Two well-understood techniques, X-ray reflection spectroscopy and thermal continuum fitting, can be used to measure the spins of black holes that are accreting at moderate rates. There is a rich set of other electromagnetic techniques allowing us to extend spin measurements to lower accretion rates.

Many accreting supermassive black holes are found to be rapidly spinning, although a population of more slowly spinning black holes emerges at masses above as expected from recent structure formation models.

Many accreting stellar-mass black holes in X-ray binary systems are rapidly spinning and must have been born in this state.

The advent of gravitational wave astronomy has enabled the detection of spin effects in merging binary black holes. Most of the premerger black holes are found to be slowly spinning, a notable exception being an object that may itself be a merger product.

The stark difference in spins between the black hole X-ray binary and the binary black hole populations shows that there is a diversity of formation mechanisms.

两种众所周知的技术，X 射线反射光谱和热连续谱拟合，可用于测量以中等速度吸积的黑洞的自旋。有一组丰富的其他电磁技术使我们能够扩展自旋测量以降低吸积率。

许多吸积的超大质量黑洞被发现正在快速旋转，尽管在上方的质量处出现了一群旋转速度更慢的黑洞 正如最近的结构形成模型所预期的那样。

X射线双星系统中的许多吸积恒星质量黑洞正在快速旋转，并且一定是在这种状态下诞生的。

引力波天文学的出现使得能够检测合并双黑洞的自旋效应。大多数合并前黑洞被发现正在缓慢旋转，一个值得注意的例外是一个本身可能是合并产物的物体。

黑洞 X 射线双星和双黑洞群之间自旋的明显差异表明，形成机制存在多样性。