Using more than 100,000 giant stars from LAMOST, APOGEE and Gaia, the team found star formation drops sharply 35,000 to 40,000 light-years from the galactic centre.
A U-shaped stellar age pattern showed younger stars out to that radius, then older stars farther out, indicating the outer disc is dominated by stars that migrated outward on near-circular orbits.
The finding supports inside-out growth of the Milky Way, while the cause of the boundary remains unclear, with the central bar and outer warp among possible explanations.
What mysterious force halts new star formation beyond 40,000 light-years in our galaxy, and could it affect the future of the Milky Way?
Could the newly discovered edge of star formation challenge what we know about how galaxies like the Milky Way grow and evolve?
How did the Sun’s ancient migration shape the conditions for life on Earth—and what does it reveal about the safety of other star systems?
Discovering the Milky Way’s Star-Forming Boundary and Its Impact on Galactic Evolution
Overview
A landmark 2026 study precisely mapped the Milky Way's star-forming edge at 35,000 to 40,000 light-years from its center, revealing a sharp drop in star formation beyond this boundary. This edge marks where the Galaxy's disk growth, driven from the inside out, slows dramatically. The study uncovered a U-shaped pattern in stellar ages, with the youngest stars near the edge and older stars both inside and far beyond it. This pattern arises from two key processes: inside-out star formation and radial migration, where stars gradually move outward due to gravitational effects from spiral arms. Additionally, the central bar's gravitational resonance and the Galaxy's warped disk limit cold gas supply, causing the star-formation cutoff. Together, these findings place the Milky Way within a common class of spiral galaxies with similar structural breaks.