What happens to the star when it gets old?

 

A star is formed by the condensation of the gas clouds.

This phase is called as the protostar phase. With age the protostar evolve into a sequence star.

In the sequence phase , huge amount of energy is emmited due to the fusion of H to He.

With further time , more condensation occurs. This evolves the sequence star into a Red giant . In the Red giant phase the fusion of He to C occurs. The mass in the enveloping surface of the Red giant gradually condense.

With the exhaustion of the He that has condensed into C , the Red giant transforms into a white dwarf. It has a carbon core and all the mass in the envelop has disappeared.

The white dwarf evolves into a Supernova if the mass is around 1.4 times that of sun. This in turn evolves into a dense neutron star.

However, if the mass is around three times that of our Sun, it evolves into a black hole which is so dense that even light cannot escape from it.

Thus the evolution history of a star is as follows.

Protostar -> Sequence star-> Red giant -> White dwarf -> Supernova -> Neutron star -> Black hole.