X射线卫星发现了宇宙里最大的一次碰撞
沿轨道运行的X射线天文望远镜XMM-NEWTON和钱德拉共同捕捉到了一对正在合并成一个巨大星系团的两个星系。这个发现增添个一个让人兴奋的证据，星系能够比以前所认为的更加快速的碰撞。当个别的一些星系碰撞并卷人另一个当中去时，他们清除掉热气体延长而横过太空所留下的痕迹，提供了残缺星系的标识。识别在整个星系团之间的碰撞标志，但是这并不容易。无畏的Renato Dupke和来自密西根州大学的同事Ann Arbor，使用ESA的XMM-NEWTON和NASA的钱德拉X射线天文台，解开了星系团之迷，Abell 576。
以前X射线波段的观测已经暗示气体的移动不是均匀的通过星系团，利用XMM-NEWTON极高敏感度和光谱分辨率与钱德拉的高空间分辨率，Dupke通过星系团中两个位置的读数，发现了气体有着明显不同的速度。其中一个看上去远离我们的速度要比另一个快。
难题在于按照天体的标准，移动的气体本身是寒冷的，假设这些气体高速移动，那他应该已经有了超过两次测量所得5000万摄氏度的温度值，“唯一的解释就是将子弹星团放于视线的同一直线上，也就是说其中一个星系已经在另一个的后面了”Dupke说到。
Dupke意识到Abell 576同样也是一个碰撞的产物，但是只能看到前面的一个，所以其中一个现在已经几乎全部在另一个的后面了。‘冷云’是每个星系团的核心，并存留在碰撞的初期，但最后会合并成一个。
数据显示了星系团是以3300KM/S的速度发生碰撞。这是个有趣的事，因为一些星系碰撞的电脑模拟显示，这么高的一个速度是无法达到的。
尽管如此，子弹星团的碰撞速度仍被估计与Abell 576系统相差不多。“现在有个正在酝酿生成的一个论据说明这样的高速碰撞是可能的”Dupke说到。如今解释这些高速的工作得依靠宇宙学。
较大的星团之间的碰撞，人们期望越少越好，通过估计他们的发生频率，发现在少于1/1000到1/100这个范围内。在碰撞中，他们内部的气体平衡被打破并且如果不能被识别，将导致对其质量有5%到20%的估计不足。
这事非常重要，因为众多星系的质量通常是被拿来估算宇宙学参数的，也就是用来描述宇宙如何膨胀的数据。所以，鉴别碰撞系统对于我们了解宇宙是非常重要的。
The orbiting X-ray telescopes XXM-Newton and Chandra have caught a pair of galaxy clusters merging into a giant cluster. The discovery adds to existing evidence that galaxy clusters can collide faster than previously thought.
When individual galaxies collide and spiral into one another, they discard trails of hot gas that stretch across space, providing signposts to the mayhem. Recognising the signs of collisions between whole clusters of galaxies, however, is not as easy. Undaunted, Renato Dupke and colleagues from the University of Michigan, Ann Arbor, have used ESA's XMM-Newton and NASA's Chandra orbiting X-ray observatories, to disentangle the puzzling galaxy cluster, Abell 576.
The puzzle was that the moving gas itself was cold by astronomical standards. If this gas moved at such high speeds, it should have had a temperature of more than double the measured 50 million degrees Celsius. "The only explanation was to take the Bullet Cluster and turn it in the line of sight, such that one galaxy cluster is directly behind the other" says Dupke.
The Bullet Cluster is a much-studied pair of galaxy clusters, which have collided head on. One has passed through the other, like a bullet travelling through an apple. In the Bullet Cluster, this is happening across our line of sight, so we can clearly see the two clusters.
Dupke realised that Abell 576 is also a collision, but seen head on, so one cluster is now almost directly behind the other. The 'cold' clouds of gas are the cores of each cluster, which have survived the initial collision but will eventually fall back together to become one.
The data reveals that the clusters have collided at a speed of over 3300 km/s. This is interesting because there are some computer models of colliding galaxy clusters that suggest that such a high speed is impossible to reach.
Nevertheless, the Bullet Cluster is estimated to have a collision speed similar to the Abell 576 system. "There is now a growing body of evidence that these high collision velocities are possible," says Dupke. The job of explaining these high speeds now rests with the cosmologists.
Major cluster-cluster collisions are expected to be rare, with estimates of their frequency ranging from less than one in a thousand clusters to one in a hundred. On collision, their internal gas is thrown out of equilibrium and if unrecognised, causes underestimation of its mass by between 5 and 20 percent.
This is important because the masses of the various galaxy clusters are used to estimate the cosmological parameters that describe how the Universe expands. So, identifying colliding systems is extremely important to our understanding of the Universe.
自翻
URL：http://spacespin.org/article.php ... s-biggest-collision
大图
http://esamultimedia.esa.int/images/Science/1e0657_H1.jpg
模拟碰撞图
主要FALSH提取不出来，所以就只能提取里面的一些图片，做成GIF了
[ 本帖最后由 江涛 于 2008-3-1 13:19 编辑 ] PL哇，期待江兄更多的好图啊::0020:: 呵呵，你小子有段时间没见到你了。。。 子弹头星云么。。。以前有贴过 看来又重复了。。。那就锁了把。。。::luguo:: 那个的内容没你的丰富。。。
页:
[1]