Investigations in Gravitational Radiation

爱因斯坦的广义相对论(GR)预测，处于强引力场中的动力系统将以引力辐射的形式释放大量能量。引力波是时空结构中的涟漪，以光速从其来源传播，携带有关导致其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的最难以捉摸的信号之一。旨在检测它们的实验已经发展了几十年，但直到现在，灵敏度才达到可能在几年内真正检测到的水平。全球的干涉探测器网络包括德国-英国的GEO600、法国-意大利的处女座和美国的激光干涉仪引力波天文台。这些探测器都达到了接近其设计目标的灵敏度，并获得了迄今为止最敏感的数据。不同项目之间的合作使得能够在大部分天空中对广泛的来源和现象敏感地持续获取数据。来自GEO、LIGO和处女座的数据已经开始影响我们对天文现象的理解。例如，使用这些探测器的最新观测已经(A)表明Crab脉冲星的辐射功率中只有不到2%是引力波，(B)排除了将双星中子星合并为伽马暴070201(如果它发生在M31)的可能性，以及(C)对随机引力波背景的强度设定了新的最佳上限。虽然目前的观测阶段(大约2010-2011年)有真正的机会产生第一次探测--可能是从致密的双星聚合，但不能保证。然而，有很大的信心，先进的探测器将例行观测引力波。加的夫和格拉斯哥的小组已经发起并领导了对天文来源的搜索，这要归功于自八年前开始第一次数据采集以来一直得到支持的算法和分析工作。我们提议继续改进GEO600的方案，并参与描述和分析地球观测组织和全球干涉仪网络所产生的数据。特别是，我们将搜索*聚合的双中子星、中子星-黑洞双星和黑洞双星*可能来自超新星的引力波爆发，以及*来自脉冲星和其他旋转中子星的连续信号。与此同时，我们正在提议研究和开发探测器前沿。探测器的灵敏度主要受限于与反射镜的衬底、其反射涂层和其悬挂元件相关的热噪声，以及由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做出创新性的改进。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的升级方面处于领先地位，并在介质和波导镜涂层、硅衬底和低温悬浮液领域增强高级LIGO计划和未来的干涉仪。总而言之，格拉斯哥、卡迪夫和斯特拉斯克莱德小组的目标是在其创新发展的基础上，率先使用探测器直接探测引力波。一旦达到这一里程碑，常规观测将帮助我们将这一辐射作为一种观测和理论工具，以了解超新星和中子星的核心、伽马射线爆发引擎、黑洞和中子星之间的相互作用等。特别是，聚结的致密双星是自我校准的标准蜡烛或警报器，这将是宇宙学的一种新的精密工具，并将使广义相对论的强大现场测试成为可能。

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.