Magnetic field amplification and magnetically supported explosions of collapsing, non-rotating stellar cores
Magnetic field amplification and magnetically supported explosions of collapsing, non-rotating stellar cores
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DOI：
10.1093/mnras/stu1969
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发表时间：
2014-05
影响因子：
4.8
通讯作者：
M. Obergaulinger;T. Janka;Miguel 'Angel Aloy Tor'as
中科院分区：
文献类型：
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作者：
M. Obergaulinger;T. Janka;Miguel 'Angel Aloy Tor'as
在轴对称的情况下，研究了15个太阳质量的非自转星的核心在崩塌过程中的磁场放大和反弹后的演化。为此，我们在两矩近似下求解了磁流体力学和中微子输运的耦合方程。坠落前的磁场通过在瀑布中的压缩而被强烈放大。1010G量级的初始场转化为与在脉冲星中观察到的类似的原中子星场，而更强的初始场产生类似于磁星的终末场强度。核反弹后，磁场平流通过流体动力不稳定的中微子加热层，在那里对流和站立吸积激波不稳定导致的非径向流动进一步放大了磁场。因此，由此产生的五阶放大系数是在通过震后层的平流时间尺度内发生的小涡翻转次数的结果。由于这一限制，我们的大多数模型没有达到动能和磁能的均分，因此，演化过程类似于非磁情况，当一个或几个高熵气泡持续几个动力学时间尺度时，大约800毫秒后爆炸。在我们研究的初始场最强的模型10^12 G中，实现了流与场的均分，磁张力有利于这种长寿命的高熵气泡更早地发展，并强制形成相当有序的大尺度流型。因此，这个模型在表现出非常规则的冲击振荡后，比非磁性模型爆炸得早得多。
We study the amplification of magnetic fields in the collapse and the post-bounce evolution of the core of a non-rotating star of 15 solar masses in axisymmetry. To this end, we solve the coupled equations of magnetohydrodynamics and neutrino transport in the two-moment approximation. The pre-collapse magnetic field is strongly amplified by compression in the infall. Initial fields of the order of 1010 G translate into proto-neutron star fields similar to the ones observed in pulsars, while stronger initial fields yield magnetar-like final field strengths. After core bounce, the field is advected through the hydrodynamically unstable neutrino-heating layer, where non-radial flows due to convection and the standing accretion shock instability amplify the field further. Consequently, the resulting amplification factor of order five is the result of the number of small-eddy turnovers taking place within the time scale of advection through the post-shock layer. Due to this limit, most of our models do not reach equipartition between kinetic and magnetic energy and, consequently, evolve similarly to the non-magnetic case, exploding after about 800 ms when a single or few high-entropy bubbles persist over several dynamical time scales. In the model with the strongest initial field we studied, \$10^{12}\$ G, for which equipartition between flow and field is achieved, the magnetic tension favours a much earlier development of such long-lived high-entropy bubbles and enforces a fairly ordered large-scale flow pattern. Consequently, this model, after exhibiting very regular shock oscillations, explodes much earlier than non-magnetic ones.