Describe some differences between quasars and normal galaxies.
Describe the arguments supporting the idea that quasars are at the distances indicated by their redshifts.
In what ways are active galaxies like quasars but different from normal galaxies?
Why could the concentration of matter at the center of an active galaxy like M87 not be made of stars?
Describe the process by which the action of a black hole can explain the energy radiated by quasars.
Describe the observations that convinced astronomers that M87 is an active galaxy.
Why do astronomers believe that quasars represent an early stage in the evolution of galaxies?
Why were quasars and active galaxies not initially recognized as being “special” in some way?
What do we now understand to be the primary difference between normal galaxies and active galaxies?
What is the typical structure we observe in a quasar at radio frequencies?
What evidence do we have that the luminous central region of a quasar is small and compact?