Dynamical friction from self-interacting dark matter

TL;DR

This paper investigates how self-interacting dark matter influences the dynamical friction experienced by inspiralling black holes, revealing that self-interactions can both enhance and reduce the force compared to collisionless dark matter, affecting gravitational wave signals.

Contribution

It provides the first detailed analysis of the impact of dark matter self-interactions on dynamical friction using N-body simulations, highlighting potential deviations from classical models.

Findings

Dynamical friction is typically enhanced by dark matter self-interactions.

At low velocities, self-interactions can reduce dynamical friction.

Chandrasekhar formula may underestimate the deceleration in self-interacting dark matter scenarios.

Abstract

Context. Merging compact objects such as binary black holes provide a promising probe for the physics of dark matter (DM). The gravitational waves emitted during inspiral potentially allow one to detect DM spikes around black holes. This is because the dynamical friction force experienced by the inspiralling black hole alters the orbital period and thus the gravitational wave signal. Aims. The dynamical friction arising from DM can potentially differ from the collisionless case when DM is subject to self-interactions. This paper aims to understand how self-interactions impact dynamical friction. Methods. To study the dynamical friction force, we use idealised N-body simulations, where we include self-interacting dark matter. Results. We find that the dynamical friction force for inspiralling black holes would be typically enhanced by DM self-interactions compared to a collisionless medium (ignoring differences in the DM density). At lower velocities below the sound speed, we find that the dynamical friction force can be reduced by the presence of self-interactions. Conclusions. DM self-interactions have a significant effect on the dynamical friction for black hole mergers. Assuming the Chandrasekhar formula may underpredict the deceleration due to dynamical friction.