Shore, Steven N. Department of Physics “Enrico Fermi,” University of Pisa, Italy.
Last reviewed:January 2021
- Development of concept
- Populations in galaxies
- Characteristics of populations
- Delineation of populations
- Related Primary Literature
- Additional Reading
One of the categories into which stars may be classified, based on their place in the evolution of the galaxy that they occupy. The stellar component of the Milky Way Galaxy consists of three populations: the thin disk, the thick disk, and the halo. The thin disk, originally referred to as population I, is the youngest, located amid most of the molecular and cold atomic gas, and confined to a height of order 1 kiloparsec (3.3 × 103 light-years or 3.1 × 1016 km or 1.9 × 1016 mi) from the plane. The bulge and halo, roughly corresponding to the original population II, is a much older, far more extended structure, having an approximately spherical distribution with a scale length of order 3.5 kpc.
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