DFG-NSF: Gravitational Waves from Neutron Star and Black Hole Mergers

LIGO首次直接探测到合并黑洞发出的引力波，是引力物理学的历史性突破。由于我们现在可以探测和研究引力波，一扇通往宇宙的新窗口已经打开。预计会有来自各种其他天体物理来源的观测。一个特别有希望的来源是当两颗中子星围绕彼此运行并合并时。只要这两个紧密的天体相隔很远，后牛顿计算就可以给出关于轨道和发出的引力波的高精度和天体物理上现实的预测。然而，随着这两个天体越来越近，需要对爱因斯坦方程进行完全非线性的计算机数值模拟，以预测最终的灵感合并和随后的合并。这个项目的目的是通过进行数值模拟来详细了解这种天体物理情景。该计划是使用和改进高效的BAM计算机代码，该代码由德国耶拿大学的数值相对论小组和佛罗里达大西洋大学(FAU)的小组开发。这种对发射引力波的理论预测对于从观测到的引力波信号中提取最大信息量是很重要的。该奖项由国际科学与工程办公室共同资助。期望从黑洞双星探测到更多引力波信号，并预期探测到含有中子星的双星，目标是显著提高对此类系统在物理学方面的理论理解，特别是关于中子星自转的理论理解。该项目计划探索天体物理上逼真的致密天体双星。特别是解决了几个关键的物理问题，如：(I)双星中的中子星自转、质量比和偏心率如何影响合并后的灵感、合并和最终对象的演化？(2)研究这类双星发出的引力波：利用解析近似方法，如有效一体方法，研究引力波的频谱并产生混合波形。(3)如何以一致和现实的方式包括中子星初始数据中的磁场？(4)如何通过消除人工数值大气来改进中子星的演化，目前使用的是数值大气，而不是恒星之间的真真空？(V)如何使用双曲面面理来获得更精确的引力波？通过提供引力波模板，拟议的活动对于最大限度地提高LIGO等引力波探测器的科学产出至关重要。中子星合并和由此产生的盘动力学将阐明这样的合并是否是伽马射线暴的引擎的问题，并有助于确定目前未知的超核密度下的状态方程。这项研究将与由布鲁格曼博士领导的耶拿大学相对论小组密切合作进行。这两个机构的教职员工、博士后和学生都计划定期访问。这一交流对FAU和耶拿大学的博士后和学生都有教育意义。

The first direct detection of gravitational waves emitted from merging black holes by LIGO was a historic breakthrough in gravitational physics. Since we can now detect and study gravitational waves, a new window to the universe has been opened. Observations from a variety of other astrophysical sources are anticipated. One particularly promising source is when two neutron stars orbit around each other and merge. As long as the two compact objects are widely separated, post-Newtonian calculations can give highly accurate and astrophysically realistic predictions about the orbits and the gravitational waves emitted. Yet, as the two objects get close, fully non-linear numerical computer simulations of the Einstein equations are required to make predictions about the final part of the inspiral and subsequent merger. This project is aimed at gaining a detailed understanding of such astrophysical scenarios by performing numerical simulations. The plan is to use and improve the highly efficient BAM computer code, which has been developed by the numerical relativity groups at the University of Jena in Germany and the group at Florida Atlantic University (FAU). Such theoretical predictions of the emitted gravitational waves are important to extract the maximum amount of information from observed gravitational wave signals. This award is co-funded by the Office of International Science and Engineering.Expecting the detection of more gravitational wave signals from black hole binaries and anticipating the detection of binaries containing neutron stars, the goal is to significantly enhance the theoretical understanding of such systems in terms of physics, in particular with regard to neutron star spins. This project proposes to explore astrophysically realistic compact-object binaries. In particular, addressing several key physics issues such as: (i) How does neutron star spin, mass ratio and eccentricity in binaries affect the evolution of the inspiral, the merger, and final object after merger? (ii) Study the gravitational waves emitted by such binaries: Investigate spectra of the waves and create hybrid waveforms using analytic approximations such as the effective-one-body approach. (iii) How can magnetic fields in neutron star initial data be included in a consistent and realistic way? (iv) How can neutron star evolutions be improved by removing the artificial numerical atmosphere, that is currently used instead of true vacuum between the stars? (v) How can we use hyperboloidal foliations to obtain more accurate gravitational waves? By providing gravitational wave templates, the proposed activities are critical for maximizing the science output of gravitational wave detectors such as LIGO. Neutrons star mergers and the resulting disk dynamics will shed light on the question whether such mergers are engines for Gamma Ray Bursts, and help determine the currently unknown equation of state at supranuclear densities. This research will be carried out in close collaboration with the relativity group at the University of Jena led by Dr. Bruegmann. Regular visits by faculty, postdocs and students from both institutions are planned. This exchange will have educational benefits for postdocs and students from both FAU and the University of Jena.