Astronomers Spot First Extragalactic Stellar Stream, Offering New Dark-Matter Probe
A faint ribbon of stars around the ultra-diffuse galaxy UGC 9050-Dw1 marks the first globular-cluster stellar stream identified beyond the Milky Way, allowing researchers to map its hidden dark-matter halo.
An international team led by researchers from Northwestern University, the University of Copenhagen and the Technical University of Denmark identified a delicate stellar stream emanating from a disrupted globular cluster in the ultra-diffuse galaxy UGC 9050-Dw1, about 115 million light-years distant. The stream’s faint, narrow arc was visible in Hubble Space Telescope data thanks to the galaxy’s sparse stellar background.
By tracing the stream’s trajectory, the scientists reconstructed the galaxy’s gravitational field and derived estimates of its total mass, revealing a substantial dark-matter component. Extensive computer simulations explored different dark-matter configurations to match the stream’s appearance, confirming the method’s viability beyond the Milky Way. The researchers suggest that similar streams could serve as sensitive detectors of dark-matter substructures, and upcoming surveys by ESA’s Euclid mission and NASA’s Roman Space Telescope may uncover many more examples. The study appears in Nature and was supported by VILLUM FONDEN, the European Union, the NSF and NASA.
Why it matters
It provides a new way to map invisible dark matter in distant galaxies, advancing our understanding of the universe’s dominant mass component.
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