Interacting Stellar EMRIs as Sources of Quasi-periodic Eruptions in Galactic Nuclei

Brian D. Metzger, Nicholas C. Stone, Shmuel Gilbaum

Research output: Contribution to journalArticlepeer-review

37 Scopus citations


A star that approaches a supermassive black hole (SMBH) on a circular extreme mass ratio inspiral (EMRI) can undergo Roche lobe overflow (RLOF), resulting in a phase of long-lived mass transfer onto the SMBH. If the interval separating consecutive EMRIs is less than the mass-transfer timescale driven by gravitational wave emission (typically ∼1-10 Myr), the semimajor axes of the two stars will approach each another on scales of ≤2 hundreds to thousands of gravitational radii. Close flybys tidally strip gas from one or both RLOFing stars, briefly enhancing the mass-transfer rate onto the SMBH and giving rise to a flare of transient X-ray emission. If both stars reside in a common orbital plane, these close interactions will repeat on a timescale as short as hours, generating a periodic series of flares with properties (amplitudes, timescales, sources lifetimes) remarkably similar to the "quasi-periodic eruptions"(QPEs) recently observed from galactic nuclei hosting low-mass SMBHs. A cessation of QPE activity is predicted on a timescale of months to years, due to nodal precession of the EMRI orbits out of alignment by the SMBH spin. Channels for generating the requisite coplanar EMRIs include the tidal separation of binaries (Hills mechanism) or Type I inward migration through a gaseous AGN disk. Alternative stellar dynamical scenarios for QPEs, that invoke single stellar EMRIs on an eccentric orbit undergoing a runaway sequence of RLOF events, are strongly disfavored by formation rate constraints.

Original languageAmerican English
Article number101
JournalAstrophysical Journal
Issue number1
StatePublished - 1 Feb 2022

Bibliographical note

Funding Information:
We thank the anonymous reviewer for providing helpful insights and suggestions. We acknowledge helpful conversations with Riccardo Arcodia, Aleksey Generozov, Zoltan Haiman, Yuri Levin, Ann-Marie Madigan, Itai Linial, Eliot Quataert, Mathieu Renzo, and Marta Volonteri. This research was supported by through an NSF-BSF joint funding research grant (NSF grant AST-2009255 to BDM and BSF grant 2019772 to NCS and SG). B.D.M. acknowledges additional support from NASA (grant NNX17AK43G). N.C.S. acknowledges additional support from the Israel Science Foundation (Individual Research Grant 2565/19).

Publisher Copyright:
© 2022. The Author(s). Published by the American Astronomical Society.


  • Active galactic nuclei
  • Supermassive black holes
  • X-ray transient sources


Dive into the research topics of 'Interacting Stellar EMRIs as Sources of Quasi-periodic Eruptions in Galactic Nuclei'. Together they form a unique fingerprint.

Cite this