nucleosynthesis
Nucleosynthesis is the formation of atomic nuclei from pre-existing nucleons in cosmic settings. It encompasses fusion, neutron capture, and other nuclear reactions occurring in stars, stellar remnants, and the early universe. The term contrasts with nuclear decay, which reduces nuclei to lighter species.
Big Bang nucleosynthesis occurred within minutes after the Big Bang, producing most of the universe's light
Stellar nucleosynthesis powers stars and builds heavier elements. Hydrogen burning converts H to He in main-sequence
Beyond fusion, nucleosynthesis also proceeds via neutron capture. The slow s-process builds heavier nuclei gradually in
Additional production mechanisms include cosmic ray spallation, which creates light elements like lithium, beryllium, and boron.