# Presentation: 250618

## Neutrino-Nucleus Interactions and the Core Collapse Supernova Mechanism 

**Notes:**
Terascale Supernova Initiative is funded by DoE as part of the Scientific Discovery through Advanced Computing (SciDAC)

## Weak reactions & Stellar Evolution

**Weak reactions & ****Stellar Evolution**

- Iron core mass and neutronization depend on e- capture and  decay rates for A<65

- Heger, Woosley, Martinez-Pinedo & Langanke ‘01

- New shell model rates reduce e- capture rates, decreasing the core neutronization

## Electron Capture Puzzle 

- New progenitor models with reduced neutronization made little difference in collapse behavior.
- e-/ 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?

## Captures on Nuclei a la Bruenn (1985)

- EOS (Lattimer & Swesty 1991) identifies average heavy nucleus
- e- and capture via generic 1f7/21f5/2 GT transition (Bethe et al 1979), quenched at N=40, with Q=n-p-3 MeV
- decay suppressed by large e

## 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.

## Needed Electron Capture Rates

- Nuclei with A>120 are present in collapsing core.

## Nuclear Electron Capture Rates

- Shell Model calculations are currently limited to 0*h* 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.

- Electron capture on heavy nuclei remains important throughout collapse.

- Langanke et al (2003)

## Approaches to Nuclear Composition

- Thomas-Fermi
-     free nucleons,  particles,
-     and a heavy nucleus

- Nuclear Saha Equation
-     All nuclei for which mass
-     and partition function are
-     available

- Provides detailed composition
- Transitions easily to non NSE regions

- Lighter computational requirement
- Transitions easily to nuclear matter

- Strengths

**Need Both!**

## 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.

- Reduces initial mass interior to the shock by 20%

- Hix, Messer, Mezzacappa, et al ‘03

## Effects on Shock propagation

- “Weaker” shock is faster.

- Lepton and entropy gradients are altered.

- Maximum excursion of the shock is 10 km further

- and 30 ms earlier.

- Hix, Messer, Mezzacappa, et al ‘03

## Changes in Neutrino Emission

- e burst slightly delayed and prolonged.
- Other luminosities minimally affected (~1%).

- Mean  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

## 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.

## Neutrino Capture on Nuclei

- Recent multi-group neutrino transport simulations show decreased neutronization in the innermost ejecta.

## Discussion

- This includes neutrino-nucleus interactions

- 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

## Slide 15

## Neutrino Transport

**Neutrino Transport**

- -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  isotropy.
- Must also track  angular dist.
- Boltzmann Transport is Required

## Neutrino Interactions:

- e±/ capture on nucleons and -nucleon elastic scattering
-     + recoil & relativity (Reddy et al. ‘98)
-     + weak magnetism (Horowitz ‘02)
-     + correlations (Burrows & Sawyer ‘97, Pons et al. ‘99)
- -electron scattering / pair production /  annihilation
-     + ee (Burras, et al ‘02)
-     + Bremsstrahlung (Hannestad & Raffelt ‘98, Burrows et al. ‘00)
-     + Plasmon decay (Schinder & Shapiro ‘82)
- e-/ capture on nuclei and-nucleus elastic scattering
-     + Inelastic Scattering (Bruenn & Haxton ‘91)

- Bruenn (1985) and improvements

## Convection...

** ****Neutrino-Driven **
**    ****(beneath stalled shock)**

**Enhances **
**    ****Explosions**

** ****Proto-Neutron Star **
**    ****(beneath neutrinospheres)**

**boosts neutrino **
**luminosities.**

**enhances efficiency and **
**boosts shock radius.**

**Convection...**

## Convection is no guarantee

- Janka & Müller ‘96

**Convection is no guarantee**

- Mezzacappa, Calder, et. al ‘98

## 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