Astronomers have observed a supermassive black hole at the center of galaxy SDSS1335+0728 turning active, a phenomenon not previously seen in real-time. This galaxy had been unremarkable until December 2019, when its central brightness began to increase significantly. Researchers believe this marks the awakening of the black hole.
Supermassive black holes can be either quiet or active, the latter involving a state of feeding where they emit significant light, sometimes outshining their host galaxies. This emission stems from gas and dust falling into the black hole, heating up due to intense gravitational forces. Since December 2019, SDSS1335+0728 has radiated more in infrared, visible, and ultraviolet light, and began emitting X-rays in February 2024.
“This behaviour is unprecedented,” lead author Dr Paula Sánchez Sáez, an astronomer at the European Southern Observatory (ESO) in Germany, said in a statement. “Imagine you’ve been observing a distant galaxy for years, and it always seemed calm and inactive. Suddenly, its [core] starts showing dramatic changes in brightness, unlike any typical events we’ve seen before.”
“The most tangible option to explain this phenomenon is that we are seeing how the [core] of the galaxy is beginning to show (…) activity,” added co-author Lorena Hernández García, from the Millennium Institute of Astrophysics and the University of Valparaíso in Chile. “If so, this would be the first time that we see the activation of a massive black hole in real time.”
The team is considering whether this is a typical active galactic nucleus (AGN) or an unusually long Tidal Disruption Event (TDE), where a black hole consumes a star or gas cloud that ventured too close. This event would need to last much longer than previous TDEs, such as the notable Scary Barbie event, which has persisted for over two years.
The black hole, approximately one million times the mass of the Sun, remains under observation. Whether an AGN activation or a unique TDE, this event offers new insights into black hole growth and evolution. There is much to learn about these processes, including whether they might occasionally occur in otherwise quiet supermassive black holes like Sagittarius A* in our galaxy. The behavior of SDSS1335+0728 is expected to provide valuable information to help solve the puzzle of supermassive black holes.