Deck 12: The Milky Way Galaxy

Question 1

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

Answer 1

the heavy elements were made in previous generations of stars.

Question 2

The period-luminosity relation is 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 that contain Cepheid variables.
E) the mass of the Milky Way galaxy.

Answer 2

the distance to globular clusters that contain Cepheid variables.

Question 3

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.

Answer 3

all galaxies would have only two smooth spiral arms.

Question 4

____ 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 5

____ galaxies have a great many short spiral segments branching from the spiral arms.

A) Grand design
B) Super spiral
C) Cepheid
D) RR Lyra
E) Flocculent

Question 6

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.

Question 7

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 8

Population II stars
I. are primarily found in the disk of the galaxy.
II. contain more heavy metals than population I stars.
III. are primarily old low mass stars.
IV. are located in globular clusters.

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

Question 9

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 10

A group of 10 to 100 stars that formed at the same time but are so widely scattered in space their mutual gravity cannot hold them together is called

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

Question 11

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

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

Question 12

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 13

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

A) Henrietta Leavitt
B) Edwin Hubble
C) John Glenn
D) Carl Sagan
E) Annie Cannon

Question 14

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 15

Good tracers of the spiral tracers are all
I. very old.
II. very young.
III. very luminous.
IV. moving with large radial velocities.

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

Question 16

____ 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 17

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 18

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 19

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 20

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*.

Question 21

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 proto-galactic material.

Question 22

Sgr A* is believed to be the center of the Milky Way galaxy because
I. It lies in the general direction of the center of the galaxy based on observations of globular clusters in the plane of the Milky Way.
II. Long wavelength dust penetrating images show it to be a region crowded with stars
III. Orbits of stars around it indicate a mass several million times that of the Sun within a volume a few light hours in size
IV. Radio observations show it is a concentrated source at the center of swirling clouds of gas

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

Question 23

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

Question 24

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 25

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 26

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 27

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 28

The traditional theory of the formation of our galaxy cannot explain

A) the existence of the disk of the galaxy
B) the fact that the oldest stars in the galaxy are not metal free.
C) the spherical distribution of the globular clusters
D) the difference in metal abundance of the population I and II stars.
E) the existence of the nuclear bulge.

Question 29

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 30

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 31

Refer to the figure. 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} using a scientific calculator.

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

Question 32

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 33

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

Question 34

Refer to the figure. 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 35

If a star with a large peculiar proper motion and/or speed with respect a typical disk star is found what other property would you expect it to have?

A) Low luminosity.
B) Poor metal content compared to the Sun.
C) Old age.
D) All of the above.

Question 36

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 37

The traditional theory states that the galaxy formed

A) as 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

The orbits of population I stars
I. are confined to disk of the galaxy.
II. are very elliptical.
III. are nearly circular.
IV. are randomly inclined to the disk of the galaxy.

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

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

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

Question 41

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

Question 42

Spiral tracers tend to be old, luminous stars.

Question 43

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

Question 44

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

Question 45

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

Question 46

Henrietta Leavitt discovered the period-luminosity relationship for ____________________.

Question 47

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

Question 48

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

Question 49

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

Question 50

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

Question 51

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

Question 52

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

Question 53

The disk of the galaxy is older than the halo.

Question 54

Population II stars contain more metals than Population I stars.

Question 55

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

Question 56

The center of our galaxy shows signs of past eruptions.

Question 57

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

Question 58

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

Question 59

Giant molecular cloud complexes are located in spiral arms.

Question 60

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

Question 61

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

Question 62

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

Question 63

Describe the central 25 pc of our galaxy.

Question 64

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

Question 65

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

Question 66

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

Question 67

Why are all spiral tracers young?

Question 68

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

Question 69

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

Question 70

Compare and contrast the properties of disk and halo stars.