Dating the Milky Way's halo

We live in the Milky Way galaxy. Earth is located in one of the galaxy's spiral arms, affording those of us who live in darker parts of the world a view of a band of light snaking across the sky. That band of light is the subject of intense study, as astronomers try to answer questions about its origin and development.

Jason S. Kalirai, an assistant astronomer at the Space Telescope Science Institute (STScI) in Baltimore, has developed a new technique for measuring the age of stars in the Milky Way's halo. The halo is the spherical space around the flatter disk of the galaxy, which contains dense clusters of stars called globular clusters and older stars.

Kalirai's technique makes use of newly formed white dwarf stars to determine the age of their parent stars in the halo to within 0.7 billion years. This is much more precise than the two other techniques available to measure stellar ages in the halo, which are accurate to between 1 and 3 billion years, depending on the technique.

So why do we want to know how old stars in the Milky Way's halo are? The more precisely astronomers can determine those stars' ages, the more precisely they can determine the age of the galaxy itself, which in turn informs the theories of our galaxy's formation and evolution.

Read Kalirai's full study at Nature.com.