NASA's Chandra telescope reveals the Milky Way's outer arms are farther away

Astronomers using NASA's Chandra X-ray Observatory and ESA's XMM-Newton telescope have discovered that the Milky Way's spiral arms extend much farther than previously known. This finding may require revising fundamental measurements such as our galaxy's mass.

Scraper SystemJuly 04, 2026, 10:43 PM

NASA's Chandra telescope reveals the Milky Way's outer arms are farther away

Astronomers have discovered that the Milky Way galaxy's spiral arms extend much farther than previously known. The discovery was made using data from NASA's Chandra X-ray Observatory and the European Space Agency's (ESA) XMM-Newton telescope.

The researchers took advantage of rare and powerful gamma-ray bursts in distant galaxies. As the X-rays from these bursts passed through the Milky Way, they reflected off dust clouds, creating rings that could be measured with extraordinary precision.

The study's lead researcher, Italian PhD student Beatrice Vaia, said, "This is a way to directly measure the distances to the Milky Way's spiral arms based solely on geometry." Vaia noted that other methods rely on assumptions about the galaxy's rotation, which become increasingly uncertain in the outer regions.

The team estimated that a dust cloud in the farthest spiral arm is about 3,500 light-years wide. Although astronomers have been aware of the Milky Way's arms for about a century, the fact that Earth lies within one of these arms has always made mapping difficult.

Study co-author Ilaria Fornasiero said that even minor revisions in distances could affect fundamental measurements such as the galaxy's mass. "This could mean that astronomers need to revise their estimates of the galaxy's mass because it affects how far the arms extend," Fornasiero said.

The only downside of the new technique is that suitable gamma-ray bursts are extremely rare. Over the past 25 years, researchers have been able to detect only a few bursts bright enough and in the right position to measure the Milky Way's spiral arms. Co-author Andrea Tiengo said, "We will keep looking for more."

NASA's Chandra telescope reveals the Milky Way's outer arms are farther away