Answer Key for Exam A 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. 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. 3. 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 1 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 5. 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. 6. 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 7. 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 2 8. Hawking radiation is emitted by a black hole when: (a) the black hole rotates quickly. (b) the black hole accretes material. (c) avirtualpairofparticlesiscreatedfromthevacuumofspace. (d) synchrotron radiation is emitted by infalling charged particles. 9. 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) 10. Normally, muons created by cosmic rays at high altitudes decay in a very short time, a time so short that they should not reach the ground. From the figure below, which muon is most likely to be detected on the ground? (a) muon A (b) muon B (c) muon C (d) muon D 11. 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) 3 12. The event horizon of a black hole is defined as: (a) the point of maximum gravity. (b) the radius of the original neutron star before it became a black hole. (c) the point at which shock waves emanate from the strong gravitational distortion the black hole creates in the fabric of spacetime. (d) the radius at which the escape speed equals the speed of light. 13. 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 14. 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 15. 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 16. 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) 17. 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 4 18. 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 19. Besides shape, what characteristic clearly separates elliptical galaxies from spiral galax- ies? (a) size (b) age (c) shape (d) color 20. 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. 21. 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. 22. The property of a star that determines its destiny is its: (a) density (b) radius (c) luminosity (d) mass 23. Detection of solar neutrinos confirms that: the Sun’s (a) core is powered by proton-proton fusion. (b) transport by radiation occurs throughout much of the solar interior. (c) magnetic fields are responsible for surface activity on the Sun. (d) convection churns the base of the solar atmosphere. 5 24. 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. 25. is the result of mass distorting the fabric of spacetime. (a) Energy (b) Fusion (c) Radiation (d) Gravity 26. Which star spends the least time as a main-sequence star? (a) 0.5 M (b) 3 M (c) 1 M (d) 10 M 27. 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 6 28. 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) 29. Stars reach the Zero Age Main Sequence (ZAMS) when: (a) They start burning helium in their cores (b) They cross the birth line (c) They start burning hydrogen in their cores (d) They start burning hydrogen in a shell 30. 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 31. 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 32. 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 33. 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 7 34. Stars less than 8 M will end up as: (a) helium white dwarfs (b) neutron stars (c) carbon/oxygen white dwarfs (d) black holes 35. Most of the luminosity from the sun is emitted from the: (a) Corona (b) Chomosphere (c) Photosphere (d) Solar Wind 36. 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 37. 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 38. Stars leave the main sequence when (a) They start burning helium in their cores (b) They ascend the red giant branch (c) They run of of hydrogen in their cores (d) They start burning hydrogen in a shell 8 39. 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. 40. The energy for solar activity comes from (a) Radiation (b) Magnetic Fields (c) Convection (d) Conduction 41. 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 42. 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. 43. 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. 44. 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 9 45. An iron core cannot support a massive main-sequence star because iron: (a) has poor nuclear binding energy.