Albert Einstein's general theory of relativity, published over 100 years ago, predicted the phenomenon of gravitational lensing. And that's what gives these distant galaxies such a whimsical appearance, seen through the looking glass of X-ray and optical image data from the Chandra and Hubble space telescopes. Nicknamed the Cheshire Cat galaxy group, the group's two large elliptical galaxies are suggestively framed by arcs. The arcs are optical images of distant background galaxies lensed by the foreground group's total distribution of gravitational mass. Of course, that gravitational mass is dominated by dark matter. The two large elliptical "eye" galaxies represent the brightest members of their own galaxy groups which are merging. Their relative collisional speed of nearly 1,350 kilometers/second heats gas to millions of degrees producing the X-ray glow shown in purple hues. Curiouser about galaxy group mergers? The Cheshire Cat group grins in the constellation Ursa Major, some 4.6 billion light-years away.?

阿爾伯特·愛因斯坦100多年前發(fā)表的廣義相對論預(yù)言了引力透鏡現(xiàn)象。這就是為什么從錢德拉（X射線太空望遠鏡）和哈勃太空望遠鏡的X射線和光學(xué)圖像數(shù)據(jù)中，可以看到這些遙遠星系如此異想天開的外觀。綽號為柴郡貓星系群的該星系群的兩個大型橢圓星系由弧形構(gòu)成。這些弧線是遙遠背景星系的光學(xué)圖像，由前星系群的總引力質(zhì)量分布透鏡化。當然，引力質(zhì)量是由暗物質(zhì)控制的。這兩個巨大的橢圓“眼”星系代表著它們正在合并的星系群中最亮的一員。它們的相對碰撞速度接近1350公里/秒，將氣體加熱到數(shù)百萬度，產(chǎn)生紫色的X射線輝光。你對銀河系內(nèi)的星團合并好奇嗎？柴郡貓星群在大約46億光年遠的大熊座笑著。