極環(Polar Ring)星系
Polar Ring Galaxy NGC 2685 <br />
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<img src="http://i9.tinypic.com/2ns2zrk.jpg" border="0" onclick="zoom(this)" onload="attachimg(this, 'load')" alt="" /><br />
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Credit & Copyright: Ken Crawford (Rancho Del Sol Observatory) <br />
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<font color="navy">Explanation: </font><br />
<font color="dimgray">NGC 2685 is a confirmed polar ring galaxy - a rare type of galaxy with stars, gas and dust orbiting in rings perpendicular to the plane of a flat galactic disk. The bizarre configuration could be caused by the chance capture of material from another galaxy by a disk galaxy, with the captured debris strung out in a rotating ring. Still, observed properties of NGC 2685 suggest that the rotating ring structure is remarkably old and stable. In this fascinating view of the peculiar system also known as Arp 336 or the Helix galaxy, the strange, perpendicular rings are easy to trace as they pass in front of the galactic disk, along with other disturbed outer structures. NGC 2685 is about 50,000 light-years across and 40 million light-years away in the constellation Ursa Major. </font><br />
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<font color="navy">說明:</font><br />
<font color="dimgray">NGC 2685 是 一個證實為極環(Polar Ring)星系，一種很稀有種類的 星系，因為它的星球、氣體及塵埃垂直地環繞著盤面。 這種奇怪的結構可能是因為剛好被其他星系的 重力吸引，使它的星系物質離開原本的旋轉盤面上。這 觀測到的 奇怪的特性還包括非常古老且穩定的旋轉結構。 像是這張 照片中的特別系統，還有Arp 336 以及螺旋狀星系(Helix galaxy)，這種奇怪的 垂直方向的星系環 很容易因為，當它們沿著外面擾動系統的方向從盤面前通過而發現。 NGC 2685 的寬度大約五萬光年，距離我們四千萬光年，位於 大熊星座(Ursa Major)。 </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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