Astrophysics at Oxford: 2010-2015

牛津大学的天体物理学家正试图确定关于宇宙的六件基本事情。它是什么做的？宇宙似乎正处于加速膨胀时期的开端，这种加速膨胀是由某种被称为“暗能量”的神秘物质驱动的。爱因斯坦对此有一个理论：他称之为宇宙常数。我们将通过测量遥远的爆炸恒星（超新星）的表观亮度来检验他的理论，通过测量由于附近星系的引力使光线弯曲而造成的遥远星系的扭曲，以及通过测量大约一百万个星系的精确位置来检验他的理论。(2)宇宙中氢的历史是什么？氢——宇宙中最丰富的元素——是制造恒星最重要的建筑材料。氢原子在密集的云中结合成分子，这些云为新恒星的诞生提供了温床。我们将使用新的巨型望远镜，在毫米和无线电波长下观测，从而理解宇宙大部分历史中的这一过程。(3)从目前观测到的星系中，我们可以了解到星系是如何形成的？我们参与的大型观测项目可以被视为附近星系的“考古学”，寻找它们历史上重要事件的线索，例如，通过寻找围绕休眠超大质量黑洞运行的快速移动气体。我们还通过研究星系中光学光内外的恒星轨道来研究恒星种群与暗物质之间的关系。(4)关于星系是如何从早期观测到的遥远星系形成的，我们能了解到什么？由于光速有限，当宇宙及其内部的星系还年轻时，人们就能看到遥远的星系，而这些星系往往尘土飞扬，只有通过红外和无线电观测才能有效地研究它们。我们利用广角成像（拍照）和光谱学（将光扩散到组成它的颜色）的结合，绘制出遥远宇宙中星系的大规模分布。我们研究这些系统的形成和演化，有时是在与超大质量黑洞相关的恒星形成的戏剧性爆发中。第一个星系是什么时候形成的？宇宙中的氢在大爆炸后大约30万年形成了原子，但在所谓的再电离时代，大部分被再电离（转化回质子和电子）。我们使用巨大的地面望远镜和卫星（例如哈勃太空望远镜）来研究这些第一批星系，并确定是否与这些星系或其中的恒星的诞生有关的辐射导致了再电离。(6)黑洞如何影响恒星和星系的形成？黑洞通过“吞噬”气体和恒星而成长，这一过程被称为吸积。这一过程似乎通常会以风和喷流的形式产生流出物，后者能够达到非常接近光速的速度。我们在我们自己的星系和遥远的星系中研究这些系统，以确定这种“反馈机制”的物理学原理（黑洞的生长被与黑洞相关的过程驱动的流出物所阻止，尽管是暂时的）。我们的目标是在更大的物理尺度上了解（致密）黑洞对恒星、星系和星系团形成的影响。

Astrophysicists at Oxford are trying to determine six basic things about the Universe. (1) What is it made of? The Universe appears to be at the beginning of a period of accelerated expansion driven by some mysterious stuff known as 'dark energy'. Einstein had a theory for what this stuff is: he called it the Cosmological Constant. We will be testing his theory by measuring the apparent brightnesses of distant exploding stars (supernovae), by measuring the distortions of distant galaxies as light is bent by the gravity of more nearby galaxies, and by measuring the precise positions of about one million galaxies. (2) What is the history of Hydrogen in the Universe? Hydrogen - the most abundant element in the Universe - is the most important building material for making stars. Atoms of Hydrogen combine into molecules within dense clouds, and these clouds provide the nursery for the birth of new stars. We will be using giant new telescopes operating at millimetre and radio wavelengths to observe, and hence understand, this process throughout most of the history of the Universe. (3) What can we learn about how galaxies formed from galaxies observed at current times? We are involved in large observational programmes that can be viewed as 'archaeology' of nearby galaxies looking for clues of important events in their history, for example by finding fast-moving gas orbiting a dormant supermassive black hole. We also study the relation between stellar populations and dark matter by studying the orbits of stars within and beyond the optical light in a galaxy. (4) What can we learn about how galaxies formed from distant galaxies observed at earlier times? Because of the finite speed of light, distant galaxies are seen when the Universe, and the galaxies within it, were young, and often these galaxies are so dusty that they are only effectively studied using infrared and radio observations. We map out the large-scale distribution of galaxies in the distant Universe using a combination of wide-field imaging (taking pictures) and spectroscopy (spreading light out into its constituent colours). We study these systems as they form and evolve, sometimes in dramatic bursts of star formation associated with supermassive black holes. (5) When did the first galaxies form? The Hydrogen in the Universe formed atoms about 300,000 years after the Big Bang, but was largely re-ionized (converted back to protons and electrons) during the so-called Epoch of Reionization. We use giant ground-based telescopes and satellites (e.g. the Hubble Space Telescope) to study these first galaxies and determine whether it was radiation associated with the birth of these galaxies, or stars within them, that was responsible for the re-ionization. (6) How do black holes influence star and galaxy formation? Black holes grow by 'gobbling up' gas and stars in a process called accretion. This process seems commonly to yield outflows in the form of winds and jets, the latter capable of reaching speeds very close to the speed of light. We study these systems in our own galaxy and in distant galaxies to determine the physics of such 'feedback mechanisms' (growth of the black hole is halted, albeit temporarily, by outflows driven by processes associated with the black hole). Our aim is to understand the influence of (compact) black holes on the formation of stars, galaxies and clusters of galaxies on much large physical scales.