A ghostly ribbon of stars reveals hidden dark matter

A recent discovery of a faint, narrow ribbon of stars in an ultra-diffuse galaxy marks the first time a stellar stream has been identified outside the Milky Way. This cosmic ribbon, composed of stars that once belonged to a globular cluster, offers astronomers a novel way to study one of the universe's biggest mysteries: dark matter.

Dark matter, which accounts for about 85% of all matter in the universe, cannot be seen directly as it does not emit or reflect light. Astronomers detect its presence through its gravitational influence on visible objects like stars and galaxies. By analyzing the shape of the stellar stream, researchers reconstructed the gravitational field of the galaxy it belongs to and used this information to estimate how much unseen dark matter influenced the paths of the stars.

The study, published in the journal Nature, was led by an international team of astrophysicists from Northwestern University, the University of Copenhagen, and the Technical University of Denmark. The breakthrough was made possible by archival observations from NASA's Hubble Space Telescope, which captured the dim, faint structure against the bright backdrop of its host galaxy.

The discovery opens up new possibilities for investigating dark matter in galaxies beyond our own. Thin stellar streams, like the one discovered in UGC 9050-Dw1, may be especially valuable because small concentrations of dark matter can potentially disturb them, creating visible gaps or clumps. Future observatories, such as the European Space Agency's Euclid mission and NASA's Nancy Grace Roman Space Telescope, are designed to survey larger regions of the sky and may make these elusive structures much easier to find.