What event halts the energy-producing process in a massive star destined for a core-collapse supernova?

Answer

When the iron core accumulates to a critical size, as fusing iron consumes energy

The formation of an inert core composed of iron signals the end of energy generation. Since fusing iron requires an input of energy rather than releasing it, the outward pressure supporting the star vanishes, leading to collapse.

What event halts the energy-producing process in a massive star destined for a core-collapse supernova?
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