Astronomers Discover the Milky Way's Faintest Satellite

Astronomers have discovered the faintest satellite galaxy of the Milky Way, a small, ultra-low-mass galaxy named Ursa Major III/UNIONS 1 (UMa III/U1). This diminutive galaxy is so faint that it is only about 100 times brighter than the faintest stars visible to the naked eye.

UMa III/U1 was discovered by an international team of astronomers using the Dark Energy Survey (DES) camera on the Blanco Telescope in Chile. The team was searching for faint dwarf galaxies near the Milky Way using DES data, which covers about one-third of the night sky.

UMa III/U1 is located about 300,000 light-years from the Milky Way in the constellation Ursa Major. It is about 1,000 light-years across and contains only about 10,000 stars. This makes it the smallest and least luminous satellite galaxy of the Milky Way that has ever been discovered.

The discovery of UMa III/U1 is a significant finding because it provides new insights into the formation and evolution of dwarf galaxies. Dwarf galaxies are small, irregular galaxies that contain only a fraction of the stars of a large galaxy like the Milky Way. They are thought to be the building blocks of larger galaxies, and their study can help us to understand how galaxies form and grow.

The discovery of UMa III/U1 also raises questions about the number of dwarf galaxies that exist in the Milky Way. Based on the number of dwarf galaxies that have been discovered so far, astronomers estimate that there are about 10 times more dwarf galaxies orbiting the Milky Way than have been observed. The discovery of UMa III/U1 suggests that there may be even more dwarf galaxies out there that are too faint to be detected with current telescopes.

The discovery of UMa III/U1 is a testament to the power of modern astronomical surveys like DES. These surveys are able to image large areas of the sky and detect very faint objects, which is allowing us to make new discoveries about the Universe all the time.