Why does the formation of an iron core trigger an instantaneous, catastrophic collapse in a massive star?

Answer

Fusing iron consumes energy instead of releasing it, instantly removing thermal support

When the core becomes iron, fusion stops releasing the necessary outward pressure to resist gravity. This loss of support leads to a complete, freefall gravitational collapse in milliseconds.

Why does the formation of an iron core trigger an instantaneous, catastrophic collapse in a massive star?

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