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SN 1987a Sk 202-69 Neutrino-Nucleus Interactions and the Core Collapse Supernova Mechanism W.R. Hix (UTenn./ORNL)
Weak reactions & Stellar Evolution Iron core mass and neutronization depend on e- capture and b decay rates for A<65 Heger, Woosley, Martinez-Pinedo & Langanke ‘01 New shell model rates reduce e- capture rates, decreasing the core neutronization W.R. Hix (UTenn./ORNL)
Messer, Hix, Liebendörfer & Mezzacappa ‘03 Electron Capture Puzzle New progenitor models with reduced neutronization made little difference in collapse behavior. e-/n capture on nuclei cease for A>65, allowing e- capture on protons to dominate. For these conditions, Yp is a strong function of Ye, so differences in Ye are “washed out”. Is this due to physics or our approximation? W.R. Hix (UTenn./ORNL)
EOS (Lattimer & Swesty 1991)identifies average heavy nucleus e- and n capture via generic 1f7/21f5/2 GTtransition (Bethe et al 1979), quenched at N=40, with Q=mn-mp-3 MeV b-decay suppressed by large me Captures on Nuclei a laBruenn (1985) W.R. Hix (UTenn./ORNL)
Messer, Hix, Liebendörfer & Mezzacappa ‘03 Testing the effects of e- Capture on Nuclei Replaced quenching term with parameter (NpNh) = 0.1-1000. Without quenching, e- capture on nuclei dominates until bounce. Significant impact (~.1 M) on the location of bounce shock formation. W.R. Hix (UTenn./ORNL)
Needed Electron Capture Rates Nuclei with A>120 are present in collapsing core. W.R. Hix (UTenn./ORNL)
Nuclear Electron Capture Rates Shell Model calculations are currently limited to 0hw in the pf shell (A~65). Langanke et al (2003) have employed a hybrid of shell model (SMMC) and RPA to calculate a scattering of rates for A<110. Langanke et al (2003) Electron capture on heavy nuclei remains important throughout collapse. W.R. Hix (UTenn./ORNL)
Approaches to Nuclear Composition Nuclear Saha Equation All nuclei for which mass and partition function are available Thomas-Fermi free nucleons, a particles, and a heavy nucleus Strengths Lighter computational requirement Transitions easily to nuclear matter Provides detailed composition Transitions easily to non NSE regions Need Both! W.R. Hix (UTenn./ORNL)
Effects of Nuclear Electron Capture during Core Collapse Constructed average capture rate using Saha-like NSE and Langanke et al (2003) rates. Compared to Bruenn (1985), results in more electron capture at high densities but less electron capture at low densities. Hix, Messer, Mezzacappa, et al ‘03 Reduces initial mass interior to the shock by 20% W.R. Hix (UTenn./ORNL)
Effects on Shock propagation Lepton and entropy gradients are altered. “Weaker” shock is faster. Hix, Messer, Mezzacappa, et al ‘03 Maximum excursion of the shock is 10 km further and 30 ms earlier. W.R. Hix (UTenn./ORNL)
Changes in Neutrino Emission ne burst slightly delayed and prolonged. Other luminosities minimally affected (~1%). • Mean nEnergy altered: • 1-2 MeV during collapse • ~1 MeV up to 50ms after bounce • ~.3 MeV at late time Hix, Messer, Mezzacappa, et al ‘03 W.R. Hix (UTenn./ORNL)
Convection in context Fluid instabilities which drive convection result from complete neutrino radiation-hydrodynamic problem. Hix, Messer, Mezzacappa, et al ‘03 Example: Updated nuclear electron capture inhibits proto-neutron star convection. W.R. Hix (UTenn./ORNL)
Martinez-Pinedo, Hauser, Hix, Liebendörfer, Mezzacappa & Thielemann ‘03 Neutrino Capture on Nuclei Recent multi-group neutrino transport simulations show decreased neutronization in the innermost ejecta. W.R. Hix (UTenn./ORNL)
Discussion • Modern treatment of nuclear electron capture significantly changes supernova evolution. • - Homologous Core reduced by 20% • - Neutrino Emission boosted 15% after bounce • - Slower collapse of outer layers allows shock to propagate further Only multi-D models with complete (weak/nuclear, n transport, EOS, magnetic?) physics will determine what the core collapse supernova mechanism is. This includes neutrino-nucleus interactions W.R. Hix (UTenn./ORNL)
Mezzacappa, Liebendörfer, Messer, Hix, Thielemann & Bruenn ’01 Liebendörfer, Mezzacappa, Thielemann, Messer, Hix & Bruenn ‘01 Neutrino Transport n-sphere is energy dependent. Neutrino distribution is nonthermal. Gray transport unreliable. Modeling of Energy Spectrum Required Shock revitalization occurs in the semi-transparent regime. Heating rate depends on n isotropy. Must also track n angular dist. Boltzmann Transport is Required W.R. Hix (UTenn./ORNL)
Neutrino Interactions: Bruenn (1985)and improvements e±/n capture on nucleons and n-nucleon elastic scattering + recoil & relativity(Reddy et al. ‘98) + weak magnetism(Horowitz ‘02) + correlations(Burrows & Sawyer ‘97, Pons et al. ‘99) n-electron scattering / pair production / nn annihilation + nene nm nm(Burras, et al ‘02) + Bremsstrahlung(Hannestad & Raffelt ‘98, Burrows et al. ‘00) + Plasmon decay(Schinder & Shapiro ‘82) e-/n capture on nuclei and n-nucleus elastic scattering + Inelastic Scattering(Bruenn & Haxton ‘91) W.R. Hix (UTenn./ORNL)
Convection… Fryer & Warren ‘02 Totani, Sato, Dalhed & Wilson ‘98 Herant, Benz, Hix, Fryer & Colgate ‘94 Enhances Explosions • Proto-Neutron Star (beneath neutrinospheres) boosts neutrino luminosities. • Neutrino-Driven (beneath stalled shock) enhances efficiency and boosts shock radius. W.R. Hix (UTenn./ORNL)
Convection is no guarantee Janka & Müller ‘96 Mezzacappa, Calder, et. al ‘98 W.R. Hix (UTenn./ORNL)
Stellar Evolution End Game Core collapse is the inevitable end of the life of a massive star. Question is which stars produce neutron stars (and supernovae) and which produce black holes. This division and the details of the explosions which result depend on their initial models Rauscher, Heger, Hoffman & Woosley ‘02 W.R. Hix (UTenn./ORNL)