Deck 19: Our Galaxy

Question 1

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

Answer 1

D

Question 2

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

Answer 2

A

Question 3

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

Answer 3

E

Question 4

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

Question 5

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.

Question 6

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

Question 7

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

Question 8

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.

Question 9

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

Question 10

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

Question 11

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

Question 12

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

Question 13

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.

Question 14

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.

Question 15

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

Question 16

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

Question 17

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

Question 18

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

Question 19

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

Question 20

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

Question 21

How do we know that halo stars are older,on average,than disk stars?

A)Halo stars orbit in random directions but disk stars have more ordered orbits.
B)There are no blue halo stars.
C)There are no red disk stars.
D)Theories of galaxy formation tell us that the halo formed earlier than the disk.
E)We see evidence for new stars forming in the disk today.

Question 22

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.

Question 23

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

Question 24

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.

Question 25

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.

Question 26

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

Question 27

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.

Question 28

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.

Question 29

Which constellation lies in the direction toward the galactic center?

A)Orion
B)the Big Dipper
C)Leo
D)Sagittarius
E)Taurus

Question 30

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.

Question 31

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

Question 32

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.

Question 33

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

Question 34

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.

Question 35

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

Question 36

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

Question 37

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

Question 38

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.

Question 39

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.

Question 40

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

Question 41

What evidence do we have that the halo 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.

Question 42

Most of the halo stars are very old.

Question 43

Most of the current star formation in the Milky Way occurs in spiral arms.

Question 44

Open clusters and young stars are generally found only in the disk of the galaxy and not in the halo.

Question 45

Briefly explain why stars that formed early in the history of the galaxy contain a smaller proportion of heavy elements than stars that formed more recently.

Question 46

The Sun is located at the edge of the galaxy,approximately 50,000 light-years from the galactic center.

Question 47

Nebulae that scatter light are bluer than the stars that illuminate them.Earth's sky is bluer than the Sun.Is this a coincidence? Explain why or why not.

Question 48

Shapley used the distribution of globular clusters in the galaxy to determine that the Sun was not at the center of the Milky Way.

Question 49

The average speed of stars relative to the Sun in the solar neighborhood is about 20 km/s.Suppose you discover a star in the solar neighborhood that is moving relative to the Sun at a much higher speed,say,200 km/s.What kind of orbit does this star probably have around the Milky Way? In what part of the galaxy does it spend most of its time? Explain.

Question 50

Briefly describe the star-gas-star cycle.

Question 51

The Milky Way looks the same in X-rays as it does at infrared wavelengths.

Question 52

Suppose you discovered a star made purely of hydrogen and helium.How old do you think it would be? Explain.

Question 53

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

Question 54

We can see most of the galaxy with visible light.

Question 55

All heavy elements are made during supernova events.

Question 56

What evidence suggests that we live inside a hot local bubble?

Question 57

Explain why,in space,"no one can hear you scream."

Question 58

Observing the galaxy at radio wavelengths allows us to see beyond the dust in the disk of the galaxy that obscures our view.

Question 59

Almost all elements heavier than hydrogen and helium were made inside stars.

Question 60

The star-gas-star cycle will continue forever because stars are continually recycling gas.

Question 61

Which of the following analogies best describes how the structure of the galaxy's spiral arms is maintained?

A)Like military jets flying in formation above a football stadium,the stars in the spiral arms keep a spiral-shaped formation as they orbit the galaxy.
B)Like cars slowing in traffic to look at an accident,stars slow as they pass through the spiral arms.
C)Like a coiling rope,the spiral arms wind up tighter with every galactic rotation.
D)Like the fins of a giant pinwheel toy,the spiral arms carry a set of bright stars around as they sweep through the galaxy.

Question 62

What produces the striking red,blue,and black colors of ionization nebulae?

Question 63

How do disk stars orbit the center of the galaxy?

A)They all orbit in roughly the same plane and in the same direction.
B)They have orbits randomly inclined and in different directions relative to the galactic center.
C)They follow spiral paths along the spiral arms.
D)They follow orbits that move up and down through the disk,typically taking them about 50,000 light-years above and below the disk on each orbit.

Question 64

What are cosmic rays?

A)another name for gamma rays and X-rays
B)fast moving dust particles in the interstellar medium
C)subatomic particles that travel close to the speed of light
D)lasers used as weapons by extraterrestrials

Question 65

The primary way that we observe the atomic hydrogen that makes up most of the interstellar gas in the Milky Way is with

A)ground-based visible-light telescopes.
B)space-based ultraviolet telescopes.
C)X-ray telescopes.
D)radio telescopes observing at a wavelength of 21 centimeters.

Question 66

Process of Science: Explain how observations of other galaxies can help us understand our own.

Question 67

How does the diameter of the disk of Milky Way Galaxy compare to its thickness?

A)The diameter and thickness are roughly equal.
B)The diameter is about 100 times as great as the thickness.
C)The diameter is about 10 times as great as the thickness.
D)The diameter is about 100,000 times as great as the thickness.

Question 68

Why do spiral arms have a blue color?

Question 69

What do we mean by the interstellar medium?

A)the dust that fills the halo of the Milky Way Galaxy
B)the middle section of the Milky Way Galaxy
C)the gas and dust that lies in between the stars in the Milky Way Galaxy
D)the name of an oracle who can channel messages from beings that live near the star called Vega

Question 70

Astronomers observe huge bubbles of hot gas,some over a thousand light-years across,in the Milky Way.What is their cause?

Question 71

What do we mean by the star-gas-star cycle?

A)It is the idea that stars in close binary systems can exchange gas with one another.
B)It is the set of nuclear reactions by which heavy elements are produced in the cores of massive stars.
C)It describes the orbits of the stars and interstellar medium around the center of the galaxy.
D)It is the continuous recycling of gas in the galactic disk between stars and the interstellar medium.

Question 72

What do we mean by a protogalactic cloud?

A)a cloud of hydrogen and helium that contracts to become a galaxy
B)a term once used historically to refer to any galaxy
C)the cloud-like halo that surrounds the disks of spiral galaxies
D)a cloud of gas that was once a galaxy

Question 73

Process of Science: How did scientists determine the location of the center of the Milky Way,and why had they been wrong in their previous estimate (where they placed the Sun near the center)?

Question 74

The Sun's location in the Milky Way Galaxy is

A)very near the galactic center.
B)in the halo of the galaxy,about 28,000 light-years above the galactic disk.
C)at the very outer edge of the galactic disk.
D)in the galactic disk,roughly halfway between the center and the outer edge of the disk.

Question 75

What are the Magellanic Clouds?

A)two small galaxies that probably orbit the Milky Way Galaxy
B)two nebulae located in the disk of the Milky Way Galaxy and visible only from the Southern Hemisphere
C)star-forming clouds found in the constellation Orion
D)the clouds of dust and gas found interspersed in many places throughout the Milky Way Galaxy

Question 76

How do we know the total mass of the Milky Way Galaxy that is contained within the Sun's orbital path?

A)by counting the number of stars visible in this region of the galaxy
B)by estimating the amount of gas and dust in between the stars
C)by using the law of conservation of angular momentum to calculate the orbital speeds of nearby stars
D)by applying Newton's version of Kepler's third law to the orbits of the Sun or other nearby stars around the center of the Galaxy

Question 77

Elements heavier than hydrogen and helium constitute about ________ of the mass of the interstellar medium.

A)0.002%
B)2%
C)70%
D)98%

Question 78

Most stars in the Milky Way's halo are

A)very old.
B)found inside molecular clouds.
C)very young.
D)blue or white in color.

Question 79

What do we call the bright,sphere-shaped region of stars that occupies the central few thousand light-years of the Milky Way Galaxy?

A)the galaxy's disk
B)the galaxy's bulge
C)a globular cluster
D)the galaxy's halo

Question 80

Process of Science: The theory of spiral arms explain why short-lived,massive stars are found there but longer-lived,low mass stars should last for many orbits around a galaxy and therefore be much more spread out.How might you test that prediction?