t2testbank

pdf

School

Johns Hopkins University *

*We aren’t endorsed by this school

Course

675.601

Subject

Astronomy

Date

Apr 3, 2024

Type

pdf

Pages

Uploaded by JudgeTitaniumGoldfinch40

Formation of the Solar System 1) What percentage of the mass of the solar nebula consisted of elements other than hydrogen and helium? 2 percent 2) Where did the elements heavier than hydrogen and helium come from? They were produced inside stars. 3) Why did the solar nebula heat up as it collapsed? As the cloud shrank, its gravitational potential energy was converted to kinetic energy and then into thermal energy. 4) Why did the solar nebula flatten into a disk? It flattened as a natural consequence of collisions between particles in the spinning nebula, changing random motions into more orderly ones. 5) What happened during the accretion phase of the early solar system? Particles grew by colliding and sticking together. 6) According to our theory of solar system formation, why do all the planets orbit the Sun in the same direction and in nearly the same plane? The laws of conservation of energy and conservation of angular momentum ensure that any rotating, collapsing cloud will end up as a spinning disk. 7) Which of the following lists the ingredients of the solar nebula from highest to lowest percentage of mass of the nebula? light gases (H, He), hydrogen compounds (H 2 O, CH 4 , NH 3 ), rocks, metals 8) What percentage of the solar nebula's mass consisted of hydrogen and helium gases? 98 percent 9) What percentage of the solar nebula's mass consisted of rocky material? 0.4 percent 10) What kind of material in the solar nebula could remain solid at temperatures as high as 1,500 K, such as existed in the inner regions of the nebula? B) metals 11) What was the frost line of the solar system? The distance from the Sun where temperatures were low enough for hydrogen compounds to condense into ices, between the present-day orbits of Mars and Jupiter 12) Why are the inner planets made of denser materials than the outer planets? In the inner part of the nebula only metals and rocks were able to condense because of the high temperatures, whereas hydrogen compounds, although more abundant, were only able to condense in the cooler outer regions. 13) Which of the following is the origin of almost all the large moons around the jovian planets? They were formed by condensation and accretion in a disk of gas around the planet. 14) What is the most likely reason that there are no giant planets beyond Neptune? By the time planetesimals grew to a large enough mass to hold onto an atmosphere, the solar nebula had been blown away. 15) Observations of young stars (as well as theory) tell us that when the Sun was young the solar wind Was stronger than it is today. 16) Which of the following has not been detected around other stars in the Galaxy? Terrestrial planets 17) At first, the Sun's present-day rotation seems to contradict the prediction of the nebular theory because the theory predicts that the Sun should have been rotating fast when it formed, but the actual rotation is fairly slow. 18) According to our theory of solar system formation, why does the Sun rotate slowly today? The Sun once rotated much faster, but it transferred angular momentum to charged particles caught in its magnetic field and then blew the particles away with its strong solar wind. 19) Which of the following are relatively unchanged fragments from the early period of planet building in the solar system? the moons of Mars, asteroids, Kuiper belt comets, Oort cloud comets 20) According to the nebular theory, what are asteroids and comets? They are leftover planetesimals that never accreted into planets. 21) According to the nebular theory, how did the Kuiper belt form? It is made of planetesimals that formed beyond Neptune's orbit and never accreted to form a planet. 22) According to our theory of solar system formation, why do we find some exceptions to the general rules and patterns of the planets? Most of the exceptions are the result of giant impacts.

Star Stuff 17.1 Multiple-Choice Questions 1) What do astronomers mean when they say that we are all "star stuff"? That the carbon, oxygen, and many elements essential to life were created by nucleosynthesis in stellar cores 2) Which two energy sources can help a star maintain its internal thermal pressure? Nuclear fusiosn and gravitational contraction 3) What type of star is our Sun? Low-mass star 4) What is the range of star masses for high-mass stars? Between 8 and about 100 solar masses 5) What can we learn about a star from a life track on an H-R diagram? What surface temperature and luminosity it will have at each stage of its life 6) Which of the following statements about degeneracy pressure is not true? Degeneracy pressure varies with the temperature of the star. 7) All of the following are involved in carrying energy outward from a star's core except Conduction 8) Which stars have convective cores? High-mass stars 9) Which of the following spectral types is more likely to be a flare star? MV 10) Which of the following properties make flare stars so active? Fast rotation rates, deep convection zones 11) What happens when a star exhausts its core hydrogen supply? Its core contracts, but its outer layers expand, and the star becomes bigger and brighter. 12) What is happening inside a star while it expands into a subgiant? It is fusing hydrogen into helium in a shell outside the core 13) Compared to the star it evolved from, a red giant is Cooler and brighter. 14) At approximately what temperature can helium fusion occur? e100 million K 15) Why does a star grow larger after it exhausts its core hydrogen? Hydrogen fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward. 16) How many helium nuclei fuse together when making carbon? 3 17) The helium fusion process results in the production of Carbon. 18) What happens after a helium flash ? The core quickly heats up and expands. 19) What is a carbon star ? A red giant star whose atmosphere becomes carbon-rich through convection from the core 20) What is a planetary nebula? The expanding shell of gas that is no longer gravitationally held to the remnant of a low-mass star 21) What happens to the core of a star after a planetary nebula occurs? It becomes a white dwarf. 22) Which of the following sequences correctly describes the stages of life for a low-mass star? protostar, main-sequence, red giant, white dwarf 23) Compared to the star it evolved from, a white dwarf is hotter and dimmer. 24) Most interstellar dust grains are produced in the atmospheres of red giant stars.

The following questions refer to the H-R diagram below that shows the life track of a 1-solar-mass star, with various stages labeled with Roman numerals. 25) During which stage is the star's energy supplied by gravitational contraction? A) ii 26) During which stage does the star have an inert (nonburning) helium core? B) iv 27) During which stage does the star have an inert (nonburning) carbon core? E) viii 28) Which stage lasts the longest? B) iii 29) What will happen to the star after stage viii? It will eject a planetary nebula. 30) In the end, the remaining core of this star will be left behind as a white dwarf made primarily of carbon and oxygen. The following questions refer to the sketch below of an H-R diagram for a star cluster. 31) Based on its main-sequence turnoff point, the age of this cluster is about 10 billion years. 32) Which statement about this cluster is not true? It is the type of cluster known as an open cluster of stars. 33) Consider the star to which the arrow points. How is it currently generating energy? by hydrogen shell burning around an inert helium core 34) Consider the star to which the arrow points. Which of the following statements about this star is not true? It is significantly less massive than the Sun. 35) What is the CNO cycle ? a type of hydrogen fusion that uses carbon, nitrogen, and oxygen atoms as catalysts 36) Which element has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission? D) iron 37) What happens when the gravity of a massive star is able to overcome neutron degeneracy pressure? The core contracts and becomes a black hole. 38) What types of stars end their lives with supernovae? stars that are at least several times the mass of the Sun 39) Which of the following statements about stages of nuclear burning (i.e., first-stage hydrogen burning, second-stage helium burning, etc.) in a massive star is not true? Each successive stage lasts for approximately the same amount of time. 40) Suppose the star Betelgeuse (the upper left shoulder of Orion) were to become a supernova tomorrow (as seen here on Earth). What would it look like to the naked eye? Betelgeuse would remain a dot of light but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime. 41) Which event marks the beginning of a supernova? the sudden collapse of an iron core into a compact ball of neutrons 42) After a supernova event, what is left behind? either a neutron star or a black hole 43) Why is Supernova 1987A particularly important to astronomers? It was the nearest supernova detected in nearly 400 years.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

44) You discover a binary star system in which one member is a 15 M Sun main-sequence star and the other star is a 10 M Sun giant. Why should you be surprised, at least at first? D) The two stars should be the same age, so the more massive one should have become a giant first. 45) You discover a binary star system in which one member is a15 M Sun main-sequence star and the other star is a 10 M Sun giant. How do we believe that a star system such as this might have come to exist? The giant must once have been the more massive star but transferred some of its mass to its companion. 46) Why do scientists think that our solar system must have formed sometime after nearby supernovae explosions? Existence of heavy elements 17.2 True/False Questions 1) Photographs of many young stars show long jets of material apparently being ejected from their poles. Answer: TRUE 2) Although some photographs show what looks like jets of material near many young stars, we now know that these "jets" actually represent gas from the surrounding nebula that is falling onto the stars. Answer: FALSE 3) In any star cluster, stars with lower masses greatly outnumber those with higher masses. Answer: TRUE 4) There is no limit to the mass with which a star can be born. Answer: FALSE 5) Stars with high masses live longer than stars with lower masses. Answer: FALSE 6) Stars of lower mass have deeper convection zones outside their cores than stars of higher mass. Answer: TRUE 7) Convection never occurs in the core of any type of star. Answer: FALSE 8) The helium fusion process works by fusing two helium nuclei into one beryllium nucleus. Answer: FALSE 9) Our Sun will end its life in a planetary nebula and become a white dwarf. Answer: TRUE 10) The most massive stars generate energy at the end of their lives by fusing iron in their cores. Answer: FALSE 11) The heaviest element produced by stars or in supernovae is silicon. Answer: FALSE 12) All stars that become supernovae will leave behind a neutron star. Answer: FALSE 17.3 Short Answer Questions Choose from the list below for the following questions. You may use a choice more than once. A. H fusion by the proton-proton chain B. H fusion by the CNO cycle C. helium fusion D. matter-antimatter annihilation E. gravitational contraction 1) Which method of energy generation is used by the Sun today? Answer: A 2) Which one provided the energy that made the Sun hot in the first place? Answer: E 3) Which method of energy generation provides the source of energy for a protostar ? Answer: E 4) Which process leads to the production of carbon? Answer: C 5) When a 1-solar-mass star stabilizes as a giant for about a billion years, which method of energy generation occurs in its central core? Answer: C 6) Which one is used by a main-sequence star of spectral type B2? Answer: B 7) Which method of energy generation provides the source of energy for a 10 M Sun main-sequence star? Answer: B

8) Do you think it is possible that a 10-solar-mass main- sequence star could harbor an advanced civilization? Explain your reasoning. Answer: A 10-solar-mass star has a very short lifetime. It also produces copious amounts of ultraviolet radiation, which may discourage living organisms. 9) Do you think it is possible that a flare star could harbor an advanced civilization? Explain your reasoning. Answer: A flare star has violent flare activity that might disrupt the upper atmosphere of a planet and send energetic particles and X rays flying through living organisms – not very pleasant. 10) Do you think it is possible that a carbon star could harbor an advanced civilization? Explain your reasoning. Answer: A carbon star is a very old low-mass star, after it has passed through the red giant phase. Earth may survive the red giant phase of the Sun, as planets in similar systems have, but. the cool red radiation may make processes such as photosynthesis difficult. Maybe an advanced civilization could have developed around this star, but it would have had to make special arrangements to survive the red giant phase of its mother star. 11) Do you think it is possible that a 1.5-solar-mass red giant could harbor an advanced civilization? Explain your reasoning. Answer: A 1.5-solar-mass red giant is a temporary stage of life for a low-mass star. If an advanced civilization had already developed around this star, which is possible, then it may have had the resources to respond to its expanding, reddened sun. 12) Do you think it is possible that a 1-solar-mass horizontal branch star could harbor an advanced civilization? Explain your reasoning. Answer: A 1-solar-mass horizontal branch star is a late- stage low-mass star, burning helium. Life had time to develop, but it would have had to be very clever, with natural resources and probably a lot of cooperation to persist. 13) Do you think it is possible that a red supergiant could harbor an advanced civilization? Explain your reasoning . Answer: A red supergiant is a late-stage high-mass star in the advanced state of nuclear burning, that is, burning elements heavier than helium in its core. Its envelope is gigantic. Its age at this point is rather young since massive stars live short lives. With our assumptions above, an advanced civilization probably does not have enough time to develop. 14) Lithium, beryllium, and boron are elements with atomic number 3, 4, and 5, respectively. Even though they are three of the five simplest elements, why are they rare compared to many heavier elements? Answer: Helium fuses into carbon by combining three helium nuclei (atomic number 2) into one carbon nucleus (atomic number 6), therefore bypassing the elements lithium, beryllium, and boron, with atomic numbers 3 through 5. Therefore, fusion processes in the cores of stars do not form these three elements. (Beyond the scope of this book: Trace amounts of lithium and perhaps beryllium and boron formed in the Big Bang. Most of the beryllium and boron may have formed via cosmic-ray collisions with heavier elements. The exact origin of these elements is still a topic of astronomical research. These three elements are also rather fragile and tend to be destroyed in the cores of stars rather than being created there.) 15) What are the three types of pressure that can push against the inward force of gravity? Explain what causes each pressure and where it would be likely to occur. Answer: (1) Thermal pressure occurs when the particles inside a star are heated enough so that their random motions cause an outward pressure. The two energy sources of internal thermal pressure are gravitational contraction, found in protostars and when a star has used up a fusionable material in its core, and nuclear fusion, which can occur in the core or in a shell of a star. (2) Degeneracy pressure arises from the idea of quantum mechanics that two electrons (or neutrons) cannot occupy the same state. Degeneracy pressure occurs in the cores of low-mass stars before a helium flash, maintains equilibrium in white dwarfs and neutron stars, and may be present immediately before a supernova event. (3) Radiation pressure exists only in massive stars where fusion rates are so high that photons transfer momentum to the surrounding gas and apply a third kind of pressure. 16) Briefly summarize the stages of life for a low-mass star. Answer: The protostar assembles from the molecular clouds, heats up from gravitational contraction, and begins hydrogen fusion in the core. The star settles onto the main sequence, where it will fuse hydrogen in its core for 10 billion years. When the core hydrogen is used up, the core contracts until it is degenerate, hydrogen fusion continues in a shell outside the core, and the outer layers expand and cool the star becomes a red giant. Helium fusion begins in the core, but since the core is degenerate a helium flash takes place and rapidly spreads throughout the core. Helium fusion stabilizes, and the star moves left on the H-R diagram. Core helium is used up and helium begins fusing in a shell outside the core, with hydrogen still fusing in a

shell above it. The outer layers expand, and the star again becomes a red giant. The star undergoes thermal pulses and loses its outer layers through a stellar wind. The core shrinks and heats up but is not able to fuse any more elements. The star becomes a planetary nebula as heat from the core blows away and heats up the gas left over from the red giant phase. Only the naked degenerate core is left, a white dwarf. 17) Briefly summarize the stages of life for a high-mass star. Answer: The first stages are similar to those of a low-mass star, except that they happen over much shorter time periods. While on the main sequence, the star fuses hydrogen by the CNO cycle and remains at this stage only for several million years. In addition to helium fusion, high- mass stars also undergo alpha-capture, which creates heavier elements by fusing a helium nucleus with an existing atom. After helium is used up in the core, the core contracts while helium and hydrogen fusion continue in outer shells. The core contracts until carbon ignition occurs, and the star moves left again on the H-R diagram while carbon fusion occurs in the core. The process continues for stars of still higher mass, zigzagging across the H-R diagram as heavier elements are fused in the core and used up as fuel. Each fusion stage requires less time until iron is finally produced in the core. Iron cannot be fused to produce energy, so the core collapses and pressures increase so that electrons and protons are converted to neutrons. A high quantity of neutrinos is released, which may help force the outer layers violently outward in an explosion called a supernova. Elements heavier than iron are created, the outer layers move away from the core at great velocities, and only a neutron star or black hole is left as a remnant. 18) Briefly explain why high-mass stars have shorter lifetimes than low-mass stars. Answer: High-mass stars have 10 to 100 times more mass (fuel) than a typical low-mass star. This greater mass produces a much higher downward gravitational pressure, leading to much higher core temperatures and higher rates of fusion. The luminosity of such stars is therefore 1,000 to 1 million times greater than in low-mass stars. So, although high-mass stars have more fuel to burn, they burn it at a much higher rate and therefore run out of fuel much more quickly. 19) Based on what you learned in this chapter, would you expect life to be able to evolve around first- generation stars in our universe? Why or why not? Answer: Most would say no, as the first-generation stars should not have yet been enriched with the heavy elements we believe are necessary for life. A student could also argue that life could form without these and our current understanding of life is incomplete. 20) Explain how patterns in cosmic abundances (Fig 12.15) fit theoretical predictions for the origin of the elements. Answer: Heavier elements are rarer as they are produced in shorter-lived phases of rare, massive stars. Iron is relatively abundant because its production is energetically favored as the end step of fusion and there is only a short time during the supernova phase when it can be destroyed by fission. The abundances of nuclei with even numbers of protons is greater than neighboring nuclei with odd numbers of protons as expected for nuclear reactions through the addition of helium nuclei. 21) How do observations of stars help us understand the theory of atomic nuclei? Answer: Many nuclear reactions occur during the late stages of stellar evolution. By observing how stars evolve and the production of different elements, we can learn about how nuclei react. 17.4 Mastering Astronomy Reading Quiz 1) Which of the following stars will live longest? a 1-solar-mass star 2) In the context of understanding stellar lives, "high- mass" stars have masses more than about 8 times the mass of our Sun. 3) Which of the following lists the stages of life for a low- mass star in the correct order? A) protostar, main-sequence star, red giant, planetary nebula, white dwarf 5) The main source of energy for a star as it grows in size to become a red giant is hydrogen fusion in a shell surrounding the central core. 6) The overall helium fusion reaction is three helium nuclei fuse to form one carbon nucleus. 7) What is a helium flash ? The sudden onset of helium fusion in the core of a low- mass star. 8) An H-R diagram for a globular cluster will show a horizontal branch — a line of stars above the main- sequence but to the left of the subgiants and red giants. Which of the following statements about these horizontal branch stars is true ? They generate energy through both hydrogen fusion and helium fusion.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

9) What is a planetary nebula? gas ejected from a low-mass star in the final stage of its life 11) Which low-mass star does not have fusion occurring in its central core? a red giant 12) How are low-mass red giant stars important to our existence? These stars manufactured most of the carbon atoms in our bodies. 13) Which of the following pairs of atomic nuclei would feel the strongest repulsive electromagnetic force if you tried to push them together? helium and helium 14) Which of the following stars will certainly end its life in a supernova? a 10-solar-mass star 15) What is the CNO cycle? a set of steps by which four hydrogen nuclei fuse into one helium nucleus 16) In order to predict whether a star will eventually fuse oxygen into a heavier element, what do you need to know about the star? its mass 17) Why is iron significant to understanding how a supernova occurs? Iron cannot release energy either by fission or fusion. 18) After a supernova explosion, the remains of the stellar core be either a neutron star or a black hole. 19) Why is Supernova 1987A particularly important to astronomers? It is the nearest supernova to have occurred at a time when we were capable of studying it carefully with telescopes. 20) Algol consist of a 3.7 M Sun main-sequence star and a 0.8 M Sun subgiant. Why does this seem surprising, at least at first? The two stars should be the same age, so we'd expect the subgiant to be more massive than the main-sequence star. 21) Where does gold (the element) come from? It is produced during the supernova explosions of high- mass stars. 17.5 Mastering Astronomy Concept Quiz 2) Which of the following types of data provide evidence that helps us understand the life tracks of low-mass stars? H-R diagrams of globular clusters 3) Why is a 1 solar-mass red giant more luminous than a 1 solar-mass main-sequence star? Fusion reactions are producing energy at a greater rate in the red giant. 4) Which of the following describes a star with a hydrogen-burning shell and an inert helium core? It is a subgiant that grows in luminosity until helium fusion begins in the central core. 5) Which of the following observations would not be likely to provide information about the final, explosive stages of a star's life? Decades of continuous monitoring of red giants in a globular cluster 6) Which is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf system? Planetary nebula formation is more common. 12) Carbon fusion occur in high-mass stars but not in low-mass stars because the cores of low-mass stars never get hot enough for carbon fusion. 16) Suppose that hydrogen, rather than iron, had the lowest mass per nuclear particle. Which of the following would be true? D) Nuclear fusion could not power stars. 17) 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? At the end of a high-mass star's life, it produces new elements through a series of helium capture reactions. 18) A spinning neutron star has been observed at the center of a supernova remnant. 20) Tidal forces are very important to the Algol system today, but were not important when both stars were still on the main sequence. Why not? A) Main-sequence stars in a system like the Algol system are small compared to their physical separation.

23) Based on our current theory of Earth's formation, the water we drink comes from comets that impacted Earth. 24) The heavy bombardment phase of the solar system lasted several hundreds of millions of years. 25) Which of the following is not evidence supporting the giant impact theory for the formation of the Moon? Scientists have found several meteorites that appear to be the remains of the object that caused the giant impact. 26) Which of the following puzzles in the solar system cannot be explained by a giant impact event? The orbit of Triton in the opposite direction to Neptune's rotation 27) The nebular theory of the formation of the solar system successfully predicts all but one of the following. Which one does the theory not predict? The equal number of terrestrial and jovian planets 28) The age of our solar system is approximately 4.6 billion years. 29) The age of the solar system can be established by radioactive dating of the oldest meteorites. 30) What do meteorites reveal about the solar system? They reveal that the age of the solar system is approximately 4.6 billion years. 31) Suppose you find a rock that contains some potassium-40 (half-life of 1.3 billion years). You measure the amount and determine that there are 5 grams of potassium-40 in the rock. By measuring the amount of its decay product (argon-40) present in the rock, you realize that there must have been 40 grams of potassium-40 when the rock solidified. How old is the rock? 3.9 billion years 8.2 True/False Questions 1) All the planets in the solar system rotate in the same direction as they orbit the Sun. Answer: FALSE 2) As viewed from above Earth's North Pole, all of the planets orbit the Sun in the same (counterclockwise) direction. Answer: TRUE 3) The more massive planets in the solar system tend to be less dense than the lower mass planets. Answer: TRUE 4) Within the frost line, planetesimals were composed entirely of rock and outside the frost line planetesimals were composed entirely of ice. Answer: FALSE 5) Impacts were extremely common in the young solar system but no longer occur today. Answer: FALSE 6) Earth's atmosphere resulted from the impact of icy planetesimals that originated in the outer regions of the Solar System. Answer: TRUE 7) The Moon probably formed at the same time that Earth formed, rather like the formation of a double planet. Answer: FALSE 8) Some radioactive isotopes found in meteorites suggest that the solar system may have been formed shortly after a supernova occurred nearby. Answer: TRUE 9) Based on our theory of how our own solar system formed, we would expect that other solar systems would be quite common. Answer: TRUE 10) Nebular theory predicts that other solar systems that formed in the same way should also have 8 planets. Answer: FALSE 11) We cannot test the nebular theory for the formation of the Solar System in a rigorous scientific way because the Sun and planets formed in the distant past. Answer: FALSE 8.3 Short Answer Questions 1) Briefly summarize the observed patterns of motion in our solar system that are consistent with the nebular theory. Answer: (a) All planets orbit the Sun counterclockwise when seen from above Earth's North Pole. (b) All planetary orbits lie nearly in the same plane. (c) Almost all planets travel on nearly circular orbits. (d) The spacing between planetary orbits increases with distance from the Sun. (e) Most planets orbit in the same direction in which they rotate, counterclockwise. (f) Almost all moons orbit their planet in the same direction as the planet's rotation and near

the planet's equatorial plane. (g) The Sun rotates in the same direction in which the planets orbit. 3) Suppose the entire solar nebula had cooled to a very low temperature before the solar wind cleared it away. Do you think Earth would be the same? Why or why not? Answer: Ices would have condensed in the inner solar system, significantly increasing the size and mass (or possibly number) of terrestrial planets. Water and other hydrogen compounds would be much more abundant. 4) Suppose the planet Jupiter had never formed. How do you think the distribution of asteroids and comets in our solar system would be different? Explain. Answer: If Jupiter had never existed, its gravity would not have prevented asteroidal material from accreting into a single planet outside of Mars. Comets would not have been flung into the Oort cloud or completely out of the solar system to as great a degree (though the outer jovian planets may have performed this function). 5) Explain why the early Earth did not form with water, and how it gained it later in its formation. Answer: Earth, and all terrestrial planets, formed inside the frost line from rocky and metallic planetesimals. The temperature of the solar nebula was too hot for water ice to exist and Earth was too small to hold onto a substantial atmosphere of hot gases. Earth gained its water later during the heavy bombardment phase when water-rich planetesimals that formed beyond the frost line were scattered into the inner solar system, predominantly through gravitational encounters with Jupiter, and impacted Earth. 6) Briefly describe the modern theory of how our Moon formed. Answer: The Moon formed from a giant impact of a Mars- size object with Earth. This impact blasted material into Earth orbit that eventually coalesced to form the Moon. 9) If we were to re-run the formation of the solar system, what would likely be the same and what would likely be different? Answer: As with our solar system, planets would likely orbit in a thin disk, with small, dense planets close to the Sun and larger, jovian-like planets further away because these properties are due to the cumulative effects of cloud flattening during collapse and enhanced heating close to the star. The properties of our solar system that would be less likely to be repeated would be those due to chance events (giant impacts), such as the backward rotation of Venus, the formation of Earth's Moon, and the sideways tilt of Uranus. 10) Process of Science : A scientific theory must produce testable hypotheses that are then evaluated when data are available. What testable hypotheses does nebular theory predict? Describe two hypotheses about solar systems that come from nebular theory that we can test when more data on other solar systems become available. Answer: 1. Larger planets should be in the outer solar system. 2. Planets should orbit in the same direction. 3. Planets should lie in approximately the same plane. 12) Process of Science: Now that Pluto is no longer considered a planet, the number if planets in the Solar System has dropped from 9 to 8. Does this mean that the nebular theory of the Solar System was incorrect? Answer: No, the nebular theory of the Solar System explain broad patterns of motion and composition of the planets, but did not predict their exact number. 8.4 Mastering Astronomy Reading Quiz 1) In essence, the nebular theory holds that our solar system formed from the collapse of an interstellar cloud of gas and dust. 3) The terrestrial planets are made almost entirely of elements heavier than hydrogen and helium. According to modern science, where did these elements come from? They were produced by stars that lived and died before our solar system was born. 4) According to our theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size? It got hotter, its rate of rotation increased, and it flattened into a disk. 5) Which of the following types of material can condense into what we call ice at low temperatures? hydrogen compounds 6) According to our present theory of solar system formation, which of the following lists the major ingredients of the solar nebula in order from the most abundant to the least abundant? Hydrogen and helium gas; hydrogen compounds; rock; metal 9) According to our present theory of solar system formation, why were solid planetesimals able to grow larger in the outer solar system than in the inner solar system? B) because only metal and rock could condense in the inner solar system, while ice also condensed in the outer solar system

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

10) According to our basic scenario of solar system formation, why do the jovian planets have numerous large moons? As the growing jovian planets captured gas from the solar nebula, the gas formed swirling disks around them, and moons formed from condensation accretion within these disks. 12) According to our theory of solar system formation, where did the comets of the Oort cloud form? in the region of the jovian planets 13) What do we mean by the period of heavy bombardment in the context of the history of our solar system? the first few hundred million years after the planets formed, which is when most impact craters were formed 14) What is the giant impact hypothesis for the origin of the Moon? The Moon formed from material blasted out of the Earth's mantle and crust by the impact of a Mars-size object. 15) Suppose you start with 1 kilogram of a radioactive substance that has a half-life of 10 years. Which of the following statements will be true after 20 years pass? A) You'll have 0.25 kilogram of the radioactive substance remaining. 8.5 Mastering Astronomy Concept Quiz 1) Which of the following best explains why we can rule out the idea that planets are usually formed by near- collisions between stars? Stellar near-collisions are far too rare to explain all the planets now known to orbit nearby stars. 2) According to our modern science, which of the following best explains why the vast majority of the mass of our solar system consists of hydrogen and helium gas? Hydrogen and helium are the most common elements throughout the universe, because they were the only elements present when the universe was young. 3) According to our theory of solar system formation, which law best explains why the central regions of the solar nebula got hotter as the nebula shrank in size? The law of conservation of energy 4) According to our theory of solar system formation, which law best explains why the solar nebula spun faster as it shrank in size? The law of conservation of angular momentum 5) According to our present theory of solar system formation, which of the following best explains why the solar nebula ended up with a disk shape as it collapsed? It flattened as a natural consequence of collisions between particles in the nebula. 6) What is the primary basis upon which we divide the ingredients of the solar nebula into four categories (hydrogen/helium; hydrogen compound; rock; metal)? the temperatures at which various materials will condense from gaseous form to solid form 7) According to our present theory of solar system formation, which of the following statements about the growth of terrestrial and jovian planets is not true? The jovian planets began from planetesimals made only of ice, while the terrestrial planets began from planetesimals made only of rock and metal. 8) Many meteorites appear to have formed very early in the solar system's history. How do these meteorites support our theory about how the terrestrial planets formed? The meteorites appearance and composition is just what we'd expect if metal and rock condensed and accreted as our theory suggests. 10) According to our present theory of solar system formation, how did Earth end up with enough water to make oceans? The water was brought to the forming Earth by planetesimals that accreted beyond the orbit of Mars. 11) What is the primary reason that astronomers suspect that some jovian moons were captured into their current orbits? D) Some moons have orbits that are "backwards" or highly inclined to their planet's equator. 12) Which of the following is not a line of evidence supporting the hypothesis that our Moon formed as a result of a giant impact? A) The Pacific Ocean appears to be a large crater — probably the one made by the giant impact. 13) Why are terrestrial planets denser than jovian planets? Only dense materials could condense in the inner solar nebula.

16) The region of our solar system between Mercury and Mars has very few asteroids, while the region between Mars and Jupiter has many asteroids. Based on what you have learned, what is the most likely explanation for the lack of asteroids between Mercury and Mars? There were very few planetary leftovers in this region, because most of the solid material was accreted by the terrestrial planets as the planets formed. 17) About 2% of our solar nebula consisted of elements besides hydrogen and helium. However, the very first generation of star systems in the universe probably consisted only of hydrogen and helium. Which of the following statements is most likely to have been true about these first-generation star systems? There were no comets or asteroids in these first-generation star systems. The Bizarre Stellar Graveyard 18.1 Multiple-Choice Questions 1) Degeneracy pressure is the source of the pressure that stops the crush of gravity in all the following except a very massive main-sequence star. 2) White dwarfs are so called because they are both very hot and very small. 3) A teaspoonful of white dwarf material on Earth would weigh a few tons. 4) Which of the following is closest in mass to a white dwarf? E) the Sun 5) Why is there an upper limit to the mass of a white dwarf? B) The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, so more mass cannot be added without breaking the degeneracy pressure. 6) What is the ultimate fate of an isolated white dwarf? A) It will cool down and become a cold black dwarf. 7) Suppose a white dwarf is gaining mass because of accretion in a binary system. What happens if the mass someday reaches the 1.4-solar-mass limit? A) The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy. 8) Which of the following statements about novae is not true? C) Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5 billion years from now. 9) What kind of pressure supports a white dwarf? B) electron degeneracy pressure 10) What is the upper limit to the mass of a white dwarf? D) 1.4 solar masses 11) How does a 1.2-solar-mass white dwarf compare to a 1.0-solar-mass white dwarf? B) It has a smaller radius. 12) Which of the following is closest in size (radius) to a white dwarf? A) Earth 13) What kind of star is most likely to become a white-dwarf supernova? D) a white dwarf star with a red giant binary companion 14) Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova ? C) The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not. 15) After a massive-star supernova, what is left behind? E) either a neutron star or a black hole 16) A teaspoonful of neutron star material on Earth would weigh C) more than Mt. Everest.

17) Which of the following is closest in size (radius) to a neutron star? B) a city 18) Which of the following best describes what would happen if a 1.5-solar-mass neutron star, with a diameter of a few kilometers, were suddenly (for unexplained reasons) to appear in your hometown? A) The entire mass of Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star. 19) From an observational standpoint, what is a pulsar ? B) an object that emits flashes of light several times per second or more, with near perfect regularity 21) What causes the radio pulses of a pulsar? B) As the star spins, beams of radio radiation sweep through space. If one of the beams crosses Earth, we observe a pulse. 22) How do we know that pulsars are neutron stars? No massive object, other than a neutron star, could spin as fast as we observe pulsars spin. 23) What is the ultimate fate of an isolated pulsar? D) It will slow down, the magnetic field will weaken, and it will become invisible. 24) What is the basic definition of a black hole ? C) any object from which the escape velocity exceeds the speed of light 25) How does the gravity of an object affect light? B) Light coming from a compact massive object, such as a neutron star, will be redshifted. 26) How does a black hole form from a massive star? A) During a supernova, if a star is massive enough for its gravity to overcome neutron degeneracy of the core, the core will be compressed until it becomes a black hole. 27) Which of the following statements about black holes is not true? If the Sun magically disappeared and was replaced by a black hole of the same mass, Earth would soon be sucked into the black hole. 28) In some cases, a supernova in a binary system may lead to the eventual formation of an accretion disk around the remains of the star that exploded. All of the following statements about such accretion disks are true except several examples of flattened accretion disks being "fed" by a large companion star can be seen clearly in photos from the Hubble Space Telescope. 29) 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 force us to immediately rule out the possibility of a black hole? C) sudden, intense X-ray bursts 31) A 10-solar-mass main-sequence star will produce which of the following remnants? B) neutron star 32) What do we mean by the singularity of a black hole? C) It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions. 33) How do we know what happens at the event horizon of a black hole? E) We don't know for sure: we only know what to expect based on the predictions of general relativity. 34) Prior to the 1990s, most astronomers assumed that gamma-ray bursts came from neutron stars with accretion disks. How do we now know that this hypothesis was wrong? C) Observations from the Compton Gamma-Ray Observatory show that gamma-ray bursts come randomly from all directions in the sky. 35) Why do astronomers consider gamma-ray bursts to be one of the greatest mysteries in astronomy? C) because the current evidence suggests that they are the most powerful bursts of energy that ever occur anywhere in the universe, but we don't know how they are produced

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

39) If you were to come back to our Solar System in 6 billion years, what might you expect to find? B) a white dwarf 40) Black holes, by definition, cannot be observed directly. What observational evidence do scientists have of their existence? B) Gravitational interaction with other objects. 18.2 True/False Questions 1) Brown dwarfs, white dwarfs, and neutrons stars are all kept from collapsing by degeneracy pressure. Answer: TRUE 2) The upper limit to the mass of a white dwarf is 1.4 solar masses. Answer: TRUE 3) More massive white dwarfs are smaller than less massive white dwarfs. Answer: TRUE 4) There is no upper limit to the mass of a neutron star. Answer: FALSE 5) The remnant left behind from a white-dwarf supernova is a neutron star. Answer: FALSE 6) Our Sun will likely undergo a nova event in about 5 billion years. Answer: FALSE 7) All pulsars are neutron stars, but not all neutron stars are pulsars. Answer: TRUE 8) Neutron stars are the densest objects that we can observe in the universe. Answer: TRUE 9) No visible light can escape a black hole, but things such as gamma rays, X rays, and neutrinos can. Answer: FALSE 10) Light from white dwarfs shows a gravitational redshift. Answer: TRUE 11) All massive-star supernovae leave behind black holes as remnants. Answer: FALSE 12) Planets have been detected around a pulsar. Answer: TRUE 18.3 Short Answer Questions 1) Could our Sun ever undergo a nova or a white- dwarf supernova event? Why or why not? Answer: No, because both events occur on white dwarfs in close binary systems. Even after our Sun becomes a white dwarf, such events won't occur because our Sun is not part of a close binary. 2) Why does the size of a white dwarf decrease with increasing mass? Answer: A massive white dwarf has a stronger gravitational force that compresses the matter within it to a greater density. The degeneracy pressure that supports a white dwarf against collapse increases as the density increases and reaches a balance (if the mass is less than the Chandrasekhar limit) such that the more massive the white dwarf, the smaller it is. 3) Briefly describe how a nova event occurs. Answer: A white dwarf in a close binary system accretes mass from its companion star. This mass is mostly hydrogen from the companion's outer layers. When enough builds up on the white-dwarf surface, the hydrogen undergoes fusion, generating the nova. 4) Why do white-dwarf supernovae all have the same maximum luminosity? Answer: White-dwarf supernovae occur when the mass of the white dwarf has just exceeded 1.4 M Sun . Since the mass is the same and the entire object – made of degenerate matter – explodes at once, the maximum luminosity is the same. 5) What is an X-ray burster? What causes the X- ray bursts? Answer: It is a neutron star in a close binary system; the bursts are caused by helium fusion on the surface of the neutron star.

6) What would happen if a small piece (say the size of a paper clip) of neutron star material struck Earth? Answer: The extremely dense material could not be supported by the ordinary material on Earth and it would plunge to the center of Earth under the action of gravity. Its momentum would carry it past the center, back to the other side and it would continue to oscillate back and forth through Earth creating a small hole each time (that would rapidly fill with molten rock) until friction finally brought it to rest at the center of Earth. 7) Suppose you find an X-ray binary that exhibits X-ray bursts. Is it possible that the system's X-ray binary consists of a red giant and a black hole? Why or why not? Answer: No, because bursts occur on a surface; a black hole has no surface. 8) Briefly describe what you would see if your friend plunged into a black hole. Answer: As he approached the black hole, he would be stretched by tidal forces, his time would run slow, and light coming from him would be redshifted. The closer he got to the event horizon, the slower time would run. You would never see him cross the event horizon, but he would disappear from view when his light became redshifted out of the range of detection. 9) Why would Earth's orbit be unaffected were the Sun to suddenly become a black hole? Answer: Earth's orbit (and those of the other planets) would remain unchanged since they are far enough away that Newton's law of gravity applies and the gravitational force depends only on the masses of the objects and the distance between them, not on their composition or density. 10) What is the evidence that gamma-ray bursts originate from beyond the Milky Way Galaxy? Answer: The distribution of gamma-ray bursts is distributed uniformly on the sky, unlike the distribution of X-ray binaries, neutron stars, and other objects within the Galaxy. Further, the afterglow of some gamma-ray bursts have now been detected and detailed observations at other wavelengths show that they are located at the position (and redshift) of distant galaxies. 11) How were neutron stars discovered? Answer: They were detected as pulsars due to their beams of radiation. 12) Can we ever really know what happens within the event horizon of a black hole? Answer: No, because no light can escape and we can therefore never make observations and test predictions for what happens within the event horizon. 13) Describe a hypothetical observation of a white dwarf that, if made and verified by others, would dramatically challenge our physical understanding of them. Answer: The discovery of a white dwarf with a mass greater than the Chandrasekhar limit. 18.4 Mastering Astronomy Reading Quiz 3) If you had something the size of a sugar cube that was made of white dwarf matter, it would weigh A) as much as a truck. 5) What is an accretion disk ? B) a disk of hot gas swirling rapidly around a white dwarf, neutron star, or black hole 6) According to our modern understanding, what is a nova ? A) an explosion on the surface of a white dwarf in a close binary system 7) Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass limit? C) The white dwarf will explode completely as a white dwarf supernova. 8) A neutron star is C) the remains of a star that died in a massive star supernova (if no black hole was created). 9) A typical neutron star is more massive than our Sun and about the size (radius) of A) a small asteroid (10 km in diameter).

10) If you had something the size of a sugar cube that was made of neutron star matter, it would weigh D) about as much as a large mountain. 12) How is an X-ray burst (in an X-ray binary system) similar to a nova? A) Both involve explosions on the surface of stellar corpse. 14) Based on current understanding, the minimum mass of a black hole that forms during a massive star supernova is roughly C) 3 solar masses. 15) What do we mean by the event horizon of a black hole? D) It is the point beyond which neither light nor anything else can escape. 17) What do we mean by the singularity of a black hole? A) It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions. 18) What makes us think that the star system Cygnus X-1 contains a black hole? A) It emits X rays characteristic of an accretion disk, but the unseen star in the system is too massive to be a neutron star. 20) Scientists have detected thousands of gamma ray bursts. The evidence suggests that most or all of these bursts B) have occurred in distant galaxies. 21) Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true? A) 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 18.5 Mastering Astronomy Concept Quiz 1) Which of the following statements about degeneracy pressure is not true? D) Degeneracy pressure can arise only from interactions among electrons. 2) The more massive a white dwarf, the B) smaller its radius. 4) The white dwarf that remains when our Sun dies will be mostly made of C) carbon. 5) Which statement about accretion disks is not true? C) The primary factor determining whether a white dwarf has an accretion disk is the white dwarf's mass. 6) According to present understanding, a nova is caused by hydrogen fusion on the surface of a white dwarf. 7) Which of the following is not true about differences between novae and supernovae? B) Supernovae eject gas into space but novae do not. 8) Will our Sun ever undergo a white dwarf supernova explosion? Why or why not? C) No, because it is not orbited by another star. 9) Which of the following best describes what would happen if a 1.5-solar-mass neutron star, with a diameter of a few kilometers, were suddenly (for unexplained reasons) to appear in your home town? A) The entire Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star. 11) Which statement about pulsars is not thought to be true? B) Pulsars can form only in close binary systems. 12) How does an accretion disk around a neutron star differ from an accretion disk around a white dwarf? C) The accretion disk around a neutron star is much hotter and emits higher-energy radiation. 13) Which statement concerning black hole masses and Schwarzschild radii is not true? A) In a binary system with a black hole, the Schwarzschild radius depends on the distance from the black hole to the companion star.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

14) Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice? D) Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted. 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? A) intense X-ray bursts 17) Which of the following observatories is most likely to discover a black hole in a binary system? B) the Chandra X-Ray Observatory 18) Which of the following statements about gamma ray bursts is not true? D) Based on their distribution in the sky, we can rule out a connection between gamma ray bursts and X-ray binaries in the Milky Way Galaxy. 19) 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. Sometime within the next million years or so, the civilization's planet is likely to be doomed because A) the red giant will probably supernova within the next million years.

t2testbank

Related Documents