Core‐Collapse Supernovae with Nonuniform Magnetic Fields

Abstract

We perform two-dimensional numerical simulations on the core collapse of a massive star with strong magnetic fields and differential rotations using the numerical code ZEUS-2D. Changing field configurations and laws of differential rotation parametrically, we compute 14 models and investigate the effects of these parameters on the dynamics. In our models we do not solve the neutrino transport but instead employ a phenomenological parametric EOS that takes into account the neutrino emissions. As a result of the calculations, we find that the field configuration plays a significant role in the dynamics of the core if the initial magnetic field is large enough. Models with initially concentrated fields produce more energetic explosions and more prolate shock waves than the uniform field. Quadrupole-like fields produce a remarkably collimated and fast jet, which might be important for gamma-ray bursts (GRBs). The Lorentz forces exerted in the region where the plasma is less than unity are responsible for these dynamics. The pure toroidal field, on the other hand, does not lead to any explosion or matter ejection. This suggests that the presupernova models, in which toroidal fields are predominant are disadvantageous for the magnetorotation-induced supernova considered here. Models with initially weak magnetic fields do not lead to explosion or matter ejection, either. In these models magnetic fields play no role, as they do not grow on the timescale considered in this paper and the magnetic pressure could be comparable to the matter pressure. This is because the exponential field growth as expected in MRI is not seen in our models. The magnetic field is amplified mainly by field compression and field wrapping in our simulations.

Special Relativistic Simulations of Magnetically Dominated Jets in Collapsing Massive Stars

“…As we mention below, these studies are complimentary in the sense that the different epochs are focused on, with the different initial conditions for the numerical modeling being taken. In addition to the elaborate studies in the conventional supernova context (see recent reviews for Kotake et al 2006;Janka et al 2007), much attention has been paid recently to the roles of rapid rotation and magnetic fields for studying the formation of magnetars and its possible application to the collapsars (Yamada & Sawai 2004;Takiwaki et al 2004;Kotake et al 2004b;Sawai et al 2005;Matt et al 2006;Moiseenko et al 2006;Obergaulinger et al 2006;Nishimura et al 2006;Burrows et al 2007;Cerdá-Durán et al 2007;Scheidegger et al 2007;Komissarov & Barkov 2007). After the failed or weak explosion, the accretion to the central objects may lead to the formation of a BH (phase 2).…”

The Effect of Neutrino Radiation on Magnetorotational Instability in Proto–Neutron Stars

“…Toroidal magnetic components are amplified from the poloidal one via various dynamo processes in the stellar evolutionary phases (Spruit 1999(Spruit , 2002. The toroidal component is about $10 9 G, which dominates over the poloidal one of $10 6 G. Assuming the conservation of magnetic flux (B / 2/3 ), the envelope of the PNSs have B ¼ 10 13 G and B z ¼ 10 9 G. This would be the lower limit of the field strengths, because the magnetic fields could be amplified by turbulent dynamos or field wrapping during the core collapse (Sawai et al 2005). The typical radius and density of PNSs are R $ 3 ; 10 6 cm and $ 10 12 g cm À3 , respectively.…”

“…The shapes of the shock wave and the neutrinosphere are modified aspherically by the coupling effects of the rotation and magnetic fields, and anisotropic neutrino radiations could lead to jetlike explosions (Kotake et al 2003. Magnetic pressure-driven explosions are also investigated in the context of magnetorotational core collapse Mizuno et al 2004;Takiwaki et al 2004;Ardeljan et al 2005;Sawai et al 2005;Moiseenko et al 2006). In these studies, strong magnetic fields (k10 15 G) are generated by the field compression, field wrapping, and the MRI, which lead to the prompt explosions of core-collapse supernovae.…”

Neutrino transport and hydrodynamic stability of rotating proto-neutron stars

“…Many studies model rotation of the collapsing core by the angular velocity profile that depends on the spherical radius r alone, Ω = Ω(r) (see, e.g., Akiyama et al 2003;Kotake et al 2004;Thompson et al 2005;Sawai et al 2005). Such a shellular rotation can be justified if the progenitor rotates with the angular velocity that depends on r alone (Mönchmeyer & Müller 1989).…”