Youhei Masada

Multimessengers from core-collapse supernovae: Multidimensionality as a key to bridge theory and observation

Core-collapse supernovae are dramatic explosions marking the catastrophic end of massive stars. The only means to get direct information about the supernova engine is from observations of neutrinos emitted by the forming neutron star, and through gravitational waves which are produced when the hydrodynamic flow or the neutrino flux is not perfectly spherically symmetric. The multidimensionality of the supernova engine, which breaks the sphericity of the central core such as convection, rotation, magnetic fields, and hydrodynamic instabilities of the supernova shock, is attracting great attention as the most important ingredient to understand the long-veiled explosion mechanism. Based on our recent work, we summarize properties of gravitational waves, neutrinos, and explosive nucleosynthesis obtained in a series of our multidimensional hydrodynamic simulations and discuss how the mystery of the central engines can be unraveled by deciphering these multimessengers produced under the thick veils of massive stars.

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

Neutrino radiation takes a major role in the momentum, heat, and lepton transports in proto-neutron stars (PNSs). These diffusive processes affect the growth of the magnetorotational instability (MRI) in PNSs. We perform a local linear analysis for the axisymmetric and nonaxisymmetric MRI including the effects of neutrino transport and ohmic dissipation. We find that the MRI can grow even in the multidiffusive situations that are realized in neutrino-loaded PNSs. When the toroidal magnetic component dominates over the poloidal one, nonaxisymmetric MRI modes grow much faster than axisymmetric modes. These results suggest the importance of the nonaxisymmetric MRI in PNSs. Thus, understanding the three-dimensional nonlinear evolution of the MRI is necessary for revealing the explosion mechanism of core-collapse supernovae.

LOCAL SIMULATIONS OF THE MAGNETOROTATIONAL INSTABILITY IN CORE-COLLAPSE SUPERNOVAE

Bearing in mind the application to core-collapse supernovae, we study nonlinear properties of the magneto-rotational instability (MRI) by means of three- dimensional simulations in the framework of a local shearing box approximation. By changing systematically 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 (

Nonaxisymmetric Magnetorotational Instability in Proto-Neutron Stars

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Effects of Penetrative Convection on Solar Dynamo

) and the shear- vorticity ratio (

Axisymmetric Magnetorotational Instability in Viscous Accretion Disks

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SCALING LAW OF RELATIVISTIC SWEET-PARKER-TYPE MAGNETIC RECONNECTION

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Dead Zone Formation and Nonsteady Hyperaccretion in Collapsar Disks: A Possible Origin of Short-Term Variability in the Prompt Emission of Gamma-Ray Bursts

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Two-dimensional Numerical Study for Rayleigh-Taylor and Richtmyer-Meshkov Instabilities in Relativistic Jets

with its index

EFFECT OF INTERACTING RAREFACTION WAVES ON RELATIVISTICALLY HOT JETS

\delta \sim 0.5