In hierarchical clustering theories, smaller masses generally collapse earlier than larger masses and so are denser on the average. The core of a small mass halo could be dense enough to resist disruption and survive undigested, when it gets incorporated into a bigger object, and determine the halo structure in the inner regions. We examine in this talk the possible consequences of this idea in determining the structure of dark halo cores, by considering, both simple scaling arguments, and a novel fluid approach to self-similar collapse solutions for the dark matter phase space density.
