Figure 13-13 Two Views of the Galactic Nucleus (a) A radio image taken at the VLA of the galactic nucleus and environs. This image covers an area of the sky 8 times wider than the Moon. SNR means supernova remnant. The numbers following each SNR are its right ascension and declination. The Sgr (Sagittarius) features are radio-bright objects. (b) The colored dots superimposed on this infrared image show the motion of seven stars in the vicinity of the unseen massive object at the position of the radio source Sagittarius A*, part of Sgr A in (a). The orbits were measured over a 17-year period. The star with the fastest known orbit goes around once every 11.5 years. This plot indicates that the stars are held in orbit by a 4.3 × 106 M⊙ black hole.