Astronomers are keeping a close watch on the star Betelgeuse, which may be showing signs of end of life.

The giant star Betelgeuse, one of the brightest stars in the Milky Way, has seen its luminosity drop in recent weeks. The event has astronomers excited because it could herald its explosion as a supernova, an extremely rare phenomenon in our galaxy.

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

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 favorite observation sites” to provide additional measurements, says this CNRS researcher. Several hypotheses have been put forward: it could be an ejection of gas that forms dust and hides the radiation, or the death of Betelgeuse.

Future supernova?

The latter scenario would result in a supernova explosion. Although it seems unlikely in the near future, it is a dream come true for astronomers: the star at the end of its life would no longer have “fuel” (from nuclear fusion), its heart would collapse on itself and form a neutron star. This very compact object creates a shock wave that completely dislocates the star, all in just a few hours.

From the Earth, one would then observe with the naked eye a point as bright as the Moon in the celestial vault during the day and at night. In addition to this, there would be a beautiful spectacle, “that of an echo of light propagating around it, like circles in the water,” says 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 humanity. I hope to see a supernova in my lifetime,” says Eric Lagadec. This phenomenon occurs only once a century in the Milky Way, and the last supernova formation observed dates back to 1604. The explosion of Betelgeuse is expected since the star, which is “only” 10 million years old, is well and truly at the end of its life.

However, it is difficult to predict precisely when it will die, because there is no warning sign. Its death could therefore occur in the coming weeks, as in 100,000 years. In any case, this event would be harmless for our planet, of which Betelgeuse is 600 light years away. “If we see it explode from here, it will mean that the explosion physically took place 600 years ago,” recalls Pierre Kervalla.

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