Question 1

The source of energy for a contracting protostar comes from

Accepted Answer

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

Question 2

Dust reddens starlight because

Accepted Answer

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. 
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.

Question 3

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

Accepted Answer

Molecular clouds are denser (m

Question 4

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?

Accepted Answer

A)    . 
B)    . 
C)    . 
D)    . 
A)    . 
B)    . 
C)    . 
D)    .

Question 5

The most common types of stars in our galaxy are

Accepted Answer

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. 
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.

Question 6

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.

Accepted Answer

A) True 
 B)False

Question 7

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

Accepted Answer

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. 
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.

Question 8

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

Accepted Answer

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. 
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.

Question 9

Magnetic fields inside a molecular cloud act to

Accepted Answer

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. 
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.

Question 10

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   ,   .

Accepted Answer

If the one side of the cube ha

Question 11

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

Accepted Answer

A)    . 
B)    . 
C)    . 
D)    . 
A)    . 
B)    . 
C)    . 
D)    .

Question 12

How long does it typically take for a protostar to form a   star?

Accepted Answer

A)    
B)    
C)  3,000 years 
D)  300 years 
A)    
B)    
C)  3,000 years 
D)  300 years

Question 13

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

Accepted Answer

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

Question 14

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

Accepted Answer

A) True 
 B)False

Question 15

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

Accepted Answer

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

Question 16

A typical molecular cloud has a temperature of approximately

Accepted Answer

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

Question 17

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

Accepted Answer

A) True 
 B)False

Question 18

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

Accepted Answer

A) True 
 B)False

Question 19

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.

Accepted Answer

The Stefan-Boltzmann law says

Question 20

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

Accepted Answer

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

Exam 15: Star Formation and the Interstellar Medium

The source of energy for a contracting protostar comes from

Dust reddens starlight because

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

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?

The most common types of stars in our galaxy are

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

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

Magnetic fields inside a molecular cloud act to

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

How long does it typically take for a protostar to form a star?

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

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

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

A typical molecular cloud has a temperature of approximately

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

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

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

Why Learn Astronomy

Patterns in the Skymotions of Earth

Gravity and Orbitsa Celestial Ballet

Light

The Tools of the Astronomer

The Birth and Evolution of Planetary Systems

The Terrestrial Planets and Earths Moon

Atmospheres of the Terrestrial Planets

Worlds of Gas and Liquidthe Giant Planets

Gravity Is More Than Keplers Laws

Planetary Adornmentsmoons and Rings

Dwarf Planets and Small Solar System Bodies

Taking the Measure of Stars

A Run-Of-The-Mill G-Type Starour Sun

Stars in the Slow Lanelow-Mass Stellar Evolution

Live Fast,die Younghigh-Mass Stellar Evolution

Our Expanding Universe

Galaxies

The Milky Waya Normal Spiral Galaxy

Modern Cosmology

The Origin of Structure

Life

Filters

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

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

Dust appears dark in wavelengths and bright in wavelengths.