Superclusters are large groups of smaller galaxy clusters or galaxy groups and are among the largest known structures of the cosmos. The Milky Way is in the Local Group galaxy cluster (that contains more than 54 galaxies), which in turn is in the Laniakea Supercluster. This supercluster spans over 500 million light years, while the Local Group spans over 10 million light years. The number of superclusters in the observable universe is estimated to be 10 million.
Galaxies are grouped into clusters instead of being dispersed randomly. Clusters of galaxies are grouped together to form superclusters. Typically, superclusters contain dozens of individual clusters throughout an area of space about 150 million light years across. Unlike clusters, superclusters are not bound together by gravity. They are all shifting away from each other due to the Hubble flow.
The Milky Way galaxy falls within the Local Group, which is a poor and irregular cluster of galaxies. Poor clusters may contain only a few dozen galaxies as compared to rich clusters that can contain hundreds or even thousands. The Local Group is near the Local Supercluster (also known as the Virgo Supercluster) which has a diameter of 100 million light years. The Local Supercluster contains a total of about 1015 times the mass of the Sun.
The biggest cluster in the observable universe is called the Great Attractor. Its gravity is so strong that the Local Supercluster, including the Milky Way, is moving in a direction towards it at a rate of several hundred kilometers per second. The biggest supercluster outside of the local universe is the Perseus-Pegasus Filament. It contains the Perseus supercluster and it spans about a billion light years, making it one of the largest known structures in the universe.
Supercluster, a group of galaxy clusters typically consisting of 3 to 10 clusters and spanning as many as 200,000,000 light-years. They are the largest structures in the universe.
In 1932 American astronomers Harlow Shapley and Adelaide Ames introduced a catalog that showed the distributions of galaxies brighter than 13th magnitude to be quite different north and south of the plane of the Milky Way Galaxy. Their study was the first to indicate that the universe might contain substantial regions that departed from the assumption of homogeneity and isotropy. The most prominent feature in the maps they produced in 1938 was the Virgo cluster, though already apparent at that time were elongated appendages that stretched on both sides of Virgo to a total length exceeding 5 107 light-years. This configuration is the kernel of what came to be known later—through the work of Swedish astronomer Erik Holmberg, French-born American astronomer Gérard de Vaucouleurs, and American astronomer George O. Abell—as the Local Supercluster, a flattened collection of about 100 groups and clusters of galaxies including the Local Group. The Local Supercluster is centred approximately on the Virgo cluster and has a total extent of roughly 2 108 light-years. Its precise boundaries, however, are difficult to define inasmuch as the local enhancement in numbers of galaxies above the cosmological average in all likelihood just blends smoothly into the background.
Also apparent in the Shapley-Ames maps were three independent concentrations of galaxies, separate superclusters viewed from a distance. Astronomers now believe superclusters fill perhaps 10 percent of the volume of the universe. Most galaxies, groups, and clusters belong to superclusters, the space between superclusters being relatively empty. The dimensions of superclusters range up to a few times 108 light-years. For larger scales the distribution of galaxies is essentially homogeneous and isotropic—that is, there is no evidence for the clustering of superclusters. This fact can be understood by recognizing that the time it takes a randomly moving galaxy to traverse the long axis of a supercluster is typically comparable to the age of the universe. Thus, if the universe started out homogeneous and isotropic on small scales, there simply has not been enough time for it to become inhomogeneous on scales much larger than superclusters. This interpretation is consistent with the observation that superclusters themselves look dynamically unrelaxed—that is, they lack the regular equilibrium shapes and central concentrations that typify systems well mixed by several crossings.
Everything in the Universe seems to be part of something bigger. Our Earth is part of the Solar System, the Solar System is part of the Milky Way, and even our Milky Way is part of the Local Group. The Local Group is part of the Virgo Cluster. But there is an end to this, the largest structures in the Universe are the superclusters, measuring hundreds of millions of light-years across and containing millions of galaxies.
Our own Milky Way is part of the Virgo Supercluster. This giant formation fills a volume of space 110 million light-years across and contains at least 100 galaxy groups and clusters. And you might be amazed to know that the Virgo Supercluster is just one of millions of superclusters in the observable Universe.
A typical supercluster contains 1015 times the mass of the Sun; that’s a quadrillion solar masses. It contains all the galaxy groups and galaxy clusters that seem to be associated with one another through mutual gravitational attraction. Astronomers have estimated that there are 130 superclusters located within 1.3 billion light-years of the Milky Way. Some example superclusters include Hydra-Centaurus, Perseus, and Cetus. Superclusters are typically named after the constellation they’re found in.
Superclusters show that our Universe is not evenly distributed. Instead, the large scale structure of the Universe is these giant superclusters connected together in long filaments. Seen from far enough away, the Universe would look foamy in texture, with superclusters strung out in filaments surrounding vast voids.
We have written many articles about galaxies for Universe Today. Here’s an article about a supercluster ruled by the pull of dark matter.