On the Nature of Core-Collapse Supernova Explosions

Abstract

We investigate in this paper the core-collapse supernova explosion mechanism in both one and two dimensions. With a radiation/hydrodynamic code based upon the PPM algorithm, we verify the usefulness of neutrino-driven overturn (\convection") between the shock and the neutrinosphere in igniting the supernova explosion. The 2-D simulation of the core of a 15M star that we present here indicates that the breaking of spherical symmetry may be central to the explosion itself and that a multitude of bent and broken ngers is a common feature of the ejecta. As in one-dimension, the explosion seems to be a mathematically critical phenomenon, evolving from a steady-state to explosion after a critical mass accretion rate through the stalled shock has been reached. In the 2-D simulation we show here, the pre-explosion convective phase lasted 30 overturns ( 100 milliseconds) before exploding. The pre-explosion steady-state in 2-D is similar to that achieved in 1-D, but, in 2-D, due to the higher dwell time of matter in the overturning region, the average entropy achieved behind the stalled shock is larger. In addition, the entropy gradient in the convecting region is atter. These e ects, together with the dynamical pressure of the buoyant plumes, serve to increase the steady-state shock radius (Rs) over its value in 1-D by 30%{100%. A large Rs enlarges the volume of the gain region, puts shocked matter lower in the gravitational potential well, and lowers the accretion ram pressure at the shock for a given _ M. The critical condition for explosion is thereby relaxed. Since the \escape" temperature (Tesc) decreases with radius faster than the actual matter temperature (T ) behind the shock, a larger Rs puts a larger fraction of the shocked material above its local escape temperature. T > Tesc is the condition for a thermally-driven corona to lift o of a star. In one, two, or three dimensions, since supernovae are driven by