超大质量黑洞的自转

黑洞自转速度能有多快？由常规物质构成的任何物体，如果自转过快就会裂成碎片，但黑洞应该不会，虽然我们对它的自转速度还一无所知。理论物理学家通常采用爱因斯坦广义相对论的克尔解来建立快速自转的黑洞模型，而且还计算出一些很有意思的奇异结果，其中最容易验证的也许就是，落入高速自转黑洞中的物质，在我们能从远处看到它的最后时刻，可能以近乎光速绕黑洞旋转。这一预言，最近通过了美国宇航局核星望远镜及欧洲航天局的牛顿X射线多镜望远镜的双重测试，通过观测螺旋星系 NGC 1365 的中央大质量黑洞，在它的吸积盘内缘测到了核子辐射的升温与谱线加宽现象，证明其速度已接近光速上限。上图是艺术家绘制的示意图，展示了由常规物质绕黑洞旋转组成的吸积盘及黑洞上产生的喷流。由于随机落入黑洞的物质并不会使黑洞加速自转，核星与牛顿卫星的观测结果也就证实了黑洞周围存在吸积盘。

Spin up of a Supermassive Black Hole

Illustration Credit:Harvard-SmithsonianCenter for Astrophysics

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 usual model rapidly rotating black holes with theKerr solutionto Einstein'sGeneral Theory of Relativity, which predicts severalamazingandunusualthings. Perhaps its most easily testable prediction, though, is that matter entering amaximally rotating black holeshould be last seen orbiting at near the speed of light, as seen from far away.This predictionwas tested recently by NASA'sNuSTARand ESA'sXMMsatellites by observing the supermassive black hole at the center ofspiral galaxy NGC 1365. The nearlight-speed limitwasconfirmed by measuringthe heating andspectral line broadeningof nuclear emissions at the inner edge of the surroundingaccretion disk.Pictured aboveis an artist's illustration depicting an accretion disk of normalmatter swirlingaround a black hole, with ajetemanating from the top. Since matter randomly fallinginto the black hol< a >eshould not spin up a black hole this much, the NuSTAR and XMM measurements also validate the existence of thesurrounding accretion disk.