Hirschegg Supernova core collapse. dynamics of core collapse. simple and efficient parameterization of deleptonization

Transcription

1 Hirschegg 2006 Supernova core collapse M. Liebendörfer University of Basel U.-L. Pen & C. Thompson Canadian Institut for Theoretical Astrophysics dynamics of core collapse simple and efficient parameterization of deleptonization three-dimensional simulations of collapse and bounce

2 Core collapse and bounce Velocity [km/s] 0 x t pb = -0.4 ms t pb = -0.2 ms t pb = -0.1 ms t pb = 0.0 ms Enclosed Mass [Msol] homologous core, subsonic infall, causal connection outside ~free infall, supersonic velocities, no outgoing waves bounce at nuclear densities shock formation at transition to supersonic infall

3 Core collapse and bounce log 10 (Density [g/cm 3 ]) Within 2-4 milliseconds after bounce: cool, bulk nuclear matter (1) shock formation hot, dissociated matter (2) infalling heavy nuclei neutrino losses Enclosed Mass [Ms] x Velocity [km/s] size of inner core determines initial shock strength dissociation losses neutrino losses shock turns into accretion front accretion front continues to expand due to accumulated hot matter

4 Deleptonization in collapse 10 2 m e m e - m n +m p t = 100 electrons provide pressure Energy [MeV] 10 1 t = 1 E n E equil. t = 10 free streaming diffusion trapped thermalization * average neutrino production most probable neutrino escape trajectory baryons subject to gravity electrons/baryon=:ye determines inner core size Ye evolves by diffusion/thermalization process in density/energy space Density [g/cm 3 ] (Martinez-Pinedo, Liebendörfer, Frekers 2004) it is a fairly 'local' transport problem

5 Postbounce phase Luminosity Accretion front accretion controls >50% of luminosity up- or downflow absorb and emit neutrinos differently Neutron star sphere Accretion Fluid instabilities luminosity controls the accretion rate => 3D nonlocal transport problem: leakage schemes beware! Buras et al. ( ) Livne et al. (2004) Walder et al. (2004) Cardall & Mezzacappa (2005) Fryer & Warren (2004) Myra & Swesty (2005)

6 Boltzmann neutrino transport Comparison of spherically symmetric simulations: Oak Ridge/Basel group and Garching group Liebendörfer, Rampp, Janka, Mezzacappa, ApJ 620 (2005) electronic edition: datafiles.tar.gz of simulations. excellent agreement: No explosions for progenitors >11 Msol! -> Transport approximations and GR effects not responsible for failures (Liebendörfer et al. 2001, Rampp & Janka 2002, Thompson et al. 2003) -> Technically complete and accurate GR solution in spherical symmetry (Bruenn et al., Rampp & Janka, Liebendörfer et al.) -> Useful to evaluate new input physics and transport approximations (Marek et al., A&A 2006)

7 Parameterization of neutrinos But the parameterization of the thermalization/diffusion in the collapse phase could be successful: Electron fraction model G15 in Liebendörfer et al Density [g/cm 3 ] r c = g/cm 3 r c = g/cm 3 r c = g/cm 3 r c = g/cm 3 r c = g/cm 3 r c = max the time dependence of the Ye-profile is very small! Electron fraction fitting formula: N13 data fit Density [g/cm 3 ] force hydrodynamics to follow given Yeprofile?

8 Parameterization of neutrinos Electron fraction ms ms 0ms +2ms Enclosed mass [M sol ] differences of 5% correlate with differences between bounce template and intermediate stages nice agreement at bounce neutrino burst not captured (Liebendörfer, ApJ 2005)

9 Parameterization of neutrinos Entropy per Baryon [k B ] ms -2ms 0ms +2ms (~10MeV) Enclosed mass [M sol ] information about deleptonization allows estimate for entropy changes at densities < 2x10^12 g/cm^3 trapping assumed at higher density similar agreement in evolution of entropy: cooling by neutrino burst not captured (Liebendörfer, ApJ 2005)

10 Parameterization of neutrinos x 10 4 influence of neutrino stress somewhat more difficult to estimate: 0 1 trapped neutrinos -> gas component Velocity [km/s] ms 2ms 0.2ms 0ms +2ms deleptonization gives luminosity estimate deleptonization in template at trapping density contains opacity information -> neutrino stress Enclosed mass [M ] sol (Liebendörfer, ApJ 2005)

11 More degrees of freedom Leblanc & Wilson 1979, Symbalisty 1984: Unphysically strong magnetic field leading to jets Akiyama et al. 2003, Ardeljan et al. 2004: Magnetic field growth until magnetic pressure becomes relevant Thompson, Quataert, Burrows 2005: Magneto-Rotational Instability as source of viscosity, leading to additional heating how restrictive is axisymmetry? convective turnover is always toroidal narrow downflow restricted to cones instead of tubes Kotake et al. 2004: Magentic field leading to asymmetries in the propagation of the shock front Burrows et al. 2005: Excitation of neutron star g-modes and shock heating by acoustic waves Shijie Zhong 2005

12 More degrees of freedom 3D MHD (Pen, Arras, Wong 2003) new parallelization: cubic domain decomposition divergence free magnetic field spherical effective general relativistic potential (Marek et al. 2006) ~10'000km 1D 600km 3D explicit MHD with neutrino parameterization 600x600x600 zones implicit hydro: Agile comparison with Boltzmann transport: Velocity [cm/s] x GR effective potential, no rotation, no magnetic fields 1D 3D Enclosed mass [Ms] velocity profiles electron fraction Lattimer-Swesty EOS Parameterization of weak interactions (Liebendörfer 2005) compare resolution to pixels on 600 laptop screens! Y e parameterization misses neutrino burst 1D Boltzmann 3D Enclosed mass [Ms]

13 Simulation setup Abs. magnetic field [G] 13 Msol progenitor (Nomoto & Hashimoto 1988) imposed rotation: Omega = 31 rad/s Ro = 100km poloidal qualitative! Density [g/cm 3 ] 0ms 10ms 20ms Abs. magnetic field [G] rather large initial magnetic field -poloidal -toroidal Bo ~ 10^12 G toroidal 0ms 10ms 20ms Density [g/cm 3 ] less winding qualitative! the following results belong to improved models 15 Msol Progenitor (Woosley & Weaver 1995) accurate collapse physics as described poloidal initial field rotation setup should be improved

14 3D MHD & parameterized n's

15 3D MHD & parameterized n's

16 3D MHD & parameterized n's

17 3D MHD without n-burst

18 3D MHD, incomplete n-cooling

19 3D MHD, incomplete n-cooling

20 Summary the deleptonization in the collapse phase is a fairly local thermalization/diffusion process it can be parameterized as a function of density from accurate simulations with Boltzmann neutrino transport implemented in 3D hydrodynamics, the collapse and bounce phase in spherical symmetry is accurately reproduced due to the new efficiency, 3D collapse simulations with magnetic fields become feasible the postbounce phase is more difficult to approximate, but a good glimpse at 3D dynamics with magnetic fields seems in reach (Hirschegg 2006)