The Coma Cluster is a very large cluster of galaxies in Coma Bereneces. The center of the cluster contains two supergiant eliptical galaxies, NGC 4874 and NGC 4889 but the entire cluster consists of over 1,000 galaxies. The average distance of the galaxies in the cluster is 321 million light years though being a huge cluster, some are closer and some are further.

The Coma Cluster provided one of the first clues that dark matter might exist. In 1933, Fritz Zwicky determined that the members of the cluster were moving too fast to remain gravitationally bound based on the observable matter. He postulated “dark matter” — matter that doesn’t emit or reflect light. It took a long time for that to become accepted but today the evidence for dark matter is strong. We still don’t know what dark matter is but we know a lot about what it can’t be. There’s a Nobel Prize waiting out there for someone to solve that mystery.

For all the technical details see astrobin.