Dozens of hidden star streams found in the outskirts of our Milky Way galaxy

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Astronomers have discovered dozens of faint ribbons of stars on the outskirts of the Milky Way using data from the European Space Agency’s Gaia mission.

The discoveries were made using a new algorithm that more than quadruples the number of known candidates for these so-called “stellar streams.” This discovery could offer new clues about how our galaxy evolved and how it dark matter is distributedsay the study’s researchers.

Stellar streams are arcs of stars that form when compact star clusters pass through the world. Milky WayThe star’s gravitational field releases stars that extend into long, trailing ribbons.

“It’s like riding a bike with a sandbag, only the bag has a hole,” study co-author Oleg Gnedin, a theoretical astrophysicist at the University of Michigan, said in a paper statement. “These grains of sand are like stars left in their path.”

The discovery of stellar flows is valuable because the shapes and movements of these phenomena preserve a record of the gravitational forces that have acted on them over time. This makes them powerful tools for mapping the mass of the Milky Way, and this mass measurement would include its elusive dark matter halo — dark matter is the invisible “glue” believed to hold galaxies together, but has yet to be directly observed despite decades of effort.

The new study, led by Yingtian “Bill” Chen of the University of Michigan, identifies 87 candidates for stellar streams associated with globular clusters, which are ancient dense groupings of stars orbiting the Milky Way. Previously, fewer than 20 stellar streams had been identified, often by chance in Gaia data, leaving astronomers with too small a sample to draw general conclusions.

Most known stellar currents come from dwarf galaxies or clusters that are already largely torn apart. Flows from still-surviving globular clusters, like those identified in the new study, are much rarer and particularly useful because astronomers can compare the flow directly with its parent cluster.

To find them, Chen developed a computer algorithm called StarStream, which searches for streams using a physics-based model rather than relying solely on visual patterns, according to the study. The team then applied the method to Gaia data, which mapped the positions and movements of billions of stars in the Milky Way from 2014 to 2025.

“It turns out that it’s a lot easier to find things when you have a theoretical expectation of what you’re looking for and you have a simple phenomenological picture,” Gnedin said in the release.

The results also revealed that many streams do not meet typical expectations for fine, well-aligned trails. Instead, the study reports that some of the newly discovered streams are shorter, wider, or even misaligned with the orbits of their parent clusters, suggesting that previous research may have missed them by focusing only on the most obvious structures.

The expanded sample also provides evidence that some diffuse globular clusters are losing stars at unusually high rates, a sign that they may be on the verge of completely disrupting the tides, the study reports.

However, not all 87 candidates are expected to be confirmed, as some detections have a lower confidence level due to background contamination from unrelated stars, the researchers say.

The study’s results, along with the algorithm applied to them, can be tested with upcoming observations from next-generation facilities, including the Vera C. Rubin Observatory, NASA’s Nancy Grace Roman Space Telescope and the Dark Energy Spectroscopic Instrument, to help verify which fluxes are real, Chen said in the release.

“It will be very easy to adjust the algorithm for future missions,” he said. “Once we have the data, it will be very simple to apply it.”

This research is described in a paper published March 23 in The Astrophysical Journal.