Black holes and Einstein's gravity revealed by X-ray astronomy

Abstract:
Black holes are the ultimate triumph of gravity; spacetime is so warped that not even light can escape. But detecting black holes on the black background of space is almost impossible, and they remained a speculative extrapolation of Einstein's General Relativity until the advent of the space age in the 1960s. Rockets carrying simple X-ray detectors above Earth's opaque (at these energies) atmosphere discovered intense sources of cosmic X-ray radiation that was produced as material from a binary companion star spiralled inwards towards the black hole. I will describe what we know about black holes, and how this accretion power transforms the darkest objects in the Universe into the brightest X-ray sources, giving observational tests of Einstein's gravity in the strong field limit.