“In late 2019 the previously unremarkable galaxy SDSS1335+0728 suddenly started shining brighter than ever before.”
SDSS1335+0728 sits 300 million light-years away and switched on in December 2019. It is still getting brighter more than four years later. The Zwicky Transient Facility flagged the change and a classifier algorithm in Chile sorted it. ESO calls it the first black hole awakening seen in real time, and its own team still can’t rule out a slow star being torn apart.