On the fragmentation of magnetized cloud cores

Recent calculations with a two-fluid smoothed particle hydrodynamics (SPH) code of the collapse of a magnetized dense core have found little evidence for fragmentation. These calculations have been interpreted as implying that magnetic braking by magnetic tension forces is sufficient to inhibit fragmentation, contrary to a suggestion by Boss that magnetic fields might encourage fragmentation. However, the type of fragmentation considered by Boss did not require the presence of significant rotation, contrary to the case with the SPH calculations, so the relevance of magnetic braking to Boss’ suggestion is unclear. The SPH calculations used a barotropic equation of state which tended to produce a single central clump that resisted fragmentation in clouds where the Eddington approximation radiative transfer used by Boss led to fragmentation. While a definitive calculation has yet to be accomplished, fragmentation seems to remain as a possible outcome of the collapse of magnetic clouds.