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Paper: Nonlinear Dynamical Friction in a Gaseous Medium
Volume: 444, 5th International Conference of Numerical Modeling of Space Plasma Flows (ASTRONUM 2010)
Page: 69
Authors: Kim, W.-T.
Abstract: Dynamical friction (DF) of massive objects due to gaseous media is of great importance in various astronomical systems ranging from protoplanetary disks to galaxy clusters. Previous studies on the gaseous DF consider a low-mass perturber moving on a straight-line trajectory, with the induced density wakes in the linear regime. However , there are many astronomical situations such as in mergers of black holes near galaxy centers, where perturbers follow curvilinear orbits and are so massive that the induced wakes are fully nonlinear. Here, I review the recent results of analytic and numerical studies that have investigated the effects of the perturber mass, size, and the orbit shape on the gaseous DF. Unlike in the low-mass perturber cases where Mach waves are attached to a perturber, a very massive perturber quickly develops nonlinear flows that produce a detached bow shock in the front side. The flows around the perturber evolve rapidly toward a quasi-steady state in which a supersonic wake consists of a hydrostatic envelope surrounding the perturber, an upstream bow shock, and a trailing low-density region. Increasing the perturber mass increases the detached shock distance and symmetrizes the density wake near the perturber. This makes the nonlinear drag force much smaller than the linear prediction, and becomes independent of the perturber size if the perturber is massive enough. Astronomical implications of these results are briefly discussed.
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