Milky Way Edge Revealed: Star-Forming Boundary About 40,000 Light-Years Out

New analysis of 100k giant stars from APOGEE-DR17, LAMOST-DR3, and Gaia shows the Milky Way’s edge lies at 11.28–12.15 kpc (about 40,000 ly) from the center, defined as the end of the star-forming region; the observed U-shaped age trend (older inwards, younger toward the edge, then older beyond) reflects star migration under spiral arms and the bar, with three factors—outer Lindblad resonance, a galactic warp, and thin gas—likely causing the cut-off, classifying the Galaxy as Type-II.