GW170817

GW170817
The GW170817 signal as measured by the LIGO and Virgo gravitational wave detectors. Signal is invisible in the Virgo data
Event typeGravitational wave
Datec. 130 million years ago
(detected 17 August 2017, 12:41:04.4 UTC)
Durationc. 1 minute and 40 seconds
InstrumentLIGO, Virgo
Right ascension13h 09m 48.08s[1]
Declination−23° 22′ 53.3″[1]
EpochJ2000.0
Distancec. 130 million ly
Redshift0.0099
HostNGC 4993
Progenitor2 neutron stars
Other designationsGW170817
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GW170817 was a gravitational wave (GW) signal observed by the LIGO and Virgo detectors on 17 August 2017, originating from the shell elliptical galaxy NGC 4993, about 140 million light years away. The signal was produced by the last moments of the inspiral process of a binary pair of neutron stars, ending with their merger. It was the first GW observation to be confirmed by non-gravitational means.[1][2] Unlike the five previous GW detections—which were of merging black holes and thus not expected to produce a detectable electromagnetic signal[3]—the aftermath of this merger was seen across the electromagnetic spectrum by 70 observatories on 7 continents and in space, marking a significant breakthrough for multi-messenger astronomy.[1][2][4][5][6][7][8][9] The discovery and subsequent observations of GW170817 were given the Breakthrough of the Year award for 2017 by the journal Science.[6][10]

The gravitational wave signal, designated GW170817, had an audible duration of approximately 100 seconds, and showed the characteristic intensity and frequency expected of the inspiral of two neutron stars. Analysis of the slight variation in arrival time of the GW at the three detector locations (two LIGO and one Virgo) yielded an approximate angular direction to the source. Independently, a short (~2 seconds' duration) gamma-ray burst, designated GRB 170817A, was detected by the Fermi and INTEGRAL spacecraft beginning 1.7 seconds after the GW merger signal.[1][5][11] These detectors have very limited directional sensitivity, but indicated a large area of the sky which overlapped the gravitational wave position. It had been a long-standing hypothesis that short gamma-ray bursts are caused by neutron star mergers.

An intense observing campaign then took place to search for the expected emission at optical wavelengths. An astronomical transient designated AT 2017gfo (originally, SSS 17a) was found, 11 hours after the gravitational wave signal, in the galaxy NGC 4993[8] during a search of the region indicated by the GW detection. It was observed by numerous telescopes, from radio to X-ray wavelengths, over the following days and weeks, and was shown to be a fast-moving, rapidly-cooling cloud of neutron-rich material, as expected of debris ejected from a neutron-star merger.

In October 2018, astronomers reported that GRB 150101B, a gamma-ray burst event detected in 2015, may be analogous to GW170817. The similarities between the two events, in terms of gamma ray, optical, and x-ray emissions, as well as to the nature of the associated host galaxies, are considered "striking", and this remarkable resemblance suggests the two separate and independent events may both be the result of the merger of neutron stars, and both may be a hitherto-unknown class of kilonova transients. Kilonova events, therefore, may be more diverse and common in the universe than previously understood, according to the researchers.[12][13][14][15] In retrospect, GRB 160821B, another gamma-ray burst event is now construed to be another kilonova,[16] by its resemblance of its data to AT2017gfo, part of the multi-messenger now denoted GW170817. In December 2022, astronomers suggested that kilonovae could also be found in long-duration GRBs.[17][18]

  1. ^ a b c d e Cite error: The named reference ApJ was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference PhysRev2017 was invoked but never defined (see the help page).
  3. ^ Connaughton V (2016). "Focus on electromagnetic counterparts to binary black hole mergers". The Astrophysical Journal Letters (Editorial). The follow-up observers sprang into action, not expecting to detect a signal if the gravitational radiation was indeed from a binary black-hole merger. [...] most observers and theorists agreed: the presence of at least one neutron star in the binary system was a prerequisite for the production of a circumbinary disk or neutron star ejecta, without which no electromagnetic counterpart was expected.
  4. ^ Landau E, Chou F, Washington D, Porter M (16 October 2017). "NASA missions catch first light from a gravitational-wave event". NASA. Retrieved 16 October 2017.
  5. ^ a b Cite error: The named reference NYT-20171016 was invoked but never defined (see the help page).
  6. ^ a b Cho A (December 2017). "Cosmic convergence". Science. 358 (6370): 1520–1521. Bibcode:2017Sci...358.1520C. doi:10.1126/science.358.6370.1520. PMID 29269456.
  7. ^ Cite error: The named reference SkyandTelescope was invoked but never defined (see the help page).
  8. ^ a b Cite error: The named reference SM-20171016 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference NAT-20170825 was invoked but never defined (see the help page).
  10. ^ "Breakthrough of the year 2017". Science | AAAS. 22 December 2017.
  11. ^ Cite error: The named reference MN-20171016 was invoked but never defined (see the help page).
  12. ^ "All in the family: Kin of gravitational wave source discovered – New observations suggest that kilonovae – immense cosmic explosions that produce silver, gold and platinum – may be more common than thought". University of Maryland. 16 October 2018. Retrieved 17 October 2018 – via EurekAlert!.
  13. ^ Troja E, Ryan G, Piro L, van Eerten H, Cenko SB, Yoon Y, et al. (October 2018). "A luminous blue kilonova and an off-axis jet from a compact binary merger at z = 0.1341". Nature Communications. 9 (1): 4089. arXiv:1806.10624. Bibcode:2018NatCo...9.4089T. doi:10.1038/s41467-018-06558-7. PMC 6191439. PMID 30327476.
  14. ^ Mohon L (16 October 2018). "GRB 150101B: A distant cousin to GW170817". NASA. Retrieved 17 October 2018.
  15. ^ Wall M (17 October 2018). "Powerful cosmic flash is likely another neutron-star merger". Space.com. Retrieved 17 October 2018.
  16. ^ Troja E, Castro-Tirado AJ, Becerra González J, Hu Y, Ryan GS, Cenko SB, et al. (2019). "The afterglow and kilonova of the short GRB 160821B". Monthly Notices of the Royal Astronomical Society. 489 (2): 2104. arXiv:1905.01290. Bibcode:2019MNRAS.489.2104T. doi:10.1093/mnras/stz2255. S2CID 145047934.
  17. ^ Troja E, Fryer CL, O'Connor B, Ryan G, Dichiara S, Kumar A, et al. (December 2022). "A nearby long gamma-ray burst from a merger of compact objects". Nature. 612 (7939): 228–231. arXiv:2209.03363. Bibcode:2022Natur.612..228T. doi:10.1038/s41586-022-05327-3. PMC 9729102. PMID 36477127.
  18. ^ "Kilonova Discovery Challenges our Understanding of Gamma-Ray Bursts". Gemini Observatory. 7 December 2022. Retrieved 11 December 2022.