First observation of gravitational waves

GW150914
LIGO measurement of the gravitational waves at the Livingston (right) and Hanford (left) detectors, compared with the theoretical predicted values
Event typeGravitational wave
Datec. 1.4 billion years ago
(detected 14 September 2015, 9:50:45 UTC)
Durationc. 200 milliseconds
InstrumentLIGO
ConstellationSouthern hemisphere
Distancec. 1.4 billion ly
Redshift0.093+0.030
−0.036[1]
Progenitor2 black holes
Total energy output3.0+0.5
−0.5 M☉ × c2[2][a]
Other designationsGW150914
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The first direct observation of gravitational waves was made on 14 September 2015 and was announced by the LIGO and Virgo collaborations on 11 February 2016.[3][4][5] Previously, gravitational waves had been inferred only indirectly, via their effect on the timing of pulsars in binary star systems. The waveform, detected by both LIGO observatories,[6] matched the predictions of general relativity[7][8][9] for a gravitational wave emanating from the inward spiral and merger of two black holes (of 36 M☉ and 29 M☉) and the subsequent ringdown[b] of a single, 62 M☉ black hole remnant. The signal was named GW150914 (from gravitational wave and the date of observation 2015-09-14).[3][11] It was also the first observation of a binary black hole merger, demonstrating both the existence of binary stellar-mass black hole systems and the fact that such mergers could occur within the current age of the universe.

This first direct observation was reported around the world as a remarkable accomplishment for many reasons. Efforts to directly prove the existence of such waves had been ongoing for over fifty years, and the waves are so minuscule that Albert Einstein himself doubted that they could ever be detected.[12][13] The waves given off by the cataclysmic merger of GW150914 reached Earth as a ripple in spacetime that changed the length of a 1,120 km LIGO effective span by a thousandth of the width of a proton,[11] proportionally equivalent to changing the distance to the nearest star outside the Solar System by one hair's width.[14][c] The energy released by the binary as it spiralled together and merged was immense, with the energy of 3.0+0.5
−0.5 c2 M☉ (5.3+0.9
−0.8×1047 joules or 5300+900
−800 foes) in total radiated as gravitational waves, reaching a peak emission rate in its final few milliseconds of about 3.6+0.5
−0.4×1049 watts – a level greater than the combined power of all light radiated by all the stars in the observable universe.[3][4][15][16][d]

The observation confirmed the last remaining directly undetected prediction of general relativity and corroborated its predictions of space-time distortion in the context of large scale cosmic events (known as strong field tests). It was heralded as inaugurating a new era of gravitational-wave astronomy, which enables observations of violent astrophysical events that were not previously possible and allows for the direct observation of the earliest history of the universe.[3][18][19][20][21] On 15 June 2016, two more detections of gravitational waves, made in late 2015, were announced.[22] Eight more observations were made in 2017, including GW170817, the first observed merger of binary neutron stars, which was also observed in electromagnetic radiation.

  1. ^ Cite error: The named reference Improved was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference Properties was invoked but never defined (see the help page).
  3. ^ a b c d Cite error: The named reference PRL-20160211 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference Nature_11Feb16 was invoked but never defined (see the help page).
  5. ^ The Editorial Board (16 February 2016). "The Chirp Heard Across the Universe". New York Times. Retrieved 16 February 2016.
  6. ^ Cite error: The named reference BBC_11Feb16 was invoked but never defined (see the help page).
  7. ^ Pretorius, Frans (2005). "Evolution of Binary Black-Hole Spacetimes". Physical Review Letters. 95 (12): 121101. arXiv:gr-qc/0507014. Bibcode:2005PhRvL..95l1101P. doi:10.1103/PhysRevLett.95.121101. ISSN 0031-9007. PMID 16197061. S2CID 24225193.
  8. ^ Campanelli, M.; Lousto, C. O.; Marronetti, P.; Zlochower, Y. (2006). "Accurate Evolutions of Orbiting Black-Hole Binaries without Excision". Physical Review Letters. 96 (11): 111101. arXiv:gr-qc/0511048. Bibcode:2006PhRvL..96k1101C. doi:10.1103/PhysRevLett.96.111101. ISSN 0031-9007. PMID 16605808. S2CID 5954627.
  9. ^ Baker, John G.; Centrella, Joan; Choi, Dae-Il; Koppitz, Michael; van Meter, James (2006). "Gravitational-Wave Extraction from an Inspiraling Configuration of Merging Black Holes". Physical Review Letters. 96 (11): 111102. arXiv:gr-qc/0511103. Bibcode:2006PhRvL..96k1102B. doi:10.1103/PhysRevLett.96.111102. ISSN 0031-9007. PMID 16605809. S2CID 23409406.
  10. ^ Castelvecchi, Davide (23 March 2016). "The black-hole collision that reshaped physics". Nature. 531 (7595): 428–431. Bibcode:2016Natur.531..428C. doi:10.1038/531428a. PMID 27008950.
  11. ^ a b Naeye, Robert (11 February 2016). "Gravitational Wave Detection Heralds New Era of Science". Sky and Telescope. Retrieved 11 February 2016.
  12. ^ Pais, Abraham (1982), "The New Dynamics, section 15d: Gravitational Waves", Subtle is the Lord: The science and the life of Albert Einstein, Oxford University Press, pp. 278–281, ISBN 978-0-19-853907-0
  13. ^ Blum, Alexander; Lalli, Roberto; Renn, Jürgen (12 February 2016). "The long road towards evidence". Max Planck Society. Retrieved 15 February 2016.
  14. ^ Cite error: The named reference Guardian_11Feb16 was invoked but never defined (see the help page).
  15. ^ Harwood, W. (11 February 2016). "Einstein was right: Scientists detect gravitational waves in breakthrough". CBS News. Retrieved 12 February 2016.
  16. ^ Drake, Nadia (11 February 2016). "Found! Gravitational Waves, or a Wrinkle in Spacetime". National Geographic News. Archived from the original on 12 February 2016. Retrieved 12 February 2016.
  17. ^ Stuver, Amber (12 February 2016). "Your Questions About Gravitational Waves, Answered". Gizmodo (Interview). Interviewed by Jennifer Ouellette. Gawker Media. Retrieved 24 February 2016. ...  Now assume that we are 2 m (~6.5 ft) tall and floating outside the black holes at a distance equal to the Earth's distance to the Sun. I estimate that you would feel alternately squished and stretched by about 165 nm (your height changes by more than this through the course of the day due to your vertebrae compressing while you are upright) ...
  18. ^ Cite error: The named reference tests was invoked but never defined (see the help page).
  19. ^ Cite error: The named reference astrophysics was invoked but never defined (see the help page).
  20. ^ CNN quoting Prof. Martin Hendry (University of Glasgow, LIGO) – "Detecting gravitational waves will help us to probe the most extreme corners of the cosmos – the event horizon of a black hole, the innermost heart of a supernova, the internal structure of a neutron star: regions that are completely inaccessible to electromagnetic telescopes."
  21. ^ Ghosh, Pallab (11 February 2016). "Einstein's gravitational waves 'seen' from black holes". BBC News. Retrieved 19 February 2016. With gravitational waves, we do expect eventually to see the Big Bang itself.
  22. ^ Overbye, Dennis (15 June 2016). "Scientists Hear a Second Chirp From Colliding Black Holes". New York Times. Retrieved 15 June 2016.


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