Astronomy Reports最新文献

This paper presents the results of MHD simulations of astrophysical and laboratory supersonic jets under a superposition of poloidal (({{B}_{r}}), ({{B}_{z}})) and toroidal (({{B}_{phi }})) magnetic fields. It is shown that the escaping matter is quickly collimated by the magnetic field. A shock wave of an elongated shape is formed, which moves from the target to the boundary of the chamber, leaving behind a stable flow. A periodic shock wave structure is observed inside the main conical expanding shock wave. It is shown that the toroidal component of the magnetic field remains in the region throughout the entire calculation and plays a role in the collimation of the flow. The poloidal magnetic field decreases in the region of the jet cone, but remains in the simulation region throughout the calculation and also participates in flow collimation. Thus, both components ({{B}_{z}}) and ({{B}_{phi }}) take part in the collimation of the flow by the magnetic field. The width of the jet and the opening angle of the cone (theta ) depend on the magnitude of the magnetic field induction. As the field increases, the jet becomes narrower and the cone angle decreases. Initially, we do not specify the rotation of the jet (Omega ). However, due to the presence of the ({{B}_{phi }}) field, the substance acquires angular velocity and twists along the (z) axis. The simulation results are in agreement with laboratory jets arising in the experiment at the Neodymium laser installation, and with the previously obtained results of MHD modeling of jet formation separately, in poloidal or toroidal magnetic field.

This paper describes the results of a laboratory experiment on the sub-Alfvén expansion of a quasi-spherical laser plasma cloud into a vacuum magnetic field in the regime of nonmagnetized ions. The role of Hall fields and currents in the anomalously fast dynamics of the magnetic field during the collapse phase of a diamagnetic cavity is considered. Detailed spatial measurements of the azimuthal Hall fields configuration are demonstrated and their relationship to diamagnetic cavity collapse is determined. As a result of the experiment, data were obtained confirming the hypothesis about the transfer of the main magnetic field by the movement of electrons associated with Hall currents.

The use of “plasma focus” type facilities, such as PF-3 (Kurchatov Institute), allows carrying out well-controlled and diagnosable laboratory experiments to study laboratory jets with scale parameters close to the jets of young stars. In this paper, we present the results of numerical modeling of plasma outburst propagation in PF-3. A self-consistent configuration was chosen as the initial conditions, which correctly describes the internal structure of the jet. This allowed us to obtain a detailed structure of the interaction between the magnetized emission and the ambient gas. Due to the scalability of such a structure, one should expect such a structure from the head shock waves of jets of young stars.

Using ground-space VLBI data from the RadioAstron project archive, the phase distortions of the cross-spectrum caused by the ionosphere have been calculated and their influence on the results of determination of the visibility function has been studied. The Arecibo Observatory’s 300-m antenna served as the ground station for the interferometer. The separation of ionospheric phase distortions from the influence of the interstellar and interplanetary medium and instrumental errors is based on different frequency dependencies of these effects. The amplitude of ionospheric phase variation caused by electron density fluctuations in the ionosphere above the Arecibo radio telescope is several radians per observation session of about one hour. The structure function of phase variations indicates a continuous spectrum of electron density fluctuations at typical times of ( gtrsim )2–5 min with no pronounced signs of quasi-periodic processes. Ionospheric phase f-luctuations during pulsar observations increase the width of the maximum of the amplitude of the visibility function as a function of the residual fringe rate by 5–10 mHz with a decrease in the value at the maximum of ( approx {kern 1pt} 10% ). When constructing images of radio galaxies and quasars from ground-based VLBI observations, these phase shifts can significantly distort the final results.

In April 2017, the Event Horizon telescope received an image of a supermassive black hole in the Sagittarius A* source. This image consists of a ring-like structure that contains three areas with increased brightness (spots). If we assume that these spots are associated with flares near the event horizon of a black hole, then we can estimate its spin. Our estimate gives a value of the order of (a approx 0.9).

The paper presents the principle of operation, the main components and the results of the work of the software created in the Sternberg Astronomical Institute of Moscow State University. The PC is designed for processing of large volumes of space geodetic data. The developed software was used to process inter-satellite measurements of a space-based constellation intended to measure the parameters of the Earth’s gravitational field (EGF). The experimental option of the software enables working with both simulated data and real data of GRACE and GRACE Follow-on missions. This experimental version was used to recover the EGF parameters on real GRACE and GRACE-FO mission data. Solutions were developed for every month within the measurement time intervals from 2010 to 2021, as well as for extended time intervals of 4.3 and 7.6 years. A comparison of the obtained solutions with the results of the EGF recovery obtained by other researchers is presented.

The estimation of the initial spin period of pulsars involves the important questions such as the late stage evolution of massive stars and the formation process of neutron stars. However, the estimated initial spin exists the bias based on the magnetic dipole radiation (MDR) model, since the braking index of a dozen of observed pulsars ranges in (1 < n < 3) that is deviated from the expected value of 3 by MDR. The magnetic dipole radiation plus wind (MDRW) model for a pulsar successfully explains the evolution of the braking index between 1 and 3, by which we calculate the initial spins of the pulsars with the measured braking index, and obtain their distribution between ( sim {kern 1pt} 18) and ( sim {kern 1pt} 50) ms. This result is consistent with the statistics of the observed young pulsars, less than the fastest spin period of 16 ms of the rotation-powered X-ray pulsar PSR J0537–6910.

At present, there is little doubt that accretion discs surrounding compact astrophysical objects such as black holes, white dwarfs, and neutron stars may have magnetic field structures. Thus, they explain the transfer of angular momentum between different parts of the disc and some other processes. There are various ways to explain the occurrence of these magnetic fields. In this paper, we study the possibility of generation of magnetic fields due to the Biermann battery mechanism. It is associated with radial flows of protons and electrons. Due to their different masses, they interact differently with the rotating medium, producing circular currents that generate magnetic fields. Previously, a similar process was studied for galactic discs and it was shown that the battery mechanism can generate initial magnetic fields in such objects. Here, we discuss the action of the Biermann battery for accretion disks. This requires solving an integral equation of the second kind, which arises if we take into account the self-interaction of the magnetic field. It is shown that co-rresponding fields are quite significant and can play an important role in the evolution of magnetic fields in discs.

In the present research work, we have carried out an analysis of the non-linear stability of the circular restricted three-body problem (CR3BP) with Kerr-like primaries. The model discussed here includes three bodies, two of which are Kerr primaries that spin on their axes and at the same time, revolve around the mutual center of mass (origin) and the third is an infinitesimal mass. We take here, the parameter (epsilon ) which represents the transition from Newtonian dynamics to beyond-Newtonian dynamics. With this perturbation, we evaluate the equation of motion of infinitesimal mass and then discuss the nonlinear stability of triangular stationary points ({{mathbb{L}}_{4}}) and ({{mathbb{L}}_{5}}). We use the KAM Theorem for the stability analysis and obtained some meaningful conclusions numerically. Further, these obtained results on stability and other dynamical properties like the location of ({{mathbb{L}}_{4}}) and ({{mathbb{L}}_{5}}), potential surfaces, and regions of motions have been discussed graphically.

Depending on the distance of the exoplanet from the central star and the properties of this star, different regimes of stellar wind flow around it arise. If the exoplanet is located at a distance up to the Alfvén radius, where the wind speed is equal to the Alfvén speed, or the Alfvén Mach number ({{M}_{{text{A}}}} = 1), the exoplanet generates Alfvén wings. If it is situated beyond the Alfvén radius, a comet-like magnetosphere appears, similar to that of the planets of the Solar System. The paper examines how the transition from one flow regime to another can be described on the base of a paraboloid model of the magnetospheric magnetic field using the example of exoplanet HD 209458b.