The Betelgeuse star, seen by the European Southern Observatory (ESO) - ESO / SIPA

The giant star Betelgeuse, one of the brightest in the Milky Way, has seen its luminosity fall for a few weeks. The event puts astronomers in turmoil because it could announce its explosion in a supernova, an extremely rare phenomenon in our galaxy.

Located in the constellation Orion, this "red super giant", almost a thousand times larger than the Sun, shines brightly in the winter sky, where it is visible to the naked eye thanks to its orange color. The star was among the 10 brightest in the galaxy, but since mid-November, "its brightness has dropped drastically, by around 70%," explains Pierre Kervalla, of the Paris Observatory - PSL.


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All telescopes observe it

Alerted by amateur observers, astronomers launched a vast observation campaign in December, mobilizing the largest telescopes on the planet, including the Very Large Telescope, in Chile. "It's boiling!" We have set up a research group around the world to use all the instruments capable of imaging the surface of Betelgeuse, ”says Eric Lagadec, astrophysicist at the Observatoire de la Côte d'Azur.

Hundreds of amateur astronomers are also involved, and "spend their nights in their gardens or their favorite observation sites" in order to provide additional measures, says this CNRS researcher. Several hypotheses are put forward: it could be an ejection of gas forming dust and hiding the radiation or the death of Betelgeuse.

Betelgeuse has recently lost its luminosity in the visible light domain but not in the infrared.

This rather indicates an ejection of gas (then preventing visible light from diffusing) and not a supernova.

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Future supernova?

The latter scenario would result in a supernova explosion. If it seems unlikely in the near future, it makes astronomers dream: the star at the end of its life having no more "fuel" (from nuclear fusion), its heart would collapse on itself and would form a neutron star. This very compact object creates a shock wave completely dislocating the star, all in just a few hours.

From Earth, we would then observe with the naked eye a point as bright as the Moon in the day and night sky. To this would be added a nice spectacle, "that of an echo of light propagating around, like circles in the water", specifies Pierre Kervalla. After several weeks, this point would disappear and form a nebula, visible in the sky for thousands of years, like that of the Crab, residue of a supernova that occurred in 1054.

A rare event

“It would be an unforgettable spectacle for all of humanity. I hope to be able to see a supernova in my lifetime, ”says Eric Lagadec. This phenomenon only happens once a century in the Milky Way, and the last formation of supernova observed dates back to 1604. The explosion of Betelgeuse is expected since the star, aged "only" 10 million years, is indeed at the end of its life.

However, it is difficult to predict exactly when she will die, as there are no warning signs. His death could therefore occur in the coming weeks, as in 100,000 years. Anyway, this event would be safe for our planet, Betelgeuse which is 600 light years away. "If we see it explode from here, it will mean that the explosion took place physically 600 years ago," recalls Pierre Kervalla.


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