PLANETARY NEBULA

A planetary nebula is a short lived emission nebula surrounding a star that has essentially died. As the star runs out of fuel in the final stages of its red giant phase it becomes increasingly unstable. The outer layers of the star’s atmosphere are expelled into space and what is left behind is the exposed core of the star. Even though it is no longer creating energy via fusion, the core is initially still hot enough to produce ultraviolet energy. This energy causes the expelled gas to glow. Ultimately though, the gas will continue to disperse into space, the core will cool and the nebula will disappear.