Warped and eccentric discs around black holes

TL;DR

This paper explores how warps and eccentricities in black hole accretion discs, caused by misaligned spins and resonances, can propagate inward and potentially trigger observable phenomena like quasi-periodic oscillations.

Contribution

It provides a linear analysis of disc deformations and identifies conditions for significant activity in the inner disc regions.

Findings

Warp and eccentricity propagation depends on disc thickness and dissipation.

Stationary waves can form in the inner disc regions.

Potential link to observed quasi-periodic oscillations.

Abstract

Accretion discs around black holes in X-ray binary stars are warped if the spin axis of the black hole is not perpendicular to the binary orbital plane. They can also become eccentric through an instability involving a resonance with the binary orbit. Depending on the thickness of the disc and the efficiency of dissipative processes, these global deformations may be able to propagate into the innermost part of the disc in the form of stationary bending or density waves. We describe the solutions in the linear regime and discuss the conditions under which a warp or eccentricity is likely to produce significant activity in the inner region, which may include the excitation of quasi-periodic oscillations.