| Research Abstract |
(1) Black hole/pulsar electrodynamics
Black hole magnetospheres are divided by the general-relativistic effect (dragging of the inertial frame) into the two parts, the outer and inner magnetospheres with plasma source between in the quasi-stationary state (Okamoto 1992) . The spacetime in the outer magnetosphere is almost flat and well approximated by the pulsar-type magnetosphere in which the outgoing wind flows more or less along field lines towards to infinity, whereas the inner one with the ingoing plasma flow toward the event horizon is itself generated by dragging of the inertial frame.Okamoto investigated, together with Mestel and Horiuchi, the electric field coupled with the toroidal magnetic field, simplifying the poloidal field, in the inner magnetosphere.They revealed the necessary formation of the BETA-parallel electric field EPSILON and resulting particle acceleration, follwed by gamma-ray radiation, radiation damping and pair-creation (Horiuchi, Mestel and Okamoto 1994) . Kaburaki with Kudoh studied the structure of resistive-MHD wind from rapidly rotating strongly magnetized stars (Kudoh and Kaburaki 1994) .
(2) Black hole thermodynamics
Okamoto and Kaburaki, together with Katz, carried out stability analysis of Kerr and Kerr-Newman black holes, using the turning point method (Kaburaki, Katz and Okamoto 1993 ; Katz, Okamoto and Kaburaki 1993) . Okamoto, together with Katz and Parentani, studied thermodynamic metastability and fluctuations of Hawking radiation with or without a black hole (Okamoto, Katz and Parentani 1995 ; Parentani, Katz and Okamoto 1995 ; Okamoto 1995) . They indicated that the composite system and self-gravitating radaition, respectively, survive their metastable states up to the very points of thermodynamic instabilty.Kaburaki (1994) reexam-ined and refined the criterion of thermodynamic stability.
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