Because the density of galaxies is high within clusters, galaxy collisions occur ... are attempting to measure millions of galaxies and map their distribution in space. We are only beginning ...

Most of the visible material in a cluster is in the form of a hot, X-ray emitting plasma, but about 90% of the mass of a cluster is dark matter. We use observations of the different components of ...

Take a tour of the Hydra I galaxy cluster. A galaxy in the region, NGC 3312, is "losing cold gas as it moves through the hot gas within the cluster," according to the European Southern Observatory.