NGC 2440

NGC 2440 is a planetary nebula, made up of gas and dust ejected by a dying star. The central star of NGC 2440 is one of the hottest known, with a surface temperature near 200,000 degrees Celsius. The complex structure of the surrounding nebula suggests to some astronomers that there have been periodic, oppositely directed outflows from the central star, but these outflows have been projected in different directions during each episode. The nebula is also rich in clouds of dust, some of which form long, dark streaks pointing away from the central star. In addition to the bright nebula, which glows because of fluorescence due to ultraviolet radiation from the hot star, NGC 2440 is surrounded by a much larger cloud of cooler gas, which is invisible in ordinary light but can be detected with infrared telescopes.