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Planetary Nebula or Supernov3

Planetary Nebula or Supernov3 - of doubly-ionized...

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Planetary Nebula or Supernova In this next-to-last stage of a star's life, the outer layers are ejected as the core shrinks to its most compact state. A large amount of mass is lost at this stage as the outer layers are returned to the interstellar medium. For the common low-mass stars (those with masses of 0.08 to about 6 or 7 times the mass of the Sun during their main sequence stage), the increased number of photons flowing outward from the star's hot, compressed core will push on the carbon and silicon grains that have formed in the star's cool outer layers to eject the outer layers and form a planetary nebula . The ultraviolet from the hot exposed core, called a white dwarf, causes the gases to fluoresce. Most noticeable is the red emission from the excited hydrogen and nitrogen, the green emission from doubly-ionized oxygen, and the blue emission from excited helium. Planetary nebulae can be distinguished from H II regions by their compact shape and strong emission lines
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Unformatted text preview: of doubly-ionized oxygen (that give them their green color), doubly-ionized neon, and singly-ionized helium. (The image of the Ring Nebula on the left is courtesy of Palomar Observatory .) AAO image Planetary nebula get their name because some looked like round, green planets in early telescopes. They are now known to be entirely different than the planets and are about one or more light years across (much larger than our solar system!). Originally, we thought planetary nebulae were simple expanding spherical shells that look like rings on the sky because when you look along the edge of the expanding spherical shell, you look through more material than when you look toward the center of the shell. The round soap bubbles you made as a child (or still do!) look like rings for the same reason. Indeed, many of the planetary nebulae first seen, like the Ring Nebula in Lyra and the Helix Nebula in Aquarius look like rings....
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