X-ray outbursts from optically nonactive galaxies provide important information on the presence of SMBHs in these galaxies, and the link between active and normal galaxies. In particular, the capture and disruption of stars by SMBHs is one of the three major processes studied in the context of black hole growth, together with accretion of interstellar matter and black hole - black hole merging. The relative importance of these three processes in feeding black holes is still under investigation. Different processes may dominate in different stages of the evolution of galaxies.
Future X-ray all-sky surveys will be valuable in finding more of these outstanding events [e.g., 7]. Rapid follow-up observations at all wavelengths will then be important. We estimate that the planned all-sky survey mission eROSITA will detect a few hundred flares during the first years of its operation, which will allow us to study these events in detail.
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