X-ray bursts from two previously quiescent galaxies: massive black holes awakening?
Riccardo Arcodia (MPE)
Tuesday 01/06/2021 @ 14:00, Sala IV piano Battiferro
A new type of exotic X-ray signals from massive black holes within galactic nuclei was recently discovered and called Quasi-Periodic Eruptions (QPEs). We have used the eROSITA telescope aboard SRG to systematically search for new QPEs and found two (doubling the sample of known sources) in the first year of operations. The new QPEs brought many new insights, since they were found in two previously quiescent galaxies, which was not the case for the two QPEs in the literature. This might suggest that no pre-existing accretion flow typical of AGN is required to trigger QPEs. Currently, the most promising scenario for their origin is the presence of a second compact object orbiting the massive black hole, and data suggest it should be smaller than the main body. This is reminiscent of a channel of gravitational waves emission detectable by LISA in the future, called extreme mass-ratio inspirals (EMRIs). Data incoming over the next year will allow us to test this model by studying the putative orbital evolution of the system. QPEs could then cover a fundamental role in the future of multi-messenger astrophysics over the next decades.