On the Stability of Accretion Disks

1977 ◽  
pp. 51-51
Author(s):  
Mario Livio ◽  
Giora Shaviv
Keyword(s):  
Accretion Disks ◽  
The Stability

scholarly journals General Discussion of Accretion Disks

1999 ◽  
Vol 194 ◽  
pp. 321-322
Author(s):  
Vahagn G. Gurzadyan
Keyword(s):  
Magnetic Field ◽  
Accretion Disks ◽  
Galactic Nuclei ◽  
The Other ◽  
Seminal Paper ◽  
Physical Conditions ◽  
Electron Positron ◽  
Free Parameters ◽  
The Stability ◽  
Electron Positron Pair

Even 25 years after the Shakura-Sunyaev seminal paper on the α-disk, we cannot claim that we have a reliable theory of accretion disks in galactic nuclei. Why? Because the problem is extremely complicated, it is essentially nonlinear and contains a number of parameters (i.e. is many-dimensional). The key point is whether it is possible to determine the magneto-hydrodynamical viscosity self-consistently, i.e. as a function of parameters of the disk - the temperature, matter and radiation densities, magnetic field, radius, etc., both in the radiation dominated and matter dominated regions. Another class of fundamental problems concerns the stability of the disk; Krolik mentioned only one instability - in the radiation dominated region, but there are many other types of instabilities which are quite sensitive to the physical conditions in the disk, for example, to the anisotropy of the ion pressure in the outer regions and possible electron-positron pair production near the inner edge of the disk. The other problems include those of the radiative transfer within the disk in various conditions, Comptonization of the outgoing radiation, radiation reflections by the desk, etc. Therefore it is not suprising that one can ‘explain' almost whatever he wants - spectra, variability, jets, wind, etc., by proper fit of the ‘free’ (which are never free) parameters and ignoring the instabilities and so on.

scholarly journals Accretion disks around a mass with quadrupole QUADRUPOLE

2021 ◽  
Vol 79 (1) ◽  
pp. 352-358
Author(s):  
S. Toktarbay ◽  
◽  
A.Zh. Abylaeva ◽  
G.N. Khudaibergenova ◽  
B.S. Nasyrova ◽  
...  
Keyword(s):  
Accretion Disk ◽  
Accretion Disks ◽  
Test Particle ◽  
Compact Objects ◽  
Geodesic Line ◽  
Field Equations ◽  
Schwarzschild Solution ◽  
Test Particles ◽  
Line Equation ◽  
The Stability

In this work, we consider the exterior static axisymmetric gravitational of compact objects. We investigate the properties of the q-metric which is the simplest generalization of the Schwarzschild solution that contains a quadrupole parameter. The geodesic line equation is derived from the field equations and the orbits of the test particle are investigated. We consider the stability properties of test particles moving along circular orbits around a mass with quadrupole. We show that the quadrupole modifies drastically the properties of an accretion disk made of such test particles.

The radial–azimuthal instability of accretion disk with anomalous viscosity

2014 ◽  
Vol 92 (5) ◽  
pp. 395-400
Author(s):  
Yue Qi Chen ◽  
Wei Qun Jiang
Keyword(s):  
Numerical Simulations ◽  
Accretion Disk ◽  
Accretion Disks ◽  
Radiation Pressure ◽  
Gas Pressure ◽  
Thermal Mode ◽  
Acoustic Modes ◽  
Anomalous Viscosity ◽  
The Stability ◽  
Inner Region

The stability of the accretion disk is solved by numerical simulations when the radial and azimuthal perturbations are considered, where we adopt the anomalous viscosity model, which is close to real accretion disks. The results are discussed in the inner, intermediate, and outer regions of the accretion disk, respectively. With the increase of viscosity, α, the thermal mode and the viscous mode, as well as the acoustic modes, become more unstable in the disk dominated by radiation pressure (inner region). The instability is also influenced by the azimuthal perturbation wavenumber, n. With the increase of n, the thermal mode becomes more unstable, while the in-mode and out-mode become more stable no matter if the disk is dominated by radiation pressure or by gas pressure (intermediate and outer regions). There are many differences between our results and others’ results, especially in the inner region of the disk, when the anomalous viscosity is considered.

The Contribution of Degenerate Electron Pressure to The Stability of The Outer Region of Thin Keplerian Accretion Disks Around a Neutron Star

2015 ◽  
Vol 11 (1) ◽  
pp. 2886-2891
Author(s):  
Abbi Seyoum Demissie
Keyword(s):  
Neutron Star ◽  
Accretion Disks ◽  
Outer Region ◽  
Thin Disk ◽  
Gas Pressure ◽  
Degenerate Electron ◽  
Small Temperature ◽  
Radial Perturbation ◽  
The Stability ◽  
Definite Temperature

The stability analysis of a geometrically thin, gas-pressure dominated accretion disk around a neutron star is presented. In purely radial perturbation case, thin disk is stable to thermal modes. The stability is analyzed at a small temperature, that is temperature approaching zero and at definite temperature. The contribution of both fully and partially degenerate electrons pressure for the stability of the disk in its outer region is investigated. We find that the disk is stable in this region, where the gas pressure is more dominant than radiation pressure.

scholarly journals ASASSN-14ho: Longest-period dwarf nova with multiple rebrightenings

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Taichi Kato
Keyword(s):  
Mass Transfer ◽  
Radial Velocity ◽  
Accretion Disks ◽  
Orbital Period ◽  
Formal Solution ◽  
Dwarf Novae ◽  
X Ray ◽  
Dwarf Nova ◽  
Orbital Periods ◽  
The Stability

Abstract The post-outburst rebrightening phenomenon in dwarf novae and X-ray novae is still one of the most challenging subjects for theories of accretion disks. It has been widely recognized that post-outburst rebrightenings are a key feature of WZ Sge-type dwarf novae, which predominantly have short (≲0.06 d) orbital periods. The author found four post-outburst rebrightenings in ASASSN-14ho during its 2014 outburst, whose orbital period was recently measured to be exceptionally long [0.24315(10) d]. Using the formal solution of the radial velocity study in the literature, this paper discusses the possibility that this object could be an SU UMa-type dwarf nova near the stability border of the 3 : 1 resonance, despite its exceptionally long orbital period. Such objects are considered to be produced if mass transfer occurs after the secondary has undergone significant nuclear evolution, and they may be hidden in a significant number of dwarf novae showing multiple post-outburst rebrightenings.

scholarly journals SPH Simulations of Accretion Disks and Narrow Rings

1996 ◽  
Vol 13 (1) ◽  
pp. 66-70 ◽  
Author(s):  
Sarah T. Maddison ◽  
James R. Murray ◽  
Joe J. Monaghan
Keyword(s):  
Accretion Disks ◽  
Initial Condition ◽  
Initial State ◽  
Single Ring ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Set Up ◽  
The Stability ◽  
Sph Simulation ◽  
Axisymmetric Instability

AbstractWe model a massless viscous disk using smoothed particle hydrodynamics (SPH) and note that it evolves according to the Lynden-Bell & Pringle (1974) theory until a non-axisymmetric instability develops at the inner edge of the disk. This instability may have the same origin as the instability of initially axisymmetric viscous disks discussed by Lyubarskij, Postnov & Prokhorov (1994). To clarify the evolution we evolved single and double rings of particles. It is actually inconsistent with the SPH scheme to set up a single ring as an initial condition because SPH assumes a smoothed initial state. As would be expected from an SPH simulation, the ring rapidly breaks up into a band. We analyse the stability of the ring and show that the predictions are confirmed by the simulation.

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