Question 1

Which object is NOT an abundant physical component of the interstellar medium?

Accepted Answer

A)   atoms and ions
B)   molecules
C)   dust
D)   radioactive elements D

Question 2

Which mechanism is NOT thought to be significant in the formation of new stars in the interstellar medium?

Accepted Answer

A)   heating of an interstellar cloud by concentrated beams of neutrinos from nearby stars
B)   compression of cold interstellar gas by radiation pressure from light from very bright stars
C)   condensation of matter by the shock wave from a nearby supernova
D)   collision of two cold interstellar clouds

Question 3

About 3000 stars are visible to the unaided eye on a clear night,and the majority of these are giants and supergiants.However,our theories predict the most numerous stars should be red dwarfs.Do we have an explanation for this discrepancy? If so,what is it?

Accepted Answer

A)   Our location in the galactic plane is particularly rich in gas and dust, so an unusually large number of giants and supergiants formed here.
B)   Early in the history of our Galaxy, a shock wave passed through our part of the spiral arm, creating a large number of stars all at one time. These stars are now mostly in their giant phases.
C)   This is an example of a selection effect. The bright giants and supergiants are the most likely to be seen, even though they are not in the majority numerically.
D)   We do not have an explanation for this discrepancy.

Question 4

The evolutionary track of a star represents:

Accepted Answer

A)   its orbit around the center of the galaxy in which it resides.
B)   changes in its luminosity and temperature on a graph of these two parameters as the star ages.
C)   its path across Earth's sky as a consequence of its true motion in space.
D)   changes in its size and mass on a graph of these two parameters as the star ages.

Question 5

A T Tauri star is a:

Accepted Answer

A)   protostar that is ejecting mass near the end of its pre-main-sequence lifetime.
B)   young, massive O or B star.
C)   young protostar embedded in a cocoon of dust clouds, visible only by infrared radiation.
D)   high-mass yellow giant star that pulsates regularly in size and brightness. A

Question 6

The interstellar medium,as usually defined,contains all of the following EXCEPT ONE.Which is the exception?

Accepted Answer

A)   isolated atoms
B)   isolated molecules
C)   small pieces of dust
D)   meteoroids

Question 7

Horizontal-branch stars have a wide range of temperatures and luminosities between 50 and 100 times that of the Sun,so they are in what stage of their lives?

Accepted Answer

A)   gravitational contraction before the start of core hydrogen burning
B)   hydrogen-shell burning, with a degenerate helium core
C)   core helium burning
D)   core hydrogen burning

Question 8

The total lifespan of the Sun is believed to be:

Accepted Answer

A)   a few million years.
B)   half a billion years.
C)   10 billion years.
D)   infinite.

Question 9

How long will the Sun have spent as a main-sequence star when it finally begins to evolve toward the red giant phase?

Accepted Answer

A)   1 billion years
B)   1 million years
C)   10¹¹ years
D)   10¹⁰ years

Question 10

Which statement about the rate of stellar evolution is true?

Accepted Answer

A)   The more massive the original star, the faster is the evolution.
B)   The chemical make-up of the original nebula is the major factor in deciding the rate of evolution, whatever the mass of the star.
C)   Star mass has no bearing on stellar evolution since all stars evolve at the same rate, controlled by nuclear fusion.
D)   The more massive the original star, the slower is the evolution since there is more material for thermonuclear burning.

Question 11

The total time the Sun will spend as a main-sequence star is:

Accepted Answer

A)   at least 200 billion years (2 × 10¹¹)  years.
B)   about 1 million years.
C)   about 4.5 million years.
D)   about 10 billion years (10¹⁰ years) . D

Question 12

The periods of Type I Cepheids and Type II Cepheids are different for stars of the same luminosity.What is the physical difference between these stars that causes the periods to be different?

Accepted Answer

A)   Type II Cepheids are older, having evolved from Type I Cepheids.
B)   The two types have different metallicities.
C)   Type I Cepheids are members of binary systems, whereas Type II Cepheids are solitary stars.
D)   Type II Cepheids have gone through the helium flash, whereas Type I Cepheids have yet to do so.

Question 13

What is the most important property of a star that governs its evolution and lifetime?

Accepted Answer

A)   mass
B)   surface temperature
C)   abundance of heavy elements
D)   speed of rotation

Question 14

What is the "safety valve" that operates in normal (nondegenerate) stars?

Accepted Answer

A)   If thermonuclear reactions proceed too quickly, the star runs out of fuel before anything drastic happens.
B)   If the stellar gas is suddenly heated, it expands and cools.
C)   If the star gets too big, it collapses into a black hole.
D)   If the pressure becomes too high, electrons combine with protons to relieve the pressure.

Question 15

Brown dwarfs and Jovian planets have many similarities.In which aspect are they NOT similar?

Accepted Answer

A)   Neither produces energy by hydrogen fusion.
B)   They are primarily composed of hydrogen and helium.
C)   They produce similar spectra.
D)   They are both fully convective at various stages.

Question 16

Red dwarfs are fully convective.In this,they are like:

Accepted Answer

A)   white dwarfs.
B)   brown dwarfs.
C)   the Sun.
D)   variable stars.

Question 17

Which condition does NOT characterize a pre-main-sequence star in its final stages?

Accepted Answer

A)   The star is fusing hydrogen into helium in its core.
B)   The star is no longer contracting.
C)   The gas and dust around the pre-main-sequence star have largely dissipated.
D)   Helium burning has begun as the principal energy generating mechanism in the star's core.

Question 18

Which easily observed molecular species is used as a tracer for the fundamental but difficult to observe H₂ molecules in giant molecular clouds?

Accepted Answer

A)   hydroxyl (OH) 
B)   water vapor (H₂O) 
C)   carbon dioxide (CO₂) 
D)   carbon monoxide (CO)

Question 19

In star-forming regions in interstellar space,which molecule is the easiest to detect?

Accepted Answer

A)   ammonia (NH₃) 
B)   hydrogen (H₂) 
C)   formaldehyde (H₂CO) 
D)   carbon monoxide (CO)

Question 20

A star of which solar mass would be expected to experience a helium flash?

Accepted Answer

A)   0.2
B)   1.2
C)   2.6
D)   4.2

Exam 11: The Lives of the Stars From Birth Through Middle Age

Which object is NOT an abundant physical component of the interstellar medium?

Correct AnswerverifiedD

Which mechanism is NOT thought to be significant in the formation of new stars in the interstellar medium?

Correct AnswerverifiedShow Answer

About 3000 stars are visible to the unaided eye on a clear night,and the majority of these are giants and supergiants.However,our theories predict the most numerous stars should be red dwarfs.Do we have an explanation for this discrepancy? If so,what is it?

Correct AnswerverifiedShow Answer

The evolutionary track of a star represents:

Correct AnswerverifiedShow Answer

A T Tauri star is a:

Correct AnswerverifiedA

The interstellar medium,as usually defined,contains all of the following EXCEPT ONE.Which is the exception?

Correct AnswerverifiedShow Answer

Horizontal-branch stars have a wide range of temperatures and luminosities between 50 and 100 times that of the Sun,so they are in what stage of their lives?

Correct AnswerverifiedShow Answer

The total lifespan of the Sun is believed to be:

Correct AnswerverifiedShow Answer

How long will the Sun have spent as a main-sequence star when it finally begins to evolve toward the red giant phase?

Correct AnswerverifiedShow Answer

Which statement about the rate of stellar evolution is true?

Correct AnswerverifiedShow Answer

The total time the Sun will spend as a main-sequence star is:

Correct AnswerverifiedD

The periods of Type I Cepheids and Type II Cepheids are different for stars of the same luminosity.What is the physical difference between these stars that causes the periods to be different?

Correct AnswerverifiedShow Answer

What is the most important property of a star that governs its evolution and lifetime?

Correct AnswerverifiedShow Answer

What is the "safety valve" that operates in normal (nondegenerate) stars?

Correct AnswerverifiedShow Answer

Brown dwarfs and Jovian planets have many similarities.In which aspect are they NOT similar?

Correct AnswerverifiedShow Answer

Red dwarfs are fully convective.In this,they are like:

Correct AnswerverifiedShow Answer

Which condition does NOT characterize a pre-main-sequence star in its final stages?

Correct AnswerverifiedShow Answer

Which easily observed molecular species is used as a tracer for the fundamental but difficult to observe H₂ molecules in giant molecular clouds?

Correct AnswerverifiedShow Answer

In star-forming regions in interstellar space,which molecule is the easiest to detect?

Correct AnswerverifiedShow Answer

A star of which solar mass would be expected to experience a helium flash?

Correct AnswerverifiedShow Answer

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D

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