Relativistic drag forces on black holes from scalar dark matter clouds of all sizes

TL;DR

This paper uses numerical simulations to validate analytic models of relativistic drag forces on black holes caused by scalar dark matter clouds of various sizes and masses, revealing the significance of accretion effects.

Contribution

It provides a comprehensive numerical validation of semi-analytic formulas for dynamical friction and accretion in relativistic regimes across different scalar dark matter parameters.

Findings

Accretion significantly affects the force on black holes even for small scalar masses.

The transition between wave-like and particle-like regimes depends on scalar mass.

Numerical results confirm the validity of analytic expressions across regimes.

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.