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。这些星系团是我们宇宙历史早期的化石，当时恒星形成的频率比今天要高得多。构成我们星球的化学元素，以及所有的生物，都是在这些古老恒星的生死过程中形成的。据观察，较小星团中的恒星都具有几乎相同的元素丰度。然而，对于球状星团来说就不是这样了，因为它们的丰度分布很广。这可能会为它们是如何形成的提供重要线索。最终，这将帮助我们理解我们自己的起源。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：不是作为一个大星团，而是许多随后坠落在一起的更小的星团。每个小星团都有自己统一的元素丰度。当它们落在一起形成一个大星团时，它是所有小星团的混合物，所以它有丰富的分布。对球状星团的观察最近证明，在仔细检查的几乎每个物体中都存在多个或分散的主序列群体，元素丰度各不相同。这与质量较小的疏散星系团，甚至是观察到的年轻大质量星系团形成了鲜明的对比，后者具有相对均匀的元素丰度。根据恒星形成率的时间变异性提出的多种解释与当前的观测结果相矛盾。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。他们将对恒星形成的气体和恒星本身进行建模，在每个时间步耦合在一起的不同程序中。他们正在建立一个自适应网格程序来模拟气体。这种创新的方法将在科学和工程中有许多其他应用。他们的工作在以下领域产生了更广泛的影响。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克塞尔示范性合作教育项目的研究。它还将为美国自然历史博物馆在教授地球(和空间)科学方面创新的、以常驻为基础的艺术硕士提供知识基础，并为广泛使用的本科教科书提供知识基础。在外展方面，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，并授权给世界各地的40家机构。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.