Why does the core fusion process cease abruptly in massive stars once the core primarily consists of iron ($ ext{Fe}$)?

Answer

Fusing iron requires an input of energy rather than releasing it.

Elements lighter than iron release energy during fusion, supporting the star, but fusing iron itself is an endothermic process, meaning it consumes energy and causes the star to lose its energy source instantly.

Why does the core fusion process cease abruptly in massive stars once the core primarily consists of iron ($	ext{Fe}$)?
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