A well-known star is behaving oddly and appears to have changed shape, according to astronomers

Betelgeuse – a red supergiant that can be seen in the constellation Orion – has historically been one of the sky's brightest stars. But in recent months it has started to dim in a way never before seen, and without explanation.

Some astronomers had initially speculated that the star could be about to explode into a supernova, in a dramatic event that would be visible from Earth. But astronomers now think that something else is happening, which is changing the star in unexpected ways.

Now new images show that fading brightness of the star, as well as the fact that the shape as it appears to us appears to be changing.

As it has continued to dim, Betelgeuse is now about 36 per cent of its normal brightness. That is so dramatic that it can be seen with the naked eye, but further investigations with telescopes have attempted to learn more about the mysterious dimming.

Since December, astronomers have observed the star using the ESO's Very Large Telescope, in an attempt to understand the strange behaviour of the star.

They have now revealed a stunning new image of the star's surface. Helpfully, they took a very similar image, using the same instrument, in January 2019 and before the dimming began – allowing them to compare the two images, and understand more about the changes that Betelgeuse has undergone.

Researchers now speculate that the star is not in fact about to go supernova, but is undergoing some other, similarly dramatic process. The new research helps give insight into red supergiants like Betelgeuse and what could happen to cause such unusual behaviour.

"The two scenarios we are working on are a cooling of the surface due to exceptional stellar activity or dust ejection towards us," said Miguel Montargès, an astronomer from KU Leuven in Belgium, who led the new study. "Of course, our knowledge of red supergiants remains incomplete, and this is still a work in progress, so a surprise can still happen."

Other images taken using the same Very Large Telescope show that the dust around Betelgeuse is emitting infrared light. That appears to happen when the material that makes up the star is spewed back into space.

"The phrase 'we are all made of stardust' is one we hear a lot in popular astronomy, but where exactly does this dust come from?" siad Emily Cannon, a PhD student at KU Leuven.

"Over their lifetimes, red supergiants like Betelgeuse create and eject vast amounts of material even before they explode as supernovae. Modern technology has enabled us to study these objects, hundreds of light-years away, in unprecedented detail giving us the opportunity to unravel the mystery of what triggers their mass loss."

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