Astronomers find evidence of first globular cluster stream beyond Milky Way in UGC 9050-Dw1
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Astronomers using the Hubble Space Telescope identify evidence for the first globular cluster stellar stream beyond the Milky Way, in the ultra-diffuse galaxy UGC 9050-Dw1. The stream, named Oyashio, lies about 2.5 kiloparsecs from the galaxy's centre and points to a massive dark matter host halo. The feature appears independently in Hubble and Canada-France-Hawaii Telescope imaging, ruling out data artefacts.
The Oyashio Stream
The stream-like feature, named Oyashio after a cold Pacific current, appears in deep Hubble Space Telescope imaging of UGC 9050-Dw1 as one arm of a stellar stream extending from a globular cluster candidate. It lies about 2.5 kiloparsecs from the galaxy's centre. The presumed host, UGC 9050-Dw1, is probably associated with the low-surface-brightness spiral galaxy UGC 9050 at a distance of 35.2 ± 2.5 megaparsecs. The feature is identified independently in Hubble and Canada-France-Hawaii Telescope data, ruling out imaging or processing artefacts. UGC 9050-Dw1 was first detected in CFHT images during a diffuse dwarf galaxy search.
Dark Matter Halo Constraint
Generative stream modelling fits dynamical models directly to the stream's morphology and points to a globular cluster origin. The models suggest a massive dark matter host halo, providing the first stream-based halo constraint for an ultra-diffuse galaxy. Stellar streams from globular clusters are sensitive probes of dark matter halos and substructure, but before this work they had been observed only in the Milky Way. Such tidal arms can persist for billions of years. The authors also reproduce the observed surface brightness with simulated globular cluster stellar populations, extending stream analysis to external galaxies.
What's Next
Follow-up spectroscopic observations of UGC 9050-Dw1 may be needed to confirm the stream's kinematics and the progenitor's mass. It remains unclear whether similar globular cluster streams are common across the broader population of ultra-diffuse galaxies.
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Astronomers find evidence of first globular cluster stream beyond Milky Way in UGC 9050-Dw1
