结晶白矮星中热盐对流对磁场的输运
Transport of Magnetic Fields by Thermohaline Convection in Crystallizing White Dwarfs
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中文总结 AI 辅助
本研究通过三维磁流体模拟发现，结晶白矮星中的热盐对流虽难自生强磁场，但可向外输运内部原有磁场，为观测到的强磁场提供解释。
中文摘要 AI 辅助
许多白矮星中观测到的强磁场的起源尚不确定。最近的观测表明，这类磁场在具有结晶核心的白矮星中更为常见。结晶过程会产生不稳定的成分梯度，驱动恒星流体包层中的热盐对流，这可能对磁场的浮现起到重要作用。我们使用布辛涅斯克近似，在周期性笛卡尔盒子中，对具有不同强度和方向磁场的热盐对流进行了三维磁流体动力学模拟。我们的模拟表明，当磁普朗特数较大（即磁扩散率较低）时，热盐对流可以产生磁场，但这些磁场可能太弱，无法解释磁白矮星中观测到的磁场。然而，模拟表明，强磁场可以被热盐对流向外平流而不会被破坏，这取决于净磁通量。因此，结晶诱导的热盐混合可能将最初被困在白矮星内部的磁场输运到其外层，使其能够被观测到。然而，需要使用更真实的几何结构和磁场配置进行额外模拟，以确认这种可能性。
英文摘要
The origins of strong magnetic fields observed in many white dwarfs are uncertain. Recent observations show that such fields are more common for white dwarfs with crystallized cores. Crystallization creates a destabilizing composition gradient that drives thermohaline convection in the star's fluid envelope, which may play an important role in magnetic field emergence. We perform 3D magnetohydrodynamical simulations of thermohaline convection with magnetic fields of various strengths and orientations, using the Boussinesq approximation in periodic Cartesian boxes. Our simulations suggest that thermohaline convection can generate magnetic fields when the magnetic Prandtl number is large (i.e., low magnetic diffusivity), but they are likely too weak to account for those observed in magnetic white dwarfs. However, the simulations indicate that strong magnetic fields can be advected outwards by the thermohaline convection without being destroyed, depending on the net magnetic flux. Hence, crystallization-induced thermohaline mixing may transport magnetic fields initially trapped in white dwarf interiors to their outer layers, allowing them to be observed. However, additional simulations using more realistic geometry and magnetic field configurations will be needed to confirm this possibility.
发表机构
- TAPIR, California Institute of Technology（加州理工学院 TAPIR）
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