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加速超大质量黑洞
图示提供: Robert Hurt, NASA/JPL-Caltech

说明: 黑洞能转多快呢？如果一般物质组成的物体转速过快，它会分崩离析，但黑洞可能不会，不过我们对它的最大转速仍一无所知。理论物理学家通常用爱因斯坦广义相对论的克尔解，来建快速旋转黑洞的模型，并预测了不少神奇且不寻常的现象。其中或许最容易测试的，是从远方看过去，物质掉入最高速旋转的黑洞后，在消失之前会以接近光速的速度绕转之预言。美国航空航天局的核光谱望远镜阵列（NuSTAR）及欧洲航天局的XMM-牛顿卫星，最近经由观测螺旋星系NGC 1365中心的超大质量黑洞，对这项预测进行测试。从黑洞吸积盘内缘量测到的核子加热及幅射谱线加宽，证实了物质旋转的速度的确接近光速极限。上面这张画家创作的图示，呈现了由一般物质组成吸积盘，以及从顶端射出的喷流。由于随机掉进黑 洞的物质，不会让黑洞的自旋速度增加太多，因此，核光谱望远镜阵列和XMM-牛顿卫星的观测，也证实了黑洞的周围真的有吸积盘。



Illustration Credit: Robert Hurt, NASA/JPL-Caltech
Explanation: How fast can a black hole spin? If any object made of regular matter spins too fast — it breaks apart. But a black hole might not be able to break apart — and its maximum spin rate is really unknown. Theorists usually model rapidly rotating black holes with the Kerr solution to Einstein’s General Theory of Relativity, which predicts several amazing and unusual things. Perhaps its most easily testable prediction, though, is that matter entering a maximally rotating black hole should be last seen orbiting at near the speed of light, as seen from far away. This prediction was tested by NASA’s NuSTAR and ESA’s XMM satellites by observing the supermassive black hole at the center of spiral galaxy NGC 1365. The near light-speed limit was confirmed by measuring the heating and spectral line broadening of nuclear emissions at the inner edge of the surrounding accretion disk. Pictured here is an artist’s illustration depicting an accretion disk of normal matter swirling around a black hole, with a jet emanating from the top. Since matter randomly falling into the black hole should not spin up a black hole this much, the NuSTAR and XMM measurements also validate the existence of the surrounding accretion disk.