Illustration showing the structure of a black hole. A black hole is formed when a sufficiently massive mass collapses under its own weight, forming a singularity of zero volume and infinite density at its centre. Matter near the black hole is drawn to it, forming an accretion disc of material that circles the black hole. The material becomes hotter (changing from red to bright yellow) as it nears the event horizon, the edge of the black hole and the point beyond which nothing, not even light, can escape. Some of the superheated matter is ejected in a high energy particle jet before it reaches the event horizon. Photons that travel too close to the black hole become trapped in orbit, forming a perfect ring of light known as a photon ring or photon sphere.
