A team led by Karl Fiteni, then at the University of Malta, has pinpointed the outer edge of the Milky Way’s star‑forming disk. By analysing more than 100,000 red‑giant stars from LAMOST, APOGEE and Gaia, the researchers identified a sharp decline in new star birth beyond roughly 40,000 light‑years from the galactic centre, and confirms previous hints of a truncation.

Inside that radius, abundant cold gas fuels continuous formation, yielding a youthful stellar population. Past the break, the study shows older stars dominate, having migrated outward on near‑circular orbits rather than forming in situ. This creates the characteristic U‑shaped age profile seen in simulated disks and a handful of external galaxies, confirming a common evolutionary pattern, and suggests radial mixing shapes outer discs.

Victor Debattista of the University of Lancashire notes that the outer disk’s stars move on close‑to‑circular paths, implying they were born in the inner disk and carried outward by spiral‑wave dynamics. The finding narrows a long‑standing question in galactic archaeology and provides a concrete metric for future surveys such as 4MOST and WEAVE to refine models of disk growth. These insights aid chemical evolution models.