Question: what causes a star to die

Heather Campbell answered on 19 Nov 2014:

Its basically when the star runs out of fuel to keep it going. If we take a star like our sun then:
The star burn hydrogen, by nuclear fusion to helium, in thier cores. When that is all used up then the core of helium begins to contract and reactions begin to occur in the outer shells. If the core is hot enough helium will undergo nuclear fusion to carbon. At the same time the outer layers start expanding, cool and begin to be fainter, this is called a Red Giant.
When the helium runs out in the core, the outer layers float away as shells of gas, called a Planetary Nebula. About 80% is left behind in the sore and that collapse down to form a dense star called an White Dwarf, which has about a rhinos of mass in the size of a sugar cube! It cools and dims and eventually becomes a Black Dwarf.