Sirius B became a white dwarf about 120 million years ago. The two stars orbit each other every 50 years. This orbital motion reveals that Sirius A, the brighter star, has 2.02 ± 0.03 solar masses and Sirius B, the white dwarf, has 1.00 ± 0.02 solar masses. It's very difficult to age individual stars, but it is estimated that the Sirius system is about 200 - 300 million years old.