paper

Global dynamics of radiatively inefficient accretion flows: advection versus convection

arXiv:astro-ph/0404153 · doi:10.1111/j.1365-2966.2004.07897.x

Abstract

We obtain global solutions of radiatively inefficiently accretion flows around black holes. Whether and where convection develops in a flow are self-consistently determined with the mixing-length theory. The solutions can be divided into three types according to the strength of normal viscosity. Type I solution corresponds to large viscosity parameter $α\ga 0.1$, which is purely advection-dominated and with no convection, and has been extensively studied in the literature. Type II solution is for moderate , which has a three-zone structure. The inner zone is advection-dominated, the middle zone is convection-dominated and ranges from a few tens to a few thousands of gravitational radii, and the outer zone is convectively stable and matches outward a Keplerian disc. The net energy flux throughout the flow is inward as in type I solution. Type III solution which is for small $α\la 0.001$ consists of two zones as Abramowicz et al. suggested previously: an inner advection-dominated zone and an outer convection-dominated zone, separated at a radius of a few tens of gravitational radii. This type of solution has an outward net energy flux. In both type II and III solutions the radial density profile is between the 1/2 law of self-similar convection-dominated accretion flow model and the 3/2 law of self-similar advection-dominated accretion flow model, and the efficiency of energy release is found to be extremely low. Our results are in good agreement with those of recent numerical simulations.

arXiv comment13 pages, 2 figures, accepted for publication in MNRAS

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