ABSTRACT
The evidence for supermassive black holes at the centres of quasars and active galactic nuclei (AGNs) has been strong but not conclusive for several decades. Recently, the evidence for massive black holes in one particular AGN, in our own Galaxy, and in the Local Group Galaxy M32 has become extremely convincing. Thus, questions concerning gravitational waves generated by the interaction of massive black holes with smaller compact objects and with each other have become of strong interest. Signals from such sources also are likely to provide the strongest possible tests of general relativity.
