New Astronomy Reviews最新文献

The Gaia mission has revolutionized our view of the Milky Way and its satellite citizens. The field of Galactic Archaeology has been piecing together the formation and evolution of the Galaxy for decades, and we have made great strides, with often limited data, towards discovering and characterizing the subcomponents of the Galaxy and its building blocks. Now, the exquisite 6D phase-space plus chemical information from Gaia and its complementary spectroscopic surveys has handed us a plethora of data to pore over as we move towards a quantitative rather than qualitative view of the Galaxy and its progenitors. We review the state of the field in the post-Gaia era, and examine the key lessons that will dictate the future direction of Galactic halo research.

This review highlights the role of the Gaia space mission in transforming white dwarf research. These stellar remnants constitute 5%–7% of the local stellar population in volume, yet before Gaia the lack of trigonometric parallaxes hindered their identification. The mission’s Data Release 2 in 2018 provided the first unbiased colour-absolute magnitude diagram of the local stellar population, identifying 260 000 white dwarfs, with the number later increasing to over 355 000 in Data Release 3. Since then, more than 400 white dwarf studies have made critical use of Gaia data, establishing it as a fundamental resource for white dwarf identification, fundamental parameter determination and more recently spectral type characterisation. The review underscores the routine reliance on Gaia parallaxes and extensive use of its photometry in white dwarf surveys. We also discuss recent discoveries firmly grounded in Gaia data, including white dwarf mergers, exotic compact binaries and evolved planetary systems.

Star clusters are among the first celestial objects catalogued by early astronomers. As simple and coeval populations, their study has been instrumental in charting the properties of the Milky Way and providing insight into stellar evolution through the 20th century. Clusters were traditionally spotted as local stellar overdensities in the plane of the sky. In recent decades, for a limited number of nearby clusters, it became possible to identify cluster members through their clustering in proper motion space. With its astrometric data of unprecedented precision, the Gaia mission has completely revolutionised our ability to discover and characterise Milky Way star clusters, to map their large-scale distribution, and to investigate their internal structure. In this review we focus on the population of open clusters, residing in the Galactic disc. We summarise the current state of the Gaia-updated cluster census and studies of young clusters and associations. We discuss recent developments in techniques for cluster detection and age estimation. We also review results enabled by Gaia data concerning the dynamical evolution of gravitationally bound clusters and their stellar inventory.

Wormholes have captured the interest of scientists and readers of science fiction as a fascinating possibility for traveling through huge cosmic distances or presumably enabling time travel. This review aims to present a thorough overview of wormholes in the context of modified gravity, highlighting the theoretical foundations, and significant developments in this rapidly developing area. In this article, we first give an overview of the concept of a wormhole in the different frameworks of modified gravities. Then this is followed by the wormhole framework, embedding diagrams, the existence of the wormholes, and thorough analysis in various modified gravities like $f\left(R\right)$, $f\left(G\right)$, $f\left(T\right)$, $f(R,L_m)$, $f\left(R,T\right)$, $f\left(Q\right)$, and $f\left(Q,T\right)$. For distinct purposes, various models have been created. Many authors have used a variety of techniques to get a solution. Hereafter, the emphasis will be on the stability analysis of wormholes through different approaches namely Energy Conditions (ECs), Tolman–Oppenheimer–Volkoff (TOV), Volume Integral Quantifier(VIQ), Active Gravitational Mass(AGM), and Total Gravitational Energy (TGE). The possible observable features of such wormholes are briefly discussed. All the solutions are organized by the suggested framework to demonstrate broad concepts of wormhole solutions.

Stellar multiplicity is among the oldest and richest problems in astrophysics. Binary stars are a cornerstone of stellar mass and radius measurements that underpin modern stellar evolutionary models. Binaries are the progenitors of many of the most interesting and exotic astrophysical phenomena, ranging from type Ia supernovae to gamma ray bursts, hypervelocity stars, and most detectable stellar black holes. They are also ubiquitous, accounting for about half of all stars in the Universe. In the era of gravitational waves, wide-field surveys, and open-source stellar models, binaries are coming back stronger than a nineties trend. Much of the progress in the last decade has been enabled by the Gaia mission, which provides high-precision astrometry for more than a billion stars in the Milky Way. The Gaia data probe a wider range of binary separations and mass ratios than most previous surveys, enabling both an improved binary population census and discovery of rare objects. I summarize recent results in the study of binary stars brought about by Gaia, focusing in particular on developments related to wide ($a\gtrsim 100$  au) binaries, evidence of binarity from astrometric noise and proper motion anomaly, astrometric and radial velocity orbits from Gaia DR3, and binaries containing non-accreting compact objects. Limitations of the Gaia data, the importance of ground-based follow-up, and anticipated improvements with Gaia DR4 are also discussed.

The recent hint of correlated $\gamma$-ray and neutrino emission from the blazar TXS 0506+056 has renewed interest in blazars as the source of high-energy neutrinos, in which the possible neutrino emission involved hadronic acceleration in the jet of blazars. In this review, we summarize the recent advances in the multi-wavelength and neutrino observations of blazars. We focus on the discussion of the current understanding of blazar emission processes in the leptonic and hadronic model. The future multi-messenger observations combining electromagnetic and neutrino measurements will help us to constrain blazar emission models and understand the origins of the high-energy $\gamma$-rays and neutrinos.

Modern radio telescopes will generate, on a daily basis, data sets on the scale of exabytes for systems like the Square Kilometre Array (SKA). Massive data sets are a source of unknown and rare astrophysical phenomena that lead to discoveries. Nonetheless, this is only plausible with the exploitation of machine learning to complement human-aided and traditional statistical techniques. Recently, there has been a surge in scientific publications focusing on the use of machine/deep learning in radio astronomy, addressing challenges such as source extraction, morphological classification, and anomaly detection. This study provides a comprehensive and concise overview of the use of machine learning techniques for the morphological classification of radio galaxies. It summarizes the recent literature on this topic, highlighting the main challenges, achievements, state-of-the-art methods, and the future research directions in the field. The application of machine learning in radio astronomy has led to a new paradigm shift and a revolution in the automation of complex data processes. However, the optimal exploitation of machine/deep learning in radio astronomy, calls for continued collaborative efforts in the creation of high-resolution annotated data sets. This is especially true in the case of modern telescopes like MeerKAT and the LOw-Frequency ARray (LOFAR). Additionally, it is important to consider the potential benefits of utilizing multi-channel data cubes and algorithms that can leverage massive datasets without relying solely on annotated datasets for radio galaxy classification.

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.