As mentioned in Section 16.4, the fact that quasars can vary in brightness in just a few hours or days suggests that their size is only a few light hours or light days across. Explain how we can make...

As mentioned in Section 16.4, the fact that quasars can vary in brightness in just a few hours or days suggests that their size is only a few light hours or light days across. Explain how we can make this statement.

Sometimes astrophysicists refer to “hot dark matter.” What do you suppose that is? Research the topic on the web and discuss.