Second Core Formation and High-Speed Jets: Resistive Magnetohydrodynamic Nested Grid Simulations

Abstract

The stellar core formation and high-speed jets driven by the formed core are studied using three-dimensional resistive MHD nested grid simulations. Starting with a Bonnor-Ebert isothermal cloud rotating in a uniform magnetic field, we calculate the cloud evolution from the molecular cloud core (nc = 106 cm-3) to the stellar core (nc 1023 cm-3), where nc denotes the central density. For comparison, we calculate two models: resistive and ideal MHD models. Both the resistive and ideal models have the same initial condition, but the former includes the dissipation process of magnetic field while the latter does not. The magnetic fluxes in the resistive MHD model are extracted from the first core during 1012 cm-3 < nc < 1016 cm-3 by ohmic dissipation. Magnetic flux density of the formed stellar core (nc 1020 cm-3) in the resistive MHD model is 2 orders of magnitude smaller than that in ideal MHD model. Since magnetic braking is less effective in the resistive MHD model, a rapidly rotating stellar core (the second core) is formed. After stellar core formation, the magnetic field of the core is largely amplified, and high-speed (45 km s-1) jets are driven by the second core, which results in strong mass ejection. A cocoon-like structure around the second core also forms with clear bow shocks.