A doughnut-shaped ring of gas and dust surrounding a supermassive black hole.In the context of active galactic nuclei, a torus is a doughnut-shaped ring of gas and dust that surrounds a supermassive black hole. This structure plays a crucial role in the unified model of active galactic nuclei, explaining why some black holes appear as quasars while others are hidden from view. The torus absorbs optical and ultraviolet light from the accretion disk and re-emits it in the infrared, making it a key observational signature.
The torus concept was introduced in the 1980s as part of the unified model of active galactic nuclei, primarily through the work of Robert Antonucci and Joseph Miller.
The torus is thought to be fed by material falling toward the black hole, which forms a rotating, flattened structure due to conservation of angular momentum. The inner edge of the torus is heated by the accretion disk to temperatures of hundreds to thousands of kelvin, producing strong infrared emission. Depending on the viewing angle, the torus can obscure the central engine, leading to different observed classes of active galactic nuclei.
Crucial for interpreting observations of quasars and Seyfert galaxies, and for estimating the masses of supermassive black holes from infrared reverberation mapping.
The torus can be so thick that it completely hides the black hole's accretion disk from our line of sight, making the object appear as a 'type 2' AGN rather than a bright quasar.

















