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The Life Cycle of Massive Stars: From Fusion to Stellar Wind and Element Formation in the Universe

Explore the fascinating life cycle of massive stars in this detailed workshop series. Learn how energy from nuclear fusion counteracts the force of gravity, shaping the destiny of a star. Discover the process of stellar winds in Wolf-Rayet stars and the transformation of helium to heavier elements as stars evolve into red giants. Understand the critical moment when fusion ceases at iron and the implications for stellar fate. This workshop covers the complexities of stellar evolution, the creation of heavy elements, and the eventual dispersal of these elements into the cosmos.

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The Life Cycle of Massive Stars: From Fusion to Stellar Wind and Element Formation in the Universe

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  1. Element Building in Large Stars Life Cycle of Stars - Part 2 Elements 2002 Workshop

  2. Re: Principles of Stellar Evolution • The bigger it is, the hotter and the faster a star burns its life away. • Energy released from nuclear fusion counter-acts inward force of gravity. • Throughout its life, these two forces determine the stages of a star’s life.

  3. Annie J Cannon (1863-1941) All Types of Stars Oh Big And Ferocious Gorilla, Kill My Roommate Next Saturday !

  4. Nuclear Fusion ! • At 15 million degrees Celsius in the center of the star, fusion ignites ! • 4 (1H) --> 4He + 2 e+ + 2 neutrinos + energy • Where does the energy come from ? • Mass of four 1H > Mass of one 4He E = mc2

  5. Stellar Winds in High Mass Stars • Wolf-Rayet stars may have winds up to thousands of km/s • These stars are hot, massive O stars • But are only 1-2% of normal stars in galaxy • Mass loss equivalent to ~1/3 mass of earth per year. • Elements pushed by intense photon radiation emitted by the star. • We observe He, N, C, O, Si, Fe

  6. Reprise: the Life Cycle Sun-like Stars Massive Stars

  7. The beginning of the end: Red Giants

  8. Red Giants • After Hydrogen is exhausted in core, • Core collapses, releasing energy to the outer layers • Outer layers expand • Meanwhile, as core collapses, • Increasing Temperature and Pressure ...

  9. More Fusion ! • At 100 million degrees Celsius, Helium fuses: • Triple Alpha Process • 4He + 4He --> 8Be + energy • 4He + 8Be --> 12C + energy • 3 (4He) --> 12C + energy • (Only 7.3 MeV produced) • Energy sustains the expanded outer layers • of the Red Giant

  10. Fate of high mass stars • After Helium exhausted, core collapses again until it becomes hot enough to fuse Carbon into Magnesium or Oxygen. • 12C + 12C --> 24Mg OR 12C + 4H --> 16O • Through a combination of processes, successively heavier elements are formed and burned.

  11. Light Elements Heavy Elements 4 (1H) 4He + energy C-N-O Cycle 3(4He) 12C + energy 4He + 16O 20Ne + energy 16O + 16O 32S + energy 28Si + 7(4He) 56Ni + energy 56Fe 4He + 12C 16O + energy 12C + 12C 24Mg + energy Periodic Table

  12. The End of the Line for Massive Stars • Massive stars burn a succession of elements. • But the process stops at Iron.

  13. The Stop Light at Iron • Iron is the most stable element and cannot be fused further. • Instead of releasing energy, it uses energy. • Why ? Binding energy • Mass of atomic nucleus < Sum of masses of individual neutrons and protons • Difference is energy which holds nucleus together. • (= amount of energy to break nucleus apart)

  14. Fission Fusion Binding Energy/Nucleon Fusion or Fission results in more tightly bound nuclei (I.e. less stable --> more stable + energy)

  15. S-Processes - Going beyond Iron • In Asymptotic Giant Branch Stars, He burning occurs in a shell around Carbon core. • Here reactions occur which release neutrons. • These neutrons help build heavy isotopes: • Fe56 + n --> Fe57 • Fe57 + n --> Fe58 • Fe58 + n --> Fe59 • This process is slow - thousands of years between captures.

  16. S-Process: Creating Heavy Elements • Beta Decay of unstable nuclei produce new elements: • 26Fe59 --> 27Co59 + e- + neutrino • (Decay occurs before another neutron can be captured) • Then Co59 + n --> Co60 --> Ni60 + e- • All the way up to 82Pb208 and 83Bi209

  17. Dispersal of S-Process Elements • Heavy elements enter convection layers of star. • Stellar winds then disperse them.

  18. S-Process Elements from Large Stars Slow Addition of Neutrons

  19. All Elements from Large Stars Dispersed via Stellar Winds

  20. The Next Step ... • Once Iron core forms, • Energy Source disappears • Gravity takes over …

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