Speaker
Jeong-Gyu Kim
(Seoul National University)
Description
The neutral component of the interstellar medium (ISM) is segregated
into the cold neutral medium (CNM) and warm neutral medium (WNM) as
a result of thermal instability. It was found that the CNM--WNM
evaporation interface, across which the CNM undergoes thermal
expansion, is linearly unstable to corrugational disturbances, in
complete analogy with the Darrieus-Landau instability (DLI) of
terrestrial flames. To explore dynamical consequences of the DLI in
the ISM, we perform a full linear stability analysis of the DLI as
well as nonlinear hydrodynamic simulations in the presence of
thermal conduction but without magnetic fields. We find that the DLI
is suppressed at short length scales via heat transport. The time
and length scales of the fastest growing mode are squarely and
inversely proportional to the evaporation flow speed of the CNM
relative to the interface, respectively. In the nonlinear stage, the
front deforms into a finger-like structure, rather than a cusp,
protruding toward the WNM, and soon reach a steady state where the
evaporation rate is increased by a factor of ~2.4 compared to
the initial value. We demonstrate that the front shape and the
enhancement in the evaporation rate are determined primarily by the
density ratio between the CNM and WNM.
Author
Jeong-Gyu Kim
(Seoul National University)