The Untimely Deaths of Star Clusters

大多数恒星，包括我们的太阳，都是由数百到数百万颗恒星组成的星团。当这些星团变老时，它们很快就开始失去恒星。这既来自于恒星之间的引力，也来自于附近大质量气体云的引力。这些恒星从星团中向外扩散，但仍然以相似的速度移动。在太阳附近可以观察到这样的恒星群一起运动。恒星用紫外线辐射、风和超新星爆炸加热气体。研究人员将使用计算机模拟来研究集群是如何形成和分散的。 这项工作有三个目标：1）预测一个给定的气体云会形成什么样的星团; 2）测试模型中从星团中消失的恒星是否像太阳附近的真实的观测恒星一样; 3）测试气体云的引力是否可以解释大星团如何随着时间的推移而缩小，就像观测到的星团一样。 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显示，并鼓励他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。调查人员将利用多种软件工具的组合来研究星星团的形成和毁灭。在小尺度上，他们将用开源的Torch软件模拟星系团的形成和气体排出。这使用的AMUSE框架耦合Flash自适应网格细化磁流体动力学代码与直接N体代码，模型碰撞恒星动力学和恒星演化代码，遵循每个星星的长期演化，确定它们随着时间的推移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、辐射冷却和自引力。在大尺度上，他们将使用AREPO代码中的SMUGGLE星星形成和反馈框架来确定自洽的初始条件和潮汐场。本工作的科学目标是：（1）建立半解析模型，将自洽致密气体云的性质（a）与由此产生的团簇质量、大小、中心浓度和维里参数联系起来，（B）确定团簇在强涨落潮汐力作用下的质量损失。(2)比较从低质量星团分散出来的恒星的性质，与在太阳附近观测到的运动集团、星协和星团系统，以及从疏散星团观测到的不对称潮汐尾。(3)使用半解析模型通过自洽的银河潮汐场来跟踪星团的种群，以检验这些潮汐决定年轻大质量星团从幂律质量分布到老球状星团对数正态分布的演化的假设。该奖项反映了NSF的法定使命，并通过使用基金会的智力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.