M2-9, Twin Jet Nebula, a butterfly nebula

M2-9 is a striking example of a 'butterfly' or bipolar planetary nebula. A more revealing name might be the 'Twin Jet Nebula'. If the nebula is sliced across the star, each side of it appears much like a pair of exhausts from jet engines. Given the nebula's shape and the measured velocity of the gas, in excess of 1 million kilometres per hour, astronomers believe that the description as a supersupersonic jet exhaust is quite apt. Ground-based studies have shown that the nebula's size increases with time, suggesting that the stellar outburst that formed the lobes occurred just 1200 years ago.