scholarly journals Three-Dimensional Simulations of Accretion Disks

1997 ◽  
Vol 163 ◽  
pp. 179-189 ◽  
Author(s):  
John F. Hawley ◽  
Steven A. Balbus
Keyword(s):  
Angular Momentum ◽  
Accretion Disk ◽  
Accretion Disks ◽  
Three Dimensional ◽  
Spiral Waves ◽  
Central Issue ◽  
Transport Mechanisms ◽  
Mhd Turbulence ◽  
Mhd Instability ◽  
Three Dimensional Simulations

AbstractThe transport of angular momentum is the central issue in accretion disk dynamics. We review recent three-dimensional simulations that investigate possible transport mechanisms. Purely hydrodynamic local instabilities and turbulence are ruled out; global spiral waves remain a possibility. MHD turbulence, arising from a local MHD instability, has been shown effective in transporting angular momentum at dynamically important rates. These results establish the basic picture of accretion disk transport.

MHD Turbulence in an Accretion Disk

1995 ◽  
Vol 12 (2) ◽  
pp. 159-164 ◽  
Author(s):  
John F. Hawley ◽  
Steven A. Balbus
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Shear Flow ◽  
Accretion Disk ◽  
Accretion Disks ◽  
Reynolds Stresses ◽  
Mhd Turbulence ◽  
Mhd Instability ◽  
Standing Problem ◽  
Disk Shear

AbstractA long-standing problem in the theory of astrophysical accretion disks has been to determine the nature of the stress that transports orbital angular momentum outward. The discovery of a local MHD instability is strong evidence that transport occurs through turbulent Maxwell and Reynolds stresses. Using numerical simulations, we have demonstrated that a weak seed magnetic field in an accretion disk shear flow is unstable and leads to sustained MHD turbulence at dynamically important levels.

AGN torus threaded by large scale magnetic field

2018 ◽  
Vol 27 (10) ◽  
pp. 1844006
Author(s):  
A. Dorodnitsyn ◽  
T. Kallman
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Accretion Disk ◽  
Large Scale ◽  
Three Dimensional ◽  
X Ray ◽  
Radiative Feedback ◽  
Large Scale Magnetic Field ◽  
Three Dimensional Simulations

Large scale magnetic field can be easily dragged from galactic scales toward AGN along with accreting gas. There, it can contribute to both the formation of AGN “torus” and help to remove angular momentum from the gas which fuels AGN accretion disk. However the dynamics of such gas is also strongly influenced by the radiative feedback from the inner accretion disk. Here we present results from the three-dimensional simulations of pc-scale accretion which is exposed to intense X-ray heating.

scholarly journals Angular momentum transport in accretion disks: a hydrodynamical perspective

2019 ◽  
Vol 82 ◽  
pp. 391-413 ◽  
Author(s):  
S. Fromang ◽  
G. Lesur
Keyword(s):  
Angular Momentum ◽  
Accretion Disk ◽  
Accretion Disks ◽  
Dynamical Evolution ◽  
Theoretical Work ◽  
Momentum Transport ◽  
Angular Momentum Transport ◽  
Recent Developments ◽  
The Many ◽  
The Universe

The radial transport of angular momentum in accretion disk is a fundamental process in the universe. It governs the dynamical evolution of accretion disks and has implications for various issues ranging from the formation of planets to the growth of supermassive black holes. While the importance of magnetic fields for this problem has long been demonstrated, the existence of a source of transport solely hydrodynamical in nature has proven more difficult to establish and to quantify. In recent years, a combination of results coming from experiments, theoretical work and numerical simulations has dramatically improved our understanding of hydrodynamically mediated angular momentum transport in accretion disk. Here, based on these recent developments, we review the hydrodynamical processes that might contribute to transporting angular momentum radially in accretion disks and highlight the many questions that are still to be answered.

scholarly journals Accretion-Disk Corona Advected by External Radiation Drag

1998 ◽  
Vol 188 ◽  
pp. 413-414
Author(s):  
Y. Watanabe ◽  
J. Fukue
Keyword(s):  
Angular Momentum ◽  
Radiation Field ◽  
Accretion Disk ◽  
Accretion Disks ◽  
External Radiation ◽  
Radiation Fields ◽  
Almost All ◽  
Strong Radiation ◽  
Radiative Interaction ◽  
Standard Disk

Accretion-disk corona (ADC) is required from observational as well as theoretical reasons. In almost all of traditional studies, however, a stationary corona has been assumed; i.e., the corona gas corotates with the underlying (Keplerian) accretion disk, and the radial motion is ignored. Recently, in the theory of accretion disks a radiative interaction between the gas and the external radiation field has attracted the attention of researchers. In particular the radiation drag between the gas and the external radiation field becomes important from the viewpoint of the angular-momentum removal. We thus examine the effect of radiation drag on the accretion-disk corona above/below the accretion disk (Watanabe, Fukue 1996a, b). We suppose that an accretion disk can be described by the standard disk, and that radiation fields are produced by the central luminous source and the accretion disk, itself. In general an accretion-disk corona under the influence of strong radiation fields dynamically infalls (advected) toward the center.

Local Three-dimensional Simulations of an Accretion Disk Hydromagnetic Dynamo

1996 ◽  
Vol 464 ◽  
pp. 690 ◽  
Author(s):  
John F. Hawley ◽  
Charles F. Gammie ◽  
Steven A. Balbus
Keyword(s):  
Accretion Disk ◽  
Three Dimensional ◽  
Hydromagnetic Dynamo ◽  
Three Dimensional Simulations

scholarly journals Turbulence, Vorticity Generation and Angular Momentum Transport via the Baroclinic Instability in Accretion Disks

2004 ◽  
Vol 202 ◽  
pp. 350-352
Author(s):  
Hubert Klahr ◽  
Peter Bodenheimer
Keyword(s):  
Angular Momentum ◽  
Accretion Disks ◽  
Baroclinic Instability ◽  
Three Dimensional ◽  
Gravitational Energy ◽  
Momentum Transport ◽  
Angular Momentum Transport ◽  
Accretion Rates ◽  
Background Shear ◽  
2D And 3D

We propose the global baroclinic instability as a source for vigorous turbulence leading to angular momentum transport in Keplerian accretion disks. We know from analytical considerations and three-dimensional radiation hydro simulations that, in particular, protoplanetary disks have a negative radial entropy gradient, which makes them baroclinic. Two-dimensional numerical simulations show that this baroclinic flow is unstable and produces turbulence. These findings were tested for numerical effects by performing barotropic simulations which show that imposed turbulence rapidly decays. The turbulence in baroclinic disks draws energy from the background shear, transports angular momentum outward and creates a radially inward bound accretion of matter, thus forming a self consistent process. Gravitational energy is transformed into turbulent kinetic energy, which is then dissipated, as in the classical accretion paradigm. We measure accretion rates in 2D and 3D simulations of Ṁ = −;10−9 to −10−7 M⊙ yr−1 and viscosity parameters of α = 10−4–10−2, which fit perfectly together and agree reasonably with observations. The turbulence creates pressure waves, Rossby waves, and vortices in the (R – ø) plane of the disk. We demonstrate in a global simulation that these vortices tend to form out of little background noise and to be long-lasting features, which have already been suggested to lead to the formation of planets.

scholarly journals Nature of Turbulence: Governing Factor of Accretion Disk Dynamics

1998 ◽  
Vol 11 (2) ◽  
pp. 786-789
Author(s):  
J. G. Lominadze
Keyword(s):  
Angular Momentum ◽  
Accretion Disk ◽  
Accretion Disks ◽  
Recent Advances ◽  
Governing Factor ◽  
Different Sources

It has long been suggested that turbulence provide viscous torques to transport angular momentum outward and flow mass inward in accretion disks (von Weizsäcker 1948, Shakura & Sunyaev 1973). Recent advances in subject of understanding of accretion disk turbulence are mach linked with magnetised disks (cf. Vishniac & Diamond 1992, Balbus, Gammie & Hawley 1994, Brandenburg et al. 1995, Stone et al 1996). However, not all the disks are magnetically coupled (see Balbus, Hawley & Stone 1996). Two different sources that are able to sustain turbulence in not magnetised accretion disk are the following:

scholarly journals Angular Momentum Transport by MHD Turbulence in Accretion Disks

2004 ◽  
Vol 155 ◽  
pp. 409-410 ◽  
Author(s):  
Takayoshi Sano ◽  
Shu-ichiro Inutsuka ◽  
Neal J. Turner ◽  
James M. Stone
Keyword(s):  
Angular Momentum ◽  
Accretion Disks ◽  
Momentum Transport ◽  
Mhd Turbulence ◽  
Angular Momentum Transport

scholarly journals The Role of Opacities in Accretion Disks

1995 ◽  
Vol 10 ◽  
pp. 597-598
Author(s):  
R. Wehrse
Keyword(s):  
Angular Momentum ◽  
Neutron Star ◽  
Potential Energy ◽  
Accretion Disk ◽  
Accretion Disks ◽  
Heat Generation ◽  
White Dwarf ◽  
Young Stellar Object ◽  
Central Object

An accretion disk is formed when matter with angular momentum is flowing on a gravitating object (as e.g. a white dwarf, a neutron star, a young stellar object, or a black bole). It radiates because the transport of angular momentum (required for the matter to reach the central object) necessarily implies the conversion of potential energy into a form of energy that corresponds to higher entropy. Many aspects of the physics (as e.g. the mechanism for the heat generation) are not yet well understood but they are presently one of the centers of astronomical interest (see e.g. the books by Frank, King, and Raine, 1992, or by Wheeler, 1993).

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