Chapter 19

What is the diameter of the disk of the Milky Way?
A) 100 light-years
B) 1,000 light-years
C) 10,000 light-years
D) 100,000 light-years
E) 1,000,000 light-years

D) 100,000 light-years

What is the thickness of the disk of the Milky Way?
A) 100 light-years
B) 1,000 light-years
C) 10,000 light-years
D) 100,000 light-years
E) 1,000,000 light-years

B) 1,000 light-years

What kinds of objects lie in the halo of our galaxy?
A) open clusters
B) O and B stars
C) globular clusters
D) gas and dust
E) all of the above

C) globular clusters

What kinds of objects lie in the disk of our galaxy?
A) open clusters
B) O and B stars
C) old K and M stars
D) gas and dust
E) all of the above

E) all of the above

Which of the following comprise the oldest members of the Milky Way?
A) the Sun and other solar mass stars
B) O stars
C) red giant stars in spiral arms
D) Cepheid variables
E) globular clusters

E) globular clusters

What makes up the interstellar medium?
A) open clusters
B) O and B stars
C) K and M stars
D) gas and dust
E) all of the above

D) gas and dust

If you were to take a voyage across the Milky Way, what kind of material would you spend most of your time in?
A) empty space–a pure vacuum
B) dusty molecular clouds
C) star clusters
D) warm, rarefied clouds of atomic hydrogen
E) cool, dense clouds of atomic hydrogen

D) warm, rarefied clouds of atomic hydrogen

How does the interstellar medium obscure our view of most of the galaxy?
A) It produces so much visible light that it is opaque and blocks our view of anything beyond it.
B) It reflects most light from far distances of the galaxy away from our line of sight.
C) It absorbs all wavelengths of light.
D) It absorbs visible, ultraviolet, and some infrared light.
E) all of the above

D) It absorbs visible, ultraviolet, and some infrared light.

How can we see through the interstellar medium?
A) by observing in high-energy wavelengths such as X rays and long wavelengths of light such as radio waves
B) by observing only the brightest visible sources
C) by using only the biggest telescopes
D) by using telescopes above the Earth's atmosphere
E) We cannot see through the interstellar medium.

A) by observing in high-energy wavelengths such as X rays and long wavelengths of light such as radio waves

Harlow Shapley concluded that the Sun was not in the center of the Milky Way Galaxy by
A) looking at the shape of the "milky band" across the sky.
B) mapping the distribution of stars in the galaxy.
C) mapping the distribution of globular clusters in the galaxy.
D) mapping the distribution of gas clouds in the spiral arms.
E) looking at other nearby spiral galaxies.

C) mapping the distribution of globular clusters in the galaxy.

Approximately how far is the Sun from the center of the galaxy?
A) 27 light-years
B) 270 light-years
C) 2,700 light-years
D) 27,000 light-years
E) 27 million light-years

D) 27,000 light-years

What do astronomers consider heavy elements?
A) elements that are heavier than iron
B) elements that are heavier than carbon
C) elements that are heavier than hydrogen
D) elements that are heavier than uranium
E) all elements besides hydrogen and helium

E) all elements besides hydrogen and helium

Where are most heavy elements made?
A) in the interstellar medium
B) in stars and supernovae
C) in the Big Bang, when the universe first began
D) none of the above
E) all of the above

B) in stars and supernovae

Why are we unlikely to find Earth-like planets around halo stars in the Galaxy?
A) Planets around stars are known to be extremely rare.
B) Halo stars formed in an environment where there were few heavy elements to create rocky planets.
C) Any such planets would have been ejected long ago by galactic mergers.
D) Halo stars do not have enough mass to hold onto planets.
E) Halo stars formed in a different way from disk stars.

B) Halo stars formed in an environment where there were few heavy elements to create rocky planets.

How are interstellar bubbles made?
A) by the collapse of a gas cloud to form stars
B) by planetary nebulae from low-mass stars
C) by the winds of massive stars and supernovae
D) by collisions between galaxies
E) by the rapidly rotating magnetic fields of pulsars

C) by the winds of massive stars and supernovae

What is a superbubble?
A) a very low-density region of interstellar space, formed by the merger of several bubbles
B) a very high-density region of interstellar space, filled with gas ejected from nearby star
systems
C) a bubble so large that it fills much of the galactic halo
D) the region of space cleared by a powerful supernova
E) a cloud of gas that can form a million or more stars

A) a very low-density region of interstellar space, formed by the merger of several bubbles

Sound waves in space
A) do not exist.
B) travel so slowly that they are unnoticeable.
C) travel much faster than sound on Earth but have such low density that they are inaudible.
D) travel much faster than sound on Earth and are therefore very loud.
E) can travel through the halo but not the disk of the galaxy.

C) travel much faster than sound on Earth but have such low density that they are inaudible.

What is a shock front?
A) a wave of pressure that moves faster than the speed of sound
B) a wave of pressure that moves slightly slower than the speed of sound
C) a wave of pressure that moves faster than the speed of light
D) a wave of electromagnetic energy that can create electrical shocks
E) the wave created when protons slam into electrons

A) a wave of pressure that moves faster than the speed of sound

What are cosmic rays?
A) subatomic particles that travel close to the speed of light
B) gamma rays and X rays
C) fast-moving dust particles in the interstellar medium
D) any light waves from space
E) lasers used as weapons by extraterrestrials

A) subatomic particles that travel close to the speed of light

What can cause a galactic fountain?
A) winds and jets from newly-formed protostars
B) a supernova occurring in the halo
C) multiple supernovae occurring together
D) the combined effect of spiral density waves
E) molecular clouds falling towards the galactic center

C) multiple supernovae occurring together

What is the galactic fountain model?
A) the idea that there is a lot of interstellar water vapor
B) the theory that the Milky Way is a spiral galaxy and looks like a whirlpool from above
C) the theory that hot, ionized gas blows out of the galactic center like a jet or fountain
D) the theory that hot, ionized gas blown out of the galactic disk and into the halo by superbubbles cools down and falls back into the disk
E) none of the above

D) the theory that hot, ionized gas blown out of the galactic disk and into the halo by superbubbles cools down and falls back into the disk

What evidence supports the galactic fountain model?
A) We see a jet of ionized gas shooting out of the bulge of our galaxy.
B) We have mapped several spiral arms of the Milky Way Galaxy.
C) We see hot gas above the disk of the galaxy and cool gas that appears to be raining down from the halo.
D) We have observed a lot of water molecules in the interstellar medium.
E) We have no evidence yet for the galactic fountain model.

C) We see hot gas above the disk of the galaxy and cool gas that appears to be raining down from the halo.

What is the most common form of gas in the interstellar medium?
A) molecular hydrogen
B) molecular helium
C) atomic hydrogen
D) atomic helium
E) ionized hydrogen

C) atomic hydrogen

What produces the 21-cm line that we use to map out the Milky Way Galaxy?
A) atomic hydrogen
B) ionized hydrogen
C) molecular hydrogen
D) carbon monoxide
E) helium

A) atomic hydrogen

Where do most dust grains form?
A) in supernovae
B) in the winds of red giant stars
C) in planetary nebulae
D) in molecular clouds
E) all of the above

B) in the winds of red giant stars

Suppose you read somewhere that 10 percent of the matter in the Milky Way is in the form of dust grains. Should you be surprised? If so, why?
A) There is nothing surprising about 10 percent of the matter being dust grains because dust grains are the material from which stars are born.
B) Given how easily dust grains form, 10 percent is a surprisingly low fraction of material to be in that form.
C) Ten percent is surprisingly high because dust grains can form only at low temperatures.
D) The 10 percent figure cannot be correct, because dust grains are solid but only about 2 percent of the matter in our galaxy is made of anything besides hydrogen and helium.

D) The 10 percent figure cannot be correct, because dust grains are solid but only about 2 percent of the matter in our galaxy is made of anything besides hydrogen and helium.

The image of our galaxy in radio emission from CO, mapping the distribution of molecular clouds, is closest to the image of our galaxy in
A) 21-cm-line radio emission from atomic hydrogen.
B) visible light, showing the edges of supernova bubbles.
C) visible light, which is closest to how the night sky appears from Earth.
D) X rays from hot gas bubbles in the disk.
E) infrared emission from interstellar dust grains.

E) infrared emission from interstellar dust grains.

Compared with our Sun, most stars in the halo are
A) young, red, and dim and have fewer heavy elements.
B) young, blue, and bright and have much more heavy element material.
C) old, red, and dim and have fewer heavy elements.
D) old, red, and dim and have much more heavy element material.
E) old, red, and bright and have fewer heavy elements.

C) old, red, and dim and have fewer heavy elements.

Compared with stars in the disk, orbits of stars in the halo
A) are relatively uniform to each other.
B) are elliptical, with random orientation.
C) are elliptical but orbiting in the same direction.
D) do not have to be around the galactic center.
E) do not have to pass through the plane of the galaxy.

B) are elliptical, with random orientation.

Approximately how long does it take the Sun to orbit the Milky Way Galaxy?
A) 23,000 years
B) 230,000 years
C) 2.3 million years
D) 230 million years
E) 23 billion years

D) 230 million years

Where does most star formation occur in the Milky Way today?
A) in the halo
B) in the bulge
C) in the spiral arms
D) in the Galactic center
E) uniformly throughout the Galaxy

C) in the spiral arms

How do we know that spheroidal stars are older, on average, than disk stars?
A) Spheroidal stars orbit in random directions but disk stars have more ordered orbits.
B) There are no blue spheroidal stars.
C) There are no red disk stars.
D) Theories of galaxy formation tell us that the spheroid formed earlier than the disk.
E) We see evidence for new stars forming in the disk today.

B) There are no blue spheroidal stars.

Which of the following statements about globular clusters is false?
A) Globular clusters contain many thousands of stars.
B) Globular cluster stars are more than 12 billion years old.
C) Globular cluster ages increase with distance from the Milky Way.
D) Globular clusters are distributed spherically around the Milky Way.
E) Globular cluster stars are very metal-poor relative to the Sun.

C) Globular cluster ages increase with distance from the Milky Way.

Which of the following statements about the disk of the Milky Way is false?
A) The average age of disk stars is less than that of halo stars.
B) Disk stars are all younger than 5 billion years.
C) Disk stars have a higher proportion of heavy elements, on average, than halo stars.
D) Disk stars orbit in the same direction around the Galactic center.
E) The length of the disk is about 100 times its thickness.

B) Disk stars are all younger than 5 billion years.

Which of the following statements about halo stars is false?
A) Halo stars have random orbits about the Milky Way center.
B) Halo stars are no longer being formed at the current epoch.
C) All halo stars are less massive than our Sun.
D) Halo stars are made entirely of hydrogen and helium with no heavy elements.
E) Halo stars are some of the oldest known objects in the universe.

D) Halo stars are made entirely of hydrogen and helium with no heavy elements.

What evidence suggests that the protogalactic cloud that formed the Milky Way resulted from several collisions among smaller clouds?
A) The stars in the halo of the Milky Way are organized into several dense clusters arranged throughout the halo.
B) The Milky Way resembles an elliptical galaxy more than other spirals do.
C) Halo stars differ in age and heavy-element content, but these variations do not seem to depend on the stars' distance from the galactic center.
D) The bulge of the Milky Way is surrounded by many globular clusters, just as elliptical galaxies are.
E) The Milky Way is the central galaxy of a cluster of galaxies.

C) Halo stars differ in age and heavy-element content, but these variations do not seem to depend on the stars' distance from the galactic center.

Which constellation lies in the direction toward the galactic center?
A) Orion
B) the Big Dipper
C) Leo
D) Sagittarius
E) Taurus

D) Sagittarius

How do we learn about what is going on in the center of our own galaxy (the Milky Way)?
A) We have learned it only recently, thanks to the great photographs obtained by the Hubble Space Telescope.
B) We cannot see the galactic center with visible or ultraviolet light, but radio and X rays from the center can be detected.
C) The gas and dust in the Milky Way prevent any type of direct observation of the galactic center, but theoretical models allow us to predict what is happening there.
D) We must look at the centers of other galaxies and hope that ours is just like others.
E) We can study it with visible telescopes as with any other star in the Galaxy.

B) We cannot see the galactic center with visible or ultraviolet light, but radio and X rays from the center can be detected.

Which of the following does not accurately describe what we observe toward the Galactic center?
A) at radio wavelengths, we see giant gas clouds threaded by powerful magnetic fields
B) at infrared wavelengths, we see a massive stellar cluster
C) at optical wavelengths, we see a cluster of old, red stars
D) at X rays, we see faint emission from an accretion disk around a black hole

C) at optical wavelengths, we see a cluster of old, red stars

What evidence supports the theory that there is a black hole at the center of our galaxy?
A) We observe an extremely bright X-ray source at the center of our galaxy.
B) We can see gas falling into an accretion disk and central mass at the center of our galaxy.
C) The motions of the gas and stars at the center indicate that it contains a million solar masses within a region only about 1 parsec across.
D) We observe a large, dark object that absorbs all light at the center of our galaxy.
E) all of the above

C) The motions of the gas and stars at the center indicate that it contains a million solar masses within a region only about 1 parsec across.

What is SgrA*?
A) a source of bright X-ray emission coming from the entire constellation of Sagittarius
B) a source of bright radio emission in the center of our galaxy
C) a source that is bright in the visible wavelengths in the center of our galaxy
D) the brightest star in the constellation Sagittarius
E) the bulge at the center of our galaxy

B) a source of bright radio emission in the center of our galaxy

What evidence do we have that the spheroidal population of stars are older than other stars in the galaxy?
A) They are farther away
B) They have higher masses than other stars in the galaxy
C) They have fewer planets
D) They have a smaller proportion of heavy elements
E) They move slower than other stars in the galaxy

D) They have a smaller proportion of heavy elements