2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/12889The nature of the obscuring material in active galactic nuclei is still uncertain. Although some sources, such as Cygnus A, show evidence for a geometrically thick ``torus'' as originally suggested, recent work on the radiation-driven warping instability discovered by Pringle suggests that obscuration by thin, warped disks may play a crucial role in AGN.8 pages, 2 figures. To appear in "Highly Redshifted Radio Lines", ed. C. Carilli, S. Radford, and G. Langston, ASP, in pressAstrophysicstext