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)First, bear in mind that a star as big as Betelgeuse will turn into a black hole after the supernova blows. Millions of G's of gravity.
So. First, the star runs out of fuel - everything in the core's fused to iron, and as you mentioned, fusion stops very quickly.
The core collapses. To something resembling a neutron star.
But light only goes so fast, and this is a star so big that in our own solar system, it will consume Mercury, Venus, Earth, Mars, and maybe Jupiter, and its outer layers go almost out to Saturn. It takes a bit before the radiation from the core stops reaching the next layers out.
Then when that core radiation stops, those next layers, which were being pushed out by the intense radiation and heat, start falling inwards. Pulled by millions of G's of gravity (like I said, this is a really huge star), and I'm estimating that the fall is from a few million miles out from the core. When the surrounding layers hit the core, they will be traveling at a quarter of the speed of light.
That matter slams into the core, with the force of gazillions of nuclear bombs, and it will compress the core, until electrons and atomic nuclei get mashed together. Electrons collide with protons, turning them into neutrons, like in a neutron star, and release huge numbers of neutrinos.
Most of the neutrinos radiate outwards, and some of them will spike neutrino detectors here on Earth 650 years later. But enough are released that a fraction of a percent of them will hit the next surrounding layers of the star's plasma, and heat them up.
And that is how one of the most powerful explosions in the universe short of the Big Bang itself happens.