Interactions among Noninteracting Particles in Planet Formation Simulations
Interactions among Noninteracting Particles in Planet Formation Simulations
复制标题
行星形成模拟中非相互作用粒子之间的相互作用
DOI：
10.3847/2041-8213/aba68d
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
K. Batygin
中科院分区：
文献类型：
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作者：
Shirui Peng;K. Batygin
近几十年来，N体模拟已经成为量化行星形成盘中引力扰动的标准工具。在这种模拟的背景下，大质量的非中心物体通常被分为“大”和“小”粒子，其中大物体与所有其他物体自洽地相互作用，而小物体与大物体相互作用，但彼此不相互作用。重要的是，这种分组转化为一种近似方案，其中小天体的轨道演化完全由大天体的动力学决定，产生相当大的计算优势，而在天体物理学精度方面几乎没有增加成本。在这里，我们指出，然而，这种方案也可以产生虚假的动力学行为，即使在没有大机构内的模拟，小机构之间的间接耦合可以导致激发的组成“非相互作用”的轨道。我们证明了这种自搅拌进行了一系列的数值实验，并确认这种效果在很大程度上是独立的时间步长或积分算法。此外，采用角动量赤字的增长作为动力学激发的代理，我们探讨了它对时间的依赖性，系统的累积质量，以及模拟中存在的粒子总数。最后，我们研究的程度，这种间接激发的背景下，传统的类地行星形成的计算，并得出结论，虽然一定程度的谨慎可能是有道理的，这种效果在驱动模拟的动力学演化中起着微不足道的作用。
Over the course of recent decades, N-body simulations have become a standard tool for quantifying the gravitational perturbations that ensue in planet-forming disks. Within the context of such simulations, massive non-central bodies are routinely classified into “big” and “small” particles, where big objects interact with all other objects self-consistently, while small bodies interact with big bodies but not with each other. Importantly, this grouping translates to an approximation scheme where the orbital evolution of small bodies is dictated entirely by the dynamics of the big bodies, yielding considerable computational advantages with little added cost in terms of astrophysical accuracy. Here we point out, however, that this scheme can also yield spurious dynamical behavior where, even in the absence of big bodies within a simulation, indirect coupling among small bodies can lead to excitation of the constituent “non-interacting” orbits. We demonstrate this self-stirring by carrying out a sequence of numerical experiments, and confirm that this effect is largely independent of the time-step or the integration algorithm employed. Furthermore, adopting the growth of angular momentum deficit as a proxy for dynamical excitation, we explore its dependence on time, the cumulative mass of the system, as well as the total number of particles present in the simulation. Finally, we examine the degree of such indirect excitation within the context of conventional terrestrial planet formation calculations, and conclude that although some level of caution may be warranted, this effect plays a negligible role in driving the simulated dynamical evolution.