DYNAMO ACTIVITIES DRIVEN BY MAGNETOROTATIONAL INSTABILITY AND THE PARKER INSTABILITY IN GALACTIC GASEOUS DISKS
DYNAMO ACTIVITIES DRIVEN BY MAGNETOROTATIONAL INSTABILITY AND THE PARKER INSTABILITY IN GALACTIC GASEOUS DISKS
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DOI：
10.1088/0004-637x/764/1/81
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发表时间：
2013-01
期刊：
影响因子：
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通讯作者：
M. Machida;K. Nakamura;T. Kudoh;T. Akahori;Y. Sofue;R. Matsumoto
中科院分区：
文献类型：
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作者：
M. Machida;K. Nakamura;T. Kudoh;T. Akahori;Y. Sofue;R. Matsumoto
我们在不假设赤道对称的情况下对银河系气态盘中的发电机活动进行了全局三维磁流体动力学模拟。数值结果表明方位磁场的增长与赤道面不对称。随着磁旋转不稳定性 (MRI) 的增加，磁场的平均强度会放大，直到磁压力达到气体压力的 10%。当盘表面附近的局部等离子体β(=pgas/pmag)变得小于5时，在盘的一旋转周期内，磁通量由于帕克不稳定性而从盘逃逸。相干磁场的浮逸逃逸通过产生极性相反的盘磁场来驱动发电机活动，以满足磁通量守恒。来自磁盘的方位角磁通量的浮动以及随后由 MRI 驱动器在 10 个旋转周期的时间尺度上准周期反转方位角磁场对磁盘磁场的放大。由于旋转速度随半径减小，因此方位磁场反转之间的间隔随半径增大。根据数值结果计算的旋转测量显示对应于偶极场的对称性。
We carried out global three-dimensional magnetohydrodynamic simulations of dynamo activities in galactic gaseous disks without assuming equatorial symmetry. Numerical results indicate the growth of azimuthal magnetic fields non-symmetric to the equatorial plane. As the magnetorotational instability (MRI) grows, the mean strength of magnetic fields is amplified until the magnetic pressure becomes as large as 10% of the gas pressure. When the local plasma β (=pgas/pmag) becomes less than 5 near the disk surface, magnetic flux escapes from the disk by the Parker instability within one rotation period of the disk. The buoyant escape of coherent magnetic fields drives dynamo activities by generating disk magnetic fields with opposite polarity to satisfy the magnetic flux conservation. The flotation of the azimuthal magnetic flux from the disk and the subsequent amplification of disk magnetic field by the MRI drive quasi-periodic reversal of azimuthal magnetic fields on a timescale of 10 rotation periods. Since the rotation speed decreases with radius, the interval between the reversal of azimuthal magnetic fields increases with radius. The rotation measure computed from the numerical results shows symmetry corresponding to a dipole field.