New Astronomy Reviews最新文献

Within the central few hundred parsecs of the Milky Way, extending from longitude l = −1° to 1.5°, lies the Central Molecular Zone of the Galactic Centre. This extraordinary region is defined by a diverse variety of ISM features in numerous stages of evolution. Molecular cloud H₂ volume densities range from 10^3-8 cm⁻³ with an average of 10⁴ cm⁻³, two orders of magnitude above that of the galactic disk. The CMZ contains ∼3-5 × 10⁷ M_☉ of molecular gas, corresponding to around 5-10% of the content of the entire galaxy, and a similar fraction of its infrared luminosity. Gas temperatures, pressures and turbulent mach numbers are also significantly raised here, providing one of the more extreme environments for star formation within our observational reach.

We have hence been provided with a unique laboratory for probing the effects of these environments on the interplay between the ISM and star formation, and high resolution observations of both individual features and the large-scale structure of the CMZ can improve our understanding of the formation and evolution of this region, which we can then apply to similar regions in nearby galaxies.

This review will address historical and recent advancements in our observational and theoretical interpretations of the morphologies, dynamics and processes occurring in the ISM and massive stellar populations in the central few hundred parsecs. It will demonstrate how, across various spatial scales, episodic cycles of star formation, matter transport and feedback can be identified and potentially linked to observed features. The evolutionary states of molecular clouds, star forming regions and stellar clusters can be linked to their positions along orbits spanning the CMZ, and may be regulated by episodic processes such as material inflow or feedback. The concentric series of expanding bubbles and fronts visible in various electromagnetic bands can be related to echoes of past activity in the central cluster and Sgr A*. The ensemble of stellar ages and populations in the highly inhospitable environment of the central few parsecs points towards a series of accretion and starburst events.

The range of timescales and spatial scales involved in the aforementioned processes raises the possibility of a nested series of episodic cycles occurring concurrently, in which shorter timescale cycles regulate longer ones. The resulting complex and highly time-variable picture can help to explain many of the currently observed characteristics of the Galactic Centre, such as its deficient star forming efficiency, and can be applied to our understanding of the evolution of the galaxy as a whole.

Dark sector, constituting about 95% of the Universe, remains the subject of numerous studies. There are lots of models dealing with the cause of the effects assigned to “dark matter” and “dark energy”. This brief review is devoted to the very recent theoretical advances in these areas: only to the advances achieved in the last few years. For example, in section devoted to particle dark matter we overview recent publications on sterile neutrinos, self-interacting dark matter, dibarions (hexaquarks), dark matter from primordial “bubbles”, primordial black holes as dark matter, axions escaping from neutron stars, and dark and usual matter interacting via the fifth dimension. We also overview the second flavor of hydrogen atoms: their existence was proven by analyzing atomic experiments and is also evidenced by the latest astrophysical observations of the 21 cm spectral line from the early Universe. While discussing non-particle models of the cause of dark matter effects, we refer to modified Newtonian dynamics and modifications of the strong equivalence principles. We also consider exotic compact objects, primordial black holes, and retardation effects. Finally, we review recent studies on the cause of “dark energy effects”. Specifically, we cover two disputes that arose in 2019 and 2020 on whether the observations of supernovas, previously interpreted as the proof of the existence of dark energy, could have alternative explanations. Besides, we note a study of 2021, where dark energy is substituted by a new hypothetical type of dark matter having a magnetic-type interaction. We also refer to the recent model of a system of nonrelativistic neutral gravitating particles providing an alternative explanation of the entire dynamics of the Universe expansion – without introducing dark energy or new gravitational degrees of freedom.

ESA’s INTEGRAL space mission has achieved unique results for solar and terrestrial physics, although spacecraft operations nominally excluded the possibility to point at the Sun or the Earth. The Earth avoidance was, however, exceptionally relaxed for special occultation observations of the Cosmic X-ray Background (CXB), which on some occasions allowed the detection of strong X-ray auroral emission. In addition, the most intense solar flares can be bright enough to be detectable from outside the field of view of the main instruments. This article presents for the first time the auroral observations by INTEGRAL and reviews earlier studies of the most intense solar flares. We end by briefly summarising the studies of the Earth’s radiation belts, which can be considered as another topic of serendipitous science with INTEGRAL.

The numerous compact sources associated with neutron stars and white dwarfs discovered in recent decades are analyzed in terms of the Gravimagnetic Rotator model (GMR paradigm–Lipunov, 1987a, 1992). We offer the instrument for understanding of various observed features and evolutionary relationships of neutron stars and white dwarfs. We depict in a single diagram all objects from radio pulsars and dwarf novae to ultra luminous X-ray sources and a radio pulsating white dwarf. This diagram directly demonstrates the genetic link between different types of compact sources thereby making it possible to confirm and illustrate clearly the established evolutionary connections–such as that between bulge X-ray sources and millisecond pulsars. This approach allows us to understand the evolutionary status of Ultra Luminous X-ray sources. In addition, we propose an additional evolutionary branch of the formation of Magnetars. When our work was completed, an article by Kirsten et al.2021, was published, which reports the localization of FRB 20,200,120 in one of the globular clusters of the galaxy M81. This shows that the accretion-induced collapse scenario of the white dwarf (Lipunov and Postnov, 1985), considered in detail in this work, is a possible genealogical branch of Magnetar production.

When astrophysical jets were discovered one hundred years ago, the field of numerical simulations did not yet exit. Since the arrival of programmable computers though, numerical simulations have increasingly become an indispensable tool for dealing with “tough nut” problems which involve complex dynamic and non-linear phenomena. Astrophysical jets are an ideal example of such a tough nut, where multi-scale plasma physics, radiative and non-thermal processes, turbulence and relativity combine to present a formidable challenge to researchers.

Highlighting major achievements obtained through numerical simulations concerning the validity and nature of the Blandford–Znajek mechanism, the launching, collimation, acceleration and stability of jets, their interaction with the surrounding plasma, jet-galaxy feedback mechanisms etc., we trace how the field developed from its first tentative steps into the age of “maturity”. We also give a brief and personal outlook on how the field may evolve in the foreseeable future.

The major revolution in modern astronomy recognizing the universe as teeming with exoplanets, the discovery of liquid water in solar moons, and the continuing focus on Mars exploration, all accelerate the re-evaluation of potential biomarkers for extraterrestrial life. Based on life on planet Earth which relies heavily on chiral molecules and especially on homochiral families, the detection of molecules with these structural properties appears in all road-maps as prime indicators of extraterrestrial life. This review analyzes the strengths, bounds and potential weaknesses of relying on chirality and on homochirality as biomarkers, along with recommendations of how to practically use it. Some of the main issues presented, discussed and answered include: what is the extent to which chirality can be expected to be a universal feature of life; is detection of chirality enough or do we need also to detect homochirality; how justified is it to view life on Earth as purely homochiral; what are the weaknesses of the need to invent an arbitrary label of handedness (needed to define homochirality) and what are the pitfalls that emerge from these weaknesses; what stands behind a detected specific value of enantiomeric excess and what affects its values as we consider old, extinct life, just emerging embryonic life, or extant but rare life; how can one quantify the degree of homochirality; and, what are relevant experimental approached for detecting chirality on-ground and from distance? Finally, a summary with a concise list of recommendations is provided, along with a brief outlook.