A ghostly object orbiting the Milky Way has left astronomers questioning its composition: Is it a dark-matter-dominated dwarf galaxy or a star cluster bound by a hidden swarm of black holes?
Ursa Major III/Unions 1 (UMa3/U1), the faintest known…
The Milky Way’s faintest satellite may not be what astronomers thought. ‘These results solve a major mystery in astrophysics’
