Title: Dynamical Friction in a Gaseous Medium

Dr Hyosun Kim (Institute of Astronomy and Astrophysics, Academia Sinica)

Abstract
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A massive object in orbital motion suffers from orbital decay
due to a negative torque caused by gravitational interaction
with its own gravitationally induced wake created in the
background medium. This process, commonly referred to
as dynamical friction (DF), occurs in not only collisionless
environments but also collisional gaseous backgrounds.
The DF in a gaseous medium is of great importance in
understanding the formation and evolution of planets, binary
stars, supermassive black holes, etc, it has nevertheless
been insufficiently understood so far in realistic situations.
In particular, I will report on the results of semianalytic and
numerical calculations on how dependent the drag force is
on the shape of orbits, what effects are brought on by the
wake of a companion in binary systems, and what happens
when the moving object is massive enough that an induced
wake is nonlinear. It will be also discussed that what we can
derive from observations of the density wake itself.