A new article appearing in the April 2020 Scientific American is “A New Map of the Milky Way” by astronomers Mark J. Reid and Xin-Wu Zheng.
The article describes recent parallax studies, using Very Long Base Line Interferometry(VLBI) radio astronomy in Japan and North America, to more accurately determine the spiral structure of our Milky Way galaxy. The studies indicate also that the Sun is closer to the central plane of the Milky Way than previously thought.
These VLBI studies utilize natural MASERs that are produced by molecules of water and methyl alcohol in ionized regions just outside hot stars. Hot stars are always short lived, not lasting more than a few million years, because they rapidly burn through their nuclear fuel at their higher temperatures. They therefore are found close to their original location of birth. They are one of the features that define a galaxy’s spiral arms. And so to map the location of the hot star MASERS is a means to map the spiral structure of the galaxy. Radio astronomy VLBI enables angular position measurements to high resolution. The angular position measurements are used to measure the parallax over the course of a year, and therefore measure distance to more accuracy. The more accurate determination of angular position in the sky and distance therefore enables a more accurate mapping.