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Red star Betelgeuse, one of the brightest, not going supernova soon. It just coughed up dust

The bright red star underwent a Great Dimming in 2019-20, prompting some astronomers to speculate if it would go supernova. Findings help us understand giant stars better.

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Bengaluru: In the December of 2019, astronomers started to report that Betelgeuse, the bright reddish star in the constellation Orion, had started to undergo a sudden and drastic dimming in its luminosity, even visible to the naked eye.

The dimming peaked in mid February of 2020, where it reached 35 per cent of its brightness. The star’s brightness went back up, but the astronomy community was captivated.

​Many speculated that the star was probably going supernova, exploding in a dramatic burst of light that will shine brighter than the Sun in the sky for a brief period of time.

​However, a new study published Wednesday in Nature journal, made from observations of the dimming by the Very Large Telescope (VLT) in Chile, says the loss in light was concentrated in the star’s Southern Hemisphere only and was likely caused by a giant cloud of dust.

​Betelgeuse is a red supergiant, belonging to a category of the largest stars in the universe. It is the tenth brightest star in the sky, and appears distinctly reddish. It was about 20 times the mass of the Sun when it began its life, and is much younger than the Sun, at less than 10 million years old. It evolved rapidly because of its large mass and now has 900 times the radius of the sun.

​Its large size, and its relative proximity at about 550 light years makes it one of the well-imaged and better understood stars.

Also read: What caused rare 2015 supernova? Indian astronomers on space quest trace it to rarer star

What caused the dimming?

Betelgeuse is at a stage of its lifecycle where it is starting to transition from fusing hydrogen in its core to fusing helium. As it cools, expands, and ages, it will start fusing heavier and heavier elements in its core, before imploding into itself. This implosion is a supernova, where the star blows off all its outer layers and is only left with a remnant — a white dwarf, neutron star, or black hole.

The process is quite rapid, and red supergiants lose mass at a dramatic pace as well. This caused many in the astronomy and amateur astronomy community to speculate that the star could likely explode at any time.

However, when astronomer Miguel Montargès and his team compared the images of the star before and after the dimming, they noticed that the dimming was visible only in the Southern Hemisphere. The star hadn’t dimmed overall in its brightness, which indicated that there was an obstruction between the star and the Earth.

​The team thinks it might have been caused by a combination of cooling as well as a localised, large cloud of dust. The two theories had been proposed before, but independently and at odds with each other. The new study says both could happen together.

In fact, previous observations show that the star had started to undergo some loss of mass, releasing large quantities of gas a year before the dimming event. So the team theorises that a convection-driven cold patch in the star’s Southern Hemisphere cooled the local environment, causing the recently released gas to accumulate to dust.

But while the findings do not support a supernova event, they do not contradict the fact that Betelgeuse is still expected to undergo a supernova explosion at some point in the future. The event would occur suddenly and is impossible to predict. It is thought that this will happen within the next 100,000 years.

The anticlimactic findings, however, are extremely valuable to the field of stellar physics research. They raise questions, such as whether other red supergiants undergo dimming events. They also offer insights into the lifecycle of such large stars, and the future of our own.

Also read: NASA announces two new missions to Venus as it seeks to ‘rediscover the planet’


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