Stellar Nucleosynthesis: Observation, Measurement & Evidence

Hydrogen burning creates helium, helium burning creates carbon and oxygen, and massive stars undergo additional stages that produce nuclei through neon, oxygen, and silicon burning toward the iron group. Neutron-capture processes create many nuclei heavier than iron, while explosive burning alters abundances during supernovae and mergers.

Stellar spectra reveal abundance patterns predicted by nuclear networks, meteorites contain isotopic signatures of different processes, supernova remnants show freshly synthesized elements, and observations of old stars preserve chemical fingerprints from earlier stellar generations.

Fusion of light nuclei releases energy while product nuclei become more tightly bound up to the iron region. Beyond that region, fusion generally requires net energy, so heavy-element production depends strongly on neutron capture, radioactive decay, and explosive conditions rather than ordinary exothermic core fusion.

Element and isotope abundances in stars, meteorites, supernova remnants, and ejecta can be compared with reaction-network calculations. Old metal-poor stars are especially valuable because they preserve signatures of a small number of early enrichment events.