Black hole. Computer model of distortions in the view of an accretion disc due to the immense gravity of the rotating black hole it orbits. Temperature is colour-coded: red (coolest) to blue/white (hottest). Four hot spots have been added to the disc. The one behind the hole is seen as an arc; its light has been bent over the hole by gravitational lensing. The light is blue shifted (left) and red shifted (right) due to the disc's anticlockwise rotation. A black hole is a region where the gravitational field is so strong that light cannot escape. Work done at Johns Hopkins University, Maryland, USA.