Main Sequence Stars Stars spend most of their active lives in a stable state fusing hydrogen to helium. This stable state is known as the star's main sequence. The Sun for example is a main sequence star. It has been fusing hydrogen to helium for about five billion years and will do so for about another five billion years.
Bigger stars fuse hydrogen to helium faster and live shorter lives.
Smaller stars fuse hydrogen to helium slower and live longer lives.