Fragmentation of magnetized cloud cores

Using a fully three-dimensional, Lagrangian two-fluid magnetohydrodynamics code, we simulate the collapse and fragmentation of a rotating molecular cloud core. The code used is able to describe the dynamics of partially ionized fluids and takes account of ambipolar diffusion and magnetic braking. We model both magnetized and non-magnetized cores. The magnetized cores are chosen to be initially thermally supercritical, but magnetically subcritical. Therefore, before they can collapse, magnetic support must be lost through ambipolar diffusion. Our results imply that magnetic braking is so effective in removing angular momentum that fragmentation is inhibited. These results cast doubt on the suggestion by Boss that the likelihood of core fragmentation is increased by a magnetic field.