Collaborative Research: The Physics of Accretion Disks

Johns Hopkins University, Baltimore MD

Investigators

Abstract

AST-0908336/0908869 Krolik/Hawley Armed by an understanding that the fundamental mechanism of accretion is angular momentum transport due to magnetohydrodynamic (MHD) turbulence driven by the magneto-rotational instability, it has become possible to investigate at a detailed level the astrophysical properties of accretion onto black holes. With previous NSF support, this team has developed a suite of Newtonian and general relativistic MHD numerical simulation codes suitable for exploring the global properties of accretion flows onto black holes and the jets they sometimes generate. This collaborative project, led by Dr. Krolik, will now extend prior work to consider accretion thermodynamics and energetics, the impact of large-scale magnetic fields, and how an accretion flow oriented obliquely to the black hole rotation axis at large distances interacts with Lense-Thirring torques. Emphasis will be placed throughout on creating quantitative links between dynamical simulation data and observable properties. This work should provide genuine guidance for the controversy over how much large-scale magnetic flux may be brought deep into the accretion flow. It should also reveal how accretion flows stressed by magnetic fields with intrinsic large-scale structure may differ from those without. In addition, computing MHD stresses within the accretion flow is essential to the question of the extent of disk bending by gravitomagnetic forces, and it should soon be possible to calculate disk structure with sufficient resolution to address this issue. Both simulation codes and data from specific models will be made available to the community, strengthening the software infrastructure of the discipline. The project will provide graduate student training in numerical simulation techniques. Successful public outreach efforts based on simulation results will continue, including planetarium shows and television documentaries.