... Exploring quasars and active galaxies in the distant universe, astronomers have come to believe that most galaxies have massive black holes at their centers. Swirling stars and a strong, variable radio source offer convincing evidence that even our own Milky Way galaxy's center harbors such a bizarre object, a mere 30,000 light-years away. A Big Black Hole Floats By . ... A black hole glides silently through space. ... NGC 7635: The Bubble Nebula . ... NGC 6791: An Old, Large Open Cluster . ...