NATS 1740 Assignment 18

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Where are most of the Milky Way's globular clusters found?

1. in the disk
2. in the bulge
3. in the halo

3. in the halo

Why do disk stars bob up and down as they orbit the galaxy?

1. because the gravitational pull of other disk stars always pulls them toward the disk
2. because of friction with the interstellar medium
3. because the halo stars keep knocking them back into the disk

1. because the gravitational pull of other disk stars always pulls them toward the disk

How do we determine the Milky Way's mass outside the Sun's orbit?

1. from the Sun's orbital velocity and its distance from the center of our galaxy
2. from the orbits of halo stars near the Sun
3. from the orbits of stars and gas clouds orbiting the galactic center at greater distances than the Sun

3. from the orbits of stars and gas clouds orbiting the galactic center at greater distances than the Sun

We measure the mass of the black hole at the galactic center from:

1. the orbits of stars in the galactic center.
2. the orbits of gas clouds in the galactic center.
3. the amount of radiation coming from the galactic center.

1. the orbits of stars in the galactic center.

What is the diameter of the disk of the Milky Way?

1. 1,000 light-years
2. 1,000,000 light-years
3. 100,000 light-years
4. 10,000 light-years
5. 100 light-years

3. 100,000 light-years

What is the thickness of the disk of the Milky Way?

1. 1,000,000 light-years
2. 100 light-years
3. 100,000 light-years
4. 1,000 light-years
5. 10,000 light-years

4. 1,000 light-years

What kinds of objects lie in the halo of our galaxy?

1. globular clusters
2. O and B stars
3. gas and dust
4. open clusters
5. all of the above

1. globular clusters

What kinds of objects lie in the disk of our galaxy?

1. open clusters
2. gas and dust
3. old K and M stars
4. O and B stars
5. all of the above

5. all of the above

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

1. O stars
2. the Sun and other solar mass stars
3. Cepheid variables
4. globular clusters
5. red giant stars in spiral arms

4. globular clusters

How does the interstellar medium obscure our view of most of the galaxy?

1. It produces so much visible light that it is opaque and blocks our view of anything beyond it.
2. It absorbs all wavelengths of light.
3. It reflects most light from far distances of the galaxy away from our line of sight.
4. It absorbs visible, ultraviolet, and some infrared light.
5. all of the above

4. It absorbs visible, ultraviolet, and some infrared light.

How can we see through the interstellar medium?

1. by using only the biggest telescopes
2. by observing only the brightest visible sources
3. by using telescopes above the Earth's atmosphere
4. by observing in high-energy wavelengths such as X rays and long wavelengths of light such as radio waves
5. We cannot see through the interstellar medium.

4. by observing in high-energy wavelengths such as X rays and long wavelengths of light such as radio waves

Harlow Shapley concluded that the Sun was not in the center of the Milky Way Galaxy by

1. mapping the distribution of gas clouds in the spiral arms.
2. mapping the distribution of stars in the galaxy.
3. looking at the shape of the "milky band" across the sky.
4. looking at other nearby spiral galaxies.
5. mapping the distribution of globular clusters in the galaxy.

5. mapping the distribution of globular clusters in the galaxy.

Approximately how far is the Sun from the center of the galaxy?

1. 280 light-years
2. 28 light-years
3. 28,000 light-years
4. 28 million light-years
5. 2,800 light-years

3. 28,000 light-years

Why are we unlikely to find Earth-like planets around halo stars in the Galaxy?

1. Planets around stars are known to be extremely rare.
2. Any such planets would have been ejected long ago by galactic mergers.
3. Halo stars do not have enough mass to hold onto planets.
4. Halo stars formed in a different way from disk stars.
5. Halo stars formed in an environment where there were few heavy elements to create rocky planets.

5. Halo stars formed in an environment where there were few heavy elements to create rocky planets.

How are interstellar bubbles made?

1. by collisions between galaxies
2. by planetary nebulae from low-mass stars
3. by the rapidly rotating magnetic fields of pulsars
4. by the winds of massive stars and supernovae
5. by the collapse of a gas cloud to form stars

4. by the winds of massive stars and supernovae

What is the galactic fountain model?

1. 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
2. the theory that hot, ionized gas blows out of the galactic center like a jet or fountain
3. the idea that there is a lot of interstellar water vapor
4. the theory that the Milky Way is a spiral galaxy and looks like a whirlpool from above
5. none of the above

1. 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

What is the most common form of gas in the interstellar medium?

1. molecular helium
2. ionized hydrogen
3. atomic helium
4. atomic hydrogen
5. molecular hydrogen

4. atomic hydrogen

What produces the 21-cm line that we use to map out the Milky Way Galaxy?

1. carbon monoxide
2. molecular hydrogen
3. atomic hydrogen
4. ionized hydrogen
5. helium

3. atomic hydrogen

Where does most star formation occur in the Milky Way today?

1. uniformly throughout the Galaxy
2. in the bulge
3. in the spiral arms
4.in the halo
5. in the Galactic center

3. in the spiral arms

How do we learn about what is going on in the center of our own galaxy (the Milky Way)?

1. 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.
2. We must look at the centers of other galaxies and hope that ours is just like others.
3. We have learned it only recently, thanks to the great photographs obtained by the Hubble Space Telescope.
4. We cannot see the galactic center with visible or ultraviolet light, but radio and X rays from the center can be detected.

4. We cannot see the galactic center with visible or ultraviolet light, but radio and X rays from the center can be detected.

What evidence supports the theory that there is a black hole at the center of our galaxy?

1. We observe a large, dark object that absorbs all light at the center of our galaxy.
2. We can see gas falling into an accretion disk and central mass at the center of our galaxy.
3. We observe an extremely bright X-ray source at the center of our galaxy.
4. 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.
5. all of the above

4. 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.

What evidence do we have that the spheroidal population of stars are older than other stars in the galaxy?

1. They are farther away
2. They have a smaller proportion of heavy elements
3. They have higher masses than other stars in the galaxy
4. They have fewer planets

2. They have a smaller proportion of heavy elements

Which of the following statements correctly summarize key differences between the disk and the halo?
Check all that apply.

1. Clusters of young stars are found only in the disk.
2. Gas and dust are abundant in the disk but not in the halo.
3. Stars in the disk all orbit in the same direction and nearly the same plane, while halo stars have more randomly oriented orbits.
4. Disk stars come in a broad range of masses and colors, while halo stars are mostly of low mass and red.

1. Clusters of young stars are found only in the disk.
2. Gas and dust are abundant in the disk but not in the halo.
3. Stars in the disk all orbit in the same direction and nearly the same plane, while halo stars have more randomly oriented orbits.
4. Disk stars come in a broad range of masses and colors, while halo stars are mostly of low mass and red.

The following figures show several stars found in the disk and halo of the Milky Way Galaxy. Rank the stars based on their current age, from oldest to youngest. If two (or more) stars have approximately the same age (that is, ages within a few million years), rank them as equal by dragging one on top of the other(s).

- the Sun
- Red Main-sequence star in globular cluster M13
- Red giant in globular cluster
- hot, blue main-sequence star in disk

- Red Main-sequence star in globular cluster M13 (TIED #1)
- Red giant in globular cluster (TIED #1)
- the Sun
- hot, blue main-sequence star in disk

Listed following are several stars found in the disk and halo of the Milky Way Galaxy. Assume that both the blue and yellow disk stars are members of the same open cluster. Rank the stars based on the abundance of elements heavier than carbon that you would expect to find in each of the stars, from highest to lowest. If you expect two (or more) stars to have approximately the same abundance, rank them as equal by dragging one on top of the other(s).

- red main-sequence star in globular cluster M13
- yellow main-sequence star in open cluster in disk
- hot, blue main-sequence star in open cluster in disk
- red giant in globular cluster M13

- hot, blue main-sequence star in open cluster in disk (TIED #1)
- yellow main-sequence star in open cluster in disk (TIED #1)
- red main-sequence star in globular cluster M13 (TIED #2)
- red giant in globular cluster M13 (TIED #2)

Listed following are several locations in the Milky Way Galaxy. Rank these locations based on their distance from the center of the Milky Way Galaxy, from farthest to closest.

- a cloud of gas and ust in the outskirts of the disk
- globular cluster in the outskirts of the halo
- our solar system
- the edge of the central bulge

- globular cluster in the outskirts of the halo
- a cloud of gas and ust in the outskirts of the disk
- our solar system
- the edge of the central bulge

Imagine a photon of light traveling the different paths in the Milky Way described in the following list. Rank the paths based on how much time the photon takes to complete each journey, from longest to shortest.

- from the Sun to the center of the galaxy
- across the diameter of the galactic disk
- across the diameter of the central bulge
- through the disk from top to bottom
- across the diameter of the galactic halo

- across the diameter of the galactic halo
- across the diameter of the galactic disk
- from the Sun to the center of the galaxy
- across the diameter of the central bulge
- through the disk from top to bottom

Each item below belongs either with the population of disk stars or the population of halo stars of the Milky Way Galaxy. Match each item to the appropriate population.

- youngest stars
- oldest stars
- stars that all orbit in nearly the same plane
- globular clusters
- the Sun
- stars whose orbits can be inclined at any angle
- high-mass stars
- stars with the smallest abundance of heavy elements

Disk stars (yellow)
- high-mass stars
- the Sun
- youngest stars
- stars that all orbit in nearly the same plane

Halo stars (green)
- globular clusters
- oldest stars
- stars with the smallest abundance of heavy elements
- stars whose orbits can be inclined at any angle

Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each word only once.

Sentences
1.The circular but relative flat protion of the galaxy is the ___.
2. The first portion of the galaxy to form was the __.
3. A tightly packed group of a few hundred thousand very old stars is a ___.
4. A ___ stands out in a photo of a galaxy because it shines brightly with light form massive young stars and glowing clouds of gas and dust.
5. Our Milky Way galaxy is a ___.
6. Stars orbiting in the ___ near the galaxy's center can have orbits highly inclined to the galactic plane.
Words
a. spiral galaxy
b. disk
d. halo
e. globular cluster
f. spiral arm

1. b
2. d
3. e
4. f
5. a
6. c

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