Dynamical Friction, Buoyancy, and Core-stalling. I. A Nonperturbative Orbit-based Analysis

We examine the origin of dynamical friction using a non-perturbative, orbit-based approach. Unlike standard perturbative approach, in which arises from LBK torque due to pure resonances, this alternative, complementary view nicely illustrates how massive perturber significantly changes energies and angular momenta field particles on near-resonant orbits, with arising an imbalance between that gain energy those lose energy. treat spherical host system as restricted three-body problem. This treatment is applicable `slow' regime, sinks slowly framework fails onset non-linearities. Hence it especially suited investigate core-stalling: cessation central constant-density cores. identify three different families near-co-rotation-resonant orbits dominate contribution friction. Their relative governed by Lagrange points (fixed co-rotating frame). In particular, one families, we call Pac-Man because their appearance frame, unique cored density distributions. When reaches core, bifurcation drastically orbital make-up, becoming dominant. addition, relatively small gradients distribution function inside net these becomes positive (enhancing), thereby effectuating buoyancy. argue core stalling occurs where buoyancy balanced