Question 1

The thermal pressure of a gas depends on

Accepted Answer

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

Question 2

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

Accepted Answer

A) True 
 B)False

Question 3

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

Question 4

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. 
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 5

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. 
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.

Question 6

Molecular clouds appear more transparent at longer wavelengths.

Accepted Answer

A) True 
 B)False

Question 7

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

Question 8

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. 
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 9

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

Question 10

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. 
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 11

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 
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 12

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

Question 14

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 
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 15

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 16

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. 
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 17

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 
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 18

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. 
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 19

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 
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 20

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

Exam 16: Star Birth

The thermal pressure of a gas depends on

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

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

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

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

Molecular clouds appear more transparent at longer wavelengths.

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

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

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

What do we mean by the interstellar medium?

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

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

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

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

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

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?

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?

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

When does a star become a main-sequence star?

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.

A Modern View of the Universe

Discovering the Universe for Yourself

The Science of Astronomy

Making Sense of the Universe: Understanding Motion, Energy, and Gravity

Light and Matter: Reading Messages from the Cosmos

Telescopes: Portals of Discovery

Our Planetary System

Formation of the Solar System

Planetary Geology: Earth and the Other Terrestrial Worlds

Planetary Atmospheres: Earth and the Other Terrestrial Worlds

Jovian Planet Systems

Asteroids, Comets, and Dwarf Planets: Their Nature, Orbits, and Impacts

Other Planetary Systems: The New Science of Distant Worlds

Our Star

Surveying the Stars

Star Stuff

The Bizarre Stellar Graveyard

Our Galaxy

Galaxies and the Foundations of Modern Cosmology

Galaxy Evolution

The Birth of the Universe

Dark Matter, Dark Energy, and the Fate of the Universe

Life in the Universe

Celestial Timekeeping and Navigation

Space and Time

Spacetime and Gravity

Building Blocks of the Universe

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