Faint stellar stream beyond Milky Way discovered by NASA's Hubble Telescope

A faint trail of stars discovered in a galaxy about 115 million light-years from Earth could offer astronomers new insights into dark matter and the formation and evolution of galaxies.

Researchers identified the extremely faint stellar feature in archival observations from the Hubble Space Telescope. The discovery marks the first detection of a stellar stream originating from a globular cluster outside the Milky Way, NDTV reported.

The stream was found in UGC 9050-Dw1, an ultra-diffuse galaxy. It is believed to be the remnant of a dense star cluster whose stars are gradually being pulled away by the gravitational force of their host galaxy. As stars escape from such a cluster, they can form long and narrow streams.

While dozens of stellar streams have been identified within the Milky Way, detecting them in other galaxies has remained difficult because of their faintness. The findings were detailed in a study published in the journal Nature.

By modelling the newly discovered stream, researchers were able to study the gravitational field of UGC 9050-Dw1 and estimate its overall mass, including both visible matter and dark matter. The shape and movement of a stellar stream are influenced by the gravity of the galaxy in which it exists, making such structures useful tools for examining otherwise invisible matter.

Co-lead author Julie Kiel Holm said the discovery of a stellar stream beyond the Milky Way opened up exciting possibilities for further research. She noted that studying these structures in other galaxies could expand astronomers’ ability to investigate dark matter beyond our own galaxy.

Dark matter cannot be directly observed, but scientists can detect its presence through its gravitational influence on stars and galaxies. Researchers estimate that it accounts for roughly 80 to 85 per cent of the universe’s matter, making it a major focus of astronomical research.

Scientists have previously used stellar streams within the Milky Way to examine the distribution and properties of dark matter. The newly discovered stream could make it possible to apply similar methods to other galaxies and gain a better understanding of how dark matter is distributed beyond the Milky Way.

The discovery was made possible in part by the nature of UGC 9050-Dw1, which is classified as an ultra-diffuse galaxy because of its low brightness and widely spread-out structure. Researchers believe these characteristics may have helped make the faint stellar stream easier to detect.

Co-lead author Sarah Pearson noted that, despite their diffuse appearance, such galaxies can possess substantial mass. She explained that a galaxy must have sufficient gravitational influence to gradually pull stars away from their original cluster.