Amplification of Interstellar Magnetic Fields by Supernova-driven Turbulence
Amplification of Interstellar Magnetic Fields by Supernova-driven Turbulence
复制标题
超新星驱动的湍流增强星际磁场
DOI：
10.1086/425297
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发表时间：
2004
期刊：
影响因子：
--
通讯作者：
G. Mathews
中科院分区：
文献类型：
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作者：
D. Balsara;Jongsoo Kim;M. Mac Low;G. Mathews
几条证据表明，在原银河系和银河系环境中，磁场增长迅速。然而，平均场发电机理论一直表明磁场增长相当缓慢，需要大约一个哈勃时间才能达到观测值。当系统具有高磁雷诺数时，理论上的困难只会变得更糟，就像银河系和原银河系环境的情况一样。如果能够快速放大磁场，这种差异就可以得到调和。继2001年的工作Balsara和同事，我们表明，星际介质，是由现实的能量输入超新星爆炸占主导地位，将自然成为一个强烈的湍流介质与大的积极和消极的动力学螺旋度值。尽管介质是由可压缩运动驱动的，但在这种高马赫数流中的动能主要集中在螺线管而不是可压缩运动中。这些结果源于强激波之间的相互作用以及它们在我们的模型中自洽产生的星际湍流。此外，这种相互作用也产生了大的动力学螺旋的任何符号。湍流，我们的模型有两个其他特点的快速发电机：磁能增长独立的规模和增长时间，是可比的涡流周转时间。这种线性增长阶段允许磁场快速增长，直到磁能达到动能的约1%。在那个阶段，其他产生磁场的天体物理过程可以接管。本文研究了湍流的能量学、功率谱、统计学和结构。激波-湍流相互作用被证明是螺旋度产生和磁场放大的一种非常普遍的机制，适用于阻尼Lyα系统、原星系、银河系、星暴星系、团内介质和分子云。
Several lines of evidence suggest that magnetic fields grow rapidly in protogalactic and galactic environments. However, mean field dynamo theory has always suggested that the magnetic fields grow rather slowly, taking of order a Hubble time to reach the observed values. The theoretical difficulties only become worse when the system has a high magnetic Reynolds number, as is the case for galactic and protogalactic environments. The discrepancy can be reconciled if fast processes for amplifying the magnetic field could operate. Following the 2001 work of Balsara and coworkers, we show that an interstellar medium that is dominated by realistic energy input from supernova explosions will naturally become a strongly turbulent medium with large positive and negative values of the kinetic helicity. Even though the medium is driven by compressible motions, the kinetic energy in this high Mach number flow is mainly concentrated in solenoidal rather than compressible motions. These results stem from the interaction of strong shocks with each other and with the interstellar turbulence they self-consistently generate in our model. Moreover, this interaction also generates large kinetic helicities of either sign. The turbulent flow that we model has two other characteristics of a fast dynamo: magnetic energy growth independent of scale and a growth time that is comparable to the eddy turnover time. This linear phase of growth permits the field to grow rapidly until the magnetic energy reaches about 1% of the kinetic energy. At that stage, other astrophysical processes for producing magnetic fields can take over. Energetics, power spectra, statistics, and structures of the turbulent flow are studied here. Shock-turbulence interaction is shown to be a very general mechanism for helicity generation and magnetic field amplification, with applicability to damped Lyα systems, protogalaxies, the Galaxy, starburst galaxies, the intracluster medium, and molecular clouds.