The Untimely Deaths of Star Clusters

大多数恒星，包括我们自己的太阳，都是由成百上千万颗恒星组成的星团。随着这些星团年龄的增长，它们很快就会开始失去恒星。这既是由于恒星之间的引力作用，也是由于附近大质量气体云的引力作用。这些恒星从星团中扩散开来，但仍以相似的速度运行。在太阳附近可以观察到这样的恒星群在一起运动。恒星通过紫外线辐射、风和超新星爆炸来加热气体。研究人员将使用计算机模拟来研究星团如何形成和分散。拟议中的工作有三个目标：1)预测由给定的气态云形成的星团的类型；2)测试从模型中的星团中消失的恒星是否表现得像太阳附近的真实观测恒星一样；3)测试气态云的引力是否能解释大型星团如何随着时间的推移而收缩，就像观察到的星团似乎所做的那样。一个国际合作将为K-12教师开发一本教科书和教育资源。两名硕士研究生将开发新模型的图形展示，并鼓励在公共活动中使用它们。他们计划举办一场海登天文馆太空展，供全国和世界各地的数百万人观看。研究人员将使用多种软件工具研究星团的形成和破坏。在小范围内，他们将使用开源火炬软件模拟星团形成和气体排放。它使用AMUSE框架将Flash自适应网格精化磁流体动力学程序与直接N体程序结合起来，后者模拟碰撞恒星动力学和跟踪每颗恒星的长期演化的恒星演化代码，确定它们随着时间的推移产生的辐射和机械能。它们包括对恒星光电离以及喷流、风、超新星、辐射冷却和自引力的光线追踪处理。在大尺度上，他们将使用AREPO代码中的走私星形成和反馈框架来确定自洽的初始条件和潮汐场。这项工作的科学目标是：(1)发展半解析模型，将自洽致密气体云的性质(A)与由此产生的星系团的质量、大小、中心浓度和维里参数联系起来，以及(B)确定受到强烈波动潮汐作用力的星系团的质量损失。(2)比较从低质量星团散布的恒星与在太阳附近观察到的移动群、组合和星团系统的性质，以及与来自疏散星团的不对称潮汐尾巴的观测结果。(3)使用半解析模型跟踪星系团种群穿过自洽的银河系潮汐场来检验这样的假设，即这些潮汐决定了从年轻质量星系团的幂函数质量分布到旧球状星系团的对数正态分布的演化。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Most stars, including our own Sun, form in clusters of hundreds to millions of stars. As these clusters grow older, they quickly begin to lose stars. This happens both from stars pulling on each other with gravity, and from the gravity of nearby massive gas clouds. These stars spread out from the cluster but still move with a similar velocity. Such groups of stars moving together are observed in the neighborhood of the Sun. The stars heat the gas with ultraviolet radiation, winds, and supernova explosions. The investigators will study how clusters form and disperse, using computer simulations. The proposed work has three goals: 1) to predict the kind of cluster that will form from a given gas cloud; 2) to test whether the stars lost from clusters in the model behave like real, observed stars in the neighborhood of the Sun; 3) to test whether the force of gravity from gas clouds can explain how large clusters shrink over time, as observed clusters appear to do. An international collaboration will develop a textbook and educational resources for K-12 teachers. Two master’s students will develop graphical displays of the new models and encourage their use at public events. They plan a Hayden Planetarium Space Show to be viewed by millions around the country and the world.The investigators will study star cluster formation and destruction using a combination of multiple software tools. At the small scale, they will model cluster formation and gas expulsion with the open-source Torch software. This uses the AMUSE framework to couple the Flash adaptive mesh refinement magnetohydrodynamics code with direct N-body codes that model collisional stellar dynamics and stellar evolution codes that follow the secular evolution of each star, determining the radiative and mechanical energy they produce over time. They include a ray-tracing treatment of stellar photoionization as well as jets, winds, supernovae, radiative cooling, and self-gravity. At the large scale, they will use the SMUGGLE star formation and feedback framework in the AREPO code to determine self-consistent initial conditions and tidal fields. The scientific goals of this work are to: (1) Develop semi-analytic models that connectproperties of self-consistent dense gas clouds (a) to the resulting cluster mass, size, central concentration, and virial parameter and (b) that determine the mass loss from clusters subject to strongly fluctuating tidal forces. (2) Compare the properties of stars dispersing from low-mass clusters to the systems of moving groups, associations, and clusters observed in the Solar neighborhood, and to observations of asymmetric tidal tails from open clusters. (3) Use the semi-analytic models to follow populations of clusters through a self-consistent galactic tidal field to test the hypothesis that these tides determine the evolution from power-law mass distributions of young massive clusters to log normal distributions of old globular clusters.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.