Gravitational Wave Astrophysics with LIGO: The Oregon Experimental Relativity Group

2015年，LIGO首次发现了引力波，这是实验科学的胜利，也是基础物理学的重大突破。它证实了爱因斯坦一个世纪前提出的广义相对论的一个重要预言。它的重要性反映在2017年诺贝尔物理学奖授予NSF PIs Weiss， Thorne和Barish。美国国家科学基金会的激光干涉引力波天文台（LIGO）在2015年观测到的引力波是两个黑洞碰撞产生的，每个黑洞的质量大约是太阳的30倍。如此惊人的事件只有通过引力波才能观测到——引力波是时空中的涟漪，向外传播，穿越宇宙数百万光年，最终可能会被LIGO天文台观测到。它强调了LIGO在天文学、天体物理学和宇宙学方面做出独特贡献的潜力。自2015年以来，LIGO已经记录了大约100次这样的碰撞，大多数是黑洞对，但也有黑洞与中子星和中子星对的碰撞。事实上，有了这个独特的收集，LIGO已经能够对宇宙中大质量恒星的起源做出新的陈述，并与更传统的天文观测相结合，为我们在地球上的生命至关重要的重元素的起源提供了新的见解。与此同时，通过艰苦的工作和创新，LIGO天文台对越来越小的时空涟漪变得越来越敏感。这使得有可能有新的发现——从不同类型的天体物理物体（不是黑洞和/或中子星对的物体）观测引力波。该奖项将为LIGO引力波搜索提供新的来源，即坍缩黑洞和极度磁化的中子星。前者与被称为（长）伽马射线暴（GRBs）的爆炸现象有关，而后者与磁星x射线耀斑和快速射电暴有关。就像2015年的发现一样，人们可以预期，从新来源获得的最初发现将会带来新的天体物理学见解和理解。该奖项将主要用于支持俄勒冈大学（UO）的研究生，他们将开发新方法来进行这些新颖的搜索。与UO最近的历史保持一致，预计这些学生将继续在该领域工作，或者进入私营部门，在那里他们将把他们在数据科学和分析方面的专业知识用于其他目标。UO小组将继续向公众展示结果，并为俄勒冈州的高中教师举办研讨会，这样他们就可以反过来把最新的研究成果带给学生。该奖项将结合天体物理学的两个新兴领域，以探测来自非紧密双星合并的祖星的引力波来源。第一个领域是多信使天文学（MMA）。第二个领域是寻找没有波形模板的引力波信号——即所谓的突发分析。搜索将从根本上依赖于MMA方法。来自天体物理能量事件的x射线、伽玛射线或无线电瞬态信号提供了一个时间和天空位置，这也标志着假定的引力波发射的一个插曲。这些为引力波数据分析提供了所谓的触发器，将触发器附近的时间标记为“源”（或信号）数据段，并将非源数据作为背景。相对于背景的过量信号功率是与触发伽马射线暴（GRB）、磁星x射线耀斑或快速射电暴（FRB）相关的潜在引力波探测的指标，视情况而定。这种方法不依赖于引力波的任何预先确定的数学形式。除了搜索之外，该小组还将开发方法，从可靠的探测中确定天体物理上有趣的参数，或者从非观测中约束这些参数，视情况而定。例如，这些参数可能包括与磁星搜索的中子星状态方程有关的参数，或者与长伽马射线暴的吸积盘性质有关的参数。俄勒冈小组在以前的MMA-GW突发搜索和相应的方法开发方面有着强大的领导历史。如今，LIGO观测站的灵敏度不断提高，使得这类搜索有可能带来新的发现。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The initial discovery of gravitational waves in 2015 by LIGO represented a triumph of experimental science and a momentous breakthrough in fundamental physics. It confirmed a crucial prediction of General Relativity made by Einstein a century earlier. Its importance was reflected by the 2017 Nobel Prize in physics awarded to NSF PIs Weiss, Thorne, and Barish. The gravitational waves observed by NSF's Laser Interferometric Gravitational-Wave Observatory (LIGO) in 2015 resulted from the collision of two black holes, each roughly thirty times more massive than our sun. Such an amazing event is only observable by gravitational waves -- the ripples in spacetime which propagate outward across the cosmos for millions of light-years and may eventually be noticed by the LIGO observatories. It underscores the potential of LIGO to make unique contributions to astronomy, astrophysics, and cosmology. Since 2015, LIGO has recorded approximately 100 such collisions, mostly of pairs of black holes, but also of black holes with neutron stars, and pairs of neutron stars. Indeed, with this unique collection in hand, LIGO has been able to make new statements about the origins of massive stars in the universe, and paired with more conventional astronomical observations, provided new insights into the origin of heavy elements which are crucial to our life on Earth. Meanwhile, through hard work and innovation, the LIGO observatories have become increasingly sensitive to ever smaller spacetime ripples. This has enabled the potential for new discoveries -- the observation of gravitational waves from different types of astrophysical objects, objects which are not pairs of black holes and/or neutron stars. This award will set up LIGO gravitational wave searches from new sources, namely collapsing black holes and extremely magnetized neutron stars. The former are associated with the explosive phenomena known as (long) gamma-ray bursts (GRBs), while the latter are associated with magnetar x-ray flares and fast radio bursts. As was the case for the 2015 discovery, it might be expected that initial discoveries from new sources will be followed by new astrophysical insight and understanding. This award will largely be used to support graduate students at University of Oregon (UO), who will develop new methods to carry out these novel searches. In keeping with the recent history at UO, it is expected that these students will either continue in the field or will enter the private sector, where they will carry their expertise in data science and analysis to other targets. The UO group will continue to present results to the public and carry out workshops for Oregon high school teachers, so they can, in turn, bring the latest in research to their students.This award will combine two emerging areas of astrophysics to probe sources of gravitational waves from progenitors which are not compact binary mergers. The first area is multi-messenger astronomy (MMA). The second area is the search for gravitational-wave signals without waveform templates – the so-called burst analyses. The searches will fundamentally rely on MMA methods. X-ray, gamma-ray, or radio transient signals from astrophysically energetic events provide a time and sky location which also mark an episode of putative gravitational-wave emission. These provide the so-called triggers for the gravitational-wave data analysis, which labels the time near the trigger as the “on-source” (or signal) data segment, and the off-source data as the background. Excess signal power relative to background is an indicator of a potential gravitational-wave detection in association with the triggering gamma-ray burst (GRB), magnetar x-ray flare, or fast radio bursts (FRB), as the case may be. This method does not rely on any predetermined mathematical form for the gravitational waves. Alongside the searches, the group will develop methods for determining astrophysically interesting parameters from a confident detection, or for constraining such parameters from non-observations, as the case may be. Such parameters might include, for example, those related to the neutron star equation of state for the magnetar searches, or accretion disk properties for the long GRBs. The Oregon group has a strong history of leadership for previous MMA-GW burst searches and the corresponding methods developments. The ever improving sensitivity of the LIGO observatories now makes it plausible for such searches to provide new discoveries.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.