Stellar stream discovered in distant galaxy may reveal dark matter distribution

Astronomers have discovered a faint stellar stream in the ultra-diffuse galaxy UGC 9050-Dw1, located approximately 115 million light-years from Earth. Identified through archival observations from the Hubble Space Telescope and the Canada-France-Hawaii Telescope, the feature—named ‘Oyashio’—is believed to be the first detection of a stellar stream originating from a globular cluster outside the Milky Way.

The stream is a thin ribbon of stars, roughly 2 kiloparsecs long and 72 parsecs wide, created as tidal forces pull stars away from a dense star cluster. Because the shape and movement of such streams are dictated by the gravitational field of their host galaxy, researchers can use this discovery to map the distribution of both visible and dark matter.

By modeling the stream, scientists were able to estimate the overall mass of UGC 9050-Dw1. This discovery provides a new method for investigating dark matter in galaxies far beyond our own, as dark matter's presence is detected through its gravitational influence on these stellar structures.