halo Population II

In astronomy, Population II stars are among the oldest observed stars, forming approximately 10 to 13 billion years ago. These stars are rich in hydrogen and helium but have significantly lower abundances of elements heavier than helium, as these elements had not yet been widely created at the time of their formation. Population II stars are primarily found in the halos of spiral galaxies and within globular clusters, as well as in elliptical galaxies. The term "halo Population II" specifically refers to a nearly spherical system of these ancient stars. In contrast, Population I stars are younger and contain a higher proportion of heavier elements.12