Planetary Nebula
An expanding shell of ionized gas ejected from a red giant star in the late stages of stellar evolution. Despite the name, it has no connection to planets. The glowing gas is illuminated by the hot core of the dying star.
Source: science.nasa.gov
APODs including "Planetary Nebula"
NGC 2440 Nucleus: The Hottest Star?
30/11/1995
In the center of the above photograph lies a star with one of the hottest surface temperatures yet confirmed. This bright white dwarf star's surface has been measured at greater than 200,000 degrees Celsius - more than 30 times hotter than that of our own Sun. The white dwarf's extreme heat makes it glow extraordinarily bright: intrinsically more than 250 times brighter than the Sun. The star is at the center of the planetary nebula titled NGC 2440, which lies inside our Milky Way Galaxy. The above computer sharpened image was taken by the Hubble Space Telescope.