Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. For the first time in history, astronomers have measured the spin of a black hole by detecting the mind-bending relativistic effects that warp space-time at the very edge of its event horizon. Yet, one of the challenges of studying black holes is that it is extremely difficult to measure the spin of such objects. Nonetheless, the rapidly-rotating inner edge of the disk of hot material has provided direct information about how fast the black hole is spinning by closely controlling the X-ray emissions from iron ions which are trapped in the black hole’s accretion disc. It is important to note that the event horizon is the point of no return. Scientists have proved that even light can hardly escape the event horizon. Moreover, black holes grow by consuming matter and in the centers of galaxies they can grow to huge size. In fact, astronomers have observed particularly the NGC 1365’s black hole with the help of the NuSTAR and XMM-Newton observatories and have detected that the latter is spinning so fast that the outer edge is moving at very nearly the speed of light!