On the theory of ambipolar diffusion, with applications to astrophysical jets

Abstract

Numerically simulated magnetohydrodynamical jets are not at all morphologically similar to most of those which are observed in nature. Jets in nature are actually quite morphologically similar to pure hydrodynamical simulations. However, it is well known that jets in nature are launched magnetically and likely transport dynamically important magnetic fields. Therefore, a gap seems to exist in the model of jets based upon a pure magnetohydrodynamical outflow. In this thesis, I show that the theory of ambipolar diffusion may provide a plausible solution to the morphology problem by running simulations which use the non-isothermal single fluid approximation of ambipolar diffusion. However, using resolution studies on the numerical simulations, I show that there exists a numerical instability caused by the single fluid approximation which produces unreliable results when applied to this problem. Accordingly, I develop a full non-isothermal two-fluid model of ambipolar diffusion from first principles and show that this reduces correctly to the single fluid model of ambipolar diffusion widely used in the literature. Suggestions on how this may be incorporated into a numerical model are then made.