What is the primary reason the core collapse of a massive star occurs?

Answer

The iron core builds up past a critical point, causing the outward pressure to vanish instantly.

In massive stars, fusion continues until the core is composed of iron. Since fusing iron consumes energy instead of releasing it, the outward pressure supporting the star disappears, allowing gravity to cause an immediate, catastrophic collapse.

What is the primary reason the core collapse of a massive star occurs?
astronomystellar evolutionsupernovastar deathviolent