A narrow beam of intense electromagnetic radiation released during a supernova event, as a rapidly rotating, high-mass star collapses to form a black hole. They are the brightest events known to occur in the universe, and can last from milliseconds to several minutes (typically a few seconds). The initial burst is usually followed by a longer-lived 'afterglow' emitted at longer wavelengths (X-ray, ultraviolet, optical, infrared and radio).