行星狀星雲
Planetary Nebula NGC 2440 <br />
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<img src="http://i7.tinypic.com/4ckxjpx.jpg" border="0" onclick="zoom(this)" onload="attachimg(this, 'load')" alt="" /><br />
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影像提供: NASA, ESA, K. Noll (STScI) <br />
誌謝: Hubble Heritage Team (STScI / AURA) <br />
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<font color="navy">Explanation: </font><br />
<font color="dimgray">Planetary nebula NGC 2440 has an intriguing bow-tie shape in this stunning view from space. The nebula is composed of material cast off by a dying sun-like star as it enters its white dwarf phase of evolution. Details of remarkably complex structures are revealed within NGC 2440, including dense ridges of material swept back from the nebula's central star. Near the center of the view, the star itself is one of the hottest known, with a surface temperature of about 200,000 kelvins. About 4,000 light-years from planet Earth toward the nautical constellation Puppis, the nebula spans over a light-year and is energized by ultraviolet light from the central star. The false-color image was recorded earlier this month using the Hubble's Wide-Field Planetary Camera 2(WFPC2), demonstrating still impressive imaging capabilities following the failure of the Advanced Camera for Surveys. </font><br />
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<font color="navy">說明:</font><br />
<font color="dimgray">這幅迷人太空影像裡的行星狀星雲NGC 2440，具有很有趣的蝴蝶結外觀。行星狀星雲的物質，是來自臨死類太陽恆星演化至白矮星階段所拋出的氣殼。影像中可看見NGC 2440內部有許多非常複雜的構造，其中包括指離星雲中心星的緻密物質稜。位在影像中心的中心星，表面溫度高達二十萬度，是現知最熾熱的恆星之一。這個星雲位在航海星座的船尾座內，離地球約有四千光年遠，大小略高於一光年，在中心星紫外輻射的激發下發光。這張假色影像，是這個月初由哈伯太空望遠鏡的廣角行星相機所拍攝的，目的在於證明先進巡天相機故障後，哈伯望遠鏡還是具有絕佳的成像能力。 </font><br />
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<font size="2">資料來源: Scientific American<br />
Department of Physics, NCKU</font><font color="white"><font size="1"><br />
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