Earlier Hubble observations suggested that a massive black hole lived in the center of M87, but this observation proved it practically beyond doubt. Astronomers discovered that a disk of hot gas in the galactic core is rotating so rapidly that it contains a massive black hole at its hub. A black hole, which Albert Einstein predicted in his general theory of relativity, is an object so massive and compact that nothing can escape its gravitational pull, including light. The object at the center of M87 fits that description. It weighs as much as three billion suns, but is concentrated in a space no larger than the solar system. The region contains only a fraction of the number of stars needed to create such a powerful attraction, leading astronomers to believe that there must be something else there that can't be seen. The giant galaxy is located 50 million light-years away in the constellation Virgo.