Yunnan University study reveals 'U-shaped' stellar age pattern

A research team led by Professor Lian Jianhui from the South-western Institute for Astronomy Research at Yunnan University has published a new finding in Nature Astronomy, revealing a distinctive "U-shaped" age distribution of stars in the Milky Way that is drawing attention from the astrophysics community.

The study shows that stellar ages do not decrease steadily from the Galactic center outward. Instead, within about 36,000 light-years from the center, stars become progressively younger with increasing distance. Beyond this region, however, the trend reverses: stellar ages begin to increase again, stabilizing at around 5 billion years at distances beyond roughly 45,000 light-years, forming a clear "old-young-old" U-shaped pattern.

Researchers attribute this phenomenon not to an outside-in formation of the Galaxy, but to radial migration of stars within the galactic disk. Influenced by the Milky Way's spiral arms and central bar structure, stars can gradually shift their orbits over time, allowing older stars formed in the inner disk to move outward to the Galaxy's periphery.

This discovery provides important observational evidence for understanding the structural evolution of the Milky Way and offers a new method to constrain stellar migration rates. It may also be extended to studies of other galaxies, helping to reveal broader principles of galaxy evolution.