A fusion reaction that takes place in older stars in which three nuclei of a helium atom fuse to form a nucleus of carbon. Temperatures exceeding 108 kelvin and enough helium nuclei are needed to start the triple alpha process, so it occurs at the end of the lifetime of a star that has run out of hydrogen fuel and has begun to contract and therefore heat up. Typical stars undergoing the triple alpha process are red giants. Extremely high temperatures are needed because it is a low probability process. The nucleus of beryllium, formed by the fusion of two alpha particles, is very unstable. It must therefore meet the helium nucleus in a very short time, which is what the high temperature allows. As a side effect of this reaction, oxygen is also synthesised. The star thus produces carbon and oxygen, the elements necessary for life.