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Roughly half of the quasi-periodic eruption (QPE) sources in galactic nucleiexhibit a remarkably regular alternating "long-short'' pattern of recurrencetimes between consecutive flares. We show that a main-sequence star (broughtinto the nucleus as an extreme mass-ratio inspiral; EMRI) which passes twiceper orbit through the accretion disk of the supermassive black-hole (SMBH) on amildly eccentric inclined orbit, each time shocking and ejectingoptically-thick gas clouds above and below the midplane, naturally reproducesobserved properties of QPE flares. Inefficient photon production in the ejectarenders the QPE emission much harder than the blackbody temperature, enablingthe flares to stick out from the softer quiescent disk spectrum. Destruction ofthe star via mass ablation limits the QPE lifetime to decades, precluding along-lived AGN as the gaseous disk. By contrast, a tidal disruption event (TDE)naturally provides a transient gaseous disk on the requisite radial scale, witha rate exceeding the EMRI inward migration rate, suggesting that many TDEsshould host a QPE. This picture is consistent with the X-ray TDE observedseveral years prior to the QPE appearance from GSN 069. Remarkably, a secondTDE-like flare was observed from this event, starting immediately afterdetectable QPE activity ceased; this event could plausibly result from the(partial or complete) destruction of the QPE-generating star triggered byrunaway mass-loss, though other explanations cannot be excluded. Our model canalso be applied to black hole-disk collisions, such as those invoked in thecontext of the candidate SMBH binary OJ 287.

EMRI + TDE = QPE: Periodic X-ray Flares from Star-Disk Collisions in Galactic Nuclei