Population II stars are metal poor star
s, containing about 0.1% metals. These stars can be found in the spherical portion of the galaxy (the halo
and the bulge
). Often these stars have tipped and elliptical orbit
s. These stars are relatively old, aged from 2 - 14 billion years. Extreme Population II stars (the most metal poor) are found in the halo and the globular cluster
s and are the oldest stars. Intermediate Population II stars are located in the bludge and are slightly more metal rich than the extreme Population II stars, but are still far less metal
rich than the intermediate Population I stars
The difference in metal content and age between Population I stars and Population II stars suggests that Population II stars formed early during the formation of the galaxy, when the galaxy contained nearly pure hydrogen and helium. As the Population II stars evolved, they produce metals through fusion. Stellar winds and novae carried these metals into the galaxy. Hence, the younger stars would be metal rich before fusion began.