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Journal articles on the topic 'Shakura-Sunyaev α-parameter'

Author: Grafiati
Published: 6 September 2023

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1

MUKHOPADHYAY, BANIBRATA. "ESTIMATE OF THE SHAKURA–SUNYAEV VISCOSITY PARAMETER IN THE KEPLERIAN ACCRETION DISK FROM HYDRODYNAMIC TURBULENCE." International Journal of Modern Physics D 17, no. 03n04 (2008): 467–73. http://dx.doi.org/10.1142/s0218271808012139.

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Recently, in a series of papers, Mukhopadhyay and his collaborators have argued for possible pure hydrodynamic turbulence in a Keplerian accretion disk. This is essentially important to solving the puzzle of the transport mechanism in cold accretion disk systems where the temperature could be lower than 5000 K, where magnetorotational instability seems not to be working to trigger turbulence. Here we quantify the corresponding instability and turbulence in terms of turbulent viscosity and obtain the famous Shakura–Shunyaev viscosity parameter, α. It is exciting that the range of α obtained fro
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2

CASSARO, P., F. SCHILLIRÓ, V. COSTA, G. BELVEDERE, R. A. ZAPPALÁ, and G. LANZAFAME. "THE ENGINE OF OUTFLOWS IN AGN: THE ROLE OF PHYSICAL TURBULENT VISCOSITY." International Journal of Modern Physics D 17, no. 09 (2008): 1635–40. http://dx.doi.org/10.1142/s0218271808013248.

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Adopting the smoothed particle hydrodynamics (SPH) numerical method, we performed a grid of evolving models of a 3D, axially symmetric, physically viscous accretion disc around a black hole (BH) in an AGN. In such disc models, the role of the specific angular momentum λ and of the physical turbulent viscosity parameter α, according to the Shakura and Sunyaev prescription, are examined. One or two shock fronts develop in the radial inviscid flow, according to the assigned initial kinematic and thermodynamic conditions. Couples of (α, λ) values determine radial periodical oscillations in the sho
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3

Chen, Yi-Xian, Yan-Fei Jiang, Jeremy Goodman, and Eve C. Ostriker. "3D Radiation Hydrodynamic Simulations of Gravitational Instability in AGN Accretion Disks: Effects of Radiation Pressure." Astrophysical Journal 948, no. 2 (2023): 120. http://dx.doi.org/10.3847/1538-4357/acc023.

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Abstract We perform 3D radiation hydrodynamic local shearing-box simulations to study the outcome of gravitational instability (GI) in optically thick active galactic nuclei (AGNs) accretion disks. GI develops when the Toomre parameter Q T ≲ 1, and may lead to turbulent heating that balances radiative cooling. However, when radiative cooling is too efficient, the disk may undergo runaway gravitational fragmentation. In the fully gas-pressure-dominated case, we confirm the classical result that such a thermal balance holds when the Shakura–Sunyaev viscosity parameter (α) due to the gravitationa
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4

Bi, Jiaqing, and Jeffrey Fung. "Dust Dynamics in Transitional Disks: Clumping and Disk Recession." Astrophysical Journal 928, no. 1 (2022): 74. http://dx.doi.org/10.3847/1538-4357/ac53ac.

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Abstract The role of radiation pressure in dust migration and the opening of inner cavities in transitional disks is revisited in this paper. Dust dynamics including radiation pressure is often studied in axisymmetric models, but in this work, we show that highly non-axisymmetric features can arise from an instability at the inner disk edge. Dust grains clump into high density features there, allowing radiation to leak around them and penetrate deeper into the disk, changing the course of dust migration. Our proof-of-concept, two-dimensional, vertically averaged simulations show that the combi
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5

Sellek, Andrew D., Richard A. Booth, and Cathie J. Clarke. "The evolution of dust in discs influenced by external photoevaporation." Monthly Notices of the Royal Astronomical Society 492, no. 1 (2019): 1279–94. http://dx.doi.org/10.1093/mnras/stz3528.

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ABSTRACT Protoplanetary discs form and evolve in a wide variety of stellar environments and are accordingly exposed to a wide range of ambient far-ultraviolet (FUV) field strengths. Strong FUV fields are known to drive vigorous gaseous flows from the outer disc. In this paper we conduct the first systematic exploration of the evolution of the solid component of discs subject to external photoevaporation. We find that the main effect of photoevaporation is to reduce the reservoir of dust at large radii and this leads to more efficient subsequent depletion of the disc dust due to radial drift. E
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6

Trapman, Leon, Benoît Tabone, Giovanni Rosotti, and Ke Zhang. "Effect of MHD Wind-driven Disk Evolution on the Observed Sizes of Protoplanetary Disks." Astrophysical Journal 926, no. 1 (2022): 61. http://dx.doi.org/10.3847/1538-4357/ac3ed5.

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Abstract It is still unclear whether the evolution of protoplanetary disks, a key ingredient in the theory of planet formation, is driven by viscous turbulence or magnetic disk winds. As viscously evolving disks expand outward over time, the evolution of disk sizes is a discriminant test for studying disk evolution. However, it is unclear how the observed disk size changes over time if disk evolution is driven by magnetic disk winds. Combining the thermo-chemical code DALI with the analytical wind-driven disk-evolution model presented in Tabone et al., we study the time evolution of the observ
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7

Proga, Daniel, Janet E. Drew, and James M. Stone. "Radiation driven winds from CV accretion disks." International Astronomical Union Colloquium 163 (1997): 782. http://dx.doi.org/10.1017/s0252921100043967.

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AbstractWe present some initial results of our numerical, 2D hydrodynamical models of line driven flows from the accretion disk in cataclysmic variables. We assume the disk radiation pressure pushes out the isothermal material from a flat, geometrically thin, Keplerian disk.We calculate the disk radiation field using the surface brightness of a standard “α disk” (Shakura & Sunyaev 1973). We do not include a bright boundary layer in the calculations. We approximate the total radiative line acceleration, adopting the formalism due to Castor, Abbott, & Klein (1975). We use our generalized
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8

Delage, Timmy N., Satoshi Okuzumi, Mario Flock, Paola Pinilla, and Natalia Dzyurkevich. "Steady-state accretion in magnetized protoplanetary disks." Astronomy & Astrophysics 658 (February 2022): A97. http://dx.doi.org/10.1051/0004-6361/202141689.

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Context. The transition between magnetorotational instability (MRI)-active and magnetically dead regions corresponds to a sharp change in the disk turbulence level, where pressure maxima may form, hence potentially trapping dust particles and explaining some of the observed disk substructures. Aims. We aim to provide the first building blocks toward a self-consistent approach to assess the dead zone outer edge as a viable location for dust trapping, under the framework of viscously driven accretion. Methods. We present a 1+1D global magnetically driven disk accretion model that captures the es
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9

Granada, A., C. E. Jones, and T. A. A. Sigut. "The Viscosity Parameter for Late-type Stable Be Stars." Astrophysical Journal 922, no. 2 (2021): 148. http://dx.doi.org/10.3847/1538-4357/ac222f.

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Abstract Using hydrodynamic principles we investigate the nature of the disk viscosity following the parameterization by Shakura & Sunyaev adopted for the viscous decretion model in classical Be stars. We consider a radial viscosity distribution including a constant value, a radially variable α assuming a power-law density distribution, and isothermal disks, for a late-B central star. We also extend our analysis by determining a self-consistent temperature disk distribution to model the late-type Be star 1 Delphini, which is thought to have a nonvariable, stable disk as evidenced by Hα emi
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10

Ma, Zhen Guo, and Xi Zhen Zhang. "Prediction of the Black-Hole Mass in 3C 273 by Multiband Observations." Symposium - International Astronomical Union 214 (2003): 281–86. http://dx.doi.org/10.1017/s0074180900194574.

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With the determined black-hole (BH) spin of 3C 273 by data-fitting to the detected iron Kα line emission in the soft X-ray band, the BH mass of the galaxy is predicted by formulations of both the observed disk-luminosity in the optical-UV band and the observed jet-precession in the radio band. The multiband synthesis suggests that the BH is supermassive, 2.4 × 109M⊙. Simultaneously, other physical parameters are self-consistently obtained at the precessing radius of 230.2rg: the accretion rate of the disk is 74.9M⊙ yr−1, the Shakura-Sunyaev viscosity α is 0.134, and the radial & orbital ve
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11

Mao, Shunyuan, Ruobing Dong, Lu Lu, Kwang Moo Yi, Sifan Wang, and Paris Perdikaris. "PPDONet: Deep Operator Networks for Fast Prediction of Steady-state Solutions in Disk–Planet Systems." Astrophysical Journal Letters 950, no. 2 (2023): L12. http://dx.doi.org/10.3847/2041-8213/acd77f.

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Abstract We develop a tool, which we name Protoplanetary Disk Operator Network (PPDONet), that can predict the solution of disk–planet interactions in protoplanetary disks in real time. We base our tool on Deep Operator Networks, a class of neural networks capable of learning nonlinear operators to represent deterministic and stochastic differential equations. With PPDONet we map three scalar parameters in a disk–planet system—the Shakura–Sunyaev viscosity α, the disk aspect ratio h 0, and the planet–star mass ratio q—to steady-state solutions of the disk surface density, radial velocity, and
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12

Gurzadyan, Vahagn G. "General Discussion of Accretion Disks." Symposium - International Astronomical Union 194 (1999): 321–22. http://dx.doi.org/10.1017/s0074180900162205.

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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. Anoth
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13

Riffert, H., T. Dörrer, R. Staubert, and H. Ruder. "The Vertical Structures of Accretion Disks in AGN." Symposium - International Astronomical Union 159 (1994): 478. http://dx.doi.org/10.1017/s0074180900176557.

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Radiation emitted from an accretion disk around a central black hole is the widely accepted model for the observed optical to UV emission from AGN. We have calculated the properties of a standard α-accretion disk (Shakura and Sunyaev, 1973). We present a fully self-consistent model of the structure and the spectrum of such a disk, i.e. the internal vertical density and temperature profiles are calculated simultaneously with the local spectra. Constant density models have been presented by (Ross et al., 1992). The central object is assumed to be a Kerr black hole (BH); relativistic corrections
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14

Shende, Mayur B., Prashali Chauhan, and Prasad Subramanian. "X-ray Dips in AGN and Microquasars – Collapse Timescales of Inner Accretion Disc." Monthly Notices of the Royal Astronomical Society, December 12, 2020. http://dx.doi.org/10.1093/mnras/staa3838.

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Abstract The temporal behaviour of X-rays from some AGN and microquasars is thought to arise from the rapid collapse of the hot, inner parts of their accretion discs. The collapse can occur over the radial infall timescale of the inner accretion disc. However, estimates of this timescale are hindered by a lack of knowledge of the operative viscosity in the collisionless plasma comprising the inner disc. We use published simulation results for cosmic ray diffusion through turbulent magnetic fields to arrive at a viscosity prescription appropriate to hot accretion discs. We construct simplified
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15

Sánchez-Salcedo, F. J., R. O. Chametla, and O. Chrenko. "Estimating the depth of gaps opened by planets in eccentric orbit." Monthly Notices of the Royal Astronomical Society, October 6, 2022. http://dx.doi.org/10.1093/mnras/stac2856.

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Abstract Planets can carve gaps in the surface density of protoplanetary discs. The formation of these gaps can reduce the corotation torques acting on the planets. In addition, gaps can halt the accretion of solids onto the planets as dust and pebbles can be trapped at the edge of the gap. This accumulation of dust could explain the origin of the ring-like dust structures observed using high-resolution interferometry. In this work we provide an empirical scaling relation for the depth of the gap cleared by a planet on an eccentric orbit as a function of the planet-to-star mass ratio q, the di
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