Figure 14-33 The Rotation Curve of the Core of M31 This graph plots radial velocity of matter in the core of M31 versus the angular distance from the galaxy’s center. Note the sharp peaks, one blueshifted and one redshifted, within 5 arcsec of the galaxy’s center. This indicates the presence of a compact, very massive object at the center of the galaxy. At the distance of M31, 1 arcsec corresponds to 12 ly.