Chapter 14 Homework Key

11/10/2019 Ch 14 HW Ch 14 HW Due: 11:59pm on Tuesday, November 12, 2019 You will receive no credit for items you complete after the assignment is due. Grading Policy Prelecture Overview: The Bizarre Stellar Graveyard First, launch the video below. Then, close the video window and answer the questions at right. You can watch the video again at any point. Part A Degenearcy pressure arises when ________. Hint 1. What happens to an inflated balloon when you heat it? If you heat an inflated balloon, what happens to it? ANSWER: he gas particles inside it move faster, causing it to expand until it stabilizes at a new, larger size. he gas particles inside it move slower, causing it to contract until it stabilizes at a new, smaller size. he rate of nuclear fusion skyrockets inside the balloon. ANSWER: ubatomic particles are packed as tightly as the laws of quantum mechanics allow he speeds of subatomic particles reach the speed of light star's core is producing less energy than the star is radiating away from its surface he temperature reaches a critically high value n object becomes as small or smaller than Earth Correct That is why, unlike ordinary (thermal) pressure, degeneracy pressure does not depend on temperature. Part B Gravitational waves were first detected directly in 2015. According to models, the source of these gravitational waves was __________. ANSWER: neutron star supernova he supernova of an extremely massive star white dwarf supernova ery powerful x-ray bursts he merger of two black holes 1/31 1/31 11/10/2019 Ch 14 HW Correct The two orbiting black holes would have had slowly decaying orbits because of the emission of gravitational waves, and their ultimate merger produced the strong burst of gravitational waves that was detected on Earth. Part C Match words at the left to the correct blanks in the sentences at right. Not all words will be used. ANSWER: Reset dark center The event horizon Help marks the boundary between the inside and outside of a black hole. A(n) nova occurs when fusion ignites on the surface of a white dwarf. A(n) pulsar is rapidly rotating neutron star. white dwarf supernova proton degeneracy pressure 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. A neutron star can remain stable in size because of neutron degeneracy pressure . The singularity is the place to which all of a black hole's mass is in principle located within the black hole. Correct Vocabulary in Context: White Dwarfs Part A Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each word only once. Hint 1. The definition of electron degeneracy pressure The electron degeneracy pressure is a type of pressure that arises when electrons are packed as tightly as the laws of quantum physics allow. Unlike ordinary (thermal) pressure, the strength of electron degeneracy pressure does not depend on an object’s temperature. Hint 2. The definition of the white dwarf limit The white dwarf limit is its maximum possible mass, which is about 1.4 . It is sometimes called the Chandrasekhar limit, after the man who first calculated it. For an object with mass above this limit, gravity is too strong to be resisted by electron degeneracy pressure. Hint 3. The definition of an accretion disk An accretion disk is a rapidly rotating disk of material, which gradually falls inward as it orbits a star-like object (e.g., white dwarf, neutron star, or black hole). Hint 4. The definition of a nova A nova is the dramatic brightening of a star, which lasts for a few weeks and then subsides. It occurs when a burst of hydrogen fusion ignites in a shell on the surface of an accreting white dwarf in a binary star system. Hint 5. The definition of a white dwarf supernova 2/31 2/31 11/10/2019 Ch 14 HW A white dwarf supernova occurs when an accreting white dwarf reaches the white dwarf limit, ignites runaway carbon fusion, and explodes like a bomb. It is often called a Type Ia supernova. Hint 6. The definition of a massive star supernova A massive star supernova occurs when a massive star dies, initiated by the catastrophic collapse of its iron core. It is often called a Type II supernova. ANSWER: Reset Help 1. The radius of a white dwarf is determined by a balance between the inward force of gravity and the outward push of electron degeneracy pressure . 2. A white dwarf in a close binary system will explode as a supernova if it gains enough mass to exceed the white dwarf limit (1.4 solar masses) . 3. A(n) accretion disk consists of hot, swirling gas captured by a white dwarf (or neutron star or black hole) from a binary companion star. 4. A(n) nova occurs when hydrogen fusion ignites on the surface of a white dwarf in a binary system. 5. A(n) white dwarf supernova can occur only in a binary system, and all such events are thought to have about the same luminosity. 6. A(n) massive star supernova occurs when fusion creates iron in the core of a star. Correct Sorting Task: Distinguishing Massive Star and White Dwarf Supernovae Learning Goal: To distinguish between properties of the two major types of supernovae: massive star supernovae and white dwarf supernovae. All supernovae represent the explosions of stars, but current understanding suggests there are two basic types of supernovae: one that occurs when a massive star reaches the end of its life, and the other that occurs when a white dwarf star explodes because its mass has exceeded the white dwarf limit (also called the Chandrasekhar limit) of 1.4 solar masses. Part A Match the items below with the correct type of supernova. Drag the appropriate items to their respective bins. Hint 1. The ages of stars that explode as supernovae One key to sorting the items correctly is to keep in mind that the two types of supernovae involve stars of very different ages: Massive star supernovae always involve young stars, because massive stars live short lives of only a few million years. White dwarf supernovae always involve old stars, because white dwarfs are the remains of low-mass stars that live billions of years before they even become white dwarfs. These facts should allow you to sort the items relating to the kinds of star clusters and galaxies in which the two types of supernovae can occur. Hint 2. What are the masses of white dwarfs, neutron stars, and black holes? Rank the items representing the three types of compact object by their maximum masses. 3/31 3/31 11/10/2019 Ch 14 HW Rank the mass of the objects from lowest to highest. To rank items as equivalent, overlap them. ANSWER: Reset white dwarf neutron star Help black hole Hint 3. What can make a white dwarf's mass rise above the white-dwarf limit? A white dwarf explodes as a supernova when its mass exceeds the white-dwarf limit of 1.4 solar masses. How does this happen? ANSWER: Mass transfer from or merger with a companion star can raise a white dwarf's mass above the limit. star that ends its life leaves behind a compact object with a mass greater than 1.4 solar masses. White dwarfs increase in density as they age, so they can eventually exceed the limit. Hint 4. What are white dwarfs made of? White dwarfs are made mostly of __________. ANSWER: on ydrogen and helium arbon and oxygen Hint 5. Supernova light curves The following figure contrasts the typical light curves of massive-star and white-dwarf supernovae. You can use this figure to determine which supernova type has the higher peak luminosity. 4/31 4/31 11/10/2019 Ch 14 HW ANSWER: Reset Help Star explodes completely, leaving no compact object behind. Can only occur in a galaxy with ongoing star formation Can only occur in a binary system Can occur in a very old star cluster Black hole or neutron star left behind Has a brighter peak luminosity Spectra always lack strong hydrogen lines. Correct Think carefully about the reasons behind these answers, so that you are prepared to complete Part B. Part B Each item below describes an observation of a hypothetical supernova. Classify each observation as either "Not surprising" if it fits in with our current understanding of supernovae, or "Surprising" if the observation would cause us to rethink our understanding of supernovae. Drag the appropriate items to their respective bins. Hint 1. The ages of stars that explode as supernovae One key to sorting the items correctly is to keep in mind that the two types of supernovae involve stars of very different ages: Massive star supernovae always involve young stars, because massive stars live short lives of only a few million years. White dwarf supernovae always involve old stars, because white dwarfs are the remains of low-mass stars that live billions of years before they even become white dwarfs. These facts should allow you to sort the items relating to the kinds of star clusters and galaxies in which the two types of supernovae can occur. Hint 2. How do we detect black holes? In general, we can detect a black hole left behind by a dead star __________. ANSWER: 5/31 5/31 11/10/2019 Ch 14 HW nly if mass is being transferred to it by another star s long as its mass is greater than about 3 solar masses n all cases ANSWER: Reset A white dwarf supernova in a galaxy of only old stars Two massive star supernovae occur in the same young star cluster. A massive star supernova leaves behind no detectable compact object. A massive star in a binary system explodes. Help An isolated star like our Sun explodes as a white dwarf supernova. A young (5 million years) star explodes as a white dwarf supernova. Correct Note that either of the two "Surprising" observations would force us to reconsider our ideas about supernovae if we actually witnessed them (we haven't). Visual Skills Check 14.1 shows how the luminosities of supernovae change with time. Answer the following questions, using the information provided in the figure. Part A At peak brightness, the white dwarf supernova is approximately __________ times as luminous as the massive star supernova at its peak brightness. ANSWER: 6/31 6/31 11/10/2019 Ch 14 HW .5 0 00 Correct Part B For the white dwarf supernova, the luminosity 175 days after it reaches peak brightness is about __________ of the luminosity at peak brightness. ANSWER: 0 0 Correct Part C Approximately how many days does it take for a white dwarf supernova to decline to 10 of its peak brightness? ANSWER: days 0 days 70 days 00 days Correct Part D Approximately how many days does it take for a massive star supernova to decline to 10 of its peak brightness? ANSWER: 0 days 0 days 00 days 00 days Correct Part E Approximately how many days does it take for a massive star supernova to decline to 1 of its peak brightness? ANSWER: 7/31 7/31 11/10/2019 Ch 14 HW days 0 days 70 days 00 days Correct Black Holes Tutorial NOTE: These activities use Flash, and are therefore not screen-reader accessible and may not work on a mobile device. If the browser you’re using no longer supports Flash, try a different browser and download the Flash plug-in for this content. This tutorial will help you understand what a black hole is and the evidence for their existence. Part A Your work within the launched tutorial will automatically save, but your score will not be recorded until you click the Submit button below. Clicking within the tutorial will bring you back to this screen. You must click Submit (below) to record your score to the MasteringAstronomy gradebook. It is not possible to do any more work toward your score once you have clicked Submit.Your score is based 50% on working through the “Lessons” portion of the launched tutorial and 50% on your first answer to each question in the “Exercises” section of the launched tutorial. ANSWER: launchtutorial Your final score on this tutorial is 94% Score Submitted You have now submitted your score and completed this tutorial. A message from your instructor... 8/31 8/31 11/10/2019 Ch 14 HW Hints: Use the hints - they WILL help you. Random guessing will only frustrate you in questions where there are many more solutions than you can guess (multiple select). The hints provided in these assignment hints are pretty useful too, so review them in advance of starting the assignment. Sorting Task: The Bizarre Stellar Graveyard Part A Listed following are distinguishing characteristics of different end states of stars. Match these to the appropriate consequence of stellar death. Hint 1. Description of a white dwarf A white dwarf is the hot, compact corpse of a low-mass star, typically with a mass similar to the Sun compressed to a volume the size of the Earth. Hint 2. Description of a neutron star A neutron star is the compact corpse of a high-mass star left over after a supernova. It typically contains a mass comparable to the mass of the Sun in a volume just a few kilometers in radius. Hint 3. Description of a black hole A black hole is an object in which gravity has overcome all sources of pressure support, causing it to collapse without end. Its event horizon is the place from within which no information can leave the black hole. The Schwarzschild radius of the black hole essentially defines the “size” of the event horizon. ANSWER: Reset Help supported by electron degeneracy pressure typically about the size (diameter) of Earth has a mass no greater than 1.4 MSun sometimes appears as a pulsar usually has a very strong magnetic field viewed from afar, time stops at its event horizon size defined by its Schwarzschild radius in a binary system, it can explode as a supernova Correct A message from your instructor... The following tasks require you to reason carefully about the properties of white dwarfs, neutron stars, black holes. Guessing answers without knowing anything about these objects is unlikely to be very productive. Re-read Chapter 14.1-14.3. For the following Ranking Task, assume a "typical" white dwarf is 1.0 solar masses. Ranking Task: The Size of Planets, Stars, and Stellar Remnants Part A 9/31 9/31 11/10/2019 Ch 14 HW Listed following are several astronomical objects. Rank these objects based on their diameter, from largest to smallest. (Note that the neutron star and black hole in this example have the same mass to make your comparison easier, but we generally expect black holes to have greater masses than neutron stars.) Hint 1. How large is a white dwarf? A typical (one-solar-mass) white dwarf star is approximately the same size (diameter) as _____. ANSWER: he Sun aturn arth luto small asteroid Hint 2. How large is a neutron star? The diameter of a typical neutron star is __________. ANSWER: bout the same as the diameter of the Sun bout the same as the diameter of Earth bout the same as the diameter of Pluto bout 20 kilometers Hint 3. How large is the Moon? The Moon’s diameter is __________. ANSWER: arger than Earth’s diameter bout one-fourth the diameter of Earth bout 1 percent of the diameter of Earth ANSWER: 10/31 10/31 11/10/2019 Ch 14 HW Reset Help Correct The main-sequence star is obviously much larger than a planet such as Jupiter. A one-solar-mass white dwarf is about the size of Earth, which makes it larger than the Moon. A neutron star will be larger than a black hole of the same mass, because while light can escape from a neutron star, the same mass in a black hole must be more concentrated so that its gravity is strong enough to prevent light from escaping. Part B Listed following are several astronomical objects. Rank these objects based on their mass, from largest to smallest. (Be sure to notice that the main-sequence star here has a different spectral type from the one in Part A.) Hint 1. How massive is a neutron star? True or False? A typical neutron star is less massive than the Sun. ANSWER: rue alse Hint 2. How massive is a typical black hole? A black hole that forms when a star dies in a supernova must have a mass __________. ANSWER: much less than that of the Sun bout the same as that of the Sun reater than the neutron star limit of about 2 to 3 solar masses ANSWER: 11/31 11/31 11/10/2019 Ch 14 HW Reset Help Correct Note that while the rankings shown are correct for “typical” white dwarfs, neutron stars, and black holes, each of these objects comes in a range of masses and so there may be some exceptions. Part C Listed following are several astronomical objects. Rank these objects based on their density, from highest to lowest. ANSWER: Reset Help Correct The singularity of a black hole is a place where density approaches infinity, so it is clearly the most dense of the objects shown. Neutron stars are much more dense than white dwarfs, which in turn are much more dense than main-sequence stars. 12/31 12/31 11/10/2019 Ch 14 HW A message from your instructor... In the following Extra Credit process of science task, it may be useful to know that neutron stars do not have to accrete material in order to emit radiation. The crust of neutron stars emits thermal radiation, like anything else that is opaque and has a temperature greater than absolute zero. Like the task before this, this task will be impossible if you have not read chapter 14. Process of Science: Identifying Stellar Corpses Learning Goal: To understand how observations allow scientists to determine whether a compact object is a white dwarf, neutron star, or black hole. Part A The following items describe observational characteristics that could indicate that an object is either a white dwarf or a neutron star. Match each characteristic to the correct object. Hint 1. What can cause an object to dim and brighten rapidly? You observe an object that periodically dims and brightens at a rapid rate, such as once per second. A reasonable explanation for this dimming and brightening is that the object is __________. ANSWER: enerating energy in its core by nuclear fusion, and rapid changes in the core temperature cause rapid changes in the fusion rate apidly rotating so that we see a bright spot with each rotation eriodically passing in front of and behind an ordinary star, so that we see changes in brightness with these transits and eclipses Hint 2. What is the difference between a nova and an X-ray burst? According to current theory, both nova explosions and X-ray bursts occur in binary systems in which an ordinary star orbits either a white dwarf or a neutron star. However, novae involve hydrogen fusion on the surface of a stellar corpse, while X-ray bursts involve helium fusion. What can you conclude from this fact? ANSWER: -ray bursts must occur on objects with much stronger surface gravity than those that produce novae. Novae must occur much more frequently than X-ray bursts. Novae must involve much higher temperatures than X-ray bursts. Hint 3. The white dwarf mass limit (Chandrasekhar limit) Theoretical calculations show that the maximum possible mass for a white dwarf is 1.4 times the mass of the Sun (1.4 solar masses). ANSWER: 13/31 13/31 11/10/2019 Ch 14 HW Reset may be surrounded by a planetary nebula emits most strongly in visible and ultraviolet may be in a binary system that undergoes nova explosions Help may repeatedly dim and brighten more than once per second may be surrounded by a supernova remnant may be in a binary system that undergoes X-ray bursts can have a mass of 1.5 solar masses Correct Be sure you understand why each of these observations goes with the indicated object. For example, white dwarfs may be surrounded by planetary nebulae because they are the remains of low-mass stars, while neutron stars form only in supernovae. Part B The following items describe observational characteristics that may indicate that an object is either a neutron star or a black hole. Match each characteristic to the correct object; if the characteristic could apply to both types of object, choose the bin labeled "Both neutron stars and black holes." Hint 1. What is an X-ray binary? An X-ray binary is a binary star system in which gas from an ordinary star is accreting onto a compact object. The accreting gas emits X rays because it _________. ANSWER: contains a great deal of mass s very hot onsists mostly of hydrogen from the outer layers of the companion star Hint 2. What are X-ray bursts? An X-ray burst is thought to occur when __________. ANSWER: wo stars collide and merge in a binary system n accretion disk is hot enough to emit X rays as accreting onto the surface of a neutron star undergoes a sudden burst of fusion Hint 3. What is a pulsar? Pulsars were originally discovered when astronomers observed sources that emitted rapid pulses of radio waves. It was soon realized that all pulsars are actually __________. ANSWER: 14/31 14/31 11/10/2019 Ch 14 HW apidly rotating neutron stars ighly magnetized black holes eutron stars in binary systems Hint 4. If black holes emit no light, how can we detect them? No light can escape from a black hole. Therefore, to detect a black hole, we must observe __________. ANSWER: round, black disk in space hermal radiation that peaks in the black part of the spectrum adiation coming from hot gas that is falling toward a black hole Hint 5. Is there a maximum mass for a black hole? In principle, a black hole can have a mass __________. ANSWER: nly up to 1.4 solar masses f any amount nly up to about 3 solar masses ANSWER: Reset may emit rapid pulses of radio waves may be in a binary system that undergoes X-ray bursts is detectable only if it is accreting gas from other objects can have a mass of 10 solar masses Help may be surrounded by a supernova remnant may be located in an X-ray binary Correct Be sure you understand why each of these observations goes with the indicated object(s). For example, radio pulses and X-ray bursts cannot come from black holes, because both are caused by events that happen on the surface of a compact object. Note also that the fact that two important items go in the "Both" bin indicates that it can be more difficult to distinguish between neutron stars and black holes than between white dwarfs and neutron stars. 15/31 15/31 11/10/2019 Ch 14 HW You should now be ready to consider a "mystery object" to see how astronomers would determine its nature. Part C The Chandra X-Ray Observatory has detected X rays from a star system that contains a main-sequence star of spectral type B6. The X-ray emission is strong and fairly steady, and no sudden bursts have been observed. Which of the following statements are reasonable conclusions about this system? Check all that apply. Hint 1. What is an X-ray binary? An X-ray binary is a binary star system in which gas from an ordinary star is accreting onto a compact object. The accreting gas emits X rays because it __________. ANSWER: onsists mostly of hydrogen from the outer layers of the companion star s very hot ontains a great deal of mass ANSWER: he main-sequence star must orbit a white dwarf. as from the main-sequence star makes an accretion disk around another object. he main-sequence star orbits either a neutron star or a black hole. ome time in the next few decades, this system will undergo a nova explosion. he main-sequence star orbits either a white dwarf or a neutron star. he main-sequence star must orbit a black hole. he main-sequence star must orbit a neutron star. he main-sequence star is emitting X rays. Correct The system is an X-ray binary, which means the companion to the main-sequence star can be either a neutron star or a black hole. The X rays come from the hot accretion disk consisting of gas that the compact object’s gravity is pulling away from the main-sequence star. Part D What is the key observation needed to determine whether the compact object in Part C is a neutron star or a black hole? ANSWER: Obtain high-resolution images of the compact object, so that you can determine whether it emits any light. Measure Doppler shifts in the spectrum of the main-sequence star so that you can determine the mass of the compact object. tudy the X-ray emission to determine the temperature of the gas in the accretion disk. Correct The Doppler shifts will allow you to determine the speed (or at least the component of the speed that is in your line of sight) of the main-sequence star as it orbits the compact object. You can then use this speed along with the known mass of the main-sequence star to determine the compact object’s mass (or a lower limit on its mass). If this mass is greater than the neutron star limit of about 3 solar masses, then the object must be a black hole. Process of Science: Constancy of the Speed of Light 16/31 16/31 11/10/2019 Ch 14 HW Learning Goal: To understand why the constancy of the speed of light implies that faster-than-light travel is not possible. Introduction. A fundamental premise of Einstein's theories of relativity is that the speed of light through empty space is a constant, . This tutorial will help you to understand the consequences of this premise. You'll need to refer to the four figures to the left as you answer the questions; each figure shows you on Earth, observing Jackie as she goes by in her spaceship. Part A Examine the first figure, in which you see Jackie's spaceship traveling at 1000 as she throws the baseball at a speed of 100 . How fast would you say the baseball is going? Hint 1. Computing the speed of the baseball Because the speeds in this case are much slower than the speed of light, you can add the speeds as you would without relativity. For example, to find a ball's speed when someone throws it from a moving train, you add the speeds of the ball and the train if they are both going in the same direction, or subtract the ball's speed from the train's speed if they are going in opposite directions. ANSWER: 00,000 100 00 00 Correct Before Jackie throws the ball, you will see it moving with her at a speed of 1000 you see her moving, you will see the ball moving at . Therefore, because she throws it in the same direction that . Part B Examine the second figure, in which you see Jackie's spaceship traveling at 1000 , with the ship's headlight on. According to special relativity, Jackie would say that a beam of light from the headlight is traveling at __________, and you would say that the beam of light is traveling at __________. Check two responses below, one for each of the two blanks in the question. 17/31 17/31 11/10/2019 Ch 14 HW Hint 1. What does it mean to say that the speed of light is constant? When we say that the speed of light is a constant, what do we mean? ANSWER: he speed of light is constant from stationary light sources, but it must be added to the speed of a moving light source. ifferent wavelengths of light move at different speeds but keep this same speed for as long as they travel. ou will always measure the same speed for light through space—about 300,000 —no matter how you or the light source are moving. ANSWER: Blank 1) Blank 1) Blank 1) Blank 2) r Blank 2) Blank 2) Correct A fundamental premise of relativity is that everyone always measures the same speed of light, c, no matter how the observer or the light source may be moving. Note that this makes light different from material objects such as baseballs (see Part A). Part C Examine the third figure, in which you see Jackie's spaceship traveling at . This time, Jackie would say that a beam of light from the headlight is traveling at __________ and you would say that the beam of light is traveling at __________. Check two responses below, one for each of the two blanks in the question. 18/31 18/31 11/10/2019 Ch 14 HW Hint 1. What does it mean to say that the speed of light is constant? When we say that the speed of light is a constant, what do we mean? ANSWER: ou will always measure the same speed for light through space—about 300,000 —no matter how you or the light source are moving. Different wavelengths of light move at different speeds but keep this same speed for as long as they travel. he speed of light is constant from stationary light sources, but it must be added to the speed of a moving light source. ANSWER: Blank 1) Blank 1) Blank 1) Blank 2) Blank 2) Blank 2) Correct Even though Jackie is now traveling by you at 99% of the speed of light, both of you will still find that the light beam is traveling at the speed of light, c. This is a consequence of the fact that everyone always measures the same speed of light through space. Part D Examine the fourth figure, which shows Jackie with her spaceship engines on, so that she accelerates continuously. As she accelerates, Jackie would say that __________ and you would say that __________. Check two responses below, one for each of the two blanks in the question. 19/31 19/31 11/10/2019 Ch 14 HW Hint 1. What happens to the speed of a spaceship that accelerates continuously? Suppose you are watching a spaceship that is accelerating because its engines are constantly firing. According to relativity, the spaceship's speed will __________. ANSWER: tay constant lways increase at the same rate lways increase, but the rate of increase will get smaller as it approaches the speed of light ANSWER: Blank 1) she is going so fast that she can't see the headlight beam Blank 1) the headlight beam is always racing away from her at Blank 1) her speed gradually catches up to the speed of the headlight beam Blank 2) the headlight beam is always traveling 300,000 faster than Jackie is traveling Blank 2) her speed gets faster and faster until she exceeds the speed of light, at which point she disappears from view Blank 2) her speed gets faster and faster but never quite as fast as the speed of the headlight beam Correct Jackie always says the beam is racing away from her at , because everyone always measures the same speed of light. You see Jackie going faster and faster as she accelerates, but because you must also agree that she is going slower than her headlight beam—and that the headlight beam is traveling at c—you can never see her reach the speed of light. Part E Based on these thought experiments, what can you conclude? ANSWER: 20/31 20/31 11/10/2019 Ch 14 HW ackie will say that she is going faster than light, but you'll always say she's going slower than the speed of light. ou can see Jackie going faster than light, but she'll never say she's going that fast. ackie would have to accelerate for a very long time before she finally reaches the speed of light. ackie can never reach or exceed the speed of light. Correct The key point is this: Because everyone measures the same speed of light, no one can ever catch up with one's own light. Therefore, anyone else observing the traveler will see that traveler going slower than the traveler's light, which means slower than . Part F In science, it is now well accepted that the speed of light is always the same and therefore nothing can travel faster than light. These ideas gained acceptance primarily because __________. ANSWER: he logic in the thought experiments is so strong hey have been verified through actual observations and experiments o one has yet built a spaceship that can reach the speed of light instein was such an important figure in the scientific community Correct In science, an idea is accepted only if it has been verified by observations or experiments. Observations and experiments have confirmed that the speed of light through space is always the same, and experiments in particle accelerators have shown that no matter how much subatomic particles are accelerated, they never quite reach the speed of light. Visual Activity: Exploring Radial Free-Fall Toward a Black Hole Click on the image below to launch the video: Exploring Radial Free-Fall Toward a Black Hole. Once you have watched the entire video, answer the graded followup questions on the right. You can watch the video again at any point. Part A From the viewpoint of an observer in the orbiting rocket, what happens to time on the other rocket as it falls toward the event horizon of the black hole? Hint 1. Is the orbiting rocket view similar to the view of a distant, stationary observer? True or False? The view from the orbiting rocket will be similar to the view seen by a distant, stationary observer. ANSWER: 21/31 21/31 11/10/2019 Ch 14 HW rue alse ANSWER: ime runs increasingly faster as the rocket approaches the black hole. ime runs increasingly slower as the rocket approaches the black hole. ime is always the same on both rockets. Correct In this video, your view is similar to the view from the orbiting rocket. Notice that the clock on the falling rocket ticks more slowly as it approaches the black hole, indicating that time is slowing down. Part B As the falling rocket plunges toward the event horizon, an observer in the orbiting rocket would see that the falling rocket __________. Hint 1. As seen by a very distant observer, how does the falling rocket appear to move? True or False? A very distant observer would see the falling rocket speeding up as it falls toward the event horizon. ANSWER: rue alse ANSWER: lows down as it approaches the event horizon and never actually crosses the event horizon lows down near the event horizon so that it crosses the event horizon at a low speed moves at constant speed as it approaches and crosses the event horizon ccelerates as it falls and crosses the event horizon at high speed Correct Viewed from afar, time comes to a stop at the event horizon of a black hole, so falling objects never appear to cross the event horizon. Part C From Part B, you know that from afar you’ll never see the in-falling rocket cross the event horizon, yet it will still eventually disappear from view. Why? Hint 1. Why do the colors on the clock change as the rocket approaches the event horizon? In the video, notice that the clock changes color on the rocket falling toward the event horizon. This represents the fact that __________. ANSWER: 22/31 22/31 11/10/2019 Ch 14 HW ght from an object becomes redshifted as the object approaches the event horizon he blackness of the black hole gradually consumes the different colors of the rainbow me stops at the event horizon ANSWER: ven though you won’t see it cross the event horizon, it does cross it, and that means you can no longer see it. s light will become so redshifted that it will be undetectable. he black hole’s blackness will drown out the light of the rocket. idal forces will squeeze the in-falling rocket to an undetectably thin line. Correct As the video shows, viewed from afar the light of the in-falling rocket becomes increasingly redshifted. As it approaches the event horizon, the redshift approaches infinity, meaning all its light is stretched to such enormous wavelengths that no detector could see it, even in principle. Part D If you were inside the rocket that falls toward the event horizon, you would notice your own clock to be running __________. ANSWER: ncreasingly faster as you approach the event horizon t a constant, normal rate as you approach the event horizon ncreasingly slower as you approach the event horizon Correct All motion is relative, and you will always consider your own clock to be running at a normal rate. Part E If you were inside the rocket that falls toward the event horizon, from your own viewpoint you would __________. ANSWER: low down and come to a stop at the event horizon low down and cross the event horizon at low speed ccelerate as you fall and cross the event horizon completely unhindered Correct From your point of view, time runs normally in your spaceship and gravity must accelerate you as you fall toward the black hole. There is no physical barrier at the event horizon, so you cross it unhindered. Problem 14.26 Choose the best answer. Part A Which of these objects has the smallest radius? 23/31 23/31 11/10/2019 Ch 14 HW ANSWER: 1.2 white dwarf 0.6 white dwarf upiter Correct Problem 14.28 Choose the best answer. Part A If we see a nova, we know that we are observing ANSWER: rapidly rotating neutron star. gamma ray-emitting supernova. white dwarf in a binary system. Correct Problem 14.30 Choose the best answer. Part A What would happen to a neutron star with an accretion disk orbiting in a direction opposite to the neutron star's spin? ANSWER: s spin would speed up. s spin would slow down. s spin would stay the same. Correct Problem 14.50 In a massive star supernova explosion, a stellar core collapses down to form a neutron star roughly 10 kilometers in radius. The gravitational potential energy released in such a collapse is approximately equal to gravitational constant. where is the mass of the neutron star, is its radius, and is the Part A Using this formula, estimate the amount of gravitational potential energy released in a massive star supernova explosion. ANSWER: 24/31 24/31 11/10/2019 Ch 14 HW Correct Part B How does it compare with the amount of energy released by the Sun during its entire main-sequence lifetime? ANSWER: ~ ~ ~ ~ Correct Problem 14.27 Choose the best answer. Part A Which of these objects has the largest radius? ANSWER: 1.2 white dwarf 1.5 neutron star 3.0 black hole Correct Problem 14.33 Choose the best answer. Part A Viewed from a distance, how would a flashing red light appear as it fell into a black hole? ANSWER: 25/31 25/31 11/10/2019 Ch 14 HW would appear to flash more quickly. s flashes would appear bluer. s flashes would shift to the infrared part of the spectrum. Correct Problem 14.34 Choose the best answer. Part A Which of these black holes exerts the weakest tidal forces on an object near its event horizon? ANSWER: 10 black hole 100 black hole 10 black hole Correct Problem 14.29 Choose the best answer. Part A What would happen if the Sun suddenly became a black hole without changing its mass? ANSWER: he black hole would quickly suck in the Earth. arth would gradually spiral into the black hole. arth's orbit would not change. Correct Problem 14.32 Choose the best answer. Part A Which of these binary systems is most likely to contain a black hole? ANSWER: n X-ray binary containing an star and another object of equal mass binary with an X-ray burster n X-ray binary containing a star and another object of equal mass 26/31 26/31 11/10/2019 Ch 14 HW Correct Problem 14.47 Calculate the Schwarzschild radius (in kilometers) for each of the following. Part A A black hole in the center of a quasar. Express your answer using two significant figures. ANSWER: 3.00×108 Correct Part B A black hole that formed in the supernova of a massive star. Express your answer using two significant figures. ANSWER: 15 Correct Part C A mini-black hole with the mass of the Moon. Express your answer using two significant figures. ANSWER: 1.10×10−7 Correct Part D A miniblack hole formed when a superadvanced civilization decides to punish you (unfairly) by squeezing you until you become so small that you disappear inside your own event horizon. (Assume that your mass is 50 .) Express your answer using two significant figures. ANSWER: 7.40×10−29 Answer Requested Problem 14.35 Choose the best answer. Part A 27/31 27/31 11/10/2019 Ch 14 HW Where do gamma-ray bursts tend to come from? ANSWER: eutron stars in our galaxy lack holes in our galaxy xtremely distant galaxies Correct NY Times Reading Quiz 2016/02/12: Gravitational Waves Detected, Confirming Einstein's Theory Learning Goal: To read a science news article, understand it, and see how it relates to key concepts in astronomy. Read the article, "Gravitational Waves Detected, Confirming Einstein's Theory," and answer the following questions based on information in the article and what you have learned in class. [Most providers allow either free access or a limited number of free accesses per month or other time period. If you have exceeded your access limit for any provider, it is likely you are eligible for a free or discounted student educational account.] Part A What is the big announcement made in the article? ANSWER: he first confirmation of Einstein’s theory of relativity. he first detection of waves in spacetime. he detection of light waves emitted by gravity, confirming Einstein’s theory. Correct The detection of waves in spacetime, or gravitational waves, were reported for the very first time in February, 2016. Part B According to the article, how were the gravitational waves generated? ANSWER: y the merger of two neutron stars. y the merger of two massive black holes. y the merger of two galaxies. Correct The merger of two neutron stars also would generate gravitational waves but the first detection was of a more powerful event: the merger of two black holes. Part C Which technology listed below enabled this discovery? ANSWER: 28/31 28/31 11/10/2019 Ch 14 HW xtremely sensitive light measurements. xtremely sensitive sound measurements. xtremely precise length measurements. Correct The crucial measurement was to discern the change in length of the two arms of the gravitational wave detector. Part D How precise did the length measurement have to be in order to make a successful detection? ANSWER: bout 0.0004 microns. bout 4/100 the size of a hydrogen atom. bout the size of a proton. bout 4/1000 the size of a proton. bout the size of a grain of sand. Correct Part E Why are the scientists so confident that they have succeeded in making a detection? ANSWER: he signal was so strong that it could not possibly be anything else. he scientists are really smart and careful, so it’s unlikely they have made a mistake. wo independent sites detected the same event at nearly the same time. Correct Part F There are many scientists mentioned in the article. Choose the one person you think would most merit the receipt of a Nobel Prize in Physics for their role in the discovery. Justify your choice in a short essay, utilizing information from the article to make your case. ANSWER: 3799 Character(s) remaining . Submitted, grade pending Learning Goal: 29/31 29/31 11/10/2019 Ch 14 HW Read the article, "Scientists Trace Gamma Rays to Collision of Dead Stars," and answer the following questions based on information in the article and what you have learned in class. The link may require you to sign up for a free NY Times account. Part A The scientists concluded that the short gamma ray bursts were caused by ANSWER: upernova explosions. main-sequence or red giant star being eaten by a black hole. ollisions of two neutron stars or of a black hole and a neutron star. ollisions of two stars,. Correct There were several scientific papers described in this article. The following questions ask about these papers in order of appearance. To avoid confusion, the papers will be associated with the lead author mentioned by name in the article. Part B Dr. Lamb and Dr. Whitcomb discuss their paper on collisions and gravity waves and the LIGO project, which is a ground-based experiment to detect gravity waves from space. What is their main contribution to the news discussed in this article? ANSWER: single titanic collision was detected in gravitational radiation by LIGO. Many titanic collisions have been detected in gravitational radiation by LIGO. uch collisions are predicted to create gravitational waves, which could be detected by gravity wave detectors like LIGO. Correct Showing that such titanic collisions happen is a strong incentive to look for such collisions with gravity wave detectors. However, gravity wave detectors like LIGO have yet to detect anything from the cosmos except for noise. Part C Neil Gehrels is the head of the Swift satellite team. Why is he certain the burst he discovered is not from the explosion of a massive star? ANSWER: ecause the galaxy where the burst was detected only has old stars; all the massive ones already exploded. ecause he detected the burst in a galaxy, and a galaxy is not the same as a star or an exploding star. ecause the galaxy is 2.9 billlion light years away, the explosion happened 2.9 billion years ago, and no stars exploded as a supernova that long go. Correct Elliptical galaxies are full of old stars, and do not experience many if any massive-star supernova explosions. Part D The team led by Derek Fox used many telescopes to do their analysis. They argue that their detection of the afterglow of the explosion is exactly what you'd expect from the collision of two neutron stars. Which of the following telescopes were used to detect X-rays from the afterglow? ANSWER: 30/31 30/31 11/10/2019 Ch 14 HW he Hubble Space Telescope Danish telescope at the European Southern Observatory in Chile he Chandra X-ray Telescope and the High Energy Transient Explorer Correct Part E What was so strange about the July 24 burst, the one that the scientists think might be caused by a black hole swallowing a neutron star, compared to the July 9 burst? ANSWER: oth had flares 100 seconds after the initial blast, but the July 24 burst was 5 times more powerful, and flared yet again half a day later. he July 24 burst flared 100 seconds later, and again half day later. The other burst had no flares after the initial burst. he July 24 burst was five times as powerful as the July 9 burst. Correct Scientists hypothesize that the burst one-half day later was caused by material that was expelled during the collision, but eventually fell back into the black hole. That material experienced tidal stretching and compression, heating up for one last flash of light before it disappeared beyond the event horizon. Score Summary: Your score on this assignment is 103%. You received 23.84 out of a possible total of 26 points, plus 3.05 points of extra credit. 31/31 31/31