The natural life cycle of a Star

Over time, the hydrogen in the nebula is pulled together by gravity and begins to spin. Eventually the temperature reaches 15,000,000 degrees and nuclear fusion occurs in the cloud's core. The star will remain in this stage for millions to billions or years. Our sun is currently in this stage.

The life cycle of a star is determined by its mass. The larger the mass, the shorter it's life cycle. The mass is determined by the matter available in the nebula (a giant cloud of gas and dust).