WoU-MMA: Targeted Search for Binary Mergers with Multiple Harmonics in Gravitational Wave Data

黑洞和中子星是我们在宇宙中看到的恒星的一些最终终点。这些质量大、密度高的致密天体很难通过它们的电磁辐射被探测到。自2016年以来，LIGO、Virgo和KAGRA等干涉探测器通过致密天体相互融合时发出的引力波来帮助探测致密天体。随着探测器灵敏度的提高，这一领域已经从值得注意的单一探测时代进入了一个我们可以系统地调查宇宙中致密物体数量的时代。最有趣和最有信息量的检测是那些显示信号中的复杂性(如泛音和调制)的检测，因为这些影响最终会告诉我们这些二进制代码所在的环境；现有的搜索没有考虑到这些影响，因为它们使搜索算法复杂化。这项研究计划将提高搜索对此类信号的敏感性，从而将研究范围扩大到参数空间最有趣的部分--最高的质量合并(一直延伸到数百个太阳质量)，以及具有非常高质量比和错位自转的双星。探测和描述这些特殊的系统可以回答一系列基本的天体物理问题，例如恒星质量的黑洞和星系中心更大质量的黑洞之间的联系，最大质量恒星(塌缩为最大质量黑洞)的恒星演化的终点，以及黑洞双星的组装方式(从组件自转的配置和大小)。在更广泛的意义上，该研究计划还将促进NSF围绕LIGO应变数据建立外部社区的长期愿景，为分析引入新的视角，并最大限度地发挥先前存在的开放数据的潜力：这将通过为该领域举办研讨会、与当地研究人员合作以及在高中生中传播思想的现有大学项目来实现。该研究的动机是存在微妙的效应，如最响亮的个人信号中的高次谐波和广义相对论进动，以及已经检测到的天体物理人口的试探性趋势。这些事件是通过搜索管道发现的，这些管道对信号做出了简化的假设，即只包括相关物理效应的子集；最重要的假设是，源是具有与轨道角动量对齐的分量自旋的准圆形双星，并且波形由单一谐波组成。其目的是开发一种新的搜索方法，它结合了高次谐波的影响，甚至可能是进动，因此对更广泛的信号范围敏感。这将需要重新检查所有搜索算法，以便在不付出太大计算代价的情况下实现更高的敏感度。主要任务是：(A)组织模板，以考虑信号空间的多样性，同时仍然保持最大化几个几何参数的能力，这将控制模板库的大小；(B)设计以最佳方式组合各次谐波以及来自多个探测器的数据的方法。这一步对于正确地进行是至关重要的，以避免由于扩大搜索空间而对现有信号失去敏感度。这些方法建立在常规用于参数推断的现有全物理波形模型和之前使用简化波形模型的搜索结果的基础上。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Black holes and neutron stars are some of the final endpoints of stars that we see in the universe. These massive and dense compact objects are hard to detect by their electromagnetic emission. Since 2016, interferometric detectors such as LIGO, VIRGO, and KAGRA have helped detect compact objects through the gravitational waves that they emit as they merge with each other. As the detectors' sensitivity improved, the field has moved from the era of notable single detections to one in which we can systematically survey the population of compact objects in the universe. The most interesting and informative detections are those that show complexity (such as overtones and modulations) in the signal, as these effects ultimately inform us about the environment these binaries were assembled in; existing searches do not account for these effects as they complicate the search algorithms. This research program will boost the sensitivity of searches to such signals, and hence extend the reach in the most interesting parts of parameter space - the highest mass mergers (extending all the way to several hundred solar masses), and binaries with very high mass ratios and misaligned spins. Detecting and characterizing these special systems can answer a range of fundamental astrophysical questions, such as the link between stellar-mass black holes and the more massive ones at the centers of galaxies, the endpoint of stellar evolution for the most massive stars (which collapse to the most massive black holes), and the means by which black hole binaries are assembled (from the configurations and sizes of the component spins). In a broader sense, the research program will also facilitate NSF’s long-term vision of building an outside community around the LIGO strain data, introduce fresh perspectives to the analyses, and maximize the potential of pre-existing open data: this will be realized by means of a workshop for the field, and collaborations with local researchers and established university programs to disseminate ideas among high school students.The research is motivated by the presence of subtle effects such as higher harmonics and general-relativistic precession in the loudest individual signals, as well as tentative trends in the astrophysical population, that have already been detected. These events were found by search pipelines that made simplifying assumptions about the signals, i.e., included only a subset of the relevant physical effects; the most important assumption being that the sources are quasi-circular binaries with component spins that are aligned with the orbital angular momentum, and that the waveform is composed of a single harmonic. The aim is to develop a new search that incorporates the effects of higher harmonics, and possibly even precession, and hence is sensitive to a wider range of signals. This will require revisiting all search algorithms in order to achieve the increased sensitivity without paying too large a computational price. The main tasks are to (a) organize templates to account for the diversity in the space of signals, while still retaining the ability to maximize over several geometric parameters, which will control the template bank’s size, and (b) devise methods of optimally combining the individual harmonics, as well as data from multiple detectors. This step is crucial to do correctly to avoid losing sensitivity to existing signals due to enlarging the search space. The methods build on existing full-physics waveform models that are routinely used for parameter inference, and insights from previous searches that used simplified waveform models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.