regular clusterA rich cluster of galaxies exhibiting dynamical relaxation. These clusters have a smooth symmetric distribution with a high central concentration of galaxies to the core and very little subclustering. An irregular cluster is one that is dynamically less evolved, with significant substructure.
regular cluster[′reg·yə·lər ′kləs·tər]
A galaxy cluster that shows a smooth, centrally concentrated distribution of galaxies and an overall symmetric shape.