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arXiv 2108.01329gr-qcastro-ph.CO
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黑洞视界附近的引力辐射:波形正则化和出射回波

Gravitational radiation close to a black hole horizon: Waveform regularization and the out-going echo

Manu Srivastava, Yanbei Chen

摘要:

克尔黑洞的黑洞微扰理论在纽曼彭罗斯形式中得到了最好的研究,其中引力波被描述为外尔标量$ψ_0$和$ψ_4$中的微扰,其控制方程是著名的Teukolsky方程。在无限远和近地平线附近,$ψ_4$由对应于朝向正径向方向传播的波的分量主导,而$ψ_0$由对应于朝向负径向方向传播的波的分量主导。由于引力波探测器测量的是无穷远的出射波,因此研究主要集中在$ψ_4$上,而对$ψ_0$的研究较少。但在近水平区域,情况相反,需要施加入射波边界条件。因此,近视界现象,例如,潮汐加热和引力波回波从非常紧凑的对象(ECO),需要计算$ψ_0$。在这项工作中,我们明确地计算$ψ_0$ Teukolsky方程的源项由于一个点粒子陷入克尔黑洞。我们强调需要正规化的解决方案的$ψ_0$ Teukolsky方程使用格林函数技术。为此,我们提出了一个正则化方案,并继续计算的$ψ_0$波形接近史瓦西视界的两种类型的轨迹的下落粒子。我们比较了直接从Teukolsky方程计算的$ψ_0$波形与通过使用$ψ_4$上的Starobinsky-Teukolsky恒等式获得的$ψ_0$波形。我们还计算出的出射回波波形接近无穷远,使用近地平线$ψ_0$直接计算从Teukolsky方程和玻尔兹曼边界条件的ECO表面上。我们表明,这个回声是定量不同(强)比使用以前的处方得到的回声。(节略)

英文摘要:

Black hole perturbation theory for Kerr black holes is best studied in the Newman Penrose Formalism, in which gravitational waves are described as perturbations in the Weyl scalars $ψ_0$ and $ψ_4$, with the governing equation being the well-known Teukolsky equation. Near infinity and near horizon, $ψ_4$ is dominated by the component that corresponds to waves propagating towards the positive radial direction, while $ψ_0$ is dominated by the component that corresponds to waves that propagate towards the negative radial direction. Since gravitational-wave detectors measure out-going waves at infinity, research has been mainly focused on $ψ_4$, leaving $ψ_0$ less studied. But the scenario is reversed in the near horizon region where the in-going-wave boundary condition needs to be imposed. Thus, the near horizon phenomena, e.g., tidal heating and gravitational-wave echoes from Extremely Compact Objects (ECOs), require computing $ψ_0$. In this work, we explicitly calculate the source term for the $ψ_0$ Teukolsky equation due to a point particle plunging into a Kerr black hole. We highlight the need to regularize the solution of the $ψ_0$ Teukolsky equation obtained using Green's function techniques. We suggest a regularization scheme for this purpose and go on to compute the $ψ_0$ waveform close to a Schwarzschild horizon for two types of trajectories of the in-falling particle. We compare the $ψ_0$ waveform calculated directly from the Teukolsky equation with the $ψ_0$ waveform obtained by using the Starobinsky-Teukolsky identity on $ψ_4$. We also compute the out-going echo waveform near infinity, using the near-horizon $ψ_0$ computed directly from the Teukolsky equation and the Boltzmann boundary condition on the ECO surface. We show that this echo is quantitatively different (stronger) than the echo obtained using previous prescriptions. (abridged)

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