  Ultra-compact dwarf galaxies (UCDs) are stellar systems with masses of around
10^7 to 10^8 Msun and half mass radii of 10-100 pc. They have some properties
in common with massive globular clusters, however dynamical mass estimates have
shown that UCDs have mass-to-light ratios which are on average about twice as
large than those of globular clusters at comparable metallicity, and tend to be
larger than what one would expect for old stellar systems with standard mass
functions.
  One possible explanation for elevated high mass-to-light ratios in UCDs is
the existence of a substantial amount of dark matter, which could have ended up
in UCDs if they are the remnant nuclei of tidally stripped dwarf galaxies.
Tidal stripping of dwarf galaxies has also been suggested has the origin of
several massive globular clusters like Omega Cen, in which case globular
clusters could have also formed with substantial amounts of dark matter.
  In this paper, we present collisional N-body simulations which study the
co-evolution of a system composed out of stars and dark matter. We find that
the dark matter gets removed from the central regions of such systems due to
dynamical friction and mass segregation of stars. The friction timescale is
significantly shorter than a Hubble time for typical globular clusters, while
most UCDs have friction times much longer than a Hubble time. Therefore, a
significant dark matter fraction remains within the half-mass radius of
present-day UCDs, making dark matter a viable explanation for the elevated M/L
ratios of UCDs. If at least some globular clusters formed in a way similar to
UCDs, we predict a substantial amount of dark matter in their outer parts.
