When the Hubble Space Telescope took a photo of distant galaxy cluster SDSS J0146-0929, it was able to capture an immensely massive blanket of hundreds of galaxies caught in each other's gravitational pulls. In the photo, they look no more than inconsequential space dust: tiny, motionless, and remote. But in fact, the combined mass of these galaxies is so great that it causes a distortion in the fabric of space and time. That is represented by a glowing ring in the center of the image, which is actually a phenomenon called gravitational lensing. The circle of light, called the...