Betelgeuse's sudden dimming means it is about to explode
The old claim turned out to be wrong and was rejected by evidence.
TaughtWhen Betelgeuse, the red shoulder of Orion, lost two-thirds of its brightness over the winter of 2019–2020, the natural reading was that the old supergiant was finally about to die, that we were watching the prelude to a supernova bright enough to cast shadows on Earth.
NowIn August 2020, Hubble observations showed the Great Dimming was a dust cloud, not a death rattle. The star had belched a huge bubble of hot plasma from its surface; as it drifted outward it cooled into dust that briefly veiled part of the star. By April 2020 Betelgeuse had already brightened back to normal.
What actually happened
Follow-up work published in Nature in 2021 confirmed the picture: a localized cooling of the star's surface let ejected gas condense into dust grains that blocked light from about a quarter of the visible disk. Ordinary stellar weather on a monstrous scale, not the beginning of the end.
The honest caveat, in the star's favor: Betelgeuse genuinely will go supernova someday, most likely within the next 100,000 years or so. It just wasn't sending that signal in 2020.
What was disproved is the specific inference: that the dimming we watched was the countdown. It was dust.
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Who was taught this
Still standard through 2020, so anyone who finished school between 1950 and 2020 learned the earlier version.