oldest star

The oldest stars in the Galaxy almost certainly belong to globular clusters. It is suspected that all globular clusters are about the same age - around 10 or 11 billion years. By contrast the Sun formed relatively recently - about 5 billion years ago. There are several reasons for believing that globular clusters are very old. First, their more massive stars are all in advanced states of evolution, or have long since ended their lives as supernovae. Second, they are distributed throughout the spherical halo of the Galaxy, which suggests they are remnants of the era before the Galaxy collapsed to its present disc shape. Third, globular cluster stars contain very low proportions of chemical elements heavier than hydrogen or helium. This is because there were hardly any atoms of heavier elements in existence when these stars formed. The heavier elements have been created inside stars then recycled back into interstellar clouds to be incorporated in stars forming later, such as the Sun.