Galactic chemical evolution

Galactic chemical evolution is the changing abundance of chemical elements in a galaxy as stars form, synthesize elements, and return material to interstellar space.

Stellar nucleosynthesis: The production of chemical elements through nuclear reactions inside stars and during stellar explosions. Stars create many of the elements whose abundance changes across a galaxy.
Metallicity: In astronomy, the abundance of elements heavier than hydrogen and helium in an object. Metallicity summarizes how chemically enriched a star or gas cloud is.
Chemical tagging: A method of inferring common birth sites for stars from their detailed chemical abundance patterns. It can identify stellar groups that preserve the chemistry of earlier galactic environments.
Type Ia supernova: A thermonuclear explosion of a white dwarf in a binary system. Its delayed iron production contrasts with prompt enrichment from massive-star explosions.
Supernova nucleosynthesis: The creation and dispersal of elements in supernova explosions. Supernovae inject newly made elements into galactic gas.
Abundance ratio: A comparison of the abundances of two chemical elements, often expressed logarithmically relative to the Sun. Ratios distinguish enrichment sources that produce different element mixtures.
Stellar archaeology: The reconstruction of a galaxy’s history from the ages, motions, and chemical compositions of its stars. Chemical records in old stars reveal conditions in the early Milky Way.
Core-collapse supernova: The explosion that follows the collapse of the core of a massive star. It rapidly supplies alpha elements, unlike the typically delayed iron-rich Type Ia channel.
Asymptotic giant branch star: A late evolutionary stage of low- to intermediate-mass stars, marked by strong mass loss and nucleosynthesis. These stars return carbon and elements made by slow neutron capture.
Stellar population: A group of stars considered together because of shared properties such as age, composition, or motion. Populations preserve abundance patterns from distinct epochs of galactic history.

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