Astronomers have uncovered signs that our Sun may have taken part in a large-scale movement of similar stars that left the inner regions of the Milky Way about 4 to 6 billion years ago. To investigate this possibility, researchers compiled and analyzed an exceptionally precise catalog of stars using observations from the European Space Agency’s Gaia satellite. Their results offer new insights into how the Milky Way evolved, particularly the formation of the rotating bar-shaped structure located at the galaxy’s center.
On Earth, archaeology reconstructs the past by studying ancient artifacts and remains. In space, scientists use a similar approach called galactic archaeology to piece together the history of stars and galaxies.
Astronomers know that the Sun formed about 4.6 billion years ago at a location more than 10,000 light years closer to the Milky Way’s center than where it sits today. Evidence from stellar chemical compositions supports this idea, yet the explanation has long puzzled researchers. Observations of our galaxy show a massive bar-like structure in the central region that produces what scientists call a “corotation barrier.” This gravitational effect makes it difficult for stars to travel far outward from the galactic center.
Studying Solar Twins With Gaia
To investigate how the Sun might have reached its current orbit, a research team led by Assistant Professors Daisuke Taniguchi from Tokyo Metropolitan University and Takuji Tsujimoto from the National Astronomical Observatory of Japan carried out a large study of solar “twins.” These stars share nearly the same temperature, surface gravity, and chemical composition as our Sun.
The researchers relied on the Gaia satellite mission, which has collected detailed measurements for about two billion stars and other celestial objects. Using this enormous dataset, they assembled a catalog containing 6,594 solar twins. This sample is roughly 30 times larger than those used in earlier surveys.
Age Distribution Reveals a Shared Migration
With this expanded dataset, the team was able to determine the ages of these stars with unprecedented accuracy. They also corrected for selection bias that favors brighter stars that are easier for telescopes to detect.
When the researchers examined the ages of the solar twins, they found a clear concentration of stars between 4 and 6 billion years old. The Sun falls within this same age range. Many of these stars also appear to occupy similar distances from the galactic center. Together, these clues suggest that the Sun’s present location is not simply coincidental. Instead, it likely arrived here as part of a much larger outward movement of stars.
Clues to the Formation of the Milky Way’s Central Bar
The findings provide new information about the Milky Way’s structure and history. Under normal circumstances, the corotation barrier produced by the galaxy’s central bar would prevent such a large number of stars from moving away from the inner region. However, the situation could have been different if the bar structure was still forming during that period.
The ages of the solar twins not only point to when this large migration may have happened, but also suggest the time span during which the galactic bar developed.
Why the Sun’s Journey Matters for Life
The inner parts of the Milky Way are far more hostile than its outer regions. Conditions near the galactic center include stronger radiation and more frequent interactions between stars. According to the researchers, the Sun’s movement away from this crowded environment may have helped place our solar system in a calmer part of the galaxy.
This quieter region provided conditions that allowed life on Earth to eventually emerge and evolve.
This work made use of data products from the European Space Agency (ESA) space mission Gaia and the Two Micron All Sky Survey. It was supported by the Tokyo Center For Excellence Project, Tokyo Metropolitan University, JSPS KAKENHI Grant Numbers 23KJ2149 and 23H00132, the European Union’s Horizon 2020 Research and Innovation Program under SPACE-H2020 Grant Agreement Number 101004214 (EXPLORE project).