Overview

Supersonic turbulence in molecular clouds may strongly influence the very early stages of star formation. In this thesis, I present the results of a numerical study of supersonic hydrodynamic and MHD turbulence conducted using Athena, a new higher-order Godunov code. I analyze the dependence of saturation amplitude, energy dissipation characteristics, power spectra, sonic scaling, intermittency, and probability distribution functions (PDFs) in the turbulence on factors such as magnetic field strength, driving scale, energy injection rate, and numerical resolution. While convergence in the energies is reached at moderate resolutions, I find that the power spectra require much higher resolutions that are difficult to obtain. I find a power law relationship between velocity dispersion and spatial scale for hydrodynamic turbulence, while for MHD I find no such power law. The time-variability and temperature intermittency both show a dependence on the driving scale, indicating that numerically driving turbulence by an arbitrary mechanism may not allow a realistic representation of these properties. I note similarities between the power spectra of supersonic MHD turbulence and an initially-spherical MHD blast wave, implying that the power law form does not rule out shocks, rather than a turbulent cascade, playing a significant role in the regulation of energy transfer between spatial scales. I find surprisingly similar relationships between Mach number and the mean of the density PDF for driven hydrodynamic and strong-field MHD turbulence. There is, however, a large scatter about these relations, indicating a high level of temporal and spatial variability in the PDF. Thus, the PDF of the mass density is unlikely to be a good measure of magnetic field strength. I also find that the PDF of decaying MHD turbulence deviates from the relation found in the driven case. This implies that the instantaneous Mach number alone is not enough to determine the statistical properties of turbulence that is out of equilibrium. The scatter about the mean-Mach relation for driven turbulence, along with the large departure of decaying turbulence PDFs from those of driven turbulence, may illuminate one factor contributing to the large observed cloud-to-cloud variation in the star formation rate per solar mass.

Full Product Details

9781243572769

Table of Contents

Reviews

Author Information

Tab Content 6

Customer Reviews

Recent Reviews

Countries Available