Astronomers say the Sun did not form where it now resides. It appears to have been born thousands of light-years closer to the Milky Way’s center. It then joined a large-scale outward exodus of stars between 4 and 6 billion years ago. The conclusion comes from an analysis of the European Space Agency’s Gaia catalog of 6,594 “solar twins”—stars with temperatures, surface gravities, and chemical compositions similar to our Sun. It shows the Sun’s metallicity is too high for a star that would have formed in today’s outer-disk neighborhood and better matches an origin nearer the crowded galactic core, according to Scientific American.
Galactic archaeology
The work sits within “galactic archaeology,” a field that reconstructs the Milky Way’s past by tracking the ages, motions, and elemental makeups of stars to map where they formed and how they moved over time. A team at Tokyo Metropolitan University led by Daisuke Taniguchi used this approach to compare the Sun with thousands of analogs. They found that the oldest, most metal-rich solar twins tend to trace back to smaller galactocentric radii. Because the Milky Way’s inner regions formed stars more rapidly and enriched themselves with heavy elements like iron earlier than the outskirts, the ratio of a star’s age to its metal content ties it to a characteristic birthplace within the disk. In the Sun’s case, the data point to an origin thousands of light-years inward from its present orbit, which lies about 27,000 light-years (roughly 8,300 parsecs) from the galactic center.
A massive, coordinated migration
Researchers argue that a massive, coordinated migration carried many of these Sun-like stars outward roughly 4 to 6 billion years ago. Estimates suggest the Sun moved on the order of 10,000 light-years from its birthplace—possibly from a region less than 20,000 light-years from the center—to reach its current track around the disk.
The study further contends that this journey from the turbulent inner disk to quieter outskirts may have been crucial for the development of life on Earth, with the outer regions offering a more benign radiation environment and fewer disruptive stellar encounters than the crowded core.
At the heart of the Milky Way, a rotating bar-like structure stirs the disk and creates a barrier that generally blocks stars from crossing between the inner and outer regions. Computer simulations indicate that only about 1% of stars born near the Sun’s inferred birthplace could slip past this barrier within 4.6 billion years. This implies that the galactic bar was still forming during the migration epoch and had not yet become the fully stabilizing dynamical gatekeeper it is today.
Thousands of identified solar twins now found near the Sun bolster the idea that the barrier was porous when they moved, and that internal dynamical processes—interactions with spiral arms, the evolving bar, and encounters with other stars—drove their outward drift.