Ultra-compact dwarf galaxies ( UCDs ) are stellar systems with masses of around 10 ^ { 7 } to 10 ^ { 8 } M _ { \odot } 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 composed out of stars 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 , and dark matter was dragged into these nuclei prior to tidal stripping through e.g .
adiabatic gas infall .
Tidal stripping of dwarf galaxies has also been suggested as the origin of several massive globular clusters like Omega Cen , in which case one should expect that globular clusters also form with substantial amounts of dark matter in them .

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 .