# Dynamical friction in slab geometries and accretion disks

## TL;DR

This paper derives the gravitational wake and dynamical friction force for a massive object moving through a slab-like medium, revealing reduced friction compared to extended media and providing formulas for different regimes.

## Contribution

It presents the first analytical derivation of dynamical friction in slab geometries, relevant for accretion disks and similar environments.

## Key findings

- Dynamical friction is significantly reduced in slab geometries.
- Provided simple formulas for gravitational drag in subsonic and supersonic regimes.
- First analytical description of gravitational wake in slab-like media.

## Abstract

The evolution of planets, stars and even galaxies is driven, to a large extent, by dynamical friction of gravitational origin. There is now a good understanding of the friction produced by extended media, either collisionless of fluid-like. However, the physics of accretion or protoplanetary disks, for instance, is described by slab-like geometries instead, compact in one spatial direction. Here, we find, for the first time, the gravitational wake due to a massive perturber moving through a slab-like medium, describing e.g. accretion disks with sharp transitions. We show that dynamical friction in such environments can be substantially reduced relatively to spatially extended profiles. Finally, we provide simple and accurate expressions for the gravitational drag force felt by the perturber, in both the subsonic and supersonic regime.