On the Rossby Wave Instability in accretion discs surrounding spinning black holes

TL;DR

This study uses general relativistic hydrodynamics simulations to analyze the Rossby Wave Instability in accretion discs around spinning black holes, revealing how relativistic effects influence the instability's development and saturation.

Contribution

It demonstrates that RWI can occur at any disc location around spinning black holes and identifies the impact of relativistic effects on the instability's saturation level.

Findings

RWI can develop at any disc radius and spin parameter.

Relativistic effects increase the saturation level of RWI near fast-rotating black holes.

Wave propagation is affected by local time dilation in the relativistic regime.

Abstract

We have performed general relativistic hydrodynamics (GRHD) simulations of 2D discs orbiting around spinning black holes and prone to the Rossby Wave Instability (RWI). We show that the RWI can develop at any location in the disc and for any spin parameter. After recovering the overall patterns of the instability in this general relativistic context, we have analysed its development and identified some modifications induced by the combined effects of the relativistic rotational profile of the disc and local time dilatation that affects the propagation of waves in the disc. We have found in particular that the saturation level of the instability increases significantly when RWI occurs in the very close vicinity of fast-rotating black holes where general relativistic effects are strong. Such finding suggests that even more strongly than in the case of Schwarzschild black-hole, it is necessary to complement such GRHD simulations with a full GR ray-tracing processing in order to provide synthetic observations of the disc in the distant observer frame.