Deck 9: The Milky Way Galaxy

Question 1

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

Answer 1

-3.5

Question 2

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

Answer 2

−1

Question 3

What allowed Henrietta Levitt to conclude that the pulsation period of Cepheid variables was related to their intrinsic brightness?

A) Stars that are farther away appear dimmer.
B) All Cepheid variables have the same luminosity.
C) The stars in the Small Magellanic Cloud are nearly the same distance away.
D) Her stellar models predicted the behaviour of stars in the instability strip.

Answer 3

The stars in the Small Magellanic Cloud are nearly the same distance away.

Question 4

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 5

What did William and Caroline Herschel conclude based on their observations of the number of stars found in each direction?

A) The Sun is located near the centre of a disk-shaped collection of stars.
B) Giant clouds of dust and gas obscure our view of the entire galaxy.
C) The centre of the galaxy is in the direction of Sagittarius.
D) Stars appear uniformly scattered over the celestial sphere.

Question 6

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 7

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 8

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 9

What happens with stars when they enter the instability strip?

A) They become unstable and vibrate at variable speeds.
B) They become unstable and pulsate as variable stars.
C) They become unstable and produce bursts of X-rays.
D) They become unstable and turn into fast rotating dwarfs.

Question 10

Refer to the figure. A Type II Cepheid with a period of 30 days has been located in a distant globular cluster. What is the star's absolute magnitude?

A) −6
B) −2
C) −5
D) 0

Question 11

What is responsible for the pulsation cycle of Cepheid variables?

A) The rotation of the star sends flashing radio beams of light toward Earth.
B) The opacity of stellar material changes depending on the temperature.
C) The combined light of the Cepheid and an orbiting companion changes as they eclipse each other.
D) The power source alternates between fusing hydrogen and fusing helium.

Question 12

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 13

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 14

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 15

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 16

Which of the following observations first led astronomers to believe that the Sun is located in a disk-shaped collection of stars?

A) Stars appear uniformly scattered over the celestial sphere.
B) The distances to Cepheid variables revealed the position of the Sun within the galaxy.
C) The Milky Way is composed of stars and has a ring shape on the celestial sphere.
D) Globular clusters are preferentially found in the direction of Sagittarius.

Question 17

Which method did Harlow Shapley use to find the distance to a few of the nearest Cepheid variables?

A) He measured their proper motions across the sky.
B) He used the period-luminosity relation.
C) He measured their parallax.
D) He measured their spectroscopic parallax.

Question 18

Refer to the figure. A Type I Cepheid with a period of 20 days has been located in a distant globular cluster. What is its absolute magnitude?

A) -1
B) 0
C) -5
D) -2

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 is the approximate diameter of the Milky Way's disk component?

A) 300 ly
B) 6500 ly
C) 26 000 ly
D) 100 000 ly

Question 21

Approximately how old are the oldest globular clusters found in the Milky Way Galaxy?

A) 5 billion years
B) 9 billion years
C) 11 billion years
D) 13 billion years

Question 22

Our Sun takes about 210 million years to orbit the galaxy. About how long do disk stars orbiting twice as far away from the centre take to complete one orbit?

A) 150 million years
B) 210 million years
C) 420 million years
D) 594 million years

Question 23

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

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

Question 24

A star orbits within the disk of the Milky Way Galaxy, 40 000 ly from the centre. Which of the following will its orbital speed most depend on?

A) the mass of the black hole at the centre of the galaxy
B) the position of a star relative to a spiral density wave
C) the mass contained within the star's orbit
D) the abundance of metals in the star

Question 25

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 26

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 27

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 28

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

A) All spiral arms would be gas-free 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 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

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 31

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

Question 32

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 33

Which of the following is a characteristic of the stars of the disk component of our galaxy?

A) young stars
B) randomly inclined orbits
C) old stars
D) low metal abundance

Question 34

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 35

Which component of the Milky Way is associated with higher metal abundance?

A) dark halo
B) disk component
C) halo
D) globular clusters

Question 36

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.

Question 37

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

Question 38

Which of the following is now considered to be the most likely dark matter candidate?

A) massive compact halo objects
B) neutrinos
C) weakly interacting massive particles
D) supermassive black holes

Question 39

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) nearly circular orbit
B) high luminosity
C) old age
D) high mass

Question 40

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 41

Which of the following presents a challenge to the traditional hypothesis for how the Milky Way Galaxy formed?

A) Globular clusters tend to be older than open clusters.
B) Stars in the halo have very low metal abundances.
C) Stars in the disk have nearly circular orbits.
D) Some younger clusters are found in the outer halo.

Question 42

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 43

You observe a metal-rich star in a nearly circular orbit. Which of the following is most likely to apply to the star?

A) The star is a halo population star.
B) The star is an extreme Population II star.
C) The star is a disk population star.
D) The star is an intermediate Population II star.

Question 44

According to the traditional hypothesis, 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 45

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

Question 46

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

Question 47

Which of the following best describes the current state of the supermassive black hole at the centre of the galaxy?

A) It has a hot accretion disk that emits a large amount of X-rays.
B) It is launching high-energy jets along its poles.
C) It is destroying stars that get too close to the event horizon.
D) It is mostly dormant with occasional flares.

Question 48

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 49

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 50

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

Question 51

Which of the following types of radiation do we detect from the energy source at the centre of our galaxy?

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

Question 52

Which of the following are the oldest members of the Milky Way?

A) globular clusters.
B) population I stars.
C) disk population stars.
D) G and F stars.

Question 53

How does the traditional hypothesis 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 collapse of the proto-galactic material.

Question 54

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

Question 55

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

Question 56

Henrietta Leavitt discovered the period-luminosity relationship for _______________ _______________.

Question 57

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 58

Which of the following is a possible explanation for why some young clusters are found in the outer halo?

A) They were ejected from near the core due to close interactions.
B) They formed in spiral density waves.
C) Our galaxy collided with a younger galaxy.
D) There was a self-sustaining star formation.

Question 59

Elements heavier than iron are very scarce. Where are these elements mostly made?

A) in galactic halos and stars
B) in the interstellar medium and galactic halos
C) in supernovae and stars
D) in white dwarfs and pulsars

Question 60

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 61

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

Question 62

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

Question 63

When astronomers refer to an element as a metal, they mean its atoms are heavier than atoms of ______.

Question 64

Astronomers refer to all elements that are heavier than hydrogen as metals.

Question 65

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

Question 66

The disk of the galaxy is older than the halo.

Question 67

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

Question 68

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

Question 69

The centre of our galaxy shows signs of past eruptions.

Question 70

Stars with a low metal abundance and highly elliptical orbits are most likely to be classified as __________ ___________ stars.

Question 71

The locations of O and B stars help us map the positions of __________ ___________.

Question 72

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

Question 73

Spiral tracers tend to be old, luminous stars.

Question 74

The hypothesis that the Milky Way formed from the collapse of a single large cloud of dust is called the _____________ _____________ model.

Question 75

Giant molecular cloud complexes are located in spiral arms.

Question 76

Stars with a high metal abundance and nearly circular orbits are most likely to be classified as __________ ___________ stars.

Question 77

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

Question 78

The presence of two dominant spiral arms could be explained by __________ ___________ theory.

Question 79

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

Question 80

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