This tag is for questions relating to the galaxy cluster or the cluster of galaxies, gravitationally bound grouping of galaxies, numbering from the hundreds to the tens of thousands. The important fact about it is that , collisions between galaxy clusters provide a unique opportunity to study matter in a parameter space which cannot be explored in our laboratories on Earth.
Galaxies are the building blocks of the universe. Clusters of galaxies, and clusters of clusters of galaxies, called superclusters, make up the structures in the geography of the universe.
$~~~~~~~~~$A galaxy cluster, or cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity with typical masses ranging from $10^{14}–10^{15}$ solar masses. They are the largest known gravitationally bound structures in the universe and were believed to be the largest known structures in the universe until the $1980$s, when superclusters were discovered.
Large clusters of galaxies often exhibit extensive X-ray emission from intergalactic gas heated to tens of millions of degrees. Also, interactions of galaxies with each other and with the intra-cluster gas may deplete galaxies of their own interstellar gas. The Milky Way Galaxy belongs to the Local Group, which lies on the outskirts of the Virgo Cluster.
References:
Molnar S. M., $(2016)$ Cluster Physics with Merging Galaxy Clusters, Front. Astron. Space Sci. $\bf{2}$ $:7$.
Galaxies, Clusters, and Superclusters
Four Galaxy Clusters
