The black hole had shredded the star in 2018. Three years later, it is “burping” its leftover energy in an “unprecedented act.”
A black hole has removed material from a star it shredded three years ago in a find that has baffled scientists.
“This took us completely by surprise, no one had ever seen anything like this before,” Yvette Cendes, an astronomer at the Harvard-Smithsonian Center for Astrophysics who led the research, said in a statement. “It’s as if this black hole has abruptly started belching out a bunch of material from the star that it ate up years ago.”
A stellar burp
In October 2018, the black hole, located in a galaxy 665 million light-years from Earth, was observed ripping apart a star that had come too close.
That phenomenon is called a tidal disruption event (TDE) and is common among astronomers. They usually occur when objects such as stars approach black holes and the massive gravitational influence they encounter generates tidal forces that stretch the star in one direction while crushing it in the other direction, “spaghettiing” its body.
As this material falls onto the black hole, it heats up and generates a flash of light that astronomers can detect millions of light-years away. From time to time, the black hole spits some of this stellar material back into space.
However, in this new TDE called AT2018hyz , the black hole is ejecting material at around 480 million kph, about half the speed of light. The conventional number does not exceed 10% of said speed.
“This is the first time we have witnessed such a long delay between feeding and departure,” study co-author Edo Berger, a professor of astronomy at Harvard University, said in the statement.
Investigating space meals
Astronomers detected this event while looking for signs of TDEs that have occurred in recent years. Data they collected in radio waves with the Very Large Array in New Mexico showed that this black hole had mysteriously come back to life in June 2021.
The team studied the event in multiple wavelengths of light and with a variety of telescopes, including the VLA, the MeerKAT radio telescope in South Africa, and the Atacama Large Millimeter/submillimeter Array in Chile, and found that the most surprising observations of AT2018hyz were in radiofrequencies.
Now the team will investigate whether the delay between feeding and emission is unique to AT2018hyz or if it is a more common event that astronomers have missed.