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，现在已经达到了预期在几年内探测到的灵敏度水平。干涉探测器的全球网络包括德国-英国的GEO600，法国-意大利的Virgo，美国的激光干涉引力波天文台（LIGO），以及正在建设中的新探测器——日本的KAGRA。以前的探测器都达到了接近设计目标的灵敏度，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的数据已经增加了我们对天文现象的理解。在154次伽马射线爆发时对引力波的搜索，得到了有史以来最好的排除距离，并为银河系外软伽马中继器的来源提供了证据。在最近的运行中，双黑洞的距离达到了300mpc，速率上限现在非常接近一些天体物理模型的预期。对船帆座脉冲星引力波的搜索已经为辐射强度设定了一个上限，这个上限大大低于从观测到的脉冲星自旋下降速率所期望的上限，相当于该恒星椭圆率的千分之一的极限。虽然最近和目前的观测可能产生探测，但不能保证。然而，有很大的信心，目前正在建设的先进探测器将定期观测引力波。先进的LIGO探测器是基于英国为GEO 600开发的准单片二氧化硅悬浮液概念和我们在GEO 600的德国同事开发的高功率激光器。先进的处女座探测器也使用了硅悬浮技术的一种变体。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。我们提出了一项计划，以GEO600的持续运行和最近LIGO/Virgo科学运行的数据分析为基础，充分利用高级LIGO （aLIGO）的数据。特别是，我们将深入搜索合并的中子星、中子星-黑洞双星和黑洞双星；可能源自超新星的引力波爆发；脉冲星和其他旋转中子星发出的连续信号；通过相互关联方法探测到的引力波，包括宇宙背景。同时，我们提出了探测器的研究和开发。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，以及由用于传感的光的量子性质引起的噪声。我们的研究目标是在这些领域进行创新改进。我们主要负责aLIGO中的二氧化硅悬浮液，以及aLIGO探测器的增强和升级开发，以及用于低热噪声的镜面涂层，硅衬底，低温悬浮液和改进干涉仪拓扑以对抗量子噪声的领域。

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, and are now reaching sensitivity levels where detection is expected within a few years.The worldwide network of interferometric detectors includes the German-UK GEO600, the French-Italian Virgo, the American Laser Interferometer Gravitational-Wave Observatory (LIGO) and is being enhanced with a new detector under construction - KAGRA in Japan. The former 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, have already increased our understanding of astronomical phenomena. Search for gravitational waves at the times of 154 gamma-ray bursts has allowed the best ever exclusion distances and provided evidence for extra-Galactic sources of soft-gamma repeaters. The distance reach for binary black holes in the most recent runs is 300 Mpc and the rate upper limits are now very close to that expected in some of the astrophysical models. The search for gravitational waves from the Vela pulsar has set an upper bound on the strength of radiation that is significantly below that expected from the observed spin down rate of the pulsar, corresponding to a limit on the star's ellipticity of a part in a thousand. While recent and current observations may produce detections, there can be no guarantees. However, there is great confidence that the advanced detectors currently in construction will routinely observe gravitational waves. The advanced LIGO detectors are based on the quasi-monolithic silica suspension concept developed in the UK for GEO 600 and on the high power lasers developed by our German colleagues in GEO 600. The Advanced Virgo detector also uses a variant of the silica suspension technology. 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 that leads to full exploitation of data from Advanced LIGO (aLIGO), building on both continuing operation of GEO600 and analysis of data taken in the most recent LIGO/Virgo science runs. In particular we will be carrying out deep searches for* coalescing binary neutron stars, neutron star-black hole binaries, and black hole binaries* bursts of gravitational waves that may originate from supernovae, * continuous signals from pulsars and other rotating neutron stars,* gravitational waves detected by cross-correlation methods, including a cosmological background.In parallel, we propose detector research and development. 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 in sensing. Our research is targeted towards making innovative improvements in these areas. We have major responsibilities for the silica suspensions in aLIGO, and in the development of enhancements and upgrades to the aLIGO detectors, in the areas of mirror coatings for low thermal noise, silicon substrates, cryogenic suspensions and improved interferometer topologies to combat quantum noise.