In a First, Astronomers Watch a Black Hole Wake Up

A bright light erupting from a distant galaxy nearly five years ago was, in the view of researchers, way cooler than it sounds. Indeed, it was the first ever observation of the awakening of a black hole, according to a study accepted for publication in Astronomy and Astrophysics. Most galaxies have a supermassive black hole at their center, but they aren't always active, emitting energy. Before the end of 2019, the unnamed galaxy referred to as SDSS1335+0728, some 300 million light-years away in the constellation Virgo, had "always seemed calm and inactive," lead study author Paula Sanchez Saez of the European Southern Observatory says in a release, per the Washington Post. Then its core lit up like a flashlight.

"We were able to observe the awakening of the massive black hole, [which] suddenly started to feast on gas available in its surroundings, becoming very bright," says study co-author Claudio Ricci, an astronomer at Chile's Diego Portales University. This "has never been observed before." Galaxies can light up for several reasons, including supernova explosions and tidal disruption events, when a star passing too close to a black hole is ripped apart. "But these brightness variations typically last only a few dozen or, at most, a few [hundred days]," per the release. This activity has been ongoing for four and a half years.

As with other active galaxies, SDSS1335+0728 is now emitting increasing levels of ultraviolet, optical, and infrared light, in addition to X-rays. "This behavior is unprecedented," says Sanchez Saez. "The most tangible option to explain this phenomenon is that we are seeing ... the activation of a massive black hole in real time," adds study co-author Lorena Hernandez-Garcia of Chile's University of Valparaiso. Researchers will continue to work to rule out alternative explanations, including that SDSS1335+0728 is gobbling up a smaller satellite galaxy, per Science News. In the meantime, SDSS1335+0728 will be classified as having an "active galactic nucleus" at its center, per the release. (More black holes stories.)