Into the void : simulations of protostellar jets from Keplerian discs extended to observational length scales

Abstract

In this work, I present the first simulations to investigate the formation and propagation of protostellar jets that simultaneously include the launching mechanism at < 0.1 AU and the much larger observational length scales at > 10[superscript 3] AU. This is accomplished through the development and application of AZEuS , a new adaptive mesh refinement (AMR) version of the ZEUS-3D magnetohydrodynamics (MHD) fluid code. AMR has been adapted for a fully-staggered mesh, and a description of the methods employed is given. By simulating protostellar jets over 5 orders of magnitude in length, I find relationships between conditions at the disc surface and observable quantities such as jet proper motion, rotational velocity, jet radius, and mass, momentum, kinetic energy, and angular momentum fluxes. I also find that two mechanisms for jet launching are required to understand the simulation results. For strong fields, the traditional magneto-centrifugal mechanism is applicable, while for weak fields, the jet is accelerated by gradients in toroidal magnetic pressure. The jets presented here establish a magnetically-dominated region early in their evolution, regardless of the initial magnetic field strength, implying that plasma-β < 1 is required for jet launching to occur. Over time, the plasma-β [arrow right] 1, and the jets approach equipartition between thermal pressure and magnetic forces. These results demonstrate that outflows launched magnetically from discs are capable, by themselves, of producing realistic protostellar jets.