Milky Way’s Outer Arms are Further Away Than We Thought

Our galactic home is slightly wider than previously estimated. A groundbreaking international study has revealed that the Milky Way's outer spiral arms are located up to 10% further out into the cosmic void than prior models suggested— a discovery developed also as part of Beatrice Vaia’s PhD thesis in Space Science and Technology.

The research was made possible by joining the forces of Earth's premier X-ray space observatories: the European Space Agency’s (ESA) XMM-Newton and NASA’s Chandra X-ray Observatory.

To map the far side of our galaxy, which is normally hidden by thick interstellar dust, the team analyzed archival data spanning from 2003 to 2022. They focused on the expanding X-ray rings, known as "light echoes," produced when X-rays from three exceptionally bright Gamma-Ray Bursts (GRBs), including the record-breaking event GRB 221009A, were scattered by clouds of interstellar dust. Because the scattering angle depends on the distance of the dust clouds, measuring the size and expansion of these rings provided a highly accurate way to determine their distances, effectively turning the rings into a cosmic ruler. 

The study, led by Beatrice Vaia, now a researcher at Italy's National Institute for Astrophysics (INAF-IASF Milano), in collaboration with an international team, pushed the boundaries of cosmic cartography. Conducted as part of her PhD in Space Science and Technology, the research highlights the program's contribution to redrawing the map of our own galactic backyard.

Read the full articles and press releases here:

• ESA Press Release
• INAF Media Article
• Chandra / NASA Press Release