55 pages, 5 figures. Published in: "Astrophysics of Black Holes - From fundamental aspects to latest developments", Ed. Cosimo Bambi, Springer: Astrophysics and Space Science Library. Additional corrections made
In the standard paradigm, astrophysical black holes can be described solely by their mass and angular momentum - commonly referred to as `spin' - resulting from the process of their birth and subsequent growth via accretion. Whilst the mass has a standard Newtonian interpretation, the spin does not, with the effect of non-zero spin leaving an indelible imprint on the space-time closest to the black hole. As a consequence of relativistic frame-dragging, particle orbits are affected both in terms of stability and precession, which impacts on the emission characteristics of accreting black holes both stellar mass in black hole binaries (BHBs) and supermassive in active galactic nuclei (AGN). Over the last 30 years, techniques have been developed that take into account these changes to estimate the spin which can then be used to understand the birth and growth of black holes and potentially the powering of powerful jets. In this chapter we provide a broad overview of both the theoretical effects of spin, the means by which it can be estimated and the results of ongoing campaigns.
Biases in estimates of black hole kicks from the spin distribution of binary black holes
LIGO和Virgo引力波天文台现已观测到超过50个二元黑洞合并。虽然中子星在超新星诞生时被赋予了很大的速度，但黑洞是否会受到类似的撞击，以及多大的撞击，仍然是一个悬而未决的问题。最近，Callister等人（2021）在假设它们都是通过孤立的双星演化形成的前提下分析了双星黑洞群，并声称合并的双星黑洞的自旋分布需要大的黑洞反冲（在99%的置信度下大于260 km/s）才能与观测结果相匹配。在这里，我们强调Callister等人（2021）提出的一个关键假设-所有次级黑洞都可以潮汐旋转-并不是由物理模型驱动的，并且可能导致他们对黑洞撞击幅度的估计存在偏差。我们只对Callister et al.（2021）模型进行了微小的修改，考虑了潮汐同步无效的更广泛的合并双星。我们表明，这自然会产生一个双峰自旋分布的二级黑洞，并在二进制黑洞人口中观察到的自旋轨道错位可以解释为更典型的黑洞踢的顺序100公里/秒，踢推断银河X射线双星包含黑洞一致。我们的结论是，大多数的二进制黑洞人口是一致的形成通过孤立的二进制演化。
