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

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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.