Supercluster
A supercluster is one of the largest structures in the universe. It is a region where galaxies, groups of galaxies and clusters of galaxies are packed more closely than usual, joined to one another by long threads of galaxies called filaments.[1] Astronomers describe superclusters as being among the largest structures known, but because they are all linked together, their edges are hard to draw.[2]
Size
Superclusters vary a great deal. According to a 2025 review by the Estonian astronomer Maret Einasto, the richest superclusters may hold several tens of large galaxy clusters and stretch about ten times as far as poor ones. Poorer ones, such as the Local or Virgo Supercluster, which contains our own Local Group of galaxies, have only one rich cluster surrounded by filaments of smaller groups, and are roughly a tenth of that size.[3]
Discovery
The American astronomer Harlow Shapley noticed "clusters of clusters" of galaxies as early as 1930. The structure he saw is now called the Shapley Supercluster, the richest supercluster in our part of the universe.[4]
Are they held together?
Most superclusters, as astronomers usually map them, are not held together by gravity as a single system.[5] For very large ones, only the densest central parts may eventually pull together.[6]
Laniakea
In 2014 a team led by R. Brent Tully noted that the word "supercluster" is not precise, and proposed a new way to define one. They mapped how galaxies move, apart from the general expansion of the universe, and looked for boundaries where these flows split apart, like water at a watershed. They defined a supercluster as the region inside such a boundary, and named our home supercluster Laniakea.[7] According to the National Radio Astronomy Observatory, Laniakea, which includes the Milky Way, is about 500 million light-years across and contains about 100,000 galaxies.[8]
References
- ↑ Maret Einasto (2025). "Galaxy Superclusters and Their Complexes in the Cosmic Web". Universe. 11: 167. doi:10.3390/universe11060167. Retrieved 20 October 2026.
High-density regions of the cosmic web, which embed galaxies, groups, and clusters connected by filaments, are called galaxy superclusters.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ↑ "Newly Identified Galactic Supercluster Is Home to the Milky Way". National Radio Astronomy Observatory. 2014. Retrieved 20 October 2026.
Superclusters are among the largest structures in the known Universe. ... Though these structures are interconnected, they have poorly defined boundaries.
- ↑ Maret Einasto (2025). "Galaxy Superclusters and Their Complexes in the Cosmic Web". Universe. 11: 167. doi:10.3390/universe11060167. Retrieved 20 October 2026.
The richest superclusters may embed several tens of rich (Abell) clusters and their sizes may reach 200 h−1 Mpc, while poor superclusters like our own, Local or Virgo supercluster, consist of only one rich cluster surrounded by filaments of poorer groups, including the Local Group of galaxies, and having an extent of approximately 20 h−1 Mpc.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ↑ Maret Einasto (2025). "Galaxy Superclusters and Their Complexes in the Cosmic Web". Universe. 11: 167. doi:10.3390/universe11060167. Retrieved 20 October 2026.
The presence of superclusters or clusters of clusters (second-order clusters) in the distribution of galaxy clusters was noticed already by Harlow Shapley in 1930 (Shapley, 1930). This structure is now known as the Shapley supercluster, and it is the richest supercluster in the nearby Universe
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ↑ Maret Einasto (2025). "Galaxy Superclusters and Their Complexes in the Cosmic Web". Universe. 11: 167. doi:10.3390/universe11060167. Retrieved 20 October 2026.
Typically, superclusters determined using these criteria are not gravitationally bound.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ↑ Maret Einasto (2025). "Galaxy Superclusters and Their Complexes in the Cosmic Web". Universe. 11: 167. doi:10.3390/universe11060167. Retrieved 20 October 2026.
In the case of large BoAs, such as the Laniakea supercluster (Tully et al., 2014), only the central, highest-density parts may collapse in the future
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ↑ R. Brent Tully, Hélène Courtois, Yehuda Hoffman, Daniel Pomarède (2014). "The Laniakea supercluster of galaxies". Nature. 513: 71–73. doi:10.1038/nature13674. Retrieved 20 October 2026.
Extended regions with a high concentration of galaxies are called 'superclusters', although this term is not precise. ... We define a supercluster to be the volume within such a surface, and so we are defining the extent of our home supercluster, which we call Laniakea.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ↑ "Newly Identified Galactic Supercluster Is Home to the Milky Way". National Radio Astronomy Observatory. 2014. Retrieved 20 October 2026.
This so-called Laniakea Supercluster is 500 million light-years in diameter and contains the mass of one hundred million billion Suns spread across 100,000 galaxies.