11.11 The reactions of the proton-proton chain

Most stars are powered by hydrogen fusing into helium. In the proton-proton chain, two hydrogen atoms (protons) collide and fuse into heavy hydrogen and release energy by ejecting a positively charged electron (a positron) and a tiny neutral particle called a neutrino. The heavy hydrogen collides with another proton and fuses into a light form of helium (called Helium three), releasing energy and a gamma ray. Finally, another helium three collides with the first one. They fuse into an atom of ordinary helium (helium four), releasing yet more energy and ejecting two protons.