Rubin Observatory finds two new Milky Way satellites

Astronomers using preview data from the Simonyi Survey Telescope at the NSF-DOE Vera C. Rubin Observatory have identified two previously unknown satellites of the Milky Way, according to miragenews.com. miragenews.com The data were taken between April 2025 and January 2026. miragenews.com One study, published in Research Notes of the AAS, describes the ultra-faint galaxy Aquarius IV in the Milky Way's distant outskirts. miragenews.com The other, published Oct. 28 in The Astrophysical Journal Letters, describes the star cluster Rubin-GC1. miragenews.com

Two new objects

Rubin-GC1 is located on the far side of the Milky Way, inside a murky region shrouded by cosmic dust. miragenews.com Both objects came out of test data covering just 15% of the full LSST footprint, said Peter Ferguson, a University of Washington (UW) postdoctoral scholar and co-author of both studies. miragenews.com

Ultra-faint galaxies such as Aquarius IV have a fraction of the stars of a larger galaxy and, according to the researchers, are almost entirely composed of dark matter. miragenews.com William Cerny of Yale University, lead author of the Aquarius IV study, said such satellites give new opportunities to test models of galaxy formation, trace the assembly history of the Milky Way and investigate the nature of dark matter. miragenews.com

Catalog quality and the survey

Large galaxies are often orbited by small galaxies or star clusters, but many are extremely faint. The telescope's 3.2 gigapixel sensor is the largest digital camera ever built. miragenews.com More than 20 UW researchers worked on in-focus images, data validation before releases and an accurate catalog of known stars, galaxies and other phenomena. miragenews.com According to Ferguson, a handful of misclassified galaxies or spurious detections can wash out the signal of an object as faint as Aquarius IV. miragenews.com

The Rubin Observatory began its 10-year Legacy Survey of Space and Time (LSST) in June. miragenews.com One of its main tasks is to map the Milky Way's halo, the cloudlike sphere of gas, stars and dark matter around the main part of the galaxy, and to find hidden satellites and other substructures. miragenews.com About 65 satellites of the Milky Way are known, and there is speculation that hundreds more remain undetected. miragenews.com Marla Geha, a professor at Yale University and co-author of both studies, said continued discoveries will allow astronomers to complete the census of the Milky Way's satellite galaxies. miragenews.com

Rubin Observatory preview data reveal two new Milky Way satellites: Aquarius IV and Rubin-GC1

Two new objects

Catalog quality and the survey

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