Magnetic Effects at the Edge of the Solar System: MHD Instabilities, the de Laval Nozzle Effect, and an Extended Jet

To model the interaction between the solar wind and the interstellar wind,magnetic fields must be included. Recently Opher et al. 2003 found that, byincluding the solar magnetic field in a 3D high resolution simulation using theUniversity of Michigan BATS-R-US code, a jet-sheet structure forms beyond thesolar wind Termination Shock. Here we present an even higher resolutionthree-dimensional case where the jet extends for $150AU$ beyond the TerminationShock. We discuss the formation of the jet due to a de Laval nozzle effect andit's su bsequent large period oscillation due to magnetohydrodynamicinstabilities. To verify the source of the instability, we also perform asimplified two dimensional-geometry magnetohydrodynamic calculation of a planefluid jet embedded in a neutral sheet with the profiles taken from our 3Dsimulation. We find remarkable agreement with the full three-dimensionalevolution. We compare both simulations and the temporal evolution of the jetshowing that the sinuous mode is the dominant mode that develops into avelocity-shear-instability with a growth rate of $5 \times 10^{-9}sec^{-1}=0.027 years^{-1}$. As a result, the outer edge of the heliospherepresents remarkable dynamics, such as turbulent flows caused by the motion ofthe jet. Further study, e.g., including neutrals and the tilt of the solarrotation from the magnetic axis, is required before we can definitively addresshow this outer boundary behaves. Already, however, we can say that the magneticfield effects are a major player in this region changing our previous notion ofhow the solar system ends.Comment: 24 pages, 13 figures, accepted for publication in Astrophysical Journal (2004