A Hubble Space Telescope (HST) image of NGC 6751. Image credit: NASA
NGC 6751 was chosen to commemorate Hubble's tenth anniversary in orbit. The colors were chosen to represent the relative temperatures of gas (blue, orange and red, from hot gas to colder gas). These are the winds of intense heat and the radiation of the central star that create the characteristic form of the nebulae. This central star dying, shines like 9000 Suns. It expels its outer gas layers and exposes its burning nucleus whose strong ultraviolet radiation illuminates the expelled gas.
Winds and radiation from the intensely hot central star (140mil degrees Celsius) have apparently created serpentine-like structures in the nebula. The actual diameter of the nebula is about 0.8 light-years which is about 600 times the size of our solar system. NGC 6751 is 6,500 light-years away in the high constellation of the Eagle.