On the detection of gravitational waves by the Laser Interferometer Gravitational-Wave Obsevatory (LIGO)

The direct detection of gravitational waves is one of those events long-expected by physicists that are nevertheless a significant occurrence which excites the world scientific community as if something unexpected has happened. The event that happened on September 14, 2015 was not kept in utmost secrecy; however, everybody was waiting for the press conference that took place on February 11, 2016

(the link can be found, e.g., here ) and, most importantly, the paper. Many rumors leaked ahead of the conference, and the fact that something (that is, a signal corresponding to gravitational waves) was discovered by LIGO (Laser Interferometer Gravitational-Wave Observatory) was discussed on the sidelines. The details of the observations and data analysis by the LIGO collaboration (over 1000 people) became available on the arXiv server on February 12, 2016. These papers, including the technical ones, are listed below:

• The LIGO Scientific Collaboration, the Virgo Collaboration. Astrophysical Implications of the Binary Black-Hole Merger GW150914. ApJL, 818, L22, 2016. arXiv:1602.03846
• B. P. Abbott, R. Abbott, T. D. Abbott, et al. The Rate of Binary Black Hole Mergers Inferred from Advanced LIGO Observations Surrounding GW150914. arXiv:1602.03842
• The LIGO Scientific Collaboration, the Virgo Collaboration. GW150914: Implications for the stochastic gravitational wave background from binary black holes. arXiv:1602.03847
• The LIGO Scientific Collaboration: B. P. Abbott, et al. Calibration of the Advanced LIGO detectors for the discovery of the binary black-hole merger GW150914. 1602.03845
• The LIGO Scientific Collaboration, the Virgo Collaboration. Characterization of transient noise in Advanced LIGO relevant to gravitational wave signal GW150914. arXiv:1602.03844
• The LIGO Scientific Collaboration, the Virgo Collaboration. Observing gravitational-wave transient GW150914 with minimal assumptions. 1602.03843
• The LIGO Scientific Collaboration, the Virgo Collaboration. Properties of the binary black hole merger GW150914. arXiv:1602.03840
• The LIGO Scientific Collaboration, the Virgo Collaboration. GW150914: First results from the search for binary black hole coalescence with Advanced LIGO. arXiv:1602.03839
• The LIGO Scientific Collaboration, the Virgo Collaboration. GW150914: The Advanced LIGO Detectors in the Era of First Discoveries. arXiv:1602.03838
• The LIGO Scientific Collaboration, the Virgo Collaboration. Observation of Gravitational Waves from a Binary Black Hole Merger. Physical Review Letters 116, 061102 (2016), arXiv:1602.03837.

At the same time, papers by authors who, apparently, expected this day knowing about the LIGO results, appeared on arXiv:

• P.A. Evans, J.A. Kennea, S.D. Barthelmy, et al. Swift follow-up of the Gravitational Wave source GW150914. To be submitted to MNRAS letters. arXiv:1602.03868
• I.Bartos, B.Kocsis, Z.Haiman, S.Marka. Rapid and Bright Stellar-mass Binary Black Hole Mergers in Active Galactic Nuclei. arXiv:1602.03831
• J. J. Eldridge, E. R. Stanway. BPASS predictions for Binary Black-Hole Mergers. Submitted to MNRAS. arXiv:1602.03790
• T.L. Campante, I.Lopes, D.Bossini, et al. Asteroseismology of red-giant stars as a novel approach in the search for gravitational waves. Submitted to Astronomy in Focus, to appear in the Proc. IAU XXIX GA. arXiv:1602.03667
• J. P. W. Verbiest, L. Lentati, et al. The International Pulsar Timing Array: First Data Release. Accepted for publication in MNRAS. arXiv:1602.03640
• Maurice H.P.M. Van Putten. Directed searches for broadband extended gravitational-wave emission in nearby energetic core-collapse supernovae. To appear in ApJ. arXiv:1602.03634
• R. Ruffini, J. A. Rueda, M. Muccino, et al. On the rate and on the gravitational wave emission of short and long GRBs. arXiv:1602.03545
• E.Calabrese, N.Battaglia, D.N. Spergel. Testing Gravity with Gravitational Wave Source Counts. (Comments: Comments welcome, congratulations to the LIGO team) arXiv:1602.03883
• M.A.Resco, A. de la Cruz-Dombriz, F.J. Llanes Estrada, et al. On neutron stars in f(R) theories: small radii, large masses and large energy available for emission in a merger. arXiv:1602.03880

 

We can note the FERMI collaboration preprint (V. Connaughton, E. Burns, A. Goldstein, Fermi GBM Observations of LIGO Gravitational Wave event GW150914. ) which was not posted to arXiv at the time [ the paper appeared on arXiv on February 15, 2016: arXiv:1602.03920. ]. Also, several important popular-science comments from physicists and astrophysicists appeared on the RuNet during the first three days, and some even earlier (we list only a few of them here):

• Postnauka website:
  1) K. Postnov Gravitational waves: research history and the LIGO discovery.
  2) S. Popov, E. Akhmedov, V. Rubakov, A. Zasov. Point of view: What will the discovery of gravitational waves change?
• Elementy.ru website:
  1) I. Ivanov. Gravitational waves - discovered! , and numerous links at the end of the article.
  2) Discussion on the "Science 2.0" TV channel (video). A. Semikhatov and K. Postnov.
• "Troitsky Variant - Science"  newspaper:
  1) B. Stern. What the LIGO detectors saw.
  2) A. Levin. Gravitational waves: road to discovery.

We should point out straight away that the attempts to register and investigate experimentally the gravitational waves, which were predicted in Albert Einstein's general theory of relativity, were started in the 60's by Joseph Weber, a professor of physics at the University of Maryland (USA). Despite the pessimistic results of the experiments, the research was continued in many countries, including the USSR. We should mention that the principle of using a laser interferometer (also employed in LIGO) to detect gravitational waves was proposed in the works of Soviet physicists (M.E. Gertsenshtein, V.I. Pustovoit, JETP, 43, 605, 1962) back in 1962, and later also by J. Weber. Active investigations in this field are (and have been) carried out by members of the group lead by V.B. Braginsky at the physics faculty of MSU (see the interview with Sergey Vyatchanin and the book by Kip Thorne "Black Holes and Time Warps"), also included in the LIGO collaboration [among the useful Russian-language links we note also (V.M. Lipunov The gravitational wave sky. ISSEP, V.6, No 4, p. 77 (2000); V. N. Rudenko. "The search for gravitational waves". Chapter in a book published by "Vek 2", 2007)].

The construction of LIGO began in the 90's (by the initiative of Rainer Weiss, Ronald Drever, and Kip Thorne). Observations were conducted with LIGO in 2002-2010, with no results. In September 2015, during the calibration measurements for the modernized "Advanced LIGO" project, a signal was detected with a significance above 5.1 sigma, corresponding to the one expected for the merger of two massive compact objects.

Here we need to show several figures available from the LIGO website.