HYDRODYNAMICAL NUMERICAL SIMULATION OF WIND PRODUCTION FROM BLACK HOLE HOT ACCRETION FLOWS AT VERY LARGE RADII

Abstract

ABSTRACT Previous works show that strong winds exist in hot accretion flows around black holes. Those works focus only on the region close to the black hole, so it is unknown whether or where the wind production stops at large radii. In this paper, we investigate this problem with hydrodynamical simulations. We take into account the gravities of both the black hole and the nuclear star clusters. For the latter, we assume that the velocity dispersion of stars is a constant and its gravitational potential ∝ &sgr; 2 ln ( r ) ?> , where σ is the velocity dispersion of stars, and r is the distance from the center of the galaxy. We focus on the region where the gravitational potential is dominated by the star cluster. We find that, just as for the accretion flow at small radii, the mass inflow rate decreases inward, and the flow is convectively unstable. However, a trajectory analysis shows that there is very little wind launched from the flow. Our result, combined with the results of Yuan et al.’s study from 2015, indicates that the mass flux of wind launched from hot accretion flow M ˙ wind = M ˙ BH ( r / 20 r s ) ?> , with r ≲ R A ≡ GM BH / &sgr; 2 ?> . Here, M ˙ BH ?> is the accretion rate at the black hole horizon, and R A is similar to the Bondi radius. We argue that the inward decrease of inflow rate is not due to mass loss via wind, but to convective motion. The disappearance of wind outside R A must be due to the change of the gravitational potential, but the exact reason remains to be probed.