Fig11_1planetary_nebula_hs-2000-12-a-full_tif.jpg

Fig11_1planetary_nebula_hs-2000-12-a-full_tif.jpg

Fig. 11.1 . When a Sun-like star uses up its nuclear fuel, the starís center collapses into an Earth-sized white dwarf star while its outer gas layers are ejected into space. Such a planetary nebula is named after its round shape, which resembles a planet as seen visually in small telescopes, and has nothing to do with planets. The shells of gas in the planetary nebula NGC 6751, shown here, were ejected several thousand years ago. The hot stellar core, exposed by the expulsion of the material surrounding it, has a disk temperature of about 140,000 K. Its intense ultraviolet radiation causes the ejected gas to fluoresce as a planetary nebula. (A Hubble Space Telescope image courtesy NASA/STScI/AURA/Hubble Heritage Team.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University