Formation Rate of Quasiperiodic Eruptions in Galactic Nuclei Containing Single and Dual Supermassive Black Holes

TL;DR

This paper models the formation rates of quasiperiodic eruptions in galactic nuclei, showing dual supermassive black holes significantly increase the likelihood of QPEs, especially in postmerger galaxies.

Contribution

It provides the first detailed calculation of QPE formation rates considering both single and dual SMBH systems using scattering experiments and loss-cone theory.

Findings

Dual SMBH systems enhance QPE rates by 3-4 orders of magnitude.

Most QPEs with periods >100 days form in dual SMBH systems.

A significant fraction of long-period QPEs originate from postmerger galaxies.

Abstract

Quasiperiodic eruptions (QPEs) are a novel class of transients recently discovered in a few extragalactic nuclei. It has been suggested that a QPE can be produced by a main-sequence star undergoing repeated partial disruptions by the tidal field of a supermassive black hole (SMBH) immediately after getting captured on a tightly bound orbit through the Hills mechanism. In this Letter, we investigate the period-dependent formation rate of QPEs for this scenario, utilizing scattering experiments and the loss-cone theory. We calculate the QPE formation rates in both a single-SMBH and a dual-SMBH system, motivated by the overrepresentation of postmerger galaxies as QPE hosts. We find that for SMBHs of mass $10^{6}$--$10^{7}M_{\odot}$, most QPEs formed in this scenario have periods longer than $\simeq 100$ days. A single-SMBH system generally produces QPEs at a negligible rate of $10^{-10}$--$10^{-8}\ \rm{yr}^{-1}$ due to inefficient two-body relaxation. Meanwhile, in a dual-SMBH system, the QPE rate is enhanced by 3-4 orders of magnitude, mainly due to a boosted angular momentum evolution under tidal perturbation from the companion SMBH (galaxy). The QPE rate in a postmerger galactic nucleus hosting two equal-mass SMBHs separated by a few parsecs could reach $10^{-6}$--$10^{-5}\ \rm{yr}^{-1}$. Our results suggest that a nonnegligible fraction ($\simeq 10$--$90\%$) of long-period QPEs should come from postmerger galaxies.