What causes a star to die

As a star ages it eventually, runs out of fuel. The star finally cools into a white dwarf, then a black dwarf. This is what happens when a normal-sized star dies. If a really huge star dies, it has so much mass that after the helium is used up, it still has enough carbon to fuse it into heavy elements like iron. When the core turns to iron, it no longer burns.

The core finally cools going into a white dwarf state, then into a black dwarf.