The giant star Betelgeuse, one of the brightest in the Milky Way, diminished its luminosity for a few weeks and the event stirred astronomers as it could announce its explosion in supernova, a rare phenomenon in our galaxy.
Located in the constellation Orion, this “super red giant”, almost a thousand times larger than the sun, shines brightly in the winter sky, where it is visible thanks to its red color.
The star was among the 10 brightest in the galaxy, but since mid-November, “its luminosity dropped dramatically, by 70%,” Pierre Kervalla of the Paris-PSL Observatory told AFP.
Alerted by amateur observers, astronomers began a vast observation campaign in December, mobilizing the largest telescopes on the planet, including the Very large telescope in Chile.
“It’s the turmoil! We set up a research group in the world to use all the instruments capable of capturing images of the Betelgeuse surface,” says Eric Lagadec, of the Lagrange laboratory of the Côte d’Azur observatory.
Hundreds of amateur astronomers are contributing and “spend their nights in their favorite gardens or observation sites” to provide complementary measurements, says the CNRS researcher.
Several hypotheses are advanced: it could be an ejection of gas that produces dust and hides the luminosity or … of the death of Betelgeuse.
This last possibility would lead to a supernova explosion.
Although it seems unlikely in the near future, this makes astronomers dream: to the extent that the star at the end no longer has “fuel” (emerged from nuclear fusion), its heart would collapse on itself and form a star of neutrons, a very compact object that creates a shock wave that completely dislocates the star, all in just a few hours.
“An unforgettable show for humanity”
From Earth, a bright spot like the moon in the day or night sky would be seen with the naked eye. To which would be added a beautiful show, “that of an echo of light spreading around, like waves in the water,” says Pierre Kervalla.
In a few weeks that point would disappear and form a nebula, visible in the sky for thousands of years, such as the Crab, a residue of the supernova that emerged in 1054 (recorded by Chinese astronomers).
“It would be an unforgettable show for all of humanity. I look forward to seeing a supernova during my life,” says Eric Lagadec. For that phenomenon only occurs rarely through the centuries in the Milky Way, and the last supernova observed was in 1604.
The explosion of Betelgeuse is expected, as the star, only 10 million years old, is about the end of his life.
But it is difficult to predict when he will die, because there is no warning sign: “It is more or less like an earthquake; the day before the explosion, the star will be the same,” Kervalla emphasizes. This could happen in the coming weeks or within 100 thousand years.
“We have no means to know,” says Andrea Chivassia.
Whatever happens, there is no danger to our planet, since Betelgeuse is 600 light years away. “If we see it explode here, that would mean that the explosion occurred physically 600 years ago,” says Pierre Kervalla.
On the scientific level, the event would make it easier for astronomers to follow live and for the first time in history, the different phases of the explosion, a precious opportunity to measure the expansion of the Universe.
“It would be understood in this way what will happen to the future generation of stars,” according to Chivassia.