Question 1

Although some photographs show what looks like jets of material near many young stars,we now know that these "jets" actually represent gas from the surrounding nebula that is falling onto the stars.

Accepted Answer

A) True 
 B)False

Question 2

We do not know for certain whether the general trends we observe in stellar birth masses also apply to brown dwarfs.But if they do,then which of the following would be true?

Accepted Answer

A)  Brown dwarfs would outnumber all ordinary stars.
B)  Brown dwarfs would be responsible for most of the overall luminosity of our Milky Way Galaxy.
C)  Brown dwarfs would be extremely rare.
D)  Most of the brown dwarfs in the Milky Way Galaxy would be quite young in age.

Question 3

Where would a brown dwarf be located on an H-R diagram?

Accepted Answer

A)  above and to the left of the highest part of the main sequence
B)  in the upper right corner of the H-R diagram
C)  in the lower left corner of the H-R diagram
D)  below and to the right of the lowest part of the main sequence

Question 4

The most common constituent of molecular clouds,H₂,is rarely detected within them.

Accepted Answer

A) True 
 B)False

Question 5

Why does a cloud collapse rapidly at first,and then slow down as the it gets denser?

Accepted Answer

The self-gravity causes the cloud to col...

Question 6

What law explains why a rotating,collapsing cloud forms a flat protostellar disk around a protostar?

Accepted Answer

A)  Kepler's third law
B)  the universal law of gravitation
C)  Wien's law
D)  conservation of angular momentum

Question 7

What do we mean by the interstellar medium?

Accepted Answer

A)  The gas and dust that lies in between the stars in the Milky Way Galaxy.
B)  The dust that fills the halo of the Milky Way Galaxy.
C)  The middle section of the Milky Way Galaxy.
D)  The name of an oracle who can channel messages from beings that live near the star called Vega.

Question 8

When is thermal energy trapped in the dense center of a cloud?

Accepted Answer

A)  when the gravity becomes so strong that photons cannot escape
B)  when excited molecules collide with other molecules before they can release a photon
C)  when the cloud becomes so hot and dense that nuclear fusion begins
D)  when magnetic fields trap the radiation
E)  when the cloud cools down so much that less light escapes than is produced by contraction

Question 9

8) Angular momentum plays an important role in star formation.Which of the following characteristics of a protostellar system is probably not strongly affected by the star's angular momentum?

Accepted Answer

A)  the existence of protostellar jets
B)  the strength of protostellar winds
C)  the onset of core hydrogen fusion
D)  the formation of a protostellar disk

Question 10

Astronomers estimate that new stars form in our galaxy at the rate of about

Accepted Answer

A)  one per year.
B)  a few (2-3) per year.
C)  ten per year.
D)  20-30 per year.
E)  100 per year.

Question 11

Which process is required to allow a gravitationally-collapsing gas cloud to continue to collapse?

Accepted Answer

A)  The cloud must trap most of its thermal energy.
B)  The cloud must collide with other clouds.
C)  New dust particles must continually be made in the cloud.
D)  The cloud must radiate away much of its thermal energy.

Question 12

The thermal pressure of a gas depends on

Accepted Answer

A)  density only.
B)  temperature only.
C)  density and temperature.
D)  composition.
E)  gravity.

Question 13

If you wanted to observe stars behind a molecular cloud,in what wavelength of light would you most likely observe?

Accepted Answer

A)  ultraviolet
B)  visible
C)  infrared
D)  X-ray
E)  gamma-ray

Question 14

Molecular clouds appear more transparent at longer wavelengths.

Accepted Answer

A) True 
 B)False

Question 15

Most interstellar clouds remain stable in size because the force of gravity is opposed by ________ within the cloud.

Accepted Answer

A)  degeneracy pressure
B)  radiation pressure
C)  stellar winds
D)  thermal pressure

Question 16

When does a star become a main-sequence star?

Accepted Answer

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

Question 17

Why do we think the first generation of stars would be different from stars born today?

Accepted Answer

A)  Without heavy elements,the clouds could not reach as low a temperature as today and had to be more massive to collapse.
B)  Without heavy elements,the nuclear reactions at the center of the stars would be very different.
C)  Without heavy elements,there was no dust in the clouds and they collapsed faster.
D)  The Universe was much denser when the first stars were born.
E)  There were no galaxies when the first stars were born.

Question 18

Which two processes can generate energy to help a star or gas cloud maintain its internal thermal pressure?

Accepted Answer

A)  nuclear fusion and nuclear fission
B)  nuclear fusion and supernovae
C)  nuclear fission and supernovae
D)  nuclear fusion and gravitational contraction

Question 19

When does hydrogen first begin to fuse into helium in the star formation process?

Accepted Answer

A)  when the cloud first begins to contract
B)  when the thermal pressure is trapped at the center of the cloud
C)  when the protostars undergoes convective contraction
D)  when the protostar undergoes radiative contraction
E)  only when the star reaches the main-sequence

Question 20

What is the likely reason that we cannot find any examples of the first generation stars?

Accepted Answer

A)  The first generation stars are too faint to be visible now.
B)  The first generation stars formed such a long time ago that the light from them has not yet had time to reach us.
C)  The first generation stars were all very massive and exploded as supernova.
D)  The first generation stars formed with only H and He and therefore have no spectral features.
E)  We do not know how the first generation stars were formed.

Exam 16: Star Birth

The most common constituent of molecular clouds,H₂,is rarely detected within them.

Correct AnswerverifiedShow Answer

If you wanted to observe stars behind a molecular cloud,in what wavelength of light would you most likely observe?

Correct AnswerverifiedShow Answer

What law explains why a rotating,collapsing cloud forms a flat protostellar disk around a protostar?

Correct AnswerverifiedShow Answer

When is thermal energy trapped in the dense center of a cloud?

Correct AnswerverifiedShow Answer

Why does a cloud collapse rapidly at first,and then slow down as the it gets denser?

Correct AnswerverifiedThe self-gravity causes the cloud to col...View AnswerShow Answer

What is the likely reason that we cannot find any examples of the first generation stars?

Correct AnswerverifiedShow Answer

Which process is required to allow a gravitationally-collapsing gas cloud to continue to collapse?

Correct AnswerverifiedShow Answer

When does hydrogen first begin to fuse into helium in the star formation process?

Correct AnswerverifiedShow Answer

Astronomers estimate that new stars form in our galaxy at the rate of about

Correct AnswerverifiedShow Answer

When does a star become a main-sequence star?

Correct AnswerverifiedShow Answer

Molecular clouds appear more transparent at longer wavelengths.

Correct AnswerverifiedShow Answer

Why do we think the first generation of stars would be different from stars born today?

Correct AnswerverifiedShow Answer

Most interstellar clouds remain stable in size because the force of gravity is opposed by ________ within the cloud.

Correct AnswerverifiedShow Answer

Which two processes can generate energy to help a star or gas cloud maintain its internal thermal pressure?

Correct AnswerverifiedShow Answer

Although some photographs show what looks like jets of material near many young stars,we now know that these "jets" actually represent gas from the surrounding nebula that is falling onto the stars.

Correct AnswerverifiedShow Answer

What do we mean by the interstellar medium?

Correct AnswerverifiedShow Answer

Where would a brown dwarf be located on an H-R diagram?

Correct AnswerverifiedShow Answer

8) Angular momentum plays an important role in star formation.Which of the following characteristics of a protostellar system is probably not strongly affected by the star's angular momentum?

Correct AnswerverifiedShow Answer

The thermal pressure of a gas depends on

Correct AnswerverifiedShow Answer

We do not know for certain whether the general trends we observe in stellar birth masses also apply to brown dwarfs.But if they do,then which of the following would be true?

Correct AnswerverifiedShow Answer

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The self-gravity causes the cloud to col...
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