"Dead quasars" in nearby galaxies?
The nuclei of some galaxies undergo violent activity, quasars being the most extreme instances of this phenomenon. Such activity is probably short-lived compared to galactic lifetimes, and was most prevalent when the universe was only about one-fifth of its present age. A massive black hole seems the inevitable end point of such activity, and dead quasars should greatly outnumber active ones. In recent years, studies of stellar motions in the cores of several nearby galaxies indicate the presence of central dark masses which could be black holes. This article discusses how such evidence might be corroborated, and the potential implications for our understanding of active galaxies and black holes.
Rees
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