The Butterfly Nebula belongs to the class of bipolar planetary nebulae. A dark, dusty and disc-like structure — unfortunately not visible in this image — obscures the central star from our view. However, its strong radiation escapes perpendicular to the disk and heats and illuminates the material deposited there by the stellar wind.
The origin of the dark disk may be due to the central star being a member of a double star system. This has been shown to be the case in some other bipolar nebulae in which, contrary to the Butterfly Nebula, there is a direct view towards the star.
