General Discussion
In reply to the discussion: Is Betelgeuse, one of the sky's brightest stars, on the brink of a supernova? [View all]backscatter712
(26,355 posts)Red giants like Betelgeuse are know to vary quite a lot in brightness, so for all we know, this might be just a normal fluctuation.
But yeah, it's rapidly running out of gas. Like you said, it's already used up the hydrogen - turned it into helium. Now it's burning helium, and starting to make heavier elements like carbon and oxygen, which eventually get fused into even heavier elements..
And the cycle stops at iron - fusing atoms into iron consumes rather than releases energy. At that point, the fusion reaction at the star's core stops. The core collapses, then the outer layers collapse onto the core, with a gravity of millions of G's. Then the core and the collapsing layers get mashed into a plasma soup that's gazillions of degrees hotter than a normal stellar core, and that's when the star goes supernova, and that soup of plasma gets turned into most of the elements on the periodic table, and gets scattered across the galaxy.