This week on the Astronomy Cast podcast the topic was galaxy formation. Apparently, before the luminous (baryonic) galaxies coalesced under gravity, the non-baryonic dark matter had already begun collecting into large structures that eventually formed the scaffolding for the galaxies. As I understand it, so-called dark matter is affected by gravity but does not interact with light (except to alter its trajectory by bending spacetime).

Here is my question: If dark matter is affected by gravity (and exerts its own gravitational pull, or bends spacetime in the same way and to the same extent as baryonic matter of equal mass), then shouldn't we expect to find dark matter in the middle of large gravity wells of baryonic matter? Shouldn't the dark matter and the regular matter "fall down the same holes"?

Two follow-ups: (1) If so, then won't a certain amount of the mass of the sun actually be dark matter? And if that's so, then wouldn't the actual amount of elemental fuel for the successive types of fusion be less than expected? (2) If not, then what keeps the dark matter out?

--Ken Sibley, Greentown, IN