Question 1

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

Accepted Answer

Hot intercloud gas is heated b

Question 2

Interstellar clouds are

Accepted Answer

A)  hydrogen gas condensed out of the interstellar medium, like water clouds in Earth's atmosphere. 
B)  regions where hydrogen tends to be denser than the surrounding gas. 
C)  regions where water condenses out of the interstellar medium. 
D)  oxygen gas condensed out of the interstellar medium, like water clouds in Earth's atmosphere. 
E)  regions where hydrogen combines with oxygen to create water molecules. 
A)  hydrogen gas condensed out of the interstellar medium, like water clouds in Earth's atmosphere. 
B)  regions where hydrogen tends to be denser than the surrounding gas. 
C)  regions where water condenses out of the interstellar medium. 
D)  oxygen gas condensed out of the interstellar medium, like water clouds in Earth's atmosphere. 
E)  regions where hydrogen combines with oxygen to create water molecules.

Question 3

Molecular hydrogen atoms can be found

Accepted Answer

A)  nowhere in the universe. 
B)  in dense clouds where they are shielded from stellar radiation. 
C)  only in the disk surrounding forming protostars. 
D)  in low-density clouds of hot gas surrounding hot stars. 
E)  only in the atmospheres of the giant planets, such as Jupiter. 
A)  nowhere in the universe. 
B)  in dense clouds where they are shielded from stellar radiation. 
C)  only in the disk surrounding forming protostars. 
D)  in low-density clouds of hot gas surrounding hot stars. 
E)  only in the atmospheres of the giant planets, such as Jupiter.

Question 4

Why do stars form most often within molecular clouds?

Accepted Answer

Because that is wher

Question 5

Describe how planets form around a forming star, and at least two physical processes that will affect that planet's eventual suitability for life.

Accepted Answer

Planets form from gas in the disk around

Question 6

Explain why a star of higher mass must have a higher core temperature.

Accepted Answer

The higher the mass of the star,the larg

Question 7

The images in the figure below are both of the Milky Way.Why can more detail be seen in the infrared image than in the visible light image?

Accepted Answer

The dark spots in the visible

Question 8

When looking at the space between stars, what are you most likely to see?

Accepted Answer

A)  nothing; it is empty 
B)  spacecraft 
C)  gas 
D)  dark matter 
E)  planets 
A)  nothing; it is empty 
B)  spacecraft 
C)  gas 
D)  dark matter 
E)  planets

Question 9

The figure below shows the spectrum of a star as it was emitted the star (right), and the spectrum after the light from this star has passed through a cloud of interstellar dust.After the star's light has passed through the dust, the star appears

Accepted Answer

A)  twice as bright as before, but redder. 
B)  the same brightness, but redder than before. 
C)  half as bright, but bluer. 
D)  more than 10 times dimmer, and much redder. 
E)  non-existent; its light is completely blocked and only the emission from the dust is seen. 
A)  twice as bright as before, but redder. 
B)  the same brightness, but redder than before. 
C)  half as bright, but bluer. 
D)  more than 10 times dimmer, and much redder. 
E)  non-existent; its light is completely blocked and only the emission from the dust is seen.

Question 10

What critical event transforms a protostar into a normal main-sequence star?

Accepted Answer

A)  Planets form in the accretion disk. 
B)  The star grows suddenly larger in radius. 
C)  Triple-alpha reactions begin in the core. 
D)  Nuclear fusion begins in the core. 
E)  Convection begins throughout the star's interior. 
A)  Planets form in the accretion disk. 
B)  The star grows suddenly larger in radius. 
C)  Triple-alpha reactions begin in the core. 
D)  Nuclear fusion begins in the core. 
E)  Convection begins throughout the star's interior.

Question 11

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 12

A protostar is

Accepted Answer

A)  in hydrostatic equilibrium as it collapses. 
B)  not in hydrostatic equilibrium as it collapses. 
C)  heated to millions of degrees as it collapses. 
D)  flattened into a disk as it collapses. 
E)  powered by chemical reactions. 
A)  in hydrostatic equilibrium as it collapses. 
B)  not in hydrostatic equilibrium as it collapses. 
C)  heated to millions of degrees as it collapses. 
D)  flattened into a disk as it collapses. 
E)  powered by chemical reactions.

Question 13

Radio waves with 21-cm wavelengths are important because they

Accepted Answer

A)  allow us to study the deep interiors of stars. 
B)  allow us to image magnetic fields directly. 
C)  allow us to study neutral hydrogen in the interstellar medium. 
D)  is produced by every object in the universe. 
E)  is the longest wavelength of light that can be naturally produced. 
A)  allow us to study the deep interiors of stars. 
B)  allow us to image magnetic fields directly. 
C)  allow us to study neutral hydrogen in the interstellar medium. 
D)  is produced by every object in the universe. 
E)  is the longest wavelength of light that can be naturally produced.

Question 14

How are typical interstellar gas clouds different from the clouds that we see in Earth's sky?

Accepted Answer

ISM gas clouds are mostly made

Question 15

We detect neutral gas in the interstellar medium by looking for radiation at 21 cm that arises when

Accepted Answer

A)  an electron moves from the n = 1 to n = 2 state in a hydrogen atom. 
B)  an electron is ionized from a hydrogen atom. 
C)  carbon monoxide (CO) gas is excited by stellar radiation. 
D)  an electron's magnetic poles flip and align with the magnetic poles of a proton in a hydrogen atom. 
E)  an electron combines with a proton to make a hydrogen atom. 
A)  an electron moves from the n = 1 to n = 2 state in a hydrogen atom. 
B)  an electron is ionized from a hydrogen atom. 
C)  carbon monoxide (CO) gas is excited by stellar radiation. 
D)  an electron's magnetic poles flip and align with the magnetic poles of a proton in a hydrogen atom. 
E)  an electron combines with a proton to make a hydrogen atom.

Question 16

Why do molecular clouds collapse from the inside out?

Accepted Answer

The innermost core of a molecular cloud

Question 17

In the densest molecular clouds, the average density is approximately 300 atoms/cm3.If a cube of molecular cloud gas with this density contained 100 MSUN of material (the amount needed to make a 1 MSUN star), what would be the length of a side of the cube in units of AU? For reference, the mass of the Sun is 2 *1030 kg, the mass of a hydrogen atom is 1.7 *10 - 27 kg, and 1 AU = 1.5 *1011 m.

Accepted Answer

If the one side of the cube has length X

Question 18

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 19

What is the difference between interstellar extinction and interstellar reddening?

Accepted Answer

Interstellar extinction is the decrease

Question 20

Suppose the 21-cm photon of neutral hydrogen were instead emitted at 500 nm (i.e., a visible blue photon).Would it still be a useful probe of the Milky Way's structure? Why?

Accepted Answer

No,it would not,because the light emitte

Exam 15: The Interstellar Medium and Star Formation

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

Interstellar clouds are

Molecular hydrogen atoms can be found

Why do stars form most often within molecular clouds?

Describe how planets form around a forming star, and at least two physical processes that will affect that planet's eventual suitability for life.

Explain why a star of higher mass must have a higher core temperature.

The images in the figure below are both of the Milky Way.Why can more detail be seen in the infrared image than in the visible light image?

When looking at the space between stars, what are you most likely to see?

The figure below shows the spectrum of a star as it was emitted the star (right), and the spectrum after the light from this star has passed through a cloud of interstellar dust.After the star's light has passed through the dust, the star appears

What critical event transforms a protostar into a normal main-sequence star?

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

A protostar is

Radio waves with 21-cm wavelengths are important because they

How are typical interstellar gas clouds different from the clouds that we see in Earth's sky?

We detect neutral gas in the interstellar medium by looking for radiation at 21 cm that arises when

Why do molecular clouds collapse from the inside out?

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

What is the difference between interstellar extinction and interstellar reddening?

Suppose the 21-cm photon of neutral hydrogen were instead emitted at 500 nm (i.e., a visible blue photon).Would it still be a useful probe of the Milky Way's structure? Why?

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