Dwarf galaxy gamma-ray signal could come from dark-matter collisions

Ars Technica : Last week, it was announced that several new dwarf galaxies surrounding the Milky Way had been found. Now, a team led by Alex Geringer-Sameth of Carnegie Mellon University has found that the closest of those galaxies, Reticulum 2, emits gamma rays. The finding is notable because dwarf galaxies generally lack the usual objects, such as black holes and pulsars, that produce gamma rays. And no previous dwarf galaxy has ever been found emitting gamma rays. The signal from Reticulum 2 could be detectable simply because it is the closest dwarf galaxy yet found. Because dwarf galaxies have a high concentration of dark matter, they are believed to be good candidates for study to try to find out what kind of particles dark matter is made of. Geringer-Sameth’s team believes that the gamma-ray signal could be evidence of self-interacting dark-matter particles, such as WIMPs, colliding with each other. However, there are still too many characteristics of Reticulum 2 that need to be clarified before that theory can be confirmed.