The Betelgeuse star, one of the brightest in our sky, has mysteriously lost almost 70% of its brightness. Scientists and amateurs alike thought they were witnessing the extremely rare spectacle of its explosion in a supernova. But it is not so: an international team of researchers has captured the images of its surface and publishes, this Friday, new explanations for this fascinating phenomenon. Eric Lagadec, astrophysicist at the Côte d'Azur observatory, vice-president of the French Society of Astronomy and Astrophysics, is one of the two French people behind this discovery.
What has been agitating sky observers for the past few months?
ERIC LAGADEC. Betelgeuse, until then the brightest star in the constellation of Orion, is a red supergiant, a star at the end of its life which is 700 light years from us. It has been observed for several years through the Very Large Telescop (VLT), located in Chile, and Sphere, an instrument operational since 2015 which allows to correct the effect of the atmosphere and therefore to capture images of its area.
In recent months, the star has lost 70% of its brightness, a sign, may have fantasized that it would explode in a supernova. We therefore, with an international team made up of around twenty researchers, took images of the Betelgeuse surface to get to the bottom of it. But this is not the case…
What then explains this phenomenon?
We made a whole series of observations via the VLT and Sphere. When we got our picture, we found that half of the star's hemisphere was dark. So something happened, but it's not a sign of a supernova. Two interpretations are possible: either the surface has changed temperature, has cooled, and therefore it has become more obscure, or else gigantic heaps of dust have formed between us and the star. This dust, to put it simply, are small grains of a thousandth of a millimeter which travel in clouds.
What does this discovery bring?
Betelgeuse is one of the rare stars close enough to us whose surface we can "image" - there are five or six in total. This observation is a chance: it allows us to better understand the death of the stars and the matter ejected from the stars of which we are made. We will continue and refine our study. We will make new observations and physical models to explain all this; it will soon be published in scientific journals.
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If Betelgeuse had exploded as a supernova, what would we have seen?
Everyone camped on this theory because it is the one that makes you dream. The phenomenon would be of magnitude and brilliant like the full moon. We would most likely see it in broad daylight for two months; and some say that you might even be able to read outside on a moonless night. I dream of seeing that too one day, of course…
We have recently been talking about Elon Musk's Starlink SpaceX satellites which pollute our vision of the sky and which do not facilitate your work… Are you asking for measurements?
Yes ! Less than a week ago, I created a working group within the French Society of Astronomy and Astrophysics. We are going to launch serious studies and see what actions we will be able to carry out, whether at the judicial or purely scientific level. In the sky, even with the naked eye, we can already see real pollution; and satellites are already bothering us in our image taking. But if Elon Musk continues his project, the sky as we know it now will change radically.
