Superradiant instabilities of rotating black branes and strings
Superradiant instabilities of rotating black branes and strings
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DOI：
10.1088/1126-6708/2005/07/009
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发表时间：
2005-07-01
影响因子：
5.4
通讯作者：
Yoshida, S
中科院分区：
文献类型：
--
作者：
Cardoso, V;Yoshida, S
黑膜和黑弦通常在一定范围的重力扰动下不稳定。这被称为格雷戈里-拉弗拉姆不稳定性。最近有人认为 [1, 2] 存在另一种普遍的不稳定性影响许多旋转的扩展黑色物体。这种不稳定性在某种意义上是普遍存在的，因为它是由任何无质量场引发的，而不仅仅是引力扰动。在这里，我们详细研究了这种新颖的机制。为了使这种不稳定性发挥作用，两个要素是必要的：（i）麦角区域，它会产生波的超辐射放大，以及（ii）控制所研究的特定模式演化的有效势中的“束缚”态。我们表明，黑膜 Kerr(4) x R-p 对于这种机制是不稳定的，并且我们提出了这种情况下不稳定时间尺度的数值结果。另一方面，非常令人惊讶的是，形式为 Kerr(d) x R-p 的黑膜是对于 d > 4 的机制，所有这些都是稳定的。这是一个非常出乎意料的结果，它源于这样一个事实：在高维黑洞时空中不存在稳定的圆形轨道，或者在波动图中，有效势中不存在束缚态。我们还表明，在实验室中用声学黑膜来模拟这种不稳定性是相当容易的。
Black branes and strings are generally unstable against a certain sector of gravitational perturbations. This is known as the Gregory-Laflamme instability. It has been recently argued [1, 2] that there exists another general instability affecting many rotating extended black objects. This instability is in a sense universal, in that it is triggered by any massless field, and not just gravitational perturbations. Here we investigate this novel mechanism in detail. For this instability to work, two ingredients are necessary: (i) an ergo-region, which gives rise to superradiant amplification of waves, and (ii) ''bound" states in the effective potential governing the evolution of the particular mode under study. We show that the black brane Kerr(4) x R-p is unstable against this mechanism, and we present numerical results for instability timescales for this case. On the other hand, and quite surprisingly, black branes of the form Kerr(d) x R-p are all stable against this mechanism for d > 4. This is quite an unexpected result, and it stems from the fact that there are no stable circular orbits in higher dimensional black hole spacetimes, or in a wave picture, that there are no bound states in the effective potential. We also show that it is quite easy to simulate this instability in the laboratory with acoustic black branes.