Self-Similar Solutions for Viscous and Resistive ADAF

TL;DR

This paper derives self-similar solutions for resistive ADAF with magnetic fields, revealing how magnetic diffusivity and field strength influence flow structure, velocities, and accretion rates, aligning with MHD simulations.

Contribution

It introduces a self-similar analytical framework for resistive ADAF considering variable magnetic diffusivity and azimuthal magnetic fields, extending previous models.

Findings

Radial velocity and temperature increase with magnetic effects.

Rotational velocity remains sub-Keplerian and can reach zero at certain magnetic field strengths.

Magnetic diffusivity enhances mass accretion rate, but high magnetic pressure reduces the ratio to Bondi rate.

Abstract

In this paper, the self-similar solution of resistive advection dominated accretion flows (ADAF) in the presence of a pure azimuthal magnetic field is investigated. The mechanism of energy dissipation is assumed to be the viscosity and the magnetic diffusivity due to turbulence in the accretion flow. It is assumed that the magnetic diffusivity and the kinematic viscosity are not constant and vary by position and $\alpha$-prescription is used for them. In order to solve the integrated equations that govern the behavior of the accretion flow, a self-similar method is used. The solutions show that the structure of accretion flow depends on the magnetic field and the magnetic diffusivity. As, the radial infall velocity and the temperature of the flow increase, and the rotational velocity decreases. Also, the rotational velocity for all selected values of magnetic diffusivity and magnetic field is sub-Keplerian. The solutions show that there is a certain amount of magnetic field that the rotational velocity of the flow becomes zero. This amount of the magnetic field depends on the gas properties of the disc, such as adiabatic index and viscosity, magnetic diffusivity, and advection parameters. The solutions show the mass accretion rate increases by adding the magnetic diffusivity and in high magnetic pressure case, the ratio of the mass accretion rate to the Bondi accretion rate decreases as magnetic field increases. Also, the study of Lundquist and magnetic Reynolds numbers based on resistivity indicates that the linear growth of magnetorotational instability (MRI) of the flow decreases by resistivity. This property is qualitatively consistent with resistive magnetohydrodynamics (MHD) simulations.