Stellar Evolution

Chapter 12 Clickers Stellar Evolution

Question 1 Stars like our Sun will end their lives as a) red giants. b) pulsars. c) black holes. d) white dwarfs. e) red dwarfs.

Question 1 Stars like our Sun will end their lives as a) red giants. b) pulsars. c) black holes. d) white dwarfs. e) red dwarfs. Explanation: Low-mass stars eventually swell into red giants, and their cores later contract into white dwarfs.

Question 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.

Question 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. Explanation: Massive stars create enormous core temperatures as red supergiants, fusing helium into carbon, oxygen, and even heavier elements.

Question 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.

Question 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. Explanation: When the Sun’s core becomes unstable and contracts, additional H fusion generates extra pressure, and the star will swell into a red giant.

Question 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.

Question 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. Explanation: When the collapsing core of a red giant reaches high enough temperatures and densities, helium can fuse into carbon quickly – a helium flash.

Question 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.

Question 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. Explanation: Low-mass stars forming white dwarfs slowly lose their outer atmospheres, and illuminate these gases for a relatively short time.

Question 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.

Question 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. Explanation: The H–R diagram of a cluster can indicate its approximate age. Turnoff point from the main sequence

Question 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.

Question 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. Explanation: Electrons in the core cannot be squeezed infinitely close, and prevent a low-mass star from collapsing further.

Question 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.

Question 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. Explanation: The density of a white dwarf is about a million times greater than normal solid matter.

Question 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.

Question 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. Explanation: More massive stars form much faster, and have much shorter main-sequence lifetimes. Low-mass stars form more slowly.

Question 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.

Question 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. Explanation: In the main-sequence stage,hydrogen fuses to helium. Pressure from light and heat pushing out balances gravitational pressure pushing inward.

Question 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.

Question 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. Explanation: 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.

Question 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

Question 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 Explanation: Helium nuclei have an atomic mass of 4; they act as building blocks in high-temperature fusion within supergiants.

Question 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.

Question 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. Explanation: If additional mass from aa companion star pushes a white dwarf beyond 1.4 solar masses, it can explode in a Type supernova.

Question 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.

Question 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. Explanation: Fusion of iron does not produce energy or provide pressure; the star’s core collapses immediately, triggering a supernova explosion.

Question 16 As stars evolve during their main-sequence 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.

Question 16 As stars evolve during their main-sequence 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. Explanation: 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.

Question 17 More massive white dwarfs are ______ compared with less massive white dwarfs. • a) hotter • b) smaller • c) larger • d) cooler • e) identical in size

Question 17 More massive white dwarfs are ______ compared with less massive white dwarfs. • a) hotter • b) smaller • c) larger • d) cooler • e) identical in size Explanation: Chandrasekhar showed that more mass will squeeze a white dwarf into a smaller volume, due to electron degeneracy pressure.

Stellar Evolution