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Supernova Collapse Dynamics

Supernova Collapse Dynamics. Wolfgang Bauer Michigan State University. Pre-collapse dynamics Kinetic theory for collapse Similarities to nuclear dynamics simulation. Nassau. Declared victory in search for fragmentation critical point properties. Supernova Explosion. After.

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Supernova Collapse Dynamics

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  1. Supernova Collapse Dynamics Wolfgang Bauer Michigan State University • Pre-collapse dynamics • Kinetic theory for collapse • Similarities to nuclear dynamics simulation W. Bauer, Breckenridge 03

  2. Nassau • Declared victory in search for fragmentation critical point properties W. Bauer, Breckenridge 03

  3. Supernova Explosion After • Galaxy NGC3310 Supernova 1991N Before Typical light curve N.A.Sharp, G.J.Jacoby/NOAO/AURA/NSF W. Bauer, Breckenridge 03

  4. Supernova Remnants • Cassiopeia supernova remnant observed in X-rays (Chandra), 10,000 light years from Earth • Color composite of supernova remnant E0102-72:  X-ray (blue), optical (green), and radio (red) W. Bauer, Breckenridge 03

  5. Crab Nebula Hubble • 6500 light years from here • Supernova in 1054 • Visible in broad daylight for several weeks • Left behind neutron star the size of Manhattan Chandra / Hubble Hubble W. Bauer, Breckenridge 03

  6. Supernovae • Type 1 • White dwarf exceeds its Chandrasekhar Mass (~1.4 M) due to accretion and collapses • Type 2 • Powered by gravitational energy released during star’s late stage iron core collapse • Mass range 11 M to 40 M at ZAMS (zero age main sequence; mass of star at start of its evolution) • Type 2 has hydrogen lines, type 1 does not • Here: focus on type 2 and use M=15 M W. Bauer, Breckenridge 03

  7. Stellar Evolution • Conventional stellar energy production via hydrogen fusion (t~107y for 20 M) • Late stages of evolution • Triple alpha process (t~ 106y) • Burning of C (t~300y), Ne, O (t~6months), Si (2days) occurs successively in the center of the star (higher and higher T) • Final products: 56Ni, 56Fe or 54Fe (iron core mass typically 10%) W. Bauer, Breckenridge 03

  8. Initial Conditions for Core Collapse Iron Core Woosley, Weaver 86 W. Bauer, Breckenridge 03

  9. Instabilities and Onset of Collapse • Electron Capture (dominant for ZAMS < 20 M) • Reaction • Reduced electron fraction and therefore decrease stabilizing electron pressure • Neutrinos carry entropy and energy out of star • Photodisintegration (dominant for ZAMS > 20 M) • Reactions • Also reduce temperature and therefore pressure W. Bauer, Breckenridge 03

  10. W. Bauer, Breckenridge 03

  11. Supernova Nucleosythesis Mezzacappa W. Bauer, Breckenridge 03

  12. 2D Hydro Simulations • Strong convection effects • Turbulence Mezzacappa et al. (98) W. Bauer, Breckenridge 03

  13. 3d • Explosion energy 3foe • texpl = 0.1 - 0.2 s • Fryer, Warren, ApJ 02 • Very preliminary • Similar convection as seen in their 2d work W. Bauer, Breckenridge 03

  14. Hydro Simulations • Tough problem for hydro • Length scales vary drastically in time • Multiple fluids • Strongly time dependent viscosity • Very large number of time steps • Special relativity, causality, … • Huge magnetic fields • 3D simulations needed • Giant grids W. Bauer, Breckenridge 03

  15. Simulations of Nuclear Collisions • Hydro, mean field, cascades • Numerical solution of transport theories • Need to work in 6d phase space => prohibitively large grids (203x402x80~109 lattice sites) • Idea: Only follow initially occupied phase space cells in time and represent them by test particles • One-body mean-field potentials (r, p, t) via local averaging procedures • Test particles scatter with realistic cross sections => (exact) solution of Boltzmann equation (+Pauli, Bose) • Very small cross sections via perturbative approach • Coupled equations for many species no problem • Typically 100-1000 test particles/nucleon W. Bauer, Breckenridge 03

  16. Example • Density in reaction plane • Integration over momentum space • Cut for z=0+-0.5 fm W. Bauer, Breckenridge 03

  17. Momentum Space • Output quantities (not input!) • Momentum space information on • Thermalization & equilibration • Flow • Particleproduction • Shown here:localtemperature W. Bauer, Breckenridge 03

  18. Try this for Supernovae! • 2 M in iron core = 2x1057 baryons • 107 test particles => 2x1050 baryons/test particle  • Need time-varying grid for (non-gravity) potentials, because whole system collapses • Need to think about internal excitation of test particles • Can create n-test particles and give them finite mean free path => Boltzmann solution for n-transport problem • Can address angular momentum question W. Bauer, Breckenridge 03

  19. Numerics • Test particle equations of motion • Nuclear EoS evaluated on spherical grid • Newtonian monopole approximation for gravity W. Bauer, Breckenridge 03

  20. Equation of State • Low density: • Degenerate e-gas • High density • Dominated by nuclear EoS • Isospin term in nuclear EoS becomes dominant, Ye~0.4 • High density neutron rich EoS can be explored by GSI upgrade and/or RIA W. Bauer, Breckenridge 03

  21. Electron Fraction, Ye • Strongly density dependent • Neutrino cooling W. Bauer, Breckenridge 03

  22. Internal Heating of Test Particles • Test particles represent mass of order Mearth. • Internal excitation of test particles becomes important for energy balance W. Bauer, Breckenridge 03

  23. Neutrinos • Neutrinos similar to pions at RHIC • Not present in entrance channel • Produced in very large numbers (RHIC: 103, here 1056) • Essential for reaction dynamics • Different: No formation time or off -shell effects • Represent 10N neutrinos by one test particle • Populate initial neutrino phase space uniformly • Sample test particle momenta from a thermal dist. • Neutrino test particles represent “2nd fluid”, do NOT escape freely (neutrino trapping), and need to be followed in time. W. Bauer, Breckenridge 03

  24. Neutrino Test particles • Move on straight lines (no mean field) • Scattering with hadrons • NOT negligible! • Convolution over all sAnA2 (weak neutral current) • Resulting test particle cross section angular distrib.:scm(qf) = d(qf-qi) • Center of mass picture: Pn,i pN,i Pn,f pN,f => Internal excitation W. Bauer, Breckenridge 03

  25. Effects of Angular Momentum W. Bauer, Breckenridge 03

  26. Results • “mean field” level • 1 fluid: hadrons W. Bauer, Breckenridge 03

  27. r0 Initial conditions After 2 ms After 3 ms Core bounce 1 ms after core bounce 120 km W. Bauer, Breckenridge 03

  28. Vortex Formation W. Bauer, Breckenridge 03

  29. Some Supernovae are Not Spherical! • 1987A remnant shows “smoke rings” • Cylinder symmetry, but not spherical • Consequence of high angular momentum collapse HST Wide Field Planetary Camera 2 W. Bauer, Breckenridge 03

  30. More Qualitative • Neutrino focusing along poles gives preferred direction for neutrino flux • Neutrinos have finite mass, helicity • Parity violation on the largest scale • Net excess of neutrinos emitted along “North Pole” • => Strong recoil kick for neutron star supernova remnant • => Non-thermal contribution to neutron star velocity distribution W. Bauer, Breckenridge 03

  31. The Man who did the Work Tobias Bollenbach (M.S. Thesis, MSU, 2002) Funding from NSF, Studienstiftung des Deutschen Volkes, and Alexander von Humboldt Foundation W. Bauer, Breckenridge 03

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