Global structure and dynamics of slowly rotating accretion flows

Abstract

ABSTRACT We study the global solutions of slowly rotating accretion flows around the supermassive black hole in the nucleus of an elliptical galaxy. The velocity of accreted gas surrounding the black hole is initially subsonic and then falls on to the black hole supersonically, so accretion flow must be transonic. We numerically solve equations from the Bondi radius to near the black hole. The focus of our discussion will be on the properties of slightly rotating accretion flows in which radiative losses have been ignored. This study discusses how outer boundary conditions (the temperature and specific angular momentum at the outer boundary) influence accretion flow dynamics. We investigate two physically discontinuous regimes: the Bondi-like type accretion and the disc-like type accretion. A Bondi-like accretion occurs when the specific angular momentum at the Bondi radius ℓB is smaller than the specific angular momentum at the marginally stable orbit ℓms. In comparison, a disc-like accretion occurs when the specific angular momentum at the Bondi radius ℓB is larger than the specific angular momentum of the marginally stable orbit ℓms. We also keep the assumption of hydrostatic equilibrium and compare our results with the case in which it is not considered. According to this study, considering the assumption of hydrostatic equilibrium reduces the mass accretion rate. Additionally, we find our solution for different ranges of the viscosity parameter α. Finally, we study the effect of galaxy potential on slowly rotating accretion flows.