Evolution of Stars and Gas in Galactic Nuclei
Since the discovery of quasars and other types of active galactic nuclei (AGN) various theoretical models have been proposed to explain the characteristics of these exceptional astronomical objects. Among their extreme properties are maximum luminosities exceeding 1047 erg/s, generated on very small spatial scales (less than 1 pc), the non-thermal continuum emission, polarization, the variability on short time scales and the occurrence of relativistic jets (for an overview compare e.g. Netzer 1989). As primary energy source was suggested (Lynden-Bell 1969, Hills 1975) the liberation of gravitational binding energy by accretion and dissipative processes in the vicinity of a supermassive black hole. Such a model is at least for the most luminous sources now widely accepted as a standard model (Rees 1984, Netzer 1990). One should note, however, that this standard model still poses some outstanding and serious questions; these are for example its wrong predictions for the Lyman-α to Hβ line ratios and for the FeII line intensities (see Netzer 1989 and references therein).
KeywordsAnisotropy Lution Tral
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