Kavli Affiliate: Xian Chen
| First 5 Authors: Chunyang Cao, F. K. Liu, Xian Chen, Shuo Li,
| Summary:
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.
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