No Evidence for Bardeen-Petterson Alignment in GRMHD Simulations and Semi-Analytic Models of Moderately Thin, Prograde, Tilted Accretion Disks

摘要

In this paper we introduce the first results that use data extracted directlyfrom numerical simulations as inputs to the analytic twisted disk model ofZhuravlev & Ivanov. In both numerical and analytic approaches, fullyrelativistic models of tilted and twisted disks having a moderate effectiveviscosity around a slowly rotating Kerr black hole are considered.Qualitatively, the analytic model demonstrates the same dynamics as thesimulations, although with some quantitative offset. Namely, the GRMHDsimulations generally give smaller variations of tilt and twist across thedisk. When the black hole and the disk rotate in the same sense, the simulatedtilted disk and analytic model show no sign of Bardeen-Petterson alignment,even in the innermost parts of the disk, where the characteristic time forrelaxation to a quasi-stationary configuration is of the same order as thecomputation time. In the opposite case, when the direction of the disk'srotation is opposite to that of black hole, a partial alignment is observed, inagreement with previous theoretical estimates. Thus, both fully numerical andanalytic schemes demonstrate that the Bardeen-Petterson effect may not bepossible for the case of prograde rotation provided that disk's effectiveviscosity is sufficiently small. This may have implications in modeling ofdifferent astrophysical phenomena, such as disk spectra and jet orientation.