A supermassive black hole devouring stellar matter (illustration)
Nearly 900 million light-years away, a supermassive black hole whets the appetite. About every 1200 days, the same orbiting star comes a little too close and the black hole is engulfed in a phenomenon known as a partial tidal disruption event (TDE).
This TDE, designated AT2018fyk, is only the second repeat found. Eric Coughlin Researchers from Syracuse University in New York announced the discovery on January 12 at a meeting of the American Astronomical Society in Seattle.
First spotted by astronomers in 2018, a black hole six billion times more massive than our sun suddenly brightened and remained bright for about 600 days. This happens whenever a star gets too close to a black hole, at which point it is torn apart by a strong gravitational field, creating a stream of hot, bright stellar matter that then falls into the black hole and darkens again. That particular TDE of him was recorded, and when it rapidly disappeared, astronomers thought it was the end.
But years after the black hole finished eating its treats, something strange happened. “Almost four years after it was first discovered, we went back and looked at the object again and found it bright again,” Coughlin said. “This is really strange and totally unpredictable by the standard theory of TDE.”
The second brightening looked almost the same as the first. This led Coughlin and colleagues to suggest that it was simply a second bite from the same star. Instead of ripping the star apart completely, the black hole seems to rip off a portion of it each time it gets too close, leaving the center of the star to continue in another orbit.
Each time it passes, the black hole eats up 1-10 percent of the star. “If it’s 10 percent, it’s more likely that this object will probably only survive a few more supermassive black hole encounters,” Coughlin says. “If it’s 1 percent…it might be okay for another few decades.”
At the moment, 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. They will keep an eye on it. To see what more we can learn about how black holes swallow matter.
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