In a groundbreaking discovery, a team of scientists has identified a collection of stars located 30,000 light-years away that has been dubbed the faintest and least massive Milky Way satellite ever observed.
This stellar grouping, known as Ursa Major III / UNIONS 1 (UMa3/U1), may also be largely composed of dark matter, the enigmatic substance that accounts for approximately 27% of the universe’s composition.
The fact that this system has managed to remain intact, despite its location on the periphery of our galaxy and exposure to the gravitational pull of its disk, has astounded researchers.
According to a study published earlier this year in The Astrophysical Journal, the team concluded that the stars have remained together due to their gravitational bond, suggesting that they are either a dwarf galaxy or a star cluster.
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To confirm the gravitational connection between the stars, the researchers utilized the Keck Observatory’s Deep Imaging Multi-Object Spectrograph.
As study co-author Marla Geha, an astrophysicist at Yale University, explained, “Keck was critical in showing this is not the case. Our DEIMOS measurements clearly show all the stars are moving through space at very similar velocities and appear to share similar chemistries.”
Astronomers have detected an ancient star system traveling around our galaxy, named Ursa Major III/UNIONS 1 (UMa3/U1) – the faintest and lowest-mass Milky Way satellite ever found. It contains about 60 stars that are over 10 billion years old spanning just 10 light years across. pic.twitter.com/9fTyo4nHIU
— Peter Bond (@PeterBondSpace) March 29, 2024
Despite its diminutive size, consisting of only around 60 ancient stars spanning a mere 10 light-years, UMa3/U1 has the potential to reshape our understanding of galaxy formation and the very definition of a galaxy.
Lead author Simon Smith, a researcher at the University of Victoria, noted, “UMa3/U1 had escaped detection until now due to its extremely low luminosity.
This discovery may challenge our understanding of galaxy formation and perhaps even the definition of a ‘galaxy.'”
The team’s hypothesis that UMa3/U1 is dominated by dark matter stems from the observed spread of velocities among its stars.
Dark matter acts as a gravitational glue, holding the stars together in their grouping.
While the exact nature of dark matter remains a mystery, scientists can observe its gravitational effects on visible matter.
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Further observations by the Keck Observatory may shed light on whether dark matter is indeed responsible for the system’s cohesion or if UMa3/U1 is simply a group of stars in the final stages of their existence.
