Do three-body encounters in galactic nuclei affect compact binary merger rates?

TL;DR

This study uses advanced simulations to show that three-body encounters in galactic nuclei significantly increase the merger rate of compact binaries, mainly through Kozai-Lidov mechanisms, impacting gravitational wave event predictions.

Contribution

It introduces a novel Monte Carlo simulation approach to quantify how three-body interactions influence binary merger rates near SMBHs, revealing a threefold increase in mergers.

Findings

Three-body encounters increase merger rates by a factor of 3.

Close encounters reorient binaries, enhancing Kozai-Lidov induced mergers.

Estimated binary black hole merger rate is 1.6x10^-6 per year in Milky Way-like nuclei.

Abstract

High-density cusps of compact remnants are expected to form around supermassive black holes (SMBHs) in galactic nuclei via dynamical friction and two-body relaxation. Due to the high density, binaries in orbit around the SMBH can frequently undergo close encounters with compact remnants from the cusp. This can affect the gravitational wave merger rate of compact binaries in galactic nuclei. We investigated this process by means of high accuracy few-body simulations, performed with a novel Monte Carlo approach. We find that, around a SgrA*-like SMBH, three-body encounters increase the number of mergers by a factor of 3. This occurs because close encounters can reorient binaries with respect to their orbital plane around the SMBH, increasing the number of Kozai-Lidov induced mergers. We obtain a binary black hole merger rate of 1.6x10^-6/yr per Milky Way-like nucleus.