Antarctic Astronomy Research Division, Key Laboratory for Polar Science of the State Oceanic Administration, Polar Research Institute of China, Shanghai, China.
School of Astronomy and Space Sciences, University of Science and Technology of China, Hefei, China.
Nature. 2019 Sep;573(7772):83-86. doi: 10.1038/s41586-019-1510-y. Epub 2019 Sep 4.
Quasars, which are exceptionally bright objects at the centres (or nuclei) of galaxies, are thought to be produced through the accretion of gas into disks surrounding supermassive black holes. There is observational evidence at galactic and circumnuclear scales that gas flows inwards towards accretion disks around black holes, and such an inflow has been measured at the scale of the dusty torus that surrounds the central accretion disk. At even smaller scales, inflows close to an accretion disk have been suggested to explain the results of recent modelling of the response of gaseous broad emission lines to continuum variations. However, unambiguous observations of inflows that actually reach accretion disks have been elusive. Here we report the detection of redshifted broad absorption lines of hydrogen and helium atoms in a sample of quasars. The lines show broad ranges of Doppler velocities that extend continuously from zero to redshifts as high as about 5,000 kilometres per second. We interpret this as the inward motion of gases at velocities comparable to freefall speeds close to the black hole, constraining the fastest infalling gas to within 10,000 gravitational radii of the black hole (the gravitational radius being the gravitational constant multiplied by the object mass, divided by the speed of light squared). Extensive photoionization modelling yields a characteristic radial distance of the inflow of approximately 1,000 gravitational radii, possibly overlapping with the outer accretion disk.
类星体是星系中心（或核心）异常明亮的物体，据认为是通过气体吸积到围绕超大质量黑洞的盘中而产生的。在星系和核周尺度上有观测证据表明，气体向内流入黑洞周围的吸积盘，这种流入已经在环绕中央吸积盘的尘埃环的尺度上进行了测量。在更小的尺度上，靠近吸积盘的流入被认为可以解释最近对气态宽发射线对连续谱变化的响应的建模结果。然而，实际上到达吸积盘的流入的明确观测仍然难以捉摸。在这里，我们报告了在一组类星体中检测到氢和氦原子的红移宽吸收线。这些线显示出宽的多普勒速度范围，从零连续延伸到高达约 5000 公里/秒的红移。我们将其解释为气体在接近黑洞的自由落体速度的向内运动，将最快的下落气体限制在黑洞的 10000 个引力半径内（引力半径是引力常数乘以物体质量，再除以光速的平方）。广泛的光电离建模得出了约 1000 个引力半径的流入特征径向距离，可能与外部吸积盘重叠。
