Hunting for a Giant Black Hole, Astronomers Found a Nest of Darkness No Gargantua dwells at the heart of stellar cluster NGC 6397. Instead, a few dozen smaller black holes seem to be swarming around in there, throwing their considerable masses around. The stellar cluster NGC 6397, captured by the Hubble Space Telescope, is 13 billion years old and contains about 250,000 stars, all of them old, small and dim.Credit...NASA, ESA, T. Brown, S. Casertano, and J. Anderson Listen to This Article . Two astronomers recently went looking for a monster black hole. They sifted reams of data from the most powerful telescopes on and above Earth for any sign of an invisible object hundreds of times the mass of the sun in a distant cloud of stars known as NGC 6397.