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Most galaxies have only a few neighbors. But in some places, hundreds to thousands of galaxies swarm together. This is called a cluster of galaxies. All the galaxies in it orbit one another. In the cluster, gravitational forces hold them together.
What’s at the center of a cluster of galaxies? Often it is a giant elliptical galaxy or an even larger one called a central dominant. These galaxies seem to grow by eating other galaxies. Some of them have two centers, or nuclei. That means they aren’t done with their latest meal! Let’s look at some galaxy clusters.
