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Abstract

We use numerical simulations of scalar field dark matter evolving on a moving
black hole background to confirm the regime of validity of (semi-)analytic
expressions derived from first principles for both dynamical friction and
momentum accretion in the relativistic regime. We cover both small and large
clouds (relative to the de Broglie wavelength of the scalars), and light and
heavy particle masses (relative to the BH size). In the case of a small dark
matter cloud, the effect of accretion is a non-negligible contribution to the
total force on the black hole, even for small scalar masses. We confirm that
this momentum accretion transitions between two regimes (wave- and
particle-like) and we identify the mass of the scalar at which the transition
between regimes occurs.