Abstract
The exact time-dependent solution is obtained for a magnetic field growth during a spherically symmetric accretion into a black hole (BH) with a Schwarzschild metric. Magnetic field is increasing with time, changing from the initially uniform into a quasi-radial field. Equipartition between magnetic and kinetic energies in the falling gas is supposed to be established in the developed stages of the flow. Estimates of the synchrotron radiation intensity are presented for the stationary flow. The main part of the radiation is formed in the relativistic region r ≤ 7 r g , where r g is a BH gravitational radius. The two-dimensional stationary self-similar magnetohydrodynamic solution is obtained for the matter accretion into BH, in a presence of a large-scale magnetic field, under assumption, that the magnetic field far from the BH is homogeneous and its influence on the flow is negligible. At the symmetry plane perpendicular to the direction of the distant magnetic field, the dense quasi-stationary disk is formed around BH, which structure is determined by dissipation processes. Solutions of the disk structure have been obtained for a laminar disk with Coulomb resistivity and for a turbulent disk. Parameters of the shock forming due to matter infall onto the disk are obtained. The radiation spectrum of the disk and the shock are obtained for the 10 M ⊙ BH. The luminosity of such object is about the solar one, for a characteristic galactic gas density, with possibility of observation at distances less than 1 kpc. The spectra of a laminar and a turbulent disk structure around BH are very different. The laminar disk radiates mainly in the ultraviolet, the turbulent disk emits a large part of its flux in the infrared. It may occur that some of the galactic infrared star-like sources are a single BH in the turbulent accretion state. The radiative efficiency of the magnetized disk is very high, reaching ∼ 0.5 M ˙ c 2 . This model of accretion was called recently as a magnetically arrested disk (MAD). Numerical simulations of MAD and its appearance during accretion into neutron stars, are considered and discussed.
Highlights
The aim of this paper is to present a review of works on the modeling of the accretion into a black hole (BH) of a gas with a large scale magnetic field
Universe 2019, 5, 146 arrested disk (MAD). It follows from this review, that extensive numerical simulations made by this group are still not powerful enough, to reproduce all features of the magnetically arrested disk (MAD) model, which can be studied in the simplified analytical models
It was shown in Reference [13] that during a spherically symmetric accretion into a single black hole the transformation of the kinetic energy into radiation is very small in the absence of magnetic field, with the efficiency η = Lbh / Ṁc2 of order ∼ 10−8 [13], Lbh is a luminosity and Ṁ is a mass flux into BH
Summary
The aim of this paper is to present a review of works on the modeling of the accretion into a black hole (BH) of a gas with a large scale magnetic field Earlier works on this topic made by the author [1,2], have been done using a simplified analytical solutions, along with approximate one-dimensional solutions. It follows from this review, that extensive numerical simulations made by this group are still not powerful enough, to reproduce all features of the MAD model, which can be studied in the simplified analytical models An example of it is a strong shock wave formation because of collision with a disk of the gas, falling along magnetic field lines
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