1) We know that there is a very massive black hole in the center of our galaxy, but unlike black holes at the center of other galaxies, our ssems to be giving off very little energy (at least, the material in the vicinity of the black hole, not the black hole itself, is giving off very little energy).

a) (6 pts) Briefly explain the proposed mechanism that Astronomers have used to explain why the region surrounding black hole in the center of our galaxy is so "quiet" (giving off so little energy).

b) (4 pts) More "normal" sized black holes have been proposed to explain the dark matter in our galaxy. These black holes are presumably spread throughout the halo and affect the rotation of our galaxy. How do Astronomers feel that we can detect these black holes (that don't have surrounding bright disks of matter or companion stars)?

c) (4 pts) This detection method isn't promising because even if black holes constitute the dark matter, they are thought to be extremely rare relative to other forms of dark matter. Why are they so rare, relative to, say, MACHOs, if they exist?

2) Describe step-by-step how we use the movement of masers (bright molecular clouds) in other nearby galaxies to determine the distances to these galaxies. List all of the measurements that need to be made and show how they are used to find the distance to the galaxy.

3) An Astronomer is observing an edge-on spiral galaxy in the direction of the constellation Virgo.

a) (7 pts) What is the approximate location (altitude and azimuth) of Virgo in the sky tonight at around 10pm? Also, what is the name of a bright star in that constellation?

b) (7 pts) Describe step-by-step how to determine the distance to that spiral galaxy using the Tully-Fisher relation, assuming no interstellar material is along your line of sight to that galaxy.

4) Quasars are a relatively recent discovery. These extremely bright objects are the most distant objects observed in our Universe.

a) (7 pts) Explain how we know that quasars have an absolute luminosity that is hundreds of times (or more) the luminosity of a typical galaxy.

b) (7 pts) Astronomers think that quasars may be the precursor to galaxies. If we were to observe the composition of the gas in these "galaxies" at such great distances from the Earth (8-10 billion) light years, how would you expect the metallicity of these objects to compare to the metallicity of today's galaxies? Explain your answer.

5) Two fundamental questions we have covered in this part of the course are: "Are we alone?" and "What is the future of the Universe?" This questions asks about how we try to find solutions to each question.

a) (7 pts) Describe how we use the Drake Equation (you don't have to list the variables or define them, except one) to answer the question of whether extraterrestrial intelligence exists. What is "N" in the equation?

b) (7 pts) Aside from any effects of the cosmological constant, Astronomers hoped to determine the future of the Universe by measuring its density. Explain why the density has anything to do with the ultimate fate of the Universe. As part of your answer, explain what the critical density is.

6) Below is a simple version of the graph used in the Hubble Law distance determination technique. For simplicity, let's assume in this question that there is no comological constant, no accelerating force in the Universe. Let's also assume that gravity in the Universe is negligible and that the Universe today is 12 billion years old.

Now imagine you are an Astronomer observing the Universe 6 billion years ago when it was only 6 billion years old. How would this graph look different from its current state? Indicate your answer on the graph below (or, if the graph looked the same back then, just write "no change" on the graph). Next to the graph, explain why you changed (or didn't change) the graph in the way you did.

7) Briefly explain both the horizon problem and the flatness problem, and describe how the theory of inflation (part of the Big Bang theory) resolves both problems.

8) The observation of the Cosmic Background Radiation (CBR) has been viewed as convincing confirmation of the Big Bang theory. There is other evidence (such as Hubble's Law) that is consistent with the theory, too.

a) (6 pts) Explain why the observations of the CBR have been viewed as such a critical piece of evidence in proving the Big Bang while the Hubble's Law evidence, though extremely interesting, doesn't have the same level of significance or importance when it comes to the credibility of the Big Bang theory.

b) (8 pts) Recently, experiments to measure the CBR in detail have detected lumps in the CBR. Why did we expect the lumps to be there, and why is the size of the lumps related to the overall density of the Universe?