  We study the efficiency at which a black hole or dense star cluster
spirals-in to the Galactic centre. This process takes place on a dynamical
friction time scale, which depends on the value of the Coulomb logarithm ln(L).
We determine the accurate value of this parameter using the direct N-body
method, a tree algorithm and a particle-mesh technique with up to 2 million
plus one particles. The three different techniques are in excellent agreement.
Our result for the Coulomb logarithm appears to be independent of the number of
particles. We conclude that ln(L) = 6.6 +/- 0.6 for a massive point particle in
the inner few parsec of the Galactic bulge. For an extended object, like a
dense star cluster, ln(L) is smaller, with a value of the logarithm argument L
inversely proportional to the object size.
