THE ROLE OF TURBULENT MAGNETIC RECONNECTION IN THE FORMATION OF ROTATIONALLY SUPPORTED PROTOSTELLAR DISKS
THE ROLE OF TURBULENT MAGNETIC RECONNECTION IN THE FORMATION OF ROTATIONALLY SUPPORTED PROTOSTELLAR DISKS
复制标题
湍流磁重联在旋转支撑原星盘形成中的作用
DOI：
10.1088/0004-637x/747/1/21
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
A. Lazarian
中科院分区：
文献类型：
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作者：
R. Santos;E. M. D. G. D. Pino;A. Lazarian
从分子云核中形成原恒星盘的过程仍然没有完全弄清楚。在理想的MHD条件下，通常嵌入的磁场从盘祖的角动量的去除可能会阻止在低质量恒星的主要原恒星吸积阶段形成旋转支撑盘。这就是所谓的磁制动问题，研究最多的机制，以减轻这个问题，并帮助消除多余的磁通量在星星形成过程中，所谓的双极扩散（AD），已被证明是不足以削弱磁制动至少在这个阶段的磁盘形成。在这项工作中，在湍流环境中的磁重联的理解的最新进展的动机下，我们呼吁磁重联介导的磁场扩散作为一种替代机制，用于消除磁通量。我们在原恒星盘形成的后期阶段数值研究了这种机制，并显示了它的高效率。通过完全三维的MHD模拟，我们表明，所产生的湍流磁重联的扩散率是能够运输的磁通量的外围的磁盘祖兼容的时间尺度的崩溃，允许形成一个旋转支持磁盘周围的原恒星的尺寸为100 Au，在早期吸积阶段的近开普勒配置文件。由于MHD湍流被认为存在于原恒星盘中，这是一种自然的机制，可以消除磁通量过剩，并允许这些盘的形成。这种机制排除了文献中讨论的假设欧姆电阻率增加的必要性。与我们早期的工作表明，磁通量从分子云核心是非常有效的，这项工作要求重新考虑AD的相对作用，在星星和行星的形成过程。
The formation of protostellar disks out of molecular cloud cores is still not fully understood. Under ideal MHD conditions, the removal of angular momentum from the disk progenitor by the typically embedded magnetic field may prevent the formation of a rotationally supported disk during the main protostellar accretion phase of low-mass stars. This has been known as the magnetic braking problem and the most investigated mechanism to alleviate this problem and help remove the excess of magnetic flux during the star formation process, the so-called ambipolar diffusion (AD), has been shown to be not sufficient to weaken the magnetic braking at least at this stage of the disk formation. In this work, motivated by recent progress in the understanding of magnetic reconnection in turbulent environments, we appeal to the diffusion of magnetic field mediated by magnetic reconnection as an alternative mechanism for removing magnetic flux. We investigate numerically this mechanism during the later phases of the protostellar disk formation and show its high efficiency. By means of fully three-dimensional MHD simulations, we show that the diffusivity arising from turbulent magnetic reconnection is able to transport magnetic flux to the outskirts of the disk progenitor at timescales compatible with the collapse, allowing the formation of a rotationally supported disk around the protostar of dimensions ∼100 AU, with a nearly Keplerian profile in the early accretion phase. Since MHD turbulence is expected to be present in protostellar disks, this is a natural mechanism for removing magnetic flux excess and allowing the formation of these disks. This mechanism dismisses the necessity of postulating a hypothetical increase of the ohmic resistivity as discussed in the literature. Together with our earlier work which showed that magnetic flux removal from molecular cloud cores is very efficient, this work calls for reconsidering the relative role of AD in the processes of star and planet formation.