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太陽的未來 - 行星狀星雲
這個編號為NGC 6369的美麗行星狀星雲，是十八世紀天文學家赫歇爾 (William Herschel)用望遠鏡觀測蛇夫座時所發現的。它具有渾圓的行星狀外觀，而且相對昏暗，故有小幽靈星雲(Little Ghost Nebula)的綽號。
其實，行星狀星雲和行星沒有關聯，它們是類太陽恆星在生命末期時，外層氣殼膨脹散逸到太空中所形成的，而恆星核心則收縮成為一顆白矮星。在這張影像中心的白矮星，發出強烈的紫外波段輻射，激發擴張的雲氣發出輝光。在這張哈伯太空望遠鏡影像裡，可見到NGC 6369具有意外複雜且細緻的構造。
星雲的主要環狀結構，寬度大約有一光年，而藍、綠、與紅色的輝光，分別來自游離化的氧、氫和氮原子。小幽靈星雲離我們大約有二千光年遠；它讓我們預見了太陽未來的宿命，再過五十億年，太陽也會產生自已的行星狀星雲。
NGC 6369:小幽靈星雲
Credit: Hubble Heritage Team, NASA
原文：
Explanation: This pretty planetary nebula, cataloged as NGC 6369, was discovered by 18th century astronomer William Herschel as he used a telescope to explore the medicinal constellation Ophiucus. Round and planet-shaped, the nebula is also relatively faint and has acquired the popular moniker of Little Ghost Nebula. Planetary nebulae in general are not at all related to planets, but instead are created at the end of a sun-like star's life as its outer layers expand into space while the star's core shrinks to become a white dwarf. The transformed white dwarf star, seen near the center, radiates strongly at ultraviolet wavelengths and powers the expanding nebula's glow. Surprisingly complex details and structures of NGC 6369 are revealed in this tantalizing image composed from Hubble Space Telescope data. The nebula's main ring structure is about a light-year across and the glow from ionized oxygen, hydrogen, and nitrogen atoms are colored blue, green, and red respectively. Over 2,000 light-years away, the Little Ghost Nebula offers a glimpse of the fate of our Sun, which could produce its own planetary nebula only about 5 billion years from now.
原文網址：http://apod.nasa.gov/apod/ap120114.html
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在線雷達
發表於 2012-1-16 05:51:43
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