This is the Vela Supernova Remnant. It is located about 800 light-years away in the constellation Vela. This particular mosaic was taken by Marco Lorenzi and is over 10-degrees wide, capturing every intricate line of this fantastic object.
The supernova itself occurred between 12,300 and 11,000 years ago, meaning the light from this event finally reached earth about 800 years later. This stellar event also left behind a pulsar, a dense, but tiny remnant of the massive star responsible for creating this object.
Also related is the pencil nebula.