A giant black hole is lost in space. Here's how it's shocking astronomers.

When scientists discovered an enormous black hole thousands of light-years from where it ought to be in space, they knew they had a cosmic oddity on their hands. 

NASA's Hubble Space Telescope showed a rare black hole that looked like the kind astronomers would find at the center of a galaxy. Instead, it was about 2,600 light-years from the core, which was occupied by an even more massive black hole. The discovery of the renegade, first spotted by the Zwicky Transient Facility in California, was only possible because it happened to light up after snacking on an unlucky star. 

But this bizarre black hole, the weight of 1 million or more suns, gets even weirder. In a new study led by UC Berkeley, researchers used radio telescopes to observe the strange object's behavior and found that the event, known as AT 2024tvd, prompted two clear bright flares of radio waves, changing faster than any other that scientists have seen.

"This is truly extraordinary," said Itai Sfaradi, first author of the research published in The Astrophysical Journal Letters, in a statement. "Never before have we seen such bright radio emission from a black hole tearing apart a star, away from a galaxy’s center, and evolving this fast. It changes how we think about black holes and their behavior."

The first burst appeared about four months after the discovery and faded quickly. The second burst showed up about six months later, rising and falling even faster. The results show that powerful outflows of material were launched from the area of the black hole after the star's demise — not immediately after but months later, suggesting delayed and previously unknown processes at work.

Black holes are some of the most confounding things in space. They are regions where gravity is so intense that nothing can escape, not even light. About a half-century ago, astronomers weren't even sure they existed. Today, black holes aren't just confirmed, they're getting photographed. In 2019, the Event Horizon Telescope achieved the first image of a black hole, located 53 million light-years away in the Messier 87 galaxy.

The Hubble Space Telescope detects a tidal disruption event from a black hole, seen in this image north of the bright smudgy galactic center where another even larger supermassive black hole resides. Credit: NASA / ESA / STScI / Yuhan Yao / Joseph DePasquale

Black holes don't have surfaces. Instead, they have a boundary called an "event horizon," or a point of no return. If anything wanders too close — like the poor previously mentioned star — it will fall in, never to escape the hole's gravity.

Astronomers aren't sure how this gargantuan black hole got to its seemingly random location. One idea is that it came from another galaxy that at some point merged into its present galaxy about 600 million light-years away from Earth. Another idea is that it was evicted from the center of the galaxy by two bigger black holes in what's known as a three-body interaction.

"Theorists have predicted that a population of massive black holes located away from the centers of galaxies must exist," said Ryan Chornock, a coauthor at UC Berkeley, in a statement earlier this year, "but now we can use (these events) to find them.”

The scientific term for when a star wanders too close to a black hole is a tidal disruption event. When a black hole interacts with surrounding gas and dust, it throws out fast streams of material or narrow jets. These features can be observed in radio waves. So shortly after the tidal disruption was detected in optical and ultraviolet light, Sfaradi and colleagues set out to watch it with the Very Large Array, the Atacama Large Millimeter/submillimeter Array, and other radio dishes.

The black hole's unusual location and rapid radio changes give scientists a new way to study black holes and their effects far from galactic cores. Continued monitoring may reveal more about the speed, timing, and behavior of the material the black hole ejects. This event's unusual behavior could be connected to the black hole's off-center location, or it might represent a phenomenon scientists haven't seen before. 

"This is one of the fascinating discoveries I’ve been part of," said Assaf Horesh, a coauthor based at the Hebrew University of Jerusalem, in a statement. "The fact that it was led by my former student, Itai, makes it even more meaningful." 

The scientists used computer simulations to model how outflows or jets could produce the signals they saw. One explanation could be a single outflow launched about three months after the star was disrupted, with the double peaks in radio caused by the material hitting a complex environment around the black hole. Another possibility is that two separate outflows occurred, the first about three months after the event and the second about six months later.