From Wikipedia, the free encyclopedia For the Ring Nebula in Barnard's Galaxy, see Ring Nebula (NGC 6822). The Ring Nebula (also cataloged as Messier 57, M57 or NGC 6720) is a planetary nebula in the northern constellation of Lyra. Such objects are formed when a shell of ionized gas is expelled into the surrounding interstellar medium by a red giant star, which was passing through the last stage in its evolution before becoming a white dwarf.