A strange case of a delayed eruption surprised astronomers.
Supermassive black holes tear stars to pieces when they approach too closely. This is known as a tidal disruption event (TDE). The spewing out of material follows the destruction of the star. The intense gravity pulls the star apart, and material swirls around the black hole, causing it to light up, as we can see. But in the case of AT2018hyz, something incredible and unprecedented occurred. The star was ripped apart, and material spewed everywhere. Three years later, the black hole ejected material once more.
“This caught us completely by surprise — no one has ever seen anything like this before,” lead author of a new paper, Yvette Cendes from the Center for Astrophysics | Harvard & Smithsonian, said in a statement.
AT2018hyz was initially thought to be unremarkable when it was discovered in 2018. The emission was consistent with the black hole ripping apart a small star, one-tenth the mass of our Sun. However, while looking for other TDEs, the team noticed this object flare up again, and in an unusual way.
The material ejected by the black hole was accelerated to roughly half the speed of light. This is five times faster than most TDE outflows. Whatever is going on in this system is definitely strange.
“We have been studying TDEs with radio telescopes for more than a decade, and we sometimes find they shine in radio waves as they spew out material while the star is first being consumed by the black hole,” said Edo Berger, professor of astronomy at Harvard University and the CfA, and co-author on the new study.
“But in AT2018hyz there was radio silence for the first three years, and now it’s dramatically lit up to become one of the most radio luminous TDEs ever observed.”
The discovery of such an event raises intriguing questions about how supermassive black holes behave. Astronomers have known that these cosmic giants are messy eaters, but their feeding habits appear to be a mystery.
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