引力波直接探测的科学结果已经在2016年发表(PRL, 116, 061102(2016))。这篇绝世经典的实验结果"快报"主要内容长达9页, 有118篇文献。这篇实验结果报告信息量巨大, 以至于里面的每一个数字的具体计算细节都没有被展示。细节“彩蛋”被1000名左右的合作者隐藏在了那118篇文献中。如果您仔细阅读, 会发现LVC至少会出品1篇后续文章来解答您心中的每一个疑惑: LIGO到底是一个什么样的仪器？里面有多少先进技术？这个信号发生时的仪器噪声水平如何, 信号会不会是个噪声？到底怎么能在3分钟之内测到信号？为什么双致密星产生的引力波信号被引力波爆数据分析小组先测到了？只有16天的数据, 怎么能得到5.1 sigma？双黑洞的每个参数是怎么估算出来的？引力论不仅仅爱因斯坦一人构建过, 我们凭什么相信广义相对论的预言？后牛顿、数值广义相对论和微扰理论等方法计算的引力波波形如何衔接在一起？这个事件是不是符合天文学上黑洞生成、演化理论预言？这个事件是不是预示着宇宙中有更多的双黑洞并合？大量双黑洞并合事件构成的随机引力波背景能不能被LIGO 测到？ LIGO和其天文学伙伴们如何协作工作, 这个事件有没有更震惊的天文学发现？。。。

Science China Physics, Mechanics & Astronomy期刊特邀LIGO科学合作组成员、此次PRL文章的署名作者之一、湖北第二师范学院范锡龙博士撰写Highlight文章“The detection of gravitational wavesand the new era of multi-messenger astronomy”(《引力波直接探测与多信使天文学新时代》), 上述细节的关键答案我们给您综合到1页半导读！还有呐！都说引力波天文学时代已经开始, 我们将用包括引力波、电磁波、中微子和宇宙线在内的多信使手段探索宇宙, 这到底是怎么一事？如何具体操作呢？不要担心, 文中也会详细介绍。文章即将发表在Science China Physics, Mechanics & Astronomy 2016年59卷第4期, 欢迎阅读！

  

Highlight原文链接http://phys.scichina.com:8083/sciGe/EN/abstract/abstract510225.shtml

The detection of gravitational wavesand the new era of multi-messengerastronomy

XiLong Fan

School of Physics and Electronics Information, Hubei University of Education, Wuhan 430205, China

 

For the first time, gravitational waves (GWs), a major prediction of Einstein’s 1915 general theory of relativity (GR), has been detected directly by the two detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) [1, Figure 1, Table1]. On September 14, 2015 at 09:50:45 UTC two detectors from LIGO, located at LIGO Hanford, WA, and Livingston, LA sites,detected the coincidental GW event (referred to as GW150914, For details about these results and the associated papers and data, see https://losc.ligo.org/events/GW150914.). By interpreting the event as having originated from colliding stellar-mass black holes (BHs), the LSC and Virgo collaborations (LVC) also reported the first direct observation of a binary BH system merging to form a single BH [1].

 

As first obtained by Albert Einstein in 1916, by solving the linearized Einstein’s Equations which are valid for weak gravitational fields, GWs are transverse waves of spatial strain that travel at the speed of light. Observational evidence for these waves was first obtained from the loss in orbital energy of the binary pulsar system PSR B1913+16.

 

BHs on the other hand, were first obtained as exact solutions to the vacuum Einstein’s equations, first by Schwarzschild in the static, spherically symmetric case, and then by Kerr in the stationary, axisymmetric case. It was not until much later that people started appreciating the physical significance of these solutions, as BHs. Mathematical studies established the so-called no-hair theorems, which state that BHs are only characterized by their mass, spin and electric charge. The development of BH perturbation theory indicated that BH should be stable, and are plausible end points of gravitational collapse. Perturbative and fully numerical solutions for space-times of collapsing stars and colliding BHs have also been obtained.

 

While strong candidates of BHs have been identified through electromagnetic (EM) observations and predicted from population synthesis theories and numerical simulations of collapses and mergers, space-time structures near black holes have never been probed.

 

GW detection experiments began with Weber’s resonant mass detectors in the 1960s, followed by an international network of resonant detectors. It was later realized that large-scale, laser interferometer GW detectors should have much better sensitivity, over a much broader frequency range. Since the 1990s, aninternational network of such detectors, including LIGO, VIRGO, GEO 600, TAMA300, have been built and operated. From 2002 to 2009, a series of operations have been undertaken by the first-generation detectors, without making apositive detection. Advanced LIGO detectors [2] have just completed its first Observation Run (O1), while Advanced VIRGO is in commissioning. KAGRA, thenewly constructed Japanese gravitational-wave detector, may start operation in 2017.

 

These detectors use Michelson interferometers with orthogonal arms and mirror-endowed test masses to measure GWs, which could be seen as inducing differential changes in their arm lengths. To observe the remarkably weak GWs, Advanced LIGO detectors have several enhancements to the basic 4 km length Michelson interferometers for minimizing the impact of photo shot noise, and also adopt/develop novel approaches and technique on suspension system and materials in the test masses and their suspensions for reducing the seismic noise and thermal noise, as well as on control systems for reducing the impact of ground motions (see detail in ref. [2]). Two detectors were operating nominally, and their outputs are well calibrated during the GW150914 observation time [2-4].

 

The initial detection of GW150914 was made by low-latency search algorithms for generic GW transients [5], and recovered by subsequent matched-filter an alyses that used relativistic models of compact binary waveforms [6]. A time-shift technique was adopted by the above two searches for 16 d of data to estimate the significance of GW150914. Significance levels obtained for these two approaches were consistent with each other.

 

GW150914 was observedin the frequency band from 35 to 250 Hz, with a peak GW strain of 1.0×10^-21. The matched-filtering signal-to-noise ratiowas 24 and carried a significance greater than 5.1s [1]. GW150914 matched the waveform for the inspiral and merger of a binary BHs and the ringdown of the resulting single BH. Further parameters estimation [7] was performed using a coherent Bayesian analysis algorithm with the most accurate GR-based approximate effective models, which are constructed within two frameworks: the effective-one-body formalism and the inspiral-merger-ringdown phenomeno-logical formalism. The total energy radiated in GWs () and the peak gravitational luminosity ( erg/s) is estimated by fitting the numerical simulations of binary BH mergers [7]. The GW150914 is not well sky localized ~600 deg²(90% credible region) with onlytwo detectors (see ref. [7] and https://dcc.ligo.org/LIGO‑P1500227/public/main).

 

GW150914 is the first observation of a two-body motion in thelarge velocity, highly dynamical, nonlinear regime of general relativity.This motion leads to the formation of a final BH, after the decay of the BH’s quasi-normal modes, which have frequencies and quality factors uniquely determined by general relativity. Three waveform-based testes, including (i) the inspiral, merger and ringdown consistency test, (ii) test on parameterized deviations from the general relativistic inspral-merger-ringdown waveforms and (iii) the graviton Compton wavelength test, have been performed to determine whether or not the GW150914 is consistent with a BH system in GR. Within statistical uncertainties, GW150914 provided no evidence for violations of the predictions of GR in the genuine strong field regime of gravity [8].

 

By detecting GW150914, LIGO has opened a new window for observing the universe. GW150914 demonstrated the existence of stellar-mass BHs more massive than   as predicated in the ories/simulations, and established that binary BHs can form in nature and merge within the Hubble time [9], although this event could not tell whether the binary formed through the passive evolution of a binary star system or a dynamical formation scenario in a globular cluster. The estimated merger rate of stellar mass BH binaries inthe local universe is 2-400 Gpc^-3 yr^-1 in the comoving frame[10] consistent with the range of previous rate predictions (e.g. ref. [11]), but with the lowest event rates being excluded.The detailed range of this rate depends on the several assumptions, including the population properties of events like GW150914 and whether or not adopting other triggers in the data [10]. Because lowest rates were excluded, thestochastic background from superposition of unresolved such binary BH systems couldbe higher than previously expected [12].The possible future detection of a stochastic background from binary black holemergers, together with more individual signal detections, will provide information about the evolution of such system over the history of the universe.

 

Multi-messenger astronomy involves the joint observation of astrophysical phenomena using a combination of EM, neutrino, cosmic-ray, and GW observatories. Multi- messenger approach to GW astronomy seeks to optimally combine GW and other observations, which will improve the GW source detection efficiency, parameter estimation accuracy, and better inform our understanding of the sources themselves [13-17]. Marked the beginning of the new era of multi-messenger observations, the broader astronomy community and LVC set up evolved andgreatly expanded follow-up programs (e.g., http://www.ligo.org/scientists/GWEMalerts.php).By now, about 80 observation teams covering radio,optical, near-infrared, X-ray, and gamma-ray wavelengths, as well as the neutrino and cosmic-ray, with ground- and space-based facilities work onthe follow-up observations of GW triggers. Several joint observation results have been reported in initial LIGO-Virgo runs (e.g. refs. [18-20]), although no joint detection has been made. Thejoint analysis of follow-up observations and GW150914 are on-going (e.g. EM-GW (https://dcc.ligo.org/LIGO‑P1500227/public/main), High-energy Neutrino-GW (https://dcc.ligo.org/P1500271/public) and see more in footnote1)).

 

Efforts are underway to enhance and develop the global network [21] of so-called‘second generation’ ground- based interferometers (including Ad-LIGO, Ad-Virgo, KAGRA and a possible third LIGO detector in India) and next detectors (such as Einstein Telescope). The joint observations of these GW detectors and theastronomy facilities will enhancing their potential as probes of astrophysics and cosmology (see “Special Topic: the Next Detectors for Gravitational Wave Astronomy” [13-17]).

X. Fan thanks Y. Chen for careful reading manuscript and valuable comments, and this work was supported by the National Natural Science Foundation of China (Grant No.11303009).

1       B. Abbott, et al. (LIGO Scientific Collaboration and Virgo Collaboration), Phys. Rev. Lett. 116,061102 (2016).

2      B. Abbott, et al. (LIGOScientific Collaboration and Virgo Collaboration), [arXiv:1602.03838].

3      B. Abbott, et al. (LIGOScientific Collaboration and Virgo Collaboration), [arXiv:1602.03844].

4      B. Abbott, et al. (LIGOScientific Collaboration and Virgo Collaboration), [arXiv:1602.03845].

5      B. Abbott, et al. (LIGOScientific Collaboration and Virgo Collaboration), [arXiv:1602.03843].

6      B. Abbott, et al. (LIGOScientific Collaboration and Virgo Collaboration), [arXiv:1602.03839].

7      B. Abbott, et al. (LIGO Scientific Collaboration and Virgo Collaboration), [arXiv:1602.03840].

8      B. Abbott, et al. (LIGO Scientific Collaborationand Virgo Collaboration), [arXiv:1602.03841].

9       B. Abbott, et al. (LIGO Scientific Collaboration and Virgo Collaboration),Astrophys. J. Lett. 818, L22 (2016).

10      B. Abbott, et al. (LIGOScientific Collaboration and Virgo Collaboration), [arXiv:1602.03842].

11      J. Abadie, et al. (LIGOScientific Collaboration and Virgo Collaboration), Class. Quantum Grav. 27, 173001 (2010).

12      B. Abbott, et al. (LIGO ScientificCollaboration and Virgo Collaboration), [arXiv:1602.03847].

13       D. Blair, L. Ju, and Z. H. Zhu, Sci. China-Phys. Mech. Astron. 58(12), 120401 (2015).

14       D. Blair, L. Ju, C. N. Zhao, L. Q. Wen, Q. Chu, Q. Fang, R. G. Cai,J. R. Gao, X. C. Lin, D. Liu, L.-A. Wu, Z. H. Zhu, D. H. Reitze, K. Arai, F.Zhang, R. Flaminio, X. J. Zhu, G. Hobbs, R. N. Manchester, R. M. Shannon, C.Baccigalupi, W. Gao, P. Xu, X. Bian, Z. J. Cao, Z. J. Chang, P. Dong, X. F.Gong, S. L. Huang, P. Ju, Z. R. Luo, L.’E Qiang, W. L. Tang, X. Y. Wan, Y.Wang, S. N. Xu, Y. L. Zang, H. P. Zhang, Y.-K. Lau, and W.-T. Ni, Sci.China-Phys. Mech. Astron. 58(12),120402 (2015).

15      H. M. Lee, E.-O. Le Bigot, Z.H. Du, Z. X. Lin, X. Y. Guo, L. Q. Wen, K. S. Phukon, V. Pandey, S. Bose, X.-L.Fan, and M. Hendry, Sci. China-Phys. Mech. Astron. 58(12), 120403 (2015).  

16       V. P. Mitrofanov, S. Chao, H.-W. Pan, L.-C. Kuo, G. Cole, J.Degallaix, and B. Willke, Sci. China-Phys. Mech. Astron. 58(12), 120404 (2015).

17      D. Blair, L. Ju, C. N. Zhao, L. Q. Wen, H. X. Miao, R. G.Cai, J. R. Gao, X. C. Lin, D. Liu, L.-A. Wu, Z. H. Zhu, G. Hammond, H. J. Paik,V. Fafone, A. Rocchi, C. Blair, Y. Q. Ma, J. Y. Qin, and M. Page, Sci.China-Phys. Mech. Astron. 58(12),120405 (2015).

18      J. Abadie, et al. (LIGO Scientific Collaboration and Virgo Collaboration), Astron. Astrophys. 536, A124, (2012).

19      M. G. Aartsen, et al. (IceCube Collaboration, LIGO Scientific Collaboration and Virgo Collaboration), Phys. Rev. D 90, 102002 (2014).

20      J. Abadie, et al. (LIGO Scientific Collaboration and Virgo Collaboration), Astrophys. J. 760, 12 (2012).

 21       B. Abbott, et al. (LIGO Scientific Collaboration and Virgo Collaboration),Liv. Rev. Relat. 19, 1(2016).

 

　　作者简介: 范锡龙 湖北第二师范学院物理学副教授, 中国引力与相对论天体物理学会会员。2006年-2007年访问德国马普所引力物理研究所1年, 跟随陈雁北、温琳清等人学习。2008年在朱宗宏教授指导下获得北京师范大学硕士学位。2012年获得意大利里雅思特大学博士。曾获得英国皇家学会“Newton International Fellowships”和中国国家自然科学基金资助。

　　Science China Physics, Mechanics & Astronomy 2015年第12期出版了由西澳大学David Blair教授、鞠莉教授以及北师大朱宗宏教授组织的“the Next Detectors for Gravitational Wave Astronomy”英文学术专题, 包括4篇综述文章, 多位LIGO科学合作组成员参与撰写, 详见http://phys.scichina.com:8083/sciGe/EN/volumn/volumn_6537.shtml

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