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AST 112 Spring 2021 AST 112 - Spring 2019 Tue - Thu 10:30 - 11:45 STUDY GUIDE FOR EXAM 3 1. YOU MUST NOT USE YOUR LAPTOP, TABLET, CELLPHONE, or TEXTBOOK!!! Bring a calculator –(NOT the one on your cellphone) Do Not cheat off your neighbor! You must use only a #2 pencil – do not use a pen! 2. HINTS ON TAKING "OPEN NOTES" TESTS: a. Study as if it were a closed book test. You do not have time to look up each answer. b. Carefully read the Chapter Summary, try to do the Review Questions, and the Discussion Questions. Work as many problems as you can. Feel free to ask me if you are having problems doing them. c. Don't forget the index or the glossary in the book. d. Read the test questions carefully! e. Go through the test once and answer all the questions that you can. Then go back and do the other questions. f. You may mark on the test booklet: cross off obviously wrong answers, work the problems, and show your work. Circle the answer on the test booklet - this is the last resort if you have made a mistake on the answer sheet. g. Carefully darken in the answer on the answer sheet, do not rip, mutilate, fold, or spindle it. h. Check your answer sheet. Make sure you have answered all 50 questions. i. MAKE SURE THAT YOUR NAME IS ON THE ANSWER SHEET AND YOU HAVE PUT IN YOUR FULL UNIVERSITY ID NUMBER-LEFT JUSTIFIED. I will subtract points if this is not done. J. BRING A PICTURE ID. I may go around checking them. Make sure that you know your ID number. Chapter 13: Star deaths. 1. What is a red dwarf? How massive is a red dwarf? How long do red dwarf stars live? 2. Do we expect to find red dwarfs that formed when the galaxy was just forming and are still on the main sequence? (yes) 3. After the sun is a giant, it evolves to the horizontal branch and then up the asymptotic giant branch and gets very bright. It will probably engulf and devour the Earth. 4. Light pressure drives off the remaining hydrogen surface layers and the hot underlying star ionizes the gas and forms a planetary nebula. 5. Look at the pictures on pages 266-267 6. What happens to the star after it has ejected a planetary nebulae? What is that object called? (White Dwarf - Figure 4 on Page 267) 7. The central part of a white dwarf is crystallized carbon. We know that by another name. (diamond) 8. What happens to the size of a white dwarf as its mass gets larger? (it gets smaller in size see: Fig 13-4) 9. The sun will probably eject a planetary nebulae in about 5 billion years.(Figure 13-5) 10. Binary stars lose mass that eventually flows onto the other star. When one star is a white dwarf - it can become a nova explosion. 11. Massive stars, much more massive than the sun, will fuse hydrogen to helium, helium to carbon and oxygen, carbon to neon and magnesium, and neon to silicon and finally silicon to iron. Look at Figures 12-11, 12-12, 13-11 and Tables 13-1 and 12-3. 12. The iron core then splits into helium and it implodes -- this produces a Supernova Type II explosion also called a core-collapse supernova (Page 276 and Figure 13-3) 13. The most studied supernova remnant is the Crab Nebula which comes from a supernova that exploded on July 4, 1054. (We still celebrate that date with fireworks) (Figure 13-17) 14. When did Supernova 1987A occur? What is its importance? (Figure 13-19) 14a. I was part of the team that used SOFIA to study SN 2014j (Figure 13-21) 15. A local SN could be devastating to life on the earth. 16. Which bright star did I suggest could go SN in the near future - like tonight (check and see if it is still there)? 17. A Supernova of Type Ia (not just I) comes from the evolution of binary systems in which matter flows onto a white dwarf until its mass reaches the Chandrasekhar mass and it explodes. 18. A Supernova can become as bright as an entire galaxy (Figures 13-11, 13-12, 13-14, 13-21) Chapter 14. Neutron Stars and Black Holes 1. What are the masses and sizes of neutron stars? (About 10 km - the size of Tempe) 2. What is a pulsar? Who discovered pulsars? And when? I showed the actual tracing in class. (Figure 14-2) 3. There is a pulsar in the center of the Crab Nebulae. It is losing energy that is heating the gas that forms the nebula. Read pages 289 and 292. 4. What does a light house have to do with the observed emission from a pulsar? (see pages 290-291 5. Look at Figure 14-3 about the light curve of the Crab in the optical. 6. Hulse and Taylor were awarded the Nobel Prize for their discovery of Binary Pulsars. 7. What might it be like to live on a planet orbiting a pulsar? (Figure 14-10) 8. The escape velocity is that speed required to actually escape from the planet or star or neutron star or black hole. What is the escape velocity from the Earth? (980 cm/s2) 9. If we are sufficiently close to a black hole -- inside the event horizon -- we cannot escape no matter how fast we move. So don’t try it at home. I talked about escape velocities from the Sun, a White Dwarf, a Neutron Star and Black Hole. 10. I gave a formula in class for the size of the event horizon of a black hole. Know how to use it. (Table 14-1) 11. How big (radius) would the black hole be if the mass of the Earth were squeezed to the size where no light could escape? (About 1 cm) 12. How does the size of the event horizon increase as the mass increases? 13. We could approach to within a few 100,000 kilometers of a black hole and not be affected. 14. Skip section 14-3a I talked about the material in Section 14-3b. 15. Black Holes exist. Not only are there stellar mass black holes, there are multi-million solar mass black holes in the centers of galaxies. 16. Look at table 14-2. I was part of the team that discovered and studied V404 Cyg in 1989. I have also worked on A0620-00. These systems contain stellar mass black holes. 17. The mass of the Black Hole in M67 is 6 x 109 Solar masses. How big is its Schwarzschild Radius? (Done in class) Chapters ?: We will need a number of ideas from previous chapters: 1) Cepheid Variable stars in section 12-4b (pages 256-258) 2) Doppler Shift / Effect in section 7-3b and 7-3c (pages 138-140) 3) Introduction of the idea of Dark Matter in section 15-2b. That also requires the idea of Kepler’s “Law” as derived by Newton in section 5-2e Chapter 17: Active Galactic Nuclei: Seyferts and Quasars 1. Galaxies with central Black Holes do strange and wonderful things and Black Holes are messy eaters. This is what he means by Active. 2. Seyfert galaxies are spiral galaxies with bright nuclei. That is where a central black hole is accreting material from stars and gas that is passing by. 3. Double lobed radio sources are galaxies with central black holes that are ejecting a lot of gas in jets. 4. One “nearby” one was just imaged by the Event Horizon Telescope - M87. 5. Section 17-1c introduces Quasars (Quasi-Stellar Radio Sources) and also reintroduces the doppler shift. 3C-273 was the first Quasar discovered by Maarten Schmidt (he is Dutch) in 1963. 6. Look at pages 366-367. 7. We really don’t know how supermassive Black Holes are formed and why they are at the centers of Galaxies. 8. Note the definition of “z” = redshift =on Page 365. “z” is used throughout Chapter 18. It is just a way to use the Doppler shift and not worry when the shift is larger than one. 9. A Tidal Disruption Event is when a star passes close to a central black hole and is torn apart. We have observed a number of these with the Swift X-ray satellite. 10. Quasars seemed to have formed when galaxies were forming during an active period in the evolution of the universe about 10 billion years ago. Chapter 18: Cosmology 1. Read about Olber’s Paradox: Why is the sky dark at night? It is a question that has only recently been answered. (Figure 18-3) 2. We assume that the Universe is Isotropic and Homogeneous: It will look the same from wherever we view it and on the largest scales matter is spread uniformly through out the Universe. 3. We also have evidence that the same physical laws hold throughout the universe. 4. The Cosmological Principal means that the Universe looks the same from wherever we are standing in the Universe. 5. The Universe is expanding and carrying the Galaxies along with it. Neither the Galaxies nor clusters of Galaxies are expanding - local gravity overcomes the expansion of the Universe. 6. Read and try to understand the usefulness of the Raisin Bread Analogy. How old is the Universe? (Figure 18-4 and 18-5) 7. Read about an Open, Flat, and Closed universe.
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