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

许多迄今为止发现的最古老的恒星都是在球状星团中发现的。 这些是已知最大的星团，在一个小区域内拥有数百万颗恒星。 这些星团是宇宙历史早期的化石，当时恒星的形成远比今天频繁。构成我们星球和所有生物的化学元素是在这些古老恒星的生与死过程中形成的。 据观察，较小星团中的恒星都具有几乎相同丰度的元素。 然而，对于球状星团来说却并非如此，因为球状星团的丰度分布广泛。 这可以为它们的形成提供重要线索。最终，这将帮助我们了解我们自己的起源。研究人员将测试他们的新模型，了解簇是如何形成的：不是一个大簇，而是许多随后聚集在一起的较小簇。 每个小簇都有自己均匀的元素丰度。当它们聚集在一起形成一个大簇时，它是所有小簇的混合物，因此它具有丰富的分布。最近对球状星团的观测表明，几乎每个经过足够仔细检查的物体中都存在多个或分散的主序群体，其元素丰度各不相同。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，这些星团具有相对均匀的元素丰度。多种提出的解释依赖于恒星形成率的时间变化，与当前的观察结果相矛盾。研究人员正在开发软件工具来模拟丰度的扩散。这些模型将在 NSF 超级计算机上运行。他们将在每个时间步骤耦合在一起的单独程序中对形成恒星的气体以及恒星本身进行建模。他们正在构建一个自适应网格程序来模拟气体。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具有更广泛的影响。在教育方面，它将直接支持一名研究生和三名本科生参与德雷塞尔示范合作教育项目的研究。它还将为美国自然历史博物馆创新的、以驻场为基础的地球（和空间）科学教学文学硕士以及广泛使用的本科教科书提供知识基础。在推广方面，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这些展，并授权给全球 40 个机构。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。

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.