Artwork of a brown dwarf in the Pleiades star cluster. The Pleiades (or Seven Sisters) is a young open cluster of several dozen hot, middle-aged stars. It is about 130 parsecs away in Taurus. In the 1990s, astronomers discovered several brown dwarfs within the cluster, as illustrated in this picture. Brown dwarfs are objects which form like stars, but which do not fuse hydrogen into helium like true stars. Some, however, do undergo deuterium burning. They are mid-way in mass between large planets and small stars.