The extremes of (X-ray) variability among galaxies: Flares from stars tidally disrupted by supermassive black holes

We discuss follow-up X-ray observations of giant-amplitude, non-recurrent X-ray flares, interpreted as tidal disruptions of stars by supermassive black holes at the centers of the flaring galaxies. The flare observations open up a new window to study supermassive black holes and their environment, and the physics of accretion events, in non-active galaxies.