A Monster Black Hole 1M Times Bigger Than The Sun Just Woke Up And It’s Hungry

Astronomers using data from several space and ground-based observatories have theorized that a once dim galaxy has brightened over time because of a massive black hole at its core waking up. While a star getting too close to the massive black hole, estimated to be 1.5 million times the mass of Earth’s Sun, and getting torn apart could cause the brightening, researchers say those instances typically only last a few dozen days, or at most, a few hundred days. However, the galaxy in question is still getting brighter over four years later.

Astronomers first noticed galaxy SDSS1335+0728, located 300 million light-years from Earth, started shining brighter in 2019. The researchers remarked the brightening is unlike any they have ever seen before, causing them to look at other possibilities for why. According to the European Southern Observatory, the team attempted to understand the brightness variations using a combination of archival data and new observations from other observatories, such as the X-shooter instrument on ESO’s Very Large Telescope in Chile.

“Imagine you’ve been observing a distant galaxy for years, and it always seemed calm and inactive,” remarked Paula Sánchez Sáez, an astronomer at ESO in Germany and lead author of the study accepted for publication in Astronomy & Astrophysics. “Suddenly, its [core] starts showing dramatic changes in brightness, unlike any typical events we’ve seen before.”


Following extensive research, the team classified the galaxy as having an “active galactic nucleus,” a bright compact region powered by a massive black hole, following its brightening in 2019. The team also documented that the galaxy is now radiating a lot more light at ultraviolet, optical, and infrared wavelengths. In February 2024, it also started emitting X-rays.

“The most tangible option to explain this phenomenon is that we are seeing how the [core] of the galaxy is beginning to show (...) activity,” explained co-author Lorena Hernández García, from MAS 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.”

To put this into perspective, black holes are not eating stars and other matter in space all the time. They can only feed on what is within their gravitational reach. If nothing is close enough to munch on, the black hole will quietly wait for its next meal. An example is the supermassive black hole at the center of the Milky Way. It is not classified as being active because it is only feeding minimally. On the other hand, an active black hole will brighten, such as galaxy SDSS1335+0728.

Co-author of the recent study, Claudio Ricci, remarked, “In the case of SDSS1335+0728, 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.” Ricci added, “This is something that could happen to our own Sgr A*, the massive black hole (…) located at the center of our galaxy.”

No one is sure if or when such an event might occur with the massive black hole at the center of the Milky Way, but researchers will continue to keep a close eye on galaxy SDSS1335+0728. Other possibilities being suggested as to the cause are an unusually slow tidal disruption event, or possibly an unknown phenomenon.