Hydrodynamic Simulation of Two Component Advective Flows around Black Holes

TL;DR

This paper uses numerical simulations to demonstrate how viscous accretion flows around black holes naturally form a two-component structure, with a Keplerian disk and a sub-Keplerian halo, explaining observed spectral and timing properties.

Contribution

It provides a numerical validation of the two-component advective flow model, showing the formation and stability of Keplerian disks and sub-Keplerian halos in viscous accretion flows.

Findings

High viscosity leads to Keplerian disk formation.

Low viscosity results in sub-Keplerian flow with shock waves.

The two-component structure is stable and explains black hole spectral states.

Abstract

We carry out a series of numerical simulations of viscous accretion flows having a reasonable spatial distribution of the viscosity parameter. We add the power-law cooling throughout the flow. We show that, in agreement with the theoretical solutions of viscous transonic flows, matter having the viscosity parameter above a critical value becomes a Keplerian disk while matter having lesser viscosity remains a low angular momentum, sub-Keplerian flow. The latter component produces centrifugal pressure supported shock waves. Thus, for instance, a flow having sufficiently high viscosity on the equatorial plane and low viscosity above and below, would produce a Two Component Advective Flow (TCAF) where a Keplerian disk is surrounded by a rapidly infalling sub-Keplerian halo. We find that the post- shock region of the relatively cooler Keplerian disk is evaporated and the overall configuration is quite stable. This agrees with the theoretical model with two components which attempt to explain the spectral and timing properties of black hole candidates.