I've got a homework question that I'm particularly stuck on: Suppose that the halo, assumed spherical, of non-baryonic dark matter surrounding our galaxy has mass ~ 5 x10^12 M solar and radius 0.1 Mpc. What it its average density in Kg m-3? I think that I need to use the formula M= r v^2/ G G being the gravitational constant. What I'm really unsure of is how to rework the formula? I'm assuming that the average density will be the volume? I've come up with v= M(r)/G and then square the answer Am I anywhere close? Thanks in advance!