Reading: Web Notes (for overview), Chapter 24: Normal Galaxies, Chapter 25: Active Galactic Nuclei, Chapter 26: Cosmology, Chapter 27: The Early Universe
Do the reading, look at the questions at the end of each chapter for practice and consider the following.
Tail end of Milky Way Stuff
Roughly, what is the way black holes were defined in class? What is special about the speed of light? How fast is the speed of light? Is there a black hole at the center of the Milky Way galaxy? How could do we deduce that there is a black hole at the center of our Galaxy? For what would we be looking if we were trying to prove a black hole existed at the center of our Galaxy? What is the Schwarzschild radius, the event horizon, the singularity?
Normal Galaxies
Compare spirals, barred spirals, ellipticals, S0's (lenticulars), and Irregular (Irr) galaxies. Consider their gas and dust content, their bulges, their disks, their star formation histories, their origins, the relative ages of their stars, their colors. How are the formation processes for spirals and elliptical galaxies different?
What is the Hubble sequence? Sketch the Hubble sequence. "The Hubble sequence is a morphological sequence"; what does this mean? How does the appearance of disk like galaxies change as they move down the Hubble sequence? Contrast Sa galaxies to Sc galaxies.
Make a table or diagram which indicates the different length scales on which we see galaxies cluster. Roughly, what is the scale for an individual galaxy? What are the scales for the Great Wall and Voids? How do these compare to the size of the Universe? Consider the volume of the Universe occupied by these features. What volumes of the Universe do these features occupy? Does the observed inhomogeneity rule out the Cosmological Principle?
Active Galactic Nuclei (AGNs)
What features of AGNs differentiate them from normal galaxies? Are AGNs all fundamentally different? Are they thought to be oddballs or are they thought to fit into the scheme of galaxy evolution? What are the bases for the answers to the preceding questions? What difference would I see if I compared the spectra of AGNs to normal galaxies. What are the different types of AGNs? Roughly what are their properties? Explain the difference between stellar (thermal) and nonstellar (nonthermal) emission. What is the physical interpretation of electromagnetic radiation (as defined in class)? What is synchrotron emission?
How is Hubble's law used to infer distances to galaxies? What is the Doppler shift? What is the redshift, z? For slow speeds, how are z and the speed of the object related?
What are the principal observationalfacts which make AGNs difficult to understand? How can the time variability of an object be used to infer upper limits on its size? If the light from an object varies on a time scale of 1 hour, roughly, what is the largest size the object could have?
Black holes are the energy engines for AGNs. What are the properties of black holes which make them natural engines for AGNs? Consider their sizes and their energy generation efficiencies. Roughly how many stars per year must AGN eat to power themselves? What is meant by Accretion? What is a tidal force? Why are tidal forces important for black hole accretion? Using tidal forces as the basis for your argument, why do we think we understand why QSOs are usually seen at great distances from the Milky Way (-->they existed early in the lifetime of the Universe_? That is, why do AGNs seem to shut-off?
What is the evidence that our ideas for black hole as the energy engines for AGNs are correct? What Hubble Space Telescope (HST) observations support black holes as energy engines?
Cosmology
There are a few observational facts which drive our thoughts about cosmology; the expansion of the Universe, the existence and properties of the CMBR, the chemical composition of the Universe. Today, we interpret these observations (and some further ones) within the context of what is known as the Big Bang Theory. What are some other observations which help to fill out our understanding of cosmological models (in particular, the Big Bang)?
State Olbers's Paradox. What is the resolution for Olbers's Paradox? Is dust obscuration a possible solution? Why or why not. What assumptions must be violated? What are the principal results we may infer from the resolution of Olbers's Paradox?
What is the Cosmological constant?
In what kind of Universe are we thought to live? How can we go about deciding in which type of universe we live? Use the geometry of the different universes to infer properties of parallel lines, the interior angles of triangles, ... . Have we been able to perform tests to look at these different possibilities?
Which Cosmological principle underlies the Friedman models for the Universe? What are the three types of solutions Friedman found which could describe our Universe. What are meant by the terms, open universe, closed universe, and flat universe? What tests are used to deduce the type of Universe it is in which we live?
What is the Heisenberg Uncertainty Principle? Give some examples of how the Heisenberg Uncertainty Principle manifests itself. How can one explain the existence of the Universe in terms of the Heisenberg Uncertainty Principle? What are virtual pairs of particles? What is meant by the term Planck Era? Describe the Planck Era. What is the Compton Wavelength? What is the Schwarzschild radius? Why are these concepts relevant toward an understanding of the Planck Era? What is Cosmic Censorship? What is meant by causality? The Universe is currently envisioned within the framework of General Relativity where we consider the space-time structure of the Universe. Space and time are just coordinates which describe events in the Universe. However, in our Universe, time has somewhat of a preferred position compared to the space (position of things). What is this preferred position? Should we expect time to have this preferred status based on our current theories? How many forces currently exist in the Universe? What are these forces? How did the nature of these forces change as the Universe evolved?