1. The table at left below lists the mass-to-light ratios in several
astronomical systems. The size scale in parsecs (=3.26 light years) of
each system is also provided.
(a) Are there any systems that have a mass-to-light ratio like that
of individual stars? In which systems is dark matter more important?
(b) Compare the mass-to-light ratio in spiral galaxies with that found
in a galaxy cluster. Can the dark matter content of individual galaxies
explain the dark matter of clusters?
(c)The plot at lower right shows what these numbers would look like on log scales.
What is the simplest function that you could fit to the
graph? What can you conclude about the relative importance of dark matter
in small and large systems in the Universe?
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Image from Schombert Summary of Dark Matter and Energy |
2. Comparisons of the observed large scale structure in the Universe and simulations of Universes with different amounts of dark matter (and energy) have been very effective in setting limits on the amount of dark matter in the Universe. To get a feeling for how this works, run the "Interactive Lab", showing Simulations of Development of Large Scale Structure. In this simulation, you can try different values of the mass density of the Universe and the strength of the initial variation in local density (amplitude of density fluctuations) and compare to those actually observed (image and histogram plot). What values of the parameters provide the best match to the observed structure of the Universe? How unique do these numbers seem? Explain your reasoning.
3. Read about Dark Matter Candidates and the Search for Particle Dark Matter .
(a) Based on your reading and class notes,
briefly explain why astronomers expect that dark matter is made up of
primarily non-baryonic material.
(b) Briefly describe how astronomers are trying to directly detect
non-baryonic material. Why is it so difficult?
Last updated October 12, 2018