Superclusters are large groups of smaller galaxy groups and clusters and are among the largest known structures of the cosmos. They are so large that they are not gravitationally bound and, consequently, partake in the Hubble expansion.
The existence of superclusters indicates that the galaxies in our Universe are not uniformly distributed; most of them are drawn together in groups and clusters, with groups containing up to 50 galaxies and clusters up to several thousand galaxies. Those groups and clusters and additional isolated galaxies in turn form even larger structures called superclusters.
Superclusters form large structures of galaxies, called "filaments", "supercluster complexes", "walls" or "sheets", that may span between several hundred million light-years to one billion light-years, covering more than 5% of the observable universe. Observations of superclusters likely tell us something about the initial condition of the universe when these superclusters were created. The directions of the rotational axes of galaxies within superclusters may also give us insight into the formation process of galaxies early in the history of the Universe.[1]
According to some astronomers, no clusters of superclusters are known; the existence of structures larger than superclusters is debated (see Galaxy filament).[citation needed] Interspersed among superclusters are large voids of space in which few galaxies exist. Even though superclusters are the largest confirmed structures, the total number of superclusters leaves possibilities for structural distribution.
Superclusters are frequently subdivided into groups of clusters called galaxy clouds.
(en.wikipedia.org/wiki/Supercluster)
