An upper limit on the mass of the black hole in Ursa Minor dwarf galaxy
  The well-established correlations between the mass of massive black holes
(BHs) in the nuclei of most studied galaxies and various global properties of
their hosting galaxy lend support to the idea that dwarf galaxies and globular
clusters could also host a BH in their centers. Direct kinematic detection of
BHs in dwarf spheroidal (dSph) galaxies are seriously hindered by the small
number of stars inside the gravitational influence region of the BH. The aim of
this Letter is to establish an upper dynamical limit on the mass of the
putative BH in the Ursa Minor (UMi) dSph galaxy. We present direct N-body
simulations of the tidal disruption of the dynamical fossil observed in UMi,
with and without a massive BH. We find that the observed substructure is
incompatible with the presence of a massive BH of (2-3)x10^4 Msun within the
core of UMi. These limits are consistent with the extrapolation of the
M_{BH}-sigma relation to the M_{BH}<10^6 Msun regime. We also show that the BH
may be off-center with respect to the center of symmetry of the whole galaxy.
