Star Formation Initiated by Decay of Turbulence

点击翻译按钮获取中文摘要

Magnetohydrodynamical (MHD) waves of large amplitudes propagate in molecular clouds where star formation is now ongoing. These MHD waves are thought to prevent the molecura clouds collapsing to form stars. In other words, star formation will become active if the MHD waves decay. This idea have promoted numerical simulations which aim to derive the decay rate of the MHD waves. However, the numerical simulations so far have suffered from *erious numerical decays of the MHD waves. Also the dynamic range in the wavelength was also limited by computer resources available. We evaluated the decay due to the numerical viscosity using the analytical solution of the circularly polarized Alfven wave. We have shown that the numerical decay is small enough only when more than 32 mesh points are used to resolve a wavelength. This means that the dynamic range can be only by a factor 8 in the wavelength even when 256 mesh points are used in each spatial direction. We have also shown that the physical decay of the Alfven wave depends not only on the wavelength but on the polarization. A circularly polarized wave traveling in a filamentary cloud decays exponentially with a wavelength independent e-folding timescale. A linearly polarized one decays inversely proportional to the square of the time and the decay rate is larger for a shorter wavelength. These results were shown at two international conferences and will be shown in a refereed journal in near future.