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arXiv 1105.5474astro-ph.HE
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黑洞三种不同吸积流和出流的二维辐射-磁流体动力学模拟

Global Structure of Three Distinct Accretion Flows and Outflows around Black Holes through Two-Dimensional Radiation-Magnetohydrodynamic Simulations

Ken Ohsuga, Shin Mineshige

摘要:

我们提出了详细的全球结构的黑洞吸积流和外流通过新执行的二维辐射磁流体动力学模拟。从一个穿有弱环向磁场的环出发,通过控制初始环的中心密度ρ_0,我们可以再现三种不同的吸积流模式。模型A的中心密度最高,产生了一个光学和几何厚度的超临界吸积盘。辐射力大大超过盘面上方的重力,从而驱动强烈的外流(或喷流)。由于温和的光束,在正面视图中,表观(各向同性)光子光度为~22L_E(其中L_E是爱丁顿光度)。如果我们增加流动密度,甚至更高的视光度是可行的。在具有中等密度的模型B中,吸积流的辐射冷却是如此有效,以至于在半径大于~7R_S(其中R_S是史瓦西半径)处形成标准型、冷的、几何上薄的盘,而在其他情况下,吸积流的辐射效率是低的。该模型中出现了磁压驱动的圆盘风。在模型C中,密度太低,流动不能具有辐射效率。因此,该流动变成辐射效率低的吸积流,其在几何上是厚的并且在光学上是薄的。磁压力与气体压力共同驱动圆盘表面的外流,而流通过射流而不是辐射释放能量。观测的影响进行了简要讨论。

英文摘要:

We present the detailed global structure of black hole accretion flows and outflows through newly performed two-dimensional radiation-magnetohydrodynamic simulations. By starting from a torus threaded with weak toroidal magnetic fields and by controlling the central density of the initial torus, rho_0, we can reproduce three distinct modes of accretion flow. In model A with the highest central density, an optically and geometrically thick supercritical accretion disk is created. The radiation force greatly exceeds the gravity above the disk surface, thereby driving a strong outflow (or jet). Because of the mild beaming, the apparent (isotropic) photon luminosity is ~22L_E (where L_E is the Eddington luminosity) in the face-on view. Even higher apparent luminosity is feasible if we increase the flow density. In model B with a moderate density, radiative cooling of the accretion flow is so efficient that a standard-type, cold, and geometrically thin disk is formed at radii greater than ~7R_S (where R_S is the Schwarzschild radius), while the flow is radiatively inefficient otherwise. The magnetic-pressure-driven disk wind appears in this model. In model C the density is too low for the flow to be radiatively efficient. The flow thus becomes radiatively inefficient accretion flow, which is geometrically thick and optically thin. The magnetic-pressure force, in cooperation with the gas-pressure force, drives outflows from the disk surface, and the flow releases its energy via jets rather than via radiation. Observational implications are briefly discussed.

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