Dynamical Friction From Ultralight Dark Matter

TL;DR

This paper investigates the gravitational interactions between massive objects and ultralight dark matter using simulations, revealing complex dynamical behaviors like enhanced drag, coherent oscillations, and stochastic motions that influence black hole dynamics.

Contribution

It provides the first detailed simulations of dynamical friction and SMBH behavior within ULDM, highlighting novel effects such as gravitational collapse of wakes and breathing modes.

Findings

Wake-induced gravitational collapse increases drag force.

Large masses excite coherent breathing modes in ULDM solitons.

Point masses exhibit stochastic, non-uniform sinking trajectories.

Abstract

We simulate the gravitational dynamics of a massive object interacting with Ultralight / Fuzzy Dark Matter (ULDM/FDM), non-relativistic quantum matter described by the Schrodinger-Poisson equation. We first consider a point mass moving in a uniform background, and then a supermassive black hole (SMBH) moving within a ULDM soliton. After replicating simple dynamical friction scenarios to verify our numerical strategies, we demonstrate that the wake induced by a moving mass in a uniform medium may undergo gravitational collapse that dramatically increases the drag force, albeit in a scenario unlikely to be encountered astrophysically. We broadly confirm simple estimates of dynamical friction timescales for a black hole at the center of a halo but see that a large moving point mass excites coherent "breathing modes" in a ULDM soliton. These can lead to "stone skipping" trajectories for point masses which do not sink uniformly toward the center of the soliton, as well as stochastic motion near the center itself. These effects will add complexity to SMBH-ULDM interactions and to SMBH mergers in a ULDM universe.