In a recent paper, entitled: “Universal Clustering of dark matter in phase space”, Jesus and I have showed that dark matter haloes age very similarly to how trees age! To see how old a tree is, you look at the cross-section of the trunk and count the rings. To see how old a dark matter halo is, you look at the clustering of its phase space (what we call P2SAD), and count by how many decades it changes.
Why does this matter? It turns out that understanding this phase space structure on very small scales is very important in planning and interpreting our efforts to find dark matter. The fact that it’s universal certainly helps!