Dynamical Friction on Eccentric Orbits

Dynamical friction (DF) is the gravitational force exerted on a massive object (perturber) moving in a discrete or continuous medium, as a result of the induced density fluctuation it creates in that medium. Since the pioneering study of Chandrasekhar (1943), work has focused on linearly moving perturbers. Explicit expressions for the DF force have been obtained for some discrete and continuous backgrounds, and applied to a range of astrophysical systems. For perturbers on (bound) periodic orbits however, there have been mainly numerical implementations. In this talk, I will discuss to which extend the approach of Desjacques, Nusser, Bühler (2022) for the circular case can be generalized to perturbers moving on elliptic orbits in a gaseous medium. I will present a first, simple ansatz which works for low eccentricities and Mach number; and a second solution based on a perturbative expansion in the eccentricity. I will show that the latter can be accurate for Mach numbers M<1 even when the eccentricity is as high as e>0.9