NASA·APOD每日天文一图2022.5.11 [超高清]

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. 

阿尔伯特·爱因斯坦100多年前发表的广义相对论预言了引力透镜现象。这就是为什么从钱德拉（X射线太空望远镜）和哈勃太空望远镜的X射线和光学图像数据中，可以看到这些遥远星系如此异想天开的外观。绰号为柴郡猫星系群的该星系群的两个大型椭圆星系由弧形构成。这些弧线是遥远背景星系的光学图像，由前星系群的总引力质量分布透镜化。当然，引力质量是由暗物质控制的。这两个巨大的椭圆“眼”星系代表着它们正在合并的星系群中最亮的一员。它们的相对碰撞速度接近1350公里/秒，将气体加热到数百万度，产生紫色的X射线辉光。你对银河系内的星团合并好奇吗？柴郡猫星群在大约46亿光年远的大熊座笑着。