Members
About Us
The aim of the University of Chicago Center on Astrophysical Thermonuclear Flashes - sponsored by the Department of Energy ASC/Alliances Program - is to solve the long-standing problem of thermonuclear flashes on the surfaces of compact stars such as neutron stars and white dwarfs, and in the interior of white dwarfs (i.e., Type I supernovae). This problem is remarkable for the breadth of physical phenomena involved, ranging from accretion flow onto the surfaces of these compact stars, to shear flow and Rayleigh-Taylor instabilities on the stellar surfaces, ignition of nuclear burning under conditions leading to convection, and either deflagration or detonation, stellar envelope expansion, and the possible creation of a common envelope binary star system. The physical processes include convection and turbulence at large Reynolds and Rayleigh numbers, convective penetration of stable matter at very high densities, equations of state for high density matter, nuclear processing, radiation hydrodynamics, interface dynamics (including mixing instabilities and burning front propagation), and the interaction of stars in a close binary. Indeed, few -- if any -- astrophysical problems present a substantially greater level of physical complexity. Thus, the physical conditions, and many of the physical phenomena, are similar to those confronted by the Department of Energy Stockpile Stewardship program. The (fully ionized) plasmas are at very high temperatures and densities; and the physical problems of nuclear ignition, deflagration or detonation, turbulent mixing, and interface dynamics for complex multicomponent fluids are common to the weapons program.
Because virtually every aspect of this problem represents a computational Grand Challenge, large-scale numerical simulations are at the heart of its resolution. The computational challenges and needs include development of new scalable algorithms, structuring of large complex physics codes, domain decomposition, load balancing, parallel adaptive mesh refinement, performance diagnostics, debugging tools, parallel I/O, and visualization of the highly complex three-dimensional results.
A significant issue for the astrophysical thermonuclear flash problem is code validation. We are pursuing a layered approach: While the ultimate test is comparison with astronomical observations of the consequences of nuclear flashes on or within compact stars, we are also comparing results of subsystems (that is, the results of codes containing only partial descriptions of the full physics) with model problems for which laboratory verification is possible. These tests range from comparison with a variety of ``desk-top'' fluid dynamics experiments (for example, Rayleigh-Taylor experiments) to comparison with experiments conducted at laser-driven ignition facilities (Omega, and eventually, NIF) and at the pulsed power facilities at LANL (Pegasus/Atlas) and Sandia (Saturn).
The Center includes leading physicists in the fields of nuclear astrophysics, condensed matter physics, statistical physics and complexity theory, structure and evolution of compact stars, and astrophysical (computational) hydrodynamics and convection; computational scientists with expertise in the appropriate implementation of the physics, algorithm development, and parallelization; and computer scientists widely recognized for innovation in the development of parallel numerical methods, portable programming environments for scalable and distributed computing, parallel I/O, and immersive three-dimensional visualization. This core group includes scientists at the UofC-managed Argonne National Laboratory (ANL), who have unique capabilities in many of the areas of parallel computing essential to this project; as well as computer scientists at the Rensselaer Polytechnic Institute expert in the key computer science research areas of adaptive mesh refinement and unstructured meshes.