Answers are grounded in this paper and cite their sources.
The phase space densities of dark matter halos in well-observed nearby galaxies appear to span a very wide range. Provided only that the dark matter (DM) particles are collisionless, this result is inconsistent with warm DM models of structure formation. With cold DM facing serious difficulties on small scales and hot DM models ruled out, we may be close to excluding any simple, collisionless particle as a candidate for DM.
No takes yet. Share an insight, caveat, or question.
J. A. Sellwood (2000) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: