C131 3 次元磁気流体コードによる降着円盤と宇宙ジェットの数値実験

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We present results of three-dimensional global magnetohydrodynamic (MHD) simulations of accretion disks. Owing to the growth of the magneto-rotational instability, magnetic turbulence develops in the disk. When the initial magnetic field is toroidal and weak, magnetic energy is amplified exponentially and saturates when β=P_<gas>/P_<mag> ∿ 10. The Maxwell stress exerted by the tangled magnetic field lines efficiently transports angular momentum outward and enables accretion of the disk material. The magnetic viscosity α_B=-<B_γB_ψ/(4πP)> ∿ 0.01 is consistent with the conventional value. Magnetic reconnection taking place in the disk produces sporadic variation of the X-ray flux. The radial structure of the disk is found to be distinct from that of advection dominated accretion flows (ADAFs). When the accretion disk is initially threaded by large-scale poloidal magnetic fields, bipolar jet emanates from the surface of the disk.
2001-07-31