The process of creating elements by nuclear reactions. Helium was produced by nucleosynthesis in the few minutes following the Big Bang. Helium and heavier elements are built up by nucleosynthesis inside stars. First, hydrogen is converted to helium by the proton–proton reaction or the carbon–nitrogen cycle. When the hydrogen-to-helium phase ends, the triple-alpha process takes over. Successively heavier elements up to iron are then synthesized, each in turn using the product of the previous reaction. If a star becomes a supernova, the heaviest possible nuclei are formed and are ejected into interstellar space. New generations of stars forming from the enriched medium have a higher heavy element content than old stars. See also r-process; s-process.
Subjects: Astronomy and Astrophysics — Earth Sciences and Geography.