A Galaxy Cluster (CL) is on the order of hundreds of galaxies bound to the group by Gravity. A smaller group of galaxies is known as a Galaxy Group. Often has an Intergalactic Medium, i.e., Plasma. Typical mass is on the order of 1015 solar masses. It can be part of a Supercluster.
Cluster can also refer to star clusters such as Open Clusters, sometimes confusingly called Galactic Clusters (i.e., clusters within a galaxy).
Shock Waves from matter striking a galaxy cluster's Intracluster Medium produces X-rays, which are a sign to observers of the presence of a galaxy cluster. X-ray signals can reveal very distant clusters, the furthest currently known (CL J1001+0220) at Redshift 2.5.
Example galaxy clusters: Virgo, Fornax, Hercules, Coma.
The abbreviation CL is often included in designators for galaxy clusters, e.g., for CL J1001+0220.
Atacama Cosmology Telescope (ACT)
Brightest Cluster Galaxy (BCG)
Cold Dark Matter (CDM)
Cosmic Infrared Background (CIB)
Cosmic Distance Ladder
Dark Matter Halo
Dark Energy Survey (DES)
Velocity Dispersion (σ)
Intracluster Medium (ICM)
Intergalactic Medium (IGM)
Lambda-CDM model (ΛCDM)
Large Scale Structure (LSS)
Luminosity Function (LF)
Non Gaussian (NG)
Star Formation History (SFH)
South Pole Telescope (SPT)
Supergalactic Coordinate System
Sachs-Wolfe Effect (SWE)
Sunyaev-Zel'dovich Effect (SZ Effect)
Three Dimensional Model