Why can't stars fuse iron?

Answer: Iron fusion requires energy

Stars too cool for iron — Wrong. Stars fusing iron cores are extremely hot (~billions of Kelvin). Issue is iron fusion consumes energy instead of releasing it.

Iron atoms are too large — Wrong. Atom size isn't the issue. Iron (Fe-56) has the highest binding energy per nucleon—fusing it requires energy, not releases it.

Iron fusion requires energy ✓ — Correct! Iron-56 has maximum binding energy per nucleon—most stable nucleus. Fusing lighter elements releases energy; fusing iron consumes energy (endothermic). Massive stars build iron cores through fusion, but iron can't sustain the star. Core collapses under gravity when iron forms—triggering supernova. Elements heavier than iron form in supernovae, not stellar cores!