• Thu. Feb 2nd, 2023

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What happens when a star gets too close to a black hole? “Unusually close” observations from NASA reveal just how complex and catastrophic it can be. 

The agency’s Jet Propulsion Laboratory said on Tuesday that multiple telescopes recently watched a massive black hole about 10 times the mass of our sun located about 250 million light-years away from Earth “tearing apart an unlucky star that wandered too close.” It was the fifth-closest observation of such an occurrence, known as a tidal disruption 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 a single moment. According to NASA, it’s a long process that can take weeks or months as the black hole’s gravity slowly sucks in the star’s being. In the most recent observation, it took place over the course of about five-and-a-half months. 

“The side of the star nearest the black hole was pulled harder than the far side of the star, stretching the entire thing apart and leaving nothing but a long noodle of hot gas,” NASA said.

The observations of the event, called AT2021ehb, were published in the Astrophysical Journal in September. 

“Tidal disruption events are a sort of cosmic laboratory,” study co-author Suvi Gezari said. “They’re our window into the real-time feeding of a massive black hole lurking in the center of a galaxy.”

The study said that the event also provided an “unprecedented view” of one element of the process – the formation of a corona. This happened as the star was being demolished and spawned a “dramatic rise” in high-energy X-ray light, NASA said. As that happened, the corona formed above the black hole.

But the creation of the corona – a cloud of hot plasma – in this particular event surprised astronomers. Coronae usually come with jets of gas flowing in opposite directions from the black hole, but in this case, there were no jets at all. 

Yuhan Yao, a Caltech graduate student and lead author of the study, said this isn’t just a rare occurrence – it’s a totally new observation. 

“We’ve never seen a tidal disruption event with X-ray emission like this without a jet present, and that’s really spectacular because it means we can potentially disentangle what causes jets and what causes coronae,” they said. “Our observations of AT2021ehb are in agreement with the idea that magnetic fields have something to do with how the corona forms, and we want to know what’s causing that magnetic field to get so strong.”





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