Material: Topic 3, Normal Galaxies (Chapter 24 & 25), Topic 4, Active Galactic Nuclei (Chapters 24 & 25), Topic 5, World Views of the Universe (Chapters 26)

Hubble's Galaxy Classification Scheme and the Hubble Tuning Fork Diagram

• Sketch Hubble's Tuning Fork Diagram. Pay care to to show the flattening of ellipticals changes, how bulge size, winding of spiral arms changes from class to class. How do the properties of the galaxies in terms of gas and dust content, stellar populations vary from class to class?
• Describe Elliptical, Spiral, Barred Spiral, SBO, S0, and Irregular galaxies. What are Lenticulars? What the differences between Sa, Sb, and Sc galaxies, E0 to E7 galaxies, Irr I and Irr II galaxies.
• Is the Hubble Tuning Fork diagram an evolutionary sequence? Do galaxies evolve?
• What kinds of galactic collisions occur? What are the results of collisions between similar mass disk galaxies, galaxies of greatly differing masses? Are collisions thought to be exceedingly rare? How many of a role do galactic colliions play in galaxy evolution? What are Supergiant Ellipticals? Where do they arise? Describe the interactions suffered (and to be suffered) by the Milky Way Galaxy. Describe the evolution and apperance of the Antennae, Cartwheel, and Mice galaxies.
• What is the extragalacitc 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?
• What is the cosmological redshift?
• 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 is meant by look-back time?`
• 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?

• What is the major difference between the way normal galaxies and active galactic nuclei produce their emission (How do their spectra differ)? What is meant by thermal emission? nonthermal emission?
• Describe the different families of bright AGNs. Which class is the most luminous? Which classes are found in normal galaxies (or are all AGNs found in normal galaxies)? What fraction of bright galaxies are AGNs?
• What observed features of AGNs make them difficult to understand? Are AGNs such bizarre objects that are considered to be completely outside the realm of normal galaxies or are they considered to extreme examples of normal galactic evolution? Upon what evidence is the answer to the preceding question based?
• How is rapid variability used to determine the maximum size of a emitting region?
• How was the Hubble Law used to find distances to QSOs? What does QSO mean?
• What are the models used to explain the nonthermal spectra of AGNs, the efficient energy production of AGNs, and the small size of AGNs? What evidence supports our picture of the energy engines of AGNs?
• What are supermassive Black Holes? Describe the evidence that the Universe contains supermassive Black Holes. Describe the supermassive Black Hole in the nucleus of our Galaxy. 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?

• Cite the primary pieces of evidence which drive our world view of the Universe. Describe the Big Bang Theory.
• What is Olbers's Paradox? Describe the paradox and the resolution of the paradox. (That is, what are the assumptions which underlie Olbers's Paradox?)
• Describe the Friedman models for the Universe. What assumption did Friedman make when finding his models for the Universe? Was this assumption valid?
• What is meant by spacetime? In terms of spacetime, describe each of Friedman's models for the Universe. What is meant by positive, negative, and zero curvature? In which type of universe are we though to live? Which universe is a closed universe (and what does this mean)? Which universe is an open universe (and what does this mean)? That is meant by topology?
• 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. What is meant by cosmological redshift? Describe cosmological redshift. How does the cosmological redshift fit in with the Hubble Law? What is meant by scale factor [R(t)]? How does the scale factor behave for each type of Friedman universe?
• What is the Cosmological Constant? What is the Horizon Problem? What is the Flatness Problem?