Chapter 13 Death of Stars - From middle age heading for...

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From middle age heading for death….Leaving the main sequenceWhy and when do stars evolve offthe Main Sequence?
What are the structural changesthat occur inside the star?))
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2Mass: 0.4 - 8 solar mass(Our Sun falls in this mass range.)On the Main sequence:Amount of Helium in the coreincreasesAmount of Hydrogen in the coredecreasesCredit: John Wallin (GMU)very slight changes in stars luminosity andsurface temperature.energy still being generated at about the samerate.Credit: John Wallin (GMU)10 Byr
3star runs out of hydrogen at the corethough hydrogen remains in the envelopenuclear fusion stopsno fuel, no fire in the centervery hot, but not hot enough for helium burningthe core begins to contractno energy generated - less pressuregravity overcomes pressureCore contraction &or helium coreCredit: John Wallin (GMU)Post Main SequenceCore Contraction & Hydrogen shellburning:As H in the shell burns with ever increasing ratesurface temperature drops slightlyluminosity increasesnon-burning outer H layers increase in radiuscore is shrinkingvery high radiation pressuregravity is not able to stop themocore is shrinking and heating up, outer layersare expanding and coolingstar moves tored giant branchRadius = 3 times that of sunTemp = 4000 KRadius =100 times that of sunTemp = 4000 KLuminosity =many 100 timesof the present SunCore= very compact (in size1/1000 of entire star, but verydense about 1000 times denserthan at Main Sequence)
4Post Main SequenceCore Contraction Continues:amount of inert helium increaseshell burning adds more helium ashno energy generated in coregravity contracts coredensity and temperature increase in core dueto its contraction and shell burningdensity = 108kg/m3temperature = 100 millionPost Main SequenceHelium Fusion:temperature > 100 million K10 times hotter than main sequence corehelium fuses into carbonanother name of4He nuclei is alpha particlesnext nuclear fusion inside the core beginscalledtriple alpha process4He +4He ->8Be + energy4He +8Be ->12C + energy(three helium nuclei (or alpha particles)combine to form a nucleus of carbon.)Hydrogen burning shellStellar envelopNo energy generation there(expanding and cooling)

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Term
Spring
Professor
Dr.Nila
Tags
Astronomy, White dwarf, main sequence, Post Main Sequence

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