Question 1

The average density of the interstellar medium is:

Accepted Answer

A)  1 atom/cm3 
B)  1,000 atom/cm3 
C)  104 atom/cm3 
D)  106 atom/cm3 
E)  1012 atom/cm3 
A)  1 atom/cm3 
B)  1,000 atom/cm3 
C)  104 atom/cm3 
D)  106 atom/cm3 
E)  1012 atom/cm3

Question 2

How long does it typically take for a protostar to form a 1 M $\odot$  star?

Accepted Answer

A)  3 * 107 years 
B)  3 *105 years 
C)  3,000 years 
D)  300 years 
E)  30 years 
A)  3 * 107 years 
B)  3 *105 years 
C)  3,000 years 
D)  300 years 
E)  30 years

Question 3

We observe neutral hydrogen gas using 21-cm emission.

Accepted Answer

A) True 
 B)False

Question 4

Some molecular clouds have so much internal pressure that it exceeds their self-gravity. What keeps them from expanding and dissipating?

Accepted Answer

The pressure of the external i

Question 5

An accretion disk forms around a collapsing protostar because infalling material must conserve:

Accepted Answer

A)  energy 
B)  centrifugal force 
C)  gravity 
D)  velocity 
E)  angular momentum 
A)  energy 
B)  centrifugal force 
C)  gravity 
D)  velocity 
E)  angular momentum

Question 6

When radiation from an object passes through the interstellar medium:

Accepted Answer

A)  the object appears dimmer 
B)  the object appears bluer 
C)  the object appears bluer and dimmer 
D)  the object appears redder and dimmer 
E)  the object's apparent velocity changes 
A)  the object appears dimmer 
B)  the object appears bluer 
C)  the object appears bluer and dimmer 
D)  the object appears redder and dimmer 
E)  the object's apparent velocity changes

Question 7

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

Accepted Answer

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

Question 8

Brown dwarfs are considered failed stars because:

Accepted Answer

A)  they never reach masses larger than 50 Jupiter masses 
B)  hydrogen fusion never begins in their cores 
C)  convection never plays a role in their energy transport 
D)  they primarily shine at infrared wavelengths 
E)  they are never as luminous as the Sun 
A)  they never reach masses larger than 50 Jupiter masses 
B)  hydrogen fusion never begins in their cores 
C)  convection never plays a role in their energy transport 
D)  they primarily shine at infrared wavelengths 
E)  they are never as luminous as the Sun

Question 9

Why do H II regions mark the regions where new stars are currently being formed?

Accepted Answer

H II regions contain ionized gas that is

Question 10

Warm ionized gas in the interstellar medium appears _________ when imaged in the optical region of the electromagnetic spectrum.

Accepted Answer

A)  red 
B)  yellow 
C)  white 
D)  blue 
E)  dark 
A)  red 
B)  yellow 
C)  white 
D)  blue 
E)  dark

Question 11

Where have astronomers observed the existence of planets?

Accepted Answer

A)  in our Solar System 
B)  orbiting stars other than the Sun 
C)  orbiting stars in binary systems 
D)  traveling on their own through the Milky Way, not orbiting a star 
E)  all of the above 
A)  in our Solar System 
B)  orbiting stars other than the Sun 
C)  orbiting stars in binary systems 
D)  traveling on their own through the Milky Way, not orbiting a star 
E)  all of the above

Question 12

Figure 1
-Use Figure 1 to complete the following statement. As a protostar contracts:

Accepted Answer

A)  the luminosity decreases 
B)  the luminosity increases 
C)  the temperature increases 
D)  the temperature decreases 
E)  either the luminosity decreases or the temperature increases 
A)  the luminosity decreases 
B)  the luminosity increases 
C)  the temperature increases 
D)  the temperature decreases 
E)  either the luminosity decreases or the temperature increases

Question 13

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 H-alpha emission line 
D)  it preferentially affects light at visible and shorter wavelengths 
E)  it primarily moves away from Earth 
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 H-alpha emission line 
D)  it preferentially affects light at visible and shorter wavelengths 
E)  it primarily moves away from Earth

Question 14

When winds blow the gas away from a forming protostar it becomes visible as a T Tauri star.

Accepted Answer

A) True 
 B)False

Question 15

Which of the following stars spend the longest time on their Hayashi tracks?

Accepted Answer

A)  100 M $\odot$  stars 
B)  10 M $\odot$  stars 
C)  1 M $\odot$  stars 
D)  0.1 M $\odot$  stars 
E)  0.08 M $\odot$  stars 
A)  100 M $\odot$  stars 
B)  10 M $\odot$  stars 
C)  1 M $\odot$  stars 
D)  0.1 M $\odot$  stars 
E)  0.08 M $\odot$  stars

Question 16

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)  pressure 
D)  gravity 
E)  turbulence 
A)  magnetic fields 
B)  conservation of angular momentum 
C)  pressure 
D)  gravity 
E)  turbulence

Question 17

How are H II regions and the hot intercloud gas heated?

Accepted Answer

Hot intercloud gas is heated b

Question 18

How are each of the following types of ISM detected by astronomers: hot intercloud gas, H II regions, neutral hydrogen gas, and molecular clouds.

Accepted Answer

The hot intercloud gas is detected by X-

Question 19

What is the interstellar medium made of? Give rough percentages of each.

Accepted Answer

The ISM is

Question 20

The Hayashi track of a low-mass protostar in the H-R diagram is a path of approximately constant:

Accepted Answer

A)  density 
B)  luminosity 
C)  age 
D)  temperature 
E)  radius 
A)  density 
B)  luminosity 
C)  age 
D)  temperature 
E)  radius

Exam 15: Star Formation and the Interstellar Medium

The average density of the interstellar medium is:

How long does it typically take for a protostar to form a 1 M ⊙\odot⊙ star?

We observe neutral hydrogen gas using 21-cm emission.

Some molecular clouds have so much internal pressure that it exceeds their self-gravity. What keeps them from expanding and dissipating?

An accretion disk forms around a collapsing protostar because infalling material must conserve:

When radiation from an object passes through the interstellar medium:

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

Brown dwarfs are considered failed stars because:

Why do H II regions mark the regions where new stars are currently being formed?

Warm ionized gas in the interstellar medium appears _________ when imaged in the optical region of the electromagnetic spectrum.

Where have astronomers observed the existence of planets?

Figure 1 -Use Figure 1 to complete the following statement. As a protostar contracts:

Dust reddens starlight because:

When winds blow the gas away from a forming protostar it becomes visible as a T Tauri star.

Which of the following stars spend the longest time on their Hayashi tracks?

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

How are H II regions and the hot intercloud gas heated?

How are each of the following types of ISM detected by astronomers: hot intercloud gas, H II regions, neutral hydrogen gas, and molecular clouds.

What is the interstellar medium made of? Give rough percentages of each.

The Hayashi track of a low-mass protostar in the H-R diagram is a path of approximately constant:

Why Learn Astronomy

Patterns in the Skymotions of Earth

Motion of Astronomical Bodies

Gravity and Orbits

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 Liquid the Giant Planets

Planetary Adornmentsmoons and Rings

Dwarf Planets and Small Solar System Bodies

Taking the Measure of Stars

Our Starthe Sun

Evolution of Low-Mass Stars

Evolution of High-Mass Stars

Relativity and Black Holes

The Expanding Universe

Galaxies

The Milky Waya Normal Spiral Galaxy

Modern Cosmology

Large-Scale Structure in the Universe

Life

Filters

How long does it typically take for a protostar to form a 1 M _$\odot$ star?

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