87 Newly Detected Stellar Streams Map the Milky Way — And Could Illuminate Dark Matter
In a night sky with more space than stars, globular clusters are bright exceptions. These are balls of stars, apparently bound together by gravity, which remain poorly understood.
When these clusters fade, they leave behind characteristic “stellar streams” that astronomers can track. Faded dwarf galaxies leave other such streams. But much more rarely, stellar streams can be signs of extant globular clusters.
A new study published in the Astrophysical Journal Supplement Series has massively expanded the number of these rare stellar streams, adding 87 candidate streams to a list of just 18 that had been previously discovered. The researchers hope their findings could reveal the history of our galaxy and information about the mysterious dark matter that helped shape it.
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A Stellar Algorithm
The discoveries hinged on an algorithm developed by Yingtian “Bill” Chen, an astronomer at the University of Michigan and co-author of the new study.
A significant challenge in locating stellar streams is that they are dim and hard to spot. As globular clusters interact with much larger star groups, like our own Milky Way, tidal forces can wrest some of the stars from their path.
“It’s like riding a bike with a bag of sand, only the bag has a hole in it,” said Oleg Gnedin, an astronomer at the University of Michigan and co-author of the new study, in a statement. “Those grains of sand are like the stars left behind along their trajectory.”
Observing Stellar Streams
Astronomers first observed stellar streams decades ago. These streams were larger and more spread out because they originated from dwarf galaxies rather than smaller globular clusters. By studying the streams’ size and shape, researchers can ascertain how gravitational energies have buffeted them. They can also make inferences about how our own galaxy’s mass is distributed. This can lead to discoveries about dark matter, which makes up part of this mass.
Previous sightings of globular cluster streams have largely been by chance, said Gnedin. In the new study, Chen and Gnedin approached the problem systematically. They built a physical model to predict the conditions under which streams would form. Next, Chen used this data to build an algorithm called StarStream. Applying this algorithm to data from the European Space Agency’s Gaia spacecraft, which operated from 2014 to 2025, the team began hunting for streams.
“It turns out that it’s a lot easier to find things when you have a theoretical expectation of what you’re looking for when you have a simple phenomenological picture,” Gnedin said.
The Future of Stellar Stream Research
Some of the candidates may turn out not to be stellar streams, but the new study has given powerful space telescopes plenty of new targets to vet.
“Gaia is relatively old, but there will be new surveys including NASA’s Roman Space Telescope, the Vera Rubin Observatory, and the Dark Energy Spectroscopic Instrument, or DESI,” said Chen.
These new, powerful tools will help identify the true stellar clusters, and Chen hopes that StarStream can play a role for years to come. “It’ll be very easy to adjust the algorithm to future missions,” Chen said. “Once we have the data, it will be very straightforward to apply it.”
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