Astronomy A BEGINNER’S GUIDE TO THE UNIVERSE EIGHTH EDITION CHAPTER 12 Stellar Evolution Clickers © 2017 Pearson Education, Inc Question Stars like our Sun will end their lives as a) b) c) d) e) © 2017 Pearson Education, Inc red giants pulsars black holes white dwarfs red dwarfs Question Stars like our Sun will end their lives as a) b) c) d) e) red giants pulsars black holes white dwarfs red dwarfs Explanation: Low-mass stars eventually swell into red giants, and their cores later contract into white dwarfs © 2017 Pearson Education, Inc Question Elements heavier than hydrogen and helium were created a) b) c) d) e) © 2017 Pearson Education, Inc in the Big Bang by nucleosynthesis in massive stars in the cores of stars like the Sun within planetary nebula They have always existed Question Elements heavier than hydrogen and helium were created a) b) c) d) e) in the Big Bang by nucleosynthesis in massive stars in the cores of stars like the Sun within planetary nebula They have always existed Explanation: Massive stars create enormous core temperatures as red supergiants, fusing helium into carbon, oxygen, and even heavier elements © 2017 Pearson Education, Inc Question The Sun will evolve away from the main sequence when a) b) c) d) its core begins fusing iron its supply of hydrogen is used up the carbon core detonates, and it explodes as a Type I supernova helium builds up in the core, while the hydrogen-burning shell expands e) © 2017 Pearson Education, Inc the core loses all of its neutrinos, so all fusion ceases Question The Sun will evolve away from the main sequence when a) b) c) its core begins fusing iron its supply of hydrogen is used up 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 © 2017 Pearson Education, Inc Question The helium flash occurs a) b) c) d) e) © 2017 Pearson Education, Inc when T-Tauri bipolar jets shoot out in the middle of the main-sequence stage in the red giant stage during the formation of a neutron star in the planetary nebula stage Question The helium flash occurs a) b) c) d) e) when T-Tauri bipolar jets shoot out in the middle of the main-sequence stage in the red giant stage during the formation of a neutron star 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 © 2017 Pearson Education, Inc Question Stars gradually lose mass as they become white dwarfs during the a) b) c) d) e) © 2017 Pearson Education, Inc T-Tauri stage emission nebula stage supernova stage nova stage planetary nebula stage Question 10 A star will spend most of its “shining” lifetime a) b) c) d) e) as a protostar as a red giant as a main-sequence star as a white dwarf evolving from type O to type M Explanation: In the mainsequence stage, hydrogen fuses to helium Pressure from light and heat pushing out balances gravitational pressure pushing inward © 2017 Pearson Education, Inc Question 11 A nova involves a) mass transfer onto a white dwarf in a binary star system b) c) d) e) © 2017 Pearson Education, Inc repeated helium fusion flashes in red giants rapid collapse of a protostar into a massive O star the explosion of a low-mass star 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) c) d) e) repeated helium fusion flashes in red giants rapid collapse of a protostar into a massive O star the explosion of a low-mass star 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 © 2017 Pearson Education, Inc Question 12 What type of atomic nuclei heavier than helium are most common, and why? a) b) c) d) © 2017 Pearson Education, Inc Those heavier than iron, because of supernovae Iron, formed just before massive stars explode Odd-numbered nuclei, built with hydrogen fusion Even-numbered nuclei, built with helium fusion Question 12 What type of atomic nuclei heavier than helium are most common, and why? a) b) c) d) Those heavier than iron, because of supernovae Iron, formed just before massive stars explode Odd-numbered nuclei, built with hydrogen fusion 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 © 2017 Pearson Education, Inc Question 13 A white dwarf can explode when a) b) c) d) e) © 2017 Pearson Education, Inc its mass exceeds the Chandrasekhar limit its electron degeneracy increases enormously fusion reactions increase in its core iron in its core collapses the planetary nebula stage ends Question 13 A white dwarf can explode when a) b) c) d) e) its mass exceeds the Chandrasekhar limit its electron degeneracy increases enormously fusion reactions increase in its core iron in its core collapses the planetary nebula stage ends Explanation: If additional mass from a companion star pushes a white dwarf beyond 1.4 solar masses, it can explode in a Type I supernova © 2017 Pearson Education, Inc Question 14 A Type II supernova occurs when a) b) c) d) e) © 2017 Pearson Education, Inc hydrogen fusion shuts off uranium decays into lead iron in the core starts to fuse helium is exhausted in the outer layers a white dwarf gains mass Question 14 A Type II supernova occurs when a) b) c) d) e) hydrogen fusion shuts off uranium decays into lead iron in the core starts to fuse helium is exhausted in the outer layers 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 © 2017 Pearson Education, Inc Question 15 Supernova 1987A was important because a) b) c) d) its parent star had been studied before the explosion its distance was already known it was observed early, as its light was still increasing its evolution was captured with detailed images from the Hubble Space Telescope e) © 2017 Pearson Education, Inc All of the above are true Question 15 Supernova 1987A was important because a) b) c) d) its parent star had been studied before the explosion its distance was already known it was observed early, as its light was still increasing its evolution was captured with detailed images from the Hubble Space Telescope e) All of the above are true Explanation: Supernovae are important distance indicators in the study of galaxies beyond the Milky Way © 2017 Pearson Education, Inc Question 16 As stars evolve during their main-sequence lifetime, a) b) c) © 2017 Pearson Education, Inc they gradually become cooler and dimmer (spectral type O to type M) they gradually become hotter and brighter (spectral type M to type O) they don’t change their spectral type Question 16 As stars evolve during their main-sequence lifetime, a) b) c) they gradually become cooler and dimmer (spectral type O to type M) they gradually become hotter and brighter (spectral type M to type O) 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 © 2017 Pearson Education, Inc Question 17 More massive white dwarfs are _ compared with less massive white dwarfs a) b) c) d) e) © 2017 Pearson Education, Inc hotter smaller larger cooler identical in size Question 17 More massive white dwarfs are _ compared with less massive white dwarfs a) b) c) d) e) hotter smaller larger cooler identical in size Explanation: Chandrasekhar showed that more mass will squeeze a white dwarf into a smaller volume due to electron degeneracy pressure © 2017 Pearson Education, Inc ... Stars gradually lose mass as they become white dwarfs during the a) b) c) d) e) T-Tauri stage emission nebula stage supernova stage nova stage planetary nebula stage Explanation: Low-mass stars... Stars gradually lose mass as they become white dwarfs during the a) b) c) d) e) © 2017 Pearson Education, Inc T-Tauri stage emission nebula stage supernova stage nova stage planetary nebula stage... giants rapid collapse of a protostar into a massive O star the explosion of a low-mass star the birth of a massive star in a new cluster Explanation: Sudden, rapid fusion of new fuel dumped onto