The ability to model the evolution of compact binaries from the inspiral to coalescence is central to gravitational wave astronomy. Current waveform catalogues are built from vacuum binary black hole models, by evolving Einstein equations numerically and complementing them with knowledge from slow-motion expansions. Much less is known about the coalescence process in the presence of matter, or in theories other than general relativity. Here, we explore the close limit approximation as a powerful tool to understand the coalescence process in general setups. In particular, we study the head-on collision of two equal-mass, compact but horizonless objects. Our results show the appearance of ‘echoes’ and indicate that a significant fraction of the merger energy goes into these late-time repetitions. We also apply the close limit approximation to investigate the effect of colliding black holes on surrounding scalar fields. Notably, our results indicate that observables obtained through perturbation theory may be extended to a significant segment of the merger phase, where in principle only a numerical approach is appropriate.

中文翻译：

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极限近似的应用：无视界的紧致物体和标量场

模拟紧凑双星从吸气到聚结的演化过程的能力是引力波天文学的核心。当前的波形目录是根据真空双黑洞模型构建的，通过在数值上演化爱因斯坦方程并用慢动作扩展的知识对其进行补充。关于物质存在下的聚结过程，或者在广义相对论以外的理论中，人们知之甚少。在这里，我们将极限近似作为一种强大的工具来探索一般设置中的聚结过程。特别是，我们研究了两个质量相等、紧凑但无地平线的物体的正面碰撞。我们的结果显示了“回声”的出现，并表明合并能量的很大一部分进入了这些后期重复。我们还应用近极限近似来研究碰撞黑洞对周围标量场的影响。值得注意的是，我们的结果表明，通过微扰理论获得的可观测值可以扩展到合并阶段的重要部分，原则上只有数值方法是合适的。