Superclusters show that the galaxies in the universe are not evenly distributed. Most, perhaps all, are in groups and clusters. Groups have some dozens of galaxies, and clusters up to several thousand galaxies. Those groups and clusters plus more isolated galaxies form even larger collections called superclusters.
Superclusters themselves form even larger structures, called "filaments", "complexes", "walls" or "sheets", like the Great Wall. These may span between several hundred million light-years to 10 billion light-years, and cover more than 5% of the observable universe. Superclusters suggest something about the initial condition of the universe when these superclusters were formed. The directions of the rotational axes of galaxies within superclusters may also tell us about the formation of galaxies early in the history of the Universe.
Inside superclusters are large voids of space in which few galaxies exist. Superclusters are often subdivided into groups of clusters called "galaxy clouds".
- "An Intergalactic Heavyweight". ESO Picture of the Week. Retrieved 12 February 2013.
- Hu F.X.; et al. (2006). "Orientation of galaxies in the Local Supercluster: a review". Astrophysics and Space Science. 302 (1–4): 43–59. arXiv:astro-ph/0508669. Bibcode:2006Ap&SS.302...43H. doi:10.1007/s10509-005-9006-7.