1. Star Formation

2. Formation of the First Materials Big-Bang Event   Initial event created the physical forces, atomic particle building blocks, photons, dark matter, and dark energy – –Protons, neutrons, electrons, photons dominate atomic universe   Brief period of fusion transformed protons (H, p + ) and neutrons (n o ) into 75% H and 25% He (2p + + 2n o ) through high-energy collisions   Collisions and fusion quickly cut off as density and temperature dropped rapidly

3. Formation of the First Atomic Materials Big-Bang event created:   Mostly hydrogen (75%)   Next is helium (25% - 1/3 of the mass of atomic universe)   Small amount (10 -5 ) of deuterium ( 2 H or, or 2 D, or p + + n o )   Collisions and fusion produced an even smaller amount of 3 He (10 -6 )   Brief fusion period also produced a tiny amount of lithium (10 -10 )

4. Star Formation First stars   Formed from original 2/3 H, 1/3 He universe composition   First stars were gigantic (100-500 times Sun’s mass) – –Turbulence that thermal motion too high for small stars to form   Rapid fusion of core H into He also created other fusion products

5. Star Formation First stars   Primary energy in all stars is generated by H → He fusion (4p + → 2p + + 2n o = 4H → 4 He)   When hydrogen in the core is exhausted, fusion ends unless overlying mass is large enough to compress He to high enough temperatures to fuse into Be – –If the star is massive enough, Be fusion is followed in rapid sequence by the fusion production of C, O, Ne and so on until iron is formed – –First stars formed after the Big Bang were the largest stars to form   500 times the Sun’s mass   Fe formation initiates a cataclysmic end to fusion since higher mass nuclei absorb energy (endothermic) in the fusion process

6. Star Formation – Nuclear Fusion and Binding Energy Nuclear binding energy = Δmc 2 Mass difference between component particles (4p + ) and the resulting nucleus ( 4 He) is Δm For the helium nucleus (alpha particle) Δm = 0.0304 u which gives a binding energy of 28.3 MeV

7. Stellar Energy Fusion-fission binding energy of nucleons   Lower-mass atoms release energy in the fusion process (exothermic) – –Absorb energy in the fusion process   Higher-mass atoms release energy in the fission process (Fe and above) – –Absorb energy in the fission process (endothermic) – –Production of high- mass nuclei in the core of a star terminates fusion

8. Elements Formed in Stars End of energy production in a star’s core   Fusion fuel exhausted   Star’s core cools rapidly   A. Small stars cool to form a white dwarf   B. Large stars undergo rapid gravitational collapse – –Violent collapse creates implosion – –High-pressure, high-temperature conditions force nuclei into neutron-rich mix – –Secondary fusion process (rapid process) initiated – –Violent rebound produces a supernova for large stars (>5 Mo)   Less-explosive nova created in mid-mass stars (like the Sun) – –Material is blown away from the star’s core

9. Elements Formed in Stars Following the termination of the fusion process in a star   Core implosion creates a secondary fusion event – –Extreme pressures and temperatures force electrons to combine with neutrons   Neutron-rich core   If this survives intact, a neutron “star” is formed – –Material blasted outward contains high-mass nuclei   Secondary shell fusion – –High-energy neutrons blasted from the core implosion are fused into departing material (neutron enrichment)   Generates high-mass nuclei

10. Stellar Fusion Atomic material enrichment   Fusion process inside of stars creates helium and everything heavier   Supernova responsible for much of atomic material heavier than iron   Nuclear furnace inside larger stars can also produce heavy nuclei with the slow bombardment of nuclei by neutrons (slow process of neutron enrichment)   Atomic nuclei beyond helium are produced by supernova and by large star cores, but not equally

11. Stellar fusion Atomic material enrichment   All elements heavier than He are produced inside stars, but not in equal abundance   Lower-mass atomic material is more abundant than higher-mass elements

12. Sun’s Formation Solar system composition  Our solar system formed from a large gas cloud of H and He, enriched by nearby supernova and nova (from dying stars)  Radioisotopes found in rock samples and meteorites indicates the solar system is third-generation –Enriched by two preceding supernova events  Composition of the original gas cloud was approximately: –70% H –25% He –5% other stuff

13. Sun’s Formation Solar system composition  5% other stuff came from the elements created by previous stars and consists of atomic and molecular material, as well as simple and complex compounds  Consists mostly of –Gases (O 2, N 2, CO 2, etc.) –Ices (water, CO 2, ammonia, methane) –Silicates and oxides (rock) –Metals (mostly Fe, Ni) –All of the other elements

14. Sun’s Formation Solar system composition Element abundances in solar system are determined by  Universe composition (75% H, 25% He)  Supernova enrichment (5% other stuff)  Isotope stability and end products Material abundances in the solar system are determined by:  Element abundances from original Big Bang and supernova enrichment  Chemistry of element combinations  Radioisotope decay and resulting changes in compounds/molecules Most common materials are:  Gases - H, He, O 2, N 2, CO 2, Ar  Ices - water, CO 2, ammonia, methane  Silicates - rock  Metals - mostly Fe, Ni

15. Planet Formation Planet and moon composition Makeup of the planets and their moons is determined by:  Solar nebula (original gas cloud) composition  Heating by the Sun –More extreme closer to the Sun Makeup of the first clumps to coalesce in the planetary disk is determined by:  First by electrostatic attraction  Then by adhesion –Ices –Dust  Then by gravitational attraction –Density-gravity profile –Most dense region is closest to the Sun, but it is also the first to be swept out by the early solar winds

16. Planet Formation Planet and moon composition Inner solar system dominated by:  Silicates - rock  Metals - mostly Fe, Ni Outer solar system dominated by:  Ices - water, CO 2, ammonia, methane  Gases - H, He, O 2, N 2, CO 2, Ar

17. The End