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9-element production in thermonuclear reactions (25 solar mass star…
9-element production in thermonuclear reactions
Basic problem is lack of stable nuclei with A=5 or 8
What happens in a star
hydrogen core depletes
no more grav pressure equilibrium
hydrogen burning still happening in shell outside core generating pressure and causing the star to expand into red giant phase
hydrogen fusion increases core mass and temperature
When core heats to 10^8K He burning starts
Triple alpha process
2 resonant processes
first is endothermic, lifetime ~10^-16s
Further fusion processes
once carbon is formed further helium burning can synthesis heavier elements
eventually helium is spend and core collapses and heating triggers carbon burning, then neon, then oxygen, and lastly silicon burning
some chemical equations
silicon burning is a number of processes taking place simultaneously
photo disintigration of heavier nuclei to He-4
formation of heavier nuclei via He-4 capture
beta decays
Massive stars end with an ogre like structure
25 solar mass star timeline
H burning
7e6 yrs
0.06 e9 K
5e4 ρ
He burning
5e5 yrs
0.23 e9 K
7e5 ρ
C burning
600 yrs
0.96e9K
2e8 ρ
Ne Burning
1yr
1.7 e9K
4e9 ρ
O burning
6 months
2.3e9
1e10ρ
Si burning
few days
4.1e9K
3e10
star masses and fusion processes
0.1-0.5 Msun
H
0.5-8
H,He
8-10
H,He,C
10
all stages
core <1.4
white dwarf (He, C/O,O/Mg/Ne)
core >1.4
Core collapse supernova