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Transcript
Star evolution Chapters 17 & 18 (Yes, we skip chap. 16, star birth) Goals & Learning Objectives • Learn some simple astronomical terminology • Develop a sense of what scientists know about the overall universe, its constituents, and our location • Describe stellar evolution • Contrast the life history of a low-mass star with the life history of a high-mass star. • Explain how black holes are formed and their effect on their surrounding environment. 3 star groups (p. 565) • 3 categories of stars: – – – • • Intermediate similar to both high and low mass. Book focuses more on similarities with high mass (in section 17.1). One major difference: __________________________ ___________________________________ Which star group has the highest core pressure? 1. Low mass 2. Intermediate mass 3. High mass 0 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 Which star group has the hottest core temperature? 1. Low mass 2. Intermediate mass 3. High mass 0 0 0 So what can you conclude about the fusion rate? Luminosity? Which stars live longer? Why? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 The end of the Sun • • • • • • • • • Eventually ________________________. What did the core need fusion for? What will happen to it as a result of ___________? What happens to __________________________? What happens to the temperature of the material surrounding the core? CLICKER QUESTION (next slide). What are the surrounding layers made of? What can happen if ________________________? For Sun, this takes ___________________of years. Is there Hydrogen outside the Sun’s core? 1. Yes 2. No 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 _______________________ • • • • • • • • • In fact, the outer layers get hotter than _________. What does that tell us about ______________rate? What should we observe as a result? CLICKER The light “gets stuck” and pushes the outer layers out. What happens to gas when you _______________? Color of outside? What kind of star do we have? What is the core made of? What is the structure? See fig. 17.4 page 568 Star becomes ______ luminous 1. More 2. Less 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 What’s happening to the mass of the HELIUM core as the shell “burns”? 1. Increasing 2. Decreasing 3. Staying the same 0 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 Inside the core… • • • • _______________________ Core _____________________ More hot helium dumped onto core _________________________________from shrinking. – _____________stars: ________________________________ • Read section 16.3, page 557 and S4.4 pp. 481-483 • ______________________ – Intermediate & High mass _______________ thermal & _____________. • _______________________turns on at 100 million K – Low mass: whole _____________simultaneously: _____________ – Intermediate & high mass: “regular” fusion Next phase • • • • Structure of the star now? Figure 17.5 This lasts until … What happens to the core? – Low & intermediate mass: ____________until ___________ ______________stops it. Focus on that now. – [for High mass: ___________________________] • Back to low mass: What’s the core made of? • Shrinks to size of Earth. • What happens outside the core? – Temp, composition __________________burning • • • • Not stable Outer layers ________________ Outer layers _______________ See pictures around the planetarium – Cat’s eye, Butterfly, Ring: all “________________________” • • • • • See also figure 17.7 – more examples NOT related to planets What’s in the center of a planetary nebula? End of low & intermediate mass stars… Show interactive figure 17.4 Do low mass stars like the Sun fuse Carbon into anything? 1. Yes 2. No 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 If the universe contained only low mass stars, would there be elements heavier than carbon? 1. Yes 2. No 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 High mass star differences • ____________________________________ – Gas & thermal pressure always stronger • • • • Can fuse carbon with helium into Oxygen Can fuse Oxygen with helium into neon Etc. (magnesium, silicon, sulfur) When core hot enough, can fuse carbon with carbon, carbon with oxygen … • Etc. • Big picture: carbon and stuff fuses until you get to a core made of … • Iron (Fe on the periodic table, #26, middle section, top row, see page A-13, Appendix C) Iron • Most stable nucleus • _____________________________________ – _________________energy (uses instead of ___________) • True for everything heavier than iron, too. – Fission USES energy • True for most things lighter than iron, too. • Iron is the last element made in stable reactions in stars • Look at the periodic table on page A-13 – Find iron – Gold = Au. Mercury = Hg. Xenon = Xe. Are these made in stable stars? What we see • See figure 17.12, page 575 for onion skin model • See HR diagram on p. 575 (fig. 17.13) – Runs out of core fuel, goes right – Next fuel turns on, goes back left – Repeat until core is made of Iron • • • • • After the Iron core forms Iron core __________________ ________________than ________________________pressure _________________________more than they can tolerate Electrons merge with protons Result: _______________ – And ___________________! – (Fly straight out! We observe them first!) • • • • • • • • ________more electron degeneracy _______________support. Rapidly shrinks: ___________________________in 1 second! Lots of energy released. Turn on neutron degeneracy pressure. ___________________________. Demo ______________________________. Leaves behind core Core is made of … Called … Interactive figure 17.12 & 17.17 (crab nebula in 1054) (If the core is too heavy for neutron degeneracy pressure…) Production of Elements • High mass stars make up to _________ • _______________________made _________ __________________ – Lots of neutrons around – They merge with nuclei quickly (r-process) – Eventually nucleus decays to something stable – Like _________________________________, etc. Stellar remnants • End states for stars – Low mass stars become … – Intermediate mass also become … (Oxygen) – & high mass stars become … – The highest mass stars (O & B) become … Which stars should begin with the most heavy elements inside them? 1. The stars that formed earliest 2. The most recently formed stars 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 Summary of star death • • • • • • • When fusion runs out, core ____ & _____ Shell fusing occurs. Many shells possible. Core fusion can turn on. What’s different for low mass & high mass? Which elements get made in low & high? What’s special about iron? Degeneracy pressure (electron & neutron) – What, where, why • Possible end states; which stars make them – RG PN WD, RG SN NS or BH Chapter 18: Stellar remnants • The next few slides are material from chap 18. White dwarfs • Radius – ______________________________________ • What kind of pressure resists gravity? – _________________________________pressure • Temperature – Start ______________. [Clicker question] – Cool down (__________________eventually) • Composition: – Usually _____________________ – sometimes oxygen (intermediate mass) or helium (very low mass) • Gravity: teaspoon weighs _______________! What kind of light would a white dwarf emit most when it is first detectable? 1. 2. 3. 4. 0 0 0 0 X-rays Visible light Infrared Radio waves 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 White dwarf limit • Observed around _______________ • Can be up to ______________ • If heavier, _________________________strongly enough to resist gravity. [they’d have to move faster than c] • What happens if you add mass to a 1.4 Msun white dwarf? – Where could extra mass come from? – _____________________________! – _________________________________ (“Type 1a”) • Are a “standard candle”. What’s that? – Leaves NOTHING behind, _________________________ – LESS VIOLENT: Nova if add small amount of stuff to lower mass WD. Sirius binary system What you’d see through a telescope Ignore the spikes X-ray image & visible image superimposed Neutron stars • Composition? – Gigantic nuclei. – No empty space like in atoms (99.999% empty) • Paper clip of neutrons weighs as much as ______________! • Dropping brick: energy = an atom _____________! – As stuff falls onto a neutron star, ________________________! • Mass – Observed: __________________________________ – Can be up to _______________(we don’t know exact upper limit) – Any heavier & ____________________________strongly enough to resist gravity. • Radius: City sized (_______________). WD = _______miles! • What kind of pressure resists gravity? – _______________________pressure • Neat trivia: Escape speed = ½ c. (Gravity very strong!) Pulsars • • • • • See figures 18.7 & 18.8 Jocelyn Bell Should’ve won the Nobel Prize Rapidly spinning neutron stars 1800 known pulsars, pulsing radio, but some also emit other types: visible + X-rays and sometimes gamma. – 1 pulsar, discovered in October 2008 emits only gamma • See figure 18.9 • Is it possible to be a neutron star that’s not a pulsar? How about vice versa? [2 clicker Q’s] • Spin up to 600 times per SECOND! (Show movie!) – Larger objects would break apart Is it possible to be a neutron star but not a pulsar, as seen on Earth? 1. Yes 2. No 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 Is it possible to be a pulsar but not a neutron star, as seen on Earth? 1. Yes 2. No 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 Black holes – Remind me to reveal the information as your questions are answered Chap. 18, #18: If a black hole 10 times as massive as our Sun were lurking just beyond Pluto’s orbit, we’d have no way of knowing it was there. 1. True 2. False 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 Summary of stellar “graveyard” • • • • • White dwarf properties: mass, radius, pressure White dwarf limit, results of exceeding it Neutron star properties Pulsars Black holes – Falling in – Gravity far away – How we can find them