Chapter 17
The Evolution of the Galaxy
1. Which of these is NOT a problem in determining the structure of the Galaxy?
A. Dust cutting out visible light.
B. The sun lying in the plane of the Galaxy.
C. The low luminosity of stars in the spiral arms.
D. The turbulent motions of supernovas mixing up the gas in the arms.
2. Which is NOT used by astronomers to trace out the spiral structure of the Galaxy?
A. O and B stars.
B. Giant molecular clouds.
C. H II regions.
D. K and M stars.
3. From the rotation curve of the Galaxy, its total mass in solar masses is roughly:
A. one million.
B. one hundred billion.
C. ten billion.
D. one thousand billion (one trillion).
4. What is the distance of the sun from the center of the Galaxy?
A. 300 light years.
B. 3000 light years.
C. 30,000 light years.
D. 300,000 light years
5. In order to find out the spiral arm structure of the Galaxy, a radio astronomer needs to:
A. know the galactic rotation curve and measure the Doppler shift of 21-cm lines.
B. infer the velocities of clouds along the line of sight.
C. know the sizes of the H II regions he is observing.
D. be able to match H I regions to bright associations of young blue stars.
6. Which of the following would you NOT expect to find in a spiral arm of the Galaxy?
A. H I regions.
B. H II regions.
C. Molecular clouds.
D. Globular clusters.
7. According to the density-wave model of spiral structure, the Galaxy's spiral arms:
A. are solid entities, held together by gravity.
B. have strong magnetic fields holding them together.
C. are short-lived objects generated by spiral density waves.
D. are created by shock waves from the Galaxy's nucleus.
8. As the disk of the Galaxy evolves, we expect that the:
A. interstellar medium will have fewer heavy elements.
B. star formation will continue.
C. spiral arms will slowly disappear.
D. stellar corpses will decrease in number.
9. In the halo of the Galaxy in the future, we expect:
A. more supermassive stars to form.
B. globular clusters to orbit and hot gas to flow out from the disk.
C. brown dwarf stars to be the main type of star forming.
D. hot gas to flow inward toward the nucleus.
10. Which part of the Galaxy contains many old Population I stars?
A. Core.
B. Nuclear bulge.
C. Spiral arms.
D. Halo.
11. Where in the Galaxy is most of the Milky Way's gas and dust?
A. Core.
B. Nuclear bulge.
C. Spiral arms.
D. Halo.
12. In the Galaxy, mostly old Population II stars are found where?
A. Core.
B. Nuclear bulge.
C. Spiral arms.
D. Halo.
13. High-resolution radio observations of the nucleus of the galaxy do NOT show that:
A. some of the emission is synchrotron in origin.
B. some of the emission is from hot, ionized gas.
C. the gas has loops and bends.
D. globular clusters are all that is found there.
14. In terms of our galaxy's stellar population, stars which are born recently:
A. will be made of more hydrogen than older stars.
B. will have a higher metal content.
C. will not be made of ANY metal.
D. are less likely to explode as a supernova.
15. How do we know the position of our sun and it's rotational velocity within the Galaxy?
A. From radio waves reflected of the galactic nucleus.
B. From its Doppler shift
C. From the "fixed basis" of globular clusters in the galactic halo.
D. From the proper motions of nearby open clusters.
16. The reason we can use RR-Lyrae stars to find our distance from the Galaxy's center is:
A. of their period-luminosity relation.
B. they are all at the same distance.
C. they are all in the field of view of the galaxy center.
D. as a class, they have similar luminosities.
17. The "orbits" of the stars in our galaxy do not follow the laws of Kepler.
We understand this to be due to:
A. proportionally more mass distributed away from the galactic center.
B. angular momentum is not being conserved as the Galaxy rotates.
C. his laws are supplanted by Einstein's relativity.
D. because on a large scale, they are circular and not elliptical.
18. The size of our galactic halo:
A. is smaller than the Oort Cloud.
B. is slightly larger than the galactic disk.
C. is smaller than the galactic nucleus.
D. is about six billion kiloparsecs in radius.
19. If there is dark matter in our galaxy that contributes to the fact that the orbits of stars do not follow Kepler's laws, it should be:
A. located at the galactic center.
B. located outside of our galaxy.
C. located within the halo.
D. located in a distant galaxy.
20. How do we map out the structure and size of the arms in our galaxy?
A. With a Norton's Star Atlas.
B. Using the observation of Cepheid Variable stars.
C. With Observations of globular clusters.
D. Using a space probe at the galactic center.
21. What model best describes the formation of the arms in our galaxy?
A. The Density Wave model.
B. Thermal Synchrotron model.
C. The Outreach Model.
D. The Large Impact Hypothesis.
22. What is not a characteristic of our galaxy's center?
A. It emits X-rays
B. It emits high energy particles.
C. Optically it is very bright as viewed from the earth.
D. It probably contains a very massive black hole.
23. Why do the globular clusters exist in the galactic halo?
A. Because they formed early, not losing their angular momentum.
B. Because they formed late out of dark matter.
C. Because they were captured after the galaxy evolved.
D. Because they were ejected from the spiral arms.
24. We can verify the Sun's estimated position in our galaxy by:
A. comparing it to the 3-dimensional system of globular clusters and knowing their distances determined from the luminosities of the RR Lyrae type stars.
B. Using Kerler's period-luminosity law.
C. applying Newton's law to its motion about the galactic center.
D. looking at the distribution of bright H II regions around us.
25. We can determine the distance to positions on the spiral arms of our galaxy by:
A. counting the astronomical units with a telescope.
B. trigonometric parallax method.
C. using the mass-luminosity relation of galaxies.
D. determining the luminosity of Cepheid variable stars.
26.-29. Match these numbers with their significance to the Milky Way:
A. 25,000 B. 100,000 C. 250 million D. 100 billion
26. Approximate mass of the galaxy between us and the galactic nucleus.
27. In light years, distance from the galactic nucleus to us.
28. In years, approximate time for the sun to orbit the galactic nucleus.
29. In light years, approximate diameter of the galactic disk.
30. The galactic nucleus lies in the direction of the constellation:
A. Cygnus.
B. Orion.
C. Sagittarius.
D. Perseus.
31. Our revolution around the center of the Galaxy carries us toward:
A. Cygnus.
B. Orion.
C. Sagittarius.
D. Perseus.
32. We are not able to observe most of the Milky Way visually due to:
A. dust in the galactic plane.
B. black holes in the halo.
C. gravitational lensing by the nucleus.
D. brown dwarfs in the Local Group.
ESSAYS
1. Harlow Shapley first found our solar system's position in the Milky Way by the spatial distribution of what type of star clusters? Make a simple sketch of the Milky Way viewed edge-on, showing our own Sun's position and Shapley's distribution of these clusters.
2. Which are more useful in mapping the spiral structure of the Milky Way, H-I or H-II regions? Explain why in terms of the electromagnetic spectrum.
3. William Herschel made the first attempt to map our position in the Milky Way based on star counts of faint stars through the eyepiece of his large telescopes. As he found about equal numbers of faint stars in all directions along the plane of the Milky Way, he thought we were located near the center of the galaxy. Why was he wrong?