This visualization of a computer simulation shows off the structure of the "cosmic web" in the unverse. Purple represents the dark matter and white represents the galaxies. The dark matter dominates the gravity in the universe, and its gravitational development creates a structure of long thin filaments connected together at nodes. The distribution resembles an irregular, three-dimensional spider's web. Galaxies tend to form along the filaments and collect into clusters at the nodes. The large, mostly empty regions in between are called "voids".
Visualization: Frank Summers, Space Telescope Science Institute
Simulation: Lars Hernquist, Harvard University, and Martin White, University of California at Berkeley