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Supernovae, Their Collapsing Cores and Nuclear Physics

Supernovae, Their Collapsing Cores and Nuclear Physics. Nature of Supernova Progenitors Their sensitivity to nuclear properties How these properties are determined Ongoing experiments. Log Central Density. Woosley & Janke--Nature. Log Central Density.

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Supernovae, Their Collapsing Cores and Nuclear Physics

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  1. Supernovae, Their Collapsing Cores and Nuclear Physics Nature of Supernova Progenitors Their sensitivity to nuclear properties How these properties are determined Ongoing experiments Sam M. Austin Mitchell 4/14/06

  2. Log Central Density Woosley & Janke--Nature Log Central Density Evolution of Stellar Core for Heavy Stars Temperature vs Density After initial formation A gravitational collapse, interrupted by long nuclear burning stages. Eventually form “Fe”core, and no further nuclear energy available. Sam M. Austin Mitchell 4/14/06

  3. "Fe" core Collapses Bounce--Form Shock Wave Shock moves out Loses energy. Fe p's , n's in outer part of Fe core; neutrino emission Stalls Supernovae Core Collapse—The Mechanism Time Problem since Baade/Zwicky in 1930’s suggested SN powered by gravitational energy from collapse of normal star to neutron-star Sam M. Austin Mitchell 4/14/06

  4. Difficulty Of The Supernova Problem • Nature of the energetics—the 1% problem? • Only 1% of the available gravitational energy (1053 ergs) is emitted as explosion energy, rest as neutrinos. (Burrows argues it’s a 10% problem--90% of gravitational energy emitted prior to critical phase). But, either way, it may mean we have to do things very well. • What’s been tried • Delayed shock– re-energized by neutrinos from proto-neutron star Better neutrino transport, better weak interactions, 2 and 3-D (limitations), acoustic coupling, …… • A comment • Insufficient knowledge of nuclear physics properties causes changes at the 1-few% level • Dangerous to assume that the effects are always cancelled by negative feedback processes Scheck, Janka Sam M. Austin Mitchell 4/14/06

  5. An Example--Helium Burning WMU-MSU Rehm-ANL 10:10 Triple a makes 12C, 12C(a,g)16O turns it into 16O. Their ratio determines the amounts of C and O made and affects the nature of a star and of its iron core Sam M. Austin Mitchell 4/14/06

  6. 25 M Heger, Woosley, Boyes Fe Core Size (Solar Masses) 0.5 1.0 1.5 2.0 1.0 1.5 2.0 2.5 12C(a,g)16O Multiplier or 1/Triple alpha? SNII--Pre-collapse Fe Core Size • Pre-supernova evolution • Vary rate of 12C(a,g)16O (or Triple alpha)? • All else constant • Fe core mass changes by >0.2 M over the interesting range • Important? • Naively, yes. If homologous core mass constant, need 3 x 1051 erg to dissociate extra 0.2 M to nucleons (a,g) 160±40 keV b Brune 2006 3 alpha Fynbo 2006 Need ratio of rates to 10% Sam M. Austin Mitchell 4/14/06

  7. He Burning Core T=108 K r= 107 kg/m3 Element Production in a Supernovae Shell Burning The Result (Stellar Onion) When He is exhausted in the core the core collapses, T increases, core carbon and oxygen burning begin. H and He burning in shells • The successive core stages are H  He, gravity He  C,O, gravity C,O  Mg, Si--gravity, Si  Fe. SN blows off outer layers Need detailed element distribution/abundances to predict SN element production Sam M. Austin Mitchell 4/14/06

  8. Detailed Models-Heger and Woosley 2001 It’s more complex than the onion even in 1D:M= 22 Msun. Along the x-axis sequential episodes ofconvective carbon, neon, oxygen,and silicon burning. Affected by rates of He-burning reactions. Sam M. Austin Mitchell 4/14/06

  9. Heger, Woosley, Boyes 25 M Production Factor 12C(a,g)16O Multiplier (xBuchmann 1996) SNII Nucleosynthesis A=16-40 Explosion of 25 M star Vary rate of 12C(a,g)16O All else same Production Factor “Same” PF for 1.2 x standard 12C(a,g)16O rate 170 keV b Sam M. Austin Mitchell 4/14/06

  10. (n,p) (p,n) Weak Strength and Supernovae Core Collapse • Gamow-Teller (GT) Strength? • Mediates -decay, electron capture(EC), n induced reactions GT (allowed) Strength S=1; L = 0, e.g. 0+ 1+; GT+,GT- Lies in giant resonances Situation After silicon burning, Tcore3.3 x 109 K, density108 g/cm3. e- Fermienergy allows capture into GT+. Reduces e- pressure emits neutrinos. Speeds collapse. At higher T, GT+ thermally populated, - decays back to ground state. -  E.C. GT+ dominates process Sam M. Austin Mitchell 4/14/06

  11. 8 15 M ) 6 K 9 0 4 1 ( T T 2 0.50 WW 0.48 LMP e 0.46 Y 0.44 -3 10 ) -4 LMP-EC 1 10 - URCA s - ( LMP- -5 ½ ½ 10 ¾ e Y t -6 10 d d ¾ ½ ½ -7 10 -8 10 6 5 4 3 2 1 0 10 10 10 10 10 10 10 Time till collapse (s) Effects of Changed Weak Rates-Heger et al. Ap.J. 560 (2001) 307 11 IPM vs Shell Model WW standard Wallace-Weaver rates based on independent particle model (FFN) LMP-from large basis shell model calculations. (Langanke and Martinez-Pinedo) Significant differences Larger, lower entropy "Fe" pre-collapse core More e-'s (Ye larger), lower T core. Larger homologous core r Sam M. Austin Mitchell 4/14/06

  12. Important Electron Capture Nuclei Pre-Collapse:Nuclei in the Fe-Ni region Collapse: Heavier nuclei are important, including many with N>40 Sam M. Austin Mitchell 4/14/06

  13. Do (N>40) Nuclei Undergo Electron Capture? • Independent particle model: • No for N>40 • Transitions Pauli blocked • Shell model at finite T: Blocking removed—Has important effects From Martinez-Pinedo Sam M. Austin Mitchell 4/14/06

  14. Results of New Calculations--Langanke et al PRL Nature of calculations Shell model Monte Carlo + RPA Results Capture on nuclei dominates by x10 Neutrino energies are lower Mass enclosed by the shock is smaller by 0.1 Msun Shock is weaker Ye varies with enclosed mass Sam M. Austin Mitchell 4/14/06

  15. ? ? ? Reliability of Nuclear Models for e-Capture For pre-collapse calculations (Caurier, et al NPA 653, 439(99 : FFN (IPM) : data (n,p) (TRIUMF) : Caurier et al. (1999) Large basis SM : Caurier et al. folded with experimental resolution Quite good, some problems Further validation of models requires data for unstable isotopes especially odd-odd nuclei Sam M. Austin Mitchell 4/14/06

  16. Reliability of Nuclear Models for e-Capture-cont. • For heavier nuclei--less firmly based and not validated • General Comment • Can’t measure everything, 1000s of transitions, many from thermally excited states • But need to do enough checks to have confidence in models • Nature of measurements: Hadronic charge exchange reactions • Operators similar to b decay operator; (n,p), (d,2He), (t,3He) measure e-capture strength • B(GT) = sCEX(q = 0)/sunit , sunitcalibrated from known transitions • Accuracies in 10-20% range, better for strong transitions • Require energy of >100 MeV/nucleon to minimize 2-step processes • Reactions studied: In past (n,p), (d,2He), (t,3He); presently only (t,3He) Sam M. Austin Mitchell 4/14/06

  17. 90 Sherrill, et al 12 3 12 + 1 C(t, He) B 80 V o o Q ~ =0 1.7 e 70 lab M - 2 - 0 1 V 60 . 0 e V e M 50 M 5 160 keV . 40 Counts 7 4 . 7 30 20 10 0 90 12 3 12 + C(t, He) B 1 80 - - 2 1 V o o e V V ~ 70 e e M lab M M 0 60 Q =1.7 3.4 . 5 7 0 . . 50 4 7 230 keV 40 30 20 10 0 -2 0 2 4 6 8 10 12 E(MeV) Charge Exchange Options • (t, 3He) • Secondary triton beams 106-7/sec at MSU/NSCL, 115 MeV/A tritons • Resol: 160 keV achieved • Data on 24,26Mg, 58Ni, 63Cu, 94Mo Future (Zegers, et al.) Develop techniques for using radioactive beams: (p,n), (7Li, 7Be) in inverse kinematics to study b-decay, electron capture, respectively. Test (7Li, 7Be) expt in near future. Unique beam-spectrometer(S800), simple analysis, calibration from (3He, t) reaction at Osaka. More beam nice Sam M. Austin Mitchell 4/14/06

  18. (t,3He), (3He,t) vs (p,n) and Shell Model Sam M. Austin Mitchell 4/14/06

  19. Step I:a+a 8Be Equilibrium abundance of 8Be Step II:8Be + a12C(7.65) I Q1= -92 keV a + a Rate depends on properties of Hoyle state (7.65), mostly on Grad Hoyle state II r3aGrad(7.65)e-Q/kt Grad=Gg+Gp , -Q = Q1+Q2 Gp Q2= -287 keV a +8Be Gg Present Interests—3a and SNII (Iron core size, nucleosynthesis) 5% AGB Stars (Carbon production and carbon stars) 5% Limits on variation of “fundamental” constants Back to The Triple Alpha Process-More Formally Sam M. Austin Mitchell 4/14/06

  20. ( ) G + G G g p G = G + G = G g p p rad G G p  12% Ý Ý Ý 2.7% 9.2% 6.4%2.7% How Well Do We Know Grad Least well known quantity is G/Gp . A WMU, MSU collaboration is undertaking a new measurement: WMU Alan Wuosmaa, Jon Lighthall, Scott Marley, Nicholas Goodman MSU/NSCL Clarisse Tur, SMA Sam M. Austin Mitchell 4/14/06

  21. Top View PM PM Beam Beam PM PM PM PM Side View Liner Liner PM PM Plastic Plastic 12C Target Scint Scint Measuring Gp / G A hard measurement:Branch is small ~6 x 10-6 New measurement: WMU/MSU WMU Tandem,(p,p’) at 135o, 10.56 MeV (strong resonance for 7.65 state) Gp / G = (#-pairs/#-7.65protons) Aim: ± 5% accuracy Improved version of Robertson, et al PRC 15,1072(77) Sam M. Austin Mitchell 4/14/06

  22. WMU-MSU/NSCL Detector Sam M. Austin Mitchell 4/14/06

  23. Final Comments • Discussed two cases were nuclear uncertainties are important • Helium burning (expts on 12C(a,g) and 3alpha rates ongoing) • Electron capture (expts ongoing) • Others have not been much investigated • 12C+12C reaction rate poorly known—sensitivity of progenitor structure? • r-process nucleosynthesis could provide a diagnostic of conditions at its site—nuclear properties need to be better understood Sam M. Austin Mitchell 4/14/06

  24. Cocktail beam 78Ni Beta Lifetimes are important--Example: doubly magic 78Ni T1/2 measurement at NSCL r-process calculation Energy loss  velocity  Measured half-life of 78Ni with 11 events Acceleration of the r-process excess of heavy elements with the new shorter 78Ni half-life Result: 110 +100-60 ms (Theory: 460 ms) P. Hosmer et al. 2005 (NSCL, Mainz, Maryland collaboration) Sam M. Austin Mitchell 4/14/06

  25. Some Comments • Discussed two cases were nuclear uncertainties are important • Helium burning (expts on 12C(a,g) and 3alpha rates ongoing) • Electron capture (expts ongoing) • Others have not been much investigated • 12C+12C reaction rate poorly known—sensitivity of progenitor structure? • r-process nucleosynthesis could provide a diagnostic of conditions at its site—nuclear properties need to be better understood • 2D and 3D calculations of progenitor evolution • In their beginning phases • Will surely change the nature of the pre-SN star • Note: present 1-D models differ somewhat from group to group Sam M. Austin Mitchell 4/14/06

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