They are structures that are made up of galaxies grouped together by the force of gravity. These sets correspond to the largest known structures held together by the force of gravity in the universe. The different groupings of galaxies that make up the universe are called groups, clusters, and superclusters, depending on their size and the number of galaxies they contain. They range from small groups with a dozen galaxies to large clusters of thousands of galaxies. These colossal macrostructures are the most recent in the history of the universe.
