Astronomers Define Geographic Boundary of Milky Way Star Formation Using Unique U-Shaped Age Profile

Astronomers define the edge of the Milky Way's star-forming disc 40,000 light-years from the center, using a new "U-shaped" stellar age profile.

By: AXL Media

Published: Apr 21, 2026, 9:22 AM EDT

Source: Information for this report was sourced from EurekAlert

Quantifying the Limits of Galactic Architecture

The structural extent of the Milky Way has historically been difficult to map due to the gradual fading of its outer boundaries. However, a new study co-authored by researchers at the University of Malta provides a definitive quantitative answer to this long-standing question in galactic archaeology. By examining the distribution of stellar ages across the disc, astronomers have determined that the bulk of our Galaxy's star formation is contained within a radius of 40,000 light-years from the Galactic Centre. This discovery allows scientists to distinguish between the regions where stars are actively born and the outer reaches where stars only exist due to internal movement.

Inside-Out Growth and the U-Shaped Discovery

A diagram of the Milky Way, depicting its various named parts.

Galaxies typically evolve through a process called "inside-out" growth, where stars form first in the dense central regions before expanding outward over billions of years. This process generally results in younger stars being located further from the center. However, researchers discovered a "U-shaped" age profile in the Milky Way, where the average age of stars decreases until about 35,000 to 40,000 light-years and then begins to increase again. According to lead author Dr. Karl Fiteni, this age minimum serves as a clear marker for a sharp drop in star formation efficiency, effectively defining the true edge of the star-forming disc.

The Mechanics of Radial Stellar Migration