array9

I am assuming that dark matter interacts with gravity only.

It is difficult to see how you capture dark matter, as you cannot contain it.  You would have to slow it down with use of gravity, and then get it to oscillate around some strong gravitational source.

It is difficult to see it happening without some non-gravitational clumping of ordinary matter happening at the same time.

Indeed it is difficult to see how two bits of ordinary matter can clump by gravity alone, and it probably takes the randomness of 3+ body problems to achieve.

Martin