Cottam J, Paerels F, Mendez M
NASA Goddard Space Flight Center, Laboratory for High Energy Astrophysics, Greenbelt, Maryland 20771, USA.
Nature. 2002 Nov 7;420(6911):51-4. doi: 10.1038/nature01159.
The fundamental properties of neutron stars provide a direct test of the equation of state of cold nuclear matter, a relationship between pressure and density that is determined by the physics of the strong interactions between the particles that constitute the star. The most straightforward method of determining these properties is by measuring the gravitational redshift of spectral lines produced in the neutron star photosphere. The equation of state implies a mass-radius relation, while a measurement of the gravitational redshift at the surface of a neutron star provides a direct constraint on the mass-to-radius ratio. Here we report the discovery of significant absorption lines in the spectra of 28 bursts of the low-mass X-ray binary EXO0748-676. We identify the most significant features with the Fe XXVI and XXV n = 2-3 and O VIII n = 1-2 transitions, all with a redshift of z = 0.35, identical within small uncertainties for the respective transitions. For an astrophysically plausible range of masses (M approximately 1.3-2.0 solar masses; refs 2-5), this value is completely consistent with models of neutron stars composed of normal nuclear matter, while it excludes some models in which the neutron stars are made of more exotic matter.
中子星的基本特性为冷核物质状态方程提供了直接检验，冷核物质状态方程描述的是压力与密度之间的关系，它由构成中子星的粒子间强相互作用的物理规律所决定。确定这些特性最直接的方法是测量中子星光球层产生的谱线的引力红移。状态方程意味着质量 - 半径关系，而对中子星表面引力红移的测量则直接限制了质量与半径的比值。在此，我们报告在低质量X射线双星EXO0748 - 676的28次爆发光谱中发现了显著的吸收线。我们将最显著的特征确定为铁XXVI和XXV的n = 2 - 3跃迁以及氧VIII的n = 1 - 2跃迁，所有这些跃迁的红移均为z = 0.35，在各自跃迁的小误差范围内相同。对于天体物理学上合理的质量范围（M约为1.3 - 2.0个太阳质量；参考文献2 - 5），该值与由正常核物质构成的中子星模型完全一致，同时排除了一些中子星由更奇特物质构成的模型。
