1. The problem statement, all variables and given/known data Evidence for dark matter comes from “flat” rotation curves of galaxies. Assume that the observed matter moves in circular orbits about the center of the galaxy and that the velocity of the matter as a function of the radius v(r) is a constant. Also assume (mass of luminous matter is negligible) and the dark matter is distributed with spherical symmetry about the center of the galaxy. What is the density ρ(r) of the dark matter as a function of radius? 2. Attempt Critic density = ρ(r) = 3Ho^2 / 8piG Ho= Hubble constante because Ho = v/d then ρ(r) = 3v^2 / 8piGr^2 r= distance from the center of galaxy So we can conclude that the dark matter density in a galaxy is proportional to 1/r^2. But i found this wrong. Can somebody the me what is wrong?