Here's why:

* Fusion Process: Stars generate energy through nuclear fusion, where lighter elements are fused together to form heavier ones. This process releases enormous amounts of energy.

* Iron's Stability: Iron is the most stable element in the universe. This means that fusing iron atoms together actually requires energy instead of releasing it.

* Core Collapse: When a star runs out of lighter elements to fuse, the core becomes increasingly dominated by iron. Without the outward pressure from fusion, the core's gravity collapses inwards.

* Supernova: This rapid collapse causes a massive explosion known as a supernova, which scatters heavy elements like iron throughout the universe.

Therefore, the presence of a core dominated by iron is a crucial marker for the impending death of a solar-like star.