Dark matter remains elusive to scientists, despite making up the majority of our universe’s mass. Now, as an ancient star cluster is unraveling into a star ribbon never seen before outside of the Milky Way, researchers say they are finding the fingerprints of this mysterious, unseen material in the data.
An international team of astronomers reports their discovery of the star ribbon in a recent paper published in Nature, advancing their ideas about what it could mean in the search for elusive dark matter.
Although appearing faint against the cosmic background, their discovery marks the long-expected confirmation of a unique class of celestial objects in other galaxies.
Dark Matter Explained
Invisible because it neither emits, reflects, nor absorbs light, dark matter remains one of the great cosmic mysteries. Our leading model of the universe only holds together with the inclusion of a tremendous amount of invisible mass, yet that mass has never been directly observed. Astrophysicists have instead been able to study dark matter only through its gravitational effects on normal matter.
When researchers modeled the shape of a ribbon of stars in a distant galaxy, they had to account for the galaxy’s gravitational field, allowing them to infer dark matter’s pull on the stars. In doing so, the researchers charted a new course for studying the effects of dark matter on our universe, making this elusive phenomenon more apparent through its influence on the visible world.
“The stars in a stellar stream all travel along nearly the same orbit, and that orbit is shaped by the galaxy’s gravity,” said co-author Tjitske Starkenburg, of Northwestern University. “By modeling that gravity, we can estimate the galaxy’s total mass. We already know roughly how much of that mass comes from visible matter like stars, so the rest must be dark matter.”
Globular Clusters
Dense groups of stars known as globular clusters orbit galaxies throughout our universe. While gravity holds these clusters together, eventually the galaxy’s stronger gravitational pull can overcome it, gradually peeling stars away. Although these stars can be dispersed in different directions, they generally remain together in elongated streams, traveling along the same orbit as the cluster that produced them. How these stellar ribbons settle into orbit can provide astrophysicists with a wealth of information about the gravitational forces at play.
These stellar streams are well known in the Milky Way but, until now, have been too faint to observe in other galaxies.
Data for the study came from the archives of NASA’s Hubble Space Telescope, particularly images of an ultra-diffuse galaxy called UGC 9050-Dw1, located about 115 million light-years from Earth. In these images, co-author David Hendel identified a faint, thin arc visible against the dark background created by the galaxy’s sparse stellar population, which was eventually confirmed as a stellar stream.
Simulating Dark Matter
The team generated thousands of computer simulations to identify a scenario in which the stellar ribbon’s observed shape could arise from the galaxy’s dark matter distribution and the properties of the globular cluster that produced it. This proof of concept represents a major step toward measuring dark matter using stellar streams beyond our own galaxy.
“Our results are consistent with previous studies and what they have shown about dark matter in this ultra-diffuse galaxy,” co-author Kiel Holm of the Niels Bohr Institute at the University of Copenhagen said. “We are measuring it with a completely new tool for this type of galaxy, demonstrating that this method also works beyond our own galaxy.”
The researchers are hopeful that increasingly powerful observatories, including the European Space Agency’s Euclid mission and NASA’s Nancy Grace Roman Space Telescope, will allow future astrophysicists to apply this dark matter measurement technique to higher-quality observations covering much broader regions of the sky.
The paper, “Evidence for the First Globular Cluster Stellar Stream Beyond the Milky Way,” appeared in Nature on August 12, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org.