Source: W. M. Keck Observatory

Authors: W. M. Keck Observatory

Published Date: Fri, 29 Mar 2024 00:14:00 +0000

Summary: A team of astronomers led by the University of Victoria and Yale University has discovered an ancient star system named Ursa Major III / UNIONS 1 (UMa3/U1), the faintest and lowest-mass Milky Way satellite known, possibly dominated by dark matter. Using data from Maunakea Observatories and the Pan-STARRS on Maui, they found UMa3/U1 contains about 60 stars over 10 billion years old and spans just 10 light years. Keck Observatory’s DEIMOS confirmed the system is gravitationally bound, either as a dwarf galaxy or a star cluster, with its stars moving at similar velocities and sharing similar chemistries. The team suspects dark matter may be holding the stars together, challenging their understanding of galaxy formation. Future observations will determine if UMa3/U1 is a dark matter-dominated galaxy or a star cluster, potentially redefining what constitutes a galaxy.

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