extreme Population II

In astronomy, extreme Population II refers to a subclassification of stars and stellar assemblages that are among the oldest observed. These objects formed approximately 10 to 13 billion years ago. They are characterized by a high abundance of hydrogen and helium but a significantly lower concentration of elements heavier than helium, as these heavier elements had not yet been extensively produced at the time of their formation.1

Extreme Population II stars are typically found in the halos of spiral galaxies and within globular clusters, such as those in the Milky Way system. They are also prevalent in elliptical galaxies. The concept of stellar populations was introduced by astronomer Walter Baade in the 1950s to categorize stars based on their age, chemical composition, and location within galaxies.12