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高級超級版主 | 2009-3-28 11:02:21

The Matter of the Bullet Cluster

Composite Credit: X-ray: NASA/CXC/CfA/ M.Markevitch et al.;
Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/ D.Clowe et al.
Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.;
Explanation:
     The matter in galaxy cluster 1E 0657-56, fondly known as the "bullet cluster", is shown in this composite image. A mere 3.4 billion light-years away, the bullet cluster's individual galaxies are seen in the optical image data, but their total mass adds up to far less than the mass of the cluster's two clouds of hot x-ray emitting gas shown in red. Representing even more mass than the optical galaxies and x-ray gas combined, the blue hues show the distribution of dark matter in the cluster. Otherwise invisible to telescopic views, the dark matter was mapped by observations of gravitational lensing of background galaxies. In a text book example of a shock front, the bullet-shaped cloud of gas at the right was distorted during the titanic collision between two galaxy clusters that created the larger bullet cluster itself. But the dark matter present has not interacted with the cluster gas except by gravity. The clear separation of dark matter and gas clouds is considered direct evidence that dark matter exists.
說明:
      這張合成圖中,顯示的就是銀河星團1E 0657-56,通稱為「子彈星團」的組成物質。 在約略34億光年遠處,子彈星團的獨立銀河系在光學影像中清晰可見,不過總物質還是比圖中紅色區域的兩團星雲熱X-光釋出氣體遠遠還要少的多。 而甚至比光學銀河系以及X光氣體加在一起還要多物質,藍色部分顯示出星團中分佈的深色物質。 其實用望遠鏡的話就找不到,深色物質是在背後銀河系使用重力拍攝觀測才得以被勘測的。 在一個教科書範例中,右邊的子彈狀氣體星雲被歪曲了,由於兩個銀河星團間的超巨大相撞,並且還形成了更大的、現在的子彈星雲。 不過這兒的深色物質,除了用重力外,用星團氣體是不會互動的。 深色物質以及氣體星雲之間明顯的區隔,被認為是深色物質存在的直接證據。
資料來源: Scientific American
                 Department of Physics, NCKU

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