Twist in dark matter tale hints at shadow Milky Way

Twist in dark matter tale hints at shadow Milky Way: In 2008, when the PAMELA satellite found a similar excess of positrons, Neal Weiner of New York University and colleagues suggested that WIMPs are drawn together under a force of their own...

Observations of the orbits of stars around galaxies suggest that all galaxies, including the Milky Way, are surrounded by a spherical cloud of dark matter (see diagram). But if a fraction of dark matter particles interact with each other, they would combine into atom-like structures and eventually collapse into a spinning disc. This is how ordinary matter formed the Milky Way. The resulting shadow Milky Way could be spinning right along with the visible one, or it could end up tilted at a slight angle, she adds.