AI Insight
This study uses observations of quasi-periodic eruptions (QPEs) - repeated X-ray bursts from galactic centers - to estimate the rate of extreme mass ratio inspirals (EMRIs), where small objects orbit supermassive black holes while emitting gravitational waves. The researchers calculate that black hole EMRIs occur at a rate of approximately 6 events per million galaxies per year and could produce gravitational wave signals detectable by the planned LISA space observatory in the 1-10 millihertz frequency range, potentially exceeding LISA's sensitivity by up to two orders of magnitude. Stellar EMRIs occur at about half this rate but are tidally disrupted before reaching detectable frequencies.
Why it matters
This research provides crucial predictions for LISA's expected gravitational wave detections and helps constrain the population of EMRIs in the universe. The findings suggest that QPEs can serve as electromagnetic tracers of gravitational wave sources, enabling multi-messenger astronomy and improving our understanding of extreme gravity environments around supermassive black holes.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Abstract: Quasi-periodic eruptions (QPEs) are repeated X-ray bursts originating in galactic nuclei. Of the many proposed models, the favored model is the disk-collision model in which a stellar mass orbiter collides with a disk formed from a tidal disruption event, generating flares twice per orbit. In this model QPEs are tracers of circular extreme mass ratio inspirals (EMRIs) and can be used to infer the EMRI formation rate and estimate their contribution to the stochastic gravitational wave background (SGWB) in the Laser Interferometer Space Antenna (LISA) band. Whether the secondary is a stellar-mass black hole or a main sequence star is still debated and leads to different results for the EMRI rate and SGWB. We obtain fiducial rates — subject to systematic uncertainties — of $R_{rm SE} = 2.88times10^{-6}$ per galaxy per year for stellar EMRIs and $R_{rm BHE} = 6.07times10^{-6}$ per galaxy per year for black hole EMRIs, then estimate their contribution to the SGWB. We find that only black hole EMRIs contribute to the 1 – 10 milliHertz band resolvable by LISA, and depending on the secondary mass and formation radius can contribute from just below the LISA sensitivity curve to roughly two orders of magnitude above it. Stellar EMRIs, being tidally disrupted before reaching the 1 – 10 milliHertz band, only contribute to sub-milliHertz frequencies and remain below the LISA sensitivity curve.