Neutrinos and the deaths of Massive Stars

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Neutrinos and the deaths of Massive Stars
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Observing Supernova Neutrinos
1045 W
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Textbook Supernova
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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
but doesnt produce explosions in spherical
symmetry.
see also Rampp Janka 2000 2002, Thompson,
Burrows Pinto 2003
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Convection
Enhances Explosions

• Proto-Neutron Star
• (beneath neutrinospheres)

boosts neutrino luminosities.

• Neutrino-Driven
• (beneath stalled shock)

enhances efficiency and boosts shock radius.
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Convection is no guarantee
What Physics is missing?
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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)
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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 N40,
  with Qmn-mp-3 MeV
• b-decay suppressed by large me

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Needed Electron Capture Rates
Nuclei with Agt120 are present in collapsing core.
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Nuclear Electron Capture Rates
Shell Model calculations are currently limited to
A65. Langanke et al (2003) have employed a
hybrid of shell model (SMMC) and RPA to calculate
a scattering of rates for Alt110.
Langanke et al (2003)
Electron capture on heavy nuclei remains
important throughout collapse.
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Theory is nice, but experimental verification
is needed
?-SNS, an experimental program to study neutrino
cross sections in the region of interest for
astrophysics
Spallation Neutron Source
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
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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
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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.
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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).
Hix, Messer, Mezzacappa, et al 03
Mean n Energy altered 1-2 MeV during collapse 1
MeV up to 50ms after bounce .3 MeV at late time
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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.
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Discussion
Spherically symmetric models, even with full
Boltzmann transport, fail to explode. Convection
aids, but does not guarantee, explosions. Improvem
ents 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.
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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
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Electron Capture Puzzle
New progenitor models with reduced neutronization
made little difference in collapse
behavior. e-/n capture on nuclei cease for Agt65,
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?
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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
Provides detailed composition Transitions easily
to non NSE regions
Not limited by available nuclear data Transitions
easily to nuclear matter
Need Both!