> how do we know it isn't dark matter causing the collapse to happen faster than thought? The average density of dark matter is way too small. It's significant

> how do we know it isn't dark matter causing the collapse to happen faster than thought? The average density of dark matter is way too small. It's significant on the scale of a galaxy because it doesn't clump, so its density is basically the average density everywhere (denser towards the center and less dense further out, but still of the same rough order of magnitude), instead of being isolated clumps surrounded by huge expanses of empty space, as with ordinary matter. But on the scale of a single stellar system the density of dark matter is so small that its effect on the dynamics is negligible.