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Telescopes operated by National Aeronautics and Space Administration (NASA) recently observed a massive black hole devouring a star. The incident was the fifth-closest example of a black hole destroying a star and occurred 250 million light-years from the earth, in the centre of another galaxy.
The astronomical phenomenon of the destruction of a star by a black hole is formally called a tidal disruption event (TDE).
A tidal force is the difference in the strength of gravity between two points. If the tidal force exerted on a body is greater than the intermolecular force that keeps it together, the body will get disrupted.
During a TDE, the tidal force of a black hole disrupts the star in vicinity. While about half of the star’s debris continues on its original path, the other half is attracted by the black hole’s gravitational pull. The gradual growth of this material bound to the black hole produces a short-lived flare of emission, known as a tidal disruption event.
In the recently-observed example, a dramatic rise in high-energy X-ray light around the black hole was seen once the star was completely ruptured by the black hole’s gravity. This indicated the formation of an extremely hot structure above the black hole called a corona. According to a study published in Astrophysical Journal, the proximity of the aforementioned TDE provided a spectacular view of the corona’s formation and evaluation.
The event is formally called AT2021ehb, and took place in a galaxy with a central black hole about 10 million times the mass of our sun. It was first spotted on March 1, 2021, by the Zwicky Transient Facility in Southern California. Around 300 days later, the Nuclear Spectroscopic Telescopic Array (NuSTAR) – NASA’s most sensitive space telescope capable of observing high-energy X-rays – began observing the system. Scientists detected a corona, but they don’t know where the plasma comes from or exactly how it gets so hot. Coronae usually appear with jets of gas that flow in the opposite direction from a black hole. However, with AT2021ehb, there were no jets.
TDEs are attractive to astronomers because of their observability and short duration, and the opportunity to study the impact of black hole’s gravity on materials around it. They are also an important tool to learn how black holes influence their environments.
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