The Headphones Nebula is an old planetary nebula located around 1600 light years from Earth in the constellation of Lynx, the area of sky between Ursa Major and Gemini. It certainly lives up to its name with its characteristic shape, but don't expect to spot this nebula with ease; it is extremely faint at an apparent magnitude of +14 and is very diffuse. It is impossible to see with the naked eye and even very difficult to discern through a telescope. Consequently it was only discovered through the use of photographic plates taken at Harvard Observatory in 1939 by Rebecca Jones and R Emberson. The pair catalogued the nebula as Jones-Emberson 1. Its alternative catalogue identifier, PK 164+31.1, was given by Czechoslovakian astronomers Perek and Kahoutek, who created an extensive catalogue of all known planetary nebulae in the Milky Way in 1964.

In the centre of the nebula is a white dwarf star of magnitude +17, clearly visible in this image as a small bright blue dot. The nebula is approaching us at a speed of about 84 km/s, so the light that we see is blue shifted, but only by around 0.028%, nowhere near enough to make a typical white dwarf appear blue. The blue colour indicates an unusually high temperature around 40,000K. The planetary nebula was formed by the collapse of a star similar in size to our Sun. As the star started to exhaust its hydrogen fuel as a red giant, the core collapsed to create a white dwarf star that began to radiate strongly, heating the surrounding gas to temperatures of 10,000K. The outer shell was blown out into space and it is this expanding mass of glowing gas that we can see as the ring in the image.

Gas in a nebula is very thin and spread out, in fact it is more of a vacuum then we can create on Earth; however it is visible to us because of the sheer scale and size of the nebula. As the gas is so thin, the nebula has a low surface brightness allowing background stars to be visible through the nebula. The outer red ring in the image is mainly composed of ionised hydrogen and the inner bluer ring is mainly ionised oxygen. Eventually the cloud of gas will disperse out into space and the white dwarf will cool down, over billions of years, becoming a red dwarf, then a brown dwarf and ultimately a black dwarf at around the background temperature of the universe. The course of the star that formed this planetary nebula is similar to the fate of our own Sun; what shape will we become?