Gravitational drag on a point mass in hypersonic motion within a Gaussian disk

TL;DR

This paper presents an analytical model for gravitational drag and accretion on a hypersonic point mass in a Gaussian disk, relevant for planetary and black hole dynamics, with results validated against simulations.

Contribution

It introduces a fully analytical model for gravitational interactions in a stratified disk, simplifying to thick and thin disk limits, and compares well with hydrodynamical simulations.

Findings

Accretion rate proportional to object mass and disk surface density in thin disks.

Drag force in thin disks is independent of object velocity.

Model predictions agree with 3D hydrodynamical simulations.

Abstract

We develop an analytical model for the accretion and gravitational drag on a point mass that moves hypersonically in the midplane of a gaseous disk with a Gaussian vertical density stratification. Such a model is of interest for studying the interaction between a planet and a protoplanetary disk, as well as the dynamical decay of massive black holes in galactic nuclei. The model considers that the flow is ballistic, and gives fully analytical expressions for both the accretion rate onto the point mass, and the gravitational drag it suffers. The expressions are further simplified by taking the limits of a thick, and of a thin disk. The results for the thick disk reduce correctly to those for a uniform density environment (Cant\'o et al. 2011). We find that for a thin disk (small vertical scaleheight compared to the gravitational radius) the accretion rate is proportional to the mass of the moving object and to the surface density of the disk, while the drag force is independent of the velocity of the object. The gravitational deceleration of the hypersonic perturber in a thin disk was found to be independent of its parameters (i.e. mass or velocity) and depends only on the surface mass density of the disk. The predictions of the model are compared to the results of three-dimensional hydrodynamical simulations, with a reasonable agreement.