Question 1

Why is Supernova 1987A particularly important to astronomers?

Accepted Answer

A)  It was the first supernova detected in nearly 400 years.
B)  It occurred only a few light- years from Earth.
C)  It provided the first evidence that supernovae really occur.
D)  It is the nearest supernova to have occurred at a time when we were capable of studying it carefully with telescopes.E) A) and C)
F) A) and D)

Question 2

Which of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, and so on) in a high- mass star is not true?

Accepted Answer

A)  Each successive stage lasts for approximately the same amount of time.
B)  As each stage ends, the core shrinks and heats further.
C)  As each stage ends, the reactions that occurred in previous stages continue in shells around the core.
D)  Each successive stage creates an element with a higher atomic number and atomic mass number.E) All of the above
F) C) and D)

Question 3

Based on its main- sequence turnoff point, the age of this cluster is

Accepted Answer

A)  about 1 billion years.
B)  less than 1 billion years.
C)  about 4.5 billion years.
D)  about 10 billion years.
E)  more than 15 billion years.F) D) and E)
G) A) and D)

Question 4

During which of the following phases of life is a star's pressure and gravity out of equilibrium?

Accepted Answer

A)  white dwarf
B)  helium core fusion
C)  main sequence
D)  red giant
E)  A star is never out of equilibrium.F) A) and B)
G) B) and E)

Question 5

What happens to the core of a star after it ejects a planetary nebula?

Accepted Answer

A)  It becomes a neutron star.
B)  It contracts from a protostar to a main- sequence star.
C)  It becomes a white dwarf.
D)  It breaks apart in a violent explosion.
E)  None of the aboveF) C) and D)
G) A) and B)

Question 6

Briefly describe how a star forms.

Accepted Answer

In cold, dense molecular clouds, gravity...

Question 7

Generally speaking, how does the surface temperature and luminosity of a protostar compare to the surface temperature and luminosity of the main- sequence star it becomes?

Accepted Answer

A)  A main- sequence star is hotter and brighter than it was as a protostar.
B)  A main- sequence star is cooler and brighter than it was as a protostar.
C)  A main- sequence star is hotter and dimmer than it was as a protostar.
D)  A main- sequence star is cooler and dimmer than it was as a protostar.E) All of the above
F) A) and B)

Question 8

Approximately what core temperature is required before hydrogen fusion can begin in a star?

Accepted Answer

A)  10 billion K
B)  10 trillion K
C)  1 billion K
D)  10 million K
E)  10,000 KF) A) and D)
G) B) and C)

Question 9

Why is Supernova 1987A particularly important to astronomers?

Accepted Answer

A)  It provided the first observational evidence that supernovae actually occur.
B)  It was the nearest supernova detected in nearly 400 years.
C)  It occurred only a few dozen light- years from Earth.
D)  It was the first supernova detected in nearly 400 years.
E)  It provided the first evidence that neutron stars exist.F) C) and D)
G) B) and D)

Question 10

What can we learn about a star from a life track on an H- R diagram?

Accepted Answer

A)  how the star's distance from Earth varies at different times in its life
B)  the star's age
C)  the star's current stage of life
D)  the surface temperature and luminosity the star will have at each stage of its lifeE) All of the above
F) B) and D)

Question 11

Most interstellar dust grains

Accepted Answer

A)  are produced in the cores of low- mass stars
B)  are produced in supernova explosions.
C)  are produced in the atmospheres of red giant stars.
D)  were produced in the Big Bang.
E)  are produced in the interstellar medium.F) A) and D)
G) A) and C)

Question 12

What happens after the helium flash?

Accepted Answer

A)  The star breaks apart in a violent explosion.
B)  The core suddenly contracts.
C)  The star starts to fuse helium in a shell outside the core.
D)  The core quickly heats up and expands.
E)  The core stops fusing helium.F) B) and D)
G) A) and B)

Question 13

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?

Accepted Answer

A)  Elements with atomic mass numbers divisible by 4 tend to be more stable than elements in between.
B)  The apparent pattern is thought to be a random coincidence.
C)  At the end of a high- mass star's life, it produces new elements through a series of helium capture reactions.
D)  This pattern in elemental abundances was apparently determined during the first few minutes after the Big Bang.E) B) and C)
F) A) and D)

Question 14

What change slowly occurs during the main- sequence lifetime of a star?

Accepted Answer

A)  Its core temperature slowly increases, increasing the fusion rate and hence the luminosity.
B)  As hydrogen is used up in the core, the fusion rate decreases and reduces the luminosity.
C)  It gathers more gas from interstellar space, increasing its mass and hence the luminosity.
D)  As the solar wind blows material into space, the decreasing mass reduces pressure in the core, which in turn reduces the fusion rate and the luminosity.E) None of the above
F) C) and D)

Question 15

What can trigger the gravitational collapse of an interstellar gas cloud?

Accepted Answer

A)  a decrease in temperature
B)  an increase in density
C)  a rise in temperature
D)  A and B
E)  A and CF) A) and B)
G) A) and E)

Question 16

Which event marks the beginning of a supernova?

Accepted Answer

A)  the sudden collapse of an iron core into a compact ball of neutrons
B)  the onset of helium burning after a helium flash in a star with mass comparable to that of the Sun
C)  the beginning of neon burning in an extremely massive star
D)  the sudden outpouring of X- rays from a newly formed accretion disk
E)  the expansion of a low- mass star into a red giantF) A) and B)
G) B) and D)

Question 17

When does a star become a main- sequence star?

Accepted Answer

A)  the instant when hydrogen fusion first begins in the star's core
B)  when the rate of hydrogen fusion in the star's core is high enough to sustain gravitational equilibrium
C)  when the protostar assembles from its parent molecular cloud
D)  when a star becomes luminous enough to emit thermal radiation
E)  when hydrogen fusion is occurring throughout the star's interiorF) B) and C)
G) A) and B)

Question 18

Suppose that the star Betelgeuse (the upper left shoulder of Orion) were to supernova tomorrow (as seen here on Earth) . What would it look like to the naked eye?

Accepted Answer

A)  Because the supernova destroys the star, Betelgeuse would suddenly disappear from view.
B)  We'd see a cloud of gas expanding away from the position where Betelgeuse used to be. Over a period of a few weeks, this cloud would fill our entire sky.
C)  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.
D)  Betelgeuse would suddenly appear to grow larger in size, soon reaching the size of the full Moon. It would also be about as bright as the full Moon.E) A) and C)
F) A) and B)

Question 19

Explain how some stars form in binary systems.

Accepted Answer

As a molecular cloud contracts, it break...

Question 20

This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. What will happen to the star after stage viii?

Accepted Answer

A)  It will continue to expand gradually until carbon fusion begins in its core.
B)  It will explode as a supernova and leave a neutron star or black hole behind.
C)  It will remain in stage viii for about 10 billion years, after which its outer layers will shrink back and cool.
D)  Its outer layers will be ejected as a planetary nebula and its core will become a white dwarf.E) None of the above
F) B) and C)

Exam 13: Star Stuff

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?

Correct AnswerverifiedShow Answer

This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. What will happen to the star after stage viii?

Correct AnswerverifiedShow Answer

During which of the following phases of life is a star's pressure and gravity out of equilibrium?

Correct AnswerverifiedShow Answer

Most interstellar dust grains

Correct AnswerverifiedShow Answer

Why is Supernova 1987A particularly important to astronomers?

Correct AnswerverifiedShow Answer

What happens to the core of a star after it ejects a planetary nebula?

Correct AnswerverifiedShow Answer

What can we learn about a star from a life track on an H- R diagram?

Correct AnswerverifiedShow Answer

What can trigger the gravitational collapse of an interstellar gas cloud?

Correct AnswerverifiedShow Answer

Why is Supernova 1987A particularly important to astronomers?

Correct AnswerverifiedShow Answer

When does a star become a main- sequence star?

Correct AnswerverifiedShow Answer

Which event marks the beginning of a supernova?

Correct AnswerverifiedShow Answer

Which of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, and so on) in a high- mass star is not true?

Correct AnswerverifiedShow Answer

Approximately what core temperature is required before hydrogen fusion can begin in a star?

Correct AnswerverifiedShow Answer

What happens after the helium flash?

Correct AnswerverifiedShow Answer

Suppose that the star Betelgeuse (the upper left shoulder of Orion) were to supernova tomorrow (as seen here on Earth) . What would it look like to the naked eye?

Correct AnswerverifiedShow Answer

Explain how some stars form in binary systems.

Correct AnswerverifiedAs a molecular cloud contracts, it break...View AnswerShow Answer

What change slowly occurs during the main- sequence lifetime of a star?

Correct AnswerverifiedShow Answer

Based on its main- sequence turnoff point, the age of this cluster is

Correct AnswerverifiedShow Answer

Briefly describe how a star forms.

Correct AnswerverifiedIn cold, dense molecular clouds, gravity...View AnswerShow Answer

Generally speaking, how does the surface temperature and luminosity of a protostar compare to the surface temperature and luminosity of the main- sequence star it becomes?

Correct AnswerverifiedShow Answer

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As a molecular cloud contracts, it break...
View Answer

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In cold, dense molecular clouds, gravity...
View Answer

Correct Answer
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