Blue Snowball (NGC 7662)

About this Image

The name of this bright but small Planetary nebula is caused by it's bright blue-gree color. The color is generated by strong O-III emission, accompanied by much fainter H-alpha and H-beta emission. It is built up from 3 different shells, a 17" bright inner shell, a 30" deep green outer shell and a very faint 134" shell, not visible in this image.

Such a nebula is created, when a star throws off its outer layers and goes through a planetary nebula phase. A star can appear "normal" only so long as there are sufficient nuclear reactions in its core. Soon thereafter, gravity will win out and compress the stellar core to higher temperatures. Eventually the core becomes a white dwarf. These high temperatures somehow cause the expulsion of star's outer layers, creating a planetary nebula such as the Blue Snowball pictured above.

The nebula is found in the constellation Andromeda at approx 4000 light years distance.

North is right.
Below you find a crop on the nebula in 200% size, thanks to Volker Wendel for his processing tips!.
Even below a comparison of a Hubble Space Telescope image with a collaboration effort between
Bernd Wallner and me.

References:
Hubble images: 1. 2.
Structure investigations: 2.