Tearing up a misaligned accretion disc with a binary companion

TL;DR

This paper investigates how gravitational torques from a binary companion can cause misaligned accretion discs to break into separate planes, leading to increased accretion, confirmed through analytical calculations and hydrodynamical simulations.

Contribution

It demonstrates that binary-induced precession can cause disc breaking in misaligned accretion discs, a phenomenon supported by both theoretical analysis and simulations.

Findings

Disc breaking occurs in many binary systems with misaligned discs.

Precession from the binary companion can overcome internal disc torques.

Disc breaking generally enhances accretion onto the central object.

Abstract

Accretion discs are common in binary systems, and they are often found to be misaligned with respect to the binary orbit. The gravitational torque from a companion induces nodal precession in misaligned disc orbits. We calculate whether this precession is strong enough to overcome the internal disc torques communicating angular momentum. For typical parameters precession wins: the disc breaks into distinct planes that precess effectively independently. We run hydrodynamical simulations to check these results, and confirm that disc breaking is widespread and generally enhances accretion on to the central object. This applies in many cases of astrophysical accretion, e.g. supermassive black hole binaries and X--ray binaries.