array9

It is difficult to see how you clump dark matter together, as it is not sticky.

But you might be lucky with a black hole which is its own stickiness.

Indeed black holes might be the only way to stop dark matter just oscillating back and forth under gravity.

But it seems much more likely that matter gets taken into a black hole rather than dark matter.  You cannot make a solar system out of dark matter, and so it must be very difficult to construct a black hole.

martin