Planetary nebula. Combined X-ray and optical image of the planetary nebula NGC 7027. A planetary nebula is a bubble of hot gas and dust, many times the size of our solar system, expanding outwards from a dying, Sun-like star. The nebula consists of the ejected outer layers of the star. The optical part of this image (yellow and red) was obtained with the Hubble Space Telescope (HST). The hotter, X-ray emitting region (blue and white, centre) was imaged with the Chandra X-ray Observatory (CXO). Both the HST and CXO are telescopes in Earth orbit. NGC 7027 is around 3000 light years from Earth, in the constellation of Cygnus.