Dissipative accretion flows around a rotating black hole

TL;DR

This paper analyzes the structure of cooling-dominated, rotating accretion flows around spinning black holes, revealing how shock waves depend on flow parameters and cooling effects, with implications for observed high-frequency oscillations.

Contribution

It provides a comprehensive analysis of accretion shock solutions around rotating black holes, highlighting the effects of cooling and rotation on shock formation and location.

Findings

Shock solutions exist over a wide parameter space.

Cooling reduces the likelihood of shock formation.

Shocks form closer to the black hole with higher accretion rates.

Abstract

We study the dynamical structure of a cooling dominated rotating accretion flow around a spinning black hole. We show that non-linear phenomena such as shock waves can be studied in terms of only three flow parameters, namely, the specific energy (${\cal E}$), the specific angular momentum ($\lambda$) and the accretion rate (${\dot m}$) of the flow. We present all possible accretion solutions. We find that a significant region of the parameter space in the ${\cal E}-\lambda$ plane allows global accretion shock solutions. The effective area of the parameter space for which the Rankine-Hugoniot shocks are possible is maximum when the flow is dissipation free. It decreases with the increase of cooling effects and finally disappears when the cooling is high enough. We show that shock forms further away when the black hole is rotating compared to the solution around a Schwarzschild black hole with identical flow parameters at a large distance. However, in a normalized sense, the flow parameters for which the shocks form around the rotating black holes are produced shocks closer to the hole. The location of the shock is also dictated by the cooling efficiency in that higher the accretion rate (${\dot m}$), the closer is the shock location. We believe that some of the high frequency quasi-periodic oscillations may be due to the flows with higher accretion rate around the rotating black holes.