Most of the stars in our Milky Way galaxy sit neatly on a flat plane. But the space around our galaxy is much more chaotic. Rogue bands of stars called “stellar streams” orbit the Milky Way much like planets in our solar system orbit the sun.

Astronomers have long been fascinated by the possibility that stellar streams could indirectly reveal the presence of dark matter, that mysterious theorized substance that doesn’t interact with light or normal matter—except via gravity. However, a new University of Washington study casts doubt on a leading theory linking dark matter and stellar streams and raises new questions about both galactic phenomena.

“Dark matter makes up most of the mass in the universe and forms the scaffolding that galaxies grow on, but we still don’t know what it is,” said co-author Nora Shipp, a UW assistant professor of astronomy. “The Milky Way is one of the best laboratories we have for figuring that out, and stellar streams are one of the sharpest tools inside it.”