Jacobi capture as a pathway to off-center massive black hole binaries in dwarf galaxies

TL;DR

This paper explores how off-center black holes in dwarf galaxies can form binaries through Jacobi capture, highlighting a pathway for black hole mergers outside galactic centers.

Contribution

It introduces the role of Jacobi capture in forming off-center black hole binaries in dwarf galaxies with cored dark matter haloes, a novel pathway for black hole assembly.

Findings

13% of orbital configurations lead to black hole capture.

Captures may occur within compact stellar systems like globular clusters.

This process could facilitate off-center black hole mergers.

Abstract

The recent detection of high-redshift supermassive black holes with JWST has renewed interest in the processes driving black hole growth. At the same time, both simulations and observations point to a widespread population of off-center intermediate-mass black holes in dwarf galaxies. Their ability to merge outside galactic centers may play a key role in shaping black hole mass assembly. Here, we investigate the dynamics of off-center black holes in dwarf galaxies hosting cored dark matter haloes, where long dynamical friction timescales and core stalling naturally arise. By embedding off-center black holes into an idealized galactic potential and scanning a wide range of orbital configurations, we assess the likelihood of close interactions through Jacobi capture. We find that captures occur in about 13% of cases. Such captures, possibly sustained within compact stellar systems like stripped nuclei or globular clusters, represent a crucial first step toward assembling massive black hole binaries beyond galactic centers.