Gamma ray bursts (GRB) are short flashes of light, characterized the high energy gamma ray photons that are detected. The above image is an artist's conception of a gamma ray burst. GRB signals have high redshifts, so they must be signals from very faraway events. Also, the signal can change rapidly, so it must be coming from a relatively small source. The light coming from a GRB is so intense that we theorize that it must be beamed jets from a very high energy explosion. If light this powerful was shining out in every direction, such an explosion would be way too powerful to be physical, with hundreds of times more energy than a typical supernova being produced in a matter of seconds. GRB's can last anywhere from a few milliseconds to a few hours. When they shine, they are the brightest objects in the universe.