Master defense by David O'Neill

Title: Generalizing the Gaseous Dynamical Friction Force to Keplerian Orbits

Abstract:
The aim of this dissertation is to study the gaseous Dynamical Friction (DF) effects on Keplerian orbits. Both linear (Ostriker 1999) and circular (Kim & Kim 2007) trajectories have competent theoretical understandings, while elliptical and hyperbolic ones do not. We seek to model this force for the latter two scenarios with the prospective of applying the results to the AGN-Channel and field-channel in black hole binary formation. We find that highly eccentric elliptical trajectories experience more acceleration causing thin density tails just prior to perihelion, and wider tails near aphelion. We compute the drag force for the elliptical case with convergence tests and compare to the results of Kim & Kim 2007.

We also study the structure of hyperbolic wakes. For large Mach numbers, these density perturbations behave not too unlike linear motion-- in a bent Mach cone structure. The eccentricity determines the angle at which bending occurs. Interestingly, there can occur subsonic to supersonic transitions (and vice versa) which produce density perturbations similar to that of a "sonic boom''.

Advisors: Daniel D'Orazio, Martin Pessah, Johan Samsing
Censor: Steen Hannestad (Aarhus University)