Rapid X-ray variability
Rapid X-ray variability
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DOI：
10.1017/cbo9780511536281.003
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发表时间：
2006-04
期刊：
影响因子：
--
通讯作者：
M. Klis
中科院分区：
文献类型：
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作者：
M. Klis
研究x射线双星的主要动机之一是，中子星和黑洞的吸积为研究强引力和致密物质的物理学提供了一个独特的窗口。我们最好的引力理论——广义相对论，虽然在弱场（GM/R≪c2；例如，Taylor et al. 1992）中以极高的精度得到了测试和证实，但还没有通过在紧实物体附近的强引力场中直接观察粒子的运动来进行测试，在强引力场中，引力结合能与静止质量的顺序相同。相对论对这些区域做出的极端预测包括事件视界的存在，即黑洞（第2.4节）。1)，存在一个不存在稳定轨道的内半径，惯性系的强拖曳，以及与轨道运动速度相似的广义相对论进动，其速度是水星的1016倍。中子星的密度超过原子核的密度。哪些基本粒子出现在那里，它们的集体性质是什么，我们还不太清楚，无法预测那里物质的状态方程（EOS）或可压缩性，因此中子星的质量-半径（M-R）关系是不确定的。因此，通过测量这一关系，可以约束超核密度物质的EOS。由于中子星的轨道运动同时约束了M和R（第2.8节）。这种运动的测量关系到物质的基本性质。同样，黑洞附近的这种运动限制了给定质量黑洞的大小和旋转。为了解决这些强引力和致密物质的问题，我们需要在致密物体的几个史瓦西半径内研究重力影响下的运动，并绘制出那里的强弯曲时空。由于致密物体附近的特征速度为（GM/R） 1/2 ~ 0阶。5c，运动通过该区域的动态时间标度（r3/GM） 1/2较短；在距离1.4 M⊙的中子星约15公里处约0.1 ms，在距离102公里处约2 ms，在距离10 M⊙黑洞约102公里处约1 ms。这些毫秒级的动态时间尺度，是与任何天体物理物体相关的最短时间尺度，构成了紧凑物体紧密性的最基本表达之一。预计吸积流是紊流，并可能显示磁性结构。它的发射将随时间而变化，这是由于不均匀性在流动中或随流动而运动。这种可变性可以用来探测吸积-流动动力学。对于一个10公里的天体，90%的引力能是在内部~ 102公里释放的，因此大部分发射可能来自我们预计毫秒变异性的强场区域。这里的温度为100 ~ 10.7 K，所以大部分的辐射都是x射线。
One of the principal motivations for studying X-ray binaries is that accretion onto neutron stars and black holes provides a unique window on the physics of strong gravity and dense matter. Our best theory of gravity, general relativity, while tested, and confirmed, with exquisite precision in weak fields (GM/R≪ c2; eg, Taylor et al. 1992) has not yet been tested by direct observation of the motion of particles in the strong gravitational field near compact objects, where the gravitational binding energy is of order the rest mass. Among the extreme predictions relativity makes for these regions are the existence of event horizons, ie, black holes (Section 2.4. 1), the existence of an inner radius within which no stable orbits exist, strong dragging of inertial frames, and general-relativistic precession at rates similar to the orbital motion itself,∼ 1016 times as fast as that of Mercury. In a neutron star the density exceeds that in an atomic nucleus. Which elementary particles occur there, and what their collective properties are, is not known well enough to predict the equation of state (EOS), or compressibility, of the matter there, and hence the mass–radius (M–R) relation of neutron stars is uncertain. Consequently, by measuring this relation, the EOS of supra-nuclear density matter is constrained. As orbital motion around a neutron star constrains both M and R (Section 2.8. 1), measurements of such motion bear on the fundamental properties of matter. Likewise, such motion near black holes constrains the size and spin of black holes of given mass.For addressing these issues of strong gravity and dense matter, we need to study motion under the influence of gravity within a few Schwarzschild radii1 of compact objects and map out the strongly curved spacetime there. As the characteristic velocities near the compact object are of order (GM/R) 1/2∼ 0. 5c, the dynamical timescale (r3/GM) 1/2 for the motion through this region is short;∼ 0.1 ms at∼ 15 km, and∼ 2 ms at 102 km from a 1.4 M⊙ neutron star, and∼ 1 ms at 3RSchw (∼ 102 km) from a 10 M⊙ black hole. These millisecond dynamical timescales, the shortest associated with any astrophysical object, form one of the most basic expressions of the compactness of compact objects. The accretion flow is expected to be turbulent and may show magnetic structures. Its emission will vary in time due to the motions of inhomogeneities through, and with, the flow. This variability can be used to probe the accretion-flow dynamics. For a 10 km object, 90% of the gravitational energy is released in the inner∼ 102 km, hence the bulk of the emission likely comes from within the strong-field region from where we expect the millisecond variability. Temperatures here are>∼ 10 7 K, so most of this emission is in X-rays.