Formation and evolution of a high-density gaseous disk in a dense stellar system

Here considered is evolution of a rotating dense stellar system which could be applied to nuclei of active galaxies. In the central region of the system, a massive disk is formed out of gas supplied by stellar mass loss. As the increase of the temperature and density in the disk due to an accumulation of the liberated gas, a nuclear burning ignites at its equatorial plane. When the nuclear burning becomes thermally unstable, the disk expands rapidly, and the instability results in a sudden release of energy as much as 10--60 ergs within 106 years. The instability would develop into an explosion, provided the gaseous density of the disk is sufficiently high. (auth.)