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Title: THE EVOLUTION AND IMPACTS OF MAGNETOROTATIONAL INSTABILITY IN MAGNETIZED CORE-COLLAPSE SUPERNOVAE

Abstract

We carried out two-dimensional axisymmetric MHD simulations of core-collapse supernovae for rapidly rotating magnetized progenitors. By changing both the strength of the magnetic field and the spatial resolution, the evolution of the magnetorotational instability (MRI) and its impacts upon the dynamics are investigated. We found that the MRI greatly amplifies the seed magnetic fields in the regime where the buoyant mode, not the Alfvén mode, plays a primary role in the exponential growth phase. The MRI indeed has a powerful impact on the supernova dynamics. It makes the shock expansion faster and the explosion more energetic, with some models being accompanied by the collimated jet formations. These effects, however, are not made by the magnetic pressure except for the collimated jet formations. The angular momentum transfer induced by the MRI causes the expansion of the heating region, by which the accreting matter gain additional time to be heated by neutrinos. The MRI also drifts low-Y{sub p} matter from deep inside of the core to the heating region, which makes the net neutrino heating rate larger by the reduction of the cooling due to the electron capture. These two effects enhance the efficiency of the neutrino heating, which is found to be the key tomore » boosting the explosion. Indeed, we found that our models explode far more weakly when the net neutrino heating is switched off. The contribution of the neutrino heating to the explosion energy could reach 60% even in the case of strongest magnetic field in the current simulations.« less

Authors:
 [1];  [2]
  1. Research Organization for Information Science and Technology, Kobe, Hyogo 650-0047 (Japan)
  2. Waseda University, Shinjuku, Tokyo 169-8555 (Japan)
Publication Date:
OSTI Identifier:
22521616
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 817; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANGULAR MOMENTUM TRANSFER; AXIAL SYMMETRY; COMPUTERIZED SIMULATION; ELECTRON CAPTURE; HEATING RATE; INSTABILITY; JETS; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; NEUTRON STARS; SPATIAL RESOLUTION; SUPERNOVAE; TWO-DIMENSIONAL SYSTEMS

Citation Formats

Sawai, Hidetomo, and Yamada, Shoichi, E-mail: hsawai@rist.or.jp. THE EVOLUTION AND IMPACTS OF MAGNETOROTATIONAL INSTABILITY IN MAGNETIZED CORE-COLLAPSE SUPERNOVAE. United States: N. p., 2016. Web. doi:10.3847/0004-637X/817/2/153.
Sawai, Hidetomo, & Yamada, Shoichi, E-mail: hsawai@rist.or.jp. THE EVOLUTION AND IMPACTS OF MAGNETOROTATIONAL INSTABILITY IN MAGNETIZED CORE-COLLAPSE SUPERNOVAE. United States. doi:10.3847/0004-637X/817/2/153.
Sawai, Hidetomo, and Yamada, Shoichi, E-mail: hsawai@rist.or.jp. 2016. "THE EVOLUTION AND IMPACTS OF MAGNETOROTATIONAL INSTABILITY IN MAGNETIZED CORE-COLLAPSE SUPERNOVAE". United States. doi:10.3847/0004-637X/817/2/153.
@article{osti_22521616,
title = {THE EVOLUTION AND IMPACTS OF MAGNETOROTATIONAL INSTABILITY IN MAGNETIZED CORE-COLLAPSE SUPERNOVAE},
author = {Sawai, Hidetomo and Yamada, Shoichi, E-mail: hsawai@rist.or.jp},
abstractNote = {We carried out two-dimensional axisymmetric MHD simulations of core-collapse supernovae for rapidly rotating magnetized progenitors. By changing both the strength of the magnetic field and the spatial resolution, the evolution of the magnetorotational instability (MRI) and its impacts upon the dynamics are investigated. We found that the MRI greatly amplifies the seed magnetic fields in the regime where the buoyant mode, not the Alfvén mode, plays a primary role in the exponential growth phase. The MRI indeed has a powerful impact on the supernova dynamics. It makes the shock expansion faster and the explosion more energetic, with some models being accompanied by the collimated jet formations. These effects, however, are not made by the magnetic pressure except for the collimated jet formations. The angular momentum transfer induced by the MRI causes the expansion of the heating region, by which the accreting matter gain additional time to be heated by neutrinos. The MRI also drifts low-Y{sub p} matter from deep inside of the core to the heating region, which makes the net neutrino heating rate larger by the reduction of the cooling due to the electron capture. These two effects enhance the efficiency of the neutrino heating, which is found to be the key to boosting the explosion. Indeed, we found that our models explode far more weakly when the net neutrino heating is switched off. The contribution of the neutrino heating to the explosion energy could reach 60% even in the case of strongest magnetic field in the current simulations.},
doi = {10.3847/0004-637X/817/2/153},
journal = {Astrophysical Journal},
number = 2,
volume = 817,
place = {United States},
year = 2016,
month = 2
}
  • We investigated the impact of magnetorotational instability (MRI) on the dynamics of weakly magnetized, rapidly rotating core-collapse supernovae by conducting high-resolution axisymmetric MHD simulations with simplified neutrino transfer. We found that an initially sub-magnetar-class magnetic field is drastically amplified by MRI and substantially affects the dynamics thereafter. Although the magnetic pressure is not strong enough to eject matter, the amplified magnetic field efficiently transfers angular momentum from small to large radii and from higher to lower latitudes, which causes the expansion of the heating region due to the extra centrifugal force. This then enhances the efficiency of neutrino heating andmore » eventually leads to neutrino-driven explosion. This is a new scenario of core-collapse supernovae that has never been demonstrated by past numerical simulations.« less
  • Bearing in mind the application of core-collapse supernovae, we study the nonlinear properties of the magnetorotational instability (MRI) by means of three-dimensional simulations in the framework of a local shearing box approximation. By systematically changing the shear rates that symbolize the degree of differential rotation in nascent proto-neutron stars (PNSs), we derive a scaling relation between the turbulent stress sustained by the MRI and the shear-vorticity ratio. Our parametric survey shows a power-law scaling between the turbulent stress (((w {sub tot}))) and the shear-vorticity ratio (g{sub q} ) as ((w {sub tot})){proportional_to}g {sup {delta}} {sub q} with an index ofmore » {delta} {approx} 0.5. The MRI-amplified magnetic energy has a similar scaling relative to the turbulent stress, while the Maxwell stress has a slightly smaller power-law index ({approx}0.36). By modeling the effect of viscous heating rates from MRI turbulence, we show that the stronger magnetic fields, or the larger shear rates initially imposed, lead to higher dissipation rates. For a rapidly rotating PNS with a spin period in milliseconds and with strong magnetic fields of 10{sup 15} G, the energy dissipation rate is estimated to exceed 10{sup 51} erg s{sup -1}. Our results suggest that the conventional magnetohydrodynamic (MHD) mechanism of core-collapse supernovae is likely to be affected by MRI-driven turbulence, which we speculate, on the one hand, could harm the MHD-driven explosions due to the dissipation of the shear rotational energy at the PNS surface; or, on the other hand, its energy deposition might be potentially favorable for the working of the neutrino-heating mechanism.« less
  • Core-collapse supernovae (CCSNe) are the final fate of the massive stars, but their explosion mechanisms are still uncertain. One of the clues to the solution of the explosion mechanism is to examine the asymmetric effects. This is because most of observed CCSNe are asymmetric explosions. One of the factors to the asymmetric explosions are the magnetorotational effects. The magnetic fields are amplified intensively along the rotational axsis during the collapse, and it leads to the bipolar outflows which may eject outer mantle. To understand the role of magnetorotational effects during CCSNe, we have developed a new multidimensional magnetohydrodynamic(MHD) code andmore » calculate collapse of a 25 M{sub {center_dot}} star with various magnetic field and rotational velocity.« less
  • We present results of new three-dimensional (3D) general-relativistic magnetohydrodynamic simulations of rapidly rotating strongly magnetized core collapse. These simulations are the first of their kind and include a microphysical finite-temperature equation of state and a leakage scheme that captures the overall energetics and lepton number exchange due to postbounce neutrino emission. Our results show that the 3D dynamics of magnetorotational core-collapse supernovae are fundamentally different from what was anticipated on the basis of previous simulations in axisymmetry (2D). A strong bipolar jet that develops in a simulation constrained to 2D is crippled by a spiral instability and fizzles in fullmore » 3D. While multiple (magneto-)hydrodynamic instabilities may be present, our analysis suggests that the jet is disrupted by an m = 1 kink instability of the ultra-strong toroidal field near the rotation axis. Instead of an axially symmetric jet, a completely new, previously unreported flow structure develops. Highly magnetized spiral plasma funnels expelled from the core push out the shock in polar regions, creating wide secularly expanding lobes. We observe no runaway explosion by the end of the full 3D simulation 185 ms after bounce. At this time, the lobes have reached maximum radii of ∼900 km.« less
  • We studied the role of turbulent resistivity in the core-collapse of a strongly magnetized massive star, carrying out two-dimensional resistive-MHD simulations. Three cases with different initial strengths of magnetic field and rotation are investigated: (1) a strongly magnetized rotating core, (2) a moderately magnetized rotating core, and (3) a very strongly magnetized non-rotating core. In each case, one ideal-MHD model and two resistive-MHD models are computed. As a result of these computations, each model shows an eruption of matter assisted by magnetic acceleration (and also by centrifugal acceleration in the rotating cases). We found that resistivity attenuates the explosion inmore » cases 1 and 2, while it enhances the explosion in case 3. We also found that in the rotating cases, the main mechanisms for the amplification of a magnetic field in the post-bounce phase are an outward advection of the magnetic field and a twisting of poloidal magnetic field lines by differential rotation, which are somewhat dampened down with the presence of resistivity. Although magnetorotational instability seems to occur in the rotating models, it plays only a minor role in magnetic field amplification. Another impact of resistivity is that on the aspect ratio. In the rotating cases, a large aspect ratio of the ejected matter, >2.5, attained in an ideal-MHD model is reduced to some extent in a resistive model. These results indicate that resistivity possibly plays an important role in the dynamics of strongly magnetized supernovae.« less