Two-dimensional hydrodynamical simulation of hot accretion flows with radiative cooling
by Yuan, Feng and Bu, Defu
9 pages, 9 figures; submitted to MNRAS
The most important finding of two-dimensional hydrodynamical simulations of hot accretion flows is that the flow is convectively unstable, because of its inward increase of entropy. As a result, the profile of the mass accretion rate is a function of radius, i.e., only a small fraction of accretion gas available at the outer boundary can finally fall onto the black hole, while the rest is lost in the convective outflows. Radiation is usually neglected in these simulations. When the radiative cooling becomes more and more important, the entropy will increase slower inward. The entropy can even decrease when the radiation becomes stronger than the viscous heating, i.e, the flow enters into the luminous hot accretion flow regime. In the present paper, we investigate the convective instability and correspondingly the profile of accretion rate in the presence of strong radiative cooling by performing two-dimensional hydrodynamical numerical simulation. This problem is important because the profile of the mass accretion rate determines the observational appearance of accretion flows, the growth of black hole, and the evolution of black hole spin. We find that the flow is still strongly convectively unstable, and the radial profile of accretion rate changes little compared to the case of non-radiative flow. This is because the gradient of entropy in the gravitational direction still increases inward although the gradient of entropy decreases.