Basic Science

Accurate Determination of the Milky Way Local Spiral Arm

Prof. Xu Ye’s group from the Purple Mountain Observatory (PMO), CAS has made great progress on the nature of the Local Spiral Arm of the Milky Way. The results were published in the Astrophysical Journal （ApJ）in May, and highlighted at the 222nd meeting of the American Astronomical Society (AAS) in June, which were also reported by U.S．News and World’s Report, SPACE, Universe Today, and NRAO News. Using the highest resolution radio interferometer array, the Very Long Baseline Array (VLBA), they measured accurately the structure and kinematics of the Local Arm for the first time. The results show that the Local Arm, previously thought to be only a small spur between two large branches known as the Sagittarius and Perseus Arms, instead should appear as a prominent feature of the Milky Way. In fact, the Local Arm looks as 15000 light-years in length and 3000 light-years in width. Based on both the distances and the space motions measured, it is a major structure, maybe a branch of the Perseus Arm, or possibly an independent arm segment. This striking result was an upgrade to the status of the Local Arm, within which our Solar System resides.