1. Creation of the Chemical Elements
By Dr. Harold Williams
of Montgomery College Planetarium

2. 17.3 Life as a High-Mass Star
Our goals for learning
What are the life stages of a high-mass star?
How do high-mass stars make the elements necessary for life?
How does a high-mass star die?

3. What are the life stages of a high-mass star?

4. CNO Cycle http://en.wikipedia.org/wiki/CNO_cycle
High-mass main sequence stars fuse H to He at a higher rate using carbon, nitrogen, and oxygen as catalysts
Greater core temperature enables H nuclei to overcome greater repulsion

5. Life Stages of High-Mass Stars
Late life stages of high-mass stars are similar to those of low-mass stars:
Hydrogen core fusion (main sequence)
Hydrogen shell burning (supergiant)
Helium core fusion (supergiant)

6. How do high-mass stars make the elements necessary for life?

7. Big Bang made 75% H, 25% He – stars make everything else

8. Helium fusion can make carbon in low-mass stars

9. CNO cycle can change C into N and O

10. Helium Capture
High core temperatures allow helium to fuse with heavier elements

11. Helium capture builds C into O, Ne, Mg, …

12. Advanced Nuclear Burning
Core temperatures in stars with >8MSun allow fusion of elements as heavy as iron

13. Advanced reactions in stars make elements like Si, S, Ca, Fe

14. Multiple Shell Burning
Advanced nuclear burning proceeds in a series of nested shells

15. Iron is dead end for fusion because nuclear reactions involving iron do not release energy
(Fe has lowest mass per nuclear particle)

16. Evidence for helium capture:
Higher abundances of elements with even numbers of protons

17. How does a high-mass star die?

18. Core then suddenly collapses, creating supernova explosion
Iron builds up in core until degeneracy pressure can no longer resist gravity
Core then suddenly collapses, creating supernova explosion
Death_seq_of_high-mass_star.swf
Download a good supernova explosion movie from the Chandra Science Center (chandra.harvard.edu)

19. Supernova Explosion http://en.wikipedia.org/wiki/Supernova
Core degeneracy pressure goes away because electrons combine with protons, making neutrons and neutrinos
Neutrons collapse to the center, forming a neutron star

20. Energy and neutrons released in supernova explosion enable elements heavier than iron to form, including Au and U

21. Supernova Remnant http://en.wikipedia.org/wiki/Crab_nebula
Energy released by collapse of core drives outer layers into space
The Crab Nebula is the remnant of the supernova seen in A.D. 1054, M1, NGC 1952, Taurus A, ~6,300LY away, 3LY radius, optical and radio pulsar
5h 34min 31.97sec and +22 degrees 0’ 52.1”

22. Supernova 1987A http://en.wikipedia.org/wiki/Supernova_1987a
The closest supernova in the last four centuries was seen in 1987

23. Rings around Supernova 1987A
The supernova’s flash of light caused rings of gas around the supernova to glow

24. Impact of Debris with Rings
More recent observations are showing the inner ring light up as debris crashes into it