Kalfree 2

assignment_expert_12.docx

Question 1

·   The Jeans instability describes the   Answer

·	· 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.

1 points

Question 2

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

·	· 1.	· when it is expanding in size as a red giant or supergiant
·	· 2.	· after condensation but before nuclear reactions begin in its core
·	· 3.	· after nuclear reactions end in its core but before the red giant phase
·	· 4.	· while it is converting hydrogen into helium in its core

1 points

Question 3

·   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?   Answer

·	· 1.	· hydrogen fusion
·	· 2.	· silicon fusion
·	· 3.	· carbon fusion
·	· 4.	· helium fusion

1 points

Question 4

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

·	· 1.	· X-ray
·	· 2.	· radio
·	· 3.	· ultraviolet
·	· 4.	· visible

1 points

Question 5

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

·	· 1.	· collisions between two interstellar clouds
·	· 2.	· gravitational contraction of a hot gas cloud
·	· 3.	· radiation pressure from the intense UV radiation from hot stars
·	· 4.	· supernova explosions and the resultant shock waves

1 points

Question 6

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

·	· 1.	· 8/10 of a solar mass.
·	· 2.	· about 1/2 a solar mass.
·	· 3.	· slightly less than 1/10 of a solar mass.
·	· 4.	· slightly less than 1/100 of a solar mass.

1 points

Question 7

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

·	· 1.	· Giant molecular clouds evolve into H II regions as the molecules · other than hydrogen are used up in star formation. ·
·	· 2.	· In giant molecular clouds, H II regions surround ultraviolet-emitting · stars (types O and B), which have ionized the hydrogen around them. ·
·	· 3.	· In H II regions, giant molecular clouds are concentrations of other · molecules like CO and H2O. ·
·	· 4.	· They are two names for the same entity.

1 points

Question 8

·   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   Answer

·	· 1.	· the more massive star captured the other one into orbit some time · after the two stars had formed. ·
·	· 2.	· the more massive star formed later, from a disk of gas surrounding · the less massive star. ·
·	· 3.	· mass transfer from one of the stars to the other has occurred.
·	· 4.	stars evolve differently in binary star systems, with less massive stars evolving faster than more massive stars. ·

1 points

Question 9

·   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?   Answer

·	· 1.	· toward the upper right
·	· 2.	· toward the lower left
·	· 3.	· toward the lower right
·	· 4.	· toward the upper left

1 points

Question 10

·   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   Answer

·	· 1.	· upward and to the right, but only very slightly.
·	· 2.	· down and to the left, toward the white dwarves.
·	· 3.	· upward and to the left, along the main sequence.
·	· 4.	· straight upward as its luminosity increases.