Test 2, November 19, 2010
Astronomy 123
Summer 2010

Material: Topic 4, Active Galactic Nuclei (Chapters 24 & 25), Topic 5, World Views of the Universe (Chapters 26), Topic 6, History of the Universe (Chapters 26 and 27), Observations and the Fate of the Universe (Chapters 24-26)

Active Galactic Nuclei (AGNs)

• List two major differences between normal galaxies and active galactic nuclei. What were the most difficult properties of AGNs which needed to be explained by early researchers? What is the commonly accepted model for the energy engines of AGNs?
• Explain how the rapid variability is used to determine the maximum size of the emitting regions of AGNs.
• Describe the evidence and arguments which suggest that the Universe contains supermassive Black Holes. How are supermassive Black Holes thought to be produced?
• How efficient are black holes as energy engines? What fuels the black holes found in AGNs? What is the radius of 1 billion Solar mass black hole? Desribe the relationship between supermassive black holes and the masses of the bulges of the galaxies in which they are found. What is the significance of this relationship?

Models for the Universe

• Olbers's Paradox concerns the darkness of the night sky. Explain the nature of the paradox, that is, state the assumptions used, and outline the argument which leads to the conundrum. Explain how the Big Bang theory leads to the resolution of Olbers's paradox.
• What primary assumption underlies Friedman's models for the Universe? List Friedman's models for the Universe. Describe a test that allows us to choose the appropriate Friedman model for the Universe.
• In terms of spacetime, describe each of Friedman's models for the Universe. In what type of Friedman universe are we thought to live? Which universe is a closed universe (and what does this mean)? Which universe is an open universe (and what does this mean)?
• How can we distinguish open, closed, and flat universes? Describe the tests and the results of the tests described in class. Describe the behavior of parallel lines, triangles in the different Friedman models.
• Interpret and explain the Hubble Law in the context of an expanding Universe. Describe cosmological redshift. How does the cosmological redshift fit in with the Hubble Law?
• What is the Horizon Problem? What is the Flatness Problem? What is the Matter/Anti-Matter Asymmetry Problem? How does inflation address each of these problems?
• Carefully describe Inflation and describe the mysteries of the Universe that Inflation solves and explain how Inflation solves the problems.
• What are the four known forces of the current Universe? Have there always been only four distinct forces (four distinct ways in which things interact) in the Universe? If not, how has the situation evolved?
• What forces play dominant roles in the evolution of the Universe? How does the changing number of forces as the Universe evolves lead to inflation?

History of the Universe

• How old is the Universe? How do we arrive at this age estimate? How old are the oldest stars in the galaxy? Is there a problem with this age for the oldest stars?
• What is the correct order for the radiation era, the matter era, and the dark energy era? When did the transitions from era to era occur? What is meant by radiation era, matter era, and dark energy era?
• Describe how the Universe evolved starting from the Planck Era (what is meant by the Planck Era) to the GUTs to the Quark Era to Nuclear (Nucleosynthesis) Era and to the formation of the CMBR.
• What is the Compton wavelength? What defines the Planck Era? How long did the Planck era last? Why did the Planck era end?
• Big Bang Nucleosynthesis. When were the chemical elements present in the Universe formed? What chemical elements were produced in the Big Bang? What is the significance of the detection of dueterium?
• What is meant by symmetry breaking? What are GUTs?
• What is the Epoch of Recombination? When did it occur? What does it have to do with the CMBR?
• What is meant by pair production? What is meant by annihilation? Physicaly, what is the meaning of E = mc²? How do these notions lead to the notion of the Matter/Anti-Matter Symmetry?
• What are virtual pairs? What is the Heisenberg Uncertainty Principle? How does the notion of the Heisenberg Uncertainty Principle lead to virtual pairs.
• Cosmological Constant. How do virtual pairs lead to a possible explantion for the Cosmological Constant? How does a matter particle differ from its anti-matter twin?

Weighing the Universe and Determining the Expansion Rate for the Universe

• Describe how the following methods used to determine the ultimate fate of the Universe work:
  • Comparison of the mass of the Universe to the escape speed of the Universe. What is the result of these studies? How does it compare to the following two studies?
  • Examination of the behavior of the Hubble Law at large z. How is the Hubble Law at large z determined? What standard candles are used for this exercise? What is the fate of the Universe implied by these results?
  • Comparison of the models of the Universe to the CMBR. How did WMAP use the small fluctuations in the CMBR to determine the dark matter content of the Universe? What is the dopole anisotropy?
• What is current best model for the Universe? What is the Universe composed of for the best model?
• Describe the methods used to determine the mass (in galaxies, binary galaxies, clusters of galaxies, from peculiar motions, from gravitational lensing) of the Universe. How much mass (in terms of the critical density) is found in these studies? How are these results reconsiled with the fact that there is strong evidence (from other methods) which imply that the Universe is flat, that is, the Universe has the critical density?
• How is the expansion rate of the Universe determined? What is the most difficult aspect in the determination of the expansion rate of the Universe?
• What is the extragalactic distance ladder? What is the Tully-Fisher method (how does it work)? How do Cepheids fit into the scheme? What are other ways to determine distances of distant objects? How do TYpe Ia SN fit into the extragalactic distance ladder?
• Describe how objects cluster in the Universe. Describe the properties of clusters of galaxies (such as Virgo and Coma). Why are there no spirals found near the centers of rich clusters of galaxies? What are cD galaxies? Why are supergiant Elliptical galaxies often times found near the centers of rich clusters of galaxies? How were observations of galaxy clusters used to detect Dark Matter? Who was the first astronomer to suggest the existence of Dark Matter? (What is meant by Dark Matter?)
• What are voids, filaments, and the Sloan Great Wall? How were these features detected? Does the observed structure in the Universe rule out the Cosmological Principle as a viable asuumption concerning the nature of the Universe? Why or why not. Is the structure observed in the Universe consistent with the CMBR observations?