Question 1

The lowest-density gas in the interstellar medium is also the

Accepted Answer

A)  coldest. 
B)  least ionized. 
C)  hottest. 
D)  most localized, being found mostly around protostars. 
E)  most likely to be in a molecular state. 
A)  coldest. 
B)  least ionized. 
C)  hottest. 
D)  most localized, being found mostly around protostars. 
E)  most likely to be in a molecular state.

Question 2

As a protostar is evolving, its temperature

Accepted Answer

A)  decreases because it is radiating. 
B)  decreases because of gravitational contraction. 
C)  decreases because of angular momentum. 
D)  increases because of nuclear fusion. 
E)  increases due to the kinetic energy of infalling material. 
A)  decreases because it is radiating. 
B)  decreases because of gravitational contraction. 
C)  decreases because of angular momentum. 
D)  increases because of nuclear fusion. 
E)  increases due to the kinetic energy of infalling material.

Question 3

Dust reddens starlight because it

Accepted Answer

A)  re-emits the light it absorbs at red wavelengths. 
B)  emits mostly in the infrared due to its cold temperature. 
C)  is made mostly of hydrogen, which produces the red H-alpha emission line. 
D)  preferentially affects light at visible and shorter wavelengths. 
E)  primarily moves away from Earth. 
A)  re-emits the light it absorbs at red wavelengths. 
B)  emits mostly in the infrared due to its cold temperature. 
C)  is made mostly of hydrogen, which produces the red H-alpha emission line. 
D)  preferentially affects light at visible and shorter wavelengths. 
E)  primarily moves away from Earth.

Question 4

The average density of the interstellar medium is

Accepted Answer

A)  much denser than Earth's atmosphere. 
B)  much less dense than the best vacuum on Earth. 
C)  about the same density as air on the peak of Mount Everest. 
D)  zero. 
E)  about as dense as Earth's atmosphere at sea level. 
A)  much denser than Earth's atmosphere. 
B)  much less dense than the best vacuum on Earth. 
C)  about the same density as air on the peak of Mount Everest. 
D)  zero. 
E)  about as dense as Earth's atmosphere at sea level.

Question 5

When radiation from an object passes through the interstellar medium,

Accepted Answer

A)  the object appears refracted. 
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 refracted. 
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 6

One phenomenon that can slow star formation in a molecular cloud is

Accepted Answer

A)  a lack of rotation. 
B)  the strength of its magnetic field. 
C)  an excess of H II atoms. 
D)  a large size. 
E)  nearby type O and B stars. 
A)  a lack of rotation. 
B)  the strength of its magnetic field. 
C)  an excess of H II atoms. 
D)  a large size. 
E)  nearby type O and B stars.

Question 7

Sitting in a hot tub with water at 100°F feels much hotter than standing outside in 100°F air on a hot day.This analogy illustrates why

Accepted Answer

A)  interstellar dust is dark at optical wavelengths but bright in the infrared. 
B)  supernovae can heat their shells to such high temperatures. 
C)  an astronaut would not burn up while floating in 106 K intercloud gas. 
D)  the Solar System is immersed in a hot bubble of gas. 
E)  fusion occurs only in the cores of stars. 
A)  interstellar dust is dark at optical wavelengths but bright in the infrared. 
B)  supernovae can heat their shells to such high temperatures. 
C)  an astronaut would not burn up while floating in 106 K intercloud gas. 
D)  the Solar System is immersed in a hot bubble of gas. 
E)  fusion occurs only in the cores of stars.

Question 8

When a 3 MSUN protostar forms, it starts at the top of the Hayashi track with a luminosity of 4,000 LSUN and a temperature of 3600 K.What is its radius at this point (give the answer in units of RSUN), and how many times larger is it at this stage compared to its radius as a main-sequence star, which is about 2.5 RSUN? For reference, the Sun's temperature is 5800 K.

Accepted Answer

The Stefan-Boltzmann law says

Question 9

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 shine primarily 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 shine primarily at infrared wavelengths. 
E)  they are never as luminous as the Sun.

Question 10

Use the figure shown below to complete the following statement: A low-mass protostar remains roughly constant in ________ and decreases in ________ until it makes a turn towards the main sequence, as it follows its evolutionary track.

Accepted Answer

A)  temperature; luminosity 
B)  radius; temperature 
C)  luminosity; radius 
D)  luminosity; temperature 
E)  radius; luminosity 
A)  temperature; luminosity 
B)  radius; temperature 
C)  luminosity; radius 
D)  luminosity; temperature 
E)  radius; luminosity

Question 11

Use the figure shown below to complete the following statement: At the start of the evolution of a protostar, the radius of a 60 MSUN protostar is roughly ________ that of a 1 MSUN main-sequence star.

Accepted Answer

A)  10 times bigger than 
B)  1000 times bigger than 
C)  10 times smaller than 
D)  1000 times smaller than 
E)  the same as 
A)  10 times bigger than 
B)  1000 times bigger than 
C)  10 times smaller than 
D)  1000 times smaller than 
E)  the same as

Question 12

For an object in hydrostatic equilibrium, if the temperature inside the object were to increase, the object would

Accepted Answer

A)  expand. 
B)  contract. 
C)  implode. 
D)  remain the same size. 
E)  explode. 
A)  expand. 
B)  contract. 
C)  implode. 
D)  remain the same size. 
E)  explode.

Question 13

The H -  atom is important in protostars because it acts as a

Accepted Answer

A)  source of friction, stopping the cloud from collapsing too rapidly. 
B)  source of infrared radiation, causing the cloud to cool off rapidly. 
C)  temperature regulator. 
D)  source of buoyancy, allowing the atmosphere of the protostar to expand. 
E)  source of easily detectable radio-wave emission. 
A)  source of friction, stopping the cloud from collapsing too rapidly. 
B)  source of infrared radiation, causing the cloud to cool off rapidly. 
C)  temperature regulator. 
D)  source of buoyancy, allowing the atmosphere of the protostar to expand. 
E)  source of easily detectable radio-wave emission.

Question 14

We observe neutral hydrogen gas using

Accepted Answer

A)  X-ray radiation from highly ionized atoms. 
B)  visible radiation at 656.3 nm from recombined hydrogen. 
C)  21-cm emission. 
D)  microwave emissions. 
E)  ultraviolet radiation from helium and oxygen. 
A)  X-ray radiation from highly ionized atoms. 
B)  visible radiation at 656.3 nm from recombined hydrogen. 
C)  21-cm emission. 
D)  microwave emissions. 
E)  ultraviolet radiation from helium and oxygen.

Question 15

Herbig-Haro objects are almost always found

Accepted Answer

A)  in pairs on either side of a young protostar. 
B)  far away from molecular clouds where stars form. 
C)  close to planets that are forming around protostars. 
D)  deep inside molecular clouds. 
E)  using X-ray telescopes. 
A)  in pairs on either side of a young protostar. 
B)  far away from molecular clouds where stars form. 
C)  close to planets that are forming around protostars. 
D)  deep inside molecular clouds. 
E)  using X-ray telescopes.

Question 16

The coldest molecular clouds in our galaxy have temperatures of approximately

Accepted Answer

A)  10,000 K. 
B)  1000 K. 
C)  100 K. 
D)  10 K. 
E)  0 K. 
A)  10,000 K. 
B)  1000 K. 
C)  100 K. 
D)  10 K. 
E)  0 K.

Question 17

Why does a protostar continue to collapse as it is forming?

Accepted Answer

It continually radiates away t

Question 18

An H II region signals the presence of

Accepted Answer

A)  newly formed stars. 
B)  young stars. 
C)  ionized hydrogen gas. 
D)  O- and B-type stars. 
E)  all of these 
A)  newly formed stars. 
B)  young stars. 
C)  ionized hydrogen gas. 
D)  O- and B-type stars. 
E)  all of these

Question 19

Why do molecules readily exist in Earth's atmosphere but not in most of interstellar space?

Accepted Answer

For molecules to be created,atoms must s

Question 20

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

Accepted Answer

A)  100 MSUN stars 
B)  10 MSUN stars 
C)  1 MSUN stars 
D)  0.1 MSUN stars 
E)  0.08 MSUN stars 
A)  100 MSUN stars 
B)  10 MSUN stars 
C)  1 MSUN stars 
D)  0.1 MSUN stars 
E)  0.08 MSUN stars

Exam 15: The Interstellar Medium and Star Formation

The lowest-density gas in the interstellar medium is also the

As a protostar is evolving, its temperature

Dust reddens starlight because it

The average density of the interstellar medium is

When radiation from an object passes through the interstellar medium,

One phenomenon that can slow star formation in a molecular cloud is

Sitting in a hot tub with water at 100°F feels much hotter than standing outside in 100°F air on a hot day.This analogy illustrates why

Brown dwarfs are considered failed stars because

Use the figure shown below to complete the following statement: A low-mass protostar remains roughly constant in ________ and decreases in ________ until it makes a turn towards the main sequence, as it follows its evolutionary track.

Use the figure shown below to complete the following statement: At the start of the evolution of a protostar, the radius of a 60 MSUN protostar is roughly ________ that of a 1 MSUN main-sequence star.

For an object in hydrostatic equilibrium, if the temperature inside the object were to increase, the object would

The H - atom is important in protostars because it acts as a

We observe neutral hydrogen gas using

Herbig-Haro objects are almost always found

The coldest molecular clouds in our galaxy have temperatures of approximately

Why does a protostar continue to collapse as it is forming?

An H II region signals the presence of

Why do molecules readily exist in Earth's atmosphere but not in most of interstellar space?

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

Thinking Like an Astronomer

Patterns in the Skymotions of Earth and the Moon

Motion of Astronomical Bodies

Gravity and Orbits

Light

The Tools of the Astronomer

The Formation of Planetary Systems

The Terrestrial Planets and Earths Moon

Atmospheres of the Terrestrial Planets

Worlds of Gas and Liquidthe Giant Planets

Planetary Moons 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

Galaxies

The Milky Waya Normal Spiral Galaxy

The Expanding Universe

Cosmology

Large-Scale Structure in the Universe

Life

Filters

Use the figure shown below to complete the following statement: A low-mass protostar remains roughly constant in and decreases in until it makes a turn towards the main sequence, as it follows its evolutionary track.

Use the figure shown below to complete the following statement: At the start of the evolution of a protostar, the radius of a 60 M_SUN protostar is roughly ________ that of a 1 M_SUN main-sequence star.

The H ^- atom is important in protostars because it acts as a