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Published online by Cambridge University Press: 14 August 2015
The term “nearby galaxies” is not very precise. If we restrict ourselves to galaxies within the local group, we are really only talking about our Galaxy, M31 and M33. Since the Galactic Center has been reviewed extensively by Oort in Annual Reviews (1977), and I feel that there is nothing exceptional to say about the nuclei of M31 and M33 as far as phenomena other than their stellar content and central dynamics are concerned, to discuss interesting properties we must consider more distant objects. If we go out to the distance of the Virgo cluster, we already include objects such as NGC 5128, M82 and M87. Each of these galaxies shows or was claimed to show evidence of different kinds of violent nuclear activity. Indeed, it is obvious that within the volume occupied by the supercluster (whether or not it is really a physical entity) there must be many galaxies in which nuclear activity can be detected.