Streams of dark matter interacting with rivers of stars could provide astrophysicists with important information about the distribution and make-up of dark matter in the halo of the Milky Way. That's the conclusion of Jo Bovy of the University of Toronto, who has calculated that it should be possible to observe the effects of dark matter on the stellar streams that are known to encircle our galaxy.
The theory of cold dark matter (CDM) is one of the cornerstones in our understanding of the evolution of structure in the universe. It posits that the haloes surrounding galaxies such as the Milky Way should be clumpy, with myriad blobs of dark matter held together by gravity. The Milky Way's halo is also home to a swarm of globular star clusters and dwarf galaxies, some of which are being torn apart by gravitational tidal forces to create streams of stars that can stretch halfway around the galaxy.
For more than a decade, astrophysicists have suspected that dark-matter clumps could be detected by observing how their gravitational pull affects the motions of stars in stellar streams. Sceptics, however, point out that the Milky Way's gravity can also stretch the dark-matter clumps into long streams – and it would be much more difficult to observe the effect of such dark-matter streams on stellar streams.
Now, new research by Bovy suggests that streams of dark matter can still be detected through their interactions with stellar streams pulled from globular clusters. His calculations reveal that careful measurements of the motions of stars within these stellar streams could reveal the presence of dark-matter streams. These dark-matter streams could then be traced back to the clumps of dark matter that feed them. Ultimately, it should be possible to create a 3D map of dark matter in the Milky Way halo, he argues.
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