动圈是在旋转黑洞外面的区域。它的名称源自希腊的ergon这个字，意思是“工作”，由雷莫·鲁菲尼和约翰·惠勒在1971年命名。它得到这个名称是因为从理论上说，可以从这个区域提取黑洞的能量和质量。动圈有着扁球体的形状，在赤道有着较大的半径范围，并且在两极接触到旋转黑洞的事件视界。动圈的赤道半径（最大半径）相当于不旋转黑洞的史瓦西半径；如果黑洞达到转速的极限时，极半径（最小半径）将小到只有史瓦西半径的一半。

在动圈之内，时空会被沿着黑洞转动的方向拖曳着，相对于静止宇宙的速度略大于当地光速的一半。这个过程就是所谓的兰斯-蒂林效应效应或是参考系拖拽 。由于拖曳的效应，动圈内的物体相对于静止的宇宙是不稳定的，除非它们的运动速度超越它们所在时空的光速。一个故定在动圈之外的悬浮铅坠，在接近稳定的极限边缘时，将体验无限远/发散的径度量。在一些点，她将开始下坠，从而导致引力磁化诱导自旋向运动（spinward motion？）。空间拖曳的另一个结果是在动圈内存在着负能量。

The ergosphere is a region located outside a rotating black hole. Its name proposed by Remo Ruffini and John Archibald Wheeler during the Les Houches lectures in 1971, is derived from the Greek word ergon, which means “work”. It received this name because it is theoretically possible to extract energy and mass from this region. The ergosphere has an oblate spheroidal shape that touches the event horizon at the poles of a rotating black hole and extends to a greater radius at the equator. The equatorial (maximum) radius of an ergosphere corresponds to the Schwarzschild radius of a non-rotating black hole; the polar (minimum) radius can be as little as half the Schwarzschild radius (the radius of a non rotating black hole) in the case that black hole is rotating maximally (at higher rotation rates the black hole could not have formed).