The majority of ultra-compact dwarf galaxies, (UCDs), which are mysterious objects characterized by high stellar population counts, are actually very massive clusters of bright stars, a new study has revealed.

UCDs can be found in nearby galaxy clusters and are characterized by a compact morphology (30-300 light-years in size) and high masses (more than one million solar masses). More generally, their properties (e.g., their size, shape, or luminosity) are similar to those of both star clusters and dwarf galaxies.