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Marek A. Abramowicz - One of the best experts on this subject based on the ideXlab platform.
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the slimming effect of advection on black hole Accretion flows
Astronomy and Astrophysics, 2016Co-Authors: Jeanpierre Lasota, Rebecca Lynn Vieira, Aleksander Sadowski, Ramesh Narayan, Marek A. AbramowiczAbstract:Context. At super-Eddington rates Accretion flows onto black holes have been described as slim (aspect ratio H/R ≲ 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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Foundations of Black Hole Accretion Disk Theory
Living Reviews in Relativity, 2013Co-Authors: Marek A. Abramowicz, P. Chris FragileAbstract:This review covers the main aspects of black hole Accretion disk theory. We begin with the view that one of the main goals of the theory is to better understand the nature of black holes themselves. In this light we discuss how Accretion disks might reveal some of the unique signatures of strong gravity: the event horizon, the innermost stable circular orbit, and the ergosphere. We then review, from a first-principles perspective, the physical processes at play in Accretion disks. This leads us to the four primary Accretion disk models that we review: Polish doughnuts (thick disks), Shakura-Sunyaev (thin) disks, slim disks, and advection-dominated Accretion flows (ADAFs). After presenting the models we discuss issues of stability, oscillations, and jets. Following our review of the analytic work, we take a parallel approach in reviewing numerical studies of black hole Accretion disks. We finish with a few select applications that highlight particular astrophysical applications: measurements of black hole mass and spin, black hole vs. neutron star Accretion disks, black hole Accretion disk spectral states, and quasi-periodic oscillations (QPOs).
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theory of black hole Accretion disks
1998Co-Authors: J E Pringle, Marek A. Abramowicz, G BjornssonAbstract:Part I. Observations of Black Holes: 1. Black holes in our Galaxy: observations P. Charles 2. Black holes in Active Galactic Nuclei: observations G. M. Madejski Part II. Physics Close to a Black Hole: 3. Physics of black holes I. D. Novikov 4. Physics of black hole Accretion M. A. Abramowicz Part III. Turbulence, Viscosity: 5. Disc turbulence and viscosity A. Brandenburg Part IV. Radiative Processes: 6. The role of electron-positron pairs in Accretion flows G. Bjornsson 7. Accretion disc-corona models and X/Y-ray spectra of accreting black holes J. Poutanen 8. Emission lines: signatures of relativistic rotation A. C. Fabian Part V. Accretion Discs: 9. Spectral tests of models for Accretion disks around black holes J. H. Krolik 10. Advection-dominated Accretion around black holes R. Narayan, R. Mahadevan and E. Quataert 11. Accretion disc instabilities and advection dominated Accretion flows J.-P. Lasota 12. Magnetic field and multi-phase gas in AGN A. Celotti and M. J. Rees Part V. Discs in Binary Black Holes: 13. Supermassive binary black holes in galaxies P. Artymowicz Part VI. Stability of Accretion Discs: 14. Large scale perturbation of an Accretion disc by a black hole binary companion J. C. B. Papaloizou, C. Terquem and D. N. C. Lin 15. Stable oscillations of black hole Accretion discs M. Nowak and D. Lehr Part VI. Coherant Structures: 16. Spotted discs A. Bracco, A. Provenzale, E. A. Spiegel and P. Yecko Self-organized critically in Accretion discs P. Wiita and Y. Xiong Summary: old and new advances in black hole Accretion disc theory R. Svensson.
Jianmin Wang - One of the best experts on this subject based on the ideXlab platform.
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a limit relation between black hole mass and h beta width testing super eddington Accretion in active galactic nuclei
arXiv: Astrophysics, 2003Co-Authors: Jianmin WangAbstract:(abbreviated) We show that there is a limit relation between the black hole mass and the width at the half maximum of H$\beta$ for active galactic nuclei (AGNs) with super-Eddington Accretion rates. When a black hole has a super-Eddington Accretion rate, the empirical relation of reverberation mapping has two possible ways. First, it reduces to a relation between the black hole mass and the size of the broad line region due to the photon trapping effects inside the Accretion disk. For the Kaspi et al.'s empirical reverberation relation, we get the limit relation as $M_{\rm BH}=(2.9 - 12.6)\times 10^6M_{\odot} (\upsilon_{\rm FWHM}/10^3{\rm km s^{-1}})^{6.67}$, called as the Eddington limit. Second, the Eddington limit luminosity will be relaxed if the trapped photons can escape from the magnetized super-Eddington Accretion disk via the photon bubble instability, and the size of the broad line region will be enlarged according to the empirical reverberation relation, leading to a relatively narrow width of H$\beta$. We call this the Begelman limit. Super-Eddington Accretions in a sample composed of 164 AGNs have been searched by this limit relation. We find there are a handful of objects locate between the Eddington and Begelman limit lines, they may be candidates of super-Eddington accretors in a hybrid structure of photon trapping and photon bubble instability. The maximum width of H$\beta$ is in the reange of $(3.0 - 3.8)\times 10^3$ km s$^{-1}$ for the maximum mass black holes with super-Eddington Accretion rates among AGNs. We suggest that this limit relation is more reliable and convenient to test whether a source is super-Eddington and useful to probe the structure of the super-Eddington Accretion process.
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The role of the outer boundary condition in Accretion disk models
AIP Conference Proceedings, 2001Co-Authors: Feng Yuan, Qiuhe Peng, Jianmin WangAbstract:Taking optically thin Accretion flows as an example, we investigate the effects of the outer boundary condition (OBC) on the dynamics and the emergent spectra of Accretion flows. We find that OBC plays an important role. This is because the Accretion equations describing the behavior of Accretion flows are a set of differential equations, therefore, Accretion is intrinsically an initial-value problem. The result means that we should seriously consider the initial physical state of the Accretion flow such as its angular momentum and its temperature. An application example to Sgr A* is presented.
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The Role of the Outer Boundary Condition in Accretion Disk Models: Theory and Application
The Astrophysical Journal, 2000Co-Authors: Feng Yuan, Qiuhe Peng, Jianmin WangAbstract:In a previous paper, we find that the outer boundary conditions (OBCs) of an optically thin Accretion flow play an important role in determining the structure of the flow. Here in this paper, we further investigate the influence of OBCs on the dynamics and radiation of the Accretion how on a more detailed level. Bremsstrahlung and synchrotron radiations amplified by Comptonization are taken into account, and two-temperature plasma assumption is adopted. The three OBCs we adopted are the temperatures of the electrons and ions and the specific angular momentum of the Accretion flow at a certain outer boundary. We investigate the individual role of each of the three OBCs on the dynamical structure and the emergent spectrum. We find that when the general parameters such as the mass Accretion rate M and the viscous parameter alpha are fixed the peak flux at various bands such as radio, IR, and X-ray can differ by as much as several orders of magnitude under different OBCs in our example. Our results indicate that the OBC is both dynamically and radiatively important and therefore should be regarded as a new "parameter" in Accretion disk models. As an illustrative example, we further apply the above results to the compact radio source Sgr A* located at the center of our Galaxy. The advection-dominated Accretion flow (ADAF) model has turned out to be a great success in explaining its luminosity and spectrum. However, there exists a discrepancy between the mass Accretion rate favored by ADAF models in the literature and that favored by the three-dimensional hydrodynamical simulation, with the former being 10-20 times smaller than the latter. By seriously considering the outer boundary condition of the Accretion flow, we find that because of the low specific angular momentum of the Accretion gas the Accretion in Sgr A* should belong to a new Accretion pattern, which is characterized by the possession of a very large sonic radius. This Accretion pattern can significantly reduce the discrepancy between the mass Accretion rates. We argue that the Accretion occurred in some detached binary systems; the core of nearby elliptical galaxies and active galactic nuclei very possibly belongs to this Accretion pattern.
Matthew R. Bate - One of the best experts on this subject based on the ideXlab platform.
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Gas Accretion on to planetary cores: three-dimensional self-gravitating radiation hydrodynamical calculations
Monthly Notices of the Royal Astronomical Society, 2009Co-Authors: Benjamin Ayliffe, Matthew R. BateAbstract:We present results from three-dimensional, self-gravitating radiation hydrodynamical models of gas Accretion by planetary cores. In some cases, the Accretion flow is resolved down to the surface of the solid core – the first time such simulations have been performed. We investigate the dependence of the gas Accretion rate upon the planetary core mass, and the surface density and opacity of the encompassing protoplanetary disc. Accretion of planetesimals is neglected. We find that high-mass protoplanets are surrounded by thick circumplanetary discs during their gas Accretion phase but, contrary to locally isothermal calculations, discs do not form around accreting protoplanets with masses 50M⊕ when radiation hydrodynamical simulations are performed, even if the grain opacity is reduced from interstellar values by a factor of 100. We find that the opacity of the gas plays a large role in determining the Accretion rates for low-mass planetary cores. For example, reducing the opacities from interstellar values by a factor of 100 leads to roughly an order of magnitude increase in the Accretion rates for 10–20 M⊕ protoplanets. The dependence on opacity becomes less important in determining the Accretion rate for more massive cores where gravity dominates the effects of thermal support and the protoplanet is essentially accreting at the runaway rate. Increasing the core mass from 10 to 100 M⊕ increases the Accretion rate by a factor of ≈50 for interstellar opacities. Beyond ∼100 M⊕, the ability of the protoplanetary disc to supply material to the accreting protoplanet limits the Accretion rate, independent of the opacity. Finally, for low-mass planetary cores (20M⊕), we obtain Accretion rates that are in agreement with previous one-dimensional quasi-static models. This indicates that three-dimensional hydrodynamical effects may not significantly alter the gas Accretion time-scales that have been obtained from quasi-static models.
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gas Accretion onto planetary cores three dimensional self gravitating radiation hydrodynamical calculations
arXiv: Astrophysics, 2008Co-Authors: Benjamin Ayliffe, Matthew R. BateAbstract:We present results from three-dimensional, self-gravitating radiation hydrodynamical models of gas Accretion by planetary cores. In some cases, the Accretion flow is resolved down to the surface of the solid core -- the first time such simulations have been performed. We investigate the dependence of the gas Accretion rate upon the planetary core mass, and the surface density and opacity of the encompassing protoplanetary disc. Accretion of planetesimals is neglected. We find that high-mass protoplanets are surrounded by thick circumplanetary discs during their gas Accretion phase but, contrary to locally-isothermal calculations, discs do not form around accreting protoplanets with masses ~< 50M_Earth when radiation hydrodynamical simulations are performed, even if the grain opacity is reduced from interstellar values by a factor of 100. We find that the opacity of the gas plays a large role in determining the Accretion rates for low-mass planetary cores. For example, reducing the opacities from interstellar values by a factor of 100 leads to roughly an order of magnitude increase in the Accretion rates for 10-20M_Earth protoplanets. The dependence on opacity becomes less important in determining the Accretion rate for more massive cores where gravity dominates the effects of thermal support and the protoplanet is essentially accreting at the runaway rate. Finally, for low-mass planetary cores (~< 20M_Earth), we obtain Accretion rates that are in agreement with previous one-dimensional quasi-static models. This indicates that three-dimensional hydrodynamical effects may not significantly alter the gas Accretion timescales that have been obtained from quasi-static models.
Takashi Hosokawa - One of the best experts on this subject based on the ideXlab platform.
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evolution of massive protostars via disk Accretion
The Astrophysical Journal, 2010Co-Authors: Takashi Hosokawa, Harold W Yorke, Kazuyuki OmukaiAbstract:Mass Accretion onto (proto-)stars at high Accretion rates M-dot{sub *}> 10{sup -4} M{sub sun} yr{sup -1} is expected in massive star formation. We study the evolution of massive protostars at such high rates by numerically solving the stellar structure equations. In this paper, we examine the evolution via disk Accretion. We consider a limiting case of 'cold' disk Accretion, whereby most of the stellar photosphere can radiate freely with negligible backwarming from the Accretion flow, and the accreting material settles onto the star with the same specific entropy as the photosphere. We compare our results to the calculated evolution via spherically symmetric Accretion, the opposite limit, whereby the material accreting onto the star contains the entropy produced in the Accretion shock front. We examine how different Accretion geometries affect the evolution of massive protostars. For cold disk Accretion at 10{sup -3} M{sub sun} yr{sup -1}, the radius of a protostar is initially small, R{sub *{approx_equal}} a few R{sub sun}. After several solar masses have accreted, the protostar begins to bloat up and for M{sub *} {approx_equal} 10 M{sub sun} the stellar radius attains its maximum of 30-400 R{sub sun}. The large radius {approx}100 R{sub sun} is also a feature ofmore » spherically symmetric Accretion at the same accreted mass and Accretion rate. Hence, expansion to a large radius is a robust feature of accreting massive protostars. At later times, the protostar eventually begins to contract and reaches the zero-age main sequence (ZAMS) for M{sub *} {approx_equal} 30 M{sub sun}, independent of the Accretion geometry. For Accretion rates exceeding several 10{sup -3} M{sub sun} yr{sup -1}, the protostar never contracts to the ZAMS. The very large radius of several hundreds R{sub sun} results in the low effective temperature and low UV luminosity of the protostar. Such bloated protostars could well explain the existence of bright high-mass protostellar objects, which lack detectable H II regions.« less
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evolution of massive protostars via disk Accretion
arXiv: Solar and Stellar Astrophysics, 2010Co-Authors: Takashi Hosokawa, Harold W Yorke, Kazuyuki OmukaiAbstract:Mass Accretion onto (proto-)stars at high Accretion rates > 10^-4 M_sun/yr is expected in massive star formation. We study the evolution of massive protostars at such high rates by numerically solving the stellar structure equations. In this paper we examine the evolution via disk Accretion. We consider a limiting case of "cold" disk Accretion, whereby most of the stellar photosphere can radiate freely with negligible backwarming from the Accretion flow, and the accreting material settles onto the star with the same specific entropy as the photosphere. We compare our results to the calculated evolution via spherically symmetric Accretion, the opposite limit, whereby the material accreting onto the star contains the entropy produced in the Accretion shock front. We examine how different Accretion geometries affect the evolution of massive protostars. For cold disk Accretion at 10^-3 M_sun/yr the radius of a protostar is initially small, about a few R_sun. After several solar masses have accreted, the protostar begins to bloat up and for M \simeq 10 M_sun the stellar radius attains its maximum of 30 - 400 R_sun. The large radius about 100 R_sun is also a feature of spherically symmetric Accretion at the same accreted mass and Accretion rate. Hence, expansion to a large radius is a robust feature of accreting massive protostars. At later times the protostar eventually begins to contract and reaches the Zero-Age Main-Sequence (ZAMS) for M \simeq 30 M_sun, independent of the Accretion geometry. For Accretion rates exceeding several 10^-3 M_sun/yr the protostar never contracts to the ZAMS. The very large radius of several 100s R_sun results in a low effective temperature and low UV luminosity of the protostar. Such bloated protostars could well explain the existence of bright high-mass protostellar objects, which lack detectable HII regions.
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evolution of massive protostars with high Accretion rates
The Astrophysical Journal, 2009Co-Authors: Takashi Hosokawa, Kazuyuki OmukaiAbstract:Formation of massive stars by Accretion requires a high Accretion rate of to overcome the radiation pressure barrier of the forming stars. Here, we study evolution of protostars accreting at such high rates by solving the structure of the central star and the inner accreting envelope simultaneously. The protostellar evolution is followed starting from small initial cores until their arrival at the stage of the Zero-Age Main-Sequence (ZAMS) stars. An emphasis is put on evolutionary features different from those with a low Accretion rate of , which is presumed in the standard scenario for low-mass star formation. With the high Accretion rate of , the protostellar radius becomes very large and exceeds 100 R ☉. Unlike the cases of low Accretion rates, deuterium burning hardly affects the evolution, and the protostar remains radiative even after its ignition. It is not until the stellar mass reaches 40 M ☉ that hydrogen burning begins and the protostar reaches the ZAMS phase, and this ZAMS arrival mass increases with the Accretion rate. These features are similar to those of the first star formation in the universe, where high Accretion rates are also expected, rather than to the present-day low-mass star formation. At a very high Accretion rate of >3 × 10–3 M ☉ yr-1, the total luminosity of the protostar becomes so high that the resultant radiation pressure inhibits the growth of the protostars under steady Accretion before reaching the ZAMS stage. Therefore, the evolution under the critical Accretion rate 3 × 10–3 M ☉ yr-1 gives the upper mass limit of possible pre-main sequence stars at 60 M ☉. The upper mass limit of MS stars is also set by the radiation pressure onto the dusty envelope under the same Accretion rate at 250 M ☉. We also propose that the central source enshrouded in the Orion KL/BN nebula has effective temperature and luminosity consistent with our model and is a possible candidate for such protostars growing under the high Accretion rate.
Kazuyuki Omukai - One of the best experts on this subject based on the ideXlab platform.
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evolution of massive protostars via disk Accretion
The Astrophysical Journal, 2010Co-Authors: Takashi Hosokawa, Harold W Yorke, Kazuyuki OmukaiAbstract:Mass Accretion onto (proto-)stars at high Accretion rates M-dot{sub *}> 10{sup -4} M{sub sun} yr{sup -1} is expected in massive star formation. We study the evolution of massive protostars at such high rates by numerically solving the stellar structure equations. In this paper, we examine the evolution via disk Accretion. We consider a limiting case of 'cold' disk Accretion, whereby most of the stellar photosphere can radiate freely with negligible backwarming from the Accretion flow, and the accreting material settles onto the star with the same specific entropy as the photosphere. We compare our results to the calculated evolution via spherically symmetric Accretion, the opposite limit, whereby the material accreting onto the star contains the entropy produced in the Accretion shock front. We examine how different Accretion geometries affect the evolution of massive protostars. For cold disk Accretion at 10{sup -3} M{sub sun} yr{sup -1}, the radius of a protostar is initially small, R{sub *{approx_equal}} a few R{sub sun}. After several solar masses have accreted, the protostar begins to bloat up and for M{sub *} {approx_equal} 10 M{sub sun} the stellar radius attains its maximum of 30-400 R{sub sun}. The large radius {approx}100 R{sub sun} is also a feature ofmore » spherically symmetric Accretion at the same accreted mass and Accretion rate. Hence, expansion to a large radius is a robust feature of accreting massive protostars. At later times, the protostar eventually begins to contract and reaches the zero-age main sequence (ZAMS) for M{sub *} {approx_equal} 30 M{sub sun}, independent of the Accretion geometry. For Accretion rates exceeding several 10{sup -3} M{sub sun} yr{sup -1}, the protostar never contracts to the ZAMS. The very large radius of several hundreds R{sub sun} results in the low effective temperature and low UV luminosity of the protostar. Such bloated protostars could well explain the existence of bright high-mass protostellar objects, which lack detectable H II regions.« less
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evolution of massive protostars via disk Accretion
arXiv: Solar and Stellar Astrophysics, 2010Co-Authors: Takashi Hosokawa, Harold W Yorke, Kazuyuki OmukaiAbstract:Mass Accretion onto (proto-)stars at high Accretion rates > 10^-4 M_sun/yr is expected in massive star formation. We study the evolution of massive protostars at such high rates by numerically solving the stellar structure equations. In this paper we examine the evolution via disk Accretion. We consider a limiting case of "cold" disk Accretion, whereby most of the stellar photosphere can radiate freely with negligible backwarming from the Accretion flow, and the accreting material settles onto the star with the same specific entropy as the photosphere. We compare our results to the calculated evolution via spherically symmetric Accretion, the opposite limit, whereby the material accreting onto the star contains the entropy produced in the Accretion shock front. We examine how different Accretion geometries affect the evolution of massive protostars. For cold disk Accretion at 10^-3 M_sun/yr the radius of a protostar is initially small, about a few R_sun. After several solar masses have accreted, the protostar begins to bloat up and for M \simeq 10 M_sun the stellar radius attains its maximum of 30 - 400 R_sun. The large radius about 100 R_sun is also a feature of spherically symmetric Accretion at the same accreted mass and Accretion rate. Hence, expansion to a large radius is a robust feature of accreting massive protostars. At later times the protostar eventually begins to contract and reaches the Zero-Age Main-Sequence (ZAMS) for M \simeq 30 M_sun, independent of the Accretion geometry. For Accretion rates exceeding several 10^-3 M_sun/yr the protostar never contracts to the ZAMS. The very large radius of several 100s R_sun results in a low effective temperature and low UV luminosity of the protostar. Such bloated protostars could well explain the existence of bright high-mass protostellar objects, which lack detectable HII regions.
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evolution of massive protostars with high Accretion rates
The Astrophysical Journal, 2009Co-Authors: Takashi Hosokawa, Kazuyuki OmukaiAbstract:Formation of massive stars by Accretion requires a high Accretion rate of to overcome the radiation pressure barrier of the forming stars. Here, we study evolution of protostars accreting at such high rates by solving the structure of the central star and the inner accreting envelope simultaneously. The protostellar evolution is followed starting from small initial cores until their arrival at the stage of the Zero-Age Main-Sequence (ZAMS) stars. An emphasis is put on evolutionary features different from those with a low Accretion rate of , which is presumed in the standard scenario for low-mass star formation. With the high Accretion rate of , the protostellar radius becomes very large and exceeds 100 R ☉. Unlike the cases of low Accretion rates, deuterium burning hardly affects the evolution, and the protostar remains radiative even after its ignition. It is not until the stellar mass reaches 40 M ☉ that hydrogen burning begins and the protostar reaches the ZAMS phase, and this ZAMS arrival mass increases with the Accretion rate. These features are similar to those of the first star formation in the universe, where high Accretion rates are also expected, rather than to the present-day low-mass star formation. At a very high Accretion rate of >3 × 10–3 M ☉ yr-1, the total luminosity of the protostar becomes so high that the resultant radiation pressure inhibits the growth of the protostars under steady Accretion before reaching the ZAMS stage. Therefore, the evolution under the critical Accretion rate 3 × 10–3 M ☉ yr-1 gives the upper mass limit of possible pre-main sequence stars at 60 M ☉. The upper mass limit of MS stars is also set by the radiation pressure onto the dusty envelope under the same Accretion rate at 250 M ☉. We also propose that the central source enshrouded in the Orion KL/BN nebula has effective temperature and luminosity consistent with our model and is a possible candidate for such protostars growing under the high Accretion rate.
