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In the densest molecular clouds,the average density is approximately In the densest molecular clouds,the average density is approximately .If a cube of molecular cloud gas with this density contained of material (the amount needed to make a star),what would be the length of a side of the cube in units of AU? For reference,the mass of the Sun is ,the mass of a hydrogen atom is , . .If a cube of molecular cloud gas with this density contained In the densest molecular clouds,the average density is approximately .If a cube of molecular cloud gas with this density contained of material (the amount needed to make a star),what would be the length of a side of the cube in units of AU? For reference,the mass of the Sun is ,the mass of a hydrogen atom is , . of material (the amount needed to make a In the densest molecular clouds,the average density is approximately .If a cube of molecular cloud gas with this density contained of material (the amount needed to make a star),what would be the length of a side of the cube in units of AU? For reference,the mass of the Sun is ,the mass of a hydrogen atom is , . star),what would be the length of a side of the cube in units of AU? For reference,the mass of the Sun is In the densest molecular clouds,the average density is approximately .If a cube of molecular cloud gas with this density contained of material (the amount needed to make a star),what would be the length of a side of the cube in units of AU? For reference,the mass of the Sun is ,the mass of a hydrogen atom is , . ,the mass of a hydrogen atom is In the densest molecular clouds,the average density is approximately .If a cube of molecular cloud gas with this density contained of material (the amount needed to make a star),what would be the length of a side of the cube in units of AU? For reference,the mass of the Sun is ,the mass of a hydrogen atom is , . , In the densest molecular clouds,the average density is approximately .If a cube of molecular cloud gas with this density contained of material (the amount needed to make a star),what would be the length of a side of the cube in units of AU? For reference,the mass of the Sun is ,the mass of a hydrogen atom is , . .

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If the one side of the cube ha...

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When a molecular cloud fragments and stars form,the least massive stars are the first to form while the massive stars take longer to form.

A) True
B) False

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A young protostar is __________ than the Sun even though its surface temperature is __________.


A) less luminous;hotter
B) larger;cooler
C) more luminous;cooler
D) smaller;hotter

E) A) and B)
F) All of the above

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The H- atom is important in protostars because it acts as a powerful temperature regulator.

A) True
B) False

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Which of the following is responsible for heating the bulk of the very hot intercloud gas?


A) High-energy radiation from stars
B) Supernovae
C) Young O and B stars
D) The heating is an even mix of all three sources.

E) All of the above
F) C) and D)

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Dust appears dark in __________ wavelengths and bright in __________ wavelengths.


A) optical;ultraviolet
B) infrared;radio
C) radio;ultraviolet
D) optical;infrared

E) B) and D)
F) B) and C)

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Given the low efficiency of the star formation process,the initial mass of a molecular cloud fragment that formed a Given the low efficiency of the star formation process,the initial mass of a molecular cloud fragment that formed a star was probably close to A) . B) . C) . D) . star was probably close to


A) Given the low efficiency of the star formation process,the initial mass of a molecular cloud fragment that formed a star was probably close to A) . B) . C) . D) . .
B) Given the low efficiency of the star formation process,the initial mass of a molecular cloud fragment that formed a star was probably close to A) . B) . C) . D) . .
C) Given the low efficiency of the star formation process,the initial mass of a molecular cloud fragment that formed a star was probably close to A) . B) . C) . D) . .
D) Given the low efficiency of the star formation process,the initial mass of a molecular cloud fragment that formed a star was probably close to A) . B) . C) . D) . .

E) None of the above
F) A) and B)

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The most common types of stars in our galaxy are


A) high-mass stars.
B) low-mass stars.
C) an equal mix of high- and low-mass stars.
D) We do not yet know which types of stars are most common in our galaxy.

E) None of the above
F) A) and B)

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The source of energy for a contracting protostar comes from


A) gravitational potential energy.
B) kinetic energy.
C) thermonuclear energy.
D) radiation energy.

E) B) and C)
F) C) and D)

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Of the following processes at work in molecular clouds,which is the one that inevitably dominates the clouds' evolution?


A) Magnetic fields
B) Conservation of angular momentum
C) Gravity
D) Turbulence

E) C) and D)
F) A) and D)

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How long does it typically take for a protostar to form a How long does it typically take for a protostar to form a star? A) B) C) 3,000 years D) 300 years star?


A) How long does it typically take for a protostar to form a star? A) B) C) 3,000 years D) 300 years
B) How long does it typically take for a protostar to form a star? A) B) C) 3,000 years D) 300 years
C) 3,000 years
D) 300 years

E) A) and C)
F) A) and B)

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The only effect of interstellar dust is that it makes objects appear redder than they really are.

A) True
B) False

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A typical molecular cloud has a temperature of approximately


A) 0.3 K.
B) 10 K.
C) 300 K.
D) 1,000 K.

E) C) and D)
F) None of the above

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If a If a protostar starts out on the Hayashi track with a temperature of 3,300 K and a luminosity of ,what is its approximate radius? A) . B) . C) . D) . protostar starts out on the Hayashi track with a temperature of 3,300 K and a luminosity of If a protostar starts out on the Hayashi track with a temperature of 3,300 K and a luminosity of ,what is its approximate radius? A) . B) . C) . D) . ,what is its approximate radius?


A) If a protostar starts out on the Hayashi track with a temperature of 3,300 K and a luminosity of ,what is its approximate radius? A) . B) . C) . D) . .
B) If a protostar starts out on the Hayashi track with a temperature of 3,300 K and a luminosity of ,what is its approximate radius? A) . B) . C) . D) . .
C) If a protostar starts out on the Hayashi track with a temperature of 3,300 K and a luminosity of ,what is its approximate radius? A) . B) . C) . D) . .
D) If a protostar starts out on the Hayashi track with a temperature of 3,300 K and a luminosity of ,what is its approximate radius? A) . B) . C) . D) . .

E) B) and C)
F) A) and D)

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Magnetic fields inside a molecular cloud act to


A) inhibit gravitational collapse.
B) fragment the cloud into numerous cores.
C) modulate the temperature of the molecules.
D) increase the formation of dust grains.

E) A) and B)
F) A) and D)

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Why is it possible for self-gravity to dominate pressure in molecular clouds but not in most interstellar clouds?

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Molecular clouds are denser (m...

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Dust reddens starlight because


A) it re-emits the light it absorbs at red wavelengths.
B) it emits mostly in the infrared due to its cold temperature.
C) it is made mostly of hydrogen,which produces the red Halpha emission line.
D) it preferentially affects light at optical and shorter wavelengths.

E) B) and C)
F) A) and D)

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The average density of the interstellar medium is many times less dense than the best vacuum on Earth.

A) True
B) False

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When a When a protostar forms,it starts out at the top of the Hayashi track with a luminosity of and a temperature of 3,600 K.What is its radius at this point (give the answer in units of ),and how many times larger is it at this stage compared to its radius as a main-sequence star,which is about ? For reference,the Sun's temperature is 5,800 K. protostar forms,it starts out at the top of the Hayashi track with a luminosity of When a protostar forms,it starts out at the top of the Hayashi track with a luminosity of and a temperature of 3,600 K.What is its radius at this point (give the answer in units of ),and how many times larger is it at this stage compared to its radius as a main-sequence star,which is about ? For reference,the Sun's temperature is 5,800 K. and a temperature of 3,600 K.What is its radius at this point (give the answer in units of When a protostar forms,it starts out at the top of the Hayashi track with a luminosity of and a temperature of 3,600 K.What is its radius at this point (give the answer in units of ),and how many times larger is it at this stage compared to its radius as a main-sequence star,which is about ? For reference,the Sun's temperature is 5,800 K. ),and how many times larger is it at this stage compared to its radius as a main-sequence star,which is about When a protostar forms,it starts out at the top of the Hayashi track with a luminosity of and a temperature of 3,600 K.What is its radius at this point (give the answer in units of ),and how many times larger is it at this stage compared to its radius as a main-sequence star,which is about ? For reference,the Sun's temperature is 5,800 K. ? For reference,the Sun's temperature is 5,800 K.

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The Stefan-Boltzmann law says ...

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A protostar's evolutionary "track" in the H-R diagram traces out


A) only how the protostar's radius changes with time.
B) how the protostar's luminosity,temperature,and radius change with time.
C) only how the protostar's luminosity changes with time.
D) only how the protostar's spectral type changes with time.

E) A) and D)
F) C) and D)

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