Tidal disruptions in circumbinary discs (I): Star formation, dynamics, and binary evolution

TL;DR

This paper investigates the evolution of massive black hole binaries within circumbinary discs, focusing on star formation, stellar dynamics, and tidal disruption events, using SPH and N-body simulations to reveal high rates of stellar disruption.

Contribution

It introduces a combined simulation approach to study star formation and stellar dynamics around MBH binaries, including TDEs, in circumbinary discs.

Findings

Star disruption rate is as high as 10^{-4} per year per binary.

Gas in the disc can trigger significant in situ star formation.

Stellar clusters and individual stars contribute to tidal disruption events.

Abstract

In our current interpretation of the hierarchical structure of the universe it is well established that galaxies collide and merge with each other during their lifetime. If massive black holes (MBHs) reside in galactic centres, we expect them to form binaries in galactic nuclei surrounded by a circumbinary disc. If cooling is efficient enough, the gas in the disc will clump and trigger stellar formation in situ. In this first paper we address the evolution of the binary under the influence of the newly formed stars, which form individually and also clustered. We use SPH techniques to evolve the gas in the circumbinary disc and to study the phase of star formation. When the amount of gas in the disc is negligible, we further evolve the system with a high-accurate direct-summation $N-$body code to follow the evolution of the stars, the innermost binary and tidal disruption events (TDEs). For this, we modify the direct N-body code to (i) include treatment of TDEs and to (ii) include "gas cloud particles" that mimic the gas, so that the stellar clusters do not disolve when we follow their infall on to the MBHs. We find that the amount of stars disrupted by either infalling stellar clusters or individual stars is as large as 10^{-4}/yr per binary, higher than expected for typical galaxies.