Core Collapse

Stars more than about 8 solar masses do not end as white dwarfs. They fuse heavier and heavier elements in their cores — helium, carbon, oxygen, neon, silicon — each stage shorter than the last. Silicon fusion produces iron in the core, and iron is the dead end. Fusing iron absorbs energy instead of releasing it.

Once the iron core exceeds about 1.4 solar masses (the Chandrasekhar limit), electron pressure can no longer support it. The core collapses in less than a second, falling inward at a quarter of the speed of light.