Astrophysics at Oxford

牛津大学的天体物理学家正试图确定宇宙的三个基本特征。它是用什么做的？宇宙现在似乎开始了一段加速膨胀的时期，它是由一种相当神秘的物质驱动的，这种物质被称为“暗能量”。爱因斯坦对这些东西有一个理论，他称之为宇宙常数，我们将通过精确测量大约一百万个星系的位置来检验他的理论，更遥远的星系由于引力的弯曲而扭曲，以及遥远超新星的亮度。星系是如何形成的？现在看来，像银河系这样的星系盘有一个相当无聊的过去历史，通过正常物质和“暗物质”的逐渐吸积而增长，并逐渐形成它们的恒星。然而，宇宙中的大多数恒星都在所谓的球状星系中，它们似乎有一段更激动人心的历史。它们似乎是在与超大质量黑洞的增长相关的恒星形成的戏剧性爆发中形成的。我们可以通过做两种截然不同的“实验”来验证这一点：我们可以直接观察非常遥远的星系，由于光速有限，这些星系在宇宙及其内部的星系还很年轻的时候就可以看到；或者，我们可以对附近的星系进行“考古”，寻找令人兴奋的年轻星系的线索，例如，通过在一个休眠的超大质量黑洞周围发现快速移动的气体。像类星体这样的外来物体是如何影响宇宙的？当球状星系还很年轻，它们的黑洞还在生长的时候，它们似乎会产生喷流，向周围环境喷射物质。这个过程加热了宇宙的大部分。在我们自己的星系中也可以看到与所谓的微类星体有关的喷流，由于这些物体的输出在人类的时间尺度上是不同的，所以它们更容易研究，并且应该提供关于喷流如何工作以及它们在星系形成历史中有多重要的线索。

Astrophysicists at Oxford are trying to determine three basic things about the Universe. What is it made of? The Universe now appears to be begun a period of accelerated expansion driven by some rather mysterious stuff known as `dark energy'. Einstein had a theory for what this stuff is, he called it the Cosmological Constant, and we will be testing his theory by measuring precisely the positions of about a million galaxies, the distortions of more distant galaxies due to the bending of light by gravity, and the brightnesses of distant supernovae. How did the galaxies form? It now looks like the disks of galaxies like the Milky Way have had a rather boring past history, growing by gradual accretion of both normal and `dark' matter and forming their stars gradually. Most of the stars in the Universe, however, are in so-called spheroidal galaxies which appear to have had a much more exciting history. They seemed to have formed in dramatic bursts of star formation associated with the growth of supermassive black holes. We can see if this is true by doing two very different sorts of `experiment': we can look directly at very distant galaxies which, because of the finite speed of light, are seen at times when the Universe, and the galaxies within it, were young; or we can do `archaeology' on nearby galaxies looking for clues of an exciting youth, for example by finding fast-moving gas orbiting a dormant supermassive black hole. How do exotic objects like quasars influence the Universe? When spheroidal galaxies were young and their black holes were still growing they seemed to develop jets that squirted material into their environments. This process heated up large parts of the Universe. Jets are also seen in our own Galaxy associated with so-called microquasars, and since the output from these objects varies on human timescales, they are easier to study, and should provide clues as to how jets work and how important they were in the history of galaxy formation.