PY 228; Final Exam

The following is a sample final exam, taken from last spring semester.

Section I. 4 points each. Please give a brief explanation for your answer.

What is the only thing that can hold off gravity for eternity (Deitys do not count)?
What is the Cosmic Microwave Background, and why is it important?
Did you learn more questions or answers in this course?
Why is the isotropy of the Universe a problem for the standard Big Bang theory? How does inflation solve this problem?
Why do flat galactic rotation curves imply dark matter?
Why do low mass stars reach a degenerate state earlier in their evolution than massive stars?
Which has a higher optical depth to visible light, a four-inch thick sheet of glass or a one-hundredth of an inch thick sheet of aluminum foil?
It has been pointed out that if H_o > 120 km/s/Mpc or so, the Milky Way would be the largest spiral galaxy in the Universe. Explain this line of reasoning.
Why is there an observed dipole in the Cosmic Microwave Background?
Why is radiative cooling by molecular lines important for the star-formation process?
Describe one important observation/discovery made by the Hubble Space Telescope.
Enumerate the possible end state of stars. What quantity determines which befalls a particular star.
Sketch an H-R diagram for a young cluster of stars. Label the axes appropriately. Sketch the same cluster several billions of years later.

Section II. 8 points each. Do all questions. Show your work!

Cosmic rays are measured with energies up to 10**20 eV per particle! How fast would you be moving if you had this much kinetic energy?
Gamma ray bursts remain a mystery to us largely because we do not know their distance from Earth. If a typical burst produces a flux at the Earth of .001 erg/s/cm**2, what is the intrinsic luminosity of the burst source if its distance is 2000 Mpc? If the burst lasts 0.1 seconds, how much energy is released in the burst? Compare this with the binding energy of a neutron star.
The stellar appearing object BL Lacertae has a measured optical flux of 3x10**-10 ergs/s/cm**2. When the light from the star is blocked out the surrounding nebulosity is observed to have a redshift of z = 0.07. What is the absolute luminosity of BL Lac?
For a flat (k=0) matter-dominated Universe, show that the age of the Universe is 2/(3H_o). Evaluate the age for the current estimated range in the Hubble constant.
The quasar 1059+730 has a redshift of 0.089. What is the distance to the quasar if H_o = 50, if H_o = 100? A supernova observed in 1059+730 had an apparent magnitude of +19.6. If this was a type I SN (which have an absolute magnitude of -19.3), what is the distance to the quasar?
Given that the temperature of the Universe is proportional to one over the scale factor, what is the redshift corresponding to the epoch in the Universe when electrons and positrons were freely created? (Today, T = 3 K.)