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. found that by including the solar magnetic field in a three-dimensional high-resolution simulation using the University of Michigan BATS-R-US code, a jet-sheet structure forms beyond the solar wind termination shock. Here we present an even higher resolution three-dimensional case in which the jet extends for 150 AU beyond the termination shock. We discuss the formation of the jet due to a de Laval nozzle effect and its subsequent large-period oscillation due to magnetohydrodynamic (MHD) instabilities. To verify the source of the instability, we also perform a simplified two-dimensional geometry MHD calculation of a plane fluid jet embedded in a neutral sheet with the profiles taken from our three-dimensional simulation. We find remarkable agreement with the full three-dimensional evolution. We compare both simulations and the temporal evolution of the jet, showing that the sinuous mode is the dominant mode that develops into a velocity-shear instability with a growth rate of 5 x 10(-9) s(-1) = 0.027 yr(-1). As a result, the outer edge of the heliosphere presents remarkable dynamics, such as turbulent flows caused by the motion of the jet. Further study, including neutrals and the tilt of the solar rotation from the magnetic axis, is required before we can definitively address how this outer boundary behaves. Already, however, we can say that the magnetic field effects are a major player in this region, changing our previous notion of how the solar system ends.