Figure 24-4: Quasars Are Extinct The greater the redshift of a quasar, the farther it is from Earth and the farther back in time we are seeing it. By observing the number of quasars found at different redshifts, astronomers can calculate how the density of quasars in the universe has changed over the history of the universe. The peak of quasar activity occurred more than 10 billion years ago, and there is no significant quasar activity today. The history of quasars is reminiscent of the history of the dinosaurs, which once populated the entire Earth but today are extinct.
(Peter Shaver, European Southern Observatory)