The Collapse of Rotating Massive Stars in Three Dimensions

Most simulations of the core collapse of massive stars have focused on the collapse of spherically symmetric objects. If these stars are rotating, this symmetry is broken, opening up a number of effects that are just now being studied. The list of proposed effects spans a range of extremes: from fragmentation of the collapsed iron core to modifications of the convective instabilities above the core; from the generation of strong magnetic fields that then drive the supernova explosion to the late-time formation of magnetic fields to produce magnetars after the launch of the supernova explosion. The list of the observational effects of rotation ranges from modifications in the gamma-ray line spectra, nucleosynthetic yields, and shape of supernova remnants caused by rotation-induced asymmetric explosions to strong pulsar radiation, the emission of gravitational waves, and altered r-process nucleosynthetic yields caused by rapidly rotating stars. In this paper we present the results of three-dimensional collapse simulations of rotating stars for a range of stellar progenitors. We find that for the most rapidly spinning stars, rotation does indeed modify the convection above the proto-neutron star, but it is not fast enough to cause core fragmentation. Similarly, although strong magnetic fields can be produced once the proto-neutron star cools and contracts, the proto-neutron star does not spin fast enough to generate strong magnetic fields quickly after collapse, and, for our simulations, magnetic fields will not dominate the supernova explosion mechanism. Even so, the resulting pulsars for our most rapidly rotating models may emit enough energy to dominate the total explosion energy of the supernova. However, more recent stellar models predict rotation rates that are much too slow to affect the explosion, but these models are not sophisticated enough to determine whether the most recent or past stellar rotation rates are more likely. Thus, we must rely on observational constraints to determine the true rotation rates of stellar cores just before collapse. We conclude with a discussion of the possible constraints on stellar rotation that we can derive from core-collapse supernovae.