No evidence for intermediate-mass black holes in the globular clusters
  $\omega$ Cen and NGC 6624
  We compare the results of a large grid of N-body simulations with the surface
brightness and velocity dispersion profiles of the globular clusters $\omega$
Cen and NGC 6624. Our models include clusters with varying stellar-mass black
hole retention fractions and varying masses of a central intermediate-mass
black hole (IMBH). We find that an $\sim 45,000$ M$_\odot$ IMBH, whose presence
has been suggested based on the measured velocity dispersion profile of
$\omega$ Cen, predicts the existence of about 20 fast-moving, $m>0.5$ M$_\odot$
main-sequence stars with a (1D) velocity $v>60$ km/sec in the central 20 arcsec
of $\omega$ Cen. However no such star is present in the HST/ACS proper motion
catalogue of Bellini et al. (2017), strongly ruling out the presence of a
massive IMBH in the core of $\omega$ Cen. Instead, we find that all available
data can be fitted by a model that contains 4.6% of the mass of $\omega$ Cen in
a centrally concentrated cluster of stellar-mass black holes. We show that this
mass fraction in stellar-mass BHs is compatible with the predictions of stellar
evolution models of massive stars.
  We also compare our grid of $N$-body simulations with NGC 6624, a cluster
recently claimed to harbor a 20,000 M$_\odot$ black hole based on timing
observations of millisecond pulsars. However, we find that models with
$M_{IMBH}>1,000$ M$_\odot$ IMBHs are incompatible with the observed velocity
dispersion and surface brightness profile of NGC 6624,ruling out the presence
of a massive IMBH in this cluster. Models without an IMBH provide again an
excellent fit to NGC 6624.
