The fate of close encounters between binary stars and binary supermassive black holes

TL;DR

This study uses N-body simulations to explore how binary stars near a supermassive black hole are affected by a secondary SMBH, revealing that SMBH binaries influence event rates of TDEs, HVSs, and hypervelocity binaries, which can inform us about SMBH binary properties.

Contribution

It provides the first detailed analysis of how a secondary SMBH impacts stellar binary interactions and related event rates in galactic centers using N-body simulations.

Findings

TDE and HVS rates are affected by SMBH binary mass ratio

Secondary SMBH can produce hypervelocity binaries

Event rates can diagnose SMBH binary properties

Abstract

The evolution of main sequence binaries that reside in the Galactic Centre can be heavily influenced by the central supermassive black hole (SMBH). Due to these perturbative effects, the stellar binaries in dense environments are likely to experience mergers, collisions or ejections through secular and/or non-secular interactions. More direct interactions with the central SMBH are thought to produce hypervelocity stars (HVSs) and tidal disruption events (TDEs). In this paper, we use N-body simulations to study the dynamics of stellar binaries orbiting a central SMBH primary with an outer SMBH secondary orbiting this inner triple. The effects of the secondary SMBH on the event rates of HVSs, TDEs and stellar mergers are investigated, as a function of the SMBH-SMBH binary mass ratio. Our numerical experiments reveal that, relative to the isolated SMBH case, the TDE and HVS rates are enhanced for, respectively, the smallest and largest mass ratio SMBH-SMBH binaries. This suggests that the observed event rates of TDEs and HVSs have the potential to serve as a diagnostic of the mass ratio of a central SMBH-SMBH binary. The presence of a secondary SMBH also allows for the creation of hypervelocity binaries. Observations of these systems could thus constrain the presence of a secondary SMBH in the Galactic Centre.