What characterizes a "relaxed" galaxy cluster state?

Exhibiting a smooth, centrally peaked X-ray surface brightness profile

Galaxy clusters are observed in various evolutionary stages, contrasting 'disturbed' systems with 'relaxed' ones. A cluster that is considered relaxed has achieved a near-equilibrium state, meaning it has had sufficient cosmic time to settle dynamically following major assembly events. This dynamical maturity manifests observationally, particularly in the X-ray emission from the ICM. A relaxed cluster displays a very smooth distribution of hot gas, characterized by a surface brightness profile that is strongly peaked toward the center of the cluster. In contrast, a disturbed cluster, which is still actively assembling, shows signs of recent violent activity, such as irregular gas clumps or multiple localized peaks in X-ray emission.