How black holes turn cusps into cores
  Collapsing collisionless particle systems form gravitational bound halos with cuspy density profiles. Also hierarchical merging of these systems produce remnants with cuspy central density profiles. These results lead to the assumption of cuspy NFW profiles for the density distribution in dark matter halos. However, observed rotation curves in disk galaxies suggest dark matter halos with isothermal core. The same kind of problem can be found for globular clusters, which show cores in their density profiles but should be cuspy if they where formed through a cold collapse.We are showing how small, massive, and compact objects can efficiently transform cuspy stellar systems into density profiles with an isothermal core. 
Marc Hemsendorf