X-Ray Heartbeats from the Nuclei of Galaxies

Abstract: X-ray Quasi-Periodic Eruptions (QPEs) are the latest and perhaps the most peculiar addition to the zoo of extragalactic nuclear transients. They are high-amplitude bursts of X-ray radiation recurring every few hours to few days with a lifetime of years to decades, originating from the central black holes in the nuclei of low-mass galaxies. So far, only a dozen of such events has been found, although with rising interest in the broader community given their observational and theoretical connection with tidal disruption events and as possible low-frequency gravitational wave sources. Some of the latest models suggest that these eruptions occur in extreme mass ratio inspirals (EMRIs) systems, in which the secondary stellar-mass body interacts with the accretion flow of the primary massive black hole. I will outline the observational properties of QPE sources and the latest tests of theoretical models.