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The term stellar nucleus (or galactic stellar nucleus or galactic nucleus) is used to describe a dense group stars at the center of a galaxy. A compact stellar nucleus (CSN or nuclear star cluster, NSC) is one that is especially small, i.e., with a radius of a few parsecs at most, potentially only a fraction of a parsec. The density of stars can be extreme, e.g., millions of stars within a diameter matching the distance between the Sun and Alpha Centauri. These are common, perhaps occurring in most galaxies. They can be present in dwarf galaxies that lacks a central supermassive black hole (SMBH), and may can be present along with a galaxy's SMBH, which is true of the Milky Way, which has the S-Star Cluster surrounding its SMBH, Sag A*.