黑洞周围过热区和截断区的形成三维广义相对论辐射-磁流体动力学模拟
Formation of Overheated Regions and Truncated Disks around Black Holes; Three-dimensional General Relativistic Radiation-magnetohydrodynamics Simulations
摘要：
利用三维广义相对论辐射磁流体动力学模拟了恒星质量黑洞周围的吸积流，发现相对冷的盘（$\gtrsim 10^{7}$ K）在黑洞附近被截断.在截断半径内出现热的和较低密度的区域，其气体温度为$ \gtrsim 10^9$ K并且比辐射温度高十倍以上（过热区域）。过热区也出现在盘的上方和下方，并夹在冷盘之间，导致有效的康普顿上散射。截断半径是$\dot{M} \sim L_{\rm Edd}/c^2$的$\sim 30 r_{\rm g}$，其中$r_{\rm g}, \dot M, L_\mathrm{Edd}, c$是引力半径、质量吸积率、爱丁顿光度和光速。我们的结果是一致的观察非常高的状态，即截断盘被认为是嵌入在热稀薄区域。随着质量吸积率$\dot{M} \sim 100 L_{\rm Edd}/c^2$的增加，截断半径向内移动到$\sim 10 r_{\rm g}$，这非常接近于最内侧的稳定圆形轨道。这个模型对应于超薄磁盘状态观察到的超发光X射线源。尽管康普顿冷却有效地降低了气体温度，但过热区会缩小，但在$\dot{M} \lesssim 100L_{\rm Edd}/c^2$范围内，双晶结构并没有消失。我们的模拟还表明，在过热区域的气体温度取决于黑洞的自旋，这将是由于有效的能量传输从黑洞到磁盘通过坡印廷通量，导致气体加热。
英文摘要：
Using three-dimensional general relativistic radiation magnetohydrodynamics simulations of accretion flows around stellar mass black holes, we report that the relatively cold disk ($\gtrsim 10^{7}$K) is truncated near the black hole. Hot and less-dense regions, of which the gas temperature is $ \gtrsim 10^9$K and more than ten times higher than the radiation temperature (overheated regions), appear within the truncation radius. The overheated regions also appear above as well as below the disk, and sandwich the cold disk, leading to the effective Compton upscattering. The truncation radius is $\sim 30 r_{\rm g}$ for $\dot{M} \sim L_{\rm Edd}/c^2$, where $r_{\rm g}, \dot M, L_\mathrm{Edd}, c$ are the gravitational radius, mass accretion rate, Eddington luminosity, and light speed. Our results are consistent with observations of very high state, whereby the truncated disk is thought to be embedded in the hot rarefied regions. The truncation radius shifts inward to $\sim 10 r_{\rm g}$ with increasing mass accretion rate $\dot{M} \sim 100 L_{\rm Edd}/c^2$, which is very close to an innermost stable circular orbit. This model corresponds to the slim disk state observed in ultra luminous X-ray sources. Although the overheated regions shrink if the Compton cooling effectively reduces the gas temperature, the sandwich-structure does not disappear at the range of $\dot{M} \lesssim 100L_{\rm Edd}/c^2$. Our simulations also reveal that the gas temperature in the overheated regions depends on black hole spin, which would be due to efficient energy transport from black hole to disks through the Poynting flux, resulting gas heating.
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