Supercluster Catalog Identified in the Sloan Digital Sky Survey; Einasto Recorded as the Most Massive Galaxy Group

A collaborative effort of astronomers has led to the discovery of the new heavyweight contender in the universe.

Cosmic Metropolitan Cities

Throughout the cosmos, the galaxies are distributed in an intricate network called the cosmic web made of two-dimensional walls, one-dimensional filaments, clusters, and undersense regions. The nature of the cosmic web helps experts understand the cosmological models that govern the evolution of structures in the cosmos.

The cosmic web also contains large coherent regions which measure tens to hundreds of megaparsecs. These regions, composed of extremely massive clusters of galaxies, are cumulatively known as superclusters.

Superclusters are comparable to large metropolitan cities in space, representing the largest and the most massive collections and clusters of galaxies. However, they are not as abundant as galaxies or groups and clusters, although they are known to affect the evolution of the galaxies within them.

It remains a mystery how these gigantic structures form and evolve in the cosmic web, and exploring their nature requires detailed investigations that involve observations and simulations. To address this question, it is important to have a large catalog of superclusters which cover a wide range of redshifts and sky areas.

New Supercluster Catalog

In a recent study, a group of researchers has discovered a vast collection of superclusters in the Sloan Digital Sky Survey. They identified 662 superclusters using a modified version of the friends-of-friends algorithm applied on the Wen-Han-Liu (WHL) cluster catalog. The details of their study are described in the paper "Identification of Superclusters and Their Properties in the Sloan Digital Sky Survey Using the WHL Cluster Catalog".

Led by experts from Tartu Observatory of the University of Tartu, the astronomers determined that the typical mass of superclusters is six million times billion that of the sun, with an average size of 200 million light-years. For context, these superclusters are almost 2,000 times larger than the Milky Way galaxy.

The most prominent among these is named 'Einasto Supercluster' in honor of Professor Jaan Einasto who served as a pioneering figure in the field. It is located about three billion light-years away from the Earth and contains the mass equivalent of 26 million times billion suns. Due to the enormous size of the Einasto Supercluster, it will take 360 million years for light rays to start from one end and reach the other end.

The result of their study did not only expand our understanding of the supercluster, but also sheds light on the mystery of their formation. Since the clusters of galaxies found inside a supercluster are heavier than those residing outside, it shows that the evolution and growth of clusters of galaxies in superclusters are different from the ones located outside supercluster environments.

Studies suggest that the universe is having an accelerated expansion rate, which means that the space between galaxies is also increasing, causing them to move further apart over time. Scientists from Tartu Observatory have demonstrated that galaxies within superclusters exhibit lower expansion speeds than the overall expansion speed of the entire universe.

This property is attributed to the gravitational pull of the supercluster where it pulls back the galaxies to counteract the overall expansion of the universe. Still, this gravitational pull is not strong enough to make superclusters a gravitationally bound system. Time will come when the impact of dark energy in expanding the supercluster will take over its gravitational attraction.