In the hunt for dark matter, are axions our best bet?
A composite image of the Bullet Cluster, a much-studied pair of galaxy clusters that have collided head on. One has passed through the other, like a bullet traveling through an apple, and is thought to show clear signs of dark matter (blue) separated from hot gases (pink). (Image credit: X-ray: NASA/ CXC/ CfA/ M.Markevitch, Optical … Read more