钱德拉发现一个正在形成的巨型星系团

Astronomers using data from NASA’s Chandra X-ray Observatory and other telescopes have put together a detailed map of a rare collision between four galaxy clusters. Eventually all four clusters — each with a mass of at least several hundred trillion times that of the Sun — will merge to form one of the most massive objects in the universe.

Galaxy clusters are the largest structures in the cosmos that are held together by gravity. Clusters consist of hundreds or even thousands of galaxies embedded in hot gas, and contain an even larger amount of invisible dark matter. Sometimes two galaxy clusters collide, as in the case of the Bullet Cluster, and occasionally more than two will collide at the same time.

The new observations show a mega-structure being assembled in a system called Abell 1758, located about 3 billion light-years from Earth. It contains two pairs of colliding galaxy clusters that are heading toward one another. Scientists first recognized Abell 1758 as a quadruple galaxy cluster system in 2004 using data from Chandra and XMM-Newton, a satellite operated by the European Space Agency (ESA).

Each pair in the system contains two galaxy clusters that are well on their way to merging. In the northern (top) pair seen in the composite image, the centers of each cluster have already passed by each other once, about 300 to 400 million years ago, and will eventually swing back around. The southern pair at the bottom of the image has two clusters that are close to approaching each other for the first time.

Image Credit: X-ray: NASA/CXC/SAO/G.Schellenberger et al.; Optical:SDSS

天文学家利用NASA钱德拉X射线天文台和其他望远镜的数据，绘制了一幅详细的星系团碰撞图。最终，所有四个星团（每个星团的质量至少是太阳的数百倍）将合并成宇宙中最大的天体之一。

星系团是宇宙中由引力维系在一起的最大结构。星系团由数百甚至数千个星系组成，这些星系嵌在高温气体中，并且包含了更多的不可见的暗物质。有时两个星系团会发生碰撞，就像子弹星系团一样，有时两个以上的星系团会同时发生碰撞。

新的观测结果显示，在距离地球约30亿光年的阿贝尔1758星系中，一个巨型结构正在形成。它包含了两对相互碰撞的星系团。2004年，科学家首次利用钱德拉和XMM-牛顿(XMM-Newton)(欧洲航天局(ESA)运营的一颗卫星)的数据，确认了阿贝尔1758是一个四重星系团系统。

星系中的每一对都包含了两个正在融合的星系群。在这幅合成图中所看到的北部(顶部)对中，每个星团的中心在大约在3亿到4亿年前已经相互绕过一次，并将最终回绕。图片底部的南部有两个星团，它们第一次接近对方。

影像来源：X-ray: NASA/CXC/SAO/G.Schellenberger et al.; Optical:SDSS