Magneto-thermal evolution of neutron stars
Magneto-thermal evolution of neutron stars
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DOI：
10.1051/0004-6361:200811229
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发表时间：
2008-12
影响因子：
6.5
通讯作者：
J. Pons;J. Miralles;U. Geppert
中科院分区：
文献类型：
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作者：
J. Pons;J. Miralles;U. Geppert
上下文。中子星外壳中磁场的存在导致了非球对称的温度分布。磁扩散率和热导率的强烈温度依赖性，以及磁耗散产生的热量，将NSS的磁演化和热演化耦合在一起，这不能用分离的一维问题来表示。目标。研究了中子星壳层中轴对称的热演化和磁场演化的相互影响。考虑到实际的微物理输入，我们发现焦耳效应减缓的热释放与地壳中的电流循环是一致的，并且我们在二维冷却计算中考虑了它的影响。方法：研究方法。我们用一种混合方法(角度谱，径向有限差分格式)与热扩散方程耦合来数值求解感应方程。为了改进边界条件，我们还重新考察了包络定常解，更新了众所周知的TB−ts关系，以包括二维传热计算和新的微物理输入的影响。结果。我们首次提出了中子星磁热耦合演化的长期二维模拟。这大大改进了以前的工作，其中至少一个部分(热扩散或磁扩散)采用了非常粗糙的近似。我们的结果表明，焦耳加热和磁扩散之间的反馈很强，导致在NS的头105−106年中，强场的消散速度更快。因此，所有出生时磁场大于临界值(>；5×1013G)的中子星在后期达到相似的场强(≈2−3×1013G)。在不考虑初始磁场强度的情况下，106年后温度变得很低，以至于磁扩散时间尺度变得比射电脉冲星的典型年龄更长，从而导致老NS中的磁场明显没有分布。我们也证实了在初步工作中讨论的相对年轻的NSS的磁场与表面温度之间的强关联。具有较强内环分量的模式的有效温度系统地高于具有纯极向场的模式，这是由于储存在环场中的附加能量随着场的消散而逐渐释放。
Context. The presence of magnetic fields in the crust of neutron stars c auses a non-spherically symmetric temperature distribution. The strong temperature dependence of the magnetic diffusivity and thermal conductivity, together with the heat generated by magnetic dissipation, couple the magnetic and thermal evolution of NSs, that cannot be formulated as separated one‐dimensional problems. Aims. We study the mutual influence of thermal and magnetic evoluti on in a neutron star’s crust in axial symmetry. Taking into account realistic microphysical inputs, we find the heat rel eased by Joule effect consistent with the circulation of currents in the crust , and we incorporate its effects in 2‐dimensional cooling calculations. Methods. We solve the induction equation numerically using a hybrid method (spectral in angles, but a finite‐di fferences scheme in the radial direction), coupled to the thermal diffusion equation. To improve the boundary conditions, we also revisit the envelope stationary solutions updating the well known Tb− Ts‐relations to include the effect of 2‐D heat transfer calculations and new microphysical inputs. Results. We present the first long term 2‐dimensional simulations of t he coupled magneto-thermal evolution of neutron stars. This substantially improves previous works in which a very crude approximation in at least one of the parts (thermal or magnetic diffusion) has been adopted. Our results show that the feedback between Joule heating and magnetic diffusion is strong, resulting in a faster dissipation of the stronger fields during the first 10 5 − 10 6 years of a NS’s life. As a consequence, all neutron stars born with fields larger than a critical value (> 5×10 13 G) reach similar field strengths (≈ 2−3×10 13 G) at late times. Irrespectively of the initial magnetic field strength, after 10 6 years the temperature becomes so low that the magnetic diffusion timescale becomes longer than the typical ages of radio‐pulsars, thus resulting in apparently no diss ipation of the field in old NS. We also confirm the strong correl ation between the magnetic field and the surface temperature of relatively young NSs discussed in preliminary works. The effective temperature of models with strong internal toroidal components are systematically higher than those of models with purely poloidal fie lds, due to the additional energy reservoir stored in the toroidal field tha t is gradually released as the field dissipates.