Nonlinear Evolution of the Kelvin–Helmholtz Instability in the Presence of Radiation and Parallel Magnetic Fields

Abstract The evolution of Kelvin–Helmholtz (KH) instability in the Orion Nebula is studied using a two-dimensional radiation magnetohydrodynamic (MHD) simulation in the presence of the in-plane magnetic field parallel to the flow direction. The linear results show that the parallel component of the magnetic field can stabilize the instability due to the increase of the field line tension, while the radiation field leads to the reduced compressibility of the system and enhances the growth of the instability. When the interface is subjected to more radiation pressure, it is found that a greater saturation magnetic energy is produced, and there is a transfer of the kinetic energy to the thermal energy in the nonlinear evolution of the KH instability. The radiation pressure also accelerates the development of instability at the interface, resulting in a large vortex structure in the nonlinear phase. The results also reveal the relaxation mechanism of the velocity profile caused by momentum transport in the nonlinear phase. The complete evolution of the KH instability as the result of a combination of dynamo effects and energy release is also discussed. Based on these results, a preliminary discussion of several events observed in star-forming regions is given.