Extragalactic Astrophysics and Cosmology at Imperial College London

我们在伦敦帝国理工学院天体物理学小组的工作，从最广泛的意义上讲，是为了提高我们对宇宙演化的理解。基本框架是大爆炸模型，这是宇宙在数十亿年前的一次激烈爆炸中开始的画面。当宇宙膨胀时，它会冷却，在引力的作用下，物质会分离和凝聚，形成由恒星组成的星系。我们目前的宇宙图景在最近几十年里发生了巨大的变化，无论是在观测上还是在理论上。最重要的观测改进是望远镜的发展，它绘制了整个波长范围的天空地图，这些波长既短于可见光--伽马射线、X射线、紫外线--又长于可见光--红外、微波、无线电。从这些观察中得出了两个令人惊讶的结果。首先，宇宙中必须有比我们所能看到的更多的物质，暗物质，才能解释星系的强大引力。其次，宇宙的膨胀正在加速，只有当空空间(真空，没有)拥有能量，暗能量时，我们才能理解这一点。因此，我们在伦敦帝国理工学院工作的目的是进行观测和理论研究，以更详细地绘制这幅宇宙演化的图景。我们可以根据波长对我们的研究进行排序，从X射线开始。光的波长越短，光子的能量就越高，所以X射线可以用来研究星系中最高能量的过程，特别是物质对黑洞的吸积，我们正在使用XMM-牛顿卫星来探索这些极端环境。在大多数星系的中心有一个质量非常大的黑洞，质量是太阳的一百万倍以上，最近的一项发现是，黑洞的质量与它所在的星系的质量成正比。我们使用钱德拉卫星的工作旨在了解为什么会发生这种情况，以及对星系形成的影响。在近红外波段，我们正在利用新一代大型探测器来绘制天空的深度地图，并利用这项调查来搜索遥远的类星体。宇宙的膨胀伸展(红移)了来自遥远来源的光，所以最远的来源也是最红移的。从最远的类星体形成之时起，它们发出的光就被伸展到近红外线。通过发现第一批类星体，我们可以分析它们的光，告诉我们当时的情况，当时宇宙只有现在年龄的5%。虽然恒星发出的大部分光都在光学波长附近，但20世纪80年代和90年代的一个重要进展是发现，这些光大部分被燃烧恒星(天文学家称之为尘埃)产生的烟雾所隐藏。光被尘埃吸收，并以远红外波长重新发射。大约一半的恒星光出现在远红外波长，所以我们需要研究这些波长的星系，以全面统计我们今天看到的恒星形成的地点和时间。为此，我们将在今后几年内分析用赫歇尔卫星制作的远红外地图，该卫星将于2008年发射。最后，在微波波段，我们可以看到时间上最远的时间，直到宇宙如此之热，以至于物质以等离子体的形式存在。实际上，整个天空看起来就像太阳的表面，但光已经红移了1000倍，并延伸到微波波长。分析微波天空温度的细微变化可以提供暗物质和暗能量的量的测量。2008年发射的普朗克卫星将提供迄今最详细的微波天空地图。我们将分析这些地图中的结构，以获得这些宇宙学参数的最准确测量。

Our work in the Astrophysics Group at Imperial College London, in the broadest terms, is aimed at improving our understanding of the evolution of the Universe. The basic framework is the Big Bang model, the picture that the Universe began in a hot violent explosion several billion years ago. As the Universe expands it cools, and under the force of gravity matter segregates and condenses to form galaxies composed of stars. Our current picture of the Universe has changed dramatically in recent decades, both observationally and theoretically. The most important observational improvement has been the development of telescopes that map the sky over the complete range of wavelengths, both shorter than visual - gamma-ray, X-ray, ultraviolet - and longer than visual - infrared, microwave, radio. Two surprising results have emerged from these observations. First, there must be much more matter, dark matter, in the Universe than we can see, to explain the strong gravitational pull of galaxies. Second, the expansion of the Universe is accelerating, which we can only understand if empty space (the vacuum, nothing) possesses energy, dark energy. The aim of our work at Imperial College London, then, is to undertake observations and theoretical studies to develop this picture of the evolution of the Universe in more detail. We can order our research by wavelength, starting with X-rays. The shorter the wavelength of light, the higher the energy of photons, so X-rays can be used to study the most energetic processes in galaxies, particularly the accretion of matter onto black holes, and we are using the XMM-Newton satellite to explore these extreme environments. There is a very massive black hole, over a million times the mass of the Sun, at the centre of most galaxies, and a recent discovery has been that the mass of the black hole is proportional to the mass of the galaxy in which it lies. Our work using the Chandra satellite is aimed at understanding why this is and the implications for how galaxies form. At near-infrared wavelengths we are taking advantage of a new generation of large detectors to make a deep map of the sky, and are using this survey to search for distant quasars. The expansion of the Universe stretches (redshifts) the light from far away sources, so the most distant sources are the most redshifted. Light from the furthest quasars, from the time when they were first forming, is stretched to the near-infrared. By discovering the first quasars we can analyse their light to tell us about the conditions at that time, when the Universe was only 5% of its present age. Although stars emit most of their light near optical wavelengths, an important development in the 1980s and 1990s was the discovery that much of this light is hidden by the smoke from burning stars ('dust' to astronomers). The light is absorbed by dust and re-emitted at far-infrared wavelengths. About half of all starlight emerges at far-infrared wavelengths, so we need to study galaxies at these wavelengths to make a complete census of where and when the stars we see today formed. To this end over the next few years we will be analysing far-infrared maps made with the Herschel satellite, due to be launched in 2008. Finally, at microwave wavelengths we can see the furthest back in time, to the point when the Universe was so hot that matter was in the form of a plasma. In effect the entire sky looks like the surface of the sun, but that light has been redshifted by a factor of 1000, and stretched to microwave wavelengths. Analysis of the subtle variations in temperature of the microwave sky can provide a measurement of the amount of dark matter and dark energy. The launch of the Planck satellite in 2008 will provide the most detailed maps yet of the microwave sky. We will analyse the structure in these maps to obtain the most accurate measure of these cosmological parameters.