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Review Clicker Question 9 -s Test 3 The Sun & the Stars Copyright © 2010 Pearson Education, Inc. Question 9 - 1 The visible light we see from our Sun comes from which part? Copyright © 2010 Pearson Education, Inc. a) core b) corona c) photosphere d) chromosphere e) convection zone Question 9 - 1 The visible light we see from our Sun comes from which part? a) core b) corona c) photosphere d) chromosphere e) convection zone The photosphere is a relatively narrow layer below the chromosphere and corona, with an average temperature of about 6000 K. Copyright © 2010 Pearson Education, Inc. Question 9 - 2 The density of the Sun is most similar to that of Copyright © 2010 Pearson Education, Inc. a) a comet. b) Jupiter. c) Earth. d) interstellar gas. e) an asteroid. Question 9 - 2 The density of the Sun is most similar to that of a) a comet. b) Jupiter. c) Earth. d) interstellar gas. e) an asteroid. The Sun is a ball of charged gas, without a solid surface. Jupiter has a similar composition, but not enough mass to be a star. Copyright © 2010 Pearson Education, Inc. Question 9 - 3 The Sun is stable as a star because Copyright © 2010 Pearson Education, Inc. a) gravity balances forces from pressure. b) the rate of fusion equals the rate of fission. c) radiation and convection balance. d) mass is converted into energy. e) fusion doesn’t depend on temperature. Question 9 - 3 The Sun is stable as a star because a) gravity balances forces from pressure. b) the rate of fusion equals the rate of fission. c) radiation and convection balance. d) mass is converted into energy. e) fusion doesn’t depend on temperature. The principle of hydrostatic equilibrium explains how stars maintain their stability. Copyright © 2010 Pearson Education, Inc. Question 9 - 4 The proton–proton cycle involves what kind of fusion process? Copyright © 2010 Pearson Education, Inc. a) carbon (C) into oxygen (O) b) helium (He) into carbon (C) c) hydrogen (H) into helium (He) d) neon (Ne) into silicon (Si) e) oxygen (O) into iron (Fe) Question 9 - 4 The proton–proton cycle involves what kind of fusion process? a) carbon (C) into oxygen (O) b) helium (He) into carbon (C) c) hydrogen (H) into helium (He) d) neon (Ne) into silicon (Si) e) oxygen (O) into iron (Fe) In the P-P cycle, four hydrogen nuclei (protons) fuse into one helium nucleus, releasing gamma rays and neutrinos. Copyright © 2010 Pearson Education, Inc. Question 9 - 5 A neutrino can escape from the solar core within minutes. How long does it take a photon to escape? Copyright © 2010 Pearson Education, Inc. a) minutes b) hours c) months d) hundreds of years e) about a million years Question 9 - 5 A neutrino can escape from the solar core within minutes. How long does it take a photon to escape? a) minutes b) hours c) months d) hundreds of years e) about a million years Gamma ray photons are absorbed and re-emitted continuously in the layers above the core. They gradually shift in spectrum to visible and infrared light at the photosphere. Copyright © 2010 Pearson Education, Inc. Question 9 - 6 What is probably responsible for the increase in temperature of the corona far from the Sun’s surface? Copyright © 2010 Pearson Education, Inc. a) a higher rate of fusion b) the Sun’s magnetism c) higher radiation pressures d) absorption of X rays e) convection currents Question 9 - 6 What is probably responsible for the increase in temperature of the corona far from the Sun’s surface? a) the higher rate of fusion b) the Sun’s magnetism c) higher radiation pressures d) absorption of X rays e) convection currents Apparently the Sun’s magnetic field acts like a pump to increase the speeds of particles in the upper corona. Copyright © 2010 Pearson Education, Inc. Question 9 - 7 The number of sunspots and solar activity in general peaks Copyright © 2010 Pearson Education, Inc. a) every 27 days, the apparent rotation period of the Sun’s surface. b) once a year. c) every 5½ years. d) every 11 years. e) approximately every 100 years. Question 9 - 7 The number of sunspots and solar activity in general peaks a) every 27 days, the apparent rotation period of the Sun’s surface. b) once a year. c) every 5 ½ years. d) every 11 years. e) approximately every 100 years. The sunspot cycle shows a consistent 11-year pattern of activity dating back more than 300 years. Copyright © 2010 Pearson Education, Inc. Question 9 - 8 The solar neutrino problem refers to the fact that astronomers Copyright © 2010 Pearson Education, Inc. a) cannot explain how the Sun is stable. b) detect only one-third the number of neutrinos expected by theory. c) cannot detect neutrinos easily. d) are unable to explain how neutrinos oscillate between other types. e) cannot create controlled fusion reactions on Earth. Question 9 - 8 The solar neutrino problem refers to the fact that astronomers a) cannot explain how the Sun is stable. b) detect only one-third the number of neutrinos expected by theory. c) cannot detect neutrinos easily. d) are unable to explain how neutrinos oscillate between other types. e) cannot create controlled fusion reactions on Earth. Further experiments have shown that solar neutrinos can change into other types that were not initially detected. Copyright © 2010 Pearson Education, Inc. Question 10 - 1 Stellar parallax is used to measure the Copyright © 2010 Pearson Education, Inc. a) sizes of stars. b) distances of stars. c) temperatures of stars. d) radial velocity of stars. e) brightness of stars. Question 10 - 1 Stellar parallax is used to measure the a) sizes of stars. b) distances of stars. c) temperatures of stars. d) radial velocity of stars. e) brightness of stars. Parallax can be used to measure distances to stars accurately to about 200 parsecs (650 light-years). Copyright © 2010 Pearson Education, Inc. Question 10 - 2 The angle of stellar parallax for a star gets larger as the Copyright © 2010 Pearson Education, Inc. a) distance to the star increases. b) size of the star increases. c) size of the telescope increases. d) length of the baseline increases. e) wavelength of light increases. Question 10 - 2 The angle of stellar parallax for a star gets larger as the a) distance to the star increases. b) size of the star increases. c) size of the telescope increases. d) length of the baseline increases. e) wavelength of light increases. Astronomers typically make observations of nearby stars 6 months apart, making the baseline distance equal to 2 AU (Astronomical Units). Copyright © 2010 Pearson Education, Inc. Question 10 - 3 You can best model the size and distance relationship of our Sun & the next nearest star using Copyright © 2010 Pearson Education, Inc. a) a tennis ball here, and one on the Moon. b) two beach balls separated by 100 city blocks. c) two grains of sand 100 light-years apart. d) two golf balls 100 km apart. e) two baseballs 100 yards apart. Question 10 - 3 You can best model the size and distance relationship of our Sun & the next nearest star using a) a tennis ball here, and one on the Moon. b) two beach balls separated by 100 city blocks. c) two grains of sand 100 light- years apart. d) two golf balls 100 km apart. e) two baseballs 100 yards apart. The Sun is about one million miles in diameter. The next nearest star is about 25 million times farther away. Copyright © 2010 Pearson Education, Inc. Question 10 - 4 A star’s proper motion is its Copyright © 2010 Pearson Education, Inc. a) true motion in space. b) apparent shift as we view from opposite sides of Earth’s orbit every six months. c) annual apparent motion across the sky. d) motion toward or away from us, revealed by Doppler shifts. e) orbital motion around the galaxy. Question 10 - 4 A star’s proper motion is its a) true motion in space. b) apparent shift as we view from opposite sides of Earth’s orbit every six months. c) annual apparent motion across the sky. d) motion toward or away from us, revealed by Doppler shifts. e) orbital motion around the galaxy. A star’s “real space motion” combines its apparent proper motion with its radial motion toward or away from Earth. Copyright © 2010 Pearson Education, Inc. Question 10 - 5 In the stellar magnitude system invented by Hipparchus, a smaller magnitude indicates a _____ star. Copyright © 2010 Pearson Education, Inc. a) brighter b) hotter c) cooler d) fainter e) more distant Question 10 - 5 In the stellar magnitude system invented by Hipparchus, a smaller magnitude indicates a _____ star. Copyright © 2010 Pearson Education, Inc. a) brighter b) hotter c) cooler d) fainter e) more distant Question 10 - 6 A star’s apparent magnitude is a number used to describe how our eyes measure its Copyright © 2010 Pearson Education, Inc. a) distance. b) temperature. c) brightness. d) absolute luminosity. e) radial velocity. Question 10 - 6 A star’s apparent magnitude is a number used to describe how our eyes measure its Copyright © 2010 Pearson Education, Inc. a) distance. b) temperature. c) brightness. d) absolute luminosity. e) radial velocity. Question 10 - 7 The absolute magnitude of a star is its brightness as seen from a distance of Copyright © 2010 Pearson Education, Inc. a) one million km. b) one Astronomical Unit. c) one light-year. d) ten parsecs. e) ten light-years. Question 10 - 7 The absolute magnitude of a star is its brightness as seen from a distance of a) one million km. b) one Astronomical Unit. c) one light-year. d) ten parsecs. e) ten light-years. Astronomers use a distance of 10 parsecs (about 32 light-years) as a standard for specifying and comparing the brightnesses of stars. Copyright © 2010 Pearson Education, Inc. Question 10 - 8 Which of the following quantities do you need in order to calculate a star’s luminosity? Copyright © 2010 Pearson Education, Inc. a) apparent brightness (flux) b) Doppler shift of spectral lines c) color of the star d) distance to the star e) a and d Question 10 - 8 Which of the following quantities do you need in order to calculate a star’s luminosity? Copyright © 2010 Pearson Education, Inc. a) apparent brightness (flux) b) Doppler shift of spectral lines c) color of the star d) distance to the star e) a and d Question 10 - 9 What are the two important intrinsic properties for classifying stars on an H-R diagram? Copyright © 2010 Pearson Education, Inc. a) distance and surface temperature b) luminosity and surface temperature c) distance and luminosity d) mass and age e) distance and color Question 10 - 9 What are the two important intrinsic properties for classifying stars on an H-R diagram? a) distance and surface temperature b) luminosity and surface temperature c) distance and luminosity d) mass and age e) distance and color The H–R diagram plots stars based on their luminosities and surface temperatures. Copyright © 2010 Pearson Education, Inc. Question 10 - 10 Wien’s law tells us that the hotter an object, the _____ the peak wavelength of its emitted light. Copyright © 2010 Pearson Education, Inc. a) longer b) more green c) heavier d) shorter e) more constant Question 10 - 10 Wien’s law tells us that the hotter an object, the _____ the peak wavelength of its emitted light. a) longer b) more green c) heavier d) shorter e) more constant Wien’s law states that hotter stars appear more blue in color, and cooler stars appear more red in color. Copyright © 2010 Pearson Education, Inc. Question 10 - 11 We estimate the surface temperature of a star by using Copyright © 2010 Pearson Education, Inc. a) its color. b) the pattern of absorption lines in its spectrum. c) Wien’s law. d) differences in brightness as measured through red and blue filters. e) All of the above are used. Question 10 - 11 We estimate the surface temperature of a star by using Copyright © 2010 Pearson Education, Inc. a) its color. b) the pattern of absorption lines in its spectrum. c) Wien’s law. d) differences in brightness as measured through red and blue filters. e) All of the above are used. Question 10 - 12 Which spectral classification type corresponds to a star like the Sun? Copyright © 2010 Pearson Education, Inc. a) O b) A c) F d) G e) M Question 10 - 12 Which spectral classification type corresponds to a star like the Sun? a) O b) A c) F d) G e) M The OBAFGKM classification scheme is based on absorption lines. Copyright © 2010 Pearson Education, Inc. Question 10 - 13 Astronomers can estimate the size of a star using Copyright © 2010 Pearson Education, Inc. a) apparent brightness. b) direct observation of diameter. c) temperature. d) distance to the star. e) a, b, and c are all true. Question 10 - 13 Astronomers can estimate the size of a star using a) apparent brightness. b) direct observation of diameter. c) temperature. d) distance to the star. e) a, b, and c are all true. Brightness and temperature are used to plot the star on an H–R diagram, and indicate its approximate size. Some stars are large enough to measure directly. Copyright © 2010 Pearson Education, Inc. Question 10 - 14 Eclipsing binary stars are very useful for determining the Copyright © 2010 Pearson Education, Inc. a) ages of stars. b) absolute luminosities of stars. c) masses of stars. d) distances to stars. e) rotation rates of stars. Question 10 - 14 Eclipsing binary stars are very useful for determining the a) ages of stars. b) absolute luminosities of stars. c) masses of stars. d) distances to stars. e) rotation rates of stars. Analysis of the lightcurve of an eclipsing binary star system can reveal the masses of the stars. Copyright © 2010 Pearson Education, Inc. Question 10 - 15 What is the single most important characteristic in determining the course of a star’s evolution? Copyright © 2010 Pearson Education, Inc. a) density b) absolute brightness c) distance d) surface temperature e) mass Question 10 - 15 What is the single most important characteristic in determining the course of a star’s evolution? a) density b) absolute brightness c) distance d) surface temperature e) mass A star’s mass determines how fast it forms, its luminosity on the main sequence, how long it will shine, and its ultimate fate. Copyright © 2010 Pearson Education, Inc. Question 11 - 1 Some regions of the Milky Way’s disk appear dark because Copyright © 2010 Pearson Education, Inc. a) there are no stars there. b) stars in that direction are obscured by interstellar gas. c) stars in that direction are obscured by interstellar dust. d) numerous black holes capture all the starlight behind them. Question 11 - 1 Some regions of the Milky Way’s disk appear dark because a) there are no stars there. b) stars in that direction are obscured by interstellar gas. c) stars in that direction are obscured by interstellar dust. d) numerous black holes capture all the starlight behind them. Dust grains are about the same size as visible light, and they can Copyright © 2010 Pearson Education, Inc. scatter or block the shorter wavelengths. Question 11 - 2 When a star’s visible light passes through interstellar dust, the light we see Copyright © 2010 Pearson Education, Inc. a) is dimmed and reddened. b) appears to twinkle. c) is Doppler shifted. d) turns bluish in color. e) ionizes the dust and creates emission lines. Question 11 - 2 When a star’s visible light passes through interstellar dust, the light we see a) is dimmed and reddened. b) appears to twinkle. c) is Doppler shifted. d) turns bluish in color. e) ionizes the dust and creates emission lines. The same process results in wonderful sunsets, as dust in the air scatters the Sun’s blue light, leaving dimmer, redder light. Copyright © 2010 Pearson Education, Inc. Question 11 - 3 Astronomers use the term nebula to refer to Copyright © 2010 Pearson Education, Inc. a) outer envelopes of dying stars that drift gently into space. b) remnants of stars that die by supernova. c) clouds of gas and dust in interstellar space. d) distant galaxies seen beyond our Milky Way. e) All of the above are correct. Question 11 - 3 Astronomers use the term nebula to refer to a) outer envelopes of dying stars that drift gently into space. b) remnants of stars that die by supernova. c) clouds of gas and dust in interstellar space. d) distant galaxies seen beyond our Milky Way. e) All of the above are correct. Nebula refers to any fuzzy patch – bright or dark – in the sky. Copyright © 2010 Pearson Education, Inc. Question 11 - 4 Interstellar gas is composed primarily of Copyright © 2010 Pearson Education, Inc. a) 90% hydrogen, 9% helium, and 1% heavier elements. b) molecules including water and CO2. c) 50% hydrogen, 50% helium. d) hydrogen, oxygen, and nitrogen. e) 99% hydrogen, and 1% heavier elements. Question 11 - 4 Interstellar gas is composed primarily of a) 90% hydrogen, 9% helium, and 1% heavier elements. b) molecules including water and CO2. c) 50% hydrogen, 50% helium. d) hydrogen, oxygen, and nitrogen. e) 99% hydrogen, and 1% heavier elements. The composition of interstellar gas mirrors that of the Sun, stars, and the jovian planets. Copyright © 2010 Pearson Education, Inc. Question 11 - 5 The reddish color of emission nebulae indicates that Copyright © 2010 Pearson Education, Inc. a) gas and dust is moving away from Earth. b) hydrogen gas is present. c) dying stars have recently exploded. d) cool red stars are hidden inside. e) dust is present. Question 11 - 5 The reddish color of emission nebulae indicates that a) gas and dust is moving away from Earth. b) hydrogen gas is present. c) dying stars have recently exploded. d) cool red stars are hidden inside. e) dust is present. Glowing hydrogen gas emits red light around the Horsehead nebula. Copyright © 2010 Pearson Education, Inc. Question 11 - 6 21-centimeter radiation is important because Copyright © 2010 Pearson Education, Inc. a) its radio waves pass unaffected through clouds of interstellar dust. b) it arises from cool helium gas present throughout space. c) it can be detected with optical telescopes. d) it is produced by protostars. e) it reveals the structure of new stars. Question 11 - 6 21-centimeter radiation is important because a) its radio waves pass unaffected through clouds of interstellar dust. b) it arises from cool helium gas present throughout space. c) it can be detected with optical telescopes. d) it is produced by protostars. e) it reveals the structure of new stars. Cool atomic hydrogen gas produces 21-cm radio radiation as its electron “flips” its direction of spin. Copyright © 2010 Pearson Education, Inc. Question 11 - 7 Complex molecules in space are found Copyright © 2010 Pearson Education, Inc. a) in the photospheres of red giant stars. b) primarily inside dense dust clouds. c) in the coronas of stars like our Sun. d) scattered evenly throughout interstellar space. e) surrounding energetic young stars. Question 11 - 7 Complex molecules in space are found a) in the photospheres of red giant stars. b) primarily inside dense dust clouds. c) in the coronas of stars like our Sun. d) scattered evenly throughout interstellar space. e) surrounding energetic young stars. A radio telescope image of the outer portion of the Milky Way, revealing molecular cloud complexes. Copyright © 2010 Pearson Education, Inc. Question 11 - 8 Stars are often born within groups known as Copyright © 2010 Pearson Education, Inc. a) clans. b) spiral waves. c) aggregates. d) clusters. e) swarms. Question 11 - 8 Stars are often born within groups known as a) clans. b) spiral waves. c) aggregates. d) clusters. e) swarms. The Pleiades – a nearby open cluster – is a group of relatively young stars about 400 light-years from the Sun. Copyright © 2010 Pearson Education, Inc. Question 11 - 9 All stars in a stellar cluster have roughly the same Copyright © 2010 Pearson Education, Inc. a) temperature. b) color. c) distance. d) mass. e) luminosity. Question 11 - 9 All stars in a stellar cluster have roughly the same a) temperature. b) color. c) distance. d) mass. e) luminosity. Stars in the Pleiades cluster vary in temperature, color, mass, and luminosity, but all lie about 440 light-years away. Copyright © 2010 Pearson Education, Inc. Question 11 - 10 Globular clusters are typically observed Copyright © 2010 Pearson Education, Inc. a) in the plane of our Galaxy. b) above or below the plane of our Galaxy. c) near to our Sun. d) in the hearts of other galaxies. Question 11 - 10 Globular clusters are typically observed a) in the plane of our Galaxy. b) above or below the plane of our Galaxy. c) near to our Sun. d) in the hearts of other galaxies. Globular clusters orbit the center of the Milky Way, and are usually seen aboveInc.or below the galactic plane far from our Sun. Copyright © 2010 Pearson Education, Question 11 - 11 Stars in clusters & associations have about the same Copyright © 2010 Pearson Education, Inc. a) age. b) temperature. c) mass. d) color. e) luminosity. Question 11 - 11 Stars in clusters & associations have about the same Most of the stars in a cluster form about the same time. Stars in the Omega Centauri globular cluster are estimated to be about 14 billion years old. Copyright © 2010 Pearson Education, Inc. a) age. b) temperature. c) mass. d) color. e) luminosity. Question 11 - 12 Objects more massive than our Sun form into stars Copyright © 2010 Pearson Education, Inc. a) much slower, over billions of years. b) in about the same time. c) much faster, over tens of thousands of years. d) not at all – they are unstable. Question 11 - 12 Objects more massive than our Sun form into stars a) much slower, over billions of years. b) in about the same time. c) much faster, over tens of thousands of years. d) not at all – they are unstable. More mass faster collapse More mass faster start of fusion reactions More mass a hotter, more luminous main sequence star Copyright © 2010 Pearson Education, Inc. Question 11 - 13 How do single stars form within huge clouds of interstellar gas and dust? Copyright © 2010 Pearson Education, Inc. a) Clouds fragment into smaller objects, forming many stars at one time. b) One star forms; other matter goes into planets, moons, asteroids, & comets. c) Clouds rotate & throw off mass until only enough is left to form one star. Question 11 - 13 How do single stars form within huge clouds of interstellar gas and dust? a) Clouds fragment into smaller objects, forming many stars at one time. b) One star forms; other matter goes into planets, moons, asteroids, & comets. c) Clouds rotate & throw off mass until only enough is left to form one star. The theory of star formation predicts stars in a cluster Copyright © 2010 Pearson Education,would Inc. form about the same time. Question 11 - 14 What is a TTauri star? Copyright © 2010 Pearson Education, Inc. a) a collapsing cloud of gas about to become a protostar b) a dying star c) a cool main sequence star d) a star releasing a planetary nebula e) a protostar about to become a star Question 11 - 14 What is a TTauri star? a) a collapsing cloud of gas about to become a protostar b) a dying star c) a cool main sequence star d) a star releasing a planetary nebula e) a protostar about to become a star T-Tauri stars often show jets of gas emitted in two directions — “bipolar flow” — suggesting they are not yet stable. Copyright © 2010 Pearson Education, Inc. Question 11 - 15 A key feature of globular clusters is that they have Copyright © 2010 Pearson Education, Inc. a ) very few cool stars. b) the oldest stars in our Galaxy. c) lots of massive main sequence stars. d) stars with very different ages. e) high concentrations of metals. Question 11 - 15 A key feature of globular clusters is that they have a ) very few cool stars. b) the oldest stars in our Galaxy. c) lots of massive main sequence stars. d) stars with very different ages. e) high concentrations of metals. The H–R diagram of a globular cluster has a low “turnoff point” indicating its extreme age. Copyright © 2010 Pearson Education, Inc. Question 12 - 1 Stars like our Sun will end their lives as Copyright © 2010 Pearson Education, Inc. a) red giants. b) pulsars. c) black holes. d) white dwarfs. e) red dwarfs. Question 12 - 1 Stars like our Sun will end their lives as a) red giants. b) pulsars. c) black holes. d) white dwarfs. e) red dwarfs. Low-mass stars eventually swell into red giants, and their cores later contract into white dwarfs. Copyright © 2010 Pearson Education, Inc. Question 12 - 2 Elements heavier than hydrogen and Helium were created Copyright © 2010 Pearson Education, Inc. a) in the Big Bang. b) by nucleosynthesis in massive stars. c) in the cores of stars like the Sun. d) within planetary nebulae. e) They have always existed. Question 12 - 2 Elements heavier than hydrogen and helium were created a) in the Big Bang. b) by nucleosynthesis in massive stars. c) in the cores of stars like the Sun. d) within planetary nebula e) They have always existed. Massive stars create enormous core temperatures as red supergiants, fusing helium into carbon, oxygen, and even heavier elements. Copyright © 2010 Pearson Education, Inc. Question 12 - 3 The Sun will evolve away from the main sequence when Copyright © 2010 Pearson Education, Inc. a) its core begins fusing iron. b) its supply of hydrogen is used up. c) the carbon core detonates, and it explodes as a Type I supernova. d) helium builds up in the core, while the hydrogen-burning shell expands. e) the core loses all of its neutrinos, so all fusion ceases. Question 12 - 3 The Sun will evolve away from the main sequence when a) its core begins fusing iron. b) its supply of hydrogen is used up. c) the carbon core detonates, and it explodes as a Type I supernova. d) helium builds up in the core, while the hydrogen-burning shell expands. e) the core loses all of its neutrinos, so all fusion ceases. When the Sun’s core becomes unstable and contracts, additional H fusion generates extra pressure, and the star will swell into a red giant. Copyright © 2010 Pearson Education, Inc. Question 12 - 4 The helium flash occurs Copyright © 2010 Pearson Education, Inc. a) when T-Tauri bipolar jets shoot out. b) in the middle of the main sequence stage. c) in the red giant stage. d) during the formation of a neutron star. e) in the planetary nebula stage. Question 12 - 4 The helium flash occurs a) when T-Tauri bipolar jets shoot out. b) in the middle of the main sequence stage. c) in the red giant stage. d) during the formation of a neutron star. e) in the planetary nebula stage. When the collapsing core of a red giant reaches high enough temperatures and densities, helium can fuse into carbon quickly – a helium flash. Copyright © 2010 Pearson Education, Inc. Question 12 - 5 Stars gradually lose mass as they become white dwarfs during the Copyright © 2010 Pearson Education, Inc. a) T-Tauri stage. b) emission nebula stage. c) supernova stage. d) nova stage. e) planetary nebula stage. Question 12 - 5 Stars gradually lose mass as they become white dwarfs during the a) T-Tauri stage. b) emission nebula stage. c) supernova stage. d) nova stage. e) planetary nebula stage. Low-mass stars forming white dwarfs slowly lose their outer atmospheres, and illuminate these gases for a relatively short time. Copyright © 2010 Pearson Education, Inc. Question 12 - 6 Astronomers determine the age of star clusters by observing Copyright © 2010 Pearson Education, Inc. a) the number of main sequence stars. b) the ratio of giants to supergiants. c) the luminosity of stars at the turnoff point. d) the number of white dwarfs. e) supernova explosions. Question 12 - 6 Astronomers determine the age of star clusters by observing a) the number of main sequence stars. b) the ratio of giants to supergiants. c) the luminosity of stars at the turnoff point. d) the number of white dwarfs. e) supernova explosions. The H–R diagram of a cluster can indicate its approximate age. Turnoff point from the main sequence Copyright © 2010 Pearson Education, Inc. Question 12 - 7 The source of pressure that makes a white dwarf stable is Copyright © 2010 Pearson Education, Inc. a) electron degeneracy. b) neutron degeneracy. c) thermal pressure from intense core temperatures. d) gravitational pressure. e) helium-carbon fusion. Question 12 - 7 The source of pressure that makes a white dwarf stable is a) electron degeneracy. b) neutron degeneracy. c) thermal pressure from intense core temperatures. d) gravitational pressure. e) helium-carbon fusion. Electrons in the core cannot be squeezed infinitely close, and prevent a low-mass star from collapsing further. Copyright © 2010 Pearson Education, Inc. Question 12 - 8 In a white dwarf, the mass of the Sun is packed into the volume of Copyright © 2010 Pearson Education, Inc. a) an asteroid. b) a planet the size of Earth. c) a planet the size of Jupiter. d) an object the size of the Moon. e) an object the size of a sugar cube. Question 12 - 8 In a white dwarf, the mass of the Sun is packed into the volume of a) an asteroid. b) a planet the size of Earth. c) a planet the size of Jupiter. d) an object the size of the Moon. e) an object the size of a sugar cube. The density of a white dwarf is about a million times greater than normal solid matter. Copyright © 2010 Pearson Education, Inc. Question 12 - 9 In a young star cluster, when more massive stars are evolving into red giants, the least massive stars are Copyright © 2010 Pearson Education, Inc. a) ending their main-sequence stage. b) also evolving into red giants. c) forming planetary nebulae. d) barely starting to fuse hydrogen. e) starting the nova stage. Question 12 - 9 In a young star cluster, when more massive stars are evolving into red giants, the least massive stars are a) ending their main-sequence stage. b) also evolving into red giants. c) forming planetary nebulae. d) barely starting to fuse hydrogen. e) starting the nova stage. More massive stars form much faster, and have much shorter main-sequence lifetimes. Low-mass stars form more slowly. Copyright © 2010 Pearson Education, Inc. Question 12 - 10 A star will spend most of its “shining” lifetime Copyright © 2010 Pearson Education, Inc. a) as a protostar. b) as a red giant. c) as a main-sequence star. d) as a white dwarf. e) evolving from type O to type M. Question 12 - 10 A star will spend most of its “shining” lifetime a) as a protostar. b) as a red giant. c) as a main-sequence star. d) as a white dwarf. e) evolving from type O to type M. In the main-sequence stage, hydrogen fuses to helium. Pressure from light and heat pushing out balances gravitational pressure pushing inward. Copyright © 2010 Pearson Education, Inc. Question 12 - 11 A nova involves Copyright © 2010 Pearson Education, Inc. a) mass transfer onto a white dwarf in a binary star system. b) repeated helium fusion flashes in red giants. c) rapid collapse of a protostar into a massive O star. d) the explosion of a low-mass star. e) the birth of a massive star in a new cluster. Question 12 - 11 A nova involves a) mass transfer onto a white dwarf in a binary star system. b) repeated helium fusion flashes in red giants. c) rapid collapse of a protostar into a massive O star. d) the explosion of a low-mass star. e) the birth of a massive star in a new cluster. Sudden, rapid fusion of new fuel dumped onto a white dwarf causes the star to flare up, and for a short time become much brighter. Copyright © 2010 Pearson Education, Inc. Question 12 - 12 What type of atomic nuclei heavier than helium are most common, and why? Copyright © 2010 Pearson Education, Inc. a) those heavier than iron, because of supernovae b) iron, formed just before massive stars explode c) odd-numbered nuclei, built with hydrogen fusion d) even-numbered nuclei, built with helium fusion Question 12 - 12 What type of atomic nuclei heavier than helium are most common, and why? a) those heavier than iron, because of supernovae b) iron, formed just before massive stars explode c) odd-numbered nuclei, built with hydrogen fusion d) even-numbered nuclei, built with helium fusion Helium nuclei have an atomic mass of 4; they act as building blocks in high-temperature fusion within supergiants. Copyright © 2010 Pearson Education, Inc. Question 12 - 13 A white dwarf can explode when Copyright © 2010 Pearson Education, Inc. a) its mass exceeds the Chandrasekhar limit. b) its electron degeneracy increases enormously. c) fusion reactions increase in it’s core. d) iron in its core collapses. e) the planetary nebula stage ends. Question 12 - 13 A white dwarf can explode when a) its mass exceeds the Chandrasekhar limit. b) its electron degeneracy increases enormously. c) fusion reactions increase in it’s core. d) iron in its core collapses. e) the planetary nebula stage ends. If additional mass from a companion star pushes a white dwarf beyond 1.4 solar masses, it can explode in a Type I supernova. Copyright © 2010 Pearson Education, Inc. Question 12 - 14 A Type II supernova occurs when Copyright © 2010 Pearson Education, Inc. a) hydrogen fusion shuts off. b) uranium decays into lead. c) iron in the core starts to fuse. d) helium is exhausted in the outer layers. e) a white dwarf gains mass. Question 12 - 14 A Type II supernova occurs when a) hydrogen fusion shuts off. b) uranium decays into lead. c) iron in the core starts to fuse. d) helium is exhausted in the outer layers. e) a white dwarf gains mass. Fusion of iron does not produce energy or provide pressure; the star’s core collapses immediately, triggering a supernova explosion. Copyright © 2010 Pearson Education, Inc. Question 12 - 15 Supernova 1987A was important because Copyright © 2010 Pearson Education, Inc. a) its parent star had been studied before the explosion. b) its distance was already known. c) it was observed early, as its light was still increasing. d) its evolution was captured with detailed images from the Hubble Space Telescope. e) All of the above are true. Question 12 - 15 Supernova 1987A was important because a) its parent star had been studied before the explosion. b) its distance was already known. c) it was observed early, as its light was still increasing. d) its evolution was captured with detailed images from the Hubble Space Telescope. e) All of the above are true. Supernovae are important distance indicators in the study of galaxies beyond the Milky Way. Copyright © 2010 Pearson Education, Inc. Question 12 - 16 As stars evolve during their mainsequence lifetime Copyright © 2010 Pearson Education, Inc. a) they gradually become cooler and dimmer (spectral type O to type M). b) they gradually become hotter and brighter (spectral type M to type O). c) they don’t change their spectral type. Question 12 - 16 As stars evolve during their mainsequence lifetime a) they gradually become cooler and dimmer (spectral type O to type M). b) they gradually become hotter and brighter (spectral type M to type O). c) they don’t change their spectral type. A star’s main-sequence characteristics of surface temperature and brightness are based on its mass. Stars of different initial mass become different spectral types on the main sequence. Copyright © 2010 Pearson Education, Inc. Question 12 - 17 More massive white dwarfs are ______ compared with less massive white dwarfs. Copyright © 2010 Pearson Education, Inc. a) hotter b) smaller c) larger d) cooler e) identical in size Question 12 - 17 More massive white dwarfs are ______ compared with less massive white dwarfs. a) hotter b) smaller c) larger d) cooler e) identical in size Chandrasekhar showed that more mass will squeeze a white dwarf into a smaller volume, due to electron degeneracy pressure. Copyright © 2010 Pearson Education, Inc. Question 13 - 1 Pulsars usually show all of the following EXCEPT Copyright © 2010 Pearson Education, Inc. a) extremely rapid rotation. b) high-temperature fusion reactions. c) a narrow regular pulse of radiation. d) high-speed motion through the galaxy. e) an intense magnetic field. Question 13 - 1 Pulsars usually show all of the following EXCEPT a) extremely rapid rotation. b) high-temperature fusion reactions. c) a narrow regular pulse of radiation. d) high-speed motion through the galaxy. e) an intense magnetic field. Pulsars are neutron stars no longer undergoing fusion in their cores. Copyright © 2010 Pearson Education, Inc. Question 13 - 2 Many millisecond pulsars lie within Copyright © 2010 Pearson Education, Inc. a) emission nebulae. b) giant molecular clouds. c) globular clusters. d) planetary nebulae. e) open clusters. Question 13 - 2 Many millisecond pulsars lie within a) emission nebulae. b) giant molecular clouds. c) globular clusters. d) planetary nebulae. e) open clusters. The cores of globular clusters are densely packed with stars, suggesting that millisecond pulsars might result from “spinning up” as a result of stellar encounters. The core of globular cluster 47 Tucanae Copyright © 2010 Pearson Education, Inc.