A star is speeding at over 1.5 million mph through the center of our galaxy appears to indicate that there really is a black hole there. Basically you would need a black hole to generate such a speed...

The gravitational pull of a black hole thought to exist there is likely responsible for the extreme velocity of the star, swinging it around the center of the Milky Way. A companion star may once have traveled with the speeding star and contributed to its velocity before being trapped by the black hole. The first-of-its-kind finding not only confirms an earlier theory about the existence of such speeding stars, but also reinforces the notion that the Milky Way spins around a black hole, said Warren Brown, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics and a member of the team that discovered the star.

Source: Wired