Speaker
Kazunari Iwasaki
(Nagoya University)
Description
Nonlinear evolution of bistable interstellar medium is investigated using two-dimensional simulations with a realistic cooling rate, heat conduction, and physical viscosity. The calculation is performed in periodic boundary conditions without any external forcing. As the initial condition, spatially uniform unstable gas under thermal equilibrium is considered. At the initial stage, the unstable gas quickly segregates into two phases, or cold neutral medium (CNM) and warm neutral medium (WNM). After that, a self-sustained turbulent is observed where the CNM move around in the WNM. In a self-sustaining mechanism, it is found that interfacial medium (IFM) existing between the CNM and WNM plays a quite important role. The self-sustaining mechanism can be divided into two steps. First, the thermal conduction drives fast flows streaming into concave CNM surfaces toward the WNM. The kinetic energy of fast flows in the IFM is incorporated into that of the CNM through the phase transition. Second, turbulence inside the CNM deforms interfaces and forms other concave CNM surfaces, leading to fast flows in the IFM. The first step is repeated. In this manner, the self-sustaining mechanism works.
Author
Kazunari Iwasaki
(Nagoya University)