Coma Cluster

The Coma Cluster is a massive cluster of galaxies in the constellation Coma Berenices, about 320 million light-years from Earth. Its galaxies and hot intracluster gas are bound by gravity, including gravity from dark matter.

Galaxy cluster: A gravitationally bound system containing many galaxies, hot gas, and dark matter. The Coma Cluster is a prominent example of this larger class of cosmic structures.
Gravitational binding: The condition in which gravity keeps the components of a system from dispersing. Gravity holds Coma's galaxies and much of its intracluster gas together.
Fritz Zwicky: A Swiss astronomer who studied supernovae, galaxies, and galaxy clusters at the California Institute of Technology. Zwicky used Coma galaxy velocities in the 1930s to argue that unseen mass was present.
NGC 4874: A giant elliptical galaxy near the center of the Coma Cluster. It is one of Coma's two dominant central galaxies and a focus of cluster studies.
Virgo Cluster: The nearest rich galaxy cluster to the Milky Way, centered in the constellation Virgo. Virgo is much nearer and less centrally concentrated than Coma, offering a contrasting cluster environment.
Intracluster medium: The diffuse, hot plasma filling the space between galaxies in a galaxy cluster. X-ray observations of Coma reveal this gas throughout the cluster.
Galaxy velocity dispersion: A statistical measure of the spread in galaxies' velocities within a cluster. Coma's unusually large velocity spread indicated that its system contains substantial unseen mass.
Virial mass discrepancy: The mismatch between a system's mass inferred from its motions and the mass visible in its luminous matter. Coma supplied an early, striking example of this discrepancy.
NGC 4889: A giant elliptical galaxy near the center of the Coma Cluster. It shares Coma's core with NGC 4874 and is among the cluster's most luminous members.
Perseus Cluster: A massive galaxy cluster in the constellation Perseus, known for its bright X-ray-emitting gas. Its conspicuous central gas structures contrast with Coma's comparatively less dramatic core.

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