The colors are approximately true colors. The color image was assembled from three black-and-white photos taken through different color filters with the Hubble telescope's Wide Field Planetary Camera 2. Blue isolates emission from very hot helium (in the He II line at 4686 A), which is located primarily close to the hot central star. Green represents ionized oxygen (the famous [O III] 5007 A "nebulium" line), which is located farther from the star. Red shows ionized nitrogen ([N II] 6584 A), which is radiated from the coolest gas, located farthest from the star. The gradations of color illustrate how the gas glows because it is bathed in ultraviolet radiation from the remnant central star, whose surface temperature is a white-hot 216,000 degrees Fahrenheit (120,000 degrees Celsius).
Credit: Hubble Heritage Team (AURA/STScI/NASA)
Closer inspection of the image reveals a host of subarcsecond dark globules around the periphery of the nebula, numerous small dark clouds of dust that have formed in the gas flowing out from the star, which are silhouetted against more distant bright gas. The fact that no globules are seen projected against the central region indicates that their distribution is in fact toroidal or cylindrical, rather than spherical. These globulaes are so small that they were not detectable by earthbound telescopes, while they are easily visible in the Hubble photo.
The image here shows a magnification with a considerable number of globules.
Last Modification: 24 Feb 1999