Blackhole Mergers Through Evection Resonances

TL;DR

This paper introduces a new mechanism for black hole binary mergers via evection resonance in AGN disks, which can significantly accelerate mergers by increasing eccentricity even in near coplanar configurations.

Contribution

It proposes a novel pathway for black hole mergers through evection resonance, including effects of precession and disk interactions, expanding understanding beyond traditional high-inclination mechanisms.

Findings

Eccentricity can be excited in binaries migrating in AGN disks via evection resonance.

Eccentricity excitation can reduce merger timescales by up to 10^3-10^5.

Resonance crossing depends on migration timescale and disk mass.

Abstract

Mechanisms have been proposed to enhance the merger rate of stellar mass black hole binaries, such as the Von Zeipel-Lidov-Kozai mechanism (vZLK). However, high inclinations are required in order to greatly excite the eccentricity and to reduce the merger time through vZLK. Here, we propose a novel pathway through which compact binaries could merge due to eccentricity increase in general, including in a near coplanar configuration. Specifically, a compact binary migrating in an AGN disk could be captured in an evection resonance, when the precession rate of the binary equals their orbital period around the supermassive black hole. In our study we include precession to due first-order post Newtonian precession as well as that due to disk around one or both components of the binary. Eccentricity is excited when the binary sweeps through the resonance which happens only when it migrates on a timescale 10-100 times the libration timescale of the resonance. Libration timescale decreases as the mass of the disk increases. The eccentricity excitation of the binary can reduce the merger timescale by a factor up to $\sim 10^{3-5}$.