangement and with clear Hubble–Lemaître-like expansion motions. Straight filaments point directly to the center of expanding molecular or ionized shells, which exhibit expansion velocities of about 10–50 km (textrm{s}^{-1}). However, no young massive stars are clearly located there, probably because they moved to other places. These physical characteristics suggest that explosive outflows are short-lived in nature and possibly generated by an energetic single and brief disrupting event. The most up-to-date theoretical model for explaining their nature involves the disruption of non-hierarchical massive protostellar systems, where members may either form a close binary (with separations of a few au) or merge into a single massive star, as recently proposed for the nearest high-mass star-forming region, Orion BN/KL. The present-day number of discovered explosive outflows and their estimated duration of some thousand years have set this rate (one every 140 years) to a value similar to the Galactic supernova rate and the Galactic rate of formation of massive stars, suggesting that this mode of formation likely is occurring in most of the massive stars. Future-sensitive and detailed observations (e.g. with the James Webb Space Telescope, Atacama Large Millimeter/Submillimeter Array or in a near future the next-generation Very Large Array) to a large number of close-by high-mass star-forming regions could reveal many more of these remarkable flows and their true nature.

Identifying the sources of the high-energy astrophysical neutrinos has been one of the main topics in astrophysics since the first observation of high-energy neutrinos by the IceCube Neutrino Observatory. Active Galactic Nuclei (AGN) are sources of high-energy (gamma )-rays and are considered to be promising candidates to be sources of high-energy neutrinos and ultra-high-energy cosmic rays as well. However, several studies suggest that the neutrino emission from the (gamma )-ray blazar population only accounts for a small fraction of the total astrophysical neutrino flux. We present and discuss recent results on the search for correlations between astrophysical neutrinos and both (gamma )-ray and radio-bright AGN. The IceCube Collaboration has reported high-energy neutrino events that may come from both the radio-loud AGN TXS 0506+056 and the radio-quiet AGN NGC 1068. Other cases of possible associations between high-energy neutrino events and individual blazars were claimed with controversial results. We discuss the properties of these sources together with the different neutrino production mechanisms proposed for those sources. Finally, we outline future prospects in the field, focusing on remaining open questions, the development of upcoming neutrino facilities, and the evolving multi-frequency landscape within the multi-messenger era.

Cosmic voids, the large underdense regions of our Universe, have emerged over the past decade as powerful cosmological laboratories: their simple dynamics, sensitivity to local gravitational effects and cosmic expansion, and ability to span large volumes, make them uniquely suited to test fundamental physics. Fueled by advances in theory, simulations, and observations, void science has matured into a precision tool for constraining the parameters of the standard cosmological model and its possible extensions. In this review, we provide a comprehensive description of the statistical tools developed to characterize voids, the theoretical models that link them to cosmological parameters, and the methodologies used to extract information from survey data. We highlight the growing synergy between void-based observables and other cosmological probes, and showcase the increasingly stringent constraints derived from voids measured from current and expected for upcoming surveys’ data. With the advent of the next generation of galaxy surveys, voids are poised to play a central role in the future of cosmology, turning what was once regarded as emptiness into one of the most promising frontiers of fundamental science.

With their jet pointing towards us, blazars are ideal tools to study the physics and structure of extragalactic jets. Their powerful jets are cosmic particle accelerators and are alleged to be one of the production sites of the high-energy neutrinos detected by the IceCube Observatory. Doppler beaming of the jet nonthermal radiation increases blazar brightness, blue-shifts their emission, and shortens their variability time scales, which are observed to range from years down to minutes. This review will focus on blazar flux, spectral, and polarization variability across the electromagnetic spectrum. After introducing blazars and their peculiarities, we will consider the statistical tools that are used to characterize the variability and to reveal correlations and time delays between flux variations at different frequencies. Then we will outline the main observed properties of the blazar multiwavelength behaviour. Interpretation of blazar variability calls into question both intrinsic and extrinsic mechanisms. Shock waves, magnetic reconnection, and turbulence can accelerate particles inside the jet, while jet precession, rotation, and twisting can produce variations in Doppler beaming. Changes in the broad-band spectral energy distribution have commonly been explained by variations in the jet physical parameters in one- or two-zone models. However, microvariability observed at all wavelengths puts strong constraints on the size of the emitting regions, suggesting a multizone emitting jet. Twisting jets have been proposed to explain the long-term multiwavelength variability. They are supported by radio observations of bent or helical jets, and by results of relativistic magnetohydrodynamics simulations of plasma jets. Detection of (quasi)periodic behaviour at all frequencies and on all time scales has been ascribed to orbital motion in black hole binary systems, jet precession, kink instabilities developing inside the jet, or perturbations in the accretion disc. Gravitational microlensing has been suggested to explain blazar behaviour in some cases. Polarization is another important ingredient in blazar variability studies, providing information on the structure and behaviour of the magnetic field in the emission zones. Both the degree and angle of polarization can show strong and fast variability, which is sometimes correlated with flux. Overall, polarimetric observations indicate that turbulence must play an important role in the emitting regions. Recent results obtained by the Imaging X-ray Polarimetric Explorer (IXPE) satellite have revealed some unexpected behaviour favouring a multizone emitting jet model. The interpretation of flux, spectral, and polarization variability within a consistent picture challenges current models of blazar variability and tells us that we may still miss some tiles of the puzzle.