Ancient and Faint: Astronomers in Hawaii Discover Milky Way's Tiniest Satellite Galaxy.

 

The faintest known star system orbiting the Milky Way, named Ursa Major III / UNIONS 1 (UMa3/U1), has been discovered by a team of astronomers led by the University of Victoria and Yale University. Here are the full details about this remarkable discovery:

• Location: UMa3/U1 is situated in the Ursa Major constellation, approximately 30,000 light-years from the Sun1.
• Characteristics: This stellar system is incredibly dim and tiny, containing only about 60 stars that are over 10 billion years old, spanning just 10 light-years across1.
• Mass: With a mass of only 16 times that of the Sun, UMa3/U1 is 15 times less massive than the faintest suspected dwarf galaxy1.
• Discovery: The star system was first detected using data from the Ultraviolet Near Infrared Optical Northern Survey (UNIONS) at the Canada-France-Hawaiʻi Telescope (CFHT) and Pan-STARRS1.
• Observations: Further detailed study was conducted using the Deep Imaging Multi-Object Spectrograph (DEIMOS) at the W. M. Keck Observatory, which confirmed that UMa3/U1 is a gravitationally-bound system1.
• Significance: The system may be one of the most dark matter-dominated systems known, with a tentative spread in velocities among the stars supporting this conclusion1.

The discovery of UMa3/U1 is significant as it provides insights into the composition and evolution of our galaxy, and it highlights the ongoing search for understanding dark matter’s role in the universe.

Due to its low luminosity (brightness), UMa3/U1 went unnoticed until recently. This discovery challenges our understanding of how galaxies form and what defines a galaxy. Some theories suggest UMa3/U1 may be dominated by dark matter, making up a significant portion of its mass despite containing few stars.