The Untimely Deaths of Star Clusters

大多数恒星，包括我们的太阳，都是由数亿颗恒星组成的星团。随着这些星团变老，它们很快开始失去恒星。这是由于恒星之间的引力相互吸引，以及附近大质量气体云的引力。这些恒星从星团中散开，但仍以相似的速度运动。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。研究人员将利用计算机模拟研究集群是如何形成和分散的。提出的工作有三个目标：1)预测由给定气体云形成的星团的类型；2)测试模型中从星团中消失的恒星是否与太阳附近观测到的真实恒星行为相似；3)测试来自气体云的引力是否可以解释大型星团是如何随着时间的推移而缩小的，就像观测到的星团所做的那样。国际合作将为K-12教师开发教科书和教育资源。两名硕士生将开发新模型的图形展示，并鼓励它们在公共活动中使用。他们计划举办一场海登天文馆太空展，让全国和全世界数百万人观看。研究人员将使用多种软件工具的组合来研究星团的形成和毁灭。在小范围内，他们将用开源的Torch软件模拟星团形成和气体排出。这使用了AMUSE框架将Flash自适应网格细化磁流体力学代码与直接n体代码耦合起来，这些代码模拟碰撞恒星动力学和恒星演化代码，这些代码遵循每颗恒星的长期演化，确定它们随时间产生的辐射能和机械能。它们包括恒星光电离的射线追踪处理，以及喷流、风、超新星、辐射冷却和自重力。在大尺度上，他们将使用AREPO代码中的SMUGGLE恒星形成和反馈框架来确定自洽初始条件和潮汐场。这项工作的科学目标是：(1)建立半解析模型，将自一致致密气体云的特性(a)与由此产生的星团质量、大小、中心浓度和维里参数联系起来，(b)确定受强烈波动潮汐力影响的星团的质量损失。(2)比较低质量星团与在太阳附近观测到的运动星团、星团和星团系统，以及从疏散星团观测到的不对称潮汐尾的特性。(3)利用半解析模型通过自洽星系潮汐场跟踪星团的总体，验证了这些潮汐决定了年轻大质量星团的幂律质量分布向年老球状星团的对数正态分布演化的假设。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.