1. Fusion Fuels Run Out: Massive stars spend their lives fusing heavier and heavier elements in their core. This process releases energy, which supports the star against its own gravity.
2. Iron Build-Up: Eventually, the core of the star begins fusing iron. Iron is the most stable element, and fusing it *requires* energy instead of releasing it. This means the core starts to cool and contract.
3. Core Collapse: Without the outward pressure from fusion, the core rapidly collapses under its own gravity. This happens incredibly fast – in just a few seconds!
4. Supernova Explosion: The collapsing core creates a shock wave that travels outward through the star, triggering a violent explosion known as a supernova.
The core collapse phase is essentially the point of no return. Once the iron core begins to collapse, the star's death is inevitable, resulting in a supernova explosion and the potential formation of a neutron star or a black hole.
