Assignment Expert 12

Homework

Question 1

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  The Jeans instability describes the 

Answer

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· 1.

· conditions under which sufficient numbers of neutrinos can · trigger the collapse of an interstellar cloud. ·

· 2.

· overcoming of gas pressure by self-gravity in a cold and dense · interstellar cloud to form a star. ·

· 3.

· expansion of a gas cloud after gravitational contraction because · of build-up of great heat within the cloud from gravitational potential · energy. ·

· 4.

· explosion of a star at the end of its life, the supernova phenomenon.

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1 points  

Question 2

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  At what stage in its life does a star pass through the protostar phase? 

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· when it is expanding in size as a red giant or supergiant

· after condensation but before nuclear reactions begin in its core

· after nuclear reactions end in its core but before the red giant phase

· while it is converting hydrogen into helium in its core

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1 points  

Question 3

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  A low-mass red dwarf (0.08 M < M < 0.4 M) experiences which of the following fusion reactions as the last fusion reaction in its core?


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· hydrogen fusion

· silicon fusion

· carbon fusion

· helium fusion

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1 points  

Question 4

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  What wavelengths have astronomers used to map and study the distribution of the giant molecular clouds in space? 

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· X-ray

· radio

· ultraviolet

· visible

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1 points  

Question 5

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  Which of the following mechanisms is thought to be ineffective and inefficient in the triggering of star birth in molecular clouds? 

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· collisions between two interstellar clouds

· gravitational contraction of a hot gas cloud

· radiation pressure from the intense UV radiation from hot stars

· supernova explosions and the resultant shock waves

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1 points  

Question 6

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  The lowest mass a protostar can have and still become a star (i.e., start thermonuclear reactions in its core) is 

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· 8/10 of a solar mass.

· about 1/2 a solar mass.

· slightly less than 1/10 of a solar mass.

· slightly less than 1/100 of a solar mass.

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1 points  

Question 7

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  What is the relationship between a giant molecular cloud and an H II region? 

Answer

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· Giant molecular clouds evolve into H II regions as the molecules · other than hydrogen are used up in star formation. ·

· In giant molecular clouds, H II regions surround ultraviolet-emitting · stars (types O and B), which have ionized the hydrogen around them. ·

· In H II regions, giant molecular clouds are concentrations of other · molecules like CO and H2O. ·

· They are two names for the same entity.

· 

1 points  

Question 8

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  In some binary star systems, such as Algol, the less massive star is an old red giant and the more massive star is on the main sequence, evidence that 

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· the more massive star captured the other one into orbit some time · after the two stars had formed. ·

· the more massive star formed later, from a disk of gas surrounding · the less massive star. ·

· mass transfer from one of the stars to the other has occurred.

stars evolve differently in binary star systems, with less massive stars evolving faster than more massive stars. ·

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1 points  

Question 9

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  On the Hertzsprung-Russell diagram, in which direction does the position occupied by a star move after helium burning begins in the star’s core? 

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· toward the upper right

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· toward the lower left

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· toward the lower right

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· 4.

· toward the upper left

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1 points  

Question 10

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  From the time a star of more than 1 solar mass reaches the ZAMS until it leaves the main sequence, the star’s evolution on the main sequence is 

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· upward and to the right, but only very slightly.

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· down and to the left, toward the white dwarves.

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· upward and to the left, along the main sequence.

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· straight upward as its luminosity increases.