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 satellite of our galaxy, orbits the Milky Way at a distance of more than 30,000 light-years. It is a compact stellar system that contains only 60 visible stars.

Ursa Major III was long thought to be a dark dwarf galaxy — a small galaxy with an unusually high mass-to-light ratio suggesting it's filled with dark matter — but new evidence suggests it is instead a compact star cluster whose gravity is held together by a core of black holes and neutron stars, according to a statement from the University of Bonn in Germany.

"Dark star clusters form whe

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