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GW170817

May 03, 2023

GW 170817 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. The signal was produced by the last minutes of a binary pair of neutron stars' inspiral process, ending with a merger. It is the first GW observation that has been confirmed by non-gravitational means.[1][2] Unlike the five previous GW detections, which were of merging black holes not expected to produce a detectable electromagnetic signal,[3] the aftermath of this merger was also seen by 70 observatories on 7 continents and in space, across the electromagnetic spectrum, marking a significant breakthrough for multi-messenger astronomy.[1][2][4][5][6][7][8][9] The discovery and subsequent observations of GW 170817 were given the Breakthrough of the Year award for 2017 by the journal Science.[6][10]

GW170817
The GW170817 signal as measured by the LIGO and Virgo gravitational wave detectors. Signal is invisible in the Virgo data
Event typeGravitational wave event 
InstrumentLIGO, Virgo
Right ascension13h 09m 48.08s[1]
Declination−23° 22′ 53.3″[1]
EpochJ2000.0
Distance40 megaparsecs (130 Mly)
Redshift0.0099 
Other designationsGW170817
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The gravitational wave signal, designated GW 170817, had a duration of approximately 100 seconds, and shows the characteristics in 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 has 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 GW 170817. 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]

Announcement

It's the first time that we've observed a cataclysmic astrophysical event in both gravitational waves and electromagnetic waves – our cosmic messengers.[19]

Reitze D, LIGO executive director

The observations were officially announced on 16 October 2017 at press conferences at the National Press Club in Washington, D.C. and at the ESO headquarters in Garching bei München in Germany.[5][11][8]

Some information was leaked before the official announcement, beginning on 18 August 2017 when astronomer J. Craig Wheeler of the University of Texas at Austin tweeted "New LIGO. Source with optical counterpart. Blow your sox off!".[7] He later deleted the tweet and apologized for scooping the official announcement protocol. Other people followed up on the rumor, and reported that the public logs of several major telescopes listed priority interruptions in order to observe NGC 4993, a galaxy 40 Mpc (130 Mly) away in the Hydra constellation.[9][20] The collaboration had earlier declined to comment on the rumors, not adding to a previous announcement that there were several triggers under analysis.[21][22]

Gravitational wave detection

Artist's impression of the collision of two neutron stars. This is a general illustration, not specific to GW170817. (00:23 video.)

The gravitational wave signal lasted for approximately 100 seconds starting from a frequency of 24 hertz. It covered approximately 3,000 cycles, increasing in amplitude and frequency to a few hundred hertz in the typical inspiral chirp pattern, ending with the collision received at 12:41:04.4 UTC.[2]: 2  It arrived first at the Virgo detector in Italy, then 22 milliseconds later at the LIGO-Livingston detector in Louisiana, United States, and another 3 milliseconds later at the LIGO-Hanford detector in the state of Washington, in the United States. The signal was detected and analyzed by a comparison with a prediction from general relativity defined from the post-Newtonian expansion.[1]: 3 

An automatic computer search of the LIGO-Hanford datastream triggered an alert to the LIGO team about 6 minutes after the event. The gamma-ray alert had already been issued at this point (16 seconds post-event),[23] so the timing near-coincidence was automatically flagged. The LIGO/Virgo team issued a preliminary alert (with only the crude gamma-ray position) to astronomers in the follow-up teams at 40 minutes post-event.[24][25]

Sky localisation of the event requires combining data from the three interferometers; this was delayed by two problems. The Virgo data were delayed by a data transmission problem, and the LIGO Livingston data were contaminated by a brief burst of instrumental noise a few seconds prior to event peak, but persisting parallel to the rising transient signal in the lowest frequencies. These required manual analysis and interpolation before the sky location could be announced about 4.5 hours post-event.[26][25] The three detections localized the source to an area of 31 square degrees in the southern sky at 90% probability. More detailed calculations later refined the localization to within 28 square degrees.[24][2] In particular, the absence of a clear detection by the Virgo system implied that the source was in one of Virgo's blind spots; this absence of signal in Virgo data contributed to considerably reduce the source containment area.[27]

Gamma ray detection

 
Artistic concept: two neutron stars merge

The first electromagnetic signal detected was GRB 170817A, a short gamma-ray burst, detected 1.74±0.05 s after the merger time and lasting for about 2 seconds.[11][9][1]: 5 

GRB 170817A was discovered by the Fermi Gamma-ray Space Telescope, with an automatic alert issued just 14 seconds after the GRB detection. After the LIGO/Virgo circular 40 minutes later, manual processing of data from the INTEGRAL gamma-ray telescope also detected the same GRB. The difference in arrival time between Fermi and INTEGRAL helped to improve the sky localization.

This GRB was relatively faint given the proximity of the host galaxy NGC 4993, possibly due to its jets not being pointed directly toward Earth, but rather at an angle of about 30 degrees to the side.[8][28]

Electromagnetic follow-up

 
Hubble picture of NGC 4993 with inset showing GRB 170817A over 6 days. Credit: NASA and ESA
 
Optical lightcurves
 
The change in optical and near-infrared spectra

A series of alerts to other astronomers were issued, beginning with a report of the gamma-ray detection and single-detector LIGO trigger at 13:21 UTC, and a three-detector sky location at 17:54 UTC.[24] These prompted a massive search by many survey and robotic telescopes. In addition to the expected large size of the search area (about 150 times the area of a full moon), this search was challenging because the search area was near the Sun in the sky and thus visible for at most a few hours after dusk for any given telescope.[25]

In total six teams (One-Meter, Two Hemispheres (1M2H),[29] DLT40, VISTA, Master, DECam, and Las Cumbres Observatory (Chile)) imaged the same new source independently in a 90-minute interval.[1]: 5  The first to detect optical light associated with the collision was the 1M2H team running the Swope Supernova Survey, which found it in an image of NGC 4993 taken 10 hours and 52 minutes after the GW event[11][1][30] by the 1-meter diameter (3.3 ft) Swope Telescope operating in the near infrared at Las Campanas Observatory, Chile. They were also the first to announce it, naming their detection SSS 17a in a circular issued 12h26m post-event.[29] The new source was later given an official International Astronomical Union (IAU) designation of AT 2017gfo.

The 1M2H team surveyed all galaxies in the region of space predicted by the gravitational wave observations, and identified a single new transient.[28][30] By identifying the host galaxy of the merger, it is possible to provide an accurate distance consistent with that based on gravitational waves alone.[1]: 5 

The detection of the optical and near-infrared source provided a huge improvement in localisation, reducing the uncertainty from several degrees to 0.0001 degree; this enabled many large ground and space telescopes to follow up the source over the following days and weeks. Within hours after localization, many additional observations were made across the infrared and visible spectrum.[30] Over the following days, the colour of the optical source changed from blue to red as the source expanded and cooled.[28]

Numerous optical and infrared spectra were observed; early spectra were nearly featureless, but after a few days, broad features emerged indicative of material ejected at roughly 10 percent of light speed. There are multiple strong lines of evidence that AT 2017gfo is indeed the aftermath of GW 170817. The colour evolution and spectra are dramatically different from any known supernova. The distance of NGC 4993 is consistent with that independently estimated from the GW signal. No other transient has been found in the GW sky localisation region. Finally, various archive images pre-event show nothing at the location of AT 2017gfo, ruling out a foreground variable star in the Milky Way.[29]

The source was detected in the ultraviolet (but not in X-rays) 15.3 hours after the event by the Swift Gamma-Ray Burst Mission.[4][6] After initial lack of X-ray and radio detections, the source was detected in X-rays 9 days later[31] using the Chandra X-ray Observatory,[32][33] and 16 days later in the radio[34] using the Karl G. Jansky Very Large Array (VLA) in New Mexico.[8] More than 70 observatories covering the electromagnetic spectrum observed the source.[8]

The radio and X-ray light continued to rise for several months after the merger,[35] and have been represented to be diminishing.[36] Astronomers reported obtaining optical images of GW170817 afterglow using the Hubble Space Telescope.[37][38] In March 2020, continued X-ray emission at 5-sigma was observed by the Chandra Observatory 940 days after the merger, demanding further augmentation or refutation of prior models that had previously been supplemented with additional post-hoc interventions.[39]

Other detectors

No neutrinos consistent with the source were found in follow-up searches by the IceCube and ANTARES neutrino observatories and the Pierre Auger Observatory.[2][1] A possible explanation for the non-detection of neutrinos is because the event was observed at a large off-axis angle and thus the outflow jet was not directed towards Earth.[40][41]

Astrophysical origin and products

The gravitational wave signal indicated that it was produced by the collision of two neutron stars[9][20][22][42] with a total mass of 2.82+0.47
−0.09 times the mass of the sun (solar masses M☉).[2] If low spins are assumed, consistent with those observed in binary neutron stars that will merge within a Hubble time, the total mass is 2.74+0.04
−0.01 M☉.

The masses of the component stars have greater uncertainty. The larger (m1) has a 90% chance of being between 1.36 and 2.26 M☉, and the smaller (m2) has a 90% chance of being between 0.86 and 1.36 M☉.[43] Under the low spin assumption, the ranges are 1.36 to 1.60 M☉ for m1 and 1.17 to 1.36 M☉ for m2.

The chirp mass, a directly observable parameter which may be very roughly equated to the geometric mean of the masses, is measured at 1.188+0.004
−0.002 M☉.[43]

The origin and properties (masses and spins) of a double neutron star system like GW170817 are the result of a long sequence of complex binary star interactions.[44]

The neutron star merger event is thought to result in a spherically expanding kilonova,[45][46] characterized by a short gamma-ray burst followed by a longer optical "afterglow" powered by the radioactive decay of heavy r-process nuclei. Kilonovae are candidates for the production of half the chemical elements heavier than iron in the Universe.[8] A total of 16,000 times the mass of the Earth in heavy elements is believed to have formed, including approximately 10 Earth masses just of the two elements gold and platinum.[47]

A hypermassive neutron star was believed to have formed initially, as evidenced by the large amount of ejecta (much of which would have been swallowed by an immediately forming black hole). The lack of evidence for emissions being powered by neutron star spin-down, which would occur for longer-surviving neutron stars, suggest it collapsed into a black hole within milliseconds.[48]

One search claimed to find evidence of a gravitational wave signal from the remnant neutron star or black hole,[49] the energy of which was below the estimated sensitivity of the LIGO search algorithms at the time [50] and has recently been confirmed by a statistically independent method of analysis revealing the central engine of GRB170817A.[51]

Scientific importance

 
Artist's impression of strontium emerging from a neutron star merger.[52]

Scientific interest in the event was enormous, with dozens of preliminary papers (and almost 100 preprints[53]) published the day of the announcement, including 8 letters in Science,[8] 6 in Nature, and 32 in a special issue of The Astrophysical Journal Letters devoted to the subject.[54] The interest and effort was global: The paper describing the multi-messenger observations[1] is coauthored by almost 4,000 astronomers (about one-third of the worldwide astronomical community) from more than 900 institutions, using more than 70 observatories on all 7 continents and in space.[7][8]

This may not be the first observed event that is due to a neutron star merger; GRB 130603B was the first plausible kilonova suggested based on follow-up observations of short-hard gamma-ray bursts.[55] It is, however, by far the best observation, making this the strongest evidence to date to confirm the hypothesis that some mergers of binary stars are the cause of short gamma-ray bursts.[1][2]

The event also provides a limit on the difference between the speed of light and that of gravity. Assuming the first photons were emitted between zero and ten seconds after peak gravitational wave emission, the difference between the speeds of gravitational and electromagnetic waves, vGW − vEM, is constrained to between −3×10−15 and +7×10−16 times the speed of light, which improves on the previous estimate by about 14 orders of magnitude.[43][56][a] In addition, it allowed investigation of the equivalence principle (through Shapiro delay measurement) and Lorentz invariance.[2] The limits of possible violations of Lorentz invariance (values of 'gravity sector coefficients') are reduced by the new observations, by up to ten orders of magnitude.[43] GW 170817 also excluded some alternatives to general relativity,[57] including variants of scalar–tensor theory,[58][59][60][61][62][63][64][65] Hořava–Lifshitz gravity,[61][66][62] Dark Matter Emulators,[67] and bimetric gravity,[68] Furthermore, an analysis published in July 2018 used GW170817 to show that gravitational waves propagate through 3+1 dimensional spacetime, in line with general relativity and contradicting hypotheses of "leakage" to higher dimensions of space.[69]

Gravitational wave signals such as GW 170817 may be used as a standard siren to provide an independent measurement of the Hubble constant.[70][71] An initial estimate of the constant derived from the observation is 70.0+12.0
−8.0 (km/s)/Mpc, broadly consistent with current best estimates.[70] Further studies improved the measurement to 70.3+5.3
−5.0 (km/s)/Mpc.[72][73][74] Together with the observation of future events of this kind the uncertainty is expected to reach two percent within five years and one percent within ten years.[75][76]

Electromagnetic observations helped to support the theory that the mergers of neutron stars contribute to rapid neutron capture r-process nucleosynthesis[30] and are significant sources of r-process elements heavier than iron,[1] including gold and platinum, which was previously attributed exclusively to supernova explosions.[47] The first identification of r-process elements in a neutron star merger was obtained during a re-analysis of GW170817 spectra.[77] The spectra provided direct proof of strontium production during a neutron star merger. This also provided a direct proof that neutron stars are made of neutron-rich matter.

In October 2017, Stephen Hawking, in his last broadcast interview, presented the overall scientific importance of GW170817.[78] In September 2018, astronomers reported related studies about possible mergers of neutron stars (NS) and white dwarfs (WD): including NS-NS, NS-WD, and WD-WD mergers.[79]

See also

Notes

  1. ^ Previous constraint on the difference between the light speed and the gravitational speed was about ±20%.[56]

References

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External links

 
Wikimedia Commons has media related to GW170817.
  • "Detections". LIGO.
  • "Follow-up observations of GW 170817".
  • Related videos (16 October 2017):
    • NSF LIGO-Virgo press conference: 2 panels and Q&As (03:21) on YouTube
    • MPI: Sound of the merger (0:32) on YouTube
    • AAAS (02m42s) on YouTube
    • Caltech (03m56s) on YouTube
    • MIT (00m42s) on YouTube
    • SciNews (01m46s) on YouTube

May 03, 2023
gw170817, 170817, gravitational, wave, signal, observed, ligo, virgo, detectors, august, 2017, originating, from, shell, elliptical, galaxy, 4993, signal, produced, last, minutes, binary, pair, neutron, stars, inspiral, process, ending, with, merger, first, ob. GW 170817 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 The signal was produced by the last minutes of a binary pair of neutron stars inspiral process ending with a merger It is the first GW observation that has been confirmed by non gravitational means 1 2 Unlike the five previous GW detections which were of merging black holes not expected to produce a detectable electromagnetic signal 3 the aftermath of this merger was also seen by 70 observatories on 7 continents and in space across the electromagnetic spectrum marking a significant breakthrough for multi messenger astronomy 1 2 4 5 6 7 8 9 The discovery and subsequent observations of GW 170817 were given the Breakthrough of the Year award for 2017 by the journal Science 6 10 GW170817The GW170817 signal as measured by the LIGO and Virgo gravitational wave detectors Signal is invisible in the Virgo dataEvent typeGravitational wave event InstrumentLIGO VirgoRight ascension13h 09m 48 08s 1 Declination 23 22 53 3 1 EpochJ2000 0Distance40 megaparsecs 130 Mly Redshift0 0099 Other designationsGW170817 Related media on Commons edit on Wikidata The gravitational wave signal designated GW 170817 had a duration of approximately 100 seconds and shows the characteristics in 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 has 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 GW 170817 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 Contents 1 Announcement 2 Gravitational wave detection 3 Gamma ray detection 4 Electromagnetic follow up 5 Other detectors 6 Astrophysical origin and products 7 Scientific importance 8 See also 9 Notes 10 References 11 External linksAnnouncement EditIt s the first time that we ve observed a cataclysmic astrophysical event in both gravitational waves and electromagnetic waves our cosmic messengers 19 Reitze D LIGO executive director The observations were officially announced on 16 October 2017 at press conferences at the National Press Club in Washington D C and at the ESO headquarters in Garching bei Munchen in Germany 5 11 8 Some information was leaked before the official announcement beginning on 18 August 2017 when astronomer J Craig Wheeler of the University of Texas at Austin tweeted New LIGO Source with optical counterpart Blow your sox off 7 He later deleted the tweet and apologized for scooping the official announcement protocol Other people followed up on the rumor and reported that the public logs of several major telescopes listed priority interruptions in order to observe NGC 4993 a galaxy 40 Mpc 130 Mly away in the Hydra constellation 9 20 The collaboration had earlier declined to comment on the rumors not adding to a previous announcement that there were several triggers under analysis 21 22 Gravitational wave detection Edit source source source source source source Artist s impression of the collision of two neutron stars This is a general illustration not specific to GW170817 00 23 video The gravitational wave signal lasted for approximately 100 seconds starting from a frequency of 24 hertz It covered approximately 3 000 cycles increasing in amplitude and frequency to a few hundred hertz in the typical inspiral chirp pattern ending with the collision received at 12 41 04 4 UTC 2 2 It arrived first at the Virgo detector in Italy then 22 milliseconds later at the LIGO Livingston detector in Louisiana United States and another 3 milliseconds later at the LIGO Hanford detector in the state of Washington in the United States The signal was detected and analyzed by a comparison with a prediction from general relativity defined from the post Newtonian expansion 1 3 An automatic computer search of the LIGO Hanford datastream triggered an alert to the LIGO team about 6 minutes after the event The gamma ray alert had already been issued at this point 16 seconds post event 23 so the timing near coincidence was automatically flagged The LIGO Virgo team issued a preliminary alert with only the crude gamma ray position to astronomers in the follow up teams at 40 minutes post event 24 25 Sky localisation of the event requires combining data from the three interferometers this was delayed by two problems The Virgo data were delayed by a data transmission problem and the LIGO Livingston data were contaminated by a brief burst of instrumental noise a few seconds prior to event peak but persisting parallel to the rising transient signal in the lowest frequencies These required manual analysis and interpolation before the sky location could be announced about 4 5 hours post event 26 25 The three detections localized the source to an area of 31 square degrees in the southern sky at 90 probability More detailed calculations later refined the localization to within 28 square degrees 24 2 In particular the absence of a clear detection by the Virgo system implied that the source was in one of Virgo s blind spots this absence of signal in Virgo data contributed to considerably reduce the source containment area 27 Gamma ray detection Edit Artistic concept two neutron stars merge The first electromagnetic signal detected was GRB 170817A a short gamma ray burst detected 1 74 0 05 s after the merger time and lasting for about 2 seconds 11 9 1 5 GRB 170817A was discovered by the Fermi Gamma ray Space Telescope with an automatic alert issued just 14 seconds after the GRB detection After the LIGO Virgo circular 40 minutes later manual processing of data from the INTEGRAL gamma ray telescope also detected the same GRB The difference in arrival time between Fermi and INTEGRAL helped to improve the sky localization This GRB was relatively faint given the proximity of the host galaxy NGC 4993 possibly due to its jets not being pointed directly toward Earth but rather at an angle of about 30 degrees to the side 8 28 Electromagnetic follow up Edit Hubble picture of NGC 4993 with inset showing GRB 170817A over 6 days Credit NASA and ESA Optical lightcurves The change in optical and near infrared spectra A series of alerts to other astronomers were issued beginning with a report of the gamma ray detection and single detector LIGO trigger at 13 21 UTC and a three detector sky location at 17 54 UTC 24 These prompted a massive search by many survey and robotic telescopes In addition to the expected large size of the search area about 150 times the area of a full moon this search was challenging because the search area was near the Sun in the sky and thus visible for at most a few hours after dusk for any given telescope 25 In total six teams One Meter Two Hemispheres 1M2H 29 DLT40 VISTA Master DECam and Las Cumbres Observatory Chile imaged the same new source independently in a 90 minute interval 1 5 The first to detect optical light associated with the collision was the 1M2H team running the Swope Supernova Survey which found it in an image of NGC 4993 taken 10 hours and 52 minutes after the GW event 11 1 30 by the 1 meter diameter 3 3 ft Swope Telescope operating in the near infrared at Las Campanas Observatory Chile They were also the first to announce it naming their detection SSS 17a in a circular issued 12h26m post event 29 The new source was later given an official International Astronomical Union IAU designation of AT 2017gfo The 1M2H team surveyed all galaxies in the region of space predicted by the gravitational wave observations and identified a single new transient 28 30 By identifying the host galaxy of the merger it is possible to provide an accurate distance consistent with that based on gravitational waves alone 1 5 The detection of the optical and near infrared source provided a huge improvement in localisation reducing the uncertainty from several degrees to 0 0001 degree this enabled many large ground and space telescopes to follow up the source over the following days and weeks Within hours after localization many additional observations were made across the infrared and visible spectrum 30 Over the following days the colour of the optical source changed from blue to red as the source expanded and cooled 28 Numerous optical and infrared spectra were observed early spectra were nearly featureless but after a few days broad features emerged indicative of material ejected at roughly 10 percent of light speed There are multiple strong lines of evidence that AT 2017gfo is indeed the aftermath of GW 170817 The colour evolution and spectra are dramatically different from any known supernova The distance of NGC 4993 is consistent with that independently estimated from the GW signal No other transient has been found in the GW sky localisation region Finally various archive images pre event show nothing at the location of AT 2017gfo ruling out a foreground variable star in the Milky Way 29 The source was detected in the ultraviolet but not in X rays 15 3 hours after the event by the Swift Gamma Ray Burst Mission 4 6 After initial lack of X ray and radio detections the source was detected in X rays 9 days later 31 using the Chandra X ray Observatory 32 33 and 16 days later in the radio 34 using the Karl G Jansky Very Large Array VLA in New Mexico 8 More than 70 observatories covering the electromagnetic spectrum observed the source 8 The radio and X ray light continued to rise for several months after the merger 35 and have been represented to be diminishing 36 Astronomers reported obtaining optical images of GW170817 afterglow using the Hubble Space Telescope 37 38 In March 2020 continued X ray emission at 5 sigma was observed by the Chandra Observatory 940 days after the merger demanding further augmentation or refutation of prior models that had previously been supplemented with additional post hoc interventions 39 Other detectors EditNo neutrinos consistent with the source were found in follow up searches by the IceCube and ANTARES neutrino observatories and the Pierre Auger Observatory 2 1 A possible explanation for the non detection of neutrinos is because the event was observed at a large off axis angle and thus the outflow jet was not directed towards Earth 40 41 Astrophysical origin and products EditThe gravitational wave signal indicated that it was produced by the collision of two neutron stars 9 20 22 42 with a total mass of 2 82 0 47 0 09 times the mass of the sun solar masses M 2 If low spins are assumed consistent with those observed in binary neutron stars that will merge within a Hubble time the total mass is 2 74 0 04 0 01 M The masses of the component stars have greater uncertainty The larger m1 has a 90 chance of being between 1 36 and 2 26 M and the smaller m2 has a 90 chance of being between 0 86 and 1 36 M 43 Under the low spin assumption the ranges are 1 36 to 1 60 M for m1 and 1 17 to 1 36 M for m2 The chirp mass a directly observable parameter which may be very roughly equated to the geometric mean of the masses is measured at 1 188 0 004 0 002 M 43 The origin and properties masses and spins of a double neutron star system like GW170817 are the result of a long sequence of complex binary star interactions 44 The neutron star merger event is thought to result in a spherically expanding kilonova 45 46 characterized by a short gamma ray burst followed by a longer optical afterglow powered by the radioactive decay of heavy r process nuclei Kilonovae are candidates for the production of half the chemical elements heavier than iron in the Universe 8 A total of 16 000 times the mass of the Earth in heavy elements is believed to have formed including approximately 10 Earth masses just of the two elements gold and platinum 47 A hypermassive neutron star was believed to have formed initially as evidenced by the large amount of ejecta much of which would have been swallowed by an immediately forming black hole The lack of evidence for emissions being powered by neutron star spin down which would occur for longer surviving neutron stars suggest it collapsed into a black hole within milliseconds 48 One search claimed to find evidence of a gravitational wave signal from the remnant neutron star or black hole 49 the energy of which was below the estimated sensitivity of the LIGO search algorithms at the time 50 and has recently been confirmed by a statistically independent method of analysis revealing the central engine of GRB170817A 51 Scientific importance Edit Artist s impression of strontium emerging from a neutron star merger 52 Scientific interest in the event was enormous with dozens of preliminary papers and almost 100 preprints 53 published the day of the announcement including 8 letters in Science 8 6 in Nature and 32 in a special issue of The Astrophysical Journal Letters devoted to the subject 54 The interest and effort was global The paper describing the multi messenger observations 1 is coauthored by almost 4 000 astronomers about one third of the worldwide astronomical community from more than 900 institutions using more than 70 observatories on all 7 continents and in space 7 8 This may not be the first observed event that is due to a neutron star merger GRB 130603B was the first plausible kilonova suggested based on follow up observations of short hard gamma ray bursts 55 It is however by far the best observation making this the strongest evidence to date to confirm the hypothesis that some mergers of binary stars are the cause of short gamma ray bursts 1 2 The event also provides a limit on the difference between the speed of light and that of gravity Assuming the first photons were emitted between zero and ten seconds after peak gravitational wave emission the difference between the speeds of gravitational and electromagnetic waves vGW vEM is constrained to between 3 10 15 and 7 10 16 times the speed of light which improves on the previous estimate by about 14 orders of magnitude 43 56 a In addition it allowed investigation of the equivalence principle through Shapiro delay measurement and Lorentz invariance 2 The limits of possible violations of Lorentz invariance values of gravity sector coefficients are reduced by the new observations by up to ten orders of magnitude 43 GW 170817 also excluded some alternatives to general relativity 57 including variants of scalar tensor theory 58 59 60 61 62 63 64 65 Horava Lifshitz gravity 61 66 62 Dark Matter Emulators 67 and bimetric gravity 68 Furthermore an analysis published in July 2018 used GW170817 to show that gravitational waves propagate through 3 1 dimensional spacetime in line with general relativity and contradicting hypotheses of leakage to higher dimensions of space 69 Gravitational wave signals such as GW 170817 may be used as a standard siren to provide an independent measurement of the Hubble constant 70 71 An initial estimate of the constant derived from the observation is 70 0 12 0 8 0 km s Mpc broadly consistent with current best estimates 70 Further studies improved the measurement to 70 3 5 3 5 0 km s Mpc 72 73 74 Together with the observation of future events of this kind the uncertainty is expected to reach two percent within five years and one percent within ten years 75 76 Electromagnetic observations helped to support the theory that the mergers of neutron stars contribute to rapid neutron capture r process nucleosynthesis 30 and are significant sources of r process elements heavier than iron 1 including gold and platinum which was previously attributed exclusively to supernova explosions 47 The first identification of r process elements in a neutron star merger was obtained during a re analysis of GW170817 spectra 77 The spectra provided direct proof of strontium production during a neutron star merger This also provided a direct proof that neutron stars are made of neutron rich matter In October 2017 Stephen Hawking in his last broadcast interview presented the overall scientific importance of GW170817 78 In September 2018 astronomers reported related studies about possible mergers of neutron stars NS and white dwarfs WD including NS NS NS WD and WD WD mergers 79 See also Edit Astronomy portal Physics portalGravitational wave astronomy List of gravitational wave observations Multi messenger astronomyNotes Edit Previous constraint on the difference between the light speed and the gravitational speed was about 20 56 References Edit a b c d e f g h i j k l m n Abbott BP et al LIGO Virgo and other collaborations October 2017 Multi messenger Observations of a Binary Neutron Star Merger PDF The Astrophysical Journal 848 2 L12 arXiv 1710 05833 Bibcode 2017ApJ 848L 12A doi 10 3847 2041 8213 aa91c9 The optical and near infrared spectra over these few days provided convincing arguments that this transient was unlike any other discovered in extensive optical wide field surveys over the past decade a b c d e f g h Abbott BP Abbott R Abbott TD Acernese F Ackley K Adams C et al LIGO Scientific Collaboration amp Virgo Collaboration October 2017 GW170817 Observation of Gravitational Waves from a Binary Neutron Star Inspiral Physical Review Letters 119 16 161101 arXiv 1710 05832 Bibcode 2017PhRvL 119p1101A doi 10 1103 PhysRevLett 119 161101 PMID 29099225 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 a b 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 a b c Overbye D 16 October 2017 LIGO detects fierce collision of neutron stars for the first time The New York Times Retrieved 16 October 2017 a b c Cho A December 2017 Cosmic convergence Science 358 6370 1520 1521 Bibcode 2017Sci 358 1520C doi 10 1126 science 358 6370 1520 PMID 29269456 a b c Schilling G 16 October 2017 Astronomers catch gravitational waves from colliding neutron stars Sky amp Telescope because colliding black holes don t give off any light you wouldn t expect any optical counterpart a b c d e f g h i Cho A 16 October 2017 Merging neutron stars generate gravitational waves and a celestial light show Science doi 10 1126 science aar2149 a b c d Castelvecchi D August 2017 Rumours swell over new kind of gravitational wave sighting Nature News doi 10 1038 nature 2017 22482 Breakthrough of the year 2017 Science AAAS 22 December 2017 a b c d Krieger LM 16 October 2017 A bright light seen across the Universe proving Einstein right violent collisions source of our gold silver The Mercury News Retrieved 16 October 2017 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 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 Mohon L 16 October 2018 GRB 150101B A distant cousin to GW 170817 NASA Retrieved 17 October 2018 Wall M 17 October 2018 Powerful cosmic flash is likely another neutron star merger Space com Retrieved 17 October 2018 Troja E Castro Tirado AJ Becerra Gonzalez 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 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 doi 10 1038 s41586 022 05327 3 PMC 9729102 PMID 36477127 Kilonova Discovery Challenges our Understanding of Gamma Ray Bursts Gemini Observatory 7 December 2022 Retrieved 11 December 2022 LIGO and Virgo make first detection of gravitational waves produced by colliding neutron stars MIT News 16 October 2017 Retrieved 23 October 2017 a b McKinnon M 23 August 2017 Exclusive We may have detected a new kind of gravitational wave New Scientist Retrieved 28 August 2017 A very exciting LIGO Virgo observing run is drawing to a close August 25 LIGO 25 August 2017 Retrieved 29 August 2017 a b Drake N 25 August 2017 Strange stars caught wrinkling spacetime Get the facts National Geographic Retrieved 27 August 2017 GCN notices related to Fermi GBM alert 524666471 Gamma ray Burst Coordinates Network NASA Goddard Space Flight Center 17 August 2017 Retrieved 19 October 2017 a b c GCN circulars related to LIGO trigger G298048 Gamma ray Burst Coordinates Network NASA Goddard Space Flight Center 17 August 2017 Retrieved 19 October 2017 a b c Castelvecchi D October 2017 Colliding stars spark rush to solve cosmic mysteries Nature 550 7676 309 310 Bibcode 2017Natur 550 309C doi 10 1038 550309a PMID 29052641 Christopher B 16 October 2017 GW170817 The pot of gold at the end of the rainbow Retrieved 19 October 2017 Schilling GA January 2018 Two massive collisions and a Nobel Prize Sky amp Telescope 135 1 10 a b c Choi CQ 16 October 2017 Gravitational waves detected from neutron star crashes The discovery explained Space com Purch Group Retrieved 16 October 2017 a b c Ryan Foley and Enrico Ramirez Ruiz October 2017 GW170817 SSS17a One Meter Two Hemispheres 1M2H a b c d Drout MR Piro AL Shappee BJ Kilpatrick CD Simon JD Contreras C et al December 2017 Light curves of the neutron star merger GW170817 SSS17a Implications for r process nucleosynthesis Science 358 6370 1570 1574 arXiv 1710 05443 Bibcode 2017Sci 358 1570D doi 10 1126 science aaq0049 PMID 29038375 Troja E Piro L van Eerten H November 2017 The X ray counterpart to the gravitational wave event GW170817 Nature 551 7678 71 74 arXiv 1710 05433 doi 10 1038 nature24290 ISSN 1476 4687 S2CID 205261229 Chandra Photo Album GW170817 October 16 2017 chandra si edu Retrieved 16 August 2019 Chandra Makes First Detection of X rays from a Gravitational Wave Source Interview with Chandra Scientist Eleonora Nora Troja chandra si edu Retrieved 16 August 2019 Hallinan G Corsi A 2017 A radio counterpart to a neutron star merger Science 358 6370 1579 1583 doi 10 1126 science aap9855 PMID 29038372 S2CID 3974441 Neutron star merger creates new mysteries Kaplan D Murphy T Signals from a spectacular neutron star merger that made gravitational waves are slowly fading away The Conversation Retrieved 16 August 2019 Morris A 11 September 2019 Hubble Captures Deepest Optical Image of First Neutron Star Collision ScienceDaily com Retrieved 11 September 2019 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New method may resolve difficulty in measuring universe s expansion Neutron star mergers can provide new cosmic ruler National Radio Astronomy Observatory 8 July 2019 Retrieved 8 July 2019 via EurekAlert Finley D 8 July 2019 New method may resolve difficulty in measuring Universe s expansion National Radio Astronomy Observatory Retrieved 8 July 2019 Lerner L 22 October 2018 Gravitational waves could soon provide measure of universe s expansion Retrieved 22 October 2018 via Phys org Chen HY Fishbach M Holz DE October 2018 A two per cent Hubble constant measurement from standard sirens within five years Nature 562 7728 545 547 arXiv 1712 06531 Bibcode 2018Natur 562 545C doi 10 1038 s41586 018 0606 0 PMID 30333628 S2CID 52987203 Watson D Hansen CJ Selsing J Koch A Malesani DB Andersen AC et al October 2019 Identification of strontium in the merger of two neutron stars Nature 574 7779 497 500 arXiv 1910 10510 Bibcode 2019Natur 574 497W doi 10 1038 s41586 019 1676 3 PMID 31645733 S2CID 204837882 Ghosh P 26 March 2018 Stephen Hawking s final interview A beautiful Universe BBC News Retrieved 26 March 2018 Rueda JA Ruffini R Wang Y Aimuratov Y de Almeida UB Bianco CL et al 28 September 2018 GRB 170817A GW 170817 AT 2017gfo and the observations of NS NS NS WD and WD WD mergers Journal of Cosmology and Astroparticle Physics 2018 10 006 arXiv 1802 10027 Bibcode 2018JCAP 10 006R doi 10 1088 1475 7516 2018 10 006 S2CID 119369873 External links Edit Wikimedia Commons has media related to GW170817 Detections LIGO Follow up observations of GW 170817 Related videos 16 October 2017 NSF LIGO Virgo press conference 2 panels and Q amp As 03 21 on YouTube MPI Sound of the merger 0 32 on YouTube AAAS 02m42s on YouTube Caltech 03m56s on YouTube MIT 00m42s on YouTube SciNews 01m46s on YouTube Portals Physics Astronomy Stars Spaceflight Solar System Retrieved from https en wikipedia org w index php title GW170817 amp oldid 1144805061, wikipedia, wiki, book, books, library,

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