New Astronomy Reviews最新文献

This is the fourth paper in the series of analyses of times of minimum and period variations in W UMa eclipsing binaries, and the implications for mass exchange in these systems. In this paper, the systems discussed in Papers 1–3 for which analyses are relatively complete are sorted into three sections, arranged in order of degree of confidence that mass exchange occurrence is established and that the present rate of exchange has been determined. The higher-confidence systems are: 44 Boo, RZ Cam, VW LMi, AU Ser; the intermediate-confidence systems are: TY Boo, V1191 Cyg, AP Leo, ER Ori; and the lower-confidence systems are: AB And, XY Boo, AC Boo, AH Cnc, VW Cep, EZ Hya, XY Leo, W UMa, and GR Vir. A fourth section describes promising cases that require additional data and/or analyses. For the higher-confidence systems, selected analyses of the times of minimum and of the most comprehensive light curve (LC) and radial velocity (RV) suites of data have yielded mean mass changes to the more massive component of dM₁/dt = +2.37 (13) × 10⁻⁷ M_ʘ/y for 44 Boo, +4.00 (14) × 10⁻⁸ M_ʘ /y for RZ Com, +2.53 (7) × 10⁻⁷ M_ʘ /y for VW LMi, and -1.98 (11) × 10⁻⁷ M_ʘ /y for AU Ser.

Proto-planetary discs, the birth environment of planets, are an example of a structure commonly found in astrophysics, accretion discs. Identifying the mechanism responsible for accretion is a long-standing problem, dating back several decades. The common picture is that accretion is a consequence of turbulence, with several instabilities proposed for its origin. While traditionally this field used to be a purely theoretical endeavour, the landscape is now changing thanks mainly to new observational facilities such as the ALMA radio interferometer. Thanks to large improvements in spatial and spectral resolution and sensitivity (which have enabled the study of disc substructure, kinematics and surveys of large disc populations), multiple techniques have been devised to observationally measure the amount of turbulence in discs. This review summarises these techniques, ranging from attempts at direct detection of turbulence from line broadening, to more indirect approaches that rely on properties of the dust or consider the evolution of global disc properties (such as masses, radii and accretion rates) for large samples, and what their findings are. Multiple lines of evidence suggest that discs are in fact not as turbulent as thought one decade ago. On the other hand, direct detection of turbulence in some discs and the finite radial extent of dust substructures and in some cases the finite vertical extent strongly indicate that turbulence must be present at some level in proto-planetary discs. It is still an open question whether this amount of turbulence is enough to power accretion or if this is instead driven by other mechanisms, such as MHD winds.

The Shower Database (SD) of the Meteor Data Center (MDC) had been operating on the basis of stream-naming rules which were too complex and insufficiently precise for 15 years. With a gradual increase in the number of discovered meteor showers, the procedure for submitting new showers to the database and naming them led to situations that were inconsistent with the fundamental role of the SD — the disambiguation of stream names in the scientific literature. Our aim was to simplify the meteor shower nomenclature rules. We proposed a much simpler set of meteor shower nomenclature rules, based on a two-stage approach, similar to those used in the case of asteroids. The first stage applies to a new shower just after its discovery. The second stage concerns a repeatedly observed shower, the existence of which no longer raises any doubts. Our proposed new procedure was approved by a vote of the commission F1 of the IAU in July 2022.

The question “are we alone in the universe?” has been asked through the ages and is beginning to be addressed by deploying spacecraft and advanced observatories capable of detecting biological signatures. Apart from the certainty that life exists on the Earth, there is no clear evidence at the time of writing for extra-terrestrial life (also termed exo-life). Although the sheer number of potentially habitable extrasolar planets in our galaxy alone makes a compelling case for widespread exo-life if taken in isolation, the constraints on the emergence of life imposed by chemistry and biology provide a counterbalance to this optimistic view. In the absence of any clear sign of exo-life and therefore our ignorance about whether it exists or not, the only way forward is to apply scientific knowledge in a rational way to discriminate between different scenarios until such a time that real evidence is forthcoming, if at all. This article reviews the main features of current astrobiological research to speculate on the likelihood of each critical transition in the development of living entities, emphasising the involvement of chemistry and informational macromolecules. It concludes that carbon-based compounds may be widespread on and in exoplanets, but the organisation of these prebiotic molecules into cellular structures with anything like the complexity of the primitive organisms on Earth could be very rare or non-existent. However, if such organisms do arise, the path to multicellularity and the functional organisation required for human capabilities may not be so daunting. Some of the key genetic features required for this development may already be present in primitive cells ready to be activated or repurposed.

The study of ultraluminous X-ray sources (ULXs) has changed dramatically over the last decade. In this review we first describe the most important observations of ULXs in various wavebands, and across multiple scales in space and time. We discuss recent progress and current unanswered questions. We consider the range of current theories of ULX properties in the light of this observational progress. Applying these models to neutron-star ULXs offers particularly stringent tests, as this is the unique case where the mass of the accretor is effectively fixed.

The overwhelming majority of theories on dark matter either introduce exotic, never discovered experimentally subatomic particles or change the physical laws. In this brief review I discuss three theories that do not do this, so that they are preferable from the viewpoint of the Occam razor principle.

One of the most pressing issues facing astronomy today is the growing threat of light pollution. Light pollution affects not only astronomical observations but also sustainability in the social and environmental sense. Light pollution has been reported to cause environmental changes by altering the circadian rhythm of organisms such as birds. In this work, we conducted a systematic review of data analyses on light pollution in the literature to assist researchers and those interested in light pollution. The results of the systematic review can be divided into four distinct phases, which are research objective, data collection, data preprocessing, and data analysis. Simple popularity for each phase shows the most popular approaches are measurement as a research objective at 47.46%, ground-based sensors for data collection at 31.91%, image preprocessing at 51.61%, and statistics & machine learning for data analysis at 64.29%. The most popular combination of each phase is a measurement objective with ground-based sensors for data collection without data preprocessing or analysis. This implies that a not insignificant number of studies seek to obtain ground measurements without further analysis of the data. Data analysis as an integral part of the effort for understanding light pollution needs to be used efficiently and effectively by all stakeholders in the pursuit of sustainability.

The physics of astrophysical jets can be divided into three regimes: (i) engine and launch (ii) propagation and collimation, (iii) dissipation and particle acceleration. Since astrophysical jets comprise a huge range of scales and phenomena, practicality dictates that most studies of jets intentionally or inadvertently focus on one of these regimes, and even therein, one body of work may be simply boundary condition for another. We first discuss long standing persistent mysteries that pertain the physics of each of these regimes, independent of the method used to study them. This discussion makes contact with frontiers of plasma astrophysics more generally. While observations theory, and simulations, and have long been the main tools of the trade, what about laboratory experiments? Jet related experiments have offered controlled studies of specific principles, physical processes, and benchmarks for numerical and theoretical calculations. We discuss what has been accomplished on these fronts. Although experiments have indeed helped us to understand certain processes, proof of principle concepts, and benchmarked codes, they have yet to solved an astrophysical jet mystery on their own. A challenge is that experimental tools used for jet-related experiments so far, are typically not machines originally designed for that purpose, or designed with specific astrophysical mysteries in mind. This presents an opportunity for a different way of thinking about the development of future platforms: start with the astrophysical mystery and build an experiment to address it.

A number of challenges to the standard $\Lambda$CDM model have been emerging during the past few years as the accuracy of cosmological observations improves. In this review we discuss in a unified manner many existing signals in cosmological and astrophysical data that appear to be in some tension ($2\sigma$ or larger) with the standard $\Lambda$CDM model as specified by the Cosmological Principle, General Relativity and the Planck18 parameter values. In addition to the well-studied $5\sigma$ challenge of $\Lambda$CDM (the Hubble $H_0$ tension) and other well known tensions (the growth tension, and the lensing amplitude $A_L$ anomaly), we discuss a wide range of other less discussed less-standard signals which appear at a lower statistical significance level than the $H_0$ tension some of them known as ’curiosities’ in the data) which may also constitute hints towards new physics. For example such signals include cosmic dipoles (the fine structure constant $\alpha$, velocity and quasar dipoles), CMB asymmetries, BAO Ly$\alpha$ tension, age of the Universe issues, the Lithium problem, small scale curiosities like the core–cusp and missing satellite problems, quasars Hubble diagram, oscillating short range gravity signals etc. The goal of this pedagogical review is to collectively present the current status (2022 update) of these signals and their level of significance, with emphasis on the Hubble tension and refer to recent resources where more details can be found for each signal. We also briefly discuss theoretical approaches that can potentially explain some of these signals.

The Einstein–Maxwell (or Einstein) system of field equations plays a substantial role in the modeling of compact stars. Although due to its non-linearity getting an exact solution for the system of field equations is a difficult task, the solutions of field equations have a long and rich history. It took a year for Karl Schwarzschild to obtain the first exact solution of Einstein’s field equations since general theory of relativity was published. The number of viable solutions has been growing since then. Many authors have adopted several methods to obtain the solution. Different models have been constructed for a variety of applications. To produce feasible models of compact stars, a considerable amount of effort has been applied in gaining an understanding of the properties of anisotropic matter. Theoretical study indicates that pressure within compact stars with extreme internal density and strong gravity is mostly anisotropic. Anisotropy was found sufficient for the study of compact stars with the dense nuclear matter. It is claimed that it is important to consider the pressure experienced to be anisotropic whenever relativistic fluids are involved. In this review article, we have discussed different ways of generating a static spherically symmetric anisotropic fluid model. The purpose of the article is to present a simple classification scheme for static and spherically symmetric anisotropic fluid solutions. The known solutions are reviewed and compartmentalized as per the proposed scheme so that we can illustrate general ideas about these solutions without being exhaustive.