Betelgeuse is not about to explode, although it will soon

Updated:10/02/2021 15: 56h

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Normally, and for several million years, Betelgeuse is one of the brightest stars in the sky, located right on the left ‘shoulder’ of the Orion constellation. But lately he has shown strange behavior. In early 2020, for example, its brightness dropped sharply, leading many to believe that the huge red giant, much larger than the Sun, was about to explode like supernova, leaving behind a black hole or a compact neutron star. And all this just a few hundred light years from Earth.

Later studies, however, have already pointed out that although there is no doubt that Betelgeuse is at the end of its life, this does not imply that its explosion will take place imminently. And now, an international team of researchers has concluded, after conducting the most comprehensive study to date, that the massive star is in its helium-burning phase, putting it about 100,000 years of going supernova. A time that is equivalent to a simple blink in the long history of the star, but on a human scale it is reassuringly long.

The researchers, from the Kavli Institute for the Physics and Mathematics of the Universe, also found that Betelgeuse has a smaller mass and is closer to Earth than previously believed. Still, its size is still large enough to almost reach Jupiter if we put it in the place of the Sun. Finally, in his study, just appeared in The Astrophysical Journal, scientists show that the smallest brightness variations of Betelgeuse are due to «stellar pulsations‘And suggest that the great dimming event of 2020 was due to the passage of a dense cloud of dust.

The team, led by Meredith Joyce, from the Australian National University, analyzed the variations in the brightness of Betelgeuse with evolutionary, hydrodynamic and seismic models, which allowed them to conclude, much more clearly than in previous studies, that Betelgeuse is currently burning helium at its core. In the same way, they also showed that the pulsations of the star are due to the so-called «mecanismo kappa», Which lead Betelgeuse to light up or fade successively in two periods of 185 and 400 days, respectively. However, the great collapse of its brightness observed in 2020 is something that is unprecedented, and according to the researchers it is due to the passage of a large cloud of dust in front of Betelgeuse, which significantly obscured it when observed from our planet.

The analysis revealed that the mass of the star is between 16.5 and 19 solar masses, slightly lower than the latest estimates suggested. The study also made it possible to make a better estimate of the star’s size, as well as its distance from Earth. Previous studies suggested that it could be even larger than Jupiter’s orbit, but the results of this research show that it ‘only’ extends to about two-thirds that size, with a radius that is 750 times greater than that of the Sun.

Betelgeuse variations between January 2019 and December of the same year
Betelgeuse variations between January 2019 and December of the same year – ESO / M. Montargès et al

Once the physical size of the star is known exactly, it will also be possible to determine exactly how far it is from us. For now, the researchers’ results indicate that it is much closer than previously thought, to ‘only’ about 530 light years away, or what is the same, 25% closer than previously believed.

Taken together, the results imply that Betelgeuse is not at all about to explode, although it will soon, and that when it does, it is at a sufficient distance from us that the explosion will not have a significant impact on our planet. Of course, it will be the closest supernova we have, which will be a unique opportunity to understand what happens to these types of stars before dying in such an explosive way.

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