Department of Astronomy, University of Michigan, Ann Arbor, Michigan 48109, USA.
Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, California 91125, USA.
Nature. 2014 Mar 13;507(7491):207-9. doi: 10.1038/nature13031. Epub 2014 Mar 5.
The co-evolution of a supermassive black hole with its host galaxy through cosmic time is encoded in its spin. At z > 2, supermassive black holes are thought to grow mostly by merger-driven accretion leading to high spin. It is not known, however, whether below z ≈ 1 these black holes continue to grow by coherent accretion or in a chaotic manner, though clear differences are predicted in their spin evolution. An established method of measuring the spin of black holes is through the study of relativistic reflection features from the inner accretion disk. Owing to their greater distances from Earth, there has hitherto been no significant detection of relativistic reflection features in a moderate-redshift quasar. Here we report an analysis of archival X-ray data together with a deep observation of a gravitationally lensed quasar at z = 0.658. The emission originates within three or fewer gravitational radii from the black hole, implying a spin parameter (a measure of how fast the black hole is rotating) of a = 0.87(+0.08)(-0.15) at the 3σ confidence level and a > 0.66 at the 5σ level. The high spin found here is indicative of growth by coherent accretion for this black hole, and suggests that black-hole growth at 0.5 ≤ z ≤ 1 occurs principally by coherent rather than chaotic accretion episodes.
超大质量黑洞与其宿主星系在宇宙时间中的共同演化通过其自转编码。在 z>2 处，超大质量黑洞被认为主要通过合并驱动吸积而增长，导致高自转。然而，目前尚不清楚在 z≈1 以下这些黑洞是否继续通过相干吸积或以混沌的方式增长，尽管它们的自旋演化预计会有明显的差异。一种测量黑洞自转的既定方法是通过研究来自内部吸积盘的相对论性反射特征。由于它们离地球更远，因此在中等红移类星体中尚未检测到明显的相对论性反射特征。在这里，我们报告了对档案 X 射线数据的分析以及对 z=0.658 的引力透镜类星体的深度观测。发射源位于黑洞的三个或更少的引力半径内，这意味着黑洞的自旋参数（衡量黑洞旋转速度的指标）为 a=0.87(+0.08)(-0.15)，置信度为 3σ，而 a>0.66 的置信度为 5σ。这里发现的高自旋表明，对于这个黑洞来说，通过相干吸积来增长，并且表明在 0.5≤z≤1 处的黑洞增长主要是通过相干而不是混沌的吸积事件发生的。
