What causes a core-collapse supernova to occur in a massive star?

The star exhausts its nuclear fuel, causing the core to collapse under gravity.

Core-collapse supernovae occur specifically in stars significantly more massive than the Sun. These stars maintain stability through outward thermal pressure generated by nuclear fusion in their core. When the star burns through its fuel supply, fusion ceases, and the outward pressure vanishes. Gravity then overwhelms all remaining forces, causing the massive stellar core to rapidly collapse inward. This rapid collapse rebounds off the ultra-dense remnant core, generating a powerful explosion known as a supernova. This process is fundamentally different from Type Ia explosions which rely on mass transfer onto a white dwarf.