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arXiv 0708.0628gr-qc
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精确凹凸时空中轨道的可观测性质

Observable Properties of Orbits in Exact Bumpy Spacetimes

Jonathan R Gair, Chao Li, Ilya Mandel

摘要:

我们探索的性质测试粒子轨道在“颠簸”时空-爱因斯坦方程的固定,反射对称,渐近平坦的解决方案,有一个非克尔(异常)高阶多极矩结构,但可以任意调整接近克尔度规。未来的探测器应该观测到致密天体在吸入超大质量中心天体时产生的引力波。如果中心体偏离克尔度规,这将在发射波中表现出来。在这里,我们探讨了非克尔时空中轨道的一些特征,这些特征可能会导致可观测的签名。作为这种分析的基础,我们使用的Manko和Novikov提出的一个家庭的精确解偏离克尔度规的四极矩和更高的时刻,但我们也比较我们的结果在文献中的其他工作。我们检查隔离积分的轨道,发现大多数测地线轨道有一个近似的第四常数的运动(除了能量,角动量和静止质量)和由此产生的轨道是三周期的高精度。我们还发现,这四分之一的积分可以失去某些轨道中的一些oblastly变形的Manko-Novikov时空。然而,紧凑的物体在自然界中可能不会在这些混乱的轨道上结束。我们计算的最内层稳定的圆形轨道(ISCO)的位置,并发现附近的ISCO的orbtis的行为可以定性不同,这取决于是否ISCO是由在径向或垂直方向上的不稳定性的发病。最后,我们计算了近圆轨道和近赤道轨道在强场和弱场下的近心点和轨道平面进动,并讨论了偏心赤道轨道的弱场进动。

英文摘要:

We explore the properties of test-particle orbits in "bumpy" spacetimes - stationary, reflection-symmetric, asymptotically flat solutions of Einstein equations that have a non-Kerr (anomalous) higher-order multipole-moment structure but can be tuned arbitrarily close to the Kerr metric. Future detectors should observe gravitational waves generated during inspirals of compact objects into supermassive central bodies. If the central body deviates from the Kerr metric, this will manifest itself in the emitted waves. Here, we explore some of the features of orbits in non-Kerr spacetimes that might lead to observable signatures. As a basis for this analysis, we use a family of exact solutions proposed by Manko & Novikov which deviate from the Kerr metric in the quadrupole and higher moments, but we also compare our results to other work in the literature. We examine isolating integrals of the orbits and find that the majority of geodesic orbits have an approximate fourth constant of the motion (in addition to the energy, angular momentum and rest mass) and the resulting orbits are tri-periodic to high precision. We also find that this fourth integral can be lost for certain orbits in some oblately deformed Manko-Novikov spacetimes. However, compact objects will probably not end up on these chaotic orbits in nature. We compute the location of the innermost stable circular orbit (ISCO) and find that the behavior of orbtis near the ISCO can be qualitatively different depending on whether the ISCO is determined by the onset of an instability in the radial or vertical direction. Finally, we compute periapsis and orbital-plane precessions for nearly circular and nearly equatorial orbits in both the strong and weak field, and discuss weak-field precessions for eccentric equatorial orbits.

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