The effects of toroidal magnetic field on the vertical structure of hot accretion flows

TL;DR

This study investigates how toroidal magnetic fields influence the vertical structure and thermal equilibrium of hot, optically thin accretion flows around black holes using two-dimensional MHD equations and self-similar assumptions.

Contribution

It introduces a model incorporating both large-scale and fluctuating magnetic fields to analyze their effects on accretion disk structure and heating mechanisms.

Findings

Increased magnetic field strength reduces viscous heating.

Maximum viscous heating occurs at the disk mid-plane.

Magnetic dissipation peaks at the disk surface.

Abstract

We solved the set of two-dimensional magnetohydrodynamic (MHD) equations for optically thin black hole accretion flows incorporating toroidal component of magnetic field. Following global and local MHD simulations of black hole accretion disks, the magnetic field inside the disk is decomposed into a large scale field and a fluctuating field. The effects of the fluctuating magnetic field in transferring the angular momentum and dissipating the energy are described through the usual $ \alpha $ description. We solved the MHD equations by assuming steady state and radially self-similar approximation in $ r-\theta $ plane of spherical coordinate system. We found that as the amount of magnetic field at the equatorial plane increases, the heating by the viscosity decreases. In addition, the maximum amount of the heating by the viscous dissipation is produced at the mid-plane of the disk, while that of the heating by the magnetic field dissipation is produced at the surface of the disk. Our main conclusion is that in terms of the no-outflow solution, thermal equilibrium still exists for the strong magnetic filed at the equatorial plane of the disk.