背景势对星团演化的影响：弛豫时间尺度的延迟和失控碰撞过程
The effects of a background potential in star cluster evolution: a delay in the relaxation time-scale and runaway collision processes
摘要：
在稠密星团中失控的恒星碰撞被用来解释在这些系统的中心存在非常大质量的恒星或蓝离散星。宇宙中第一个星团也探索了这一过程，并显示出产生的恒星可能在某些点坍缩成中等质量的黑洞。虽然星团的早期演化需要对恒星形成的气体进行明确的建模，但这些计算将非常耗时，并且通常可以通过包括背景势来解释额外的引力来准确地处理气体的影响。我们应用这个近似模型的早期演化的第一个密集的星团形成在宇宙中通过执行$N$体模拟，我们的目标是了解如何额外的引力影响的增长，一个非常大质量的恒星通过恒星合并在星团的中心部分。我们的研究结果表明，背景势增加了恒星的速度，导致了星团演化的整体延迟，以及中心大质量恒星的失控增长。双星的人口是较低的，由于增加的动能的恒星，最初减少恒星碰撞的数量，我们表明，松弛过程也受到影响。尽管有这些影响，如果碰撞保持很长时间，外部电势将合并产物的质量提高$\sim$ 2倍。
英文摘要：
Runaway stellar collisions in dense star clusters are invoked to explain the presence of very massive stars or blue stragglers in the center of those systems. This process has also been explored for the first star clusters in the Universe and shown to yield stars that may collapse at some points into an intermediate mass black hole. Although the early evolution of star clusters requires the explicit modeling of the gas out of which the stars form, these calculations would be extremely time-consuming and often the effects of the gas can be accurately treated by including a background potential to account for the extra gravitational force. We apply this approximation to model the early evolution of the first dense star clusters formed in the Universe by performing $N$-body simulations, our goal is to understand how the additional gravitational force affects the growth of a very massive star through stellar mergers in the central parts of the star cluster. Our results show that the background potential increases the velocities of the stars, causing an overall delay in the evolution of the clusters and in the runaway growth of a massive star at the center. The population of binary stars is lower due to the increased kinetic energy of the stars, initially reducing the number of stellar collisions, and we show that relaxation processes are also affected. Despite these effects, the external potential enhances the mass of the merger product by a factor $\sim$2 if the collisions are maintained for long times.
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