Nucleosynthesis
Nucleosynthesis is the making of new atomic nuclei, in the Big Bang, in stars and in stellar explosions.
Nucleosynthesis is the creation of chemical elements and isotopes. Hydrogen, helium and a little lithium were made in the Big Bang. Almost everything heavier was made inside stars, which fuse light nuclei into heavier ones, and in the explosive deaths and collisions of stars.
Different stars make different mixtures of isotopes. Red giant stars produce carbon, nitrogen and many heavier elements by slowly capturing neutrons. Supernovae and neutron star mergers produce elements by rapid neutron capture, including much of the gold, platinum and uranium in the Universe.
Meteorites carry direct evidence of these processes. Presolar grains, tiny crystals that formed around other stars before the Sun existed, have isotope ratios that match predictions for particular kinds of star. Short-lived radioactive isotopes such as aluminium-26 found in the oldest meteorite inclusions show that freshly made material was added to the solar cloud shortly before planets formed. The atoms in a meteorite were forged by many generations of stars.
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