Dynamical friction from scalar dark matter in the relativistic regime

Understand

Light bosonic scalars (e.g.

• axions) may form clouds around black holes via superradiant instabilities, or via accretion if they form some component of the dark matter.
• It has been suggested that their presence may lead to a distinctive dephasing of the gravitational wave signal when a small compact object spirals into a larger black hole.
• Motivated by this, we study numerically the dynamical friction force on a black hole moving at relativistic velocities in a background scalar field with an asymptotically homogeneous energy density.