This delayed outflow of material is traveling at 50% of light speed—far faster than typical TDEs.
Key Takeaways
- A black hole is ejecting stellar material years after shredding a star, at half the speed of light.
- This delayed “burp” of material surprised astronomers, as it’s unprecedented in tidal disruption events.
- Scientists observed the phenomenon using multiple telescopes across the globe and in space.
- The disrupted star was relatively small, with only one-tenth the mass of the Sun.
- The delayed ejection could change our understanding of black holes’ feeding behavior.
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In an unexpected twist, a black hole located 665 million light-years from Earth is ejecting stellar material years after it shredded a small star. This unusual occurrence, observed by a team of astronomers led by Yvette Cendes at the Center for Astrophysics | Harvard & Smithsonian, is the first time such a significant delay has been noted in a tidal disruption event (TDE). TDEs occur when a star drifts too close to a black hole and is torn apart by intense gravitational forces, a process that typically produces a brilliant flash of light and sometimes emits outflows shortly after. However, in this case, the delayed release of material is now traveling at half the speed of light.
A Surprising New Kind of TDE
The black hole’s powerful emission, or outflow, is traveling at about 50% of light speed—significantly faster than the usual 10% of light speed seen in typical TDE outflows. “This caught us completely by surprise,” remarked Cendes, who noted that this event has set a new record for TDE radio brightness. The initial TDE, designated AT2018hyz, was observed in 2018 when the black hole first shredded the star, which had a mass only one-tenth of our Sun. At the time, the TDE seemed relatively unremarkable and quickly faded from visible light telescopes, leading astronomers to move on from observing it.
Three years later, the black hole suddenly reanimated in 2021, lighting up radio telescopes around the world. Cendes and her team, using the Very Large Array (VLA) in New Mexico, were able to detect the renewed activity and subsequently requested Director’s Discretionary Time to observe AT2018hyz with multiple observatories, including the ALMA Observatory in Chile, MeerKAT in South Africa, the Australian Telescope Compact Array, and the Chandra X-Ray Observatory in space. All of these observations confirmed the unexpectedly intense radio activity.
Shedding New Light on Black Hole Feeding Habits
Theories about black hole feeding behavior have long been evolving, and this discovery opens up fresh questions. Black holes are notorious “messy eaters,” with some of the shredded stellar material flung back into space. However, scientists have always assumed these outflows occurred immediately after a TDE, not years later. Harvard astronomer and co-author Edo Berger points out that astronomers have monitored TDEs with radio telescopes for over a decade, and until now, such a lengthy delay between a TDE and a subsequent outflow has never been documented.
The reason behind this delayed release remains unclear. It’s possible that the black hole retained a portion of the star’s material in its gravitational pull before ejecting it, or perhaps a new process caused the delayed outflow. For Cendes and her team, the next step will be to investigate whether other black holes might display similar behavior if observed over a long enough timeline. The team hopes this discovery will allow for a deeper understanding of black holes’ feeding habits and interactions with surrounding material. “The delayed outflow suggests there could be other TDEs like this that we’ve missed,” Berger said, emphasizing the importance of continued observation.
