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Creation of the Chemical Elements. By Dr. Harold Williams of Montgomery College Planetarium http://montgomerycollege.edu/Departments/planet/. 17.3 Life as a High-Mass Star. Our goals for learning What are the life stages of a high-mass star?

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creation of the chemical elements

Creation of the Chemical Elements

By Dr. Harold Williams

of Montgomery College Planetarium

http://montgomerycollege.edu/Departments/planet/

17 3 life as a high mass star
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?
cno cycle http en wikipedia org wiki cno cycle
CNO Cyclehttp://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
life stages of high mass stars
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)
how do high mass stars make the elements necessary for life
How do high-mass stars make the elements necessary for life?

http://en.wikipedia.org/wiki/Triple-alpha_process

http://en.wikipedia.org/wiki/Neon_burning_process

http://en.wikipedia.org/wiki/Silicon_burning_process

helium capture
Helium Capture
  • High core temperatures allow helium to fuse with heavier elements
advanced nuclear burning
Advanced Nuclear Burning
  • Core temperatures in stars with >8MSun allow fusion of elements as heavy as iron
multiple shell burning
Multiple Shell Burning
  • Advanced nuclear burning proceeds in a series of nested shells
slide15

Iron is dead end for fusion because nuclear reactions involving iron do not release energy

(Fe has lowest mass per nuclear particle)

slide16

Evidence for helium capture:

Higher abundances of elements with even numbers of protons

slide18

Iron builds up in core until degeneracy pressure can no longer resist gravity

Core then suddenly collapses, creating supernova explosion

supernova explosion http en wikipedia org wiki supernova
Supernova Explosionhttp://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
  • http://en.wikipedia.org/wiki/Neutron_star
slide20

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

supernova remnant http en wikipedia org wiki crab nebula
Supernova Remnanthttp://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
supernova 1987a http en wikipedia org wiki supernova 1987a
Supernova 1987Ahttp://en.wikipedia.org/wiki/Supernova_1987a
  • The closest supernova in the last four centuries was seen in 1987
rings around supernova 1987a
Rings around Supernova 1987A
  • The supernova’s flash of light caused rings of gas around the supernova to glow
impact of debris with rings
Impact of Debris with Rings
  • More recent observations are showing the inner ring light up as debris crashes into it