False colors represent X-ray intensity.
The giant elliptical galaxy M87 is the large spot. The unseen mass must be dark matter. Courtesy Richard Mushotzky and S. Snowden, Laboratory for High Energy Astrophysics , Goddard Space Flight Center. . Sure, we see a few comets and asteroids , lots of stars, gobs of gas, even the odd extrasolar planet or two. Still, most of the universe remains absolutely invisible.