Tearing up the disc: misaligned accretion on to a binary

TL;DR

This paper investigates how misaligned accretion discs around binary systems can tear and accelerate the evolution and merging of supermassive black hole binaries, revealing a mechanism that shortens merger timescales significantly.

Contribution

It extends previous work on disc tearing to binary systems, showing that tearing occurs at nearly all inclinations and can drastically speed up binary mergers.

Findings

Disc tearing occurs for almost all inclinations in binary systems.

Tearing can accelerate accretion and binary evolution by up to 10,000 times.

Potential observational signatures of SMBH binaries are identified.

Abstract

In a recent paper we have shown that the evolution of a misaligned disc around a spinning black hole can result in tearing the disc into many distinct planes. Tearing discs with random orientations produce direct dynamical accretion on to the hole in approximately 70% of all cases. Here we examine the evolution of a misaligned disc around a binary system. We show that these discs are susceptible to tearing for almost all inclinations. We also show that tearing of the disc can result in a significant acceleration of the disc evolution and subsequent accretion on to the binary - by factors up to 10,000 times that of a coplanar prograde disc with otherwise identical parameters. This provides a promising mechanism for driving mergers of supermassive black hole (SMBH) binaries on timescales much shorter than a Hubble time. Disc tearing also suggests new observational signatures of accreting SMBH binaries, and other systems such as protostellar binaries.