Milky Way Galaxy

1. Here is a full view of our galaxy as seen by the COBE satellite at microwave wavelengths. Resketch it in the space provided and label the location of the halo, disk and bulge on your sketch.

2. What kinds of objects lie in the halo of our galaxy?
   1. open clusters
   2. globular clusters
   3. gas and dust
   4. O and B stars
   5. all of the above

3. What kinds of objects lie in the disk of our galaxy?
   1. old K and M stars
   2. open clusters
   3. O and B stars
   4. gas and dust
   5. all of the above

4. What makes up the interstellar medium?
   1. open clusters
   2. K and M stars
   3. O and B stars
   4. gas and dust
   5. all of the above

5. Harlow Shapley concluded that the Sun was not in the center of the Milky Way Galaxy by
   1. mapping the distribution of stars in the galaxy.
   2. mapping the distribution of globular clusters 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 gas clouds in the spiral arms.

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

7. Compared with our Sun, most stars in the halo are
   1. old, red, and dim and have much more heavy element material.
   2. young, red, and dim and have fewer heavy elements.
   3. old, red, and dim and have fewer heavy elements.
   4. young, blue, and bright and have much more heavy element material.
   5. old, red, and bright and have fewer heavy elements.

8. Compared with stars in the disk, orbits of stars in the halo
   1. do not have to pass through the plane of the galaxy.
   2. are relatively uniform to each other.
   3. are elliptical but orbiting in the same direction.
   4. are elliptical, with random orientation.
   5. do not have to be around the galactic center.

9. How does the star-gas-star cycle lead to chemical enrichment of the Galaxy?
   
   
   
   

10. Why do we believe 90% of the mass of the Milky Way is in the form of dark matter?
    
    
    
    

11. What two observations give us the strongest evidence for a massive black hole at the center of the Milky Way.
    
    
    
    

    Galaxies

12. Suppose that we look at a photograph of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest?
    1. the one that is closest to us
    2. the one that is farthest away
    3. the one that is bluest in color
    4. the one that is reddest in color
    5. the one that most resembles an elliptical.

13. Identify the following galaxies with their general Hubble type.
14. Which of the following types of galaxies are most spherical in shape?
    1. barred spirals
    2. irregulars
    3. spirals
    4. ellipticals
    5. lenticulars

15. Which of the following types of galaxies are reddest in color?
    1. ellipticals
    2. spirals
    3. barred spirals
    4. irregulars
    5. lenticulars

16. What is the major difference between an elliptical galaxy and a spiral galaxy?
    
    
    
    
    
    
17. Which types of galaxies are most commonly found in the centers of large clusters, such as the Virgo and Coma clusters?
    1. barred spirals
    2. ellipticals
    3. spirals
    4. irregulars
    5. pinwheel galaxies

18. Active star formation is most likely to be found in irregular and what other two types of galaxies?
    
    
    
    

19. Why are Cepheid variables important?
    1. Cepheids are supermassive stars that will soon go supernovae.
    2. Cepheids are a type of young galaxy that helps us understand how galaxies form.
    3. They can be used as "standard candles" for distance measurements.
    4. Cepheid variables are stars that vary in brightness because they harbor a black hole.
    5. None of the above explains why they are important.

20. What is Hubble's law?

    
    
    
    
    

21. What is the primary practical difficulty that limits the use of Hubble's law for measuring distances?
    
    
    
    

22. Once you have a value for the Hubble constant, what two subsequent steps need to be taken to derive a distance to a galaxy?
    
    
    
    

23. Measured Parallax; Spectroscopic Parallax; variable stars; Hubble Law:
    1. What is the most accurate way to determine the distance to a nearby star?
       
       
       
    2. What is the most accurate way to determine the distance to a nearby (10 Mpc or so) galaxy?
       
       
       
       

    Cosmology

24. What do scientists mean by the critical density of the universe?
    1. the precise density needed to eventually reverse the expansion of the Universe
    2. the minimum density that a universe needs in order to form stars
    3. the minimum density that a universe needs in order to form galaxies
    4. the average density of the space between galaxies and clusters of galaxies
    5. the minimum density that a universe needs in order to create helium from hydrogen

25. Suppose H_o = 70 km/sec/Mpc. How fast would a galaxy located 400 megaparsecs distant be receding from us?
    1. 2.8 km/s
    2. 70 km/s
    3. 280 Mpc/s
    4. 28,000 km/s
    5. 0.07 times the speed of light

26. Suppose H_o = 100 km/sec/Mpc. What is the distance to a galaxy with a measured recessional velocity of 10,000 km/sec?
    1. 100 pc
    2. 1 Mpc
    3. 100 Mpc
    4. 10,000 km
    5. 1,000,000 light years

27. How do observations of distant galaxies help us learn about galaxy evolution?

    
    
    
    
    

28. Which of the following gives the two main assumptions of theoretical models of galaxy evolution?
    1. Hydrogen and helium filled all of space, and all the universe was exactly the same density.
    2. The universe was composed originally only of hydrogen, and all the other elements came from stars.
    3. Hydrogen and helium filled all of space, and certain regions of the universe were slightly denser than others.
    4. The beginning of the universe is modeled after a humongous supernova explosion.
    5. The universe has always been expanding, and denser areas contracted to form the first stars.

29. What is a quasar?
    1. the extremely bright center of a distant galaxy, thought to be powered by a massive black hole
    2. another name for very bright stars of spectral type O
    3. a starlike object that actually represents a bright patch of gas in the Milky Way
    4. a very large galaxy thought to be formed by the merger of several smaller galaxies, typically found in the center of a galaxy cluster
    5. a specialized astronomical instrument for observing distant stars.

30. The most active galactic nuclei are usually found at large distances from us; relatively few nearby galaxies have active galactic nuclei. What does this imply?
    1. Massive black holes existed only when the universe was young and no longer exist today.
    2. Active galactic nuclei can form only at large distances from the Milky Way.
    3. The jets seen in many active galactic nuclei must cause them to move far away from us.
    4. Active galactic nuclei tend to become less active as they age.

31. Why should galaxy collisions have been more common in the past than they are today?
    
    
    
    

32. What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy?
    1. observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy
    2. observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies
    3. the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies
    4. observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies
    5. all of the above

33. We have learned that the Universe is expanding, and yet we do not see our solar system or our galaxy expanding. In fact, we may collide with the Andromeda galaxy eventually (it has a negative radial velocity). Do these observations negate the expansion theory? Explain.
    
    
    
    
    
    
    
    

34. Why can't current theories describe what happened during the Planck era?
    1. The Planck era was the time before the Big Bang, and we cannot describe what happened before that instant.
    2. We do not understand the properties of antimatter.
    3. We do not yet have a theory that links quantum mechanics and general relativity.
    4. It was a time period from which we cannot receive radiation.
    5. We do not know how much energy existed during that time.

35. What do we mean by inflation?
    
    
    
    

36. Name three kinds of atomic nuclei that formed during the era of nucleosynthesis.
    
    
    
    

37. Why is the era of nucleosynthesis so important in determining the chemical composition of the universe?
    1. Except for the small amount of heavy elements produced later by stars, the chemical composition of the universe is the same now as at the end of the era of nucleosynthesis.
    2. All the elements except hydrogen were produced after the era of nucleosynthesis.
    3. We can study the processes that occurred during the era of nucleosynthesis to determine how most of the elements in the universe were created.
    4. By knowing how much matter was created during the era of nucleosynthesis, we can determine whether the universe is open or closed.
    5. We can observe spectra from this era to determine what the primordial mix of the elements was at the beginning of the universe.

38. Why did the era of nuclei end when the universe was about 300,000 years old?
    
    
    
    
    
    
    
    

39. Evidence that the cosmic background radiation really is the remnant of a Big Bang comes from predicting characteristics of remnant radiation from the Big Bang and comparing these predictions with observations. Four of the five statements below are real. Which one is fictitious?
    1. The cosmic background radiation is expected to look essentially the same in all directions, and it does.
    2. The cosmic background radiation is expected to have tiny temperature fluctuations at the level of about 1 part in 100,000. Such fluctuations were found in the COBE data.
    3. The cosmic background radiation is expected to have a perfect thermal spectrum, and observations from the COBE spacecraft verify this prediction.
    4. The cosmic background radiation is expected to have a temperature just a few degrees above absolute zero, and its actual temperature turns out to be about 3 K.
    5. The cosmic background radiation is expected to contain spectral lines of hydrogen and helium, and it does.

40. Which of the following statements about the cosmic background radiation is not true?
    1. It has a temperature of about 3 degrees K above absolute zero.
    2. It appears essentially the same in all directions (it is isotropic).
    3. It was discovered by Penzias and Wilson in the early 1960s.
    4. It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.
    5. It had a much higher temperature in the past.

41. Why does the Big Bang theory predict that the cosmic background radiation should have a perfect thermal radiation spectrum?
    1. The spectrum of pure hydrogen is a perfect thermal radiation spectrum.
    2. It doesn't predict that the cosmic background radiation should have a perfect thermal radiation spectrum.
    3. The light from all the stars and gas in the sky averaged over the entire universe is a perfect thermal radiation spectrum.
    4. The spectrum of 75% hydrogen and 25% helium is a perfect thermal radiation spectrum.
    5. The background radiation came from the heat of the universe, with a peak corresponding to the temperature of the universe.

42. Some recent but still preliminary measurements of the expansion rate of the universe suggest a problem with our standard idea about how the universe should be expanding. What is the problem?
    1. The measurements suggest that the universe may be shrinking rather than expanding.
    2. The measurements indicate that the universe is at least 30 billion years old, meaning that more than 10 billion years passed between the Big Bang and the formation of the first stars and galaxies.
    3. The measurements suggest that the universe may not be expanding at all.
    4. The data suggest that the expansion rate varies widely in different parts of the universe.
    5. The measurements suggest that the expansion may actually be accelerating, rather than slowing under the influence of gravity.

43.  
    1. What is antimatter?
       
       
       
       
    2. How were particle-antiparticle pairs created in the early universe?
       
       
       
       
    3. How were they destroyed?
       
       
       
       
    4. How do we know there was a small but significant excess of matter over anti-matter in the early universe?
       
       
       
       

44. Choose one piece of evidence supporting the Big Bang model for the origin of the Universe. How convincing do you find the evidence? Overall, do YOU think the Big Bang happened. Defend your opinion based upon SCIENTIFIC principles.

Equations

v = H_o d

m - M = 5 log d - 5

1 parsec = 3.26 light years

1 Mpc = 1 million parsecs

redshift = z = [Observed wavelength - Rest wavelength]/[Rest wavelength]