A supermassive black hole was observed belching up a star it gobbled up three years earlier — leaving astronomers puzzled by the delayed intergalactic indigestion.

“This caught us completely by surprise — no one has ever seen anything like this before,” Yvette Cendes, the lead author of a new study analyzing the unprecedented phenomenon, said.

In October 2018, astronomers witnessed a small star being ripped to shreds and swallowed when it wandered too close to a black hole in a galaxy located 665 million light years away from Earth, according to the study published last week in Astrophysical Journal.

The violent feast itself isn’t unusual, however, when the black hole started mysteriously regurgitating stellar matter in June 2021, scientists were left scratching their heads — because there was no evidence it had eaten another star, the study found.

“It’s as if this black hole has started abruptly burping out a bunch of material from the star it ate years ago,” Cendes, a research associate at the Harvard-Smithsonian Center for Astrophysics, added.

A picture of the spewed stellar matter
The long delay in the spewing of celestial matter had never been seen before and perplexed scientists.

Black holes are extraterrestrial regions where gravitational pull has drawn matter into a small space with a force so strong that nothing can escape from them, including light.

They are usually formed by the collapsing remnants of large dying stars, and can consume anything that comes too close to them, NASA explains.

When a black hole devours a star, some of the celestial material that makes up the star occasionally gets flung out back into space, which astronomers liken to black holes being messy eaters, the Centre for Astrophysics explains. 

But this process — which Cendes equates to “burping” after a meal — usually happens immediately, not three years later, according to the study.

Researchers scrambled to study the startling discovery using telescopes on three continents and in space.

They found that the black hole, dubbed AT2018hyz, was ejecting material at half the speed of light — five times faster than normal.

However, they remained in the dark about why it took three years to “burp” up the star.

“This is the first time that we have witnessed such a long delay between the feeding and the outflow,” said Edo Berger, professor of astronomy at Harvard University and the CfA, and co-author of the new study.

“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.”

The team hopes the study can help scientists better understand black holes’ feeding behavior.



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