Outlook

o The Sun's gas is on fire like flames from wood or coal, and these flames emit visible light. o The visible light comes from energy level transitions as electrons in the Sun's hydrogen atoms jump between level 1 and level 2. o Nuclear fusion in the Sun's core produces visible light photons. o Like all objects, the Sun emits thermal radiation with a spectrum that depends on its temperature, and the Sun's surface temperature is just right for emitting mostly visible light. 4. CONCEPT QUESTION 11.13 Which of the following choices is not a way by which we can study the inside of the Sun? o We can make a computer model of the Sun's interior that allow us to predict the observable properties of the Sun. o We can probe the interior of the Sun by studying the vibrations in its photosphere. o We can study solar neutrinos. o We can send a space probe into the Sun's photosphere. 5. READING QUESTION 11.7 When we say that the Sun is a ball of plasma , we mean that _________. o the Sun is roughly the same color as blood o the Sun is made of atoms and molecules o the Sun consists of gas in which many or most of the atoms are ionized (missing electrons) o the Sun is made of material that acts like a liquid acts on Earth 6. READING QUESTION 11.5 What two physical processes balance each other to create the condition known as gravitational equilibrium in stars? o gravitational force and outward pressure o gravitational force and surface tension o the strong force and the electromagnetic force o the strong force and the weak force 7. CONCEPT QUESTION 11.6 How does the Sun's mass compare to Earth's mass? o The Sun's mass is about 300,000 times the mass of the Earth. o The Sun's mass is about 300 times the mass of the Earth. o Both have approximately the same mass. o The Sun's mass is about 30 times the mass of the Earth. 8. CONCEPT QUESTION 11.14 Why does the Sun emit neutrinos? o Solar flares create neutrinos with magnetic fields. o Fusion in the Sun's core creates neutrinos. o Convection releases neutrinos, which random walk through the radiation zone. o The Sun was born with a supply of neutrinos that it gradually emits into space. o The Sun does not emit neutrinos. 9. READING QUESTION 11.17 To estimate the central temperature of the Sun, scientists _________. o send probes to measure the temperature o use hot gas to create a small Sun in a laboratory o monitor changes in Earth's atmosphere o use computer models to predict interior conditions

o 5 million years o 5000 AD o 5 billion years o 50 billion years 20. CONCEPT QUESTION 11.3 What do we mean when we say that the Sun is in gravitational equilibrium ? o There is a balance within the Sun between the outward push of pressure and the inward pull of gravity. o The Sun maintains a steady temperature. o The Sun always has the same amount of mass, creating the same gravitational force. o The hydrogen gas in the Sun is balanced so that it never rises upward or falls downward. 21. CONCEPT QUESTION 11.21 Satellites in low-Earth orbits are more likely to crash to Earth when the sunspot cycle is near solar maximum because _________. o Earth's upper atmosphere tends to expand during solar maximum, exerting drag on satellites in low orbits o of increased magnetic interference o it is too dangerous to send the Space Shuttle to service satellites during solar maximum o they are more likely to have their electronics "fried" by a solar flare during solar maximum 22. READING QUESTION 11.3 Which of the following correctly describes how the process of gravitational contraction can make a star hot? o Gravitational contraction involves nuclear fusion, which generates a lot of heat. o When a star contracts in size, gravitational potential energy is converted to thermal energy. o Heat is generated when gravity contracts, because gravity is an inverse square law force. o Gravitational contraction involves the generation of heat by chemical reactions, much like the burning of coal. 23. CONCEPT QUESTION 11.16 A salesman attempts to convince you to purchase a "solar neutrino" shield to protect you and your family. (It's even "on sale"!) Why do you turn down this excellent offer? o There's no such thing as a solar neutrino. o Neutrinos rarely, if ever, interact with other matter. o The Earth's natural magnetic field already offers excellent protection against the onslaught of solar neutrinos. o Solar neutrinos are generated by solar winds, but we're in a solar minimum now, so the risk of damage is very low. 24. VISUAL QUESTION 11.10 In terms of the global warming that has been occurring on Earth over the past few decades, what is the key message from this figure? o The Sun’s energy output (irradiance) tracks quite well with the observed warming trend.

Pre-Lecture Overview: Surveying the Stars Which of these two-star clusters contains the most massive main-sequence stars? a. The Pleiades b. M80 Part A The three bins represent three important properties of stars. Drag the items that we must measure in order to determine each property into the appropriate bin. Part B To place a star on an H-R diagram, we must know its __________. o mass only o mass and luminosity o surface temperature and radius o luminosity only o surface temperature only o surface temperature and luminosity o surface temperature and mass o radius and luminosity o mass and radius o radius only Part C On the H-R diagram, most stars fall into the region labeled ____________. o white dwarfs o giants o super giants o main sequence Part D Among main sequence stars, those with the highest surface temperatures have ___________. o the lowest masses and longest lifetimes

o It is a type of star that produces energy by gravitational contraction. o a main sequence star of spectral type F, which tends to look white in color 2. CONCEPT QUESTION 12.16 The sketch below shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents the entire main sequence while (c) and (d) represent only small parts of the main sequence. Which group represents stars that have no ongoing nuclear fusion ? o a o b o c o d o e 3. READING QUESTION 12.18 Suppose our Sun were suddenly replaced by a supergiant star. Which of the following would be true? o Earth would be inside the supergiant. o The supergiant would appear as large as the full Moon in our sky. o The supergiant's surface temperature would be much hotter than the surface temperature of our Sun. o Earth would fly off into interstellar space. 4. VISUAL QUESTION 12.10 This photo shows an object located in the halo of our Milky Way galaxy. Notice the many bright red dots in the photograph. What are they? o red giant stars o old white dwarf stars that have turned red in color o starspots o cool, red main-sequence stars of spectral type M o massive supergiant stars 5. READING QUESTION 12.20

o They are in the final stage of their lives. o They generate energy through hydrogen fusion in their core. o They all have approximately the same mass. o They are all spectral type G. 16. CONCEPT QUESTION 12.11 The sketch below shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents the entire main sequence while (c) and (d) represent only small parts of the main sequence. Which group represents stars of the largest radii ? o a o b o c o d o e 17. VISUAL QUESTION 12.4 This graph shows how the apparent brightness of an eclipsing binary system changes with time. Which of the four labeled regions represents the system at a time when one star is eclipsing the other? o I o II o III o IV o both II and IV o both I and III 18. CONCEPT QUESTION 12.10 The sketch below shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents the entire main sequence while (c) and (d) represent only small parts of the main sequence.

o apparent brightness and luminosity 27. VISUAL QUESTION 12.7 Study this H-R diagram. Which of the following stars is the largest in size (radius)? (The red arrows help you locate these stars on the diagram.) o Antares o Aldebaran o Alpha Centauri B o Canopus 28. CONCEPT QUESTION 12.4 A star with a parallax angle of 1/20 arcsecond is _________. o 20 light-years away o 1/20 parsec (≈ 0.163 light -year) away o 20 parsecs (≈ 65.2 light -years) away o 10 parsecs (≈ 32.6 light -years) away Pre-Lecture Overview: Star Birth QUESTION When the core of a star like the Sun uses up its supply of hydrogen for fusion. The core begins to ________. a. Shrink and cool b. Shrink and heat c. Shrink but maintain constant temperature d. Expand Part A Star-forming clouds appear dark in visible-light photos because the light of stars behind them is absorbed by __________. o thick hydrogen gas o dark matter o interstellar dust

a. Lithium b. Carbon c. Oxygen d. Neon e. Iron Homework #10 1. READING QUESTION 1.8 Approximately what core temperature is required before hydrogen fusion can begin in a star? o 10 million K o 10,000 K o 10 trillion K o 1 billion K o 10 billion K 2. CONCEPT QUESTION 13.22 Which is more common: a star blows up as a supernova, or a star ejects a planetary nebula? o Supernovae are more common. o They both occur in about equal numbers. o Planetary nebulas are more common. o It is impossible to say. 3. CONCEPT QUESTION 13.9 Which of the following types of data provide evidence that helps us understand the life tracks of low-mass stars? o spacecraft observations of the Sun o H-R diagrams of globular clusters o H-R diagrams of open clusters o observing a low-mass star over many years 4. VISUAL QUESTION 13.7 Suppose a particular star has a core that is undergoing multiple stages of fusion simultaneously to give it the structure shown in this diagram. Based on our understanding of stellar lives, the mass of this star is __________ o about 2 times the mass of the Sun o greater than 8 times the mass of the Sun o about the same mass as the Sun o less than 0.1 times the mass of the Sun 5. READING QUESTION 13.5

What kind of gas cloud is most likely to give birth to stars? o a hot, dense gas cloud o a cold, low-density gas cloud o a hot, low-density gas cloud o a cold, dense gas cloud 6. CONCEPT QUESTION 13.15 This diagram represents the life track of a 1 solar mass star from its pre-main-sequence stages to just before its final death. Refer to the life stages labeled with roman numerals. What will happen to the star after stage VIII? o It will explode as a supernova and leave a neutron star or black hole behind. o Its outer layers will be ejected as a planetary nebula and its core will become a white dwarf. o It will remain in stage viii for about 10 billion years, after which its outer layers will shrink back and cool. o It will continue to expand gradually until carbon fusion begins in its core. 7. READING QUESTION 13.22 To predict whether a star will eventually fuse oxygen into a heavier element, what do you need to know about the star? o its overall abundance of elements heavier than helium o how much oxygen it now has in its core o its luminosity o its mass 8. READING QUESTION 13.1 The interstellar clouds called molecular clouds are _________. o the cool clouds in which stars form o the hot clouds of gas expelled by dying stars o the clouds in which elements such as carbon, nitrogen, and oxygen are made o clouds that are made mostly of complex molecules such as carbon dioxide and sulfur dioxide 9. VISUAL QUESTION 13.10 The arrow in the photo on the left points to the location of the star that has exploded as a supernova in the photo on the right. From this photo pair alone, what can we conclude about the star that exploded? (Assume that we know the star was not a member of a binary system.)

o It is now a black hole. o Before the supernova, the star lived for at least a billion years. o It was a high-mass star with at least 8 times the mass of the Sun. o It was a red giant star. 10. CONCEPT QUESTION 13.5 Generally speaking, a main-sequence star is __________ than it was during the time it was a protostar. o hotter and brighter o cooler and brighter o hotter and dimmer o cooler and dimmer 11. CONCEPT QUESTION 13.8 Where would a brown dwarf be located on an H-R diagram? o below and to the right of the lowest part of the main sequence o in the upper right corner of the H-R diagram o in the lower left corner of the H-R diagram o above and to the left of the highest part of the main sequence 12. READING QUESTION 13.24 After a supernova explosion, the remains of the stellar core can be _________. o a white dwarf, neutron star, or black hole o a black hole only o either a neutron star or a black hole o a neutron star only 13. CONCEPT QUESTION 13.6 Consider a large molecular cloud that will give birth to a cluster of stars. Which of the following would you expect to be true? o All the stars in the cluster will be of about the same mass. o All the stars in the cluster will become main-sequence stars at about the same time. o All the stars in the cluster will have approximately the same luminosity and surface temperature. o A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage. 14. READING QUESTION 13.15 What happens when a main-sequence star exhausts its core hydrogen fuel supply? o The entire star shrinks in size. o The core shrinks while the rest of the star expands. o The star becomes a neutron star. o The core immediately begins to fuse its helium into carbon. 15. CONCEPT QUESTION 13.14 This diagram represents the life track of a 1 solar mass star from its pre-main-sequence stages to just before its final death. Refer to the life stages labeled with roman numerals.

During which stage does the star have an inert (non-fusing) carbon core surrounded by shells of helium and hydrogen fusion? o Stage ii o Stage iii o Stage iv o Stage vi o Stage viii 16. VISUAL QUESTION 13.5 This H-R diagram shows the life track of a 1 M Sun star from the time it first becomes a main-sequence star. Which numbered point represents the star when it has both hydrogen-fusing and helium-fusing shells around an inert carbon core? o Point 1 o Point 2 o Point 3 o Point 4 17. READING QUESTION 13.6 Which of the following phenomena is not commonly associated with the star formation process? o the formation of a spinning disk of material around a protostar o powerful "jets" shooting out along the rotation axis of a protostar o intense ultraviolet radiation coming from a protostar o strong winds of particles blowing out into space from a protostar 18. READING QUESTION 13.21 What is the CNO cycle? o the process by which helium is fused into carbon, nitrogen, and oxygen o the set of fusion reactions that have produced all the carbon, nitrogen, and oxygen in the universe o a set of steps by which four hydrogen nuclei fuse into one helium nucleus o the process by which carbon is fused into nitrogen and oxygen

19. CONCEPT QUESTION 13.2 Our Sun is considered to be a _________. o intermediate-mass star o low-mass star o high-mass star o brown dwarf 20. VISUAL QUESTION 13.8 According to this diagram, how much more abundant is hydrogen in the universe than nitrogen? o hydrogen is about 30% more abundant than nitrogen o hydrogen is about 10,000 times as abundant as nitrogen o hydrogen is about 4 times as abundant as nitrogen o hydrogen is about 10 times as abundant as nitrogen 21. VISUAL QUESTION 13.4 In this diagram, red balls represent protons and gray balls represent neutrons. What reaction is being shown? o fusion of carbon into oxygen o fusion of hydrogen into helium o the "iron catastrophe" that initiates a supernova o fusion of helium into carbon 22. READING QUESTION 13.4 Which part of the electromagnetic spectrum generally gives us our best views of stars forming in dusty clouds? o visible light o infrared o ultraviolet o blue light 23. CONCEPT QUESTION 13.20 Observations show that elements with atomic mass numbers divisible by 4 (such as oxygen-16, neon-20, and magnesium-24) tend to be more abundant in the universe than elements with atomic mass numbers in between. Why do we think this is the case? o The apparent pattern is thought to be a random coincidence. o This pattern in elemental abundances was apparently determined during the first few minutes after the Big Bang.

o At the end of a high-mass star's life, it produces new elements through a series of helium capture reactions. o Elements with atomic mass numbers divisible by 4 tend to be more stable than elements in between 24. READING QUESTION 13.8 Approximately what core temperature is required before hydrogen fusion can begin in a star? o 10 trillion K o 10,000 K o 10 million K o 1 billion K o 10 billion K 25. READING QUESTION 13.11 The vast majority of stars in a newly formed star cluster are _________. o red giants o very high-mass, type O and B stars o less massive than the Sun o about the same mass as our Sun Chapter 13: Quick Quiz 1. Stars can form most easily in clouds that are a. Cold and dense b. Warm and dense c. Hot and low-density 2. A brown dwarf is a. An object not quite massive enough to be a star b. A white dwarf that has cooled off c. A starlike object that is less massive than Jupiter 3. Which of these stars has the hottest core? a. A blue main-sequence star b. A red supergiant c. A red main-sequence star 4. Which of these stars does not have fusion occurring in its core? a. A red giant b. A red main-sequence star c. A blue main-sequence star 5. After the helium flash in a low- mass star, the star’s luminosity a. Goes up b. Goes down c. Stays the same 6. What would stars be like if hydrogen had the smallest mass per nuclear particle? a. Stars would be brighter b. All stars would be red giants c. Nuclear fusion would not occur in stars of any mass 7. What would stars be like if carbon had the smallest mass per nuclear particle? a. Supernovae would be more common b. Supernovae would never occur c. High-mass stars would be hotter 8. What would you be most likely to find if you returned to the solar system in 10 billion years? a. A neutron star

b. A white dwarf c. A black hole 9. Which of these stars has the shortest life expectancy? A. An isolated 1 M Sun star B. A star in a close binary system with a 0.8 M Sun star C. A star in a close binary system with a 2 M Sun star a. A b. B c. C 10. What happens to the core of a high-mass star after it runs out of hydrogen? a. It shrinks and heats up b. It shrinks and cools down c. Helium fusion begins right away Chapter 14: The Bizarre Stellar Graveyard QUESTION Why can’t we detect events that occur inside the event horizon of a black hole? a. The strong gravity prevents events from occurring b. The blackness snuffs out any light from these events c. Light cannot escape the black hole’s gravitational pull Pre-Lecture Overview: The Bizarre Stellar Graveyard Part A Degeneracy pressure arises when ________. o a star's core is producing less energy than the star is radiating away from its surface o the temperature reaches a critically high value o subatomic particles are packed as tightly as the laws of quantum mechanics allow o the speeds of subatomic particles reach the speed of light o an object becomes as small or smaller than Earth Part B Gravitational waves were first detected directly in 2015. According to models, the source of these gravitational waves was __________. o very powerful x-ray bursts o the merger of two black holes o a neutron star supernova o a white dwarf supernova o the supernova of an extremely massive star Part C Match words at the left to the correct blanks in the sentences at right. Not all words will be used. • The event horizon marks the boundary between the inside and outside of a black hole. • A neutron star can remain stable in size because of neutron degeneracy pressure . • A(n) pulsar is rapidly rotating neutron star. • A white dwarf can remain stable in size because of electron degeneracy pressure . • A(n) accretion disk can form around a white dwarf, neutron star, or black hole in a binary system. • The singularity is the place to which all of a black hole's mass is in principle located within the black hole. • A(n) nova occurs when fusion ignites on the surface of a white dwarf. Pre-Lecture Overview: Our Galaxy

Question As time passes and the star-gas-star cycle continues, how does the total amount of gas in the galaxy change? a. It stays the same b. It increases c. It decreases Part A Complete the sentences to describe the structure of the Milky Way Galaxy. Match words at the left to the correct blanks in the sentences at right. Not all words will be used. • Our galaxy consists of a large, nearly flat disk with a central bulge , all surrounded by a vast halo . • The disk of the Milky Way Galaxy is about 100,000 light-years in diameter and 1000 light-years thick.We refer to the gas and dust that resides in our galaxy as the interstellar medium . • From our location, we cannot see far into the disk with visible light because our view is blocked by dark, dusty gas clouds . • We find globular clusters of stars primarily in the galaxy's halo. Part B Star formation occurs primarily in the galaxy's ________. o bulge o center o halo o disk Part C Complete the sentences to describe the star-gas-star cycle. Match words at the left to the correct blanks in the sentences at right. Not all words will be used. • If we begin from star birth, the next key stage in the star-gas-star cycle occurs when a(n) supernova returns gas and new elements into space. • The expelled gas forms a(n) bubble that is very hot and expands in size. • As the gas cools and merges with other interstellar gas, it forms a(n) atomic hydrogen cloud . • Further cooling allows the gas to become a(n) molecular cloud , in which star formation occurs. Part D Spiral arms are __________. o another term for ionization nebulae o regions of active star formation o the only regions of the disk where gas clouds are found o the only regions of the disk where stars are found Part E According to present scientific understanding of the Milky Way's formation, which of the following statements are true? Select al that apply. o The galaxy formed from the collapse of a single, giant protogalactic cloud. o The protogalatic cloud(s) contained essentially no elements besides hydrogen and helium. o Halo stars formed before disk stars. o Disk stars formed before halo stars. o Halo stars are stars that are born in the disk and ejected into the halo by gravitational encounters. Chapter 14.3: Black Holes: Gravity Ultimate Victory Question What is the Schwarzschild radius of a 1 billion solar mass black hole?

a. 1 billion kilometers b. 3 billion kilometers c. 300 billion kilometers d. 1/3 billion kilometers Chapter 14.4: Extreme Events What should you expect to eventually happen to a neutron star binary system? a. The orbital decay will continue forever b. The orbits will eventually stabilize c. The neutron stars will eventually spiral into each other d. The neutron stars will eventually fly away from each other Chapter 14 Quick Quiz 1. Which of these objects has a smaller radius? a. A 1.2 M Sun white dwarf b. 0.6 M Sun white dwarf c. Jupiter 2. What happens if a white dwarf reaches the 1.4 M Sun limit? a. It explodes as a white dwarf supernova b. It collapses to become a neutron star c. It collapses to become a black hole 3. If we see a nova, we know that we are observing a. A rapidly rotating neutron star b. A gamma ray= emitting supernova c. A white dwarf system 4. A pulsar is a. An unstable high-mass star b. An accreting white dwarf c. A rapidly rotating neutron star 5. What would happen if the Sun suddenly became a black hole without changing its mass? a. The black hole would quickly suck in Earth b. Earth would gradually spiral into the black hole c. Earth would remain in the same orbit 6. What makes us think that Cygnus X-1 contains a black hole? a. We can directly observe that one member of the system emits no light b. The unseen object orbited by a luminous star is too massive to be a neutron star c. The strong x-ray emission from the system means it must contain a black hole 7. Viewed from a distance, how would a flashing red light appear as it fell into a black hole? a. It would appear to flash more quickly b. Its flashes would appear bluer c. Its flashes would shift to the infrared part of the spectrum 8. Which of these black holes exerts the weakest tidal forces on an object near its event horizon? a. A 10 M Sun black hole b. A 100 M Sun black hole c. A 10 6 M Sun black hole 9. Current evidence indicates that most gamma-ray bursts come from a. Supernovae that leave a black hole behind b. Unusually massive x-ray bursters c. The merger of two black holes 10. Why do some pairs of neutron stars collide and merge? a. Occasionally a neutron star moving through space will collide head-on with another neutron star

b. Gravitational waves from close neutron star binary systems carry away orbital energy and angular momentum c. Electromagnetic waves from pulsars carry away angular momentum Homework #11 1. CONCEPT QUESTION 14.15 Which of statement below about black holes is not true? o We have strong observational evidence that black holes really exist. o If you fell into a black hole, you would experience time to be running normally as you plunged rapidly across the event horizon. o If you watch someone else fall into a black hole, you will never see the person cross the event horizon; you'll only see the person fade from view as the light he or she reflects (or emits) becomes more and more redshifted. o A spaceship passing near a 10 solar mass black hole is much more likely to be destroyed than a spaceship passing at the same distance from the center of a 10 solar mass main-sequence star. 2. CONCEPT QUESTION 14.14 Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice? o Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted. o The clock will fall faster and faster, reaching the speed of light as it crosses the event horizon. o Time on the clock will run faster as it approaches the black hole, and light from the clock will be increasingly blueshifted. o The clock will fall toward the black hole at a steady rate, so that you'll see it plunge through the event horizon within just a few minutes. 3. CONCEPT QUESTION 14.18 What types of events have scientists so far been able to detect with gravitational wave observatories, such as LIGO. o the gradual decay over many years of the orbits of binary neutron stars o mergers of closely-orbiting pairs of neutron stars or black holes o x-ray bursts o supernovae 4. VISUAL QUESTION 14.3 Which of the following diagrams best represents the scale of Earth in comparison to a neutron star?

5. READING QUESTION 14.15 Based on current understanding, the minimum mass of a black hole that forms during a massive star supernova is roughly _________. o 0.5 solar masses o 10 solar masses o 1.4 solar masses o 3 solar masses 6. READING QUESTION 14.11 Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true? o In a black hole, the pressure coming from neutron degeneracy pressure is slightly greater than that coming from electron degeneracy pressure. o The life of a white dwarf is an ongoing battle between electron degeneracy pressure and neutron degeneracy pressure. o Both electron degeneracy pressure and neutron degeneracy pressure help govern the internal structure of a main-sequence star. o Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron degeneracy pressure is the main source of pressure in neutron stars. 7. READING QUESTION 14.14 What is the basic definition of a black hole ? o any object made from dark matter o an object with gravity so strong that not even light can escape o a dead star that has faded from view o a compact mass that emits no visible light 8. VISUAL QUESTION 14.5

A spacecraft is on a trajectory that happens to be taking it near a black hole. Which diagram shows how the spacecraft's orbit will be affected? 9. READING QUESTION 14.21 Observational evidence indicates that at least some gamma ray bursts are produced by __________. o supernovas of very massive stars that leave behind black holes o the same types of close binary systems that produce x-ray bursts o the central black hole of the Milky Way Galaxy o white dwarf supernovas in distant galaxies. 10. CONCEPT QUESTION 14.11 Which statement about pulsars is true? o All pulsars are neutron stars, but not all neutron stars are pulsars. o Pulsars can form only in close binary systems. o All neutron stars are pulsars. o Pulsars can "pulse" no more than about once a day. 11. READING QUESTION 14.6 According to our modern understanding, what is a nova ? o a rapidly spinning neutron star o the explosion of a massive star at the end of its life o an explosion on the surface of a white dwarf in a close binary system o the sudden formation of a new star in the sky 12. CONCEPT QUESTION 14.7 Which of the following is not true about differences between novae and supernovae? o Novae occur only in binary star systems, while supernovae can occur both among single stars and among binary star systems. o Novae are much less luminous than supernovae.

o Supernovae eject gas into space but novae do not. o The same star can undergo novae explosions more than once, but can undergo only a single supernova. 13. READING QUESTION 14.16 What do we mean by the event horizon of a black hole? o It is the point beyond which neither light nor anything else can escape. o It is the place where x-rays are emitted from black holes. o It is the distance from the black hole at which stable orbits are possible. o It is the center of the black hole. 14. CONCEPT QUESTION 14.16 When we see x-rays from an accretion disk in a binary system, we can't immediately tell whether the accretion disk surrounds a neutron star or a black hole. Suppose we then observe each of the following phenomena in this system. Which one would rule out the possibility of a black hole? o intense x-ray bursts o spectral lines from the companion star that alternately shift to shorter and longer wavelengths o bright x-ray emission that varies on a time scale of a few hours o visible and ultraviolet light from the companion star 15. READING QUESTION 14.1 A white dwarf is _________. o what most stars become when they die o an early stage of a neutron star o a brown dwarf that has exhausted its fuel for nuclear fusion o a precursor to a black hole 16. VISUAL QUESTION 14.9 This graph shows data collected by a gamma ray telescope. What kind of event is it showing? o the on and off gamma-ray light changes of a pulsar o a burst of gamma rays from a flare on a blue supergiant star o a gamma ray burst from a distant galaxy o a burst of gamma rays from an explosion on the surface of a neutron star 17. CONCEPT QUESTION 14.21 Imagine an advanced civilization living on a planet orbiting at a distance of 10 AU (1.5 billion kilometers) from a close binary star system that consists of a 15 M Sun red giant star and a 10 M Sun black hole. The black hole is surrounded by an accretion disk.

Through a bizarre (and scientifically unexplainable) fluctuation in the space-time continuum, a copy of a book from that civilization arrives on your desk; it is entitled Iguoonos: How We Evolved . In the first chapter, you learn that these beings evolved from organisms that lived 5 billion years ago. Which of the following statements should you expect to find as you continue to read this book? o They evolved on a different planet in a different star system, and moved to their current location. o As a result of traumatic experiences to their evolutionary ancestors, they dislike television. o They believe that the presence of two stars in their system was critical to their evolution. o Their immediate ancestors were chimpanzees. o They evolved from primitive wormlike creatures that had 13 legs, 4 eyes, and bald heads, thus explaining why such critters are now considered a spectacular delicacy. 18. VISUAL QUESTION 14.7 This painting shows an accretion disk around a black hole in a close binary star system. What physical law explains why matter flowing from the companion star orbits rapidly as it nears the black hole? o Newton's third law of motion o The law of conservation of angular momentum o Kepler's second law of planetary motion o Einstein's general theory of relativity 19. CONCEPT QUESTION 14.3 Which of the following best describes why a white dwarf cannot have a mass greater than the 1.4-solar-mass limit? o White dwarfs get hotter with increasing mass, and above the 1.4-solar-mass limit they would be so hot that even their electrons would melt. o White dwarfs are made only from stars that have masses less than the 1.4-solar-mass limit. o The upper limit to a white dwarf's mass is something we have learned from observations, but no one knows why this limit exists. o Electron degeneracy pressure depends on the speeds of electrons, which approach the speed of light as a white dwarf's mass approaches the 1.4-solar-mass limit. 20. READING QUESTION 14.7 What would happen if a white dwarf gained enough mass to reach the 1.4 solar mass white dwarf limit? o The white dwarf would undergo a nova explosion. o The white dwarf would explode completely as a white dwarf supernova. o The white dwarf would collapse in size, becoming a neutron star. o The white dwarf would collapse to become a black hole. 21. CONCEPT QUESTION 14.8 Will our Sun ever undergo a white dwarf supernova explosion? Why or why not? o Yes, about a million years after it becomes a white dwarf. o No, because the Sun's core will never be hot enough to fuse carbon and other heavier elements into iron. o Yes, right at the end of its double shell-fusion stage of life.

o No, because it is not orbited by another star. 22. VISUAL QUESTION 14.4 Which of the following represents the true shape of a black hole as you'd see it (or measure it) as you flew past it in a spaceship? 23. CONCEPT QUESTION 14.12 How does an accretion disk around a neutron star differ from an accretion disk around a white dwarf? o The accretion disk around a neutron star is made mostly of helium while the accretion disk around a white dwarf is made mostly of hydrogen. o The accretion disk around a neutron star is more likely to give birth to planets. o The accretion disk around a neutron star always contains much more mass. o The accretion disk around a neutron star is much hotter and emits higher-energy radiation. 24. CONCEPT QUESTION 13.23 You discover a binary star system in which one star is a 15 M Sun main-sequence star and the other is a 10 M Sun giant. How do we think that a star system such as this might have come to exist? o The two stars probably were once separate, but became a binary when a close encounter allowed their mutual gravity to pull them together. o Although both stars probably formed from the same clump of gas, the more massive one must have had its birth slowed so that it became a main sequence stars millions of years later than its less massive companion. o The giant must once have been the more massive star, but is now less massive because it transferred some of its mass to its companion. o The two stars are simply evolving normally and independently, and one has become a giant before the other. 25. READING QUESTION 14.22 Suppose two neutron stars or two black holes are closely orbiting one another. What do scientists predict will eventually happen to them, and why? o Their orbits will spiral inward as a result of friction with the surrounding gas until all the gas clears, after which their orbits will remain stable.

o Their orbits will spiral inward until the two objects merge because of energy lost through gravitational waves. o The orbits would remain stable unless there were a third object orbiting along with them. o Their orbits will gradually grow larger because of the centrifugal force involved as they circle around each other. 26. READING QUESTION 14.2 A typical white dwarf is _________. o as massive as the Sun but only about as large in size as Jupiter o about the same size and mass as the Sun but much hotter o as large in diameter as the Sun but only about as massive as Earth o as massive as the Sun but only about as large in size as Earth 27. READING QUESTION 14.12 Pulsars are thought to be _________. o unstable high-mass stars o accreting white dwarfs o rapidly rotating neutron stars o accreting black holes