Dr. Kritsuk and his team study dynamics of magnetized turbulence and star formation in molecular clouds with numerical high-resolution simulations. The computations are done with the Enzo code, an Adaptive Mesh Refinement and grid-based hybrid code (hydrodymamics and N-body), which is designed to do simulations of astrophysical and cosmological structure formation. The self-consistent computations model effects such as gravity, differential rotation, and radiative transfer on the self-organization in compressible magneto-hydrodynamic (MHD) turbulence in the multiphase interstellar medium. The models here incorporate more complex physics, a higher dynamic range of resolved scales, and employ improved numerical methods. In particular, the modeling includes the scaling of multiphase MHD turbulence and its change with the turbulence magnetization. The simulations for the dynamic range of MHD models for molecular cloud formation utilize petascale computational facilities and attempt to resolve the inertial range of supersonic magnetized turbulence in the multiphase interstellar medium. This will test competing star formation models and phenomenological theories when the simulations are compared to observations. More broadly, a better understanding of turbulence is also needed for understanding the acceleration and propagation of energetic particles, transport of momentum and energy in various astrophysical systems. As part of this project, one graduate student will be trained in the development of numerical methods for modeling supersonic MHD flows, in large-scale parallel computer simulations, and in methods for statistical analysis and visualization of magnetized multiphase turbulent flows.
Stars and planets form in the dark inside vast clouds of cold molecular gas and dust in the disk of the Milky Way. The primary objective of this research was to develop self-consistent models for molecular cloud structure with high dynamic range computer simulations. The second objective of this research was to study magnetized compressible turbulence in thermally unstable media, a subject of great importance for galactic astrophysics. The intellectual merit of this research project derives from the demonstration of a Kolmogorov-like turbulent cascade in interstellar turbulence. This was suspected by many to be the case, but no one was able to prove it so far. New advances in theory of compressible turbulence in combination with phenomenology supported by numerical simulations allowed us to come up with strong arguments in favor of a turbulent interpretation of observational Larson's laws. After decades of inconclusive debate about the origin of the correlations among molecular cloud properties that Richard Larson discovered in 1981, we argue that they indeed reflect a hierarchy of supersonic turbulent motions, showing that the debated complicating effects of gravity, magnetic fields, and multiphase structure do not fundamentally alter the basic picture of a turbulent cascade. A key outcome of the cascade picture is that the statistical properties of the turbulence within molecular clouds on scales where prestellar cores are about to form are independent on the details of large-scale energy injection processes. It is believed that the energy is added at scales comparable to the disk scale height by large scale gravitational instabilities and by the star formation feedback precesses. The broader impacts of this project stem from scientifically accurate visualisations, illustrating emerging star formation processes in turbulent molecular clouds based on the data from our numerical simulations. A 25 minute immersive all-digital fulldome planetarium show "Life: A Cosmic Story" produced by the California Academy of Sciences includes a 2 minute piece rendered by the Advanced Visualization Laboratory at the National Center for Supercomputing Applications. The show narrated by Jodie Foster won Best Fulldome Program at the 2011 Jackson Hole Wildlife Film Festival and Best Integration of Scientific Data and Best in Narration Award at the 2012 Jena Fulldome Festival in Germany. "Life" is distributed by SkySkan in English, German, Japanese, and Greek and is currently being played in 21 venues around the globe. This includes the California Academy with estimated 1.75 million visitors a year.
