Betelgeuse is one of the most emblematic stars of our celestial vault. A shiny point, symbolizing the left shoulder of the mythological hunter Orion, in the constellation of the same name.
So, when its brilliance suddenly weakened, at the end of 2019, the bets were in full swing in observatories around the world. Was it the ultimate jolt of a star at the end of its life, bloated until it reached a diameter of a thousand suns, which would suddenly explode into a supernova? Could we hope to witness this grandiose astronomical spectacle, visible even in broad daylight?
An unprecedented level of detail
This Thursday, an international scientific team, including Breton astrophysicist Eric Lagadec, delivers a solid explanation for this phenomenon, in an article published in the prestigious journal “Nature”. No, this temporary drop in brightness was not a harbinger of an impending supernova. Yes, the images of Betelgeuse recorded thanks to the Very Large Telescope (VLT) of the Eso (European Southern Observatory), in the Atacama desert, in Chile, provide a key to understanding the universe: they testify, with a unprecedented visual precision of the specific behavior of a dying red supergiant. “The first observations showed that part of the star was obscured. We continued to make them over the weeks, and we saw that Betelgeuse had returned more or less to normal, ”explains Eric Lagadec, based at the Nice – Côte d’Azur Observatory.
Two possible scenarios then: “Either the star had cooled in part, and was therefore less bright. Either dust had formed between us and the star and was absorbing its light ”. Thanks to a multitude of computer models carried out in collaboration with Miguel Montargès, from the Paris Observatory; Emily Cannon, of the KU Leuven, in Belgium, and about thirty scientists, he published, this Thursday, “the best explanation that we have found”: “Locally, matter has risen to the surface of the star, then moved away from it. This gas, dense and cold, ended up solidifying to form dust ”, details the astrophysicist from Sizun (29) who is enthusiastic about having“ seen the formation of stardust live. This is the first time that we have observed such a phenomenon so resolutely in front of a star! “.
Dust that can breed life
Stellar dust is not the kind that must be slipped under a cosmic carpet. It is a treasure of the universe. “What we see here is the death of a star that brings the galaxy to life. It enriches it with dust, which, over the course of chemical reactions, will form more and more complex molecules, and why not, one day, generate life, ”explains Eric Lagadec. These ejections of matter are not continuous and uniform, they appear in spurts, in one direction, then in another. Until it forms a dust bubble around the star, several light years in diameter, visible in the infrared.
This publication in “Nature” brings the Bretel scientist from Bételgeuse even closer. He had already participated in “imaging” the surface of the star in 2015, a world first there too. “I really like looking at it when it’s visible, to make sure it’s still there. A priori, there is very little chance that it will explode during my lifetime, we are rather in an order of magnitude of ten thousand years or more. But we never know… “
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