Excitation of trapped oscillations in discs around black holes

TL;DR

This paper explores a non-linear coupling mechanism that excites trapped inertial oscillations in accretion discs around black holes, potentially explaining high-frequency quasi-periodic oscillations observed in black hole systems.

Contribution

It introduces a novel non-linear coupling model involving disc warping and eccentricity that explains the excitation of inertial waves in black hole accretion discs.

Findings

Inertial waves are amplified through damping of negative energy waves.

Eigenfunctions and growth rates of oscillations are calculated.

The mechanism provides a possible explanation for observed high-frequency QPOs.

Abstract

High-frequency quasi-periodic oscillations detected in the light curves of black hole candidates can, according to one model, be identified with hydrodynamic oscillations of the accretion disc. We describe a non-linear coupling mechanism, suggested by Kato, through which inertial waves trapped in the inner regions of accretion discs around black holes are excited. Global warping and/or eccentricity of the disc have a fundamental role in this coupling: they combine with trapped modes, generating negative energy waves, that are damped as they approach the inner edge of the disc or their corotation resonance. As a result of this damping, inertial oscillations are amplified. We calculate the resulting eigenfunctions and their growth rates.