34.4 Dark Matter and Closure
Galactic rotation curves pointing to unseen mass, neutrino oscillation as proof of neutrino mass, and whether matter is dense enough to close the universe.
2 exercises
34.4 Exercise 5
If the dark matter in the Milky Way were composed entirely of MACHOs (evidence shows it is not), approximately how many would there have to be? Assume the average mass of a MACHO is 1/1000 that of the Sun, and that dark matter has a mass 10 times that of the luminous Milky Way galaxy with its stars of average mass 1.5 times the Sun’s mass.
34.4 Exercise 7
Assume the average density of the universe is 0.1 of the critical density needed for closure. What is the average number of protons per cubic meter, assuming the universe is composed mostly of hydrogen?
Adapted from College Physics © 2022 Rice University. Licensed under CC BY 4.0. Sources: College Physics 2e, College Physics for AP® Courses 2e. Imported at revision f98d7a7.