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arXiv 0704.0138gr-qcastro-ph
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Kerr时空中的圆形和非圆形近水平掠过轨道

Circular and non-circular nearly horizon-skimming orbits in Kerr spacetimes

Enrico Barausse, Scott A. Hughes, Luciano Rezzolla

摘要:

我们对近极值克尔黑洞附近的轨道运动进行了详细的分析。对于快速旋转的黑洞(自旋a=J/M> 0.9524 M),我们发现了一类很强的场偏心轨道,其角动量L_z随轨道相对于赤道面的倾角而增加,而保持轨道的直角距和偏心率不变。这种行为与牛顿的直觉相反,事实上与黑洞轨道的“正常”行为相反。这种行为以前在圆形轨道上被注意到;因为它只适用于非常接近黑洞的轨道,它们被命名为“近水平掠过轨道”。我们的分析概括了这一结果,映射出完整的通用(倾斜和偏心)家庭的近水平掠过轨道。早期关于圆轨道的研究报告指出,在引力辐射的作用下,近水平掠地轨道倾向于向更小的轨道倾角演化,趋向于接近赤道构型。相反,正常轨道总是表现出缓慢增长的轨道倾角(轨道朝着逆行赤道配置发展)。使用最新的Teukolsky通量,我们得出结论,早期的结果是不正确的:所有的圆形轨道,包括近地平线掠过的,表现出越来越大的轨道倾角。使用组装通量的基础上修正后牛顿膨胀与适合圆形和赤道Teukolsky通量,我们认为,偏心近地平线掠过轨道的倾斜度也增长。我们还发现,在任何情况下,倾角变化都很小。因此,我们得出结论,这些轨道不太可能对预计由天基探测器LISA测量的引力波形有明确和特殊的印记。

英文摘要:

We have performed a detailed analysis of orbital motion in the vicinity of a nearly extremal Kerr black hole. For very rapidly rotating black holes (spin a=J/M>0.9524M) we have found a class of very strong field eccentric orbits whose angular momentum L_z increases with the orbit's inclination with respect to the equatorial plane, while keeping latus rectum and eccentricity fixed. This behavior is in contrast with Newtonian intuition, and is in fact opposite to the "normal" behavior of black hole orbits. Such behavior was noted previously for circular orbits; since it only applies to orbits very close to the black hole, they were named "nearly horizon-skimming orbits". Our analysis generalizes this result, mapping out the full generic (inclined and eccentric) family of nearly horizon-skimming orbits. The earlier work on circular orbits reported that, under gravitational radiation emission, nearly horizon-skimming orbits tend to evolve to smaller orbit inclination, toward prograde equatorial configuration. Normal orbits, by contrast, always demonstrate slowly growing orbit inclination (orbits evolve toward the retrograde equatorial configuration). Using up-to-date Teukolsky-fluxes, we have concluded that the earlier result was incorrect: all circular orbits, including nearly horizon-skimming ones, exhibit growing orbit inclination. Using kludge fluxes based on a Post-Newtonian expansion corrected with fits to circular and to equatorial Teukolsky-fluxes, we argue that the inclination grows also for eccentric nearly horizon-skimming orbits. We also find that the inclination change is, in any case, very small. As such, we conclude that these orbits are not likely to have a clear and peculiar imprint on the gravitational waveforms expected to be measured by the space-based detector LISA.

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