Variability of Emission Lines in Quasar Spectra

Analysis of ultraviolet spectra of quasars obtained with IUE indicate that the permitted emission lines in quasar spectra are variable. The upper limit for the delay between a change in the continuum and the consequential change in the emission lines is about 9 month. This rapid response of the permitted emission lines to changes in the continuum leads to a number of problems in understanding the nature of quasars.