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STARS ARE A BALANCE OF GRAVITY AND CORE ENERGY FOR MOST OF THEIR LIFE

STARS ARE A BALANCE OF GRAVITY AND CORE ENERGY FOR MOST OF THEIR LIFE. STARS FORM FROM COLLAPSING MATERIAL THIS GIVES RISE FOR THE STARS, OF ENERGY COMING FROM THE RELEASE OF GRAVITATIONAL POTENTIAL ENERGY,U..IT CAN BE SHOWN THAT TYPICALLY CONTAINED IN A SPHERE OF RADIUS R

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STARS ARE A BALANCE OF GRAVITY AND CORE ENERGY FOR MOST OF THEIR LIFE

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  1. STARS ARE A BALANCE OFGRAVITY AND CORE ENERGY FOR MOST OF THEIR LIFE STARS FORM FROM COLLAPSING MATERIAL THIS GIVES RISE FOR THE STARS, OF ENERGY COMING FROM THE RELEASE OF GRAVITATIONAL POTENTIAL ENERGY,U..IT CAN BE SHOWN THAT TYPICALLY CONTAINED IN A SPHERE OF RADIUS R U = -(3/5) GM2/R SEE DERIVATION SECTION 9.1.1 (DON’T WORRY) GIVEN THE SUNS LUMINOSITY ALL THIS ENERGY WOULD BE EXPENDED IN 20 Million years (see section 9.1.2 Worry!) This is a very small lifetime in the cosmic scheme of things! Even chemical energy (OIL, COAL, GAS, ETC) Is not sufficient to account for the billions of years our Sun has existed based on the Earth’s , Moon and Meteoric determined ages.

  2. THERMAL ENERGY • THE THERMAL ENERGY WE SAW BEFORE IS (3/2) k T PER PARTICLE • N=#PARTICLES=M/m M=STAR MASS • M=HYDROGEN ATOM MASS • HENCE TOTAL THERMAL ENERGY IN STAR, K, IS • K =(3/2) NKT or • K= (3/2)(M/m) kT

  3. How Does the Stars Make Energy for their life cycle? Why a Steady Luminosity on the main sequence? Why does a Star change Dramatically in the later stages of it’s life? ANS= The NUCLEARFURNACE IN THE CORE! Planetary Nebula stellar DEATH! Some stars near the end are unstable And eject their Outer atmosphere

  4. 0 The Nuclei • Nuclei consist of a number of protons, Z, and Neutrons, N. We define the MASS Number as A = Z+N use notations for Atom AT are • A AT Z or AAT or AT-A Different numbers of neutrons↔ different isotopes • Isotopes have same Z but different A as 12C6 or 12C or C-12 and 13C or C-13 • This is the isotope • 4He2 or 4He Helium 4

  5. 0 NUCLEAR PHYSICS II NOTE 10-13J = 1 Mev Energy generation in the sun (and all other stars): Binding energydue to strong force= on short range, strongest of the 4 known forces:electromagnetic, weak,strong,gravitational Nuclear Fusion = fusing together 2 or more lighter nuclei to produce heavier ones. Nuclear fusion can produce energy up to the production of iron; For elements heavier than iron, energy is gained by nuclear fission.

  6. NUCLEAR PHYSICS I • Using Einstein’s E=mc2 if we add the energies of protons and neutrons and the the actual energy of the nucleus we find the latter is less. In other words in the assembly of the nucleus energy went into binding it, due to the Nuclear force,thus, the Binding Energy, BE • Mnucleus c2 +BE=Zmpc2 +Nmnc2 • BE = Zmpc2 + Nmnc2 -Mnucleus c2 • Recall 1eV=1.6 x 10 -12 erg • BE’s are measured in Mev and are easily found! • See Examples 9.1 and 9.2

  7. Nuclear ReactionsThe liberation of Binding Energy Reaction types that happen in the Nuclear world 3 Decays that release Energy! FISSION: BREAK APART OF NUCLEUS as in atomic reactors and bombs. FUSION: low mass nuclei build larger ones, as in stars a: Alpha: Large Nucleus emits 4He nuclei hence Z and A go down by ? Energy goes out as Kinetic in a b: Beta: np +e- +anti-u Z, N and A ?? g: Gamma: Nucleus goes from higher energy state to lower emits this E&M Radiation( a way of seeing into the nucleus! Also H-bomb and on a small scale in the laboratory

  8. Star Power Nuclear Fusion Reactions This reaction by astrophysics defines a Star! Coulomb OR FUSION barrier IS OVERCOME with? Note: u leaving! T=20,000,000 K Don’t worry You’ll meet A nice electron And Annihilate Each other Note: pn +e+ +u Needs energy ie: mn >mp 2H

  9. Positron Star Power by Proton-Proton chain conversion of H to He FUSION Deuterium 1H + 1H -> 2H + e+ + neutrino FUSION 2H + 1H -> 3He +Gamma Neutrino? Proton Hey Protons are leaving Helium 3 Gamma ray FUSION Helium 4! 3He + 3He -> 4He + 1H + 1H

  10. Proton-proton chain 1H + 1H -> 2H + e+ + neutrino 2H + 1H -> 3He +Gamma ray 3He + 3He -> 4He + 1H + 1H Net Fusion Reactions in the Sun NOTE 6 H -> 1 He and 2 H’s or….. 4 1H -> 4He +ENERGY 4 hydrogen nuclei = 6.693 x 10-27 Kg=4mp 1 helium 4 nucleus = 6.645 x 10-27 Kg= m(4He) Missing mass ? = Energy released via E = m c 2 4mp - m(4He) = 0.007 4mp equation 9.18 Our Sun requires 1038 reactions per second To Balance Gravity or 5 million tons of mass per second It takes 10 Billion years to consume core Hydrogen this way! GO OVER EXAMPLE 9.3!

  11. MARKER

  12. HW #12 • Read Chap 9 -9.3 • Problems 9.1,9.2,9.4,9.6

  13. 0 Energy Generation in the Sun: The Proton-Proton Chain --A REVIEW Basic reaction: 4 1H 4He + energy Need large proton speed ( high temperature) to overcome Coulomb barrier (electrostatic repulsion between protons). 4 protons have 0.048*10-27 kg (= 0.7 %) more mass than 4He. T ≥ 1070K = 10 million 0K • Energy gain = Dm*c2 = 0.43*10-11 J per reaction. Sun needs 1038 reactions, transforming 5 million tons of mass into energy every second, to resist its own gravity.

  14. Triple-a Process Massive stars or in evolution to a Red Giant Evolution as below H-burning shell keeps dumping He onto the core. He-core gets denser and hotter until the next stage of nuclear burning can begin in the core: T=108 K 4 H → He He He fusion through the “Triple-Alpha Process” AM I STARDUST? PROFESSOR 4He + 4He 8Be + g Some Be breaks up but 8Be + 4He 12C + g In soup of 4He

  15. In stars slightly more massive than the sun, a more powerful energy generation mechanism than the PP chain takes over: The CNO Cycle. The CNO Cycle Net Result 4 H4He +2 e+ +2u +3g

  16. Fusion Into Heavier Elements Slow n capture (s-process) b decay (Z,A)+n(Z,A+1)(Z+1,A+1)+e-+anti u 9.30 (CORRECTED) Or (Z,A)(Z-1,A)+e+ With lots of neutrons around Fusion into heavier elements than C, O: is possible. Neutron capture: (Z,A)+n(Z,A+1) 9.29 Fast n capture =r-process another n capture we get (Z,A)+n(Z,A+2) 9.31 QUIZ: What’s up?

  17. Other possible NUCLEAR FUSION reactions IN STARS Releases Energy All these reaction take place in the last stages of a Stars life

  18. Main Sequence Band ZAMS LINE FIRST APPEARENCE OF STAR NUCLEAR REACTIONS CHANGE COMPOSITION WHICH CHANGES LUMINOSITY AND SPECTRAL TYPE. .STAR EVOLVES ALONG LINES INDICATED Hence We See a Band of Stars B0 K0

  19. Nuclear Fission LET’S MAKE THE DESERTS BLOOM

  20. Weapons or Electric Power It’s up to YOU!

  21. Weapons

  22. Electric Power for all But Professor – Nuclear Power Plants Scare ME!

  23. BIG PROBLEM: only 1/3 Solar Neutrino’s detected Either we do not understand Energy Generation or our Neutrino Model It look’s today like our “Snu” model needs refinement! Super-Kamiokande -50,000 ton neutrino experiment located 1 km underground in an unused zinc mine near Kamioka, Japan.

  24. 0 The Solar Neutrino Problem The solar interior can not be observed directly because it is highly opaque to radiation. But neutrinos can penetrate huge amounts of material without being absorbed. Early solar neutrino experiments detected a much lower flux of neutrinos than expected (the “solar neutrino problem”). Recent results have proven that neutrinos change (“oscillate”) between different types (“flavors”), thus solving the solar neutrino problem. ,MAYBE???? Davis solar neutrino experiment

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