Supervoids and superclusters
To find the largest structures we could in the Universe, we used a catalog of extremely bright galaxies from the Sloan Digital Sky Survey. They occupy a vast volume; the most distant galaxies in the sample are about 10 billion light-years away, and the survey occupies about 1/4 of the sky. Using Voronoi tessellation-based algorithms called VOBOZ and ZOBOV, we found gentle supervoids, with relatively few galaxies in them, and superclusters, places slightly over-populated with galaxies over these distances. Conventional clusters of galaxies are about 10 times smaller and differ in that they are held together by gravity, while galaxies in supervoids and superclusters are riding large density waves, and are more affected by dark energy than gravity.
The supervoids and superclusters we found are likely similar to those in the picture at left (red=cluster, blue=void). This shows what the distribution of galaxies on very large scales might be like, using data from the Millennium simulation. This picture measures some seven billion light-years across. On the scale of this picture, our whole Milky Way galaxy, already unimaginably big on a human scale, would span less than a hundredth of a pixel! There is lots of smaller-scale structure in the simulation, but there really aren’t structures identifiable as voids and clusters much larger than the superstructures we’ve circled.
The movie at left (click on it for a larger version) starts at a representation of the Milky Way (it’s not to scale; really the Milky Way is much smaller), and zooms out, and then flies through the superclusters and supervoids. Each dot in the superstructures is a whole galaxy. We’ve left out the galaxies inbetween the superstructures for clarity.