Supermassive black hole snacks on the same star once every few years

Nearly 900 million light-years away, the black hole consumes a portion of its orbiting star every time it gets too close.

To Leah Crane

A supermassive black hole about 900 million light years away will whet your appetite. About every 1200 days, the same orbiting star gets a little too close and the black hole bites into what is called a Repeated Partial Tidal Destruction Event (TDE).

This TDE, designated AT2018fyk, is observed to repeat second. Eric Coughlin of Syracuse University in New York announced the discovery on January 12 at the American Astronomical Society meeting in Seattle.

Astronomers first spotted it in 2018, when a black hole six billion times more massive than our Sun suddenly brightened and remained so bright for about 600 days. This happens whenever a star gets too close to a black hole, at which point it is shredded by a strong gravitational field, creating a stream of hot, bright stellar matter that falls into the black hole and darkens again. When that particular TDE was recorded and it faded rapidly, astronomers thought it was over.

But years after the black hole finished eating, something strange happened. “Almost four years after it was first detected, we looked at this object again and found it bright again,” Coughlin said. “This is really strange and totally unpredictable by the standard theory of TDE.”

The second outburst looked almost the same as the first outburst. This led Coughlin and his colleagues to suggest that it was his second bite taken from the same star. Instead of shredding a star completely, a black hole rips apart a piece of it every time it gets too close, leaving the star’s core in a different orbit.

Each time it passes, the black hole swallows 1-10% of the stars. “If it’s 10%, it’s likely that this object will only encounter a supermassive black hole a few more times,” Coughlin said. “If it’s 1%… maybe decades.”

Currently, AT2018fyk is still bright as the black hole finishes its stellar snack, but if the researchers’ models are correct, it should fade rapidly in August 2023 and brighten again in March 2025. . To see what more we can learn about how black holes engulf matter.

Sign up for our free Launchpad newsletter and travel the galaxy and beyond every Friday