scholarly journals Inefficient angular momentum transport in accretion disc boundary layers: angular momentum belt in the boundary layer

2018 ◽  
Vol 479 (2) ◽  
pp. 1528-1541
Author(s):  
Mikhail A Belyaev ◽  
Eliot Quataert
Keyword(s):  
Boundary Layer ◽  
Angular Momentum ◽  
Boundary Layers ◽  
Accretion Disc ◽  
Momentum Transport ◽  
Angular Momentum Transport

scholarly journals On magnetohydrodynamic turbulence and angular momentum transport in accretion disk boundary layers

2012 ◽  
Vol 8 (S294) ◽  
pp. 349-352
Author(s):  
Chi-kwan Chan ◽  
Martin E. Pessah
Keyword(s):  
Boundary Layer ◽  
Angular Momentum ◽  
Energy Density ◽  
Numerical Simulations ◽  
Boundary Layers ◽  
Accretion Disk ◽  
Shear Viscosity ◽  
Momentum Transport ◽  
Turbulent Shear ◽  
Angular Momentum Transport

AbstractThe physical modeling of the accretion disk boundary layer, the region where the disk meets the surface of the accreting star, usually relies on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear viscosity, widely adopted in astrophysics, satisfies this assumption by construction. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability is inefficient in this inner disk region. I will discuss the results of a recent study on the generation of hydromagnetic stresses and energy density in the boundary layer around a weakly magnetized star. Our findings suggest that although magnetic energy density can be significantly amplified in this region, angular momentum transport is rather inefficient. This seems consistent with the results obtained in numerical simulations and suggests that the detailed structure of turbulent MHD boundary layers could differ appreciably from those derived within the standard framework of turbulent shear viscosity.

scholarly journals Magnetohydrodynamic Turbulence in Accretion Discs: Towards More Realistic Models

1997 ◽  
Vol 163 ◽  
pp. 210-214
Author(s):  
Ulf Torkelsson ◽  
Axel Brandenburg ◽  
Åke Nordlund ◽  
Robert F. Stein
Keyword(s):  
Angular Momentum ◽  
Boundary Conditions ◽  
Accretion Disc ◽  
Quantitative Change ◽  
Accretion Discs ◽  
Momentum Transport ◽  
Magnetohydrodynamic Turbulence ◽  
Accretion Flow ◽  
Angular Momentum Transport ◽  
Main Effects

AbstractThe shearing box has rapidly become the accepted way to investigate turbulence in Keplerian shear flows. In this paper we discuss to what extent and in which way the outcome of the shearing box is affected by the adopted boundary conditions, and how the shearing box can be modified to capture more of the physics of an accretion disc. The original shearing box model is too symmetric to generate a net accretion flow, but the symmetry can be broken by including the main effects of the cylindrical geometry of the real disc. However the quantitative change in the resulting angular momentum transport is small.

scholarly journals Spectral evidence of an accretion disc in wind-fed X-ray pulsar Vela X-1 during an unusual spin-up period

2020 ◽  
Vol 492 (4) ◽  
pp. 5922-5929 ◽  
Author(s):  
Zhenxuan Liao ◽  
Jiren Liu ◽  
Xueying Zheng ◽  
Lijun Gou
Keyword(s):  
Angular Momentum ◽  
Column Density ◽  
Accretion Disc ◽  
Momentum Transport ◽  
X Ray ◽  
Angular Momentum Transport ◽  
Eclipse Phase ◽  
Axisymmetric Structure ◽  
X Ray Binaries ◽  
The Continuum

ABSTRACT In classical supergiant X-ray binaries (SgXBs), the Bondi–Hoyle–Lyttleton wind accretion was usually assumed, and the angular momentum transport to the accretors is inefficient. The observed spin-up/spin-down behaviour of the neutron star in SgXBs is not well understood. In this paper, we report an extended low state of Vela X-1 (at orbital phases 0.16–0.2), lasting for at least 30 ks, observed with Chandra during the onset of an unusual spin-up period. During this low state, the continuum fluxes dropped by a factor of 10 compared to the preceding flare period, and the continuum pulsation almost disappeared. Meanwhile, the Fe K α fluxes of the low state were similar to the preceding flare period, leading to an Fe K α equivalent width (EW) of 0.6 keV, as high as the Fe K α EW during the eclipse phase of Vela X-1. Both the pulsation cessation and the high Fe K α EW indicate an axisymmetric structure with a column density larger than 1024 cm−2 on a spatial scale of the accretion radius of Vela X-1. These phenomena are consistent with the existence of an accretion disc that leads to the following spin-up of Vela X-1. It indicates that disc accretion, although not always, does occur in classical wind-fed SgXBs.

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