Investigations in Gravitational Radiation

爱因斯坦的广义相对论预言，处于强引力场中的动力系统会以引力辐射的形式释放出大量的能量。引力波是时空结构中的涟漪，以光速从源头传播，携带着有关引力波发射的物理过程的信息，这是其他任何方式都无法获得的。它们是来自宇宙最深处最难以捉摸的信号之一。旨在探测它们的实验已经进行了几十年，但直到现在，灵敏度才达到可能在几年内真正探测到的水平。干涉探测器的全球网络包括德国-英国GEO600，法国-意大利Virgo和美国激光干涉引力波天文台（LIGO）。这些探测器都达到了接近其设计目标的灵敏度，并收集了迄今为止最敏感的数据。不同项目之间的合作可以实现对大部分天空中各种来源和现象的持续数据采集。来自GEO、LIGO和Virgo的数据已经开始影响我们对天文现象的理解。例如，这些探测器的最新观测结果(a)表明蟹状星云脉冲星的辐射能量中只有不到2%来自引力波，(b)排除了GRB 070201的前身是合并的双中子星（如果它发生在M31中），(c)设定了随机引力波背景强度的新最佳上限。虽然目前的观测阶段（大约2010-2011年）有可能产生第一次探测——可能来自紧凑的双星合并，但这并不能保证。然而，有很大的信心，先进的探测器将定期观测引力波。卡迪夫和格拉斯哥的研究小组发起并领导了对天文来源的搜索，这要归功于自八年前第一次数据采集开始以来一直支持的算法和分析工作。我们提出了一个持续改进GEO600的计划，并参与GEO和全球干涉仪网络的结果数据的表征和分析。特别地，我们将进行中子星合并双子星、中子星-黑洞双子星和黑洞双子星的搜索，可能来自超新星的引力波爆发，以及脉冲星和其他旋转中子星的连续信号。与此同时，我们正在提议在探测器前沿进行研究和开发。探测器的灵敏度主要受限于与反射镜衬底、反射涂层及其悬浮元件相关的热噪声，以及用于提供照明的光的量子性质所产生的噪声。因此，我们的研究目标是在这些领域进行创新改进。特别是，我们在二氧化硅悬浮液、光学和干涉测量领域的GEO和LIGO升级方面发挥了主导作用，并在介电和波导反射镜涂层、硅衬底和低温悬浮液领域增强了高级LIGO计划和未来干涉仪的功能。总之，格拉斯哥、卡迪夫和斯特拉斯克莱德研究组的目标是，利用基于他们创新发展的探测器，率先直接探测到引力波。一旦达到这一里程碑，常规观测将帮助我们利用这种辐射作为观测和理论工具来理解超新星和中子星的核心、伽马射线爆发引擎、黑洞和中子星的相互作用等。特别是，合并紧密双星是自我校准的标准蜡烛，或称警报器，它将成为宇宙学的一种新的精密工具，并将使广义相对论能够进行强有力的现场测试

Einstein's General Theory of Relativity (GR) predicts that dynamical systems in strong gravitational fields will release vast amounts of energy in the form of gravitational radiation. Gravitational waves are ripples in the fabric of spacetime and travel from their sources at the speed of light, carrying information about physical processes responsible for their emission, obtainable in no other way. They are among the most elusive signals from the deepest reaches in the Universe. Experiments aimed at detecting them have been in development for several decades, but only now are sensitivities reaching levels where real detection is possible within a few years. The worldwide network of interferometric detectors includes the German-UK GEO600, the French-Italian Virgo and the American Laser Interferometer Gravitational-Wave Observatory (LIGO). These detectors have all reached sensitivities close to their design goals and have taken the most sensitive data to date. Cooperation amongst different projects enables continuous data acquisition, with sensitivity to a wide range of sources and phenomena, over most of the sky. Data from GEO, LIGO and Virgo, has already begun to impact our understanding of astronomical phenomena. For example, the most recent observations with these detectors have (a) shown that less than 2% of the Crab pulsar's radiated power is in gravitational waves, (b) ruled out merging binary neutron stars as the progenitor of GRB 070201 (if it occurred in M31) and (c) set a new best upper limit on the strength of the stochastic gravitational-wave background. While the present phase of observations (circa 2010-2011) have a real chance of producing the first detections - possibly from compact binary coalescences, there can be no guarantees. However there is great confidence that the advanced detectors will routinely observe gravitational waves. The Cardiff and Glasgow groups have initiated and led searches for astronomical sources, thanks to the algorithmic and analysis effort that has been supported since the first data taking runs began eight years ago. We propose a programme of continued improvement to GEO600 and to be involved in the characterization and analysis of the resulting data from GEO and the worldwide network of interferometers. In particular we will be carrying out searches for * coalescing binary neutron stars, neutron star-black hole binaries, and black hole binaries * bursts of gravitational waves that may originate from supernovae, and * continuous signals from pulsars and other rotating neutron stars. In parallel, we are proposing research and development on the detector front. Detector sensitivity is mainly limited by thermal noise associated with the substrates of the mirrors, their reflective coatings, and their suspension elements, as well as by noise resulting from the quantum nature of the light used to provide illumination. Thus our research is targeted towards making innovative improvements in these areas. In particular we are taking leading roles in the upgrading of GEO and LIGO in the areas of silica suspensions, optics and interferometry, and for enhancements to the Advanced LIGO program and future interferometers in the areas of dielectric and waveguide mirror coatings, silicon substrates and cryogenic suspensions. In summary, the goal of the Glasgow, Cardiff and Strathclyde groups is to lead the first direct detection of gravitational waves using detectors based on their innovative developments. Once this milestone is achieved, routine observations will help us use this radiation as an observational and theoretical tool to understand * cores of supernovae and neutron stars, * gamma-ray burst engines, * the interactions of black holes and neutron stars, etc. In particular, coalescing compact binaries are self-calibrating standard candles, or sirens, which will be a new precision tool for cosmology and will enable strong field tests of general relativity