Astronomers have spotted an apparent supermassive black hole snacking on a star 600 million light-years away, wandering through a galaxy with an even larger black hole at its core.
The event, dubbed AT2024tvd, was first spotted by the Palomar Observatory’s Zwicky Transient Facility and later confirmed by powerhouse space telescopes including Hubble and Chandra, which helped zero in on the cosmic crime scene. To the researchers’ surprise, the responsible black hole was not at the center of its host galaxy, as supermassive black holes tend to be. Rather, this one was 2,600 light-years from the galactic center—a huge distance on paper, but really just one-tenth the distance between our Sun and Sagittarius A*, the black hole at the center of the Milky Way.
Tidal disruption events (TDEs) like this one occur when a black hole’s gravity pulls on a star so violently that the less massive ball of gas is stretched, shredded, and swirled around the black hole, in a process delightfully called spaghettification. The fleeting burst of energy from the event is gargantuan, even rivaling a supernova—the explosive death of a massive star—in brightness. The burst of light is also visible across the electromagnetic spectrum, making TDEs an invaluable resource for spotting black holes that might otherwise be too quiet or hidden to detect, such as the recent rogue object.
What makes AT2024tvd special is that it’s the first offset TDE discovered by optical surveys, according to a forthcoming paper in The Astrophysical Journal Letters, which is also posted on the preprint server arXiv. The achievement demonstrates how rogue black holes—warping spacetime and shrouded in darkness as they move through the cosmos—can be spotted, as long as an unfortunate object sacrifices itself for the massive object to reveal itself.
“Tidal disruption events hold great promise for illuminating the presence of massive black holes that we would otherwise not be able to detect,” said study co-author Ryan Chornock, a researcher at the University of California – Berkeley and a member of the ZTF team, in a NASA release. “Theorists have predicted that a population of massive black holes located away from the centers of galaxies must exist, but now we can use TDEs to find them.”
The team has a couple of ideas about how the rogue black hole ended up offset in the galaxy, and so close to the supermassive black hole at its core. (The rogue black hole’s mass is estimated to be roughly one million solar masses, at least ten times smaller than the black hole at the galactic center.) One option is that the black hole was at the center of a smaller galaxy that was subsumed by the larger galaxy, and now the black hole is simply drifting through the larger galaxy. Another possibility is that the black hole was the weakest link in what was once a three-body system, and was pushed out by the bigger objects; in other words, two larger black holes may lurk at the galaxy’s core, and the rogue black hole was ejected thousands of light-years out.
“If the black hole went through a triple interaction with two other black holes in the galaxy’s core, it can still remain bound to the galaxy, orbiting around the central region,“ said Yuhan Yao, also a researcher at UC Berkeley and the lead author of the study, in the same release. But at the present moment, the team isn’t sure if the black hole was pushed out or is being dragged in by the larger black hole.
With future instruments like the Vera Rubin Observatory and the Roman Space Telescope coming online, astronomers are hopeful this is just the beginning of an entirely new class of discoveries. Because if there’s anything more unsettling than a black hole swallowing a star, it’s the idea that the hungry, hungry objects are just drifting through space in unexpected locations.