By Andrew Grant
A stream of high-energy gamma rays from the heart of the Milky Way is teasing scientists about the identity of the universe’s invisible matter.
The results of one study add to growing evidence that particles of dark matter, which collectively have more than five times as much mass as all the visible matter in the universe, are slamming into each other in the galactic center and emitting gamma rays. But another study of small, supposedly dark matter–rich galaxies finds no such gamma ray signal. The clashing results are the latest wrinkle in the long quest to discover the fundamental units of dark matter.