早期宇宙中的烟雾是如何消散的？
早期宇宙中的星系，如哈勃望远镜（见插图）拍下的这些暗淡的天体，为宇宙的电离化提供了帮助，使其在10亿岁时变成了透明状态。About 300,000 years after the big bang, the universe was like a smoke-filled chamber from which light could not escape. By the time the universe was a billion years old, the smoke—actually a gas of light-trapping hydrogen—had cleared almost entirely, allowing stars and galaxies to become visible. But exactly what cut through the haze has been one of the big questions in astrophysics. Now, by analyzing images taken by the Hubble Space Telescope, researchers have come close to confirming their best guess: the smoke was cleared away by a blaze of ultraviolet radiation from the earliest galaxies.
在宇宙大爆炸之后大约30万年时，宇宙就像一个充满烟雾的房间，无法透出光亮。那种烟雾实际上是一种可以阻拦光线的氢气，当宇宙10亿岁的时候，烟雾全部消散，使恒星和星系显露出来。然而，究竟是什么驱散了烟雾？这一直是天体物理学上的一个重大问题之一。现在，通过分析哈勃太空望远镜所拍下的照片，研究人员几乎证实了他们的最佳猜测：烟雾是被最早期星系所爆发的紫外线辐射驱散的。
About 300,000 years after the big bang, the first atoms formed as protons combined with electrons to make hydrogen. Because hydrogen atoms trap light, the young universe entered its "dark ages." Then about a billion years later, some sort of radiation had ionized the hydrogen, turning it into a transparent broth of electrons and ions over a period of several hundred million years; the period is known as the Epoch of Reionization.
宇宙大爆炸大约30万年之后，随着质子和电子结合生成了氢元素，第一批原子形成了。由于氢原子阻拦光线，年轻的宇宙进入了“黑暗时期”。接着，大约在10亿年之后的几亿年时间里，某种辐射将氢电离成为透光的浆状物，浆状物由电子和离子构成。这个时期被称为“再电离时期”。
Although researchers had always suspected radiation from galaxies as the primary source of ionization energy, they did not have much evidence to back up the idea. That's why some alternate mechanisms for ionization weren't ruled out—such as intense light emitted by early black holes as they gobbled up matter, or the energy released by the dark matter particles annihilating one another. The problem was that astronomers had hardly any data from the early universe, which until recently was too faint even for Hubble to get any good pictures of.
尽管研究人员过去一直怀疑来自星系的辐射是电离能的主要源泉，但是他们没有多少证据来说明这一观点，因此其他的电离化机制——例如黑洞吞噬物质时释放的强光、暗物质粒子湮灭时释放的能量等，也没有被排除在外。问题在于：此前，天文学家们几乎没有早期宇宙的资料，早期宇宙太昏暗了，甚至哈勃太空望远镜也不能拍到清晰的图片。
The Hubble's new Wide Field Camera 3 (WFC3), mounted on the space telescope in 2009, changed all that. It took pictures showing faint galaxies from a mere 600 million to 800 million years after the big bang, including one reported 2 weeks ago as the most distant object observed to date. And now a team lead by Brant Robertson, an astrophysicist at the California Institute of Technology in Pasadena, has used images from WFC3 to pin much of the responsibility for reionization on light from those early galaxies.
哈勃太空望远镜上的新一代照相机——广角相机3号（WFC3），改变了上述状况，该相机是2009年安装上去的。WFC3拍下的图片显示了宇宙大爆炸之后仅仅6亿年至8亿年时的昏暗星系，其中包括一个迄今为止所观察到的最遥远的天体，两个星期前曾报道过该天体的情况。现在，帕萨迪纳市加州理工学院的天体物理学家布兰特·罗伯特森带领一个研究小组，利用WFC3拍摄的图像，确定了造成再电离的主要原因是来自那些早期星系的光线。
By counting up the number of such galaxies and extrapolating to fainter galaxies that can't be spotted in the pictures but likely exist, Robertson and his colleagues estimated the number of ultraviolet photons emitted by these early objects. Then, they calculated what fraction of these photons made it all the way to the intergalactic medium, which at the time was hydrogen. From the calculations, the researchers determined that there were enough photons to ionize almost all of the hydrogen by the time the universe became transparent.
通过清点那些星系的数量，并且对在图片中不能看到但很可能存在的较为暗淡的星系进行数量上的推断，罗伯特森及同事估算出那些早期星系释放的紫外光子数量。然后，他们计算出这些光子中有多少一路到达星系际介质中，当时的星系际介质就是氢。通过这些计算，研究人员确定：到宇宙透光之时，拥有足够的光子来电离所有的氢。
Although researchers have yet to learn much about the stellar populations within these galaxies, one thing they do know is that "the galaxies are extremely blue," says Robertson. That indicates that a lot of new stars are forming inside them, and "they are producing lots of ionizing photons," he says.
罗伯特森说，尽管研究人员仍需要更多地去了解这些星系中的恒星群落，但有一点的确是了解的：这些星系的颜色是碧蓝碧蓝的。他说：“这表明有许多新恒星正在这些星系中形成，而且正在产生许多具有电离作用的光子。”
However, Robertson points out that the uncertainty in his team's estimation of how many faint galaxies there are is still too high to definitively conclude that radiation from galaxies was enough to do all the ionizing work. In order to get more certainty, he and his fellow authors want to use WFC3 to take even deeper pictures of space by pointing at the same patch of sky for longer durations. That will help spot the fainter galaxies, Robertson says, eliminating the need for extrapolation.
然而罗伯特森指出：他的研究小组在估计有多少暗淡的星系方面存在不确定性，由于估计的数量太多，因而还不能最终得出这个结论——来自星系的辐射足以完成所有的电离任务。为了得到更加明确的结论，罗伯特森及同事打算利用WFC3更长时间地对准同一片天区，来拍摄太空更加深邃之处的图片。罗伯特森称，这样将有助于发现那些较为暗淡的星系，不再需要使用推断法。
Martin Haehnelt, an astrophysicist at the University of Cambridge in the United Kingdom who was not involved in the work, agrees that further observations are needed. But both he and Volker Bromm, an astrophysicist at the University of Texas, Austin, say the work is a significant advance toward understanding reionization. Says Haehnelt, "The new observations with Hubble WFC-3 are a huge step forward."
英国剑桥大学的天体物理学家马丁·黑耐尔特没有参与这项研究，但他也承认需要进一步观测。然而，黑耐尔特和德克萨斯大学奥斯汀分校的天体物理学家沃尔克·布罗姆都表示，这项研究在理解再电离方面取得了重大进展。黑耐尔特说：“利用哈勃太空望远镜上的WFC3所进行的新一轮观测使研究工作向前迈出了一大步。”
译自：美国《科学》杂志网站（3 November 2010, 2:33 PM）
http://blog.sina.com.cn/s/blog_59b535840100nvg3.html ::0020:: 翻译的真好！ 类似的文章我以前翻译过，但此篇有些内容是不同的。
欢迎楼主继续翻译，以后请发翻译版，并附图。 在宇宙大爆炸之后大约30万年时，宇宙就像一个充满烟雾的房间，无法透出光亮。那种烟雾实际上是一种可以阻拦光线的氢气，当宇宙10亿岁的时候，烟雾全部消散，使恒星和星系显露出来
q零度星系 发表于 2010-11-28 13:34 http://www.astronomy.com.cn/bbs/images/common/back.gif
这个似乎有点问题：
1、退耦之后宇宙应该是透明的，现在观测的微波辐射就是退耦时的产物
2、宇宙退耦到第一代恒星产生称为宇宙的黑暗时期，这时不是不能透光而是没有光，“烟雾消散”的过程称为再电离
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