Why does the build-up of elements through standard fusion stop abruptly at iron ($ ext{Fe}$)?

Answer

Fusing iron consumes energy rather than releasing it

Unlike all lighter elements, iron fusion is an endothermic process, meaning it requires an input of energy, causing the core's outward pressure source to vanish.

Why does the build-up of elements through standard fusion stop abruptly at iron ($	ext{Fe}$)?
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