Transcript: The fusion process that dominates stars of less than about one and a half times the mass of the Sun and core temperatures less than fifteen million Kelvin is called the proton-proton chain. There are three steps in this reaction which converts hydrogen into helium. In the first step that lasts about ten million years per proton, two protons combine to form deuterium with the release of a positron and a neutrino. In the second step which occurs relatively quickly the deuterium atom has a proton added to become a helium 3 nucleus with the release of another photon. In the third step which takes about a million years two helium 3 nuclei combine to form a single helium 4 nucleus with two protons left over and the emission of a photon. Thus mass energy is converted at every step, and energy emerges in three separate forms: neutrinos which flee at the speed of light, protons which help further nuclear reactions, and photons themselves.