Astronomy 123: Third Homework Assignment


  1. Recent evidence suggests that the Universe is filled with something termed "Dark Energy". What is evidence for the existence of dark energy and what are some hypothesis as to what it is?

  2. Baryons are normal particles (e.g. protons and neutrons) which make up all of ordinary matter. Find out how much baryonic matter contributes to the total energy density of the Universe. Also, describe what has been called the "missing baryon problem". What are some resolutions to this problem and how do "Low Surface Brightness Galaxies" fit in to the problem of missing baryons.

  3. Explain how the "top-down" scenario for the formation of structure (e.g. galaxies, clusters of galaxies) in the Universe differs from the "bottom-up" scenario.

  4. Consider our galaxy to be a very thin circular disk of stars of radius approximately 40,000 light years. If there are currently 1000 civilizations in our galaxy capable of communication, what is the approximate separation of these civilizations (in units of light years) if they are uniformly (e.g. equally spaced) distributed within this circular disk of stars?