When do stars burn out?

Answer 1

Simply stated, stars burn out when they run out of fuel. Stars fuse lighter nuclei into heaver nuclei, and they will turn hydrogen into helium, and then turn helium into heavier elements toward the end of their life. Through what is called stellar nucleosynthesis, fusion continues to create heavier elements. And as the stars ages (stellar evolution), it will eventually reach a point where it is forming iron. This is where things get difficult for the star.

All the fusion reactions that create the elements up through iron release energy. Fusion reactions that create the trans-iron elements require energy to be put into the reaction. Where does this energy come from? Let's review the idea that the massive gravity of stars is always trying to cause them to collapse in on themselves. The energy released in fusion forces the material of the star outward, and these two forces struggle in equilibrium throughout the life of the star.

At the end of a star's life, if the star is sufficiently large, when it collapses because it is running out of fuel, it will supply enough energy in the collapse to cause the fusion of elements heavier than iron, and this is the supernova event. A star of insufficient mass will simply collapse and end up a white dwarf. Larger stars might go nova and end up as a white dwarf, a neutron star, or as a black hole (for the really big stars).