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__NOTOC__ The Hubble eXtreme Deep Field (XDF) is an image of a small part of space in the center of the Hubble Ultra-Deep Field (HUDF) within the constellation Fornax, showing the deepest optical view in space. While the HUDF is 2.4 arcminutes to an edge,〔http://hubblesite.org/newscenter/archive/releases/2009/31/fastfacts/〕 the XDF is 2.3 arcminutes by 2 arcminutes,〔http://hubblesite.org/newscenter/archive/releases/2012/37/fastfacts/〕 or approximately 80% the area of the HUDF. Released on September 25, 2012, the ''XDF'' image compiled 10 years of previous images and shows galaxies from 13.2 billion years ago. The exposure time was two million seconds, or approximately 23 days. The faintest galaxies are one ten-billionth the brightness of what the human eye can see. Many of the smaller galaxies are very young galaxies that eventually became major galaxies, like the Milky Way and other galaxies in our galactic neighborhood.〔 The Hubble eXtreme Deep Field, or ''XDF'', adds another 5,500 galaxies to those discovered in the Hubble Ultra-Deep Field. == Gallery == File:XDF-scale.jpg | ''XDF'' size compared with the size of the moon - several thousand galaxies, each consisting of billions of stars, are in this small view. File:XDF-separated.jpg | ''XDF'' image shows mature galaxies in the foreground plane - nearly mature galaxies from 5 to 9 billion years ago - protogalaxies beyond 9 billion years. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hubble eXtreme Deep Field」の詳細全文を読む スポンサード リンク
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