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arXiv 0910.0734gr-qc
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黑洞弹的解析处理

Analytic treatment of the black-hole bomb

Shahar Hod, Oded Hod

摘要:

撞击在旋转黑洞上的玻色子场会被放大,因为它会被黑洞散射,这种现象被称为超辐射散射。此外,如果场有一个非零的静止质量,那么质量项有效地起着镜子的作用,将散射波反射回黑洞。在这个被称为黑洞炸弹的物理系统中,波可以在黑洞和某个转折点之间来回反弹,每次都放大自己。因此,质量场随时间呈指数增长,并且不稳定。以前的分析估计的时间尺度与不稳定性被限制在制度$Mμ>>1$和$Mμ<<1$,其中$M$和$μ$是质量的黑洞和外地,分别。在这两个极限中,场的增长率被发现是非常弱的。然而,随后的数值研究表明,不稳定性实际上是最大的政权$Mμ=O(1)$,在以前的分析近似打破。因此,$Mμ=O(1)$的情况下,不稳定的时间尺度的一个新的分析研究是物理上很好的动机。在这封信中,我们第一次分析研究超辐射不稳定性(黑洞炸弹机制)的现象,在这个物理上有趣的制度-最大的不稳定性制度。我们发现一个不稳定的增长率为$τ^{-1}=ω_I=1.7\times 10^{-3}M^{-1}$的最快增长模式。这种不稳定性比以前估计的要强四个数量级。

英文摘要:

A bosonic field impinging on a rotating black hole can be amplified as it scatters off the hole, a phenomena known as superradiant scattering. If in addition the field has a non-zero rest mass then the mass term effectively works as a mirror, reflecting the scattered wave back towards the black hole. In this physical system, known as a black-hole bomb, the wave may bounce back and forth between the black hole and some turning point amplifying itself each time. Consequently, the massive field grows exponentially over time and is unstable. Former analytical estimations of the timescale associated with the instability were restricted to the regimes $Mμ>>1$ and $Mμ<<1$, where $M$ and $μ$ are the masses of the black hole and the field, respectively. In these two limits the growth rate of the field was found to be extremely weak. However, subsequent numerical investigations have indicated that the instability is actually greatest in the regime $Mμ=O(1)$, where the previous analytical approximations break down. Thus, a new analytical study of the instability timescale for the case $Mμ=O(1)$ is physically well motivated. In this Letter we study analytically for the first time the phenomena of superradiant instability (the black-hole bomb mechanism) in this physically interesting regime -- the regime of greatest instability. We find an instability growth rate of $τ^{-1}=ω_I=1.7\times 10^{-3}M^{-1}$ for the fastest growing mode. This instability is four orders of magnitude stronger than has been previously estimated.

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