What are the mysterious properties of Dark Matter?

[pjkarn6]

Published maps show dark matter as clumps and threads throughout the visible universe as modeled through gravitational lensing. I understand the concept that it does not interact with visible matter or light except through gravity. Even if we see no interaction by strong, weak or electromagnetic forces wouldn't it interact with itself gravitationally? How do clumps not grow denser to the point of aggregation? Why do we not see dark matter dark holes?

 

[Drakkith]

Published maps show dark matter as clumps and threads throughout the visible universe as modeled through gravitational lensing. I understand the concept that it does not interact with visible matter or light except through gravity. Even if we see no interaction by strong, weak or electromagnetic forces wouldn't it interact with itself gravitationally? How do clumps not grow denser to the point of aggregation? Why do we not see dark matter dark holes?

As an example, let's consider two hypothetical dark matter particles in empty space. The two particles will fall towards each other under the force of gravity, gaining kinetic energy as they accelerate. However, since they do not act via the EM force, they have no way of losing this kinetic energy except through gravity. So the two particles pass right through each other (since there is no force to stop them like there is with regular particles) and begin to slowly decelerate under gravity as they recede from one another. The two DM particles eventually wind up just as far apart as they initially were before they begin to fall back towards each other to repeat the process. In order to clump together DM must lose the kinetic energy it gains when it falls towards other objects. There simply isn't a good way for it to do this though.

 

[Mordred]

just to add to Drakkkith's excellent answer DM also does not show any strong force interaction. So there is no strong force to hold two dark matter particles together if the two particles were close enough for the strong force to act upon them