Terminology
Galaxies come in clusters.
Stars come in clusters.
Comets come in clusters?
Meteors come in clusters?
The Milky Way galaxy has smaller galaxies and clusters of stars orbiting around it. Stars orbit each other, sometimes loosely held. But why does it have to be a star? Could there be a big cluster of darker objects, comets and asteroids, orbiting our solar system. Maybe, eh? We could call them "Dark Nemisis Clusters".