Milli-Hertz Gravitational Wave Background Produced by Quasi-Periodic Eruptions

Kavli Affiliate: Xian Chen

| First 5 Authors: Xian Chen, Yu Qiu, Shuo Li, F. K. Liu,

| Summary:

Extreme-mass-ratio inspirals (EMRIs) are important targets for future
space-borne gravitational-wave (GW) detectors, such as the Laser Interferometer
Sapce Antenna (LISA). Recent works suggest that EMRI may reside in a population
of newly discovered X-ray transients called "quasi-periodic eruptions" (QPEs).
Here we follow this scenario and investigate the detectability of the five
recently discovered QPEs by LISA. We consider two specific models in which the
QPEs are made of either stellar-mass objects moving on circular orbits around
massive black holes (MBHs) or white dwarfs (WDs) on eccentric orbits around
MBHs. We find that in either case each QPE is too weak to be resolvable by
LISA. However, if QPEs are made of eccentric WD-MBH binaries, they radiate GWs
in a wide range of frequencies. The broad spectra overlap to form a background
which, between $0.003-0.02$ Hz, exceeds the background known to exist due to
other types of sources. Presence of this GW background in the LISA band could
impact the future search for the seed black holes at high redshift as well as
the stellar-mass binary black holes in the local universe.

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