https://www.sciencedaily.com/releases/2017/04/170418111504.htm The hydrogen halo is believe to be more diffused and flattened like the galaxy illustrated. The DM halo is believed to be more speherical, and to extend much further out than the hydrogen halo, but this is inferred because unless there is gravitational lensing in the vicinity, like the Coma or the Bullet clusters, you can't actually "see" anything. http://physicscentral.com/explore/action/darkmatter.cfm