In astronomy, the term compact star or compact object is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes. Most compact stars are at the endpoint of stellar evolution: They are called stellar remnants; the form of the remnant depends primarily on the mass of the star when it formed. These objects are all small for their mass. Astronomic objects with an unknown nature are often called compact star, when evidence suggests that they are very massive and that they have a small radius. A compact star which is not a black hole is sometimes called a degenerate star.