||Nonlinear Dynamical Friction in a Gaseous Medium
||444, 5th International Conference of Numerical Modeling of Space Plasma Flows (ASTRONUM 2010)
||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
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.
of these results are briefly discussed.