强磁场环境下中子星壳层结构性质研究

The study on structure properties of neutron star with strong magnetic fields is one of the focuses of front subjects. A large number of studies have shown that neutron star from outside to inside may be divided into four parts, namely, outer crust, inner crust, outer core, and inner core. Inner crust is a nonuniform system where nuclei coexist with nucleon and electron gases. As density increases, non-spherical nuclear structure, such as rod, slab, tube, and bubble, the so called nuclear pasta structure may appear in the inner crust. The microstructure of inner crust plays an important role in the astronomical observations of neutron stars such as cooling, periodicity, and gravitational wave. The astronomical observations indicate that strong magnetic fields may exist in some neutron stars. As a result, the properties of inner crust may be affected evidently by the strong magnetic fields. But, at present we still do not know the properties of nuclear pasta structure in inner crust with strong magnetic fields. Therefore, in this project, within the relativistic mean-field theory, we plan to adopt the self-consistent Thomas-Fermi approximation and the compressible liquid-drop model to study the influence of strong magnetic fields on the properties of nuclear pasta structure, radius of nucleus, and crust-core transition in neutron star. Besides, the properties of nuclear liquid-gas coexistence and finite-size effect with strong magnetic fields will be investigated systematically by using the compressible liquid-drop model in this project.

关于强磁场对中子星结构性质的影响是前沿的热点课题之一。大量研究表明，中子星主要由四部分构成，从外到内依次是外壳层、内壳层、外核、内核。内壳层是由原子核、自由中子气和电子气共存而构成的非均匀物质。随着物质密度的增加，柱形、片形、管形、泡形等非球形结构，即原子核pasta结构可能会在内壳层中出现。这些结构在中子星的冷却、自转周期、引力波辐射等天文观测中起着重要作用。天文观测发现部分中子星内部存在极强的磁场，这会对中子星的内壳层结构产生显著的影响。但是，目前人们对强磁场环境中包含pasta结构的内壳层性质还缺乏充分的研究。本项目将在相对论平均场理论框架下，采用自洽Thomas-Fermi近似方法和可压缩液滴模型研究强磁场对中子星内壳层的原子核pasta结构和壳核相变等性质的影响。此外，本项目还将利用可压缩液滴模型对强磁场环境下内壳层中的原子核液气共存和有限尺度效应等进行系统的研究。

中子星壳层结构研究是当前核物理的研究热点之一，该密度范围内的物质结构性质对检验极端条件下的原子核理论和解释相关天文观测量起着重要的作用。本项目基于相对论平均场理论，主要采用自洽Thomas-Fermi近似方法研究了强磁场环境下中子星内壳层中的原子核pasta结构性质和壳核相变性质。研究表明，和无磁场情况相比较，当磁场强度低于10$^{17}$ G时内壳层结构性质并不会发生明显改变。当磁场强度达到10$^{18}$ G时，内壳层中原子核结构会发生显著的变化，而且核子反常磁矩的效应也变得更加重要。非球形原子核出现的阈密度以及壳核相变密度会明显降低，而Wigner-Seitz原胞内的质子分支比会明显增大。总体而言，Wigner-Seitz原胞半径随磁场强度增大而减小，但原子核半径却随磁场强度增大而增加。本项目采用了TM1和IUFSU两组具有不同对称能斜率参数的相对论平均场模型以检验数值计算结果对模型的依赖性。研究发现比较小的对称能斜率参数模型会得到更加复杂的原子核pasta结构和更高的壳核相变密度，这与无磁场时的行为相一致。