Gaseous Dynamical Friction on Elliptical Keplerian Orbits

TL;DR

This paper analyzes the effects of gaseous dynamical friction on elliptical Keplerian orbits, revealing how it influences orbital decay and eccentricity evolution, with implications for astrophysical systems.

Contribution

It provides the first detailed analysis of gaseous dynamical friction on elliptical orbits, including wake morphology and secular orbital evolution, extending previous studies on rectilinear and circular motion.

Findings

Semi-major axis decreases over time.

Eccentricity decreases for subsonic, increases for supersonic orbits.

Orbits tend to become highly eccentric and supersonic over long timescales.

Abstract

We compute the Gaseous Dynamical Friction (GDF) force experienced by massive perturbers on elliptical Keplerian orbits. In this paper, we investigate the density wake morphology, dynamical friction force, and secular orbital evolution for massive single perturbers as well as equal mass binaries embedded in an homogenous, static background flow. In all cases, the rate-of-change in semi-major axis is found to be negative (as expected), whereas the rate-of-change in eccentricity is negative for strictly-subsonic trajectories and positive for strictly-supersonic trajectories. Transonic orbits can experience both positive and negative torques during the course of an orbit, with some growing in eccentricity and others circularising. We observe all initial orbits becoming highly supersonic and eccentric (over sufficiently long timescales) due to a relentless semi-major axis decay increasing the Mach number and subsequent eccentricity driving. We compare our findings to previous studies for rectilinear and circular motion, while also making our data for orbital decay available.