Collaborative Research: Globular Cluster Formation in Hierarchically Collapsing Clouds as an Origin for Multiple Stellar Populations

迄今发现的许多最古老的恒星都是在球状星团中发现的。这些是已知的最大的星团，在一个小区域内有数百万颗恒星。这些星团是我们宇宙历史早期的化石，当时恒星形成的频率远高于今天。构成我们星球和所有生物的化学元素，都是在这些古老恒星的生与死中形成的。在较小的星团中的恒星被观察到几乎都有相同的元素丰度。然而，对于球状星团来说就不是这样了，因为球状星团的丰度是分散的。这可能为它们的形成提供重要线索。最后，这将有助于我们了解我们自己的起源。研究人员将测试他们的新模型，看看这些星团是如何形成的：不是一个大的星团，而是许多较小的星团，然后聚集在一起。每一个小星团都有自己统一的元素丰度。当它们聚集在一起形成一个大的星团时，它是所有小星团的混合物，所以它的丰度是分散的。最近对球状星团的观测表明，经过足够仔细的观察，几乎在每一个天体中都存在多个或分散的主序星群，它们的元素丰度各不相同。这与质量较小的疏散星团，甚至观察到的年轻的大质量星团形成鲜明对比，后者的元素丰度相对均匀。基于恒星形成速率时间变化的多种解释与目前的观测结果相矛盾。研究人员正在开发软件工具来模拟病毒的大量传播。这些模型将在NSF的超级计算机上运行。他们将对形成恒星的气体和恒星本身进行建模，在不同的程序中，每一步都耦合在一起。他们正在构建一个自适应网格程序来模拟这种气体。这种创新方法将在科学和工程领域有许多其他应用。他们的工作在以下领域有更广泛的影响。在教育方面，它将直接支持一名研究生和三名参加德雷塞尔大学示范性合作教育项目的本科生的研究。它还将为美国自然历史博物馆创新的、以居住为基础的地球（和空间）科学教学艺术硕士课程提供知识基础，并为广泛使用的本科教科书提供知识基础。在外联方面，它将为海登天文馆太空展的策划提供基础，每年有100万游客在天文馆观看，并授权给全球40个机构。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。

Many of the oldest stars ever discovered are found in globular clusters. These are the biggest star clusters known, with millions of stars in a small region. The clusters are fossils of the time early in the history of our universe when stars formed far more often than they do today. The chemical elements that form our planet, and all living beings, were formed during the lives and deaths of such ancient stars. The stars in smaller star clusters are observed to all have almost the same abundances of elements. However, this is not true for globular clusters, which have a spread in abundances. This could give an important clue to how they formed. In the end this will help us to understand our own origins.The investigators will test their new model for how the clusters formed: not as one large cluster, but rather as many smaller clusters that then fell together. Each of the little clusters had its own uniform abundances of elements. When they fell together to make a big cluster, it was a mixture of all the little clusters, so it had a spread of abundances. Observations of globular clusters have recently demonstrated the presence of multiple or spread main sequence populations with varying elemental abundances in virtually every object examined with sufficient care. This is in distinct contrast to less massive open clusters and even observed young massive clusters, which have comparatively uniform elemental abundances. Multiple proposed explanations, which rely on time variability in the star formation rate, contradict current observations.The investigators are developing software tools to model the spread in abundances. These models will run on NSF supercomputers. They will model the gas from which the stars form, and the stars themselves, in separate programs coupled together at every time step. They are building in an adaptive mesh program to model the gas. This innovative method will have many other applications in science and engineering. Their work has broader impacts in the following areas. In education, it will directly support research by a graduate student, and three undergraduates participating in Drexel's exemplary cooperative education program. It will also provide intellectual foundations for the American Museum of Natural History's innovative, residency-based Master of Arts in Teaching Earth (and Space) Science, and for a widely used undergraduate textbook. In outreach, it will provide the foundation for the curation of Hayden Planetarium Space Shows, which are seen by a million visitors a year at the Planetarium, and are licensed to 40 institutions worldwide.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.