Nuclear astrophysics: synthesis of the chemical elements Zsolt Podolyák University of Surrey, UK
Earth: ~1890 Kelvin: ~20-40 Myears radioactivity 1905 Rutherford => billions of years age: 4.55 billion years (radioactive dating) Universe: 26 Al all-sky map: T 1/2 =0.74 My E γ =1.8 MeV continuous nucleosynthesis picture by COMTEL
What are things made of? Air: 78% nitrogen, 21% oxygen Pebbles: 47% silicon, 53% oxygen (by weight) + traces Fe, Mn
Logarithmic scale What is the world made of? Abundances in the solar system Hydrogen: 74% Helium: 24% Other: (oxygen, carbon etc) 2%
Elements and isotopes electrons neutrons (N) protons (Z) Helium 3 He 4 He chemical and physical properties: element (Z) nuclear properties (and synthesis of elements): nuclei (Z and N)
Magic numbers: 2, 10, 18, 36, 54, 86,118
Chart of nuclei Super Heavies Fewer than 300 nuclei Proton Drip Line Neutron Drip Line Magic numbers: 2, 8, 20, 28, 50, 82, 126
How do we know what the world is made of? Emission and Absorption (fingerprint) Lines Absorption lines (observation) Star light
From big bang till today Galactic Chemical Evolution
Expansion of the universe 7p & 1n 74% H & 24%He 98% of known matter Where does the rest come from? http://www.davidreneke.com
The life cycle of stars
Stars: hydrogen burning (the most important) Net effect: 4 1 H -> 4 He +2 e + +2 ν e +energy 1 H=proton
Why does it take billions of years? 1 H+ 1 H -> 2 H + e + +ν e Two steps: (i) p -> n + e + + ν e E=-1.8 MeV it needs energy! it cannot happen (classical phys.) sometimes (quantum physics) Bottle neck (ii) p+ n-> 2 H In laboratory never observed!
How are elements heavier than helium made?
energy The Hoyle state E KIN m( 8 Be)c 2 +m( 4 He)c 2 excited state right energy (7.65 MeV) right quantum numbers 0 + m( 12 C)c 2 groundstate No Hoyle state, no elements beyond helium The energy of Hoyle state determines the amount of heavier elements
Onion structure of (heavy) stars H burning: ~10 9 y He burning: ~10 6 y C burning:~10 3 y Ne, O burning: ~1 y Si burning:~ 10-2 y
Creation of elements up to iron is understood In burning (fusion) processes in stars
Based on the US National Academy of Science Report [Committee for the Physics of the Universe (CPU)] Question 3 How were the elements from iron to uranium made?
The Abundances of the elements for A = 70-210 double peaks at neutron number 46/50, 76/82, 116/126 N=50, 82, 126 are magic! (equivalent to noble gases) T 1/2 (neutron)=614 s => it has to happen in stars They are due to production by the two separate processes
Slow neutron capture process: s process low neutron flux; beta-decay time < neutron capture time abundances peaks at A=84, 138, 208 Neutron capture Beta decay Z+1 Z Rapid neutron capture process: r process high neutron flux beta-decay time > neutron capture time abundances peaks at A=80, 130, 195
proton number Ni Co Fe The slow neutron capture process (n,g) (b - ) (b + ) Zn Cu (well understood) 80 Br, t 1/2 =17 min, 92 % (b - ), 8 % (b + ) Ge Ga Se As p-only Kr Br Sr Rb r-only Zr Y 85 Kr, t 1/2 =11 a 64 Cu, t 1/2 =12 h, 40 % (b - ), 60 % (b + ) 63 Ni, neutron t 1/2 =100 number a 79 Se, t 1/2 =65 ka
The rapid neutron capture process (r-process) movie from http://compact-merger.astro.su.se/movies.html#rproc
The mystery of the r-process Where does it happen (neutron density, temperature)? supernovae explosions? neutron star mergers? What are the properties of the nuclei involved? the majority of them never studied
Neutron-star mergers movie from http://compact-merger.astro.su.se/movies.html#nsbh
Nuclear physics input The majority of nuclei involved in the r-process cannot be studied
Excite a nucleus: p n First particles are emitted.. p
Then gamma rays (bursts of energy)...
Good description of what is known
FAIR (Facility for Anti-proton and Ion Research) FUTURE >1000M Euro
Solar system abundances From solar and meteoritic abundances J.J. Cowan and F.-K. Thielemann, Physics Today, Oct. 2004, p.47
abundances Universality of the r-process (there are other stars with the same abundances) Frebel, Norris
Big Bang The origin of the elements H,He Li-B C ~Fe Sr Pb Th,U massive stars (hydrostatic buring) SN type II SN type Ia Unknown SN type II/NS merger? (r-process) massive stars (C,O burning weak s-process) Low mass AGB stars (He burning, main s-process) SN type Ia or II (p-process) 13 C, 17 O,.. Novae ( rp process ) 92,94 Mo, 96,98 Ru Unknown X-ray bursts? (rp process) Note: yellow-red all related to massive stars (>8-12 solar masses)
Summary Elements created in nuclear reactions Fusion processes in heavy stars create elements up to iron proton+proton takes billions of years all nuclei heavier than helium created via the Hoyle state Elements beyond iron created in neutron rich environment We still do not know where (NS mergers? Supernovae?) and how heavy elements were made (r-process)