Explosion Mechanisms of Massive Stars

Abstract

One of the central problems in supernova theory is the question how massive stars explode. Understanding the physical processes that drive the explosion is crucial for linking the stellar progenitors to the final remnants and for predicting observable properties like explosion energies, neutron star and black hole masses, nucleosynthetic yields, explosion anisotropies, and pulsar kicks. In this article we review different suggestions for the explosion mechanism and discuss the constraints that can or cannot be deduced from observations. The prompt hydrodynamical bounce-shock mechanism has turned out not to work for typical stellar iron cores and empirical values of the compressibility of bulk nuclear matter. Magnetohydrodynamical models on the other hand contain a number of imponderabilities and are still far behind the level of refinement that has been achieved in nonmagnetic simulations. In view of these facts the neutrino-driven mechanism must still be considered as the standard paradigm to explain the explosion of ordinary supernovae, although its viability has yet to be demonstrated convincingly.Since spherically symmetric models do not yield explosions, the hope rests on the helpful effects of convection inside the nascent neutron star, which could boost the neutrino luminosity, and convective overturn in the neutrino-heated region behind the stalled shock, which increases the efficiency of neutrino-energy transfer in this layer. Here we present the first two-dimensional simulations of these processes which have been 1

Two-dimensional hydrodynamic core-collapse supernova simulations with spectral neutrino transport

“…Its action can clearly be seen in particular if neutrino heating is too weak to drive strong postshock convection. In agreement with the adiabatic models of Foglizzo (2001Foglizzo ( , 2002 and Blondin et al (2003), Scheck et al (2004) find highest growth rates for low (l = 1, 2) modes, which produce large, global asymmetries of the supernova explosion and might explain the observed pulsar kick velocities and grossly asymmetric distribution of elements seen in supernova remnants like Cassiopeia A (see Janka et al 2005c).…”

Self-Sustained Asymmetry of Lepton-Number Emission: A New Phenomenon During the Supernova Shock-Accretion Phase in Three Dimensions

“…This effect expands the shock, increases the gain layer and, again, can enhance the efficiency of neutrino-energy deposition ) even when convection is weak or its growth is suppressed because of a small shock-stagnation radius and correspondingly fast infall velocities in the gain layer (Foglizzo, Scheck, & Janka 2006;Scheck et al 2008). This nonradial instability was first observed in 2D simulations with a full 180 • grid Mezzacappa et al 1998;Janka et al 2003Janka et al , 2004, but not immediately recognized as a new effect beyond large-scale convection. It was unambiguously identified in 2D hydrodynamical simulations of idealized, adiabatic (and thus non-convective) postshock accretion flows (Blondin, Mezzacappa, & DeMarino 2003).…”

Neutrino Burst from Supernovae and Neutrino Oscillation

“…35,36) These simulations predict less average-energy differences between flavors compared to those of the Livermore group: E x =E e $ 1:4, 35) 1.7, 36) E x =E " e e $ 1:1, 35) 1.3, 36) where E e ; E " e e , and E x are the average energies of e ; " e , and x , respectively. To see the effect of the uncertainties in the temperature differences on our analysis, we perform similar analyses varying x temperature as stated below and fixing e and " e temperatures.…”