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- Ciesielski, A., et al.
(author)
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Stability of radiation-pressure dominated disks: I. the dispersion relation for a delayed heating α-viscosity prescription
- 2012
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 538
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Journal article (peer-reviewed)abstract
- We derive and investigate the dispersion relation for accretion disks with retarded or advanced heating. We follow the α-prescription but allow for a time offset τ between heating and pressure perturbations, as well as for a diminished response of heating to pressure variations. We study in detail solutions of the dispersion relation for disks with radiation-pressure fraction, 1-β, and ξ, the ratio of viscous stress response to pressure perturbations. For τ < 0 (advanced heating) the number and sign of real solutions for the growth rate depend on the values of τ, and ξ: if the magnitude of τ is larger than a critical value (e.g., more than twice the thermal time,-τ > 2 τ th, for β = 0 and ξ = 1) two real solutions exist, which are both negative. These results imply that radiation-pressure dominated accretion disks may be stabilized when there is a time delay between stress fluctuations and fluctuations in heating. © 2012 ESO.
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| 2. |
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| 3. |
- Lasota, J. P., et al.
(author)
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The slimming effect of advection on black-hole accretion flows
- 2016
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In: Astronomy & Astrophysics. - : EDP Sciences. - 1432-0746 .- 0004-6361. ; 587
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Journal article (peer-reviewed)abstract
- Context. At super-Eddington rates accretion flows onto black holes have been described as slim (aspect ratio H/R less than or similar to 1) or thick (H/R > 1) discs, also known as tori or (Polish) doughnuts. The relation between the two descriptions has never been established, but it was commonly believed that at sufficiently high accretion rates slim discs inflate, becoming thick. Aims. We wish to establish under what conditions slim accretion flows become thick. Methods. We use analytical equations, numerical 1 + 1 schemes, and numerical radiative MHD codes to describe and compare various accretion flow models at very high accretion rates. Results. We find that the dominant effect of advection at high accretion rates precludes slim discs becoming thick. Conclusions. At super-Eddington rates accretion flows around black holes can always be considered slim rather than thick.
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| 4. |
- Sadowski, A., et al.
(author)
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Energy flows in thick accretion discs and their consequences for black hole feedback
- 2016
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In: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 456:4, s. 3915-3928
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Journal article (peer-reviewed)abstract
- We study energy flows in geometrically thick accretion discs, both optically thick and thin, using general relativistic, three-dimensional simulations of black hole accretion flows. We find that for non-rotating black holes the efficiency of the total feedback from thick accretion discs is 3 per cent - roughly half of the thin disc efficiency. This amount of energy is ultimately distributed between outflow and radiation, the latter scaling weakly with the accretion rate for super-critical accretion rates, and returned to the interstellar medium. Accretion on to rotating black holes is more efficient because of the additional extraction of rotational energy. However, the jet component is collimated and likely to interact only weakly with the environment, whereas the outflow and radiation components cover a wide solid angle.
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