These objects are organized into (*) clusters and have halos that contain globular clusters.
Halton Arp wrote an "Atlas" about the peculiar type of these objects. A plot of angular velocity of these objects against radius appears roughly flat, which Vera Rubin hypothesized was from the density of dark matter. These things are placed on a diagram that diverges at the neck of a tuning fork. The Shapley-Curtis debate asked if more than one of them exists. These objects are organized into (*) clusters and have halos that contain globular clusters. The Large and Small Magellanic Clouds are examples of these objects. Their shapes may be lenticular, irregular, elliptical, or spiral. For 10 points, name these groupings of stars such as the Milky Way.
Halton Arp wrote an "Atlas" about the peculiar type of these objects.
galaxies [or specific types of galaxies]