It's a balance of gravity pushing in on the star and heat and pressure pushing outward from the star's core. When a massive star runs out of fuel, it cools off. This causes the pressure to drop. ... The collapse happens so quickly that it creates enormous shock waves that cause the outer part of the star to explode!

What causes a star to collapse?

Gravity constantly works to try and cause the star to collapse. The star's core, however is very hot which creates pressure within the gas. This pressure counteracts the force of gravity, putting the star into what is called hydrostatic equilibrium.

Do stars explode or implode?

CAITY: So the core of a star collapses when the rest of it is exploding outward. So that core will continue to collapse under its own gravity and it can form one of two objects. It can become something called a neutron star or it can form into a black hole.