What high-energy event is triggered by the sudden cessation of outward pressure caused by the iron core collapse?

Answer

A Type II supernova

When the iron core can no longer generate energy to counter gravity, it collapses catastrophically in a fraction of a second, leading directly to one of the universe's most energetic explosions, the Type II supernova.

What high-energy event is triggered by the sudden cessation of outward pressure caused by the iron core collapse?
Elementastronomystarmassnucleosynthesis