Exam Questions Evolution of High-Mass Stars Palen Chapter 13 - Understanding Our Universe 3e Complete Test Bank by Stacy Palen. DOCX document preview.
Chapter 13: Evolution of High-Mass Stars
LEARNING OBJECTIVES
13.1 High-Mass Stars Follow Their Own Path
13.1a Explain the CNO cycle.
13.1b Compare and contrast the evolutionary paths of low-mass and high-mass stars once the core burns carbon.
13.1c Explain how standard candles are used to determine astronomical distances.
13.2 High-Mass Stars Go Out with a Bang
13.2a Explain why iron cannot undergo nuclear fusion.
13.2b Differentiate Type Ia and Type II supernovae.
13.2c Explain how core collapse of a massive star leads to a Type II supernova.
13.3 Supernovae Change the Galaxy
13.3a Explain how supernovae produce heavy elements.
13.3b Describe the components of a Type II supernova remnant.
13.3c Explain the behavior of and observable signals from a pulsar.
13.4 Einstein Moved Beyond Newtonian Physics
13.4a Explain the four implications of special relativity.
13.4b Describe observational tests of special relativity.
13.5 Gravity Is a Distortion of Spacetime
13.5a Explain why “free fall is the same as free float.”
13.5b Explain how motion along a curved surface mimics motion in a gravitational field.
13.5c Describe the four observable consequences of general relativity.
13.6 Black Holes Are a Natural Limit
13.6a Explain the significance of the Schwarzschild radius (or event horizon) of a black hole.
13.6b Describe why a black hole cannot be observed directly, but how it can be indirectly detected.
Working It Out 13.1
Working It Out 13.1a Explain why moving clocks run slow.
Working It Out 13.2
Working It Out 13.2a Calculate the Schwarzschild radius of a black hole.
Chapter 13: Evolution of High-Mass Stars
MULTIPLE CHOICE
1. If you measure the average brightness and pulsation period of a Cepheid variable star, you can also determine its
a. age. c. distance.
b. rotation period. d. mass.
2. Measuring the pulsation period of an RR Lyrae variable star will reveal its
a. luminosity. c. size.
b. mass. d. rotation period.
3. A standard candle means that the object has a known
a. brightness. c. size.
b. luminosity. d. distance.
4. What is the driving mechanism in pulsating stars?
a. variations in nuclear reactions in the core
b. ionization of atoms trapping and releasing thermal energy
c. mass variations changing gravity
d. large variations in the stellar wind
5. Which of the following is true about the instability strip on the H-R diagram?
a. Evolved stars pulsate.
b. The location of RR Lyrae and Cepheids is correct.
c. Stars show variability in their brightness.
d. All choices are valid.
6. The instability strip on the H-R diagram includes which main-sequence stars?
a. O c. B
b. G d. A
7. The carbon-nitrogen-oxygen (CNO) cycle in high-mass main-sequence stars burns __________ to __________ in their cores.
a. hydrogen; helium
b. carbon; oxygen
c. carbon; nitrogen
d. This is a trick question because the CNO cycle does not operate in high-mass main-sequence stars.
8. Which element acts as a catalyst during the CNO cycle in high-mass main-sequence stars?
a. hydrogen d. nitrogen
b. helium e. oxygen
c. carbon
9. The following graphic depicts the net reactions in the CNO cycle. What are the input components a, b, and c?
a. a: nitrogen, b: hydrogen, c: neutrinos c. a: carbon, b: hydrogen, c: neutrinos
b. a: nitrogen, b: hydrogen, c: electrons d. a: carbon, b: hydrogen, c: electrons
10. The following graphic depicts the net reactions in the CNO cycle. What are the output components d, e, and f?
a. d: oxygen, e: electrons, f: gamma rays c. d: helium, e: neutrinos, f: gamma rays
b. d: oxygen, e: neutrinos, f: electrons d. d: helium, e: electrons, f: neutrinos
11. The following graphic depicts the net reactions in the CNO cycle. What is component a that goes into the reaction and comes out the same?
a. carbon c. nitrogen
b. oxygen d. helium
12. As a high-mass main-sequence star evolves off the main sequence, it follows a __________ on the Hertzsprung-Russell (H-R) diagram.
a. nearly vertical path c. roughly horizontal path
b. path of constant radius d. None of the choices are correct.
13. The main difference between Cepheid variable stars and RR Lyrae stars is
a. their pulsation mechanisms.
b. their masses.
c. that Cepheids form at much greater distances from Earth.
d. that RR Lyrae were discovered much earlier than Cepheids.
14. If a 60-solar mass (M) main-sequence star loses mass at a rate of 
M/year, then how much mass will it lose in its 30,000-year lifetime?
a. 3 M c. 10 M
b. 8 M d. 30 M
15. A Cepheid star varies in luminosity because the
a. entire star pulsates from its core to its surface.
b. outer envelope of the star pulsates.
c. star rotates too quickly.
d. star is too massive to be stable.
16. An iron core cannot support a massive main-sequence star because iron
a. has poor nuclear binding energy.
b. cannot fuse with other nuclei to produce energy.
c. supplies too much pressure.
d. fusion only occurs in a degenerate core.
17. What is true about SN1987A (see the following image)?
a. It was a Type Ia supernova that exploded in 1987.
b. It was a Type II supernova that exploded in 1987.
c. It was a Type Ia supernova that was initially observed in 1987.
d. It was a Type II supernova that was initially observed in 1987.
18. What is true about SN1987A (see the following image)?
a. It was a supernova seen in the Large Magellanic Cloud.
b. It was visible to the naked eye for observers in the Southern Hemisphere.
c. Neutrinos were detected before the visible blast.
d. All choices are true.
19. Once carbon begins burning in the core of a high-mass star, the outer layers begin to fall inward, driving up the fusion rates and speeding up the star’s evolution primarily because
a. the number of particles in the core is decreasing, which now take up less space.
b. most of the energy is now carried away from the core by escaping neutrinos, which have few if any obstacles to leaving the star.
c. carbon is a more stable element that appears to settle the star.
d. the light given off by the fusion of carbon is a different wavelength than that given off by previous reactions, so the radiation pressure is much smaller.
20. The collapse of the core of a high-mass star at the end of its life lasts approximately
a. 1 second. c. 1 week.
b. 1 hour. d. 1 year.
21. When the core of a massive star collapses, a neutron star forms because
a. all the charged particles are ejected in the resulting explosion.
b. protons and electrons combine to form neutrons.
c. iron nuclei disintegrate into neutrons.
d. neutrinos escaping from the core carry away most of the electromagnetic charge.
22. During the post main-sequence evolution of a massive star, increasingly heavier elements are fused in the core, giving the core support for
a. decreasingly shorter times.
b. increasingly longer times.
c. an approximately equal amount of time.
d. approximately 10,000 years.
23. What remnant can be produced by the collapse and rebound of a massive star in a Type II supernova?
a. white dwarf c. neutron star
b. planetary nebula d. All of these choices are valid.
24. Why does the luminosity of a high-mass star remain nearly constant as the star burns heavy elements in its core, even though it is producing millions of times more energy per second than it did on the main sequence?
a. Most of the energy is trapped in the core, increasing the core’s temperature.
b. All of the extra energy goes into heating the shells of fusion surrounding the core.
c. Most of the energy is absorbed by the outer layers of the star, increasing the star’s radius but leaving its luminosity unchanged.
d. Most of the energy is carried out of the star by escaping neutrinos.
25. The core collapse of a high-mass main-sequence star can reach speeds of about
a. the speed of light. c. 50% the speed of light.
b. 75% the speed of light. d. 25% the speed of light.
26. What is the minimum-mass main-sequence star that becomes a Type II supernova?
a. 4 M c. 12 M
b. 8 M d. 25 M
27. Essentially all the elements heavier than iron in our galaxy were formed
a. by supernovae.
b. during the formation of black holes.
c. by fusion in the cores of the most massive main-sequence stars.
d. during the formation of planetary nebulae.
28. Neutron stars have masses that range from
a. 3.5 M to 25 M. c. 2.5 M to 10 M.
b. 1.2 M to 30 M. d. 1.4 M to 3 M.
29. Which of the following is a common characteristic of a neutron star?
a. extremely high density
b. enormous magnetic field
c. very short rotation period
d. All of these are common characteristics of a neutron star.
30. We can identify only a small fraction of all the pulsars that exist in our galaxy because
a. gas and dust efficiently block radio photons.
b. few swing their beam of synchrotron emission in our direction.
c. most have evolved to become black holes, which emit no light.
d. massive stars are very rare.
31. The Type II supernova that created the Crab Nebula (see the following image) was seen by Chinese and Arab astronomers in AD 1054. Because the star is 6,500 light-years away from us, we know the star exploded in
a. AD 7554. c. 5446 BC.
b. AD 1054. d. 7554 BC.
32. A neutron star contains a mass of up to 3 M in a sphere with a diameter approximately the size of
a. an atomic nucleus. c. a city.
b. a school bus. d. Earth.
33. What would happen if mass were continually added to a 3-M neutron star?
a. The star’s radius would increase.
b. The star would eventually become a black hole.
c. The star would erupt as a nova.
d. All of the above would occur.
34. Normally, muons created by cosmic rays at high altitudes decay in a very short time, a time so short that they should not reach the ground. From the following figure, which muon is most likely to be detected on the ground?
a. muon A c. muon C
b. muon B d. muon D
35. Assume that a group of explorers traveled to the Orion Nebula, a star-forming cloud at a distance of 1,300 light-years, using revolutionary technology that allowed them to travel at a speed very close to the speed of light. Observers back on Earth would say it took them __________ to get there, but the travelers would say it took them __________ to get there.
a. slightly more than 1,300 years; much less than 1,300 years
b. slightly more than 1,300 years; slightly less than 1,300 years
c. slightly less than 1,300 years; slightly more than 1,300 years
d. exactly 1,300 years; much less than 1,300 years
36. __________ is the result of mass distorting the fabric of spacetime.
a. Energy c. Fusion
b. Radiation d. Gravity
37. Gravitational lensing occurs when __________ distorts the fabric of spacetime.
a. a star c. a black hole
b. dark matter d. any massive object
38. Which of the following is a consequence of Einstein’s special theory of relativity?
a. Moving clocks run quicker.
b. The velocity of light depends on the speed of the observer.
c. Distances appear shorter when traveling near the speed of light.
d. Gravity arises because mass distorts spacetime.
39. The equivalence principle says that
a. being stationary in a gravitational field is the same as being in an accelerated reference frame.
b. the universe is homogeneous and isotropic.
c. at any radius inside a star, the outward gas pressure must balance the weight of the material on top.
d. mass and energy are interchangeable, and neither can be destroyed.
40. Photons have no mass, and Einstein’s theory of general relativity says
a. their paths through spacetime are curved in the presence of a massive body.
b. their apparent speeds depend on the observer’s frame of reference.
c. they should not be attracted to a massive object.
d. their wavelengths must remain the same as they travel through spacetime.
41. Light is increasingly redshifted near a black hole because
a. the photons are moving away from us very quickly as they are sucked into the black hole.
b. the photons are moving increasingly faster to escape the pull of the black hole.
c. time is moving increasingly slower in the observer’s frame of reference.
d. the curvature of spacetime is increasingly stretched near the black hole, which in turn stretches the wavelengths of the photons.
42. If Earth were to be condensed in size until it became a black hole, its Schwarzschild radius would be
a. 1 centimeter (cm). c. 1 kilometer (km).
b. 1 meter. d. 10 km.
43. Which of the following is true about Cygnus X-1?
a. It is a single star. c. It is visible.
b. It contains a black hole. d. It is a neutron star.
44. The event horizon of a black hole is defined as the
a. point of maximum gravity.
b. radius of the original neutron star before it became a black hole.
c. point at which shock waves emanate from the strong gravitational distortion the black hole creates in the fabric of spacetime.
d. radius at which the escape speed equals the speed of light.
45. If the Sun were to be instantly replaced by a 1-M black hole, the gravitational pull of the black hole on Earth would be
a. much greater than it is now.
b. the same as it is now.
c. much smaller than it is now.
d. irrelevant because Earth would be quickly obliterated by the strong tidal force of the black hole.
46. Hawking radiation is emitted by a black hole when
a. the black hole rotates quickly.
b. the black hole accretes material.
c. a virtual pair of particles is created from the vacuum of space.
d. synchrotron radiation is emitted by infalling charged particles.
47. Black holes that are stellar remnants can be found by searching for
a. dark regions at the centers of galaxies.
b. variable X-ray sources.
c. extremely luminous infrared objects.
d. objects that emit very faint radio emission.
48. While traveling the galaxy in a spacecraft, you and a colleague set out to investigate the 106 M black hole at the center of our galaxy. Your colleague hops aboard an escape pod and drops into a circular orbit around the black hole, maintaining a distance of 1 astronomical unit (AU), while you remain much farther away in the spacecraft but from which you can easily monitor your colleague. After doing some experiments to measure the strength of gravity, your colleague signals the results back to you using a green laser. What would you see?
a. the signals, because he or she is orbiting well outside the event horizon
b. the signals, but shifted to a much redder wavelength because he or she is very close to the event horizon
c. nothing, because your colleague has crossed the event horizon
d. nothing, because no light can escape the gravitational pull of a black hole no matter how close the signal is to it
49. An astronaut would feel __________ as he or she crossed the event horizon of a stellar black hole.
a. incredibly strong tidal forces c. lighter
b. intense heating d. nothing
50. What is the radius of the event horizon of a 5 solar mass black hole?
a. 3 km c. 10 km
b. 5 km d. 15 km
1. How do Cepheid variable stars differ from RR Lyrae variable stars in their masses, luminosities, and periods?
2. Why do main-sequence high-mass stars lose so much mass compared with low-mass stars?
3. Show where stars are variable in brightness in the following figure. What is this region called?
4. Why do large, high-mass main-sequence stars never go through the red giant branch or the asymptotic branch, but rather evolve horizontally along the H-R diagram?
5. Why are Cepheids important to study?
6. If an 6-M star loses mass at an average rate of 10−7 M/year in a stellar wind, how many years would it take for its mass to be reduced to 4 M? Would this amount of mass loss be possible in the star’s lifetime?
7. Name at least two processes that speed the collapse of the core of a dying high-mass star.
8. Although a Type II supernova shines with a luminosity of 100 billion L, most of the energy in the explosion is emitted in another way. What is it, and how much more energy does it carry compared with the light?
9. Why are Type II supernova not good distance indicators like those of Type Ia?
10. Examine the following figure of a pulsar. What are pulsars, and what circumstance must Earth be in for astronomers to observe one?
11. The following figure shows the relative abundances of different elements on Earth. Explain why elements less massive than iron are, in general, most common, why there is a small peak at iron, and why elements more massive than iron are less common.
12. What supports a neutron star from collapsing to form a black hole?
13. Explain how a pulsar comes to rotate more quickly than its original high-mass star that rotated much more slowly.
14. Normally, muons created by cosmic rays at high altitudes decay in a very short time, a time so short that they should not reach the ground. From the following figure, why does increasing speed of muons created by cosmic rays at high altitudes mean that additional muons will reach the ground before decaying?
15. Consider the box car experiment for special relativity as depicted here. Observer 1 is in the moving box car that sends light up to a mirror that bounces back to the floor traveling a distance of 2l in the car’s reference frame. Observer 2 is stationary and sees a longer path for the light. What fundamental precept leads to the conclusion that clocks between the two observers run differently (slower for the moving observer relative to the stationary one)?
16. Examine the following figure. Explain what the equivalence principle is in general relativity.
17. Explain why Einstein’s theory of general relativity predicts the existence of gravitational lensing.
18. Galileo supposedly experimented with gravity by dropping two objects of different masses from the Leaning Tower of Pisa at the same instant and observing that they hit the ground at the same time. If Albert Einstein had done the experiment, how would his conclusion have differed from Galileo’s?
19. What is the difference between the singularity and the event horizon of a black hole?
20. While traveling the galaxy in a spacecraft, you and a colleague set out to investigate a 2-M black hole. Your colleague hops aboard an escape pod and drops into a circular orbit around the black hole maintaining a distance of 10 km from it, while you remain much farther away inside the spacecraft. After doing some experiments to measure the strength of gravity, your colleague signals the results back to you using a green laser. What would you see, and why?
21. Where would be the best place to search for stellar black holes?