In addition to the answers above, there is also the fact that iron fusion requires even higher temperatures than silicon. In order for the star's core to reach this higher temperature is must contract. (That's how the core is heated progressively higher and higher. After each round of fusion is over, contraction takes place and heats it up until the new elements can begin to fuse and equilibrium is reached once more) However, since iron fusion doesn't release energy the contraction simply never ends, resulting in a supernova as the core collapses in on itself.Ah ok. So there are no other parts of the star capable of producing external energy besides internal fusion, because the star has used it up? But can't the net excess of energy produced from each fusion be used for iron? Why can't that happen? Once the star reaches Fe, has it used up all of its available net energy through fusion, so it can't get its energy from elsewhere?
Well, to understand that you need to understand how fusion releases energy in the first place. Fusing two atoms together releases energy because the MASS of the new atom is LESS than the combined mass of the two atoms prior to fusing. This missing mass is released as energy.Why doesn't iron fusion release energy? (Sorry if that's a redundant question which has already been answered previously by someone's response.)
Hmmm. Just to be clear, the energy it takes to fuse Fe into heavier elements is simply more than it releases. How much energy the fusion chain released prior to Fe is irrelevant.Thanks! So it basically takes more energy to fuse Fe into heavier elements than the energy available from previous fusion events. Ok, that makes sense. Thanks!