1. Neutrinos and the deaths of Massive StarsSk
SN 1987a
Terascale Supernova Initiative is funded by DoE as part of the Scientific Discovery through Advanced Computing (SciDAC)
W.R. Hix (UTenn./ORNL)

2. Observing Supernova Neutrinos
SN 1987a
1045 W
W.R. Hix (UTenn./ORNL)

3. Textbook Supernova
W.R. Hix (UTenn./ORNL)

4. Neutrino Transport n-sphere is energy dependent.
Liebendörfer, Mezzacappa,
Thielemann, Messer, Hix & Bruenn 2001
Mezzacappa, Liebendörfer, Messer,
Hix, Thielemann & Bruenn 2001
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
but doesn’t produce explosions in spherical symmetry.
see also Rampp & Janka 2000 & 2002,
Thompson, Burrows & Pinto 2003
W.R. Hix (UTenn./ORNL)

5. Totani, Sato, Dalhed & Wilson 1998
Convection…
Enhances
Explosions
Totani, Sato, Dalhed & Wilson 1998
Proto-Neutron Star
(beneath neutrinospheres)
boosts neutrino
luminosities.
Herant, Benz, Hix, Fryer & Colgate 1994
Fryer & Warren 2002
Neutrino-Driven
(beneath stalled shock)
enhances efficiency and
boosts shock radius.
W.R. Hix (UTenn./ORNL)

6. Convection is no guarantee
Buras, Rampp, Janka
& Kifonidis 2003
Janka & Müller
1996
Mezzacappa,
Calder, et. al
1998
What Physics is missing?
W.R. Hix (UTenn./ORNL)

7. Neutrino Interactions:
Bruenn (1985) and improvements
e±/n capture on nucleons and n-nucleon elastic scattering
+ recoil & relativity (Reddy, Prakash & Lattimer 1998)
+ weak magnetism (Horowitz 2002)
+ correlations (Burrows & Sawyer 1997, Reddy, Prakash, Lattimer & Pons 1999)
n-electron scattering / pair production / nn annihilation
+ nene  nm nm (Buras, Janka et al 2003)
+ Bremsstrahlung (Hannestad & Raffelt 1998, Thompson, Burrows & Horvath 2000)
+ Plasmon decay (Schinder & Shapiro 1982)
e-/n capture on nuclei and n-nucleus elastic scattering
+ Inelastic Scattering (Bruenn & Haxton 1991, Juodagalvis et al. 2004)
+ Electron capture (Langanke & Martinez-Pinedo 2000, Langanke et al. 2003)
W.R. Hix (UTenn./ORNL)

8. Captures on Nuclei a la Bruenn (1985)
EOS (Lattimer & Swesty 1991) identifies average heavy nucleus
e- and n capture via generic 1f7/21f5/2 GT transition (Bethe et al 1979), quenched at N=40, with Q=mn-mp-3 MeV
b-decay suppressed by large me
W.R. Hix (UTenn./ORNL)

9. Needed Electron Capture Rates
Nuclei with A>120 are present in collapsing core.
W.R. Hix (UTenn./ORNL)

10. Nuclear Electron Capture Rates
Shell Model calculations are currently limited to 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)

11. Theory is nice, but … experimental verification is needed
Spallation Neutron Source
-SNS, an experimental program to study neutrino cross sections in the region of interest for astrophysics
~1015  sec-1
2 universal ~ 20 tones detectors located 20 meters from the SNS target
Segmented detector for solid targets
51V, 27Al, 9Be, 11B, 52Cr, 56Fe, 59Co, 209Bi, 181Ta
Homogeneous detector for Liquid targets
2d, 12C, 16O, 127I
W.R. Hix (UTenn./ORNL)

12. 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)

13. 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)

14. Changes in Neutrino Emission
ne burst slightly delayed and prolonged.
15% boost in ne luminosity over 50 ms after bounce, other luminosities minimally affected (~1%).
Mean n Energy 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)

15. Convection in context
Fluid instabilities which drive convection result from complete neutrino radiation-hydrodynamic problem.
Hix, Messer, Mezzacappa, et al ‘03
Example:
Updated nuclear e- capture inhibits PNS convection.
W.R. Hix (UTenn./ORNL)

16. Discussion
Spherically symmetric models, even with full Boltzmann transport, fail to explode.
Convection aids, but does not guarantee, explosions.
Improvements in microscopic physics (e.g. nuclear electron capture, oscillations) can significantly change supernova evolution.
Only multi-D models with complete (weak/nuclear, n transport, EOS, magnetic?) physics will determine tell us how massive stars really die.
W.R. Hix (UTenn./ORNL)

17. What about Neutrino Oscillations?
Exchange of ntne could have beneficial effect by increasing mean neutrino energy and therefore the heating rate.
Measured mass difference implies oscillations occur well above heating region.
More exotic scenarios (e.g. active-sterile or active-active) remain under investigation.
Mezzacappa & Bruenn 1999
W.R. Hix (UTenn./ORNL)

18. 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”.
Messer, Hix, Liebendörfer & Mezzacappa ‘03
Is this due to physics or our approximation?
W.R. Hix (UTenn./ORNL)

19. Approaches to Nuclear Composition
Thomas-Fermi
free nucleons, a particles,
and a heavy nucleus
Nuclear Saha Equation
All nuclei for which mass
and partition function are
available
Strengths
Not limited by available nuclear data
Transitions easily to nuclear matter
Provides detailed composition
Transitions easily to non NSE regions
Need Both!
W.R. Hix (UTenn./ORNL)