Clumpy accretion onto black holes. I. Clumpy-ADAF structure and radiation

TL;DR

This paper models the dynamics of clumps within advection-dominated accretion flows around black holes, revealing how clump interactions influence accretion structure, radiation, and potential oscillations, with implications for various astrophysical objects.

Contribution

It provides analytical solutions for clump dynamics in ADAFs, exploring strong and weak coupling cases, and links clump behavior to accretion state oscillations and observational phenomena.

Findings

Clumps have higher velocity dispersion than ADAF in strong coupling.

Radial velocity of clumps is proportional to drag force coefficient in weak coupling.

Disrupted clumps can form debris disks, cooling the ADAF and causing oscillations.

Abstract

In this paper, we investigate the dynamics of clumps embedded in and confined by the advection-dominated accretion flows (ADAF), in which collisions among the clumps are neglected. We start from the collisionless Boltzmann equation and assume that interaction between the clumps and the ADAF is responsible for transporting angular momentum of clumps outward. The inner edge of the clumpy-ADAF is set to be the tidal radius of the clumps. We consider strong and weak coupling cases, in which the averaged properties of clumps follow the ADAF dynamics and mainly determined by the black hole potential, respectively. We get the analytical solution of the dynamics of clumps for the two cases. The velocity dispersion of clumps is one magnitude higher than the ADAF for the strong coupling case. For the weak coupling case, we find that the mean radial velocity of clumps is linearly proportional to the coefficient of the drag force. We show that the tidally disrupted clumps would lead to accumulation of the debris to form a debris disk in the Shakura-Sunyaev regime. The entire hot ADAF will be efficiently cooled down by photons from the debris disk, giving rise to collapse of the ADAF and quench the clumpy accretion. Subsequently, evaporation of the collapsed ADAF drives resuscitate of a new clumpy-ADAF, resulting in an oscillation of the global clumpy-ADAF. Applications of the present model are briefly discussed to X-ray binaries, ionization nuclear emission regions (LINERs) and BL Lac objects.