Nuclear Physics in the Cosmos Understand nuclear processes For background, see that • Power the stars • Synthesize the elements • Mediate explosive phenomena Determine • Nature of stellar evolution • Sites of astrophysical processes • Properties of universe • Neutrino properties http://www.nscl.msu.edu/~ austin/ nuclear-astrophysics.pdf
An Intellectual Opportunity This is a special time • Wealth of new astronomical observations--require new nuclear data for a credible interpretation • New accelerators of radioactive nuclei to provide this data • Growing computational power to simulate the phenomena
Outline of the Lectures The observables: Cosmic abundances, abundances in the solar system and elsewhere, fluxes of gammas and neutrinos. Nature of the nuclear processes involved: • Reaction rates • Resonant and non-resonant processes • Technical details: Gamow peak, S-factor, etc. The Big Bang and the Nature of the Universe Baryons, dark matter, dark energy Stellar evolution with some digressions • Quasistatic evolution, solar neutrinos, stellar onion • Explosive phenomena: supernovae, r-process, neutrinos • Binary systems: x-ray bursters and x-ray pulsars, the surface of neutron stars.
Outline-Continued References (www and Google) + • “Cauldrons in the Cosmos”, Rolfs and Rodney (out of print?) • “Principles of Stellar Evolution and Nucleosynthesis” D.D. Clayton, U. Chicago Press, paperback • Ann. Revs. of Nuclear and Particle Science; Astronomy and Astrophysics • Web pages of the major instruments: WMAP, SNO, Super- Kamikande, Chandra, HST,….. • Joint Institute For Nuclear Astrophysics (JINA) web page: www.jinaweb.org. See there also the link to the Virtual Journal for Nuclear Astrophysics.
Cosmic Abundances (Really solar system, mainly) • Very large range of A qualitative view-Suess-Urey Plot abundances • Names denote various creation processes Log Abundance Group Mass Fraction 1,2 H 0.71 Neut ron Capt ures 3,4 He 0.27 Li, Be, B 10-8 CNO Ne2x10 -2 2x10 -3 Na-Sc 2x10 -4 A= 50-62 10 -6 A= 63-100 10 -7 A> 100 A
A More Detailed Picture Solar abundances R-Process abundance 0 10 -1 10 -2 Nuclides made by slow (s) 10 all processes -3 10 mostly s + r and rapid (r) neutron -4 number fraction 10 -5 10 capture -6 10 -7 10 -8 10 Model s process, fairly -9 10 accurate -10 10 -11 10 -12 10 Subtract from solar � r 3 -13 10 10 0 50 100 150 200 250 mass number 2 Rapid n-capture(r) process 10 1 10 abundance Makes most of Gold 0 10 and Platinum -1 10 Makes Uranium -2 10 -3 10 0 50 100 150 200 250 mass number
Populations I, II and III What about elsewhere? Pop II stars • Reflect processes in the early galaxy • Investigation of Pop II stars is a hot area of astrophysics What are Pop III stars? • Stars that produce the material from which Pop II are made. In the halo of the galaxy find (old) stars • Probably very large (> (Pop II stars) with small (10 - 4 ) abundances 100 M sun ) fast evolving of metals (A > 4) compared to the solar stars made from products system values typical of Pop I stars. of the Big Bang.
The Stars as Element Factories Condensation Stars Interstellar Gas Nuclear Reactions Ejection-Supernovae Dust Element Synthesis Planetary nebulae Supernova remnant Star Forming Region N132D-LMC DEM192-LMC
The Big Bang Some Milestones 100 sec--Light elements ( 1,2 H, 3,4 He, 7 Li) made 300 kyear—Atoms form, CMB 200 Myear--First stars form Creation of matter Elementary particles TEMPERATURE (K) 10 20 TIME quark/gluon hadron 10 10 Light elements N U C Stars L E 1 A R P H Now Y S 3 o 10 10 years I C 10 -10 S 10 -20 1 10 20 10 40 TIME AFTER BIG BANG (seconds)
Nucleosynthesis in the Big Bang Assumptions: Reaction network Need to know noted reactions- • General relativity = Poorly known reactions • Universe isotropic, homogeneous • T now = 2.735 K (CBR)) Production of elements • 10-300 sec after BB • T ≈ 10 10 K, ρ ≈ 1g/cm 3 • Big Bang produces only lightest elements: 1,2 H, 3,4 He, 7 Li, because there are no stable mass 5 or 8. • Yield depends on density ρ B of baryons
Can we Determine the Baryon Density from the Big Bang? Nollett and Burles, PRD 61,123505 (2000) Method • Find ρ B where predicted and observed abundances equal. • If ρ B same for all nuclides, assume it is the universal density Result OK, EXCEPT for 7 Li. Perhaps predicted abundance wrong (poor cross sections) or primordial Li higher (star destroys). New data on the CMB may change our conclusions
It’s Close, Why Does It Matter? Cosmic Background Radiation Era of precision cosmology Surrounds us, Planck distribution (T~ 2.7 Far reaching conclusions must K), remnant of early BB be checked Fluctuations (at 10 -5 level) give Value of ρ B information on total density of Universe Best possibility. Need more and on ρ B. accurate cross sections for It implies several reactions affecting 7 Li. Universe is just bound Ω tot = 1 Supernova Ia Baryon density ρ B ~ 0.04 A standard candle to measure rate of expansion. Universe Dark matter density ρ D ~ 0.23 accelerating, measures dark perhaps WIMPS, weakly energy. interacting massive particles Dark energy Λ ?) ρ Λ ~ 0.73
Aside-Nature of Cosmic Background Radiation WWW site: http://map.gsfc.nasa.gov/m_mm.html WMAP: C.L. Bennet, et al, Relative Temperature, angular resolution 0.3 deg See February 2004 Scientific American
Angular Power Spectrum Analysis (G. Hinshaw, et al.) Perform angular multipole decomposition Results Good agreement with earlier results, summarized in red points Strong peak at l = 200 = > Ω tot = 1 Secondary peak l = 500 = > Baryon density
Resulting Cosmological Parameters Model parameters: from WMAP + earlier CMB measurements (COBE, CBI, ACBAR) + large scale galactic structure + Lyman forest Other results: First stars at 200 Myear, M ν < 0.23 eV
Big Bang Nucleosynthesis Revisited Assume: know η ( photons/baryons) Predict: BB nucleosynthesis Result: Agrees with observation for 2 H, not for 4 He, 7 Li To sharpen comparison need Better cross sections for 3 H( α,γ ) 7 Be for 7 Li p(n, γ ), d(p, γ ), d(d,n) for 2 H 3 He(d,p) and d(p, γ ) for 3 He Better abundance measurements Especially for 7 Li and 4 He Do stellar astrophysics with BB?? Details: RH Cyburt et al., PLB 567, Gray-observation. Black--BB 227 (2003)
What energy source powers the stars? All energy comes from mass Of the possibilities f chemical ≈ 1.5 x 10 -10 ⇒ 2200 yrs Mass initial Mass final ⇒ 10 7 yrs f gravity f nuclear ≈ 0.007 ⇒ 10 11 yrs Reaction Only nuclear sufficient Mass converted = f Mass initial Other evidence Technetium is seen in stellar Energy released spectra. BUT the longest lived f Mass initial c 2 isotope is unstable--lifetime of 4 x 10 6 yrs. Must have been Must provide solar luminosity synthesized in the star. for > 4.6 x 10 9 yrs L sun = 3.826 x 10 33 erg/sec M sun = 1.989 x 10 33 g
Reaction Rates and Energy Scales Reaction Rate Environment • k = 8.6171 x 10 -5 eV/K • Ionized gas (plasma) with N i /cm 3 of species “i” • T = 10 7 -10 10 K ⇒ kT= 1-900 keV • Assume species x moving at • Coulomb barriers MeV range velocity v through species y at • Reactions are often far sub-coulomb rest. Rate of reactions r xy is r xy = N x N y v σ xy • Average over velocity E inc distribution (Max. Boltz.) r xy = N x N y (1+ δ xy ) -1 < v σ xy > } Turning point # of pairs/cm 3 σ xy (E) ∝ tunneling probability for point coulomb charge
Non-Resonant and Resonant Reactions Non-Resonant Resonant Capture Typical case: Direct capture at Common for all but lightest stellar energies-light nuclei nuclei
Example – 7 Be(p,g) 8 B Nature of Cross Sections S Factor = σ E exp(b/E 1/2 ) Increase Rapidly with Energy Removes penetrability, nearly constant away from resonance
What Energies are Important? S contains the nuclear structure information- At what energy do we need Gamow Peak: to determine it? Maximum in product of MB distribution and penetrability of Coulomb barrier E 0 = 5.9 keV p + p 27 keV p+ 14 N 56 keV α + α 237 keV 16 O+ 16 O Cross sections at E o too small to be measured
S -- Resonant and Non-Resonant Phenomena • Rate ∝ Γ p Γ γ /(Γ p +Γ γ )• exp(-E r /kT) Resonance in Gamow Gamow Peak Peak Resonance in • Measure: Γ s, E r ⇒ Rate. dominates the rate dominates the rate • Γ s may be strong functions of E • Classic expts. with low-E accelerators: No resonance--Rate small σ ’s at low-E characterized by slowly • Measure cross sections to low-E, varying S factor at low extrapolate to E o to extract S-Factor. energy. • Long used for resonant rates, esp. E r Role of High-E facilities • Recent emphasis on new techniques to measure non-resonant rates.
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