Orbital evolution of gas-driven inspirals with extreme mass-ratios: retrograde eccentric orbits

Abstract

Using two-dimensional simulations, we compute the torque and rate of work (power) on a low-mass gravitational body, with softening length R soft , embedded in a gaseous disk when its orbit is eccentric and retrograde with respect to the disk. We explore orbital eccentricities e between 0 and 0.6. We find that the power has its maximum at e 0.25(h/0.05) 2/3 , where h is the aspect ratio of the disk. We show that the power and the torque converge to the values predicted in the local (non-resonant) approximation of the dynamical friction (DF) when R soft tends to zero. For retrograde inspirals with mass ratios 5 × 10 −4 embedded in disks with h ≥ 0.025, our simulations suggest that (i) the rate of inspiral barely depends on the orbital eccentricity and (ii) the local approximation provides the value of this inspiral rate within a factor of 1.5. The implications of the results for the orbital evolution of extreme mass-ratio inspirals are discussed.