Free Astronomy Magazine July-August 2023

9 JULY-AUGUST 2023 ASTRO PUBLISHING I n these three images of Betelgeuse are left: an interferometric image of the photosphere, center: an adaptive optics tricolor composite image, and right: an image at 10.49 µ m of the surrounding dust thermal emission. [Yaël Nazé, and Xiao Che, Nick L.J. Cox, José H. Groh, Martin Guerrero, Pierre Kervella, Chien-De Lee, Mikako Matsuura, Sally Oey, Guy S. Stringfel- low, Stephanie Wachter] convective and therefore do not carry information about the ele- ments generated in the thermonu- clear forge to the surface. The crux of the matter is precisely to understand whether the nucleus of Betelgeuse is burning helium or carbon. The models would be decisive if it were possible to “feed” them with less ap- proximate data, but since, as we have seen, this is not feasi- ble, wide freedom of interpre- tation remains, so much so that Saio’s team comes to question the paradigm of fun- damentality of the 400-420 day period, proposing that in- stead it is the one of about 2200 days that is fundamental. This would lead to a different estimate of the star’s size and a different current evolution- ary stage, with the conse- quence that Betelgeuse would already be going through the carbon fusion phase, which would significantly shorten the supernova wait time. In fact, a star with an initial mass of about twenty solar masses, as Betelgeuse probably was at the entrance to the main sequence, runs out of hydrogen in about 10 million years, helium in about one million years, carbon in just a thou- sand years. The subsequent contrac- tions of the nucleus and consequent fusions of increasingly heavier ele- ments last less and less time, until the photodisintegration of the silicon, which ends in about a day and can hinder the continuation of the chain towards nickel, cobalt and iron, ele- ments which are the last gen- erated by the stars in the imminence of their explosion. All the heavier elements pres- ent in nature are instead pro- duced by supernovae. The majority of specialists in the sector favor the scenario in which the fusion of helium into carbon is still taking place in the nucleus of Betel- geuse, also because it is about a thousand times more likely. But if reality were the one described by Saio’s team, we could be on the eve of a grandiose and rare galactic event. Considering that Betelgeuse is 600 (±100) light years away from us, the explosion may have already occurred, while we continue to see the star as it was hundreds of years ago and some amount of time prior to the explosion. T his composition shows the red supergiant Betelgeuse that pulsates, swells and shrinks asymmetrically in the UV. [Alex Lobel, Andrea Dupree, Ronald Gilliland, CfA, STScI, NASA, ESA] !