Finding galaxies with active nuclei

The nuclei of most galaxies host supermassive black holes with millions or even billions of solar-masses of material. Material in the vicinity of such black holes can accrete onto a torus of dust and gas around the black hole, and when that happens the nuclei radiate powerfully across the full spectrum. These active galactic nuclei (AGN) are among the most dramatic and interesting phenomena in extragalactic astronomy, and puzzling as well. Exactly what turns the accretion on or off is not understood, nor is how the associated processes produce the emission, generate jets of particles, or influence star formation in the galaxy.

Continued...
Source

 

Credit: NASA/Hubble; Polimera et al. 2018

The Hubble image of a galaxy spotted by Spitzer's IRAC infrared camera to be variable, probably because it harbors an active galactic nucleus. IRAC infrared surveys taken over a decade have spotted about 800 previously unknown AGN.

Source / Image Courtesy

This movie shows the galaxy gas, followed over a series of scales from a galaxy merger down to a central super-massive black hole.

This animation illustrates the anatomy of an active galactic nucleus powered by a supermassive black hole. The animation also shows how the viewing angle affects the appearance of the nucleus.