Astronomers using early data from the Vera C. Rubin Observatory in Chile found two faint companions of the Milky Way: a tiny galaxy named Aquarius IV and a dust-hidden star cluster named Rubin-GC1, Yale University said in a release republished by ScienceDaily on Nov. 7. The searches covered only about 7% of the night sky.
Related: Hubble Finds 37 Dwarf Galaxies Kept Only About 11% of the Oxygen Their Stars Made.
What was found
Aquarius IV sits in the outskirts of the Milky Way, about 355,000 light-years from Earth, according to Yale. Rubin-GC1 lies on the opposite side of the galaxy in a region thick with cosmic dust, which makes observation difficult, the university said.
The researchers used preview observations collected between April 2025 and January 2026, before the observatory’s official survey began, Yale said.
Who led the studies
William Cerny, a Yale graduate student in astronomy, led the Aquarius IV study published in Research Notes of the AAS, Yale said. He is second author of the Rubin-GC1 study, which The Astrophysical Journal Letters has accepted. Aashay Pai of the University of Chicago is first author of that paper.
Cerny said in the release that the full 10-year survey should yield many more satellite discoveries.
Why it matters
Astronomers have identified about 65 satellite galaxies around the Milky Way, and some estimates suggest hundreds remain undiscovered, Yale said. Ultra-faint galaxies help scientists test galaxy formation models and study dark matter, according to the release.
Rubin began its 10-year Legacy Survey of Space and Time in June, Yale said. It uses the 8.4-meter Simonyi Survey Telescope and a 3.2-gigapixel camera, the largest digital camera ever built. The National Science Foundation and the Department of Energy fund the observatory. More space news is in Science.
Sources
- ScienceDaily (Yale University release): Rubin Observatory discovers two hidden companions of the Milky Way
- Research Notes of the AAS: Discovery of the Distant, Ultra-faint Milky Way Satellite Aquarius IV
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