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Explained: What is causing the supergiant star Betelgeuse to dim and change its shape?

Instead of appearing round, the star Betelgeuse now appears to be “squashed into an ova”.

Betelgeuse was born as a supermassive star millions of years ago and has been “dramatically” and “mysteriously” dimming for the last six months.

Using the European Space Organisation’s (ESO) Very Large Telescope (VLT), astronomers have noticed the unprecedented dimming of Betelgeuse, a red supergiant star (over 20 times bigger than the Sun) in the constellation Orion.

What has intrigued some astronomers is the fact that along with the dimming, the star’s shape has been changing as well, as per recent photographs of the star taken using the VISIR instrument on the VLT. Instead of appearing round, the star now appears to be “squashed into an ova” as per a New York Times report.

What is happening to Betelgeuse and why is it significant?

Betelgeuse was born as a supermassive star millions of years ago and has been “dramatically” and “mysteriously” dimming for the last six months. According to a report in Sky and Telescope, among the brightest night time stars, Betelgeuse ranks 10th, but by the last week of December 2019, its brightness had dimmed so low, that the star was ranked as the 21st brightest, “a remarkable decline — and a historic low.” The report suggests that while Betelgeuse’s behaviour is out of the ordinary, it doesn’t mean that an eruption is imminent since astronomers predict the star to blast sometime (supernova explosion, which is the largest explosion to take place in space) in the next 100,000 years or so. The report goes on to say that the star may re-brighten, “but you never know what surprises may still be in store. Stars do as they please and that’s half the fun”.

A press release issued by ESO on February 14 said the star is at about 36 per cent of its brightness at the moment, a change that is noticeable even to the naked eye. Astronomers who have been observing the star since December in order to understand why it’s becoming fainter have also noticed a change in its apparent shape.

As per the ESO press release, astronomers do not think that Betelgeuse is dimming because it is going to explode. They have other hypotheses that may explain the reasons for Betelgeuse’s change in shape and dimming.

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“The two scenarios we are working on are a cooling of the surface due to exceptional stellar activity or dust ejection towards us,” Miguel Montargès, an astronomer at KU Leuven in Belgium, who has been leading the team of astronomers observing the supergiant star said. “Of course, our knowledge of red supergiants remains incomplete, and this is still a work in progress, so a surprise can still happen.”

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