Optical variability of Quasi Stellar Objects

As many as 15 percent of the 96 QSOs studied can remain quiescent with respect to optical variability over the course of a decade. Within the QSO sample, at least 70 percent of the objects having an average magnitude greater than 17 are variable; a partial explanation of this strong correlation between variability and average magnitude may lie in the discovery that almost all of the bright objects are also radio-loud, while the faint portion of the sample is composed of both radio sources and objects found by solely optical means.