Limitations on thermal and nonthermal models for the radiation from extragalactic sources.

Both thermal and nonthermal models for the radiation from QSOs and Seyfert galaxies are discussed in terms of the size limitations imposed by the models. It is concluded that if daily fluctuations in the luminosity of Seyfert galaxies are confirmed and do represent a maximum size for the sources, then neither dust models nor ordinary synchrotron models can explain the radiation. Colgate's proposal involving the production of infrared radiation by a nonthermal plasma is considered, and a more detailed theory is derived which indicates that the process cannot produce infrared radiation.