I recall reading somewhere (I can't remember where) that there is astronomical evidence that dark matter has different densities in different parts of the relatively near parts of the observable universe. Q1. Is this correct? If so, can someone please post a link to a relevant article? The following observational possibility come to mind. Consider the relationship R(r,v) between (1) the middle radius r of a cylindrical shell centered on the center of gravity a galaxy, and parallel to the axis of the total angular momentum of the stars in the galaxy, and (2) the average orbital velocity v of stars observed within that cylindrical shell. I understand that observers have noticed that this relationship R(r,v) is very much dissimilar from what would be expected if dark matter was not present. Q2. Can the density ρDM of a dark matter "cloud" surrounding a galaxy be estimated by the galaxy's relationship R(r,v)? Does anyone know whether this has been done? If "yes", does anyone know if the variability of such estimates show statistically significant differences (based on the observational error range of the individual ρDM estimates) between the individual values and their average? Q3. The same question as Q2 except applied to galaxy clusters and their galaxies, rather than galaxies and their stars. Any responding posts will be much appreciated, especially those with links to relevant articles.