Question

What physical property of iron makes it the "star killer?"

Answer 1

The physical property of iron makes it the "star killer" is its weight i.e it is heavier than other elements in the periodic table such as Hydrogen and Helium.

Iron is the element in the periodic table, that happens to be from a nuclear point of view the most stable which further means that if we take 2 protons and fuse them together, we can get out of it deuterium and which is what the sun (which is a star) does in abundance in its core and then if we fuse again deuterium together more protons can be build helium and then subsequently build up carbon, magnesium, Oxygen, all the intermediate weight elements in the periodic table up to iron

and every time this series of process occurs we get energy out as  these reactions are exothermic .ie more energy is released out of it than the input resources . so that is a way of feeding energy into the core of a star and now iron is a problem for a star such that when a star tries to fuse iron it actually takes energy in when it fuses . so if we fuse iron we are actually absorbing energy instead of letting energy out to support the star.

it will die in a few milliseconds after it begins to form iron in its core because now instead of energy supporting all that gravity its taking it up and star collapses and this collapse is the precursor to what we called as the supernova explosion.