2015/05/05 by Julian H. Krolik, John F. Hawley, Krolik, Julian H. +1
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #Solar and Space Plasma Dynamics
paper · pdf · doi:10.48550/arxiv.1505.01050
openalex publication_date 2015/05/05 · openalex created_date 2022/10/04 · openalex updated_date 2026/07/28
Using only physical mechanisms, i.e., 3D MHD with no phenomenological\nviscosity, we have simulated the dynamics of a moderately thin accretion disk\nsubject to torques whose radial scaling mimics those produced by lowest-order\npost-Newtonian gravitomagnetism. In this simulation, we have shown how, in the\npresence of MHD turbulence, a time-steady transition can be achieved between an\ninner disk region aligned with the equatorial plane of the central mass's spin\nand an outer region orbiting in a different plane. The position of the\nequilibrium orientation transition is determined by a balance between\ngravitomagnetic torque and warp-induced inward mixing of misaligned angular\nmomentum from the outer disk. If the mixing is interpreted in terms of\ndiffusive transport, the implied diffusion coefficient is\n~(0.6--0.8)cs2/Omega for sound speed cs and orbital frequency Omega. This\ncalibration permits estimation of the orientation transition's equilibrium\nlocation given the central mass, its spin parameter, and the disk's surface\ndensity and scaleheight profiles. However, the alignment front overshoots\nbefore settling into an equilibrium, signaling that a diffusive model does not\nfully represent the time-dependent properties of alignment fronts under these\nconditions. Because the precessional torque on the disk at the alignment front\nis always comparable to the rate at which misaligned angular momentum is\nbrought inward to the front by warp-driven radial motions, no break forms\nbetween the inner and outer portions of the disk in our simulation. Our results\nalso raise questions about the applicability to MHD warped disks of the\ntraditional distinction between "bending wave" and "diffusive" regimes.\n