This question come from the following information:
1) Dark matter does not electromagnetically interact with normal matter.
2) There are underground experiments to detect dark matter
directly. The hope is that a dark matter particle would hit the nucleus
of an atom. I assume that this means that there is potently a strong
force interaction between normal matter and dark mater.
3) Dark mater and normal matter interact via gravity.
If we are surrounded by a sea of dark mater that some times interacts
with the nucleus of atoms in the earth I would expect that it would be
possible that some of these dark matter particles would settle into
orbit around the earth and every other object in the universe. (Dark
matter particle on a hyperbolic orbit hits a nucleus loses some energy
and is now in an elliptical orbit.) Therefor if dark matter really does
interact with the nucleus of atoms I would expect that very sensitive
measurement of satellite orbits could revile if the earth has been
collecting orbiting dark matter for the last 4.5 billion years.
Black hole question:
If dark matter falls into a black hole will it say within the event
horizon? If so with the slow evaporation of a black hole via Hawking
radiation can a black hole turn into a pure dark matter black hole?