Grant: Discovery Grants Program - Individual

Advances in observational astronomy have enabled a greatly expanded picture of the different types of abundance patterns and chemical fingerprints that exist in the universe. In large surveys that target metal-poor stars that have formed in the early universe stars with rare and exotic abundance patterns are now frequently found. These abundance observations of stars have evolved into the important tool of galactic archeology to study the formation and evolution of galaxies, and the cosmological processes in the early universe. This project will enhance our understanding of how the elements form in the exotic stellar evolution toward black hole formation of supernova explosion. The first stars that formed shortly after the Big Bang must have possessed yet to be determined unusual modes of element formation as is evident from some of the most intriguing and anomalous abundance patterns found in the most metal-poor and oldest stars. Our approach is based on a new generation of three-dimensional simulations of the turbulent, hydrodynamic conditions of element formation. These simulations require the impressive computing power of Compute Canada's new Niagara supercomputer, that we have used earlier this year together with our international team to perform the largest simulations of turbulent core convection in a massive star. With these three-dimensional simulations we expect to be able to overcome the limitations of present-day one-dimensional spherically-symmetric stellar evolution simulations that include turbulent mixing only via a parameterized model. By including the often violent and energetic feedback from nuclear burning into realistic three-dimensional simulations at very high spatial resolution, using about one half of the entire Niagara computer's 60,000 compute cores at a given time during a simulation run, we will generate unique astrophysics simulation data sets of the turbulent conditions of convective shells in massive stars, such as the merger of a C- and O-burning shell. These simulations will provide a view of unprecedented detail on how the elements form in the final stages of a star's life before exploding as a supernova. An important goal of our research will be to improve our understanding of the exotic conditions in the first massive stars that formed after the Big Bang from the initial, pristine and metal-free material. One-dimensional models suggest that during interactions of convective H- and He-burning shells as much energy per unit time as an entire galaxy produces would be generated inside the star, although of course only for a short time. Our three-dimensional simulations will reveal how a real star would respond to such extreme and energetic events. They will show if and how the anomalous abundance patterns observed in the most metal-poor and oldest stars can originate in these first stars. In this way our research will help to solve the puzzle of element formation and evolution in the early universe.