Galaxy cluster
Galaxy cluster is a large gravitationally bound system consisting of hundreds to thousands of galaxies, along with hot gas and dark matter. It represents one of the largest known structures held together by gravity.
Galaxy clusters are discussed in astrophysics, cosmology, and large-scale structure studies.
Status
Galaxy clusters are observed through optical surveys, X-ray emission from hot intracluster gas, and gravitational lensing effects. Models of their formation, mass distribution, and dynamical evolution continue to be refined.