What event causes the catastrophic core collapse leading to a supernova in massive stars?

Answer

Fusion progressing past iron, where energy is consumed instead of produced.

Once fusion in the core progresses to iron, no more energy can be released because iron fusion consumes energy. With the energy source gone, gravity wins instantly, causing a core collapse and triggering a supernova.

What event causes the catastrophic core collapse leading to a supernova in massive stars?
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