Astronomy Picture of the Day——哈勃望远镜拍摄的斯蒂芬五重星系
Stephan's Quintet from Hubble
Image Credit: NASA, ESA, Hubble;Processing: Daniel Nobre
Explanation: When did these big galaxiesfirst begin to dance? Really only four of the five of Stephan's Quintet arelocked in a cosmic tango of repeated close encounters taking place some 300million light-years away. The odd galaxy out is easy to spot in this recentlyreprocessed image by the Hubble Space Telescope -- the interacting galaxies,NGC 7319, 7318B, 7318A, and 7317 (left to right), have a more dominantyellowish cast. They also tend to have distorted loops and tails, grown underthe influence of disruptive gravitational tides. The mostly bluish galaxy, largeNGC 7320 on the lower left, is in the foreground at about 40 millionlight-years distant, and so is not part of the interacting group. Data andmodeling indicate that NGC 7318B is a relatively new intruder. Arecently-discovered halo of old red stars surrounding Stephan's Quintetindicate that at least some of these galaxies started tangling over a billionyears. Stephan's Quintet is visible with a moderate sized-telescope toward theconstellation of Winged Horse (Pegasus).
哈勃望远镜拍摄的斯蒂芬五重星系
这些庞大星系是什么时候开始第一次跳舞的？实际上，斯蒂芬五重星系中的四个被禁锢在距离我们约3亿光年远的一处频繁发生的宇宙探戈中。在这幅由哈勃拍摄后经过再加工的图像中，很容易发现这个由多个相互作用星系构成的奇特星系，它们都呈现出淡黄色的色泽，从左到右分别是NGC 7319、7318B、7318A和7317。它们拥有扭曲的环状和尾部结构，在破坏性引力潮的影响下演变。影像左下方的庞大星系NGC 7320位于这幅图像的前景中，距离地球约4千万光年，因此它并不是相互作用星系群的一部分。数据和建模表明NGC 7318B是一个相对较新的入侵者。最近在斯蒂芬五重星系附近发现由古老红星组成的光晕表明至少有一些星系已经纠缠在一起超过了十亿年。使用一台中等大小的望远镜朝飞马座方向观察便能看到斯蒂芬五重星系。
参考文献：
https://apod.nasa.gov/apod/image/1906/StephansQuintet_HubbleNobre_1824.jpg
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Astronomy Picture of the Day——一条通往猎户座的冰冷河流