X-ray quasi-periodic eruptions: what are they?

Quasi-Periodic Eruptions (QPEs) are high-amplitude bursts of X-ray radiation recurring every few hours and originating near the central supermassive black holes in galactic nuclei. They provide a new channel to study how low-mass supermassive black holes are activated in low-mass galaxies. Currently only four-five such sources are known, classified both as actively accreting black holes and quiescent galaxies. I will give an overview of their multi-wavelength observational properties and describe the method I am currently using to find more. I will discuss additional work in preparation aimed to further study their timing and spectral properties to constrain their origin scenario. What it is currently suggested is that QPEs might be driven by the presence of one (or more) orbiting body (-ies), much smaller than the main body. This could make QPEs a viable candidate for the electromagnetic counterparts of the so-called extreme mass-ratio inspirals, with considerable implications for the future of multi-messenger astrophysics and cosmology.