Accretion into Black Hole, and Formation of Magnetically Arrested Accretion Disks

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 ≤ 7r 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 the 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 ∼ 0.5Ṁ 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.

The Polarized Image of a Synchrotron-emitting Ring of Gas Orbiting a Black Hole

“…In this general case, we need to be careful about the geometry of the magnetic field. In a three-dimensional accretion flow in which magnetic field lines penetrate the disk from one side to the other, as for instance in a magnetically arrested disk (MAD) field geometry (Igumenshchev et al 2003;Narayan et al 2003;Tchekhovskoy et al 2011;Bisnovatyi-Kogan 2019), one expects a reflection antisymmetry in B eq about the midplane. That is, B r and B f would flip sign when crossing the mid-plane, whereas B z would retain the same sign on the two sides.…”

The Polarized Image of a Synchrotron Emitting Ring of Gas Orbiting a Black Hole

“…In this general case, we need to be careful about the geometry of the magnetic field. In a three-dimensional accretion flow in which magnetic field lines penetrate the disk from one side to the other, as for instance in a magnetically arrested disk (MAD) field geometry (Narayan et al 2003;Igumenshchev et al 2003;Tchekhovskoy et al 2011;Bisnovatyi-Kogan 2019), one expects a reflection antisymmetry in B eq about the midplane. That is, B r and B φ would flip sign when crossing the midplane, whereas B z would retain the same sign on the two sides.…”

Magnetically arrrested disk around a black hole, and jet formation

“…The first and the second equations in (1.1) are related to the conservation of the magnetic flux along the radial and tangential directions. In Newtonian limit the following solution for the evolution with time of the r and θ physical components of the magnetic field was obtained [6], see also [2]. Figure 1: Alexandr Ruzmaikin (Left) A qualitative picture of a stationary accretion of matter with a large scale magnetic field onto BH, Arrows indicate the direction of motion of the matter.…”

“…Deviations from the spherical symmetry around a BH appear only due to the magnetic field. It was shown in [7,2], that the only physically relevant solution exist at y = 1, denoting equipartition between magnetic and kinetic energies everywhere. In this case only one equation remains…”