The non-isothermal stage of magnetic star formation - II. Results
The non-isothermal stage of magnetic star formation - II. Results
复制标题
磁星形成的非等温阶段 - II。
DOI：
10.1111/j.1365-2966.2010.17110.x
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发表时间：
2010
影响因子：
4.8
通讯作者：
T. Mouschovias
中科院分区：
文献类型：
--
作者：
Matthew W. Kunz;T. Mouschovias
在之前的一篇论文中，我们阐述了轴对称几何结构中磁支撑、自引力分子云中碎片（或核心）的形成和演化问题，解释了双极扩散和欧姆耗散、颗粒化学和动力学以及辐射传输的影响。在这里，我们提出了恒星形成模拟的结果，准确地跟踪了密度超过11个数量级的原恒星碎片的演化（从300到约10 14 cm -3 ），即从早期双极扩散引发的碎片阶段，经过磁超临界、动态收缩阶段和随后的磁解耦阶段，到接近流体静力平衡的原恒星核心的形成。 Fiedler 和 Mouschovias 发现，引力驱动的双极扩散导致磁超临界核心的形成和随后的动态收缩。此外，我们发现双极扩散（而不是欧姆耗散）负责将除电子之外的所有物质从磁场中解耦，其密度约为 3 × 10 12 cm -3 。磁解耦先于中心恒星物体的形成，并最终在静水核心外部产生磁通量集中（“磁墙”）——塔西斯和穆霍维亚斯通过不同的方法也发现了这一点。在大约相同的密度下，欧姆耗散变得比双极扩散（7 × 10 12 cm -3 ）更重要，颗粒携带大部分电荷和电流。前恒星核心仍然呈圆盘状，半径小至~10个天文单位，其内部的热压力变得很重要。至少对于强磁性新生恒星来说，恒星形成的磁通量问题在演化的这个阶段得到了解决，即通过中心密度 ≈10 14 cm -3 。静压核心的半径为 ≈2 au，密度为 ≈10 14 cm -3 ，温度为 ≈300 K，磁场
In a previous paper we formulated the problem of the formation and evolution of fragments (or cores) in magnetically supported, self-gravitating molecular clouds in axisymmetric geometry, accounting for the effects of ambipolar diffusion and Ohmic dissipation, grain chemistry and dynamics, and radiative transfer. Here, we present results of star formation simulations that accurately track the evolution of a protostellar fragment over 11 orders of magnitude in density (from 300 to ≈10 14 cm −3 ), i.e. from the early ambipolar-diffusion-initiated fragmentation phase, through the magnetically supercritical, dynamical-contraction phase and the subsequent magnetic decoupling stage, to the formation of a protostellar core in near hydrostatic equilibrium. As found by Fiedler & Mouschovias, gravitationally-driven ambipolar diffusion leads to the formation and subsequent dynamic contraction of a magnetically supercritical core. Moreover, we find that ambipolar diffusion, not Ohmic dissipation, is responsible for decoupling all the species except the electrons from the magnetic field, by a density of ≈3 × 10 12 cm −3 . Magnetic decoupling precedes the formation of a central stellar object and ultimately gives rise to a concentration of magnetic flux (a ‘magnetic wall’) outside the hydrostatic core – as also found by Tassis & Mouschovias through a different approach. At approximately the same density at which Ohmic dissipation becomes more important than ambipolar diffusion (7 × 10 12 cm −3 ), the grains carry most of the electric charge as well as the electric current. The prestellar core remains disc like down to radii ∼10 au, inside which thermal pressure becomes important. The magnetic flux problem of star formation is resolved for at least strongly magnetic newborn stars by this stage of the evolution, i.e. by a central density ≈10 14 cm −3 .T he hydrostatic core has radius ≈2 au, density ≈10 14 cm −3 , temperature ≈300 K, magnetic field