Paris (AFP)
The mysterious temporary fading of the giant star Betelgeuse, which could presage its imminent disappearance, was due to a cloud of dust associated with a cooling of its surface.
But everything suggests that it will continue to illuminate the Universe.
This "red super giant", among the brightest in the galaxy, is clearly visible to the naked eye in the constellation Orion.
For five months, from November 2019 to March 2020, it has paled dramatically, losing 70% of its brightness, which it has since regained.
Images from the Hubble Telescope (Nasa / ESA) last summer pointed to a potential culprit: the star's ejection of a large amount of material, which would then have formed a cloud as it cooled in contact with the deep void.
Not so simple, according to the conclusions of the international team of astronomers, published Wednesday in Nature.
Because scientists did not exclude that the decrease in luminosity of Betelgeuse is simply the result of a colder point spot, and therefore less luminous, on the surface of the star.
"We concluded that the + great fading + was the result of the combination of these two phenomena", explains to AFP Miguel Montargès, astronomer and main author of the study, who used the Very Large Telescope of the European Southern Observatory ( ESO), Chile.
- "Heart of iron" -
Betelgeuse "emitted a cloud of gas, which began to move away from it," said the post-doctoral fellow at the LESIA-Observatoire de Paris (PSL).
"A drop in luminosity at the star's surface caused its temperature to drop, allowing the gas to form dust, which hid the star's light."
Astronomers had assumed at the time that the event foreshadowed an imminent end of this "super giant".
A qualifier not stolen for this type of star, not very widespread, with here the mass of 20 suns, and a radius 900 times greater.
If Betelgeuse were in the place of the Sun, we would be inside the star.
# photo1
But "the bigger a star, the shorter its life," recalls Miguel Montargès.
Infinitely more.
With only 8 million years, "it is already dying, whereas our sun, which will still be there in a few billion years, saw it being born and will see it die".
But why were we predicting his death?
Because its passage from the color blue (which it wore in the prime of life), to the color red (no more than 100,000 years ago), signs the depletion of the stock of hydrogen that she could merge to live.
It still has resources, with helium and other elements ever heavier to burn, such as carbon.
But these mergers are going to be always faster.
And one day, "the star will develop a heart of iron, an extremely stable element", which it will not be able to consume, explains Miguel Montargès.
With the sudden slowing down of the fusion, the core will collapse on itself, in a fraction of a second, followed with a delay by the envelope of the star, which will "bounce" off it before exploding with a brilliance as brilliant as it is. 'a galaxy: a supernova, an event that no human has been able to observe with the naked eye in the Milky Way for centuries.
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Until then, Betelgeuse will continue to release a cohort of atoms and molecules of matter into space.
"We are made of stardust," said astrophysicist Hubert Reeves.
Because of the hundred chemical elements that make up our world, "ten were created by humans, but all the rest is of cosmic origin," recalls Miguel Montargès.
The super giants "can explode without warning", notes the astronomer, who nevertheless doubts the imminence of the end of Betelgeuse, because it has lost only a few percent of its mass.
While another red super-giant, VY Canis Majoris, who has lost nearly a third, could offer a dazzling spectacle in the sky in "a few centuries, or millennia" ...
© 2021 AFP