A companion star may have stripped silicon layers. While hydrogen fusion can persist for millions of years, silicon fusion may last only a few days. While all this is playing out in the star’s core, the star is also shedding gas from its surface, carried out into space by the stellar wind. Core collapseWhat happens to a massive star when its core is full of iron? Depending on how big it is to start with, the collapsed core will become a neutron star or a black hole.