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S. G. Moiseenko

Publications and source records attributed to S. G. Moiseenko.

16 recordsLinked to original sources
arXiv2023

Wave propagation and transformation in the frame of magnetohydrodynamics with a vortex electric field

Bright transient objects in different wave bands have been discovered in recent years. To explain these short (from ms to s), and very powerful events different models, galactic and extragalactic, have been considered. One of popular model is based on the suggestion of transformation of the magnetized plasma blob, presumably a MHD shock wave, moving with relativistic speed, into electromagnetic pulse after collision with some obstacle, or at entering in media with different properties. Such transformation cannot be described in the frame of classical MHD equations, which don't contain the displacement current, and don't include such transformation. Updating of the classic MHD equations by using of full set of Maxwell equation with displacement current, made recently by several authors, gave a possibility to describe hydrodynamic phenomena, together with electromagnetic ones by the same set of equations. Here we apply these equations for study of propagation of different waves with account of displacement current, and of transformation between different kind of waves in the nonuniform media. We derive a dispersion equation describing a propagation of a weak linear wave in a uniform magnetized plasma, and consider in details the cases with perpendicular and parallel motion to the magnetic field. It contains MHD, HD, Alfven and EM waves in the limiting cases, and some new types of behaviour in a general situation. We consider a plasma with zero viscosity and heat conductivity, with a finite scalar electric conductivity. We have shown, that transformation of MHD into EM wave may happen only in a highly magnetized plasma, and have found the region of parameters, where no waves exist, and only damping static perturbations may be present.

physics.plasm-ph↗
arXiv2019

3D numerical study of an anisotropic heat transfer in outer layers of magnetized neutron stars

Periodic changes in a thermal soft X-ray flux of a rotating neutron star indicate a non-uniform distribution of the surface temperature. A possible cause of this phenomenon is a suppression of the heat flux across the magnetic field lines in a crust and an envelope of magnetized neutron stars. In this paper we study three-dimensional effects, associated with non-axisymmetric magnetic fields in neutron stars. We calculate the surface temperature distribution by solving numerically a three dimensional heat transfer equation in a magnetized neutron star crust. We adopt an anisotropic (tensorial) electron thermal conductivity coefficient, which is derived as an analytical solution of the Boltzmann equation with a Chapman-Enskog method. To calculate the surface temperature distribution, we construct a local one-dimensional plane-parallel model ("Ts-Tb"-relationship) of a magnetized neutron star envelope. We then use it as an outer boundary condition for the three-dimensional problem in the crust to find the self-consistent solution. To study possible observational manifestations from anisotropic temperature distributions we calculate light curves with a composite black-body model. Our calculations show, that a non-axisymmetric magnetic field distribution can lead to the irregular non-sinusoidal shape of a pulse profile as well as in some cases a significant amplification of pulsations of the thermal flux in comparison to the pure-dipolar magnetic field configurations.

astro-ph.HE↗
arXiv2019

Magnetorotational Mechanism of the Explosion of Core-Collapse Supernovae

The idea of the magnetorotational explosion mechanism is that the energy of rotation of the neutron star formed in the course of a collapse is transformed into the energy of an expanding shock wave by means of a magnetic field. In the two-dimensional case, the time of this transformation depends weakly on the initial strength of the poloidal magnetic field because of the development of a magnetorotational instability. Differential rotation leads to the twisting and growth of the toroidal magnetic-field component, which becomes much stronger than the poloidal component. In the case where the initial configuration of the magnetic field is close to a dipole configuration, the ejection of matter has a jet character, whereas, in the case of a quadrupole configuration, there arises an equatorial ejection. In either case, the energy release is sufficient for explaining the observed average energy of supernova explosion. Neutrinos are emitted as the collapse and the formation of a rapidly rotating neutron star proceeds. In addition, neutrino radiation arises in the process of magnetorotational explosion owing to additional rotational-energy losses. In order to explain an interval of 4.5 hours between the two observed neutrino signals from SN 1987A, it is necessary to assume a weakening of the magnetorotional instability and a small initial magnetic field (10(9)-10(10)G) in the newly formed rotating neutron star. The existence of a black hole in the SN 1987A remnant could explain the absence of any visible pointlike source at the center of the explosion.

astro-ph.HE↗
arXiv2018

Gravitational waves and core-collapse supernovae

A mechanism of formation of gravitational waves in the Universe is considered for a nonspherical collapse of matter. Nonspherical collapse results are presented for a uniform spheroid of dust and a finite-entropy spheroid. Numerical simulation results on core-collapse supernova explosions are presented for the neutrino and magnetorotational models. These results are used to estimate the dimensionless amplitude of the gravitational wave with a frequency ν~1300 Hz, radiated during the collapse of the rotating core of a pre-supernova with a mass of 1:2M(sun) (calculated by the authors in 2D). This estimate agrees well with many other calculations (presented in this paper) that have been done in 2D and 3D settings and which rely on more exact and sophisticated calculations of the gravitational wave amplitude. The formation of the large-scale structure of the Universe in the Zel'dovich pancake model involves the emission of very long-wavelength gravitational waves. The average amplitude of these waves is calculated from the simulation, in the uniform spheroid approximation, of the nonspherical collapse of noncollisional dust matter, which imitates dark matter. It is noted that a gravitational wave radiated during a core-collapse supernova explosion in our Galaxy has a sufficient amplitude to be detected by existing gravitational wave telescopes.

astro-ph.HE↗
arXiv2016

Isentropic 'shock waves' in numerical simulations of astrophysical bodies

Strong discontinuities in solutions of the gas dynamic equations under isentropic conditions, i.e., with continuity of entropy at the discontinuity, are examined. Solutions for a standard shock wave with continuity of energy at the discontinuity are compared with those for an isentropic 'shock wave'. It is shown that numerical simulation of astrophysical problems in which high-amplitude shock waves are encountered (supernova explosions, modelling of jets) with conservation of entropy, rather than of energy, leads to large errors in the shock calculations. The isentropic equations of gas dynamics can be used only when there are no strong discontinuities in the solution or when the intensity of the shocks is not high and they do not significantly affect the flow.

astro-ph.HE↗
arXiv2014

Magnetorotational explosions of core-collapse supernovae

Core-collapse supernovae are accompanied by formation of neutron stars. The gravitation energy is transformed into the energy of the explosion, observed as SN II, SN Ib,c type supernovae. We present results of 2-D MHD simulations, where the source of energy is rotation, and magnetic field serves as a "transition belt" for the transformation of the rotation energy into the energy of the explosion. The toroidal part of the magnetic energy initially grows linearly with time due to differential rotation. When the twisted toroidal component strongly exceeds the poloidal field, magneto-rotational instability develops, leading to a drastic acceleration in the growth of magnetic energy. Finally, a fast MHD shock is formed, producing a supernova explosion. Mildly collimated jet is produced for dipole-like type of the initial field. At very high initial magnetic field no MRI development was found.

astro-ph.HE↗
arXiv2008

Outflows from Magnetorotational Supernovae

We discuss results of 2D simulations of magnetorotational(MR) mechanism of core collapse supernova explosions. Due to the nonuniform collapse the collapsed core rotates differentially. In the presence of initial poloidal magnetic field its toroidal component appears and grows with time. Increased magnetic pressure leads to foramtion of compression wave which moves outwards. It transforms into the fast MHD shock wave (supernova shock wave). The shape of the MR supernova explosion qualitatively depends on the configuration of the initial magnetic field. For the dipole-like initial magnetic field the supernova explosion develops mainly along rotational axis forming mildly collimated jet. Quadrupole-like initial magnetic field leads to the explosion developing mainly along equatorial plane. Magnetorotational instability was found in our simulations. The supernova explosion energy is growing with increase of the initial core mass and rotational energy of the core, and corresponds to the observational data.

astro-ph↗
arXiv2006

Magnetorotational supernovae with jets

We present results of 2D simulation of magnetorotational (MR) supernova accompanied by jet formation in the core collapse supernova explosion. Initial magnetic field used in the simulations has dipole-like symmetry. Contrary to the simulations of MR supernova with initial quadrupole-like magnetic field, where the matter was ejected mainly near the equatorial plane, in presence of the dipole-like initial magnetic field the supernova explosion is developing preferably along a rotational axis, and leads to formation of a protojet. We expect that protojet propagation through the envelope of the star will be accompanied by its collimation. The magnetorotational instability (MRI) was found in simulations, similar to the earlier considered case of the quadrupole-like initial magnetic field. Our estimations show that the characteristic time for the reconnection of the magnetic field is much larger than the MRI development time. The supernova explosion energy for the dipole-like field is about $0.61\cdot 10^{51}$erg, and about $0.13M_\odot$ of mass was ejected during the explosion.

astro-ph↗
arXiv2005

Core collapse supernovae: magnetorotational explosion

Core-collapse supernovae are connected with formation of neutron stars. Part of the gravitation energy is transformed into the energy of the explosion, observed in SN II, SN Ib,c type supernovae. The mechanism of transformation is not simple, because the overwhelming majority of the energy is going into weakly interacting neutrino. The attempts to use this energy for the explosion were not successful during about 40 years of investigation. We consider the explosion mechanism in which the source of energy is the rotation, and magnetic field serves for the transformation of the rotation energy into the energy of explosion. 2-D MHD simulations of this mechanism were performed. After the collapse the core consists of a rapidly rotating proto-neutron star with a differentially rotating envelope. The toroidal part of the magnetic energy generated by the differential rotation grows as quadratic function with time at the initial stage of the evolution of the magnetic field. The linear growth of the toroidal magnetic field is terminated by the development of magnetohydrodynamic instability, when the twisted toroidal component strongly exceeds the poloidal field, leading to a drastic acceleration in the growth of magnetic energy. At the moment when the magnetic pressure becomes comparable to the gas pressure at the periphery of the proto-neutron star the MHD compression wave appears and goes through the envelope of the collapsed core. It transforms into the fast MHD shock and produces a supernova explosion. Our simulations give the energy of the explosion $0.6\cdot 10^{51}$ ergs. The amount of the mass ejected by the explosion is $\sim 0.14M_\odot$. The implicit numerical method, based on the Lagrangian triangular grid of variable structure, was used for the simulations.

astro-ph↗
arXiv2005

Magnetorotational supernovae

We present the results of 2D simulations of the magnetorotational model of a supernova explosion. After the core collapse the core consists of rapidly a rotating proto-neutron star and a differentially rotating envelope. The toroidal part of the magnetic energy generated by the differential rotation grows linearly with time at the initial stage of the evolution of the magnetic field. The linear growth of the toroidal magnetic field is terminated by the development of magnetohydrodynamic instability, leading to drastic acceleration in the growth of magnetic energy. At the moment when the magnetic pressure becomes comparable with the gas pressure at the periphery of the proto-neutron star $\sim 10-15$km from the star centre the MHD compression wave appears and goes through the envelope of the collapsed iron core. It transforms soon to the fast MHD shock and produces a supernova explosion. Our simulations give the energy of the explosion $0.6\cdot 10^{51}$ ergs. The amount of the mass ejected by the explosion is $\sim 0.14M_\odot$. The implicit numerical method, based on the Lagrangian triangular grid of variable structure, was used for the simulations.

astro-ph↗
arXiv2004

Magnetorotational supernova simulations

We present 2D results of simulations of the magnetorotational core collapsed supernova. For the first time we obtain strong explosion for the core collapsed supernova. In 2D approximation we show that amplification of the toroidal magnetic field due to the differential rotation leads to the formation of MHD shockwave, which produces supernova explosion. The amounts of the ejected mass $0.1M_\odot$ and energy $\sim 0.5\div0.6 \cdot 10^{51}$ergs can explain the energy output for supernova type II or type Ib/c explosions. The shape of the explosion is qualitatively depends on the initial configuration of the magnetic field, and may form strong ejection neat the equatorial plane, or produce mildly collimated jets. Our simulation show that during the evolution of the magnetic field the magnetorotational instability appears and leads to exponential growth of the magnetic field strength.

astro-ph↗
arXiv2003

Magnetorotational mechanism of supernova type II exlosion

Results of 2D simulations of the magnetorotational mechanism of supernova type II are presented. Amplification of toroidal magnetic field of the star due to differential rotation of the star leads to the transformation of the rotational (gravitational) energy to the energy of the supernova explosion. In our simulation the energy of the explosion is $1.12 \cdot 10^{51}erg$. The explosion ejects about $0.11 M_\odot$.

astro-ph↗
arXiv2001

Jet Formation from Rotating Magnetized Objects

Jet formation is connected most probably with matter acceleration from the vicinity of rotating magnetized bodies. It is usually related to the mass outflows and ejection from accretion disks around black holes. Problem of jet collimation is discussed. Collapse of a rotating magnetized body during star formation or supernovae explosion may lead to a jet-like mass ejection for certain angular velocity and magnetic field distributions at the beginning of the collapse. Jet formation during magnetorotational explosion is discussed basing on the numerical simulation of collapse of magnetized bodied with quasi-dipole field.

astro-ph↗
arXiv1999

Nonstationary magnetorotational processes in a rotating magnetized cloud

We perform 2D numerical simulations of a magnetorotational explosion of a rotating magnetized gas cloud. We found that amplification of a toroidal magnetic field due to the differential rotation leads to a transformation of the part of the rotational energy of the cloud to the radial kinetic energy. Simulations have been made for 3 initial values of $ξ$ (the relation of magnetic energy to the gravitational energy of the cloud): $ξ=10^{-2},10^{-4},10^{-6}$. Part of the matter - $\sim 7%$ of the mass of the cloud ($\sim 3.3%$ of the final gravitational energy of the cloud) - gets radial kinetic energy which is larger than its potential energy and can be thrown away to the infinity. It carries about 30% of the initial angular momentum of the cloud. This effect is important for angular momentum loss in the processes of stellar formation, and for the magnetorotational mechanism of explosion suggested for supernovae. Simulations have been made on the basis of the Lagrangian 2D numerical implicit scheme on a triangular grid with grid reconstruction.

astro-ph↗
arXiv1997

Magnetorotational Supernova Explosion - 2D Numerical Simulation

Results of 2D numerical simulation of magnetorotational mechanism of supernova explosion are presented. It is shown that due to the differential rotation of the star toroidal component of magnetic field appears and grows with time. Angular momentum transfers outwards by the toroidal magnetic field. With the evolution of the process part of the envelope of the star is throwing away. The amount of thrown away mass and energy are estimated. The results of the simulation are qualitatively correspond to supernova explosion picture.

astro-ph↗