Accretion disks with a large scale magnetic field around black holes, and magnetic jet collimation

TL;DR

This paper investigates how large-scale magnetic fields form in accretion disks around black holes, emphasizing the role of disk structure and conductivity, and explores how magnetic fields can collimate jets through magneto-torsional oscillations.

Contribution

It introduces a model considering the nonuniform vertical structure of disks, showing how high conductivity prevents magnetic diffusion and supports strong magnetic fields near black holes, and analyzes jet collimation mechanisms.

Findings

High conductivity prevents magnetic field diffusion in outer disk layers.

Stationary states with strong magnetic fields near black holes are possible.

Jet radius oscillates due to magneto-torsional oscillations, either regularly or chaotically.

Abstract

We discuss the problem of the formation of a large-scale magnetic field in the accretion disks around black holes, taking into account the nonuniform vertical structure of the disk. The high electrical conductivity of the outer layers of the disk prevents the outward diffusion of the magnetic field. This implies a stationary state with a strong magnetic field in the inner parts of the accretion disk close to the black hole, and zero radial velocity at the surface of the disk. Magnetic jet collimation is considered, when the jet radius is hold due to magneto-torsional oscillations. The range of parameters is found where jet radius is oscillating, regularly or chaotically, within restricted values.