Stellar Iron Core Collapse in 3+1 General Relativity and The Gravitational Wave Signature of Core-Collapse Supernovae

Core-Collapse Supernovae are nature’s grandest explosions, liberating ∼ 1053 erg, the colossal gravitational binding energy of a neutron star. Most of this energy, 99%, is emitted in neutrinos, 1% goes into the asymptotic explosion energy and becomes visible in the electromagnetic spectrum, and a tiny fraction, perhaps less than a millionth, is radiated in gravitational waves. The work presented in this dissertation is concerned with the gravitational wave signature of corecollapse supernovae. Previous studies have identified rotating iron core collapse, core bounce and protoneutron star (PNS) ring-down pulsations, postbounce convection, anisotropic neutrino emission and postbounce nonaxisymmetric rotational instabilities as the primary processes and phases for the radiation of gravitational waves. I perform the first ever calculations of rotating stellar iron core collapse in {3+1} general relativity (GR) that start out with presupernova models from stellar evolutionary calculations and include a microphysical finite-temperature nuclear equation of state, an approximate scheme for electron captures during collapse and neutrino pressure effects. Based on the results of theses calculations, I obtain the to-datemost realistic estimates for the gravitational wave signal from collapse, bounce and early postbounce phases of core-collapse supernovae. My results show that (1) the collapse, bounce and early postbounce gravitational wave signal morphology is much more generic than previously estimated, (2) that the relevance of rotational effects is much smaller than thought and that rotational “multiple” core bounce does not occur in the range of physically plausible initial rotation rates and degrees of differential rotation, and (3) that all considered iron core rotational configurations undergo collapse, bounce and PNS ring-down in axisymmetry and none of these models reach ratios of rotational kinetic to gravitational potential energy (β = T/|W|) sufficiently high to experience a classical MacLaurin-type bar-mode instability at high-T/|W|. However, I find and analyze the development of nonaxisymmetric structures with a dominant m = 1 component that grow in a number of models due to a low-T/|W| dynamical rotational instability and whose quadrupole components lead to prolonged narrow-band gravitational wave emission, significantly enhancing the gravitational wave signature of rapidly rotating iron core collapse. I supplement my {3+1} GR simulations of rotating iron core collapse with 2D Newtonian neutrino radiation-hydrodynamic supernova calculations focussing on: (1) The late-postbounce gravitational wave emission in models of core-collapse supernovae with slowly or nonrotating progenitor cores. I find that the dominant emission process in such models may be the oscillations of the PNS core that are of predominantly g-mode character and that are excited hundreds of milliseconds after bounce and typically last for several hundred milliseconds while emitting strong gravitational waves in a narrow frequency band. (2) The gravitational wave emission in accretion induced collapse (AIC) of massive O/Ne/Mg white dwarfs to neutron stars, based on the first AIC calculations starting with rapidly rotating 2D equilibrium models. I find that efficient electron capture leads to rapid collapse largely unaffected by rotational effects, but owing to very small inner cores, to only modest gravitational wave emission from core bounce and PNS ring-down despite strong rotational flattening. At postbounce times the gravitational wave emission is dominated in amplitude by the low-frequency emission associated with rotation-induced anisotropies in the neutrino radiation fields. Based on my results I surmise that the gravitational wave emission from rapidly rotating iron core collapse and AIC events should be detectable already by initial LIGO-class observatories throughout the Milky Way and with advanced LIGO-class observatories throughout the Milky Way and the Magellanic Clouds. If persistent nonaxisymmetric deformations occur, detection to distances out to the Virgo Cluster may be marginally possible. Nonrotating or slowly rotating core collapse does not lead to a detectable gravitational wave signal from core bounce, but gravitational waves from postbounce convection and shock deformationsmay be detectable by advancedLIGOs. Initial LIGOs would detect strong PNS core oscillations throughout the Milky Way and beyond. Erratum as of April 2, 2007 • Section 2.4. 1, page 15. Discussion of equation (2.13). The terms dt̂ and dx̂ are imprecisely described as “physical time” and “physical distance”. The more precise description of dx̂ =