lecture15

lecture15 - Astronomy 3: The Nature of the Universe...

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Astronomy 3: The Nature of the Universe Professor Alice Shapley Lecture 15: Stellar Life Cycles Stellar Remnants, Black Holes (NGC 1499 Image credit: Markus Noller, Deep Sky Images)
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Logistics Quiz #8: due Monday, May 30th, 10 pm. Last one! Available at CCLE website https://ccle.ucla.edu/course/view/11S-ASTR3-2 Expansion of the Universe.” Last one!! Issue with lab #5 grading for people in Cory’s sections (2D and 2E). If you haven’t already, please come see me or one of the other Tas with your graded lab #5.
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Review from Last Time Stellar life-cycles: – star formation – lower-limit on the mass of a star (i.e. brown dwarf) – balance between outward gas pressure and inward pull of gravity
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4 Pressure vs. Gravity What happens when outward thermal pressure exceeds inward pull of gravity? Gas expands and cools. What happens when inward pull of gravity exceeds outward thermal pressure? Gas contracts and heats up.
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Review from Last Time Stellar life-cycles: – star formation, – lower-limit on the mass of a star (i.e. brown dwarf) – balance between outward gas pressure and inward pull of gravity Evolution of low-mass stars
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High-Mass Stars > 8 M Sun Low-Mass Stars < 2 M Sun Intermediate-Mass Stars Brown Dwarfs
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Our Goals for Learning • What are the life stages of a low-mass star? • How does a low-mass star die?
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SUMMARY OF THE LIFE HISTORY OF A LOW MASS STAR LIKE THE SUN FROM MAIN SEQUENCE STAR TO RED GIANT TO WHITE DWARF Helium flash
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Movie of Sun’s Life
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Early stages of main-sequence and post-main- sequence evolution 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; the star started off bigger and now becomes a red supergiant . Helium Core Burning: He fuses to C in core (no flash this time)
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CNO cycle is just another way to fuse H into He, using carbon, nitrogen, and oxygen as catalysts. CNO cycle is main mechanism for H fusion in high mass stars because core temperature is higher. Effectively 4 H nuclei go IN and 1 He nucleus plus energy comes OUT. THIS IS COMPLICATED! Just know that there is another way to make helium from hydrogen. Hydrogen Fusion in High-Mass Stars
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become red supergiants after core H runs out because they start larger and generate more heat. The luminosity doesn’t change much because the cooling is compensated by the growth in surface area. What does a horizontal track (left to right) in H-R diagram mean physically? High-mass Stars in the H-R Diagram
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lecture15 - Astronomy 3: The Nature of the Universe...

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