Astronomy Reports最新文献

We address three issues: (1) The point particle assumption inherent to non-quantum physics is singular and entails divergent fields and integrals. (2) In quantum physics electromagnetism (EM) plays an asymmetric roll. It acts on quantum wave functions (QW) but QW does not react back. We suggest to promote the one-sided action of EM on QW into a mutual action-reaction status. This enables QW to share its non-singular feature with EM and to remove the Coulomb singularity. (3) Quantum mechanics is U(1) symmetric. QW multiplied by an arbitrary phase factor and EM written in7 the same Lorentz gauge, leave both EM and QW invariant. The minimal coupling of QW to the EM 4-vector potential, ({{A}_{mu }}), is a consequence of this arbitrary gauge. Symmetry under the restricted Lorentz gauge, is left out. We propose to enlarge U(1) to accommodate the restricted Lorentz gauge as well. This in turn invites in a coupling of QW to the derivatives of the vector potential, ({{partial }_{nu }}{{A}_{mu }}), in addition to the minimal coupling. We find that (i) electron acquires a distributed charge, reminiscent of the QED-renormalized charge distributions; (ii) because of its spin, electron acquires a self induced magnetic moment with the same g-factor as in QED but without relying on QED.

The paper presents an essay on the use of spectral analysis in the 19th–early 20th centuries to study the nature of the Sun.

The latest results of the most detailed analysis of multi-epoch polarization-sensitive observations of active galactic nuclei (AGN) jets at parsecs scales by very long baseline interferometry (VLBI) reveal several characteristic patterns of linear polarization distribution and its variability [1, 2]. Some of the observed profiles can be reproduced by a simple model of a jet threaded by a helical magnetic field. However, none of the models presented to date can explain the observed polarization profiles with an increase in its degree towards the edges of the jet, and accompanied by a “fountain” type electrical vector pattern and its high temporal variability in the center. Based on simulations of the VLBI observations of relativistic jets, we show here that the observed transverse linear polarization profiles can be naturally produced in a model of jets precessing on ten-years scales. In this scenario, due to the finite resolution of VLBI arrays, the initially strong polarization along the jet axis is blurred due to the superposition of regions whose polarization angle changes significantly when projected onto the sky plane. In our simulations, we qualitatively reproduce the distribution of the electric vector and its variability, though the polarization distribution images are characterized by a bright spine due to weak suppression of polarized emission, which is poorly consistent with observations of quasars. More effective depolarization can be obtained in models with the suppressed emission of the jet spine.

Due to the high-density nuclear matter equation of state (EOS) being as yet unknown, neutron stars (NSs) do not have a confirmed limiting “Chandrasekhar” type maximum mass. However, observations of NSs (PSR J1614-2230, PSR J0348+0432, PSR J0740+6620, PSR J0952–0607) indicate that the NS’s limiting mass, if there is any, could be well over (2{{M}_{ odot }}). On the other hand, there seems to be an observational mass gap (of around (2.5{-} 5{{M}_{ odot }})) between the lightest black hole and the heaviest NS. Therefore, the “massive NSs” are prime candidates to fill that gap. Several NS EOSs have been proposed using both microscopic and phenomenological approaches. In this project, we look at a class of phenomenological nuclear matter EOSs—relativistic mean field models—and see what kind of NS is formed from them. We compute the maximum mass supported by each model EOS to observe if the mass of the NS is indeed in the “massive” NS (( > {kern 1pt} 2{{M}_{ odot }})) regime. We also observe the effects of including exotic particles (hyperons, Δs) in the NS EOS and how that affects the NS mass. However, only by introducing the magnetic field, i.e. for magnetized anisotropic NSs, we find the mass exceeding (2.5{{M}_{ odot }}). Using tidal deformability constraints from gravitational wave observations, we place a further check on how physical the EOS and NSs are.

The paper provides a general overview of the current state of solar research.

This paper makes an attempt to describe the ideas about the Sun that dominated Europe in the 17th–19th centuries.

In the past decades, several neutron stars (NSs), particularly pulsars, with mass (M > 2{{M}_{ odot }}), have been observed. Hence, there is a generic question of the origin of massive compact objects. Here we explore the existence of massive, magnetized, rotating NSs by solving axisymmetric stationary stellar equilibria in general relativity using the Einstein equation solver for stellar structure XNS code. Such rotating NSs with magnetic field and rotation axes misaligned, hence with non-zero obliquity angle, can emit continuous gravitational waves (GW). We discuss the decay of the magnetic field due to Ohmic, Hall and Ambipolar diffusion, and the decay of angular velocity, and obliquity angle with time due to angular momentum extraction by GW and dipole radiation, which determine the timescales related to the GW emission. Further, in the Alfvén timescale, a differentially rotating, massive proto-NS rapidly settles into a uniformly rotating, less massive NS due to magnetic braking and viscosity. These explorations suggest that detecting massive NSs is challenging and sets a timescale for detection. We calculate the signal-to-noise ratio of GW emission, which confirms that any detector cannot detect them immediately, but detectable by Einstein Telescope and Cosmic Explorer over months of integration time, leading to direct detection of NSs.

An optically thin advective accretion disk appears to be indispensable to explain hard-state of black hole sources. Any transport of matter therein is assumed to be led by (modified) (alpha )-viscosity when the magnetic field is weak. We explore how large scale stronger magnetic field helps in transporting angular momentum in disk and outflow/jet, depending on the field geometry and plasma-(beta ) parameter, basically by underlying magnetic shear over (alpha )-viscosity. Interestingly, while above a critical accretion rate the accretion disk turns out to be thermally unstable, in the presence of stronger magnetic fields the disk regains its stability. In the present work, we establish this by numerical simulation based on HARMPI, while the underlying theory was established by one of us earlier. This magnetically arrested advective accretion disk (MA-AAF) in the optically thin regime has far reaching implications including the explanation of ultra-luminous X-ray sources.

It is shown that a description of the solar cycle using the odd zonal harmonic of the solar magnetic field expands our capabilities in two important areas of solar research: first, in improving and expanding the forecast to the near future of evolution of the cyclic solar activity and, second, in developing a program for monitoring the spectrophotometric characteristics of radiation of solar-like stars, aimed at obtaining new information about their magnetic fields.

The results of a spectral survey of the region of massive star formation DR21OH in the 4-mm wavelength range are presented. Sixty-nine molecules and their isotopologues have been detected, ranging from simple diatomic or triatomic species such as SO, SiO and CCH, to complex organic molecules such as CH₃OCHO or CH₃OCH₃. The obtained results qualitatively repeat the results of the survey of the same source at 3 mm. The inventories of molecules found at 3 and 4 mm overlap to a great extent. However, at 4 mm we found a number of species that have no allowed transitions in the 3-mm wavelength range, e.g., DCN, DNC, or SO⁺. The bulk of the molecules detected at 4 mm are those that are common for dense cores, e.g., HC₃N or CH₃CCH, but some of the detected species are typical for hot cores. The latter include complex organic molecules CH₃OCHO, CH₃CH₂OH, CH₃OCH₃, etc. However, the detected emission of these molecules probably arises in a gas heated to 30 K only. Nine molecules, including complex species CH₃C₃N, CH₃CH₂CN, CH₃COCH₃, were found by spectral line stacking. This demonstrates the prospects of the method in the study of molecular clouds.