Dynamical friction in self-interacting ultralight dark matter

TL;DR

This paper investigates how dark matter self-interactions influence dynamical friction on objects like black holes in ultralight dark matter halos, revealing that strong repulsive interactions can significantly reduce friction effects.

Contribution

It provides the first calculation of dynamical friction in self-interacting ultralight dark matter and demonstrates the impact of self-interactions through simulations.

Findings

Dynamical friction vanishes with sufficiently strong repulsive self-interactions.

Self-interactions cause up to 70% reduction in deceleration of SMBHs.

Outcomes depend critically on the presence or absence of self-interactions.

Abstract

We explore how dynamical friction in an ultralight dark matter (ULDM) background is affected by dark matter self-interactions. We calculate the force of dynamical friction on a point mass moving through a uniform ULDM background with self-interactions, finding that the force of dynamical friction vanishes for sufficiently strong repulsive self-interactions. Using the pseudospectral solver $\texttt{UltraDark.jl}$, we show with simulations that reasonable values of the ULDM self-interaction strength and particle mass cause $\mathcal{O}(1)$ differences in the acceleration of an object like a supermassive black hole (SMBH) traveling near the center of a soliton, relative to the case with no self-interactions. For example, repulsive self-interactions with $\lambda = 10^{-90}$ yield a deceleration due to dynamical friction $\approx70\%$ smaller than a model with no self-interactions. We discuss the observational implications of our results for SMBHs near soliton centers and for massive satellite galaxies falling into ultralight axion halos and show that outcomes are dependent on whether a self-interaction is present or not.