Deck 12: The Milky Way Galaxy

Question 1

The age of the Milky Way galaxy has been estimated to be at least 13 billion years based on

A) observations of globular clusters.
B) observations of open clusters.
C) 21-cm radiation from H I regions.
D) the rotation curve of the galaxy.
E) the energy produced by Sagittarius A*.

Answer 1

observations of globular clusters.

Question 2

Pulsating variable stars are useful in determining

A) the mass of a star for which the distance is known.
B) the temperature of a star for which we know the luminosity.
C) the radius of the bulge of our galaxy.
D) the distance to globular clusters.
E) the mass of the Milky Way galaxy.

Answer 2

the distance to globular clusters.

Question 3

CO observations of the galaxy reveal

A) the location of dense neutral hydrogen clouds.
B) the location of population II stars.
C) the location of population I stars.
D) the location of the galactic corona.
E) the location of giant molecular clouds.

Answer 3

the location of giant molecular clouds.

Question 4

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

A) circular orbits
B) randomly inclined orbits
C) higher metal abundance
D) young stars
E) star-formation regions

Question 5

____ of the Milky Way contains mostly old (population II) stars and globular clusters.

A) The disk component
B) The spherical halo component
C) The hydrogen gas in the disk
D) The spiral arms
E) Sgr A^*

Question 6

____ in other galaxies should contain luminous O and B stars if they are like the Milky Way.

A) The halos
B) The bulges
C) The spiral arms
D) The globular clusters
E) The coronas

Question 7

If the spiral density wave were the only thing producing spiral arms, it would be expected that

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 and irregular pattern of short arms .
D) the Milky Way wouldn't have any spiral arms.
E) the halo component of the Milky Way would show spiral arms as well.

Question 8

The first stars to form in our galaxy

A) had circular orbits.
B) had highly elongated elliptical orbits.
C) were population I stars.
D) all had orbits in the same plane.
E) formed the galactic clusters we see today.

Question 9

Radio maps of our galaxy show spiral arms because

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.
E) the stars in the spiral arms emit most of their energy at radio wavelengths.

Question 10

Younger stars have more heavy elements because

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

Question 11

Our galaxy is suspected to be surrounded by a galactic halo or corona because the disk of the galaxy

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

Question 12

Who first used RR Lyrae variable stars to determine distances in our Milky Way Galaxy?

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

Question 13

Who first determined that the energy/s emitted by (luminosity of) Cepheid variable stars is larger the longer their period of variation is?

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

Question 14

The galactic halo or corona is believed to contain mostly

A) O and B stars.
B) G, K, and M stars.
C) open clusters.
D) globular clusters.
E) dark matter.

Question 15

An approximately spherical cluster of over 100,000 stars that formed at the same time long ago in our galaxy is

A) a globular cluster.
B) an open cluster.
C) an association.
D) a spherical component
E) an accretion disk.

Question 16

The center of our galaxy lies in the direction of (but far beyond) the stars in the constellation of

A) Ursa Minor.
B) Ursa Major.
C) Sagittarius.
D) Orion.
E) Monoceros.

Question 17

Good tracers of the spiral arms of our galaxy are all

A) I & III
B) I & IV
C) II & III
D) II & IV
E) I, III, & IV

Question 18

Population II stars

A) III & IV
B) I & II
C) II
D) IV
E) I, II, & III

Question 19

The energy source at the center of our galaxy

A) is not visible at optical wavelengths.
B) produces X-rays.
C) must be less than 10 AU in diameter.
D) all of the above.
E) none of the above.

Question 20

The chemical abundance of population I stars

A) indicates that they were formed before the population II stars.
B) indicates that the material they formed from had been enriched with material from supernovae.
C) indicates that they contain very few heavy metals compared to halo stars.
D) depends on the temperature of the star.
E) depends on the mass of the star.

Question 21

The mass of the black hole at the center of our galaxy can be estimated using the ____ of a star orbiting it.

A) semi-major axis
B) orbital period
C) Both answers a and b
D) Neither answer a nor b

Question 22

The orbits of population I stars

A) I
B) IV
C) I & IV
D) II & IV
E) I & III

Question 23

Radio maps of the spiral arms of our galaxy

A) reveal that our galaxy is a grand design spiral.
B) map the location of hot O and B stars by the radio radiation they emit.
C) reveal that the spiral arms are winding up and growing closer together.
D) reveal that the sun is currently located in the center of a spiral arm.
E) map the location of dense neutral hydrogen clouds.

Question 24

The first scientific attempt to map the Milky Way galaxy

A) showed that the sun was located in the center of the system of planets making up our galaxy.
B) showed that our galaxy is a round ball on which we live.
C) showed that our galaxy has 9 stars.
D) used globular clusters to determine the location of the center of the Earth.
E) was completed by William and Caroline Herschel.

Question 25

The traditional "top-down" hypothesis of the formation of our galaxy cannot explain

A) why not all globular clusters are the same age.
B) why the youngest globular clusters are in the outer halo.
C) why the oldest stars are metal poor but not completely metal free.
D) streams and rings of scattered stars in the halo.
E) all of the above.

Question 26

Nucleosynthesis

A) is the process by which energy is produced at the center of the galaxy.
B) is the process by which hydrogen and helium are converted into heavier elements.
C) describes the structure of a globular cluster.
D) describes how the magnetic field of the galaxy traps cosmic rays.
E) describes the method by which neutral hydrogen produces 21-cm radiation.

Question 27

The nuclear bulge of our galaxy

A) contains stars that are primarily population I stars.
B) is primarily composed of gas and dust.
C) contains stars primarily associated with the spherical component of our galaxy.
D) contains stars primarily associated with the disk component of our galaxy.
E) a, b and d

Question 28

How is the age of the galaxy determined?

A) measuring the metallicity of Population II stars
B) finding the turnoff point in the H-R diagram of globular clusters
C) from the motion of stars in the galactic halo
D) counting the number of open clusters in the spiral arms

Question 29

The energy source at the center of our galaxy is called

A) Cygnus X-1.
B) the Orion arm.
C) the sun.
D) Sagittarius A*.

Question 30

Which of the following can't be associated with the spiral arms of a galaxy?

A) dust and gas
B) metal-poor stars
C) young, massive stars
D) star formation

Question 31

Figure 12-1
Refer to Figure 12-1. A Type I Cepheid has been located in an open cluster. The period of the Cepheid variable is 30 days and the variables apparent visual magnitude, m, is 10. First, use 12-1 to estimate the absolute visual magnitude, M . Calculate the distance to this open cluster? Hint: d_pc = 10^{(m - M + 5)/5}

A) 100 pc
B) 10,000 pc
C) 20 pc
D) 300 pc
E) 2500 pc

Question 32

The Herschels' grindstone model of the Milky Way star system was too small because

A) they did not count the brightest stars.
B) they did not study the southern sky.
C) they did not have large enough telescopes.
D) they only observed stars in the disk of the galaxy and not the halo.
E) they did not know about interstellar dust clouds.

Question 33

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

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

Question 34

How did Harlow Shapley determine where the center 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 35

Sgr A* is believed to be the center of the Milky Way galaxy because

A) I & II only
B) II & III only
C) I & IV only
D) II & IV only
E) All of I, II, III, & IV

Question 36

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

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

Question 37

The traditional "top-down" hypothesis states that the galaxy formed

A) from a large spherical cloud of gas that was rotating very slowly.
B) from a large cloud of material that broke off a larger galaxy.
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.
E) as two massive galaxies collided.

Question 38

Figure 12-1

-Refer to Figure 12-1. A Type II Cepheid has been located in a distant globular cluster with a period of 10 days. What is the star's absolute magnitude?

A) (-1)
B) 0
C) (-4)
D) (- 6)
E) The absolute magnitude of a Cepheid variable cannot be determined unless its distance is known.

Question 39

What behavior do galactic rotation curves exhibit to suggest the existence of dark matter in an extended halo?

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

Question 40

The center of our galaxy lies in the direction of the constellation of

A) Ursa Minor.
B) Ursa Major.
C) Sagittarius.
D) Orion.
E) Monoceros.

Question 41

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

Question 42

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

Question 43

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

Question 44

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

Question 45

Giant molecular cloud complexes are located in spiral arms.

Question 46

In the edge-on sketch of a spiral galaxy, pick the letter corresponding most nearly to the location of globular clusters.

A) A
B) B
C) C
D) D

Question 47

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

Question 48

The disk of the galaxy is older than the halo.

Question 49

The center of our galaxy shows signs of past eruptions.

Question 50

The disk of our galaxy consists of

A) the nine known planets.
B) only stars.
C) stars, dust, and gas.
D) quasars.
E) only black holes.

Question 51

Henrietta Leavitt discovered the period-luminosity relationship for ____________________.

Question 52

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

Question 53

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

Question 54

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

Question 55

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

Question 56

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

Question 57

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

Question 58

Globular clusters are primarily found in the ____________________ component of the Galaxy.

Question 59

Spiral tracers tend to be old, luminous stars.

Question 60

This is a "thought" question. Why are few galaxies outside our own galaxy seen in the circle around the sky where the Milky Way is located? This is because

A) there aren't any galaxies in those directions.
B) dust in the Milky Way blots out our view of galaxies in those directions.
C) the missing mass is in those directions.
D) the Big Bang has blown galaxies away from those directions.

Question 61

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

Question 62

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

Question 63

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

Question 64

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

Question 65

Describe the central 25 pc of our galaxy.

Question 66

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

Question 67

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

Question 68

Why are all spiral tracers young?

Question 69

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

Question 70

Astronomers before Shapely underestimated the size of the Milky Way galaxy because they lacked telescopes.

Question 71

Compare and contrast the properties of disk and halo stars.

Question 72

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

Question 73

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

Question 74

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

Question 75

What is the difference between an open cluster, an association, and a globular cluster? In which components of the galaxy does each lie?

Question 76

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

Question 77

Population II stars contain more metals than Population I stars.

Question 78

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

Question 79

What evidence do we have that the center of our galaxy contains magnetic fields?