Active galactic nuclei (AGN) are galaxies that have very
energetic central regions, due to either the presence of a black hole or
star formation activity at the core of the galaxy. Three main types
of AGN are quasars, ("quasi-stellar objects" or QSOs),
which are very compact objects
that resemble stars in optical images;
Seyfert galaxies, characterized by fluctuations in brightness at their
cores;
and radio galaxies, which emit massive jets of gas powered by black holes
at their cores. In general, AGN have six
main properties: (1) very compact angular size; (2) high ,
many billions of times brighter than our own Sun; (3)
Continuum emission from the core,
meaning that the objects emit radiation at a range of wavelengths from
radio to x-ray; (4) ;
(5) variability of the continuum and spectral line emission, and (6)
strong emission of radiation at radio wavelengths.
Many of the images on these pages are Double Radio Sources
Associated with Galactic Nuclei (DRAGNs), which are large-scale double
radio sources produced by that
are launched by processes in AGN.
You can learn more about such sources at
.
Click on any Sub-category name below to view
all the images in that sub-category, or click any thumbnail to view the details of
that image. Other images of AGN can be found in the
and the Jodrell Bank
.
Visit
non-NRAO website for more information on active galactic nuclei.
