Deck 9: The Milky Way Galaxy

Question 1

Why do radio maps of our galaxy show spiral arms?

A)The arms have larger Doppler shifts.
B)The gas in the spiral arms is very hot.
C)The dust in spiral arms is denser.
D)The gas in spiral arms is denser.

Answer 1

The gas in spiral arms is denser.

Question 2

Which of the following is believed to make up most of the extended galactic halo?

A)dark matter
B)faint brown dwarfs
C)G, K, and M stars
D)globular clusters

Answer 2

dark matter

Question 3

If other galaxies are like the Milky Way,which parts of them should contain luminous O and B type stars?

A)the halos
B)the bulges
C)the spiral arms
D)the globular clusters

Answer 3

the spiral arms

Question 4

Why are O and B stars good tracers of spiral structure?

A)They are young and luminous.
B)They are old and have been part of the galaxy for a long time.
C)They are young and moving with large radial velocities.
D)They were formed in the galaxy's halo.

Question 5

Which of the following can be determined using the period-luminosity relation?

A)the radius of the bulge of our galaxy
B)the mass of a star for which the distance is known
C)the temperature of a star for which we know the luminosity
D)the distance to open clusters that contain Cepheid variables

Question 6

Which constellation lies in the direction of the centre of our galaxy?

A)Orion
B)Sagittarius
C)Ursa Major
D)Monoceros

Question 7

What is the main component of the central bulge of our galaxy?

A)gas and dust
B)population I stars
C)stars associated with the spherical component of our galaxy
D)stars associated with the disk component of our galaxy

Question 8

Our galaxy is suspected to be surrounded by a dark halo.What is it about the disk of the galaxy that makes us suspect this?

A)It rotates faster than expected in its outer region.
B)It rotates more slowly than expected in its outer region.
C)It is only visible during a total eclipse of our Sun.
D)It is surrounded above, below, and well beyond by the brightly glowing corona.

Question 9

What part of the Milky Way contains mostly old stars and globular clusters?

A)the spiral arms
B)the spherical halo component
C)the smooth disk component
D)the nucleus

Question 10

If spiral density waves were the only thing producing spiral arms,what result would be expected?

A)All spiral arms would be gas- and dust-free.
B)All galaxies would have only two smooth spiral arms.
C)The Milky Way would show an irregular pattern of short arms.
D)The halo component of the Milky Way would show spiral arms as well.

Question 11

Who first calibrated the Cepheid variable stars for use in determining distance?

A)Edwin Hubble
B)Henrietta Leavitt
C)Carl Sagan
D)Harlow Shapley

Question 12

Why do younger stars have more heavy elements?

A)because old stars destroy heavy elements as they age
B)because the heavy elements were made in previous generations of stars
C)because young stars burn their nuclear fuels faster
D)because heavy elements haven't had time to settle to the core of these younger stars

Question 13

Which of the following is NOT a characteristic of the stars of the disk component of our galaxy?

A)young stars
B)randomly inclined orbits
C)circular orbits
D)higher metal abundance

Question 14

The age of the Milky Way galaxy has been estimated to be at least 13 billion years.What is this estimate based on?

A)observations of globular clusters
B)observations of open clusters
C)21-cm radiation from H I regions
D)radiation produced at the centre of the galaxy

Question 15

Why are stars like the Sun a poor tracer of the Milky Way's spiral structure?

A)The spiral arms do not contain any solar-type stars.
B)Stars like the Sun are extremely rare.
C)Stars like the Sun were formed before the galaxy's disk.
D)Stars like the Sun have moved away from their original birthplaces.

Question 16

Where are Population II stars found?

A)in the galaxy's globular clusters
B)in the disk of the galaxy
C)in the centre of the galaxy
D)in the galaxy's spiral arms

Question 17

What kind of orbits did the first stars to form in our galaxy have?

A)circular orbits
B)hyperbolic orbits
C)slightly elliptical orbits, all in the same plane
D)highly elongated elliptical orbits

Question 18

What type of radiation do we detect from the energy source at the centre of our galaxy?

A)X-rays
B)visible light
C)ultraviolet light
D)gamma rays

Question 19

Who first noticed that for Cepheid variable stars there was a direct relationship between the luminosity and the period of the variation in their brightness?

A)Annie Cannon
B)Edwin Hubble
C)Harlow Shapley
D)Henrietta Leavitt

Question 20

What does the chemical abundance found in population I stars tell us about them?

A)It indicates that they are all massive stars.
B)It indicates that they were formed before the population II stars.
C)It indicates that they contain very few heavy metals compared to halo stars.
D)It indicates that the material they formed from had been enriched with material from supernovae.

Question 21

Refer to the figure.If you observe the period of a type II Cepheid and mistakenly think it's a type I Cepheid,what incorrect conclusion will you draw?

A)You will measure the wrong period.
B)You will think the Cepheid is farther away than it actually is.
C)You will think the Cepheid is closer than it actually is.
D)You will think the Cepheid is less luminous than it actually is.

Question 22

Before the twentieth century,astronomers lacked knowledge of something,and this caused them to think that the Sun was at the centre of our star system.What was that something?

A)globular clusters
B)Cepheid variable stars
C)the dimming effects of gas and dust
D)galactic rotation

Question 23

According to the traditional theory,how did the galaxy form?

A)from a large cloud of material that broke off a larger galaxy
B)from the collapse of a large spherical cloud of gas that was rotating very slowly
C)from material that had been ejected in the violent explosion of a dying galaxy
D)as a result of mergers between several smaller groups of gas, dust, and stars

Question 24

Refer to the figure.Why is it more difficult to measure the distances to globular clusters (which contain RR Lyrae stars)than the distances to open clusters (which contain Cepheids)?

A)RR Lyrae stars are dimmer and harder to see.
B)RR Lyrae stars pulsate so fast that they can't be measured.
C)RR Lyrae stars are further away than Cepheids.
D)RR Lyrae stars do not have a relationship between period and luminosity.

Question 25

How did Harlow Shapley determine where the centre of the galaxy lies?

A)He plotted the distribution of open clusters.
B)He plotted the distribution of globular clusters.
C)He made star counts in every direction of the galactic disk.
D)He measured the amount of dust obscuration in every direction of the galactic disk.

Question 26

The centre of our galaxy is believed to be occupied by the radio source known as ____________________.

Question 27

How does the traditional theory of the formation of the galaxy explain the origin of globular clusters?

A)They formed in the disk and were later ejected to the halo.
B)They built up over time from the collisions of stars in the halo.
C)They formed in other galaxies and were captured by close interactions.
D)They formed early on during the free-fall collapse of the proto-galactic material.

Question 28

In the diagram,the approximate absolute magnitude of a Type II Cepheid with a period of 30 days is _________________.

Question 29

What do radio maps of the spiral arms of our galaxy show?

A)They reveal that our galaxy is a grand design spiral.
B)They map the location of dense neutral hydrogen clouds.
C)They reveal that the Sun is currently located in the centre of a spiral arm.
D)They map the location of hot O and B stars by the radio radiation they emit.

Question 30

____________________ are groups of 100,000 to 1,000,000 population II stars firmly bound together by gravity.

Question 31

Which of the following is NOT explained by the traditional theory of the formation of our galaxy?

A)the existence of the nuclear bulge
B)the existence of the disk of the galaxy
C)the fact that the oldest stars in the galaxy are not metal-free
D)the difference in metal abundance of the population I and II stars

Question 32

Refer to the figure.Polaris is a Type I Cepheid with a period of 4 days.What is its absolute magnitude?

A)+1
B)0.0
C)-1.0
D)-3.5

Question 33

The __________________ of the galaxy contains population I stars,open clusters,and gas clouds.

Question 34

What is the best evidence that Sagittarius A* is a black hole at the centre of the Milky Way galaxy?

A)Orbits of stars indicate a mass several million times that of the Sun within a very small volume.
B)Sagittarius A* is a powerful radio source.
C)No visible light from Sagittarius A* reaches the Earth.
D)Radio maps of the region around Sagittarius A* show complicated gas structures believed to be related to massive star formation.

Question 35

What are the orbits of population I stars like?

A)circular, confined to the disk of the galaxy
B)very elliptical, confined to the disk of the galaxy
C)very elliptical, randomly inclined to the disk of the galaxy
D)circular, randomly inclined to the disk of the galaxy

Question 36

How did Harlow Shapley use the period-luminosity relationship of RR Lyrae variable stars to determine the size of the Milky Way galaxy?

A)He found the distances to open clusters found throughout the disk of the galaxy.
B)He found the distances to individual variables free-floating in the halo of the galaxy.
C)He determined the proper motion of globular clusters in the outer disk of the galaxy.
D)He found the distances to globular clusters distributed about the centre of the galaxy.

Question 37

If a star with a high speed with respect a typical disk star is found,what other property would you expect it to have?

A)young age
B)high luminosity
C)low metal content compared to the Sun
D)high mass

Question 38

Which of the following are associated with the spiral arms of a galaxy?

A)young, massive stars
B)nuclear bulges
C)metal-poor stars
D)million-solar-mass black holes

Question 39

What behaviour of galactic rotation curves suggests the existence of dark matter in an extended halo?

A)Small velocities are seen at large distances from the galactic centre.
B)Small velocities are seen at distances close to the galactic centre.
C)Large velocities are seen at large distances from the galactic centre.
D)Large velocities are seen at distances close to the galactic centre.

Question 40

Refer to the figure.A Type II Cepheid with a period of 10 days has been located in a distant globular cluster.What is the star's absolute magnitude?

A)-6
B)-4
C)-1
D)0

Question 41

The disk of the galaxy is older than the halo.

Question 42

Giant molecular cloud complexes are located in spiral arms.

Question 43

The centre of our galaxy shows signs of past eruptions.

Question 44

The rotation curve of the galaxy provides evidence for the existence of the ____________________ that extends beyond the halo of the galaxy.

Question 45

What is the difference between an open cluster,an association,and a globular cluster? In which parts of the galaxy is each found?

Question 46

The orbits of halo stars are typically circular and have a low inclination with respect to the disk.

Question 47

The density wave theory explains spurs and branches along the spiral arms.

Question 48

The disk of the Milky Way is approximately 20,000 light years in diameter.

Question 49

Why are Cepheid variable stars important in our study of the Milky Way galaxy?

Question 50

The rapid rotation of the outer disk suggests that our galaxy is more massive than previously thought.

Question 51

Why does the rotation of our galaxy suggest that it is more massive than previously thought?

Question 52

The centre of our galaxy is located in the direction of the constellation of Orion.

Question 53

Harlow Shapley found the distance to the centre of the galaxy by studying the distance to open clusters.

Question 54

Globular clusters are primarily found in the _________________ component of the galaxy.

Question 55

Spiral tracers tend to be old,luminous stars.

Question 56

What is the difference between a population I star and a population II star?

Question 57

Old stars are poor in heavy atoms because there were very few previous generations of stars before the old stars formed.

Question 58

The period-luminosity relationship is primarily used for main sequence stars.

Question 59

Henrietta Leavitt discovered the period-luminosity relationship for __________________.

Question 60

Population II stars contain more metals than Population I stars.

Question 61

Why does the average chemical composition of stars now forming differ from that of older stars?

Question 62

How do theories of the origin of the Milky Way explain its halo?

Question 63

How does the density wave theory explain the presence of young stars in the spiral arms?

Question 64

What evidence do we have that the centre of our galaxy is a powerful source of energy? A massive black hole?

Question 65

Discuss how Harlow Shapley determined the structure of the Milky Way galaxy from his study of globular clusters.

Question 66

Why are all spiral tracers young?

Question 67

Discuss how astronomers know that our galaxy contains spiral arms in its disk.

Question 68

Compare and contrast the properties of disk and halo stars.

Question 69

Describe the central few light-years of our galaxy.