The Combined Effects of Two-Body Relaxation Processes and the Eccentric Kozai-Lidov Mechanism on the EMRI Rate

TL;DR

This paper demonstrates that the combined effects of two-body relaxation and the eccentric Kozai-Lidov mechanism significantly enhance the formation rate of EMRIs around supermassive black holes, especially in SMBH binaries.

Contribution

It introduces a novel combined mechanism involving relaxation and EKL effects that increases EMRI formation rates compared to previous models.

Findings

Enhanced EMRI rate due to combined processes

Relaxation alters orbital parameters favorably for EKL

High EMRI rate predicted in SMBH binaries

Abstract

Gravitational wave (GW) emissions from extreme-mass-ratio inspirals (EMRIs) are promising sources for low-frequency GW-detectors. They result from a compact object, such as a stellar-mass black-hole (BH), captured by a supermassive black hole (SMBH). Several physical processes have been proposed to form EMRIs. In particular, weak two-body interactions over a long time scale (i.e., relaxation processes) have been proposed as a likely mechanism to drive the BH orbit to high eccentricity. Consequently, it is captured by the SMBH and becomes an EMRI. Here we demonstrate that EMRIs are naturally formed in SMBH binaries. Gravitational perturbations from an SMBH companion, known as the eccentric Kozai-Lidov (EKL) mechanism, combined with relaxation processes, yield a significantly more enhanced rate than any of these processes operating alone. Since EKL is sensitive to the orbital configuration, two-body relaxation can alter the orbital parameters, rendering the system in a more EKL-favorable regime. As SMBH binaries are expected to be prevalent in the Universe, this process predicts a substantially high EMRI rate.