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哎，昨天才用手机搜到，暗物质的那篇。。。结果今天就确认版本不是暗物质而是宇宙射线。。。算了，既然搜出来了，就贴出来吧，以后说不定还会遇到dark matter
Cosmology 101: Dark matter
宇宙大指南之暗物质
Astronomy杂志的副主编 Liz Kruesi 将会给我们讲解关于暗物质的概念，这种神秘的物质组成了我们宇宙大约90%的质量。
剧本：
在这个系列里我将给大家介绍宇宙学中的一些重要的概念。本视频是第二集，主要着眼于暗物质这个概念。
In this series I give you an overview of important ideas in the area of cosmology. This video is the second in the series, and focuses on dark matter.
通过各种不同的探测器和研究方法，天文学家发现我们宇宙中这些可见物质，包括星球、气体和尘埃，仅占宇宙总质量的5%不到。这些常见的物质，都是由质子、中子和电子组成的。科学家把这些常见物统称为“重子物质”，因为质子和中子都属于亚原子结构的重子。
Using various detectors and research methods, astronomers have determined that the stuff we see in space — stars, gas, and dust — amounts to less than 5 percent of the universe. This stuff is ordinary matter, and it's made up of protons, neutrons, and electrons. Scientists call ordinary matter "baryonic matter" because protons and neutrons are subatomic particles called baryons.
既然常见物质仅占宇宙的5%，那么剩下那95%又是什么呢？经研究，其中越23%是一种叫暗物质的东西，剩下的72%是一种神秘且无处不在的力,被称为暗能量。关于暗能量这一点，我在下一集会详细讲解。
So if ordinary matter is only about 5 percent of the universe, what's the other 95 percent? Well, about 23 percent is something called dark matter. The remaining 72 percent is a mysterious pervasive force called dark energy. I'll explain more about dark energy in my next video.
我们在回到暗物质，这种神秘的物质不会发射、吸收或反射任何形式的光波（比如，它不会发射X射线或吸收红外辐射）。也因此，暗物质是不可见的。你也许会问，既然它不可见，天文学家又是如何发现它的呢？问得好，暗物质和普通物质之间通过引力相互作用，而天文学家则正是利用这种引力效应第一次发现了暗物质的存在。
Alright, back to dark matter. This mysterious mass is a type of matter that doesn't emit, absorb, or reflect any type of light (so, for example, it doesn't emit X rays or absorb infrared radiation). Dark matter is therefore invisible. If it's invisible, how do astronomers have any idea it's there? Dark matter interacts with ordinary matter through gravity. Its gravitational interaction is how astronomers first found out dark matter exists.
瑞士的天体物理学家弗瑞兹·兹维基在1933年第一次提出暗物质的存在。他在研究后发座星系团的时候，发现星系本身的引力作用太小而不足以维持星系团的成型。
In 1933, a Swiss astrophysicist by the name of Fritz Zwicky first proposed dark matter's existence. While studying the Coma galaxy cluster, he found that the galaxies' gravity alone was much too small to hold the cluster together.
在40年后的（二十世纪）70年代又发现了大量新线索。天文学家测绘出距离星系中心不同位置的星球的速率，并画出速率比距离的数据图。这种图叫做旋转曲线。他们原本期望在速率达到最大值后，会随着（离星系中心）距离的增加而减小，然而数据显示却并非如此。速率在达到最大值后就保持在了一个相对平稳的状态。在如此重量（星球）级别下保持这种速率的话，星系边缘的星球都将被甩出轨道。实际情况却并非如此，因此，必然有某种我们看不见得物质在维持着这些星球在轨道正常运行。
The next round of evidence came about 40 years later, in the 1970s. Astronomers charted the velocity of stars at various distances from the center of a galaxy, and plotted the velocity versus the distance. This plot is called a rotation curve. They expected the velocities to reach a maximum and then decrease farther from the center — but the data showed otherwise. The velocities reach a maximum and then plateau. With velocities of this magnitude at the outer edge of galaxies, the stars should be flung out of their orbits. But they aren't. So some sort of mass that we can't detect must hold these outer stars in orbit.
大质量的星系团同样预示着暗物质的存在。一个超级天体（比如星系团）可以弯曲并放大来自它后面星系的光线。这种超级天体如同一个引力透镜。在这幅包含了Abell 2218星系团的图片里，你会看到许多弯曲的蓝弧, 这些是被星系团的引力扭曲并放大的背景星系。天文学家通过研究这些弧光的尺寸和形状可以得出星系团的质量。然后通过和那些只计算发光天体（星系）的质量进行对比，他们就能够得出星系团中有多少暗物质的存在了。
Massive galaxy clusters also show evidence of dark matter. A very massive object — such as a galaxy cluster — can bend and magnify light from galaxies behind it. That massive object acts as a gravitational lens. In this image of galaxy cluster Abell 2218, you'll see numerous blue arcs. Those are background galaxies distorted and magnified by the cluster's gravity. Astronomers study the sizes and shapes of those arcs to determine the cluster's mass. By comparing that calculated mass to the mass that comes from only luminous objects (the galaxies), they can determine how much dark matter is in the cluster.
时至今日，天文学家已经能否非常肯定的确认暗物质的存在了。他们通过各种技术绘制了大量“暗物质地图”，包括星系团的引力透镜效应。下一步的目标是研究出暗物质到底是什么东西？正如我前面所说，暗物质不会发射、吸收或反射任何形式的光波。它们就像是一种神秘的非重子微粒，这也意味着这些微粒与组成我们常见物质的微粒（质子和中子）是完全不同的。
Today, astronomers are pretty confident that dark matter does in fact exist. They've created numerous "dark matter maps" using different techniques, including gravitational lensing of galaxy clusters. The next step is finding out what it is. As I said earlier, dark matter doesn't emit, absorb, or reflect any type of light. So, it's likely some sort of mysterious non-baryonic particle, meaning it's not made up of the same stuff as ordinary matter (protons and neutrons).
天文学家把非重子暗物质分成两类：热暗物质和冷暗物质。这个名称并不是根据温度来决定的（也就是说你去碰这些物质不会感觉到冷或者热）热暗物质表示在早期宇宙，这类微粒以接近光速在运动，冷暗物质则意味着它们运动的速度要慢的多。
Astronomers split non-baryonic dark matter into two categories: hot and cold. These titles don't mean that if you touch them, you'll feel something that's hot or cold. Hot means that early in the universe, these particles traveled very, very fast — almost at the speed of light. Cold means that early in the universe the particles traveled slower.
微粒的速度和找出暗物质的性质之间有着怎样的联系呢？我们知道，早期宇宙中运动慢的微粒会相互碰撞形成小型物体，而小型物体之间又会相互碰撞和融合，并形成大型物体。天文学家相信，这就是我们宇宙形成和演变的过程。我们今天所观察到的超级天体和漩涡星系都是由那些微小的物质慢慢聚合起来的。天文学家建立了现在宇宙的模型，并用冷质模拟结构的演变。这个模拟显示，暗物质广泛分布于宇宙之中，越明亮的区域，物质密度也越大。
How does particle speed relate to figuring out what dark matter is? Well, slower particles will bunch up into small structures earlier in the universe. Those small structures will eventually collide and merge, forming larger structures. Astronomers believe this is how structure forms and evolves in our universe — smaller structures eventually merge into the massive superclusters and filaments we observe today. Astronomers simulate structure evolution with cold dark matter, and create models that resemble today's universe. This simulation shows dark matter distribution. Brighter areas represent more dense regions.
讲到了这里，那么到底什么是冷暗物质呢？这个问题问的好。科学家目前仍未能确定，但是他们相信这是一种电中性的物质，他们称这种假想的微粒为中性超对称粒子。到目前为止，他们尚未发现这种微粒的存在，但最新的研究表明，发现中性超对称粒子的日子指日可待。 |
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发表于 2012-5-12 10:54:11
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