  It is now established that several of the Local Group dwarf Spheroidal
galaxies (dSphs) have large mass-to-light ratios. We consider the possibility
that the dark matter in the halos of dSphs is composed of massive black holes
with masses in the range 10^5 to 10^7 solar masses. We use direct N-body
simulations to determine the long term evolution of a two-component dSph
composed of a pressure-supported stellar population in a black hole halo. The
black holes are initially distributed according to a Navarro, Frenk & White
profile. For black hole masses between 10^5 and 10^6 solar masses, the dark
matter halo evolves towards a shallower inner profile in less than a Hubble
time. This suggests that black holes in this mass range might provide an
explanation for the origin of the dark matter cores inferred from observations
of Low Surface Brightness galaxy rotation curves. We compare the simulated
evolution of the stellar population with observed data for the Draco dSph. The
dependence of the heating rate on the black hole mass is determined, and an
upper limit of 10^5 solar masses is placed on the individual black holes
comprising the dark matter halo of Draco, if its present stellar distribution
is representative of the initial one. We also present a simple scaling argument
which demonstrates that the dynamical heating of an initially compact, though
not self-gravitating, stellar distribution might produce a remnant distribution
similar in extent to Draco after 10 Gyr, even for black hole masses somewhat in
excess of 10^5 solar masses.
