Dynamical Evolution of Planetary Systems in Star Clusters

Geller Aaron M, Madison WI

Investigators

Abstract

Dr. Aaron Geller is awarded an NSF Astronomy and Astrophysics Postdoctoral Fellowship to carry out a program of research and education at Northwestern University. The fellow's project involves exoplanets. Today, astronomers are discovering a rich panoply of exoplanets in our Galaxy. Many of these exoplanets are in multi-planet systems. Some show surprisingly different characteristics from our own Solar System that pose serious problems for standard isolated planet formation theories. Strong evidence indicates that the majority of stars form in clusters, many of which dissolve within the age of the Universe. Therefore, many of the exoplanets observed today---in stars clusters and the field of the Galaxy---may have been born inside star clusters and subjected to past perturbations from nearby stars. Understanding how stellar encounters within this birth environment affect the dynamical evolution of planetary systems is paramount to interpreting the characteristics of all the newly discovered exoplanets and how these relate to the planet formation epoch. To address these important questions, the fellow work with a team of experts to complete development of the first computer code to self-consistently simulate the dynamical evolution of multi-planet systems in realistic star clusters. Dr. Geller and collaborators have already completed a pilot code demonstrating the feasibility of the most critical and innovative components, and the full code will be completed early in the first year of the fellowship. The fellow will then use this code to model nine open star clusters, including four in the Kepler field that have been surveyed comprehensively for transiting exoplanets. Each cluster will be modeled with multiple different initial planet populations to cover the range in characteristics of observed exoplanets. The simulations will be analyzed, accounting for the unique sensitivity limits of each transit survey, and the results will be compared directly with the observations. This project will reveal---for the first time self-consistently---how stellar encounters within star clusters of a wide range in age, density, mass, etc., influence the dynamical evolution of multi-planet systems including those like our Solar System and how the characteristics of exoplanets observed today in both clusters and the field may have been modified in the past by their birth environment. The broader impacts of this project include a significant educational component. The fellow will undertake a program of educational outreach in partnership with the Northwestern's NSF-funded GK-12 and CE21 programs to develop, test, and disseminate about 15 high school lesson plans based on the scientific research of this project. The fellow will work directly with a Northwestern graduate student to develop around five classroom-tested high school lesson plans each year. To supplement the lesson plans, the fellow will also develop a web-based student-friendly interface to both analyze the products of the proposed simulations and to allow students to run simulations of their own. During years 2 and 3 the fellow will integrate these lesson plans into teacher professional development workshops, which the PI will co-lead. Through these workshops, the fellow will train about 20 Chicago Public School and area teachers to use his lesson plans, thereby reaching about 2000 students with his curricular materials by the end of the fellowship. Both the GK-12 and CE21 programs are well established at Northwestern University and have been running successfully for years. This is a natural and mutually beneficial partnership that will help train the fellow for a future career teaching computational thinking methods in undergraduate physics and astronomy courses.