Astronomers have said that the sudden darkening of one of the brightest stars in the night sky, Betelgeuse, may be due to a dust cloud emitting from its surface.

This mystery has astonished skywatchers since the star - part of the Orion constellation - began to lose its luster in October 2019, with some experts suggesting that it might herald its exploding into a supernova.

The picture is clearer

But researchers working with the Hubble Telescope now have a clearer picture, seeing superheated plasma blasting off the surface of the star, cooling in the outer layers of the atmosphere and eventually turning into dust.

The star of Betelgeuse - which is a thousand times the size of the sun - is 725 light years from Earth, which means that the event witnessed by the telescope occurred at the beginning of the fourteenth century.

"The resulting cloud blocked the light from about a quarter of the surface of the star," the European Space Agency (ESA) said in a statement on Thursday, August 13th, adding that the star has since returned to its normal brightness.

We can see the effect of a dense, hot region in the southeastern part of the star moving outward (NASA-ESA)

Dense and hot area

"We can see the effect of a dense and hot region in the southeastern part of the star moving outward," said lead researcher Andrea Dupre of the Harvard-Smithsonian Center for Astrophysics in the United States, in a statement posted on the NASA website.

The researchers, who are due to publish their findings in The Astrophysical Journal, said they were unsure of the ultimate cause of the plasma explosion.