τ coll 10 V ff g cm 3 Core collapse triggered by K-captures, photodissociation 1000 km Collapse (only core inner ~1.5 MO) Free-fall 1010 g cm-3

Transcription

1 Core collapse triggered by Collapse (only core inner ~1.5 MO) Free-fall K-captures, photodissociation 1000 km 1010 g cm-3 30 km nuclear dens. ~ 1014 g cm-3 Bounce Shock wave Nuclear repulsion Collapse time scale Explosion V ~ 10 km s 4-1 R ρ 3 τ coll 10 V ff 10 1 g cm 3 1/ s

2 Neutrino scattering elastic scattering of free nucleons ν+n ν+n ν+p ν+p elastic scattering against nuclei (NC) ν + (Z,A) ν + (Z,A) inelastic scattering ν+e ν+e

3 Free nucleon scattering E 0 = = 0 4 me c cm Coherent scattering off bound nucleons E 1 Z Z = 0 A 1 4 sin W 1 16 A A me c [ ] sin W = E me c Mean free path [ A N X X nucleon 6A bound 1 ] 1 E MeV 1 cm

4 Mean free path E 5 = MeV 1 1 cm diffusion time scale (random walk) R t diff 3 c more exactly for spherical geometry 3R t diff c t diff E 10 MeV 11/3 s

5 t diff Typical energy E 10 MeV 1/3 E E F = MeV t diff s 11/3 MeV s t diff 40 31/ t dyn ν:s will be trapped in collapsing core above ~ 1011 g cm-3! Collapse adiabatic above trapping density γ ~ 4/3

6 Bounce Collapse (only core inner ~1.5 MO) Free-fall 1010 g cm-3 Nuclear repulsion 30 km nuclear dens. ~ 1014 g cm-3 Adiabatic index Bounce Shock wave Explosion V ~ 10 km s km

7 Collapse shock collapse Before bounce: Homologous inside sonic radius bounce

8 Explosion? Wilson 1974 collapse explosion Hillebrandt 1981 shock 1.4 MO bounce All lacking some essential physics! (neutrino transport, EOS, /3D.)

9 Success? Progenitor 11 MO Explosion Shock Collapse Neutron star Kitaura et al 006

10 Black holes in most cases! Shock Photodissociation of Fe 56 Fe + γ 13α + 4 n ν-losses Except for low mass stars (< 1 MO) shock stalls and collapse continues Rampp & Janka 000

11 Total energy = binding energy of neutron star E GM core Rn 53 ergs 3 10 Release time scale ν diffusion time scale τ diff 5 ρ s ρ nuclear Mean energy MeV Trapping equilibrium creation of all neutrino species

12 Neutrinos ν e p e n Also ~5 νs from Baksan E( ν e) ~ 6x105 ergs. Equal amounts of all 6 ν:s Etot ~ (3-4)x1053 ergs τ ~ 5 s Mean energy ~ 15 MeV

13 A history of failures Colgate & White neutrino heating Arnett, Bethe, Brown, Wilson EOS, neutrino transport prompt explosion. No! 198? J. Wilson Late neutrino heating Woosley, Nomoto: progenitor models: Fe core mass 1990 Janka, Burrows neutrino convection D, 3D Large scale instabilities, rotation, D, 3D

14 collapse ν-trapping bounce shock ν-heating Explosion, ν driven wind Janka et al 006

15 Delayed neutrino heating? νe + n e- + p J. Wilson + H. Bethe 1985 ν e + p e+ + n

16 Neutrino heating p e n n e p Heating rate H r = 4 c E E W r f E E de 3 c h f E = Dilution factor 1 ee / kt 1 1 W r = [1 1 R / r ] radius of 'neutrinosphere'

17 For cooling we need e Detailed balance i g =1 E Earlier p n f g i p i = g e = n e n e f p = E / c = E e p e pf p e E e / c p n E 1 = 0 p 4 me c e g f i p n = Ee me c

18 Cooling rate C r = 0 c 5 E f E de 3 c h me c kt C r = 0 5 h3 me c m c H r = [W r T T ] 0 5 h3

19 Net neutrino heating rate Temperature of nucleons set by energy loss due to photodiss. Fe to -particles ~ MeV/nucleon Gain radius m c H r = [W r T T ] h G M mp 3 = E bind k T r T MeV r7 1 R W r T H =C T R r 1/ 3

20 Convection in proto neutron star increases neutrino flux

21 A. Burrows

22 Windows Media Player

23 Latest ingredient: Large scale shock instabilities 0.05 s Accretion shock unstable to large scale modes l=1, SASI mechanism Standing Accretion Shock Instability Proto-neutron star oscillations excited by accretion? Scheck et al s

24

25 3 D simulation Scheck et al 006

26 Oscillations in proto-neutron star Burrows et al

27 Pulsar kicks Pulsars = isolated neutron stars: Space velocities up to 1000 km/s. Large scale anisotropy kicks high space velocities pulsar Guitar nebula

28 Pulsar spins Pulsars: Rotation periods 0 ms to ~10 s Spiral wave m = 1 pulsar spins Blondin & Mezzacappa

29 Asymmetries, element mixing common SN ejecta SN 1987A

30 Asymmetries, element mixing common Chandra Red = Si Blue = Fe Cas A (~ 340 years)

31 Explosive nucleosynthesis by shock wave neutron star Kifonidis et al r-process in neutrino driven wind during first seconds

32 n-capture (Z,A) + n (Z,A+1) + n-capture (Z,A+1) + n (Z,A+) + (Z,A) (Z+1,A+1) + e- + -decay Time scale for -decay seconds to days (short compared to evolutionary time scale) s-process: -decay before new n-capture r-process: new n-capture before -decay

33 r-process (Z,A) + n (Z,A+1) + n-capture (Z,A+1) + n (Z,A+) + (Z,A+) + n (Z,A+3) + neutron capture cross section decreases with N photodisintegration increases with N n-capture continues until equlibrium between n-capture = photodis. from this -decay (Z+1,A)

34 r-process Photodisintegration cross section large above magic n-numbers (N=8, 0, 8, 50, 8, 16, 184) pile up at magic n-numbers

35 r-process pile up at magic n-numbers

36

37 r-process

38 Site of r-process Needed: High density of neutrons during a short period Region close to neutron star during explosion ideal: High neutron density from inverse beta decays (K-captures) Many heavy seed nuclei from NSE (56Ni, 56Fe...) Correct abundance pattern? Not yet clear

39