Vera Rubin Observatory Discovers Two Hidden Companions of the Milky Way
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Using early preview data released in July 2026, the Vera C. Rubin Observatory has identified two previously unknown satellites of the Milky Way—a likely ultra-faint dwarf galaxy and a compact globular cluster hidden behind thick galactic dust—offering an early glimpse of what the observatory's full ten-year survey will uncover.
Astronomers have announced the discovery of two previously unseen companions of the Milky Way using data from the Vera C. Rubin Observatory's Early Data Preview 2 (EDP2), released in July 2026. The first object, named Aquarius IV, is most likely an ultra-faint dwarf galaxy in the outer galactic halo. It was identified by William Cerny, an astronomy student in Yale's Graduate School of Arts and Sciences, and is described as a low-luminosity, compact stellar system whose ancient, low-metallicity stellar population closely resembles those of the smallest and faintest confirmed ultra-faint dwarf galaxies—though a globular cluster classification has not been ruled out. Deeper imaging and spectroscopy will be needed to settle the question. The second object, Rubin-GC1, is a globular cluster found in the direction of the galactic bulge, where stellar density is high and dust is thick, making its detection especially impressive. Lead author Aashay Pai, a graduate student in physics at the University of Chicago, found that the cluster's stars have an intermediate age of about 9.2 billion years and are moderately metal-rich. It is most likely associated with the Sagittarius leading arm—a tidal stream of stars stripped from the Sagittarius Dwarf Spheroidal Galaxy as it merges with the Milky Way. Both discoveries arrived before Rubin's full science survey has even begun, and scientists say they represent just the start of a much larger census of Milky Way satellites that will shed new light on galaxy formation and the role of dark matter.
