It’s been conjectured that the center of the Milky Way is swarming with tens of thousands of black holes. And now we’ve actually seen them. The core of our galaxy is a wild place. The stars are so densely packed that the night sky would be 500 times brighter. A supermassive black hole, 4 million times the mass of our Sun lurks in the center. It flings nearby stars into extreme slingshot orbits. It consumes anything that gets too close is consumed, burping a blast of X-rays.  We know these things because we see them from our comfortable vantage point 28,000 light years out in the galactic disk. But  there’s…