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Title: Neutron star properties in density-dependent relativistic Hartree-Fock theory

Author(s): Bao Yuan Sun (孙保元), Wen Hui Long (龙文辉), Jie Meng (孟杰), and U. Lombardo

Source: Physical Review C
Volume: 78  Issue: 6  Page: 065805  Published: 31 December 2008

KeyWords Plus: MEAN-FIELD THEORY; ASYMMETRIC NUCLEAR-MATTER; NONLINEAR SIGMA-TERM; HEAVY-ION REACTIONS; GROUND-STATE; BOGOLIUBOV THEORY; RECENT PROGRESS; SHELL STRUCTURE; EXOTIC NUCLEI; FINITE NUCLEI

History: Received 7 October 2008

DOI: 10.1103/PhysRevC.78.065805

Abstract: With the equations of state provided by the newly developed density-dependent relativistic Hartree-Fock (DDRHF) theory for hadronic matter, the properties of the static and β-equilibrium neutron stars without hyperons are studied for the first time and compared to the predictions of the relativistic mean-field models and recent observational data. The influences of Fock terms on properties of asymmetric nuclear matter at high densities are discussed in detail. Because of the significant contributions from the σ- and ω-exchange terms to the symmetry energy, large proton fractions in neutron stars are predicted by the DDRHF calculations, which strongly affect the cooling process of the star. A critical mass of about 1.45M_o, close to the limit of 1.5M_o determined by modern soft X-ray data analysis, is obtained by DDRHF with the effective interactions PKO2 and PKO3 for the occurrence of the direct Urca process in neutron stars. The maximum masses of neutron stars given by the DDRHF calculations lie between 2.45M_o and 2.49M_o, which are in reasonable agreement with the high pulsar mass of (2.08+/-0.19)M_o from PSR B1516+02B. It is also found that the mass-radius relations of neutron stars determined by DDRHF are consistent with the observational data from thermal radiation measurements in the isolated neutron star RX J1856, quasiperiodic brightness oscillations in the low-mass X-ray binaries 4U 0614+09 and 4U 1636-536, and the redshift determined in the low-mass X-ray binary EXO 0748-676.

Figure: Mass-radius relations of neutron stars provided by the DDRHF and RMF calculations and the corresponding maximum masses ( marked by filled star symbols). For comparison are also shown the four separate observational constraints from RX J1856 (gray grided region), 4U 0614 + 09 (cyan grided area), 4U 1636-536 (yellow grided area), and EXO 0748-676 (error bar for 1σ error). The black region is excluded by causality that R > 2.9GM/c².

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晚上有幸聆听了一场大师级的科普报告，脉冲星的发现者Jocelyn Bell Burnell博士访问北大，在现代物理中心报告厅作了题为“脉冲星与极端物理（Pulsars and Extreme Physics）”的演讲，精彩至极，叹为观止。六十多岁的老太太了，还是那么精神，很难相信她在我这么大年纪时就作出了这么一项令世界轰动的发现。

报告中她深入浅出地介绍了脉冲星的基本观测特征、极端性、对包括Einstein广义相对论在内的基本物理规律的检验等。四级听力的语速，标准的英国英语，连我这么烂的听力水平都几乎完全听懂了，真是不敢相信！PPT做的相当简单，没有花哨的背景，几张图片引出主题，从讲恒星诞生一直演化到死亡变成中子星，再逐一列举脉冲星的诸多性质，简简单单的就结束了。这是大牛才能达到的境界，内容都蕴藏在她生动的讲解中，不得不佩服，这么难的物理问题，竟然被阐释的那样清楚，本科生的水平就能听懂，恐怕也只有大师才能做到了。在讲解中，为了解释多普勒效应，她将一个闹钟打开并绑在绳子的一头转起来演示；为了解释脉冲星自转发出电磁脉冲，她用手电筒来模拟。她还带大家展开充分的想象，亲临中子星表面，感受各种奇异的物理效应。讲中子星表面的洛仑兹力，说大家只能沿经线方向运动，沿纬线走就会变成“极化人”；讲表面的大气厚度不到1cm，大家要呼吸就得鼻子贴地。一切都是那么形象，这恐怕是我听过的相关报告中演绎的最完美的一次了。

真正的报告应该就是这样的，让听众听懂，并产生互动。向大师学习！

附：Jocelyn Bell Burnell博士介绍

女，1943年生于北爱尔兰，射电天文学家。她1965年获得Glasgow大学物理学学士，同年成为剑桥大学的博士生（导师：Antony Hewish教授，他因发现脉冲星而荣获1971年诺贝尔物理学奖）。剑桥大学期间，在Hewish教授的指导下建造和运行了一台81.5MHz的射电望远镜，用于研究致密源的行星际闪烁。在这项研究过程中，她于1967年意外地发现了第一颗脉冲星。Jocelyn Bell Burnell博士为英国牛津大学访问教授，1969年入选英国皇家天文学会会员。