How old is the Milky Way, in billions of years?

The Milky Way is about 13.6 billion years old. That estimate refers to the galaxy’s long formation history, which began soon after the Big Bang as matter gathered into dense regions that eventually produced the first stars and galactic structures.

The Milky Way did not appear all at once as the fully developed disk seen today. Early building blocks merged and accumulated gas. The oldest surviving stars are found mainly in the galactic halo and globular clusters, while much younger generations formed later in the rotating disk. The galaxy continues to grow by forming stars and absorbing smaller satellite galaxies.

The estimate is based partly on dating very old stars and partly on models of galactic evolution. Some individual Milky Way stars are more than 13 billion years old, placing a strong lower limit on the galaxy’s age. The figure is close to the estimated 13.8-billion-year age of the universe, but it does not mean every part of the Milky Way formed simultaneously. The Sun, by comparison, is only about 4.6 billion years old.