标题： 估计双黑洞合并的最终自旋 显示英文标题

标题： Estimating the final spin of a binary black hole coalescence

摘要： 我们提出了一种直接的方法，用于估计任意初始质量和自旋的双黑洞合并后的最终黑洞自旋。 在做一些简单的假设后，我们估计最终角动量为单个自旋之和加上一个测试粒子围绕具有最终黑洞自旋参数的克尔黑洞在最后稳定轨道上运行的轨道角动量。 我们得到的公式能够以合理的精度再现现有数值模拟的结果，但更重要的是，它可以用来研究哪些配置可能会导致有趣的动力学行为。 特别是，我们讨论了可能导致系统总角动量方向“翻转”的情况。 通过研究最终自旋对质量比和初始自旋的依赖性，我们发现我们的简单方法表明，无论涉及物体的质量比如何，通过合并情景都无法将黑洞旋转到极端值。 显示英文摘要

摘要： We present a straightforward approach for estimating the final black hole spin of a binary black hole coalescence with arbitrary initial masses and spins. Making some simple assumptions, we estimate the final angular momentum to be the sum of the individual spins plus the orbital angular momentum of a test particle orbiting at the last stable orbit around a Kerr black hole with a spin parameter of the final black hole. The formula we obtain is able to reproduce with reasonable accuracy the results from available numerical simulations, but, more importantly, it can be used to investigate what configurations might give rise to interesting dynamics. In particular, we discuss scenarios which might give rise to a ``flip'' in the direction of the total angular momentum of the system. By studying the dependence of the final spin upon the mass ratio and initial spins we find that our simple approach suggests that it is not possible to spin-up a black hole to extremal values through merger scenarios irrespective of the mass ratio of the objects involved.