The Evolution and Explosion of Massive Stars Nuclear Physics Issues S. E. Woosley, A. Heger, T. Rauscher, and R. Hoffman http://www.supersci.org
We study nuclear astrophysics because: The origin of the elements is an interesting problem Nuclear transmutation (and gravity) are the origin of all stellar energy generation. Nuclear physics determines stellar structure. We can use that understanding as a diagnostic ... of the Big Bang of stellar evolution of nova and supernova explosions of x-ray and γ -ray bursts of particle physics of the evolution of galaxies and the universe
What is a massive star? Stars are gravitationally confined thermonuclear reactors. Each time one runs out of one fuel, contraction and heating ensue, unless degeneracy is encountered. For a star over 8 solar masses the contraction and heating continue until an iron core is made that collapses.
The advanced burning stages are characterized by multiple phases of core and shell burning. The nature and number of such phases varies with the mass of the star. Each shell burning episode affects the distribution of entropy inside the helium core and the final state of the star (e.g., iron core mass) can be non-monotonic and, to some extent, chaotic. Neutrino losses are higher and the central carbon abundance lower in stars of higher mass.
Iron core collapse triggers a catastrophe. The star at death is typically a red supergiant with a highly evolved, compact core of heavy elements.
Burrows, Hayes, and Fryxell, (1995), ApJ , 450 , 830 15 Solar masses – exploded with an energy of order 10 51 erg. Paper: see also Janka and Mueller, (1996), A&A , 306 , 167 Thursday - Janka
Fryer and Warren (2002) First three-dimensional calculation of a core-collapse 15 solar mass supernova. This figure shows the iso-velocity contours (1000 km/s) 60 ms after core bounce in a collapsing massive star. Calculated by Fryer and Warren at LANL using SPH (300,000 particles). The box is 1000 km across. 300,000 particles 1.15 Msun remnant 2.9 foe 1,000,000 “ 1.15 “ 2.8 foe – 600,000 particles in convection zone 3,000,000 “ in progress
π σ = ≈ 3 4 51 4 / 3 r T Explosion energy 10 erg Explosive Reprocessing
Rauscher, Heger, Woosley, and Hoffman (2002) 15 M � Papers: nb. 62 Ni Tuesday: Heger Limongi Maeda Thursday: Nomoto
Rauscher, Heger, Woosley, & Hoffman (2002) 25 M �
``There is something fascinating about science. One gets such a wholesale return of conjecture out of such a trifling investment of fact.” Mark Twain in Life on the Mississippi As cited at the beginning of Fowler, Caughlan, and Zimmerman, ARAA , 13, 69, (1975)
PROBLEMS PARTICULAR TO NUCLEAR ASTROPHYSICS Papers: • Both product and target nuclei are frequently Tuesday: radioactive Motobayashi Thielemann • Targets exist in a thermal distribution of Wednesday excited states Kaeppeler • There are a lot of nuclei and reactions Thursday Schatz Goriely (tens of thousands) Kajino • Need weak interaction rates at extreme values Friday Smith of temperature and density Rauscher
Specific Nuclear Uncertainties: (massive stars only) • Photodisintegration rates for • 12 C( α,γ ) 16 O heavy nuclei for the γ− process – • 22 Ne( α ,n) 25 Mg Mohr, Utsunomiya • Mass excesses and half lives • 12 C(n, γ ) 13 C, 16 O(n, γ ) 17 O and for the r -process other 30 keV (n, γ ) cross sections • Reaction rates affecting the • Neutrino spallation of 4 He, 12 C, nucleosynthesis of radioactive 16 O, 20 Ne, La, Ta nuclei: 22 Na, 26 Al, 44 Ti, 56,57 Ni, 60 Co • Weak rates for the iron group -Diehl • The nuclear EOS for core collapse • Rates for the rp -process in proton- supernovae – Session 11 rich winds of young neutron stars • Electron capture rates at high • Hauser-Feshbach rates for A > 28 densities ( ρ ~ 10 11 – 10 13 ) for very heavy nuclei in core collapse (A up to several hundred)- Langanke
12 C(a, γ ) 16 O Papers: Tuesday Fey Posters: A18 Fynbo A32 Makii A47 Sagara A62 Tsentalovich
dY α = − ρ 2 3 λ 3 Y / 6 α α 3 dt 12 dY ( C) = ρ 2 3 λ − ρ 12 λ 12 Y / 6 Y ( C) Y ( C) α α α α γ 3 , dt 16 dY ( O) = ρ 12 λ 12 Y ( C) Y ( C) α α γ , dt
* Buchmann (1996) Heger, Woosley, & Boyse (2002)
Heger, Woosley, & Boyse (2002) current uncertainty 1.4 - 1.8 M �
Heger, Woosley, & Boyse (2002) uncertainty
CF88
Papers: Monday Sneden Aoki Wednesday Kaeppeler Galino Posters: A64 – Zhang B02 – Tomyo B03 – Tomyo B09 – Sonnabend
Kaeppeler et al. 1994, ApJ , 437 , 396
22 Ne(a,n) 25 Mg Jaeger et al. 2001, PRL , 87 , 30 2501
25 M �
62 Ni (n, γ ) 63 Ni ± Bao & Kaeppeler (1987) 35.5 4 mb ± Bao et al. (2000) 12.5 4 mb ± Rauscher and Gu ber (2002) 4 0.3 5 mb bigger is better .... Needs measuring. s-wave extrapolation is bad. Are there others? 40 K(n, γ ) 41 K (and 40 K(n,p) 40 Ar) ± Bao et al. (2000) 31 7 mb unmeasured ! (from Raus cher & Thielemann ) Potential C osmochronom eter !
Rauscher, Heger, Woosley, and Hoffman (2002) 15 M � nb. 62 Ni
12 C (n, γ ) 13 C ± µ Bao & Kaeppeler (1987) 0.2 0.4 b µ Reffo (1989 PC to Kaeppeler) ~20 b µ Macklin (1990) 3.2 to 14 b ± µ Nagai et al. (1991) 16.8 2.1 b ± µ Oshaki et al. (1994) 15.4 1.0 b Kikuchi et al. (1998) for higher T 16 O(n, γ) 17 O µ Allen & Macklin (1971) 0.2 b (also BK87 as used in WW95) µ Nagai et al. (1994: NIC5) 38 b ± µ Igashira et al. (1995) 3 4 b 4 58,59,60 Fe(n, γ ) 59,60,61 Fe Important for producing 60 Fe.
Solar Metallicity 25 M � 16 γ 17 with and withou t O(n, ) O
Papers: Tuesday Thielemann Friday Rauscher
Hauser-Feshbach applicable for essentially all A>28 except near closed shells.
Hoffman et al., 1999, ApJ, 521, 735 In general, variation of the Hauser-Feshbach rates results in approximately less than a factor of two variation in the nucleosynthesis of A < 70, but there are exceptions. The agreement will not be nearly so good for A > 70 since these nuclei are made by processes that are out of equilibrium.
nb. Both sets of calculations used experimental rates below A = 28 and both sets employed (n γ ) rates that had been normalized, at 30 keV, to Bao and Kaepeller (1987).
(n γ ) Cross Sections at 30 keV
The ν -Process Papers: ÷ 53 L ~ 10 erg/s 6 per flavor ν Tuesday 56 o r about x 7 10 neutrinos per second Langanke Heger in each f lavor Thielemann Mean energy around 20 Mev Wednesday High e xcitation energy in the compound nucleu s Boyd ν → → 12 12 * 11 + C ( C) B + p µ τ , Thursday Janka → 11 C + n Poster ν 20 → 20 * → 19 + N e ( Ne) F + p µ τ , A41 – → 19 Ne + n Martinez-Pinedo etc. (possibly sensitive to ν flavor mixing)
25 M � ν − Process Kolbe & Langanke (2002) vs Haxton (1990) Heger, Langanke, & Woosley (2002)
T- and ρ -dependent weak interaction rates affect both nucleosynthesis and presupernova structure. ∝ 2 Chandrasekhar Mass Y e Prior to collapse weak interactions decrease ≈ Y form 0.5 to 0.42 e They also assist in the collapse a nd Papers: d ecrease th e entropy Tuesday Langanke Posters: A34 – Sampaio A38 – Messner B18 - Borzov
For LMP rates the capture is mostly 53,54,55,56 55 on Fe, Co, 56 and Ni. For FFN rates, conv Si burning 60 capture on Co dominates These rates should still be regarded as very uncertain
Different choices of rates can give quite different results for key quantities at iron core collapse. Most of the difference here comes from WW95 using beta decay rates that were way too small. Need to know rates on nuclei heavier than mass 60 at higher temperature and density than 10 10 .
The r -Process Papers: Monday Sneden Aoki Wednesday Nishimura Thursday Goriely Kajino Sumiyoshi Friday Ryan Takahashi Wanajo Posters: A52 Ishiyama A53 Ishikawa B36 – Ishimaru B38 - Honda B30 – Tamamura B31, B32 – Terasawa B33-Panov B39 - Otsuki
Need: • Binding energies (neutron-separation energies) along the r-process path • Temperature-dependent beta-decay half-lives along the r-process path • May need neutron-induced fission cross sections • May need ν -induced decay rates and ν neutral current spallation cross sections
r-Process Site #1: The Neutrino-powered Wind Anti-neutrinos are "hotter" than the neutrinos, thus weak equilibrium implies an appreciable neutron excess, typically 60% neutrons, 40% protons * favored sensitive to the density (entropy) Nucleonic wind, 1 - 10 seconds
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