Answer Key for Exam D 2 points each Choose the answer that best completes the question. Read each problem carefully and read through all the answers. Take your time. If a question is unclear, ask for clarification during the exam. Mark your answers on the scantron sheet and on your copy of the exam. Keep your copy of the exam and check your grade with the posted answers on the course website and the grade posted on D2L. You will have 1 week to ask for corrections. 1. The Exam Version listed at the top is: (a) Version A (b) Version B (c) Version C (d) Version D 2. Sunspots appear dark because: they have lower (a) densities. (b) they have lower rotation rates. (c) they have lower temperatures. (d) they are storm systems like those on the giant planets. 1 3. The Type II supernova that created the Crab Nebula (image below) was seen by Chinese and Arab astronomers in the year A.D.1054. Because the star is 6,500 light-years away from us, we know the star exploded in the year: (a) A.D. 7554. (b) A.D. 1054. (c) 5446 B.C. (d) 7554 B.C. 4. What ionizes the gas in a planetary nebula (see the image below) and makes it visible? (a) X-ray photons emitted by a pulsar (b) ultraviolet photons emitted by the stellar core (c) the shock wave from a supernova (d) hydrogen burning in the nebular gas 2 5. We can determine how the density changes with radius in the Sun using: (a) radar observations. (b) high-energy (gamma ray) observations. (c) neutrino detections. (d) helioseismology. 6. Stars less than 8 M will end up as: (a) helium white dwarfs (b) neutron stars (c) carbon/oxygen white dwarfs (d) black holes 7. In Type Ia supernovae, the white dwarf reaches the Chandrasekhar mass and explodes because (a) there is runaway thermonuclear fusion of hydrogen on the surface (b) the hydrogen does not have time to cool burns to Carbon and Oxygen non- degenerately (supported by ordinary thermal pressure) (c) Carbon and Oxygen fusion runs away in the center due to the fact that white dwarfs are supported by quantum mechanical pressure. (d) both (b) and (c) 8. Neutron stars are supported by (a) Ordinary thermal pressure supplied by the energy from nuclear reactions (b) Quantum mechanical pressure of relativistic electrons (c) Quantum mechanical pressure of non-relativistic neutrons (d) The nuclear force 9. Which of the following galaxies can be found with a bar-like structure in them? (a) spiral (b) irregular (c) elliptical (d) all of the above 10. If the Sun were to be instantly replaced by a 1 M black hole, the gravitational pull of the black hole on Earth would be: (a) much greater than it is now. (b) the same as it is now. (c) much smaller than it is now. (d) irrelevant because Earth would be quickly obliterated by the strong tidal force of the black hole. 3 11. A low-mass main-sequence star’s climb up the red giant branch is halted by: (a) the end of hydrogen shell burning. (b) the beginning of helium fusion in the core. (c) quantum mechanical pressure in the core. (d) instabilities in the star’s expanding outer layers. 12. Pulsars are the result of (a) the rotation of a neutron star with a strong magnetic field (b) core collapse supernovae (c) little green men (d) we have no idea 13. The Hubble constant, H0, represents: (a) the rate of expansion of the universe. (b) the speed at which galaxies are moving away from us. (c) the time it takes a galaxy to move twice as far away from us. (d) the size of the universe. 14. According to Hubble’s law, as the distance of a galaxy its increases. (a) increases; luminosity (b) decreases; luminosity (c) increases; recessional velocity (d) decreases; recessional velocity 15. Besides shape, what characteristic clearly separates elliptical galaxies from spiral galax- ies? (a) size (b) age (c) shape (d) color 16. The energy for solar activity comes from (a) Radiation (b) Magnetic Fields (c) Convection (d) Conduction 4 17. The collapse of the core of a high-mass star at the end of its life lasts approximately: (a) 1second. (b) 1 hour. (c) 1 week. (d) 1 year. 18. The equivalence principle says that: (a) being stationary in a gravitational field is the same as being in an accelerated reference frame. (b) the universe is homogeneous and isotropic. (c) at any radius inside a star, the outward gas pressure must balance the weight of the material on top. (d) mass and energy are interchangeable, and neither can be destroyed. 19. Which point on the figure below represents the location on the H-R diagram where the star is expelling mass creating a planetary nebula? (a) A (b) C (c) B (d) D 20. The Collapsar model explains: (a) The formation of white dwarfs (b) The formation of magnetars (c) The formation of neutron stars (d) The formation of some gamma ray bursters (e) none of the above 5 21. If you measure the average brightness and pulsation period of a Cepheid variable star, you can also determine its: (a) age. (b) distance. (c) rotation period. (d) mass. 22. Photons have no mass, and Einstein’s theory of general relativity says: (a) their paths through spacetime are curved in the presence of a massive body. (b) their apparent speeds depend on the observer’s frame of reference. (c) they should not be attracted to a massive object. (d) their wavelengths must remain the same as they travel through spacetime. 23. The bulk of neutron stars are made of (a) neutrons of course (b) iron (c) neutrons, with some protons and electrons (d) we have no idea 24. The most likely dark matter candidate seems to be: (a) black holes (b) neutron stars (c) planets (d) neutrino-like particles (e) super symmetric matter 25. Neutron stars are produced by (a) Type Ia supernovae (b) core collapse of the iron core of a massive star (c) novae on carbon/oxygen white dwarfs (d) CNO burning in solar-type stars 26. Helium burns in the core of a horizontal branch star via and produces . (a) the triple-alpha reaction; carbon and oxygen (b) the triple-alpha reaction; oxygen and neon (c) the proton-proton chain; lithium (d) the proton-proton chain; iron 6 27. Most of the luminosity from the sun is emitted from the: (a) Corona (b) Chomosphere (c) Photosphere (d) Solar Wind 28. On the main sequence a 3 M star creates energy using: (a) the CNO cycle (b) the p-p cycle (c) the triple alpha process (d) gravitational contraction 29. The maximum mass of a white dwarf is: (a) The Chandrasekhar mass (b) About 1.4 M (c) About 0.6 M (d) both (a) and (b) 30. is the result of mass distorting the fabric of spacetime. (a) Energy (b) Fusion (c) Radiation (d) Gravity 31. You observe a supernova spectrum with no Balmer lines, but a strong Silicon line with absorption at 6150 A.˚ It means you are seeing (a) SN Ia (b) Nova (c) Core Collapse (d) Can not tell 32. You observe a supernova spectrum with strong Balmer Lines. It means you are seeing (a) SN Ia (b) Nova (c) Core Collapse (d) Can not tell 7 33. The maximum mass of a neutron star is: (a) The Chandrasekhar mass (b) At least 2.2 M (c) Not completely certain, since we haven’t yet solved nuclear physics (d) both (b) and (c) 34. Which star spends the least time as a main-sequence star? (a) 0.5 M (b) 3 M (c) 1 M (d) 10 M 35. On the main sequence the Sun creates energy using: (a) the CNO cycle (b) the p-p cycle (c) the triple alpha process (d) gravitational contraction 36. Novae occur because (a) runaway thermonuclear fusion of hydrogen on the surface (b) the hydrogen has time to cool and is supported by quantum mechanical pressure of electrons (c) Carbon and Oxygen fusion runs away in the center (d) both (a) and (b) 37. What does the Hubble tuning fork illustrate? (a) the evolutionary sequence of galaxies (b) the motions of galaxies (c) the locations of galaxies (d) aclassificationscheme 38. Asymptotic giant branch (AGB) stars have high mass-loss rates because they: (a) are rotating quickly. (b) have strong winds. (c) have weak magnetic fields. (d) have jets. 8 39. Nearly all the Carbon in the Universe is produced in (a) Core collapse supernovae (b) Type Ia supernovae (c) All types of supernovae (d) during CNO burning 40. White dwarfs are supported by (a) Ordinary thermal pressure supplied by the energy from nuclear reactions (b) Quantum mechanical pressure of relativistic electrons (c) Quantum mechanical pressure of non-relativistic neutrons (d) The nuclear force 41. The property of a star that determines its destiny is its: (a) density (b) radius (c) luminosity (d) mass 42. What is the radius of the event horizon of a 10 solar mass black hole? (a) 3 km (b) 30 km (c) 10 km (d) 100 km 43. An iron core cannot support a massive main-sequence star because iron: (a) has poor nuclear binding energy. (b) cannot fuse with other nuclei to produce energy. (c) supplies too much pressure. (d) fusion only occurs in a degenerate core. 44. The solar cycle is the result of (a) Convection (b) Winding up of the solar magnetic field (c) Di↵erential rotation (d) Both (b) and (c) 9 45.