At the Côte d’Azur Observatory, a team of astronomers is helping redefine the history of the Sun through a cutting-edge galactic archaeology approach. Their study reveals that our star did not drift alone from its birthplace, but instead took part in a large-scale, collective migration.
Formed approximately 4.6 billion years ago, the Sun is thought to have originated much closer to the center of the Milky Way than its current position. Until now, this outward journey toward the Galactic outskirts was largely considered a random process. New analyses instead point to a structured mechanism involving an entire population of stars.
The researchers identified 6,600 so-called “solar twins” within a sphere extending 1,000 light-years around us. These stars, comparable to the Sun in both chemical composition and physical properties, serve as powerful tracers of Galactic history.
By leveraging data from the European Gaia satellite—an unprecedented three-dimensional map of the Milky Way—the team assembled the most extensive database of its kind. This collection far surpasses previous catalogs and enables a robust statistical reconstruction of the evolutionary history of these stars.
The analysis of stellar ages and chemical compositions reveals a striking result: a large fraction of these stars formed between 4 and 6 billion years ago, around the same time as the Sun. Their chemical signatures also point to a shared origin in the inner regions of the Galaxy.
Now located in the Sun’s vicinity, these stars must have migrated outward together toward the outer regions of the Galactic disk, where the Sun currently resides. This finding is unexpected, as dynamical models predicted that such migration should be strongly suppressed in the central regions of the Galaxy.
The reason lies in the presence of a corotation bar at the heart of the Milky Way—a dense structure in which stars orbit in a synchronized manner. This configuration is thought to inhibit radial motion and prevent stars from straying far from their birthplaces.
However, the new results suggest that this dynamical barrier was less effective at the time the Sun formed. The Galactic bar may have been in the process of forming, profoundly altering the conditions governing stellar motions.
This transitional phase could have enabled a large-scale outward migration, carrying with it a cohort of Sun-like stars. Rather than being an exception, the Sun may thus be part of a broader episode of Galactic restructuring.
These findings offer a new perspective on the evolution of the Milky Way, demonstrating that stellar motions are not purely random but can be shaped by specific dynamical phases in the Galaxy’s history.
Beyond Galactic structure, the results also have implications for Earth’s history. The planets of the Solar System formed as the Sun began its journey toward the Galactic outskirts.
Understanding this migration helps constrain the Galactic environment in which life first emerged on our planet. Galactic archaeology therefore becomes a crucial tool for linking cosmic history with the origins of life on Earth.
Through this work, the Côte d’Azur Observatory reaffirms its leading role in the study of stellar dynamics and Galactic evolution, particularly through its major contribution to the Gaia space mission.