Editors' ChoiceNear-Field Cosmology

Milky Way satellites going in circles

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Science  02 Jun 2017:
Vol. 356, Issue 6341, pp. 919-920
DOI: 10.1126/science.356.6341.919-e

The Large Magellanic Cloud, a dwarf galaxy orbiting our Milky Way Galaxy


The satellite dwarf galaxies that orbit our Milky Way can be used to constrain models of cosmology. Cautun and Frenk examined the 10 Milky Way satellites whose three-dimensional velocities have been measured precisely and compared them with a cosmological simulation. They find that the observed velocities are mostly tangential (i.e., favoring circular orbits), whereas the simulation predicts that radial motions should dominate. That difference is unlikely but not impossible: Only a few percent of simulated galaxies are as extreme as the Milky Way. Either the observations or models are biased, the Milky Way is a statistical outlier, or our understanding of cosmology is incomplete.

Mon. Not. R. Astron. Soc. 468, L41 (2017).

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