The Milky Way galaxy is larger than scientists previously estimated, with its outer spiral arms stretching approximately 10% further into space, according to a new study. Researchers from the European Space Agency (ESA) employed an innovative method involving the analysis of X-ray echoes from cosmic explosions to refine measurements of the galaxy's structure.

Previously, the dimensions of the Milky Way's outer arms were largely modeled indirectly, based on the galaxy's rotation patterns. This indirect approach, according to Beatrice Vaia of Italy's Istituto Nazionale di Astrofisica (INAF), who led the research, left room for error. The new study utilized data from ESA's XMM-Newton and NASA's Chandra X-ray space telescopes to observe the aftermath of three bright explosions originating in the outer spiral arms.

These explosions released X-rays that propagated through the arms, creating echoes. By measuring the distance to these echoes, scientists were able to directly determine the distance to the dust grains within the arms. The findings indicate that two of the galaxy's arms, the Outer Scutum–Centaurus Arm and the Outer Arm, are located up to 10% further away than previously thought.

This direct measurement approach marks a significant shift from prior methods and could enhance understanding of the galaxy's outer regions. While our solar system is situated within the Milky Way, detailed knowledge of its structure has been limited. However, advancements in telescopic technology are providing new perspectives.

In 2020, observations from the Gaia space telescope confirmed that the Milky Way possesses four major spiral arms, resolving earlier uncertainties about whether it had two or four. The current study, by providing more precise distance measurements for the outer arms, contributes to a more accurate galactic map.

Erik Kuulkers, ESA XMM-Newton project scientist, highlighted the continued importance of long-standing missions like XMM-Newton, which launched in 1999. He noted that such missions, even in their third decade, continue to yield significant scientific discoveries, especially when collaborating with other instruments.

"It's even more exciting when missions team up, as they did here," Kuulkers stated. "Together, they can reveal huge amounts about the skies around us."