A Black Hole Shredded and Consumed a Star. Now it is Burping Up Its Stellar Remains, Astronomers Say
“Caught us completely by surprise.”
A black hole apparently swallowed a star and is having trouble digesting its meal—the outer-space void is apparently "burping up" the stellar remains years later. "We've never seen anything like this before," say astronomers from Harvard. Read on to find out what the scientists found, and why it's so unusual.
Astronomers say that in October 2018, a small star drifted too close to a black hole 665 million light years from Earth and was shredded and swallowed up by the void. Years later, the same black hole is lighting up the skies, but it hasn't gobbled up anything else. "This caught us completely by surprise — no one has ever seen anything like this before," says Yvette Cendes, a research associate at the Harvard & Smithsonian Center for Astrophysics and lead author of a new study about the sighting.
The researchers have determined that the black hole is ejecting material traveling at half of the speed of light—what Cendes compares to "burping" after a meal. They aren't sure why the burping was delayed by several years but hope their observations will help scientists understand the feeding behavior of black holes.
Cendes' team noticed the stellar ejections when they were studying recent tidal disruption events (TDEs), violent incidents when stars are basically turned into spaghetti by black holes. Data showed the black hole had reanimated for some reason in June 2021. The scientists studied the black hole, known as AT2018hyz, by radio telescope.
"We have been studying TDEs with radio telescopes for more than a decade, and we sometimes find they shine in radio waves as they spew out material while the star is first being consumed by the black hole," said Edo Berger, professor of astronomy at Harvard University and co-author on the new study. "But in AT2018hyz there was radio silence for the first three years, and now it's dramatically lit up to become one of the most radio-luminous TDEs ever observed."
"TDEs are well-known for emitting light when they occur," Harvard explained in a press release. "As a star nears a black hole, gravitational forces begin to stretch, or spaghettify, the star. Eventually, the elongated material spirals around the black hole and heats up, creating a flash that astronomers can spot from millions of light years away." "Some spaghettified material occasionally gets flung out back into space. Astronomers liken it to black holes being messy eaters — not everything they try to consume makes it into their mouths," the university explained. But these emissions usually happen soon after the TDE, not years later. "It's as if this black hole has started abruptly burping out a bunch of material from the star it ate years ago," said Cendes.
These are some serious belches: The ejected material is traveling out of the black hole as nearly 50 percent the speed of light. "This is the first time that we have witnessed such a long delay between the feeding and the outflow," Berger says. "The next step is to explore whether this actually happens more regularly and we have simply not been looking at TDEs late enough in their evolution."