In November 2019, the abnormal decrease in brightness of Betelgeuse in the sky had strongly intrigued the international community, with the hypothesis of its upcoming disappearance. But if this ultimate phase does not seem to be reached yet, it is preceded by exceptional eruptive phenomena.
| ✔ Characteristics of the star Betelgeuse Betelgeuse is one of the brightest stars in the constellation Orion (the hunter), shining like more than 100,000 suns combined. It is a red supergiant and one of the largest stars known, with a radius a thousand times that of the Sun ; it could contain a billion times our star. The supergiant is so huge that, if it replaced the Sun at the center of our Solar System, its outer surface would extend beyond the orbit of Jupiter. Such properties imply an "imminent" end for this stellar mastodon. Only a few million years old, Betelgeuse is already approaching the end of its life, with a destiny all mapped out : a supernova explosion that will make it as bright as our entire Galaxy. |
Using the Hubble Space Telescope and other ground-based instruments, scientists from an international team reconstructed the scenario after and during the flare that shook the star in late 2019.
A titanic convulsion
According to scientists, the star ejected a large amount of material into space. From this eruption, a huge cloud of gas has partially transformed into dust by cooling, leading to the occultation of the star.
The star is slowly recovering from this convulsion ; its photosphere is gradually recovering. However, its usual pulsation cycle is disturbed : its interior now sounds like a "slightly detuned bell". This does not necessarily mean that the supergiant star will explode soon, but it could continue to surprise astronomers.
In any case, the observations provide clues about how red supergiant stars lose mass at the end of their lives, as their nuclear fusion reservoir is depleted, before exploding into supernovae. The extent of mass loss during the red supergiant phase has a major influence on their fate : in the case of Betelgeuse, it will determine whether the star will end its life as a black hole or a neutron star. The answer will be revealed in about 100 000 years at the latest !
For this work, several types of observational data were used :
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A look at the facts
The titanic eruption of 2019 was likely caused by a convective plume, more than a million kilometers in diameter, that bubbled up from deep within the star. It produced shocks and pulses that ejected a chunk of photosphere, leaving the star with a large cold surface at the site of the flare. Betelgeuse is currently recovering from this injury.
Equivalent to one ten-millionth of Betelgeuse’s mass, the detached piece of photosphere escaped to space and cooled to form a dust cloud that obscured the star from the view of Earth-based observers. The loss of brightness, which began in late 2019 and lasted a few months, was very easily visible to the naked eye.
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Read also the information
on NASA’s Hubble site :
Hubble Sees Red Supergiant Star Betelgeuse Slowly Recovering After Blowing Its Top
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Another important fact is that for nearly 200 years, astronomers have been measuring the pulsation rate of Betelgeuse using variations in its brightness and surface motions. However, these pulsations have accelerated and are currently faster than the usual 400 days. This disturbance testifies to the violence of the eruption.
According to the researchers, the inner convection cells of the star, which are at the origin of its standard pulsation, could be shaking like the vibrations of an unbalanced washing machine tub. The TRES and Hubble spectra indicate that the outer layers may have returned to their normal extension, but the surface is still bouncing around like a gelatin dessert on a plate, suggesting that the photosphere is rebuilding.
Conclusion
Direct witnesses of this unprecedented event, astronomers have deduced that the star had in 2019 ejected a huge piece of its visible surface. A phenomenon of such intensity had never before been followed on a star of this type. Our Sun regularly undergoes mass ejections from its outer atmosphere, the corona. But these events are out of all proportion to what has been observed on Betelgeuse.
Therefore, red supergiant surface mass ejections and solar coronal mass ejections are different events.
NASA’s Webb Space Telescope and ESO’s ELT may be able to detect the displacement of material ejected by the star in infrared.
Reference
This research work was the subject of an article entitled "The Great Dimming of Betelgeuse : a Surface Mass Ejection (SME) and its Consequences" par Andrea K. Dupree,et.al. paru dans la revue « The Astrophysical Journal ».
DOI : https://doi.org/10.48550/arXiv.2208.01676
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June 20, 2017 Une immense tache brillante à la surface de Bételgeuse révélée par ALMA |
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July 1st,2009 Unprecedentedly sharp images of Betelgeuse reveal how supergiants lose mass |