Chapter 12 Review TRUE/FALSE. Write 'T' if the statement is true and 'F' if the statement is false. 1) As a main-sequence star, the Sun's hydrogen supply should last about 10 billion years from the zero-age main sequence until its evolution to the giant stages. 1) 2) About 90% of the star's total life is spent on the main sequence. 2) 3) Helium fusion requires a higher temperature than hydrogen fusion. 3) 4) The main reason that stars evolved off the main sequence is because they are becoming less massive as energy is lost into space from the proton-proton cycle. 4) 5) Paradoxically, while the core of the red giant is contracting and heating up, its radiation pressure causes its photosphere to swell up and cool off. 5) 6) The helium flash stage lasts several thousand years. 6) 7) A star may undergo two or more red giant expansion stages. 7) 8) A typical star burns helium for about the same amount of time it burns hydrogen. 8) 9) Our Sun will never become hot enough for carbon nuclei to fuse. 9) 10) White dwarfs were once the cores of stars that produced planetary nebulae. 10) 11) Elements heavier than iron are formed mainly in supernovae. 11) 12) Supergiant stars are burning different fuels in several shells around the core. 12) 13) A star system can become a Type I supernova several times. 13) 14) Gold is rare since the only time it can be formed is during the core collapse of a supernova. 14) 15) Chandrasekhar's limit is 1.4 times the mass of our Sun. 15) 16) Most of the energy released during a supernova is emitted as neutrinos. 16) MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 17) When a star's inward gravity and outward pressure are balanced, the star is said to be 17) A) in gravitational collapse. B) a stage 2 protostar. C) in hydrostatic equilibrium. D) in rotational equilibrium. E) in thermal expansion. 1
18) What temperature is needed to fuse helium into carbon? 18) A) 100,000 K B) 5,800 K C) 100 million K D) one billion K E) 15 million K 19) When a low mass star first runs short of hydrogen in its core, it becomes brighter because 19) A) the helium flash increases the size of the star immensely. B) it explodes as a nova. C) the core contracts, raising the temperature and extending the hydrogen burning shell outward. D) its outer, cooler layers are shed, and we see the brighter central core. E) helium fusion gives off more energy than does hydrogen. 20) A star is on the horizontal branch of the H-R diagram. Which statement is true? 20) A) It is burning both hydrogen and helium. B) It is about to experience the helium flash. C) The star is about to return to the main sequence. D) It is burning only helium. E) The star is contracting. 21) The helium flash converts helium nuclei into 21) A) beryllium. B) oxygen. C) boron. D) carbon. E) iron. 22) Can a star become a red giant more than once? 22) A) no, it will lose so much mass as to cross the Chandrasekhar Limit B) no, the planetary nebula blows off all the outer shells completely C) no, or we would see them as the majority of naked-eye stars D) yes, before and after the helium flash E) yes, before and after the Type II supernova event 23) A white dwarf has the mass of the Sun and the volume of 23) A) Mars. B) Earth. C) Eros. D) Jupiter. E) the Moon. 24) Which of these is true of planetary nebulae? 24) A) They are ejected envelopes surrounding a highly evolved low-mass star. B) They are the material which causes the eclipses in eclipsing binary systems. C) They are rings of material around protostars that will accrete into planets in time. D) They are expelled by the most massive stars in their final stages before supernova. E) They are the envelopes that form when blue stragglers merge. 25) Compared to our Sun, a typical white dwarf has 25) A) a smaller mass and twice the density. B) about the same mass and density. C) about the same mass and a million times higher density. D) a larger mass and a hundred times lower density. E) a smaller mass and half the density. 2
26) A surface explosion on a white dwarf, caused by falling matter from the atmosphere of its binary companion, creates what kind of object? A) Type I supernova B) Type II supernova C) hypernova D) gamma ray burstar E) nova 26) 27) Which of these evolutionary paths is the fate of our Sun? 27) A) planetary nebula B) supernova of Type II C) pulsar D) brown dwarf E) nova 28) Black dwarfs are 28) A) not found yet; the oldest, coldest white dwarf in the Galaxy has not cooled enough yet. B) very common, making up the majority of the dark matter in the universe. C) often made from very low mass protostars that never fuse hydrogen. D) rare, for few binary systems are close enough for this merger to happen. E) rare, for collapsing cores of over three solar masses are uncommon. 29) Of the elements in your body, the only one not formed in stars is 29) A) calcium. B) hydrogen. C) iron. D) aluminum. E) carbon. 30) An iron core cannot support a star because 30) A) iron is the heaviest element, and sinks upon differentiation. B) iron has poor nuclear binding energy. C) iron supplies too much pressure. D) iron is in the form of a gas, not a solid, in the center of a star. E) iron cannot fuse with other nuclei to produce energy. 31) A 20-solar-mass star will stay on the main sequence for 10 million years, yet its iron core can exist for only a A) day. B) week. C) year. D) century. E) month. 31) 32) As a star's evolution approaches the Type II supernova, we find 32) A) helium to carbon fusion takes at least 100 million K to start. B) the heavier the element, the higher the temperature to fuse it. C) photo disintegration of iron nuclei begins at 10 billion K to ignite the supernova. D) the heavier the element, the less time it takes to make it. E) All of the above are correct. 33) Type II supernovae occur when their cores start making 33) A) iron. B) uranium. C) oxygen. D) silicon. E) carbon. 3
34) If it gains sufficient mass from a binary companion, a white dwarf can become a 34) A) black dwarf. B) Type I supernova. C) brown dwarf. D) planetary nebula. E) Type II supernova. 35) The Chandrasekhar limit is 35) A) the lower-mass limit for a Type II supernova. B) the temperature at which helium fusion starts. C) the point at which a planetary nebula forms. D) the upper-mass limit for a white dwarf. E) the temperature at which hydrogen fusion starts. 36) The brightest stars in a young open cluster will be 36) A) massive blue main-sequence stars. B) Cepheid variables. C) T-Tauri variables. D) red giants. E) yellow main-sequence stars like the Sun. 37) What is the typical age for a globular cluster associated with our Milky Way? 37) A) 200 million years B) a few million years C) a billion years D) 10-12 billion years E) 45 billion years 38) Which is used observationally to determine the age of a star cluster? 38) A) the total number of main-sequence stars B) the number of white dwarfs C) the luminosity of the main-sequence turn-off point D) the ratio of giants to supergiants E) the amount of dust that lies around the cluster SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 39) Most of our knowledge of stellar evolution comes from studies of. 39) 40) The star clusters are younger, and their stars richer in heavier elements released in supernova events. 40) 4
Answer Key Testname: CHAPTER 12 REVIEW 1) TRUE 2) TRUE 3) TRUE 4) FALSE 5) TRUE 6) FALSE 7) TRUE 8) FALSE 9) TRUE 10) TRUE 11) TRUE 12) TRUE 13) FALSE 14) TRUE 15) TRUE 16) TRUE 17) C 18) C 19) C 20) A 21) D 22) D 23) B 24) A 25) C 26) E 27) A 28) A 29) B 30) E 31) A 32) E 33) A 34) B 35) D 36) A 37) D 38) C 39) clusters 40) open 5