The Standing Accretion Shock Instability in the Disk around the Kerr Black Hole

TL;DR

This study investigates the standing accretion shock instability (SASI) around Kerr black holes, revealing how frame dragging influences shock stability and oscillation periods, with detailed simulations and linear analysis.

Contribution

It extends previous Schwarzschild black hole studies to Kerr black holes, analyzing non-axisymmetric perturbations and the effects of frame dragging on SASI.

Findings

Instability features are similar to Schwarzschild case but affected by Kerr-specific frame dragging.

Oscillation periods depend solely on shock radius, independent of injection parameters.

Inner transonic flow properties are highly sensitive to the Kerr parameter.

Abstract

This paper is a sequel to our previous work for accretion onto a Schwarzschild black hole and the so-called standing accretion shock instability (SASI), in this paper we investigate non-axisymmetric perturbations for a Kerr black hole. The linear and non-linear phases for the shock evolution are analyzed in detail by both 2D general relativistic hydrodynamical simulations and linear analysis. Since the structure of steady axisymmetric accretion flows with a standing shock wave is very sensitive to the inner transonic flow, their properties such as Mach numbers, which are important for the stability, depend on the Kerr parameter very much. Although the essential features of the instability do not differ from the previous results for the Schwarzschild black hole, the frame dragging effects specific to the Kerr black hole is also evident. Interestingly, the oscillation periods of the fundamental unstable modes are dependent only on the shock radius irrespective of the injection parameters.