PRAC Supplement: Simulating Two-Fluid MHD Turbulence in Star Forming Molecular Clouds on the Blue Waters System

Dinshaw Balsara, University of Notre Dame

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We are at the threshold of a new data-rich and simulation-rich era in star-formation studies. The question of how stars form is fascinating in itself and has a great impact on several other areas of astrophysics.

There is a general consensus that a predominant amount of star formation in our Galaxy takes place in molecular clouds, and specifically in giant molecular clouds (GMC). The molecular cloud material consists of a highly turbulent, very weakly ionized, strongly magnetized plasma. It is within such a plasma that we observe protostellar cores – the progenitors of the stars that will eventually form

Our understanding of the star formation process has reached the point where advanced observational capabilities are required. Consequently, NASA has made multi-million dollar investments in the HAWC+ instrument aboard the SOFIA airborne observatory with the specific goal of understanding the turbulent nature of star forming clouds. At the same time, high-resolution simulations that include the appropriate physics of GMCs are also of critical importance.

The PI’s have been on the forefront of two-fluid MHD simulations on a range of NSF computing resources, including more recent work done on Blue Waters. The partially ionized fluid in a GMC is best modelled as a neutral fluid and an ionic fluid which interacts with the magnetic field.

Such simulations are extremely CPU intensive and we are the first group to have published the largest simulations of their class.  These are the first simulations that will be able to match the observations from HAWC+. Our simulations make possible a detailed match between simulations and observations.

While some high resolution simulated results from Blue Waters have been published, more are being written up and even more are planned. Using the proposed high resolution simulations, we will probe the sub-Alfvenic and super-Alfvenic regimes (i.e. strong and weak magnetic field strengths) of two-fluid supersonic MHD turbulence in giant molecular clouds. The simulations on Blue Waters are the very first that have enabled us to obtain a true scale separation between the inertial range and the dissipation scales that are regulated by ambipolar diffusion.