In recent weeks, all the largest telescopes around the world, including the Very Large Telescope, the European super telescope based in Chile, have only eyes for it. What is happening to Betelgeuse, the star star of our winter skies? Recognizable among all, thanks to its bright orange-red shine, planted on the left shoulder of the constellation of Orion, Betelgeuse, the red super giant, suddenly lost its splendor.
It was amateur astronomers who first raised the alarm. The pros have engaged. "Since the end of October, the brightness of Betelgeuse has dropped from 60 to 70%, which is quite unusual," says Pierre Kervalla, of the Paris Observatory. Normally, its brightness does not vary by more than 20%. "
Betelgeuse, which is in the top 10 of the brightest stars in our Milky Way, is it about to agonize? Will we soon see her implode before our eyes to turn into a supernova? The whole community of astronauts, like Pierre Kervalla, dreams of it ... And in France as elsewhere, many have even planted instruments in their garden, waiting for the big event.
Two suns in the sky
It is that witnessing the extinction of a star live is a rather rare spectacle. On average, we attend this big show no more than once a century in our galaxy. The first account of the death of a star speaks volumes about the amazement that the event aroused. In 1054, Chinese peasants in the south of the Ailao mountains, in southern Yunnan, were biting the rice terraces, when they could not believe their eyes: the sky has changed, it now has two suns in the place of a. Another has just invited himself to the side of the star…
According to the accounts of historians of the time, this second bright spot shone for twenty-three days in a clear blue sky ... "With Betelgeuse, the spectacle will undoubtedly be just as magnificent, estimates Pierre Kervalla, because this star is the one of the most imposing stellar objects in our galaxy. It is a really huge giant, 1000 times bigger than our sun, he insists. When it breaks up, the resulting explosion will be visible day and night, for several weeks. We will then see a luminous point as bright as the Moon settle in the sky. "
In the midst of those passionate about heaven, we are in awe. It has been more than a century and a half since he followed Betelgeuse's mood swings. We know the star at the end of its life, running out of fuel. Is the long-awaited great moment of its dislocation approaching? “It's hard to say, recognizes Pierre Kervalla, because a star dies in a few hours. The day before the explosion, it will be the same. If it has to disappear, it can therefore be tomorrow as in ... 100,000 years. "
With what risks for us? "None, says the specialist, Betelgeuse is located 600 million light years from Earth. If we wanted to get there by rocket, the trip would last 1.5 million years. It is far too far from us for us to feel any impact. »So, when do we make an appointment? "Caution, caution, tempers Pierre Kervalla, Some of the observations let us think that this fall of light could also be due to an ejection of gas on its surface," he explains. This ejection may very well have had the consequence of surrounding the star with a huge cloud of dust, like Australian mega-whales. Moreover, notes the expert, for a few days, the visible radiance of Betelgueuse has stabilized. Like all the stars, it is she who will choose the time of her release.