Milky Way’s mass 50% higher! | fr584's Blog

Observations using the Very Long Baseline Array (VLBA) radio telescope to make parallax measurements of star formation regions in the Milky Way, have revealed that our galaxy is rotating faster than previously thought. The measurements indicate that the Sun is orbiting at a speed of about 265 km s-1 rather than the 220 km s-1 previously believed . This implies that the galaxy has a mass 50% greater than previously thought, meaning it rivals the Andromeda galaxy (the other large spiral galaxy in our Local Group .

The parallax measurements of masers (objects which naturally amplify radio waves in a similar way to optical lasers) in spiral arms provide a direct determination of distance and motion that is more precise than previously used indirect methods.  The data also imply that the Milky Way has four, rather than two spiral arms.