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Born at the same time, the star that formed Sirius B started out more massive and evolved more quickly than its companion, Sirius A.
By Astronomy Staff
|
Published: May 21, 2026
| Last updated on May 22, 2026
The stars of the Sirius binary star system are about the same age, around 250 million years old. But because Sirius B (to the right in this artist’s impression) was originally more massive, it’s now further along in its stellar evolution. Credit: NASA, ESA and G. Bacon (STScI)
Sirius is a blue giant, which burns through its fuel quickly and lives only a relatively short period of time. Yet it has a white dwarf companion (Sirius B) and white dwarfs are the end result of stars like our Sun, which live for billions of years. How can a young blue giant have a companion star that’s billions of years older?
John Gould
Moab, Utah
This is a great question. It hinges on the fact that while we often say that white dwarfs are the remnants of Sun-like stars, the term Sun-like in this case is admittedly a bit of an oversimplification.
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