Download Question 1 - Homework Market

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.
.
. . 4stars 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.
.