星系团和引力透镜

http://en.wikipedia.org/wiki/Dark_matter#Galaxy_clusters_and_gravitational_lensing

Galaxy clusters and gravitational lensing
星系团和引力透镜
A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is "bent" around a massive object (such as a cluster of galaxies) between the source object and the observer. The process is known as gravitational lensing.
当非常遥远而明亮的天体光源（比如类星体）经过一个大质量天体（比如星系团）时，其光线会被弯曲而成像，这个过程，我们称之为“引力透镜”。
Dark matter affects galaxy clusters as well. X-ray measurements of hot intracluster gas correspond closely to Zwicky's observations of mass-to-light ratios for large clusters of nearly 10 to 1. Many of the experiments of the Chandra X-ray Observatory use this technique to independently determine the mass of clusters.
暗物质能像星系团一样弯曲光线。在大型星系团中，对星系际炽热气体的X线辐射测量得到的质量——光度比，接近Zwicky（早年）对星系测量获得的比值——约为10:1。（http://arxiv.org/abs/astro-ph/0507092、http://www.nature.com/nature/journal/v445/n7125/full/nature05497.html）钱德拉X线望远镜的许多观测都使用该技术来独立地测定星系团的质量。 （所谓质光比，就是说通过某种测量方法得到的星系团质量，与根据星系团光度计算的质量的比值——gohomeman1注，感谢voyagerbb的说明）

                               
登录/注册后可看大图

The galaxy cluster Abell 2029 is composed of thousands of galaxies enveloped in a cloud of hot gas, and an amount of dark matter equivalent to more than 10^14 Suns. At the center of this cluster is an enormous, elliptically shaped galaxy that is thought to have been formed from the mergers of many smaller galaxies. The measured orbital velocities of galaxies within galactic clusters have been found to be consistent with dark matter observations.
在星系团Abell 2029中，数千星系包裹在热气体云团中，估计其暗物质相当于100万亿个（10的14次方）太阳质量。星系团中心是个庞大的椭圆星系，应该是由大量小星系合并而成。（http://chandra.harvard.edu/photo/2003/abell2029/）对星系中星团运行速度的测定值，与对暗物质（上一段方法）的估计值相当。

                               
登录/注册后可看大图

Another important tool for future dark matter observations is gravitational lensing. Lensing relies on the effects of general relativity to predict masses without relying on dynamics, and so is a completely independent means of measuring the dark matter. Strong lensing, the observed distortion of background galaxies into arcs when the light passes through a gravitational lens, has been observed around a few distant clusters including Abell 1689 . By measuring the distortion geometry, the mass of the cluster causing the phenomena can be obtained. In the dozens of cases where this has been done, the mass-to-light ratios obtained correspond to the dynamical dark matter measurements of clusters.
未来测量暗物质的另一个重要工具是引力透镜。根据广义相对论，透镜效应仅依赖于质量分布，而与动力学过程无关，所以这是一种完全独立的暗物质分布测量手段。在几个遥远的星系团中，观测到强烈的引力透镜效应，背景星系的像扭曲为光弧，如上图所示（哈勃拍摄的）Abell 1689。（http://adsabs.harvard.edu/abs/1998ApJ...501..539T、http://arxiv.org/abs/astro-ph/9801158）通过对失真几何效应的测量，就能获得导致此效应的星系团的质量分布。对数十个类似例子的测量表明，其质量—光度比与根据动力学效应获得的暗物质质量值相当（http://arxiv.org/abs/astro-ph/9808179、http://dx.doi.org/10.1046%2Fj.1365-8711.1998.02055.x）。

G版啊，能告诉我我得学多久才能到你这样的水平吗..................

X射线的那个地方(就是G版说不大确定的那里),我觉得意思应该不是说是 Zwicky测量的值的十倍,而是说跟他测量的结果类似是10比1.
Zwicky一般中文就译为兹威基.

这个兹威基的测量我以前不了解，我相信voyagerbb说的应该就是原文的意思吧。你看看修改后是否更通顺些。

回复 11# gohomeman1

这样似乎更好些(意译):
通过X射线对星系团内(也就是星系际)气体的测量得到的质光比,跟兹威基测到的值一致,都是接近10:1.

回复 6# voyagerbb

请看一下短消息。

回复 3# sky4733

其实我读大学时，英语最差。能力是靠运用来提高的，不是靠学历来撑门面的。

                               
登录/注册后可看大图

A technique has been developed over the last 10 years called weak gravitational lensing, which looks at minute distortions of galaxies observed in vast galaxy surveys due to foreground objects through statistical analyses. By examining the apparent shear deformation of the adjacent background galaxies, astrophysicists can characterize the mean distribution of dark matter by statistical means and have found mass-to-light ratios that correspond to dark matter densities predicted by other large-scale structure measurements. The correspondence of the two gravitational lens techniques to other dark matter measurements has convinced almost all astrophysicists that dark matter actually exists as a major component of the universe's composition.
近10年来，弱引力透镜（http://en.wikipedia.org/wiki/Weak_gravitational_lensing）技术发展起来，通过对广域巡天图像的统计分析，发现背景星系的微小变形，进而计算前景天体的质量分布。通过对图像中相邻的背景星系的形变分析，天文学家能够描绘前景暗物质的密度分布，并（欣喜地）发现由此获得的质光比与其他大尺度测量方法相符（http://dx.doi.org/10.1146%2Fannurev.astro.41.111302.102207）。基于两种引力透镜测量结论与其他测量结果相符，绝大部分天体物理学家由此相信，暗物质是宇宙的主要构件之一。

                               
登录/注册后可看大图

The most direct observational evidence to date for dark matter is in a system known as the Bullet Cluster. In most regions of the universe, dark matter and visible material are found together, as expected because of their mutual gravitational attraction. In the Bullet Cluster, a collision between two galaxy clusters appears to have caused a separation of dark matter and baryonic matter. X-ray observations show that much of the baryonic matter (in the form of 10^7– 10^8 Kelvin gas, or plasma) in the system is concentrated in the center of the system. Electromagnetic interactions between passing gas particles caused them to slow down and settle near the point of impact. However, weak gravitational lensing observations of the same system show that much of the mass resides outside of the central region of baryonic gas. Because dark matter does not interact by electromagnetic forces, it would not have been slowed in the same way as the X-ray visible gas, so the dark matter components of the two clusters passed through each other without slowing down substantially. This accounts for the separation. Unlike the galactic rotation curves, this evidence for dark matter is independent of the details of Newtonian gravity, so it is held as direct evidence of the existence of dark matter. Another galaxy cluster, known as the Train Wreck Cluster/Abell 520, seems to have its dark matter completely separated from both the galaxies and the gas in that cluster, which presents some problems for theoretical models.
更直接的证据来自子弹星系团（http://en.wikipedia.org/wiki/Bullet_Cluster）。在宇宙的大部分区域，因为引力作用，暗物质和物质混合在一起（http://www.nature.com/nature/journal/v445/n7125/full/nature05497.html、http://www.ncbi.nlm.nih.gov/pubmed/17206154）。但在子弹星系团中，两个星系团的相撞看似导致暗物质和重子物质的分离。X线观测显示，大部分的重子物质（温度高达0.1~1亿K的等离子体）浓缩在系统中心。等离子体微粒间的电磁相互作用导致它们减速并沉淀在相撞点附近。然而，弱引力透镜观测显示，系统中还有大量的质量位于重子物质密集的中心区域外。由于暗物质不参与电磁相互作用，因此它们不能像在X线下可视的炽热气体那样减速，它们互相穿过而减速甚微，并最终分离。与星系旋转曲线不同，这个例子不依赖于牛顿力学细节，因此是存在暗物质的直接证据（http://arxiv.org/abs/astro-ph/0608407、http://dx.doi.org/10.1086%2F508162）。另外，像破碎星系团（Abell 520）这样的星系团，暗物质看似与普通的星系、星系际气体完全分离，解释它们的形成是个难题（http://chandra.harvard.edu/photo/2007/a520/）。

                               
登录/注册后可看大图

                               
登录/注册后可看大图

本主题是分割出来的，所以回复楼层数看似不对。

回复 11# vanlog


you can do it by yourself.

进来学习...

回复 16# 大地孤寂

哈勃官网维护吧，整个官网都登录不上了。每年例行一次的。

这贴里的图都没大图下载吗？

仔细研读，收获颇丰！
谢谢！