What happens when a star gets too close to a black hole? ‘Unusually close’ NASA observations reveal just how complex and catastrophic it can be.
The agency’s Jet Propulsion Laboratory said Tuesday that multiple telescopes recently observed a massive black hole about 10 times the mass of our sun located about 250 million light-years from Earth “ripping apart an unlucky star that wandered too close”. It was the fifth closest sighting of such an event, known as a tidal disturbance event, and was first spotted on March 1, 2021.
So what exactly happened when the star and the black hole crossed paths?
First of all, it’s not something that happens in an instant. According to NASA, it’s a long process that can take weeks or months as the black hole’s gravity slowly sucks the star’s being away. In the most recent observation, this took place over approximately five and a half months.
“The side of the star closest to the black hole was pulled harder than the far side of the star, stretching the whole thing and leaving only a long noodle of hot gas,” NASA said.
Observations of the event, called AT2021ehb, were published in the Astrophysical Journal in September.
“Tidal disturbance events are a kind of cosmic laboratory,” said study co-author Suvi Gezari. “They are our window into the real-time feed of a massive black hole lurking at the center of a galaxy.”
The study said the event also provided an “unprecedented view” of one element of the process – the formation of a corona. It happened as the star was being torn down and caused a “dramatic increase” in high-energy X-ray light, NASA said. When this happened, the corona formed above the black hole.
But the creation of the corona – a cloud of hot plasma – during this particular event surprised astronomers. Coronas are usually accompanied by jets of gas flowing in opposite directions from the black hole, but in this case there was no jet.
Yuhan Yao, a Caltech graduate student and lead author of the study, said this was not just a rare event, but a totally novel observation.
“We’ve never seen a tidal disturbance event with an X-ray emission like this without a jet present, and it’s really spectacular because it means we can potentially tease out what’s causing the jets and what causes coronas,” they said. “Our observations of AT2021ehb are consistent with the idea that magnetic fields have something to do with corona formation, and we want to know what makes this magnetic field so strong.”
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