PHYS 160 Astronomy Take-home Test #4 Fall 2017

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1 PHYS 160 Astronomy Take-home Test #4 Fall 2017 Instructions: This is a take-home test. The test period starts Monday 11/27/2017 at 2:10pm and ends at Wednesday 11/29/2017 at 1:10pm. The test must represent the work done by the individual student. You may use the following resources when solving these test problems: any files on the PHYS 160 web page including HW solutions and class materials any textbook or reference book your own class notes any internet resource that is available to the general public You may not use help from any person including professors, other students, or tutors (live or online). Students may ask Dr. Wright to clarify questions. her at wright@hendrix.edu if you need to ask a question outside of normal office hours. The finished test may be turned in to MCACX 104 before 1:00pm on Wednesday 11/29 or in class by 1:10pm. Ten points will be deducted for each 30 minutes over the deadline if turned in late. There is no penalty for turning the test in early. By turning in a test to be graded, you are certifying that you have followed the rules of the test.

2 I. True/False (1 point each) Circle the T if the statement is true, or F if the statement is false on your answer sheet. 1. A clock approaching the edge of a black hole would experience time dilation. 2. All low-mass stars die in a supernova explosion. 3. All neutron stars are pulsars. 4. All stars with the same surface temperature have approximately the same luminosity. 5. All things, even light are attracted by gravity. 6. A magnitude 3 star is brighter than a magnitude 5 star (if they are at the same distance from the observer). 7. As it evolves off the main sequence, a star gets larger. 8. Black holes are impossible to observe because they emit no radiation whatsoever. 9. If you could touch it, the event horizon would be very hard. 10. The Sun will get brighter as it begins to run out of fuel in its core. II. Definitions (1 point each). There are 10 definitions given. Select the word or phrase that best matches the definition from the table of words below. Put your answer on the answer sheet. Note, there are more words than there are definitions, so not all of them will be matched. Accretion disk nova Apparent magnitude Pulsar Reflection nebula singularity 21 cm radiation Supernova Binary star Event horizon White dwarf Black hole Neutron star chromosphere luminosity Corona Neutrino Instability strip photosphere Solar wind Hertzsprung-Russell diagram Planetary nebula Schwarzschild radius Main sequence 1. An orbiting disk of matter spiraling in toward a star or black hole. 2. The measure of brightness of light from a star or other object as seen from Earth. 3. An object whose gravity is so strong that the escape velocity from it exceeds the speed of light. 4. A region on the Hertzsprung-Russell diagram occupied by pulsating stars. 5. The rate at which electromagnetic radiation is emitted from a star or other object. 6. A star that experiences a sudden outburst of radiant energy, temporarily increasing its luminosity by a factor of between 10 4 and This process will repeat many times. 7. A luminous shell of gas ejected from an old, low-mass star. 8. The distance from the center to the event horizon in a black hole. 9. A place of infinite curvature of spacetime in a black hole. 10. The region in the solar atmosphere from which most of the visible light escapes into space.

3 III. Multiple Choice (1 point each) Select the letter next to the best answer for each question. Circle the letter on your answer sheet. 1. We would be more likely to get an accurate measurement of distance from Earth to a nearby star if we took the angular measurements at times separated by what time interval? a. 6 hours apart b. 12 months apart c. 6 months apart d. 12 hours apart e. 1 hour apart 2. A fusion reaction results in a. the breaking apart of a nucleus b. the building up of heavier nuclei from lighter ones c. the complete annihilation of nuclei d. the creation of neutrons 3. At what point in time did the protosun become a star? a. when it became hot enough to emit light and heat. b. when the temperature began to rise in the center. c. when the jovian planets were completely formed. d. when the terrestrial planets were completely formed. e. when the core became hot and dense enough to begin fusion of hydrogen into helium. 4. For what reason do astronomers want to observe and measure neutrinos from the sun? a. neutrinos are more energetic than photons from the sun. b. neutrinos are easier to detect than photons. c. neutrinos give direct information about the photosphere. d. neutrinos give direct information about the sun's core. e. none of the above. 5. Solar granulation is seen a. only near sunspots b. only in the chromosphere c. everywhere on the sun's photosphere except on sunspots d. in the corona e. in the chromosphere 6. The 11-year cycle of sunspots corresponds to a. the period of change in the magnetic field of the Sun. b. the rotation period of the Sun near the equator. c. the rotation of the Sun near the poles. d. the revolution period of Jupiter e. none of the above.

4 7. Which of the following statements about the energy generating process in the Sun is true? a. it can be duplicated efficiently on Earth with our present technology b. mass is converted to energy c. hydrogen becomes helium in one step d. we have detected many more neutrinos from the process than we expected to find 8. According to the astronomical definition of star, which of these objects is truly a star? a. white dwarf b. neutron star c. black hole d. red giant e. pulsar 9. A pulsar "beeps" or "blinks" at us because of its rapid a. pulsation in size b. rotation c. fluctuation in temperature d. changing magnetic field strength e. none of these 10. A star s luminosity is a. dependent on the star s size and distance b. calculated by measuring the star s parallax angle c. dependent on the star s temperature and amount of surface area d. expressed as its apparent visual magnitude 11. Binary stars are important because they allow us to calculate the of stars a. compositions b. proper motions c. radial velocities d. temperatures e. masses 12. Can a white dwarf explode? a. Yes, but only if another star collides with it, which is very unlikely b. Yes, but only if it is in a binary star system c. Yes, but only if nuclear reactions in the white dwarf core reach the stage of silicon fusion, producing iron. d. No; white dwarfs are held up by electron degeneracy pressure, and this configuration is stable against collapse or explosion.

5 13. Considering only main sequence stars, the most massive stars are the a. hottest and brightest b. hottest and dimmest c. coolest and brightest d. coolest and dimmest e. cannot tell with info given 14. How might a celestial object be proven to be a black hole? a. by measuring its mass and diameter directly b. by measuring its gravitational effects on nearby material c. by noting that nothing comes out of it d. since a black hole emits no radiation of any kind, it is impossible to even detect one, let alone prove anything about it 15. If the sun could magically and suddenly become a black hole (of the same mass) the Earth would a. continue in its same orbit. b. be pulled closer, but not necessarily into the black hole. c. be pulled into the black hole. d. fly off into space. 16. If two different main sequence stars were to form at the same time in different locations, with star A three times more massive than star B, how would their lifetimes compare? a. Both stars would have equal lifetimes. b. Star A would live much longer than star B c. Star B would live much longer than star A d. There is not enough information given to determine the answer. 17. Pulsars cannot be spinning white dwarfs because a. white dwarfs are not that common. b. white dwarfs are not dense enough. c. white dwarfs do not have magnetic fields. d. a white dwarf spinning that fast would fly apart. 18. Red giants are more luminous than white dwarfs because a. they are larger b. they are closer c. they are hotter d. all of the above e. the statement is not true

6 19. Stars on the main sequence that have a small mass are a. bright and hot b. dim and hot c. dim and cool d. bright and cool e. cannot tell from data given 20. A star that is cool and very luminous must have a. a very large radius b. a very small radius c. a very small mass d. a very great distance e. very low velocity 21. Suppose you observe a previously unknown star and find its apparent magnitude. To determine the star s absolute magnitude, you need to know the star s a. distance b. color c. velocity d. brightness as seen from Earth e. Doppler shift 22. The definition of a main-sequence star is one a. with a surface temperature equal to that of the Sun b. in which nuclear fusion reactions generate sufficient energy to oppose further collapse of the star. c. whose age after birth is about 1 million years old d. with a luminosity precisely equal to that of the Sun. 23. Theory predicts that a neutron star should spin faster than the original star because a. it was given increased speed by the supernova explosion b. it was given increased by a companion star c. it conserved mass as it collapsed d. it conserved angular momentum as it collapsed e. the statement is false, neutron stars do not spin fast. 24. The star that is seen at the center of a planetary nebula is a. a white dwarf star b. a neutron star c. the accretion disk around a black hole d. a planet in the process of formation

7 25. The Sun will at some time in the future become a. a red giant b. a white dwarf c. a black dwarf d. all of the above e. none of the above 26. Three M-class stars are identified as being main sequence, giant, and supergiant stars respectively. In what physical properties do they differ? a. luminosity b. spectral class c. surface temperature d. color index e. parallax 27. Variable stars such as Cepheid variables are used in what important measurement in astronomy? a. The measurement of the distances to stars. b. The measurement of the rotation speeds of galaxies. c. The measurement of the surface temperatures of stars. d. The keeping of accurate time. 28. What do our atmosphere and a reflection nebula surrounding a star have in common? a. They both appear blue because of preferred scattering of this color of light. b. They both have about the same temperature. c. They have almost the same average density of gas d. They both contain the same types of molecules. 29. Which of the following has a size closest to that of a neutron star? a. The Sun b. The Earth. c. A basketball d. A small city e. Our classroom. 30. What atomic transition occurs in the atoms of hydrogen gas in the spiral arm of the Milky Way to produce 21 centimeter radiation? a. the transition from n=2 to n=1 energy levels in the atomic spectrum. b. The change in rotation axis of the molecular hydrogen. c. The change in vibrational energy state of the hydrogen molecule. d. The inversion of the electron spin relative to the proton spin, from parallel to antiparallel.

8 IV. Short Answer Questions Answer any five (5) of the following questions. Each question is worth 10 points. Answers may contain paragraphs, lists, and drawings. Please put your answers on plain or lined paper. 1. Describe the Active Sun. What causes the activity? 2. What is the hydrogen fusion reaction? How is hydrogen burning fundamentally different than the burning of a log in a fireplace? 3. Compare white dwarf and a neutron star. Which is more common and why? 4. Describe how a variable star is created. How can a variable star help to determine distance to a galaxy? Describe what is changing in the variable star every few days. 5. If the temperature of a main-sequence star is known by Wien's Law, what other information can be determined by using the HR diagram? 6. What are the possible left-over objects from a supernova? Why is it easier to find a supernova remnant with a radio telescope than with an optical telescope?