First Globular Cluster Stellar Stream Found Beyond the Milky Way
A thin arc of stars around galaxy UGC 9050-Dw1, 115 million light-years away, is the first such stream found outside our galaxy and traces its dark matter.
Astronomers have found the first stellar stream from a globular cluster outside the Milky Way: a thin arc of stars pulled off a cluster orbiting the ultra-diffuse galaxy UGC 9050-Dw1, about 115 million light-years away. The Nature paper, “Evidence for the first globular cluster stellar stream beyond the Milky Way”, was co-led by Julie Kiel Holm of the University of Copenhagen and Sarah Pearson of the Technical University of Denmark, and Northwestern University reported it on August 12, 2026.
A globular cluster is a tight ball of old stars. As it orbits a galaxy, tides slowly strip stars from it and string them out along its path, like crumbs dropped from a moving hand. The team spotted this stream in archival images from the Hubble Space Telescope and confirmed it with ground-based data. Ultra-diffuse galaxies are faint, spread-out galaxies with few stars for their size.
Because the stream follows the galaxy’s gravity, its shape shows how much mass surrounds the galaxy, including mass that does not shine. The analysis indicates large amounts of dark matter, as expected for an ultra-diffuse galaxy. Thin streams are especially sensitive to how dark matter is distributed, which simulations predict follows a common density profile in every halo. Until now this method only worked inside our own galaxy. The paper title says “evidence”, and one stream gives one measurement. More in our dark matter guide.
What to watch next: wide surveys by Euclid and Roman could find many more streams around other galaxies.
Primary source
This summary is based on Northwestern University and the peer-reviewed paper. Read the original for full details, data and caveats.
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