Astronomers find first stellar stream outside Milky Way in galaxy UGC 9050-Dw1

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Astronomers find first stellar stream outside Milky Way in galaxy UGC 9050-Dw1

An international team has identified the first stellar stream ever observed outside the Milky Way, in the ultra-diffuse galaxy UGC 9050-Dw1. The faint ribbon of stars, detected in archival Hubble Space Telescope images, offers a new tool for mapping dark matter. The study was published Aug. 12 in Nature.

Key Facts

The stellar stream was found in the ultra-diffuse galaxy UGC 9050-Dw1 using archival Hubble Space Telescope images.
The study was published Aug. 12 in the journal Nature.
Northwestern University astrophysicist Tjitske Starkenburg co-authored the study, which was co-led by Julie Kiel Holm of the University of Copenhagen and Sarah Pearson of the Technical University of Denmark.
Astronomers have identified dozens of stellar streams inside the Milky Way, but none had been detected in another galaxy until now.

Discovery Details

The stream was identified by study coauthor David Hendel while examining Hubble images of UGC 9050-Dw1. Archival observations were presented by University of Arizona astronomers David Sand and Catherine Fielder. The stream appears as a faint, narrow arc of stars stripped from a globular cluster. Globular clusters are densely packed star groups whose outer stars are pulled away by the host galaxy's gravity, forming streams along the cluster's orbit.

Dark Matter Mapping

By modeling the stream's shape, researchers reconstructed the gravitational field of UGC 9050-Dw1. The gravitational model allows an estimate of the galaxy's total mass, with the difference from visible matter attributed to dark matter. Northwestern's Tjitske Starkenburg explained that stars in a stream travel along nearly the same orbit shaped by the galaxy's gravity. The findings could help scientists investigate dark matter distribution across many galaxies.

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Astronomers find first stellar stream outside Milky Way in galaxy UGC 9050-Dw1

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Astronomers find evidence of first globular cluster stream beyond Milky Way in UGC 9050-Dw1

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Astronomers find first stellar stream outside Milky Way in galaxy UGC 9050-Dw1

Key Facts

Discovery Details

Dark Matter Mapping

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