lecture_tan26 - Key Concepts Lecture 26 Evolution and Death...

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Key Concepts: Lecture 26: Evolution and Death of Massive Stars Evolution of Massive Stars Supernova explosions Neutron Stars (Pulsars) Black Holes Evolution of Massive Stars Evolution of stars with M>8 M sun differs from lower mass stars Higher core temperatures so they fuse heavier elements more easily Main sequence is still fusion of Hydrogen into Helium, but with a much shorter life Hot enough to fuse carbon into oxygen Hot enough to fuse oxygen into silicon Hot enough to fuse silicon into iron Iron is the most stable element It requires energy to break it apart into lighter elements It requires energy to fuse it into heavier elements Different layers, like an onion Red Super Giants So much energy is generated that massive stars swell to tremendous sizes These are called super giants They are 1000-10000 times larger than the Sun Time Scales for 25 Solar Mass Star Stage Core Temp Core Density Duration H burn 4x10 7 K 5x10 3 7x10 6 yrs He burn 2x10 8 7x10 5 5x10 5 yrs C burn 6x10 8 2x10 8 600 yrs Neon 1x10 9 4x10 9 1 yr Oxygen 1.5x10 9 1x10 10 6 months Silicon 3x10 9 3x10 10 1 day Collapse 5x10 9 3x10 12 0.2 sec Bounce 2x10 10 4x10 17 0.001 sec g/cm 3
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Supernova Type II: Death of Massive Stars Finish with an Iron (Fe) core – Cannot produce any energy by fusion
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