Since Dark Matter is by definition immune to electromagnetic forces, then it has no other way to interact except through gravity -- unless one wants to come up with some entirely new force, which has never been seen. If Dark Matter did have some force of its own, akin to electromagnetism, that would allow it to clump together, then what would happen is that you'd have these super-large clumps (Dark Matter Planets, etc) which would be floating around, showing off their gravitational effects in very concentrated ways. But planets and stars are held together by gravity, and not electromagnetism. So if Dark Matter can gravitate to itself, then couldn't it form Dark Stars? A Dark Star would generate no light, of course. But if it had no force similar to electromagnetism to push apart from itself, then it would all just concentrate into one single dense point -- like a black hole. So it would seem that Dark Matter would be more likely than regular matter to form black holes, right? That's what I can infer from all of this.