The fate of EMRI-IMRI pairs in AGN accretion disks: hydrodynamic and three body simulations

TL;DR

This paper investigates the complex interactions and final outcomes of stellar-mass black holes and intermediate-mass black holes within AGN accretion disks using hydrodynamic and three-body simulations, revealing possible pathways for gravitational wave sources.

Contribution

It extends previous models by incorporating 3D hydrodynamics and relativistic three-body simulations to analyze the migration and fate of black holes in AGN disks, providing new insights into their evolution.

Findings

Gaseous and tidal torques drive synchronized migration of sBH near IMBH.

sBH can be captured or ejected, leading to different gravitational wave event sequences.

Final outcomes include either two IMRIs or an EMRI followed by an IMRI.

Abstract

Extreme-mass-ratio inspirals (EMRIs) and intermediate-mass-ratio inspirals (IMRIs) are important gravitational wave (GW) sources for the Laser Interferometer Space Antenna (LISA). It has been recently suggested that EMRIs and IMRIs can both form in the accretion disk of an active galactic nucleus (AGN). Considering the likely encounter between a sBH and an IMBH during the migration in the AGN disk, Paper I showed that a gap-opening IMBH can drive a surrounding sBH to migrate synchronously. In this work, we extend the study in Paper I with a more sophisticated model. We first use 3D hydrodynamical simulations to study the co-evolution of the disk and the migration of a sBH in the vicinity of an IMBH. We find that the gaseous torque, together with the tidal torque exerted by the IMBH, can drive synchronized migration until $\sim 10$ Schwarzschild radii from the central supermassive black hole (SMBH). We further use a relativistic three-body code to study the final fate of the sBH in the GW-dominated regime. We find that the sBH can be either captured or kicked out by the IMBH, which will result in either two subsequent IMRIs or an EMRI followed by an IMRI. These events will bring rich information about the formation and evolution of sBHs and IMBHs in AGNs.