Stellar Nucleosynthesis Charles Hyde 2 March 2009

Nucleosynthesis in Stars Great triumphs of 20th century physics –Discovery that sun, stars are mostly H –Explanation of nuclear fusion reactions powering sun Nuclear Binding Energy Quantum mechanics Weak interaction ( beta decay) –Neutrino flux from sun, Ray Davis, BNL (Cl detector in Homestake mine, SD) –Neutrinos from SuperNova Kamiokande Water Cerenkov detector: SN1987a

Nucleosynthesis in the 21st Century How exactly do Supernovae explode –Complex 3D hydrodynamics –Role of neutrino mass and oscillation? See next 10 years of accelerator and reactor based neutrino experiments Exact pathways for nucleosynthesis of elements heavier than Fe –FRIB project launched at MSU, Dec 2008 Exact understanding of nuclear masses from fundamental theory –Quark mass - Higgs mechanism? FermiLab, LHC –Proton mass, nuclear force from QCD Jlab, Lattice QCD, …

Nuclear Energy in Stars E=mc2 –Release of energy by fusion reactions Pp chain CNO chain Explosive nucleosynthesis

Stellar Hydrodynamics See Lectures, Prof. Bueltmann –Astrophysics in a Nutshell, Section 3.1 Temperature, Luminosity of sun from quantum black body emission Hydrostatic/Gravity equilibrium determines temperature / pressure profile of sun. Only mildly effected by profile of nucleo-synthesis (concentrated at temperature/pressure maximum at center)

Solar Properties Temperature –Surface T=5800K, kT = 0.5eV –Center 15  10 6 K. Mass 2  kg. Radius R=7  10 8 m. Density –Average = 1.4 g/cm 3. –Central = 150 g/cm 3. Total Luminosity 7  W. Gravitational potential energy released in collapse from infinity to R –GM 2 /(2R) = 2  J.

Possible Source of Solar Luminosity Gravitational collapse –Lifetime = [Potential Energy]/Luminosity –T = [2  J] / [7  W] = 1 yr Nuclear Fusion –Enough energy –Slow enough to sustain sun for > 10 9 years Reaction rate depends upon subtle details of nuclear physics

Nuclear Energy E=mc2. Atomic mass unit (u) –1 mole of 12 C defined to have a mass of 12 g (This defines Avogadro’s number = 6.02  ) –1 neutral 12C atom has a mass = 12u –1 u = (0.012 kg)c 2 /(12N A )=1.5  J –1eV = (1.6  C)(1V)= 1.6  J –1 u = 934  10 6 eV Nuclear Wallet cards –M(H) = 1u MeV –M(n) = 1u MeV –Mass( A Z) = A  (1u)+  ( A Z)  ( 12 C)=0

E=mc 2 Unstable to  -decay, fission Heats the earth Fe, Ni, Most stable nuclei Fusion of protons to 4He Drives the sun Nucleosynthesis in Supernovae explosions Nucleosynthesis in final stages of a star before Supernovae (or white dwarf)

Nuclear Fusion Reactions Energy release in fusing 6 p + 6 n  12 C. –6  (p) + 6  (n)  0 = 92,16 MeV released –Fractional energy release ≈ 1% Mass conservation violated at 1% level –Compare to chemical energy e  +p  H: Energy Release = (13 eV)/(938 MeV) ≈ 10 . Mass is conserved (parts per billion) in chemical reactions Energy Release in pp chain –HHHH  4 He –4  (p)-  ( 4 He) = 4(8.071 MeV)  (2.424 MeV)= 30 MeV