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Lecture 16

AST 101 Lecture Notes - Lecture 16: White Dwarf, Red Giant, Black-Body Radiation


Department
Astronomy
Course Code
AST 101
Professor
Walter Freeman
Lecture
16

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The Sun
Hot innards emit blackbody radiation because of its temperature
Cooler gases ithi the Su’s atosphere asor the aelegths orrespodig to
their energy-level transitions, giving rise to the dark lines in the spectrum
Nuclear Fusion a nuclear reaction involving building larger nuclei out of smaller ones
Sun is made of hydrogen
Electrons within the sun are so hot and are under so much pressure that they are torn
off of their atoms
Like charges repel each other
o Temperature of sun can overpower that
Create an attractive nuclear force that will hold them together
One changes to a neutron, creating a new atomic nucleus between the
two of them
P + P + e = NP
P + NP = NPP
NPP + NPP = NNPP + P + P (NNPP is helium)
o Releases millions of electron volts per atom
Is the urret soure of the Su’s eergy ad ost stars i the uierse
o Hydrogen to helium fusion
The fate of the Sun
Heliu ill eetually uild up i the Su’s ore
Later reactions will need higher temperatures and release less energy
Outer layers of hydrogen falling off helium core will heat up so much under their own
gravity that they will start to fuse
o Red giant
Sun will do this becoming so large the outer layers will swallow up the
earth
Later fuse into carbon and oxygen in violent convulsions expelling the hydrogen and
helium to make a NEBULA
o Leaving behind a naked core of carbon/oxygen
A white dwarf
Only glow from residual heat, no more nuclear fusions
Summary
Nuclear fusion is the combining of light nuclei, like hydrogen, to make heavier ones, like
helium
This process releases enormous amounts of energy, but can only happen at high
temperatures and pressures
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