Gravitational Waves at the University of Portsmouth - 24/25

引力波是爱因斯坦的广义相对论中最引人注目的预言之一。这些可以被认为是时空结构中以光速传播的涟漪。引力波是由非球对称的加速质量发射的，例如两个黑洞或中子星相互环绕。引力波是非常难以探测的，但在过去的几年里，包括Advanced LIGO、Advanced Virgo和KAGRA在内的大型天文台已经达到了观测引力波的必要灵敏度。2015年9月观测到的第一个引力波信号是由两个质量约为太阳35倍的黑洞在大约10亿光年外碰撞产生的。从那时起，已经观察到另外12个双黑洞合并。迄今为止，引力波天文学的最高成就是在2017年8月观测到两颗合并的中子星。这个信号很特别，因为它是费米天文台同时观测到的伽马射线爆发，然后，在引力波天空定位区域向天文学家发布后，在整个电磁波谱中观测到。“多信使”天文学（观测具有多个“信使”的源，如引力波、光子、中微子或宇宙射线）的潜力是显着的。我们可以在最极端的环境中探索爱因斯坦理论的有效性。我们可以独立测量宇宙加速的速率。我们可以探测中子星星深处的物质性质，那里的物质密度很大，一茶匙的物质就像地球上的一座山一样重。然而，所有这些都需要我们实际观察这些引力波信号，可靠地估计它们的源参数，并且要足够快，以便我们可以提醒天文学家寻找一个符合的信号。在这项资助中，我们将开发方法来迅速搜索来自Advanced LIGO，Advanced Virgo和KAGRA的数据，以观察合并紧凑物体的引力波特征。我们将确保这些观测结果迅速定位在天空中，并将这些信息迅速传达给天文学家。我们还将开发技术来进一步提高这些搜索的灵敏度，使我们能够更深入地挖掘噪音，并观察到迄今为止尚未观察到的新型紧凑双星合并。我们还将努力更好地理解LIGO天文台产生的数据。这些引力波观测台是高度精确和复杂的机器，产生一个没有仪器噪音的“干净”数据流是一个重大挑战。我们将与LIGO站点的仪器科学家合作，以“验证”这些仪器记录的数据。这将使我们能够识别数据流中任何“缺陷”的原因。这些不完美的地方，通常在数据中表现为爆炸和哨声，损害了我们观察真正天体物理信号的能力。此外，如果我们在评估我们观察到的源的参数时不包括噪声数据的影响，我们就有可能为我们的观察引用不正确或有偏见的参数。通过识别这些信号的原因，我们可以修复仪器以阻止它们发生。我们也可以理解这些爆炸声和哨声对我们理解新观测结果的能力的影响。这个问题在在线项目Gravity Spy中得到了说明。如果有兴趣，你可以访问重力间谍网站，并帮助我们在这方面的努力！

Gravitational waves are one of the most remarkable predictions of Einstein's General Theory of Relativity. These can be thought of as ripples in the fabric of spacetime propagating at the speed of light. Gravitational waves are emitted by non-spherically symmetric accelerated masses, such as two black holes or neutron stars orbiting each other. Gravitational waves are incredibly difficult to detect, but in the last years large-scale observatories, including Advanced LIGO, Advanced Virgo and KAGRA, have reached the necessary sensitivity to observe gravitational waves.The first gravitational-wave signal observed in September 2015 was produced by two black holes roughly 35 times the mass of our Sun colliding approximately one billion light years away. Since then twelve additional binary black hole mergers have been observed. The crowning achievement of gravitational-wave astronomy to date was the observation of two merging neutron stars in August 2017. This signal was special because it was observed simultaneously as a gamma-ray burst by the Fermi observatory and then, following the release of the gravitational-wave sky localisation region to astronomers, was observed across the electromagnetic spectrum.The potential of "multi-messenger" astronomy (observing sources with multiple "messengers", such as gravitational-waves, photons, neutrinos or cosmic rays) is remarkable. We can explore the validity of Einstein's theory in one of the most extreme environments possible. We can make an independent measurement of the rate at which the Universe is accelerating. We can probe the nature of matter deep within a neutron star, where it is so dense that 1 teaspoon of material weighs as much as a mountain on the Earth.However, all of this requires us to actually observe these gravitational-wave signals, reliably estimate their source parameters and to do it quickly enough that we can alert astronomers to search for a coincident signal. In this grant we will develop methods to promptly search data from Advanced LIGO, Advanced Virgo and KAGRA to observe the gravitational-wave signature of merging compact objects. We will ensure that such observations are rapidly localised on the sky and that this information is rapidly communicated to astronomers. We will also develop techniques to further improve the sensitivity of these searches, allowing us to dig deeper into the noise, and to observe new types of compact binary mergers that have not been observed to date.We will also work to better understand the data that is produced by the LIGO observatories. These gravitational-wave observatories are highly precise and complex machines and producing a "clean" data stream free of instrumental noise is a significant challenge. We will work in collaboration with the instrument scientists at the LIGO sites to "characterise" the data being recorded by these instruments. This will allow us to identify the causes of any "imperfections" in the data stream. These imperfections, which often show up as bangs and whistles in the data, harm our ability to observe genuine astrophysical signals. Additionally, if we do not include the effects of noisy data when assessing the parameters of sources that we observe, we run the risk of quoting incorrect, or biased, parameters for our observations. By identifying the causes of such signals we can fix the instrument to stop them happening. We can also understand the effect that these bangs and whistles will have on our ability to understand our new observations. This problem is illustrated in the online project Gravity Spy. If interested, you can visit the Gravity Spy website and help us in this effort!