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Shredded 'stellar streams' could lead to the Milky Way's missing dark matter

An artist's representation of the MIlky Way surrounded by shredded stellar streams
An artist's representation of the MIlky Way surrounded by shredded stellar streams (Image credit: James Josephides and S5 Collaboration)

Vast rivers of stars swirl around the Milky Way, cutting against the current of our galaxy's halo in a complex gravitational dance. According to a new study of these so-called stellar streams, their offbeat orbits may be the key to uncovering the troves of invisible dark matter lurking within our galaxy.

In the study — which was accepted to be published in the Astrophysical Journal and is available to read on the preprint database arXiv.org — an international team of astronomers used observations from two telescopes to map the orbits, velocities and compositions of 12 stellar streams crisscrossing the Milky Way. 

Stellar streams are the remnants of ancient collisions between the Milky Way and smaller neighboring star clusters; when these petite neighbors come in contact with the comparatively massive Milky Way, our galaxy's gravity tugs and warps them, sometimes pulling them into spaghettified strands that orbit the fringes of our galaxy. 

Location of the stars in the dozen streams as seen across the sky. The background shows the stars in our Milky Way from the European Space Agency’s Gaia mission. (Image credit: Ting Li, S5 Collaboration and European Space Agency)

The team used computer models to unwind these stretched-out streams and determine where they originated. Based on the speed and composition of the stars in each stream, the team found that six of the streams came from nearby dwarf galaxies (small galaxies containing up to several billion stars), while the other six originated from globular clusters (much smaller gravitational-bound bodies that contain up to a few thousands stars). 

"This study gives us a snapshot of the Milky Way's feeding habits, such as what kinds of smaller stellar systems it 'eats'," lead study author Ting Li, a professor of astronomy and astrophysics at the University of Toronto said in a statement.

However, that's not all the research revealed. In charting the orbital paths of these 12 stellar streams, the researchers found that the streams moved in ways that the gravity of the Milky Way alone could not explain. The streams' orbits appear to be influenced by invisible clumps of dark matter — a non-luminous substance that scientists suspect accounts for about 85% of all matter in the universe. 

"Think of a Christmas tree," study co-author Geraint Lewis of the University of Sydney said in the statement. "On a dark night, we see the Christmas lights, but not the tree they are wrapped around. But the shape of the lights reveals the shape of the tree. It is the same with stellar streams — their orbits reveal the dark matter."

Researchers have detected more than 60 stellar streams swirling around the Milky Way to date, but they have never mapped this many of them at the same time, the researchers added. By studying the movement of multiple streams at the same time, the invisible distribution of dark matter in the Milky Way becomes easier to pinpoint.

This study — part of the Southern Stellar Stream Spectroscopic Survey (S5), a program dedicated to measuring the properties of stellar streams in the Milky Way — will hopefully serve as a springboard to further discoveries that help unveil the dark matter that underpins our galaxy.

Originally published on Live Science.

Brandon Specktor

Brandon has been a senior writer at Live Science since 2017, and was formerly a staff writer and editor at Reader's Digest magazine. His writing has appeared in The Washington Post, CBS.com, the Richard Dawkins Foundation website and other outlets. He holds a bachelor's degree in creative writing from the University of Arizona, with minors in journalism and media arts. He enjoys writing most about space, geoscience and the mysteries of the universe.