A Little Empty Inside

Every galaxy sits within a blob, or halo, of dark matter, whose distribution can be inferred from its gravitational effects. The most widely used dark matter models can roughly explain the structure of these halos, but they predict that the halos of many small galaxies should be denser at their centers than they actually are. Manoj Kaplinghat at the University of California, Irvine, Sean Tulin at York University in Canada, and Hai-Bo Yu at the University of California, Riverside, have now shown that so-called “self-interacting dark matter” (SIDM) models can reliably predict the density distribution of a wide range of astrophysical halos.