Rotating Accretion Flows near a Black Hole: A Numerical Study

Abstract

The characteristics of thin, axisymmetric, supersonic accretion flows near a black hole is presented. Such flows of inviscid, cold adiabatic gas are characterized by the specific angular momentum and the specific energy. Using two-dimensional numerical simulations in cylindrical geometry, we show that there are various regimes in which the accretion flows behave distinctly differently. We compare such numerical solutions with analytical solutions. We confirm that for a wide range of above parameters a stable standing shock wave with a vortex inside it forms close to the black hole. Apart from steady state solutions, we show the existence of non-steady solutions for thin accretion flows where the accretion shock is destroyed and re-generated periodically. The period is roughly equal to 4 – 6 × 10³ R _g /c depending on the angular momentum of the flow. The unstable behavior should be caused by dynamically induced instabilities, since inviscid, adiabatic gas is considered. We discuss possible relevance of the periodic behavior on quasi-periodic oscillations (QPOs) observed in galactic and extragalactic black hole candidates.