Lecture_14

Lecture_14 - THE DEATH OF STARS Life as a High-Mass Star...

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1 THE DEATH OF STARS THE DEATH OF STARS Low Mass: main sequence, red giant, planetary nebula, white dwarf Life as a High Life as a High -Mass Star 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? High-Mass Star’s Life Early stages are similar to those of low-mass star: Main Sequence: H fuses to He in core Red Supergiant: H fuses to He in shell around inert He core; supergiant and not giant because original star was more massive in first place Helium Core Burning: He fuses to C in core High-mass stars become red supergiants after core H runs out. The luminosity doesn’t change much because the cooling is compensated by the growth in surface area.
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2 How do high mass stars make the elements necessary for life? We will learn later that the Big Bang made 75% H, 25% He. But it is the stars that make all the other elements. Helium fusion can make carbon in low-mass stars (Sun) In more massive stars, with higher core temperatures, helium-capture reactions add two protons at a time to go from Carbon to Oxygen to Neon to Magnesium.
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Helium capture builds C into O, Ne, Mg, … Advanced nuclear fusion reactions require extremely high temperatures Only high-mass stars can attain high enough core temperatures before degeneracy pressure stops contraction Advanced reactions make heavier elements all the way to iron (Fe) Advanced nuclear burning occurs in multiple shells inside a high-mass star. Multiple Shell Burning
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This note was uploaded on 02/20/2012 for the course ASTRO 3 taught by Professor Mclean during the Spring '11 term at UCLA.

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Lecture_14 - THE DEATH OF STARS Life as a High-Mass Star...

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