The life span of a star depends on the mass of the star. Heavier stars burn their fuel faster, and have a shorter life span than smaller ones. Stars with a large mass burn brighter than smaller ones, and can use all of their fuel withing a few million years. Stars with a smaller mass do not burn as bright and use their fuel at a much slower rate. It's estimated that these smaller stars can have life spans of more than 100 billion years.