New X-ray measurements place the Milky Way’s Outer and Outer-Scutum-Centaurus spiral arms about 10% farther away than earlier estimates, suggesting the galaxy extends farther than thought.
Three gamma-ray bursts let researchers trace dust-scattered X-ray rings with Chandra and XMM-Newton, giving a geometry-based distance method that avoids uncertain assumptions about how the Milky Way rotates.
The same analysis put the most distant arm’s width at about 3,500 light-years, helping the team measure the arm’s full extent rather than a single dust cloud.
Those revisions could force updates to estimates of the Milky Way’s mass distribution, rotation and overall structure, though usable gamma-ray bursts are rare and only a handful have been found in 25 years.