  White Dwarfs (WD) capture Dark Matter (DM) as they orbit within their host
halos. These captured particles may subsequently annihilate, heating the
stellar core and preventing the WD from cooling. The potential wells of WDs are
considerably deeper and core temperatures significantly cooler than those of
main sequence stars. Consequently, DM evaporation is less important in WDs and
DM with masses $M_{\chi} \gtrsim 100\, \kev$ and annihilation cross-sections
orders of magnitude below the canonical thermal cross-section ($\sigmav \gtrsim
10^{-46}\, \cm^3$/s) can significantly alter WD cooling in particular
astrophysical environments. We consider WDs in globular clusters (GCs) and
dwarf galaxies. If the parameters of the DM particle are known, then the
temperature of the coolest WD in a GC can be used to constrain the DM density
of the cluster's halo (potentially even ruling out the presence of a halo if
the inferred density is of order the ambient Galactic density). Recently
several direct detection experiments have seen signals whose origins might be
due to low mass DM. In this paper, we show that if these claims from CRESST,
DAMA, CDMS-Si, and CoGeNT could be interpreted as DM, then observations of NGC
6397 limit the fraction of DM in that cluster to be $f_{\mathrm{DM}} \lesssim
10^{-3}$. This would be an improvement over existing constraints of 3 orders of
magnitude and clearly rule out a significant DM halo for this cluster...
