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GW170817
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factoids
{{r|ApJ}}
|dec={{DEC|−23|22|53.3}}{{r|ApJ}}
|epoch=J2000.0
|distance={{convert|40|Mpc|lk=on}}
|detected_by=LIGO, Virgo
}}{{Sky |13|09|48.08 |-|23|22|53.3 |130000000}}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 {{nowrap|NGC 4993}}. The GW was produced by the last minutes of two neutron stars spiralling closer to each other and finally merging, and is the first GW observation which has been confirmed by non-gravitational means.{{r|ApJ|PhysRev2017}} Unlike the five previous GW detections, which were of merging black holes not expected to produce a detectable electromagnetic signal,JOURNAL, Focus on electromagnetic counterparts to binary black hole mergers, Valerie, Connaughton, The Astrophysical Journal Letters, 2016, Editorial,weblink 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., JOURNAL, Electromagnetic counterparts to black hole mergers detected by LIGO, Loeb, Abraham, The Astrophysical Journal Letters, 819, 2, L21, March 2016, 1602.04735, 10.3847/2041-8205/819/2/L21, free, 2016ApJ...819L..21L, Mergers of stellar-mass black holes (BHs) [...] are not expected to have electromagnetic counterparts. [...] I show that the [GW and gamma-ray] signals might be related if the BH binary detected by LIGO originated from two clumps in a dumbbell configuration that formed when the core of a rapidly rotating massive star collapsed., {{r|SkyandTelescope}}{{efn|Although acknowledged as unlikely, several mechanisms have been suggested by which a black hole merger could be surrounded by sufficient matter to produce an electromagnetic signal, which astronomers have been searching for.{{r|Loeb}}JOURNAL, de Mink, S.E., King, A., Electromagnetic signals following stellar-mass black hole mergers, The Astrophysical Journal Letters, April 2017, 839, 1, L7, 10.3847/2041-8213/aa67f3, 1703.07794, 2017ApJ...839L...7D,weblink It is often assumed that gravitational-wave (GW) events resulting from the merger of stellar-mass black holes are unlikely to produce electromagnetic (EM) counterparts. We point out that the progenitor binary has probably shed a mass {{solar mass, ≳ 10, during its prior evolution. If even a tiny fraction of this gas is retained in a circum-binary disk, the sudden mass loss and recoil of the merged black hole shocks and heats it within hours of the GW event. Whether the resulting EM signal is detectable is uncertain.}}}} 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.{{r|ApJ|ApJL}}NEWS, Landau, Elizabeth, Chou, Felicia, Washington, Dewayne, Porter, Molly, NASA missions catch first light from a gravitational-wave event,weblink 16 October 2017, NASA, 16 October 2017, NEWS,weblink Neutron star discovery marks breakthrough for 'multi-messenger astronomy', Eva, Botkin-Kowacki, The Christian Science Monitor, 16 October 2017, 17 October 2017, ARXIV, Welcome to the multi-messenger era! Lessons from a neutron star merger and the landscape ahead, Brian D., Metzger, 16 October 2017, 1710.05931, astro-ph.HE, The discovery and subsequent observations of GW 170817 were given the Breakthrough of the Year award for 2017 by the journal Science.WEB, Breakthrough of the year 2017,weblink Science {{!, AAAS |language=en |date=22 December 2017}}JOURNAL, 10.1126/science.358.6370.1520, 29269456, Cosmic convergence, Science, 358, 6370, 1520–1521, 2017, Cho, Adrian, 2017Sci...358.1520C, 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.{{r|ApJ|NYT-20171016|MN-20171016}} 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 {{nowrap|NGC 4993}}{{r|SM-20171016}} 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 {{nowrap|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.NEWS, University of Maryland, 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.,weblink 16 October 2018, EurekAlert!, 17 October 2018, JOURNAL, Troja, E., etal, A luminous blue kilonova and an off-axis jet from a compact binary merger at z = 0.1341, 16 October 2018, Nature Communications, 9, 4089, 4089 (2018), 10.1038/s41467-018-06558-7, 30327476, 6191439, 2018NatCo...9.4089T, 1806.10624, NEWS, Mohon, Lee, GRB 150101B: A distant cousin to GW 170817,weblink 16 October 2018, NASA, 17 October 2018, WEB, Wall, Mike, Powerful cosmic flash is likely another neutron-star merger,weblink 17 October 2018, Space.com, 17 October 2018, In retrospect, GRB 160821B, another gamma-ray burst event is now construed to be another kilonova,E Troja, A J Castro-Tirado, J Becerra González, Y Hu, G S Ryan, S B Cenko, R Ricci, G Novara, R Sánchez-Rámirez, J A Acosta-Pulido et.al. (27 August 2019) The afterglow and kilonova of the short GRB 160821B by its resemblance of its data to GRB 170817A,29 authors (16 Oct 2017) An Ordinary Short Gamma-Ray Burst with Extraordinary Implications: Fermi-GBM Detection of GRB 170817A part of the multi-messenger now denoted GW170817.

Announcement

|author=David Reitze |source=LIGO executive director |width=30%}}
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.NEWS, Overbye, Dennis, Dennis Overbye, LIGO detects fierce collision of neutron stars for the first time,weblink 16 October 2017, The New York Times, 16 October 2017, NEWS, Krieger, Lisa M., A bright light seen across the Universe, proving Einstein right – violent collisions source of our gold, silver,weblink 16 October 2017, The Mercury News, 16 October 2017, JOURNAL, Cho, Adrian, Merging neutron stars generate gravitational waves and a celestial light show, 16 October 2017, Science (magazine), Science, 10.1126/science.aar2149,weblink 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!".NEWS, Schilling, Govert, Astronomers catch gravitational waves from colliding neutron stars,weblink Sky & Telescope, 16 October 2017, because colliding black holes don’t give off any light, you wouldn’t expect any optical counterpart., 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 {{nowrap|NGC 4993}}, a galaxy {{convert|40|Mpc|Mly|abbr=on|lk=on}} away in the Hydra constellation.NEWS, Castelvecchi, Davide, Rumours swell over new kind of gravitational-wave sighting, August 2017, Nature (journal), Nature News, 10.1038/nature.2017.22482, NEWS, McKinnon, Mika, Exclusive: We may have detected a new kind of gravitational wave,weblink 23 August 2017, New Scientist, 28 August 2017, The collaboration had earlier declined to comment on the rumors, not adding to a previous announcement that there were several triggers under analysis.NEWS, A very exciting LIGO-Virgo observing run is drawing to a close August 25,weblink 25 August 2017, LIGO, 29 August 2017, {{r|NG-20170825}}

Gravitational wave detection

File:Neutron star collision.ogv|thumb|left|Artist's impression of the collision of two neutron stars. This is a general illustration, not specific to GW170817. ((:File:Neutron star collision.ogv|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.{{rp|2}} It arrived first at the Virgo detector in Italy, then 22 milliseconds later at the LIGO-Livingston detector in Louisiana, USA, and another 3 milliseconds later at the LIGO-Hanford detector in the state of Washington, USA. The signal was detected and analyzed by a comparison with a prediction from general relativity defined from the post-Newtonian expansion.{{rp|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),WEB,weblink GCN notices related to Fermi-GBM alert 524666471, 17 August 2017, 19 October 2017, Gamma-ray Burst Coordinates Network, NASA Goddard Space Flight Center, 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.{{r|GCN|Davide_16}}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.WEB, GW170817—The pot of gold at the end of the rainbow, Christopher, Berry, 16 October 2017, 19 October 2017,weblink JOURNAL, Colliding stars spark rush to solve cosmic mysteries, Castelvecchi, Davide, 16 October 2017, Nature, 550, 7676, 309–310, 10.1038/550309a, 29052641, 2017Natur.550..309C, 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.{{r|GCN|PhysRev2017}} 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.JOURNAL, Schilling, Govert A., Two massive collisions and a Nobel Prize, Sky & Telescope, 135, 1, 10, January 2018,

Gamma ray detection

(File:Artist NSIllustration CREDIT NSF LIGO Sonoma State University A. Simonnet.jpg|thumb|150px|Artistic concept: two neutron stars merge)The first electromagnetic signal detected was GRB 170817A, a short gamma-ray burst, detected {{val|1.74|0.05|u=seconds}} after the merger time and lasting for about 2 seconds.{{r|MN-20171016|NAT-20170825}}{{rp|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 {{nowrap|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.{{r|SM-20171016}}WEB,weblink Gravitational waves detected from neutron star crashes: The discovery explained, Charles Q., Choi, 16 October 2017, Space.com, Purch Group, 16 October 2017,

Electromagnetic follow-up

(File:NGC 4993 and GRB170817A after glow.gif|thumb|Hubble picture of NGC 4993 with inset showing GRB 170817A over 6 days. Credit: NASA and ESA)(File:Eso1733f.svg|thumb|Optical lightcurves)(File:Eso1733j X-shooter spectra montage of kilonova in NGC4993.png|thumb|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.WEB,weblink GCN circulars related to LIGO trigger G298048, 17 August 2017, 19 October 2017, Gamma-ray Burst Coordinates Network, NASA Goddard Space Flight Center, 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.{{r|Davide_16}}In total six teams (SSS, DLT40, VISTA, Master, DECam, Las Cumbres Observatory (LCO) Chile) imaged the same new source independently in a 90-minute interval.{{r|ApJ|p=5}} The first to detect optical light associated with the collision was the Swope Supernova Survey, which found it in an image of {{nowrap|NGC 4993}} taken 10 hours and 52 minutes after the GW event{{r|MN-20171016|ApJ|Drout}} by the {{convert|1|m|ft|diameter|adj=mid|sp=us}} 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 12{{sup|h}}26{{sup|m}} post-event. The new source was later given an official International Astronomical Union (IAU) designation of AT 2017gfo.The SSS team surveyed all galaxies in the region of space predicted by the gravitational wave observations, and identified a single new transient.{{r|spacecom|Drout}} By identifying the host galaxy of the merger, it is possible to provide an accurate distance consistent with that based on gravitational waves alone.{{r|ApJ|p=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.{{r|Drout}} Over the following days, the color of the optical source changed from blue to red as the source expanded and cooled.{{r|spacecom}}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.{{r|ApJ}}The source was detected in the ultraviolet (but not in the X-rays) 15.3 hours after the event by the Swift Gamma-Ray Burst Mission.{{r|ApJ|page1=6}} After initial lack of X-ray and radio detections, the source was detected in the X-rays 9 days later by the Chandra X-ray Observatory,WEB,weblink Chandra :: Photo Album :: GW170817 :: October 16, 2017, chandra.si.edu, 16 August 2019, WEB,weblink Chandra Makes First Detection of X-rays from a Gravitational Wave Source: Interview with Chandra Scientist Eleonora Nora Troja, chandra.si.edu, 16 August 2019, and 16 days later in the radio by the Karl G. Jansky Very Large Array (VLA) in New Mexico.{{r|SM-20171016}} More than 70 observatories covering the electromagnetic spectrum observed the source.{{r|SM-20171016}}The radio and X-ray light continued to rise for several months after the merger,NEWS,weblink Neutron-star merger creates new mysteries, and are now fading away at a fast rate.WEB,weblink Signals from a spectacular neutron star merger that made gravitational waves are slowly fading away, Kaplan, David, Murphy, Tara, The Conversation, en, 16 August 2019, In September 2019, astronomers reported obtaining an optical image of the GW 170817 afterglow by the Hubble Space Telescope.NEWS, Morris, Amanda, Hubble Captures Deepest Optical Image of First Neutron Star Collision,weblink 11 September 2019, ScienceDaily.com, 11 September 2019, JOURNAL, Fong, W., et al., The Optical Afterglow of GW170817: An Off-axis Structured Jet and Deep Constraints on a Globular Cluster Origin, The Astrophysical Journal, 883, 1, L1, 23 August 2019, 1908.08046, 2019ApJ...883L...1F, 10.3847/2041-8213/ab3d9e,

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.JOURNAL, Abbott, B. P., etal., LIGO Scientific Collaboration & Virgo interferometer, Virgo Collaboration, GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral, Physical Review Letters, October 2017, 119, 16, 161101, 10.1103/PhysRevLett.119.161101, 29099225, free, 1710.05832,weblink 2017PhRvL.119p1101A, "MEMBERWIDE">FIRST1=B. P. COLLABORATION=LIGO, VIRGO AND OTHER COLLABORATIONS JOURNAL=THE ASTROPHYSICAL JOURNAL VOLUME=848 PAGE=L12 DOI-ACCESS=FREE URL=HTTPS://DCC.LIGO.ORG/PUBLIC/0145/P1700294/007/APJL-MMAP-171017.PDF BIBCODE=2017APJ...848L..12A, 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.ALBERT >FIRST1=A. COLLABORATION=ANTARES OBSERVATORY, ICECUBE NEUTRINO OBSERVATORY>ICECUBE COLLABORATION, PIERRE AUGER OBSERVATORY, LIGO SCIENTIFIC COLLABORATION, & VIRGO INTERFEROMETER>VIRGO COLLABORATION JOURNAL= ISSUE=2 DATE=OCTOBER 2017 URL=HTTPS://DCC.LIGO.ORG/PUBLIC/0146/P1700344/006/GW170817_NEUTRINOS.PDF DOI=10.3847/2041-8213/AA9AED, BRAVO >FIRST1=SYLVIA URL=HTTP://ICECUBE.WISC.EDU/NEWS/VIEW/539 ICECUBE NEUTRINO OBSERVATORY>ICECUBE SOUTH POLE NEUTRINO OBSERVATORY ACCESSDATE=20 OCTOBER 2017,

Astrophysical origin and products

The gravitational wave signal indicated that it was produced by the collision of two neutron stars{{r|NAT-20170825|NS-20170823}}NEWS, Drake, Nadia, Strange stars caught wrinkling spacetime? Get the facts.,weblink 25 August 2017, National Geographic (magazine), National Geographic, 27 August 2017, NEWS, Sokol, Joshua, What happens when two neutron stars collide? Scientific revolution,weblink 25 August 2017, Wired (magazine), Wired, 27 August 2017, with a total mass of {{val|2.82|0.47|0.09}} times the mass of the sun (solar masses).{{r|PhysRev2017}} If low spins are assumed, consistent with those observed in binary neutron stars that will merge within a Hubble time, the total mass is {{val|2.74|0.04|0.01|ul=solar mass}}.The masses of the component stars have greater uncertainty. The larger ({{math|m1}}) has a 90% chance of being between {{val|1.36|and|2.26|u=solar mass}}, and the smaller ({{math|m2}}) has a 90% chance of being between {{val|0.86|and|1.36|u=solar mass}}.{{r|Abbott^3_AJT}} Under the low spin assumption, the ranges are {{val|1.36|to|1.60|u=solar mass}} for {{math|m1}} and {{val|1.17|to|1.36|u=solar mass}} for {{math|m2}}.The chirp mass, a directly observable parameter which may be very roughly equated to the geometric mean of the masses, is measured at {{val|1.188|0.004|0.002|u=solar mass}}.{{r|Abbott^3_AJT}}The neutron star merger event is thought to result in a kilonova, 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.{{r|SM-20171016}} 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.AV MEDIA, Edo, Berger, 1{{sup, h, 48{{sup|m}} |url=https://www.youtube.com/watch?v=mtLPKYl4AHs |title=LIGO/Virgo Press Conference |date=16 October 2017 |accessdate=29 October 2017}}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.JOURNAL, Margalit, Ben, Metzger, Brian D., Constraining the Maximum Mass of Neutron Stars from Multi-messenger Observations of GW 170817, The Astrophysical Journal Letters, 850, 2, 21 November 2017, L19, 10.3847/2041-8213/aa991c, free, 1710.05938, 2017ApJ...850L..19M, Later searches did find evidence of spin-down in the gravitational signal, suggesting a longer-lived neutron star.JOURNAL, Maurice H P M, van Putten, Massimo, Della Valle, Observational evidence for extended emission to GW 170817, Monthly Notices of the Royal Astronomical Society: Letters, 482, 1, January 2019, L46–L49, 10.1093/mnrasl/sly166, free, 1806.02165, 2019MNRAS.482L..46V, we report on a possible detection of extended emission (EE) in gravitational radiation during GRB170817A: a descending chirp with characteristic time-scale τs = {{val, 3.01, 0.2, s, in a (H1,L1)-spectrogram up to 700 Hz with Gaussian equivalent level of confidence greater than 3.3 Ïƒ based on causality alone following edge detection applied to (H1,L1)-spectrograms merged by frequency coincidences. Additional confidence derives from the strength of this EE. The observed frequencies below 1 kHz indicate a hypermassive magnetar rather than a black hole, spinning down by magnetic winds and interactions with dynamical mass ejecta.}}

Scientific importance

Scientific interest in the event was enormous, with dozens of preliminary papers (and almost 100 preprintsWEB, ArXiv.org search for GW 170817,weblink 18 October 2017, ) published the day of the announcement, including 8 letters in Science,{{r|SM-20171016}} 6 in Nature, and 32 in a special issue of The Astrophysical Journal Letters devoted to the subject.JOURNAL, Focus on the electromagnetic counterpart of the neutron star binary merger GW 170817, The Astrophysical Journal Letters, 848, 2, Edo, Berger, Editorial,weblink 16 October 2017, It is rare for the birth of a new field of astrophysics to be pinpointed to a singular event. This focus issue follows such an event – the neutron star binary merger GW 170817 – marking the first joint detection and study of gravitational waves (GWs) and electromagnetic radiation (EM)., The interest and effort was global: The paper describing the multi-messenger observations{{r|ApJ}} 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.{{r|SkyandTelescope}}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.WEB,weblink Kilonova Alert! Hubble Solves Gamma Ray Burst Mystery, DNews, 7 August 2013, Seeker, 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.{{r|ApJ|PhysRev2017}}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.JOURNAL, 10.3847/2041-8213/aa920c, free, 848, 2, L13, Abbott, B. P., etal, Gravitational waves and gamma-rays from a binary neutron star merger: GW 170817 and GRB 170817A, The Astrophysical Journal Letters, 2017, 1710.05834, 2017ApJ...848L..13A, JOURNAL,weblink Viewpoint: Reining in Alternative Gravity, Schmidt, Fabian, 18 December 2017, Physics, 10, 10.1103/physics.10.134, {{efn|Previous constraint on the difference between the light speed and the gravitational speed was about ±20%.}} In addition, it allowed investigation of the equivalence principle (through Shapiro delay measurement) and Lorentz invariance.{{r|PhysRev2017}} 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.{{r|Abbott^3_AJT}} GW 170817 also excluded some alternatives to general relativity,NEWS, How crashing neutron stars killed off some of our best ideas about what 'dark energy' is, 13 December 2017, Thomas, Kitching, The Conversation, phys.org,weblink including variants of scalar–tensor theory,JOURNAL, Breaking a Dark Degeneracy with Gravitational Waves, Journal of Cosmology and Astroparticle Physics, 2016, 3, 031, Lucas, Lombriser, Andy, Taylor, 1509.08458, 28 September 2015, 10.1088/1475-7516/2016/03/031, 2016JCAP...03..031L, JOURNAL, Challenges to self-acceleration in modified gravity from gravitational waves and large-scale structure, Phys. Lett. B, 765, 382–385, Lucas, Lombriser, Nelson, Lima, 1602.07670, 2017, 10.1016/j.physletb.2016.12.048, 2017PhLB..765..382L, JOURNAL, Bettoni, Dario, Ezquiaga, Jose María, Hinterbichler, Kurt, Zumalacárregui, Miguel, 14 April 2017, Speed of gravitational waves and the fate of Scalar-Tensor Gravity, 1608.01982, Physical Review D, 95, 8, 084029, 10.1103/PhysRevD.95.084029, 2470-0010, 2017PhRvD..95h4029B, JOURNAL, Ezquiaga, Jose María, Zumalacárregui, Miguel, 18 December 2017, Dark energy after GW 170817: Dead ends and the road ahead, Physical Review Letters, 119, 25, 251304, 10.1103/PhysRevLett.119.251304, 29303304, 2017PhRvL.119y1304E, 1710.05901, NEWS,weblink Quest to settle riddle over Einstein's theory may soon be over, 10 February 2017, 29 October 2017, phys.org, NEWS,weblink Theoretical battle: Dark energy vs. modified gravity, 25 February 2017, 27 October 2017, Ars Technica, NEWS,weblink Gravitational waves, Science News, 1 November 2017, en, HoÅ™ava–Lifshitz gravity,JOURNAL, Dark Energy after GW 170817, Phys. Rev. Lett., 119, 25, 251302, Paolo, Creminelli, Filippo, Vernizzi, 1710.05877, 16 October 2017, 10.1103/PhysRevLett.119.251302, 29303308, 2017PhRvL.119y1302C, JOURNAL, Implications of the neutron star merger GW 170817 for cosmological Scalar-Tensor Theories, Phys. Rev. Lett., 119, 25, 251303, Jeremy, Sakstein, Bhuvnesh, Jain, 1710.05893, 16 October 2017, 10.1103/PhysRevLett.119.251303, 29303345, 2017PhRvL.119y1303S, JOURNAL, Dark energy after GW 170817: Dead ends and the road ahead, Phys. Rev. Lett., 119, 25, 251304, Jose María, Ezquiaga, Miguel, Zumalacárregui, 16 October 2017, 1710.05901, 10.1103/PhysRevLett.119.251304, 29303304, 2017PhRvL.119y1304E, Dark Matter EmulatorsJOURNAL, Boran, Sibel, Desai, Shantanu, Kahya, Emre, Woodard, Richard, 2018, GW 170817 falsifies dark matter emulators, Phys. Rev. D, 97, 4, 041501, 1710.06168, 10.1103/PhysRevD.97.041501, 2018PhRvD..97d1501B, and bimetric gravity.JOURNAL, Strong constraints on cosmological gravity from GW 170817 and GRB 170817A., Phys. Rev. Lett., 119, 25, 251301, T., Baker, E., Bellini, P.G., Ferreira, M., Lagos, J., Noller, I., Sawicki, 1710.06394, 19 October 2017, 10.1103/PhysRevLett.119.251301, 29303333, 2017PhRvL.119y1301B, Gravitational wave signals such as GW 170817 may be used as a standard siren to provide an independent measurement of the Hubble constant.JOURNAL, A gravitational-wave standard siren measurement of the Hubble constant, Nature, 551, 7678, 2017, 85–88, 0028-0836, 10.1038/nature24471, 29094696, 1710.05835, Loeb, Abraham, 1M2H Collaboration, Dark Energy Camera GW-EM Collaboration the DES Collaboration, DLT40 Collaboration, Las Cumbres Observatory Collaboration, VINROUGE Collaboration, MASTER Collaboration, NEWS, Scharping, Nathaniel, Gravitational waves show how fast the Universe is expanding,weblink 18 October 2017, Astronomy (magazine), Astronomy, 18 October 2017, An initial estimate of the constant derived from the observation is {{val|70.0|+12.0|-8.0}} (km/s)/Mpc, broadly consistent with current best estimates.{{r|Nat24471}} Further studies improved the measurement to {{val|70.3|+5.3|-5.0}} (km/s)/Mpc.JOURNAL, Hotokezaka, K., etal, A Hubble constant measurement from superluminal motion of the jet in GW 170817,weblink 8 July 2019, Nature Astronomy, 385, 10.1038/s41550-019-0820-1, 8 July 2019, 2019NatAs.tmp..385H, 1806.10596, NEWS, National Radio Astronomy Observatory, New method may resolve difficulty in measuring universe's expansion – Neutron star mergers can provide new 'cosmic ruler',weblink 8 July 2019, EurekAlert!, 8 July 2019, NEWS, Finley, Dave, New method may resolve difficulty in measuring Universe's expansion,weblink 8 July 2019, National Radio Astronomy Observatory, 8 July 2019, 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.WEB, Lerner, Louise, Gravitational waves could soon provide measure of universe's expansion,weblink 22 October 2018, Phys.org, 22 October 2018, JOURNAL, Chen, Hsin-Yu, Fishbach, Maya, Holz, Daniel E., A two per cent Hubble constant measurement from standard sirens within five years, 17 October 2018, Nature (journal), Nature, 562, 7728, 545–547, 10.1038/s41586-018-0606-0, 30333628, 2018Natur.562..545C, 1712.06531, Electromagnetic observations helped to support the theory that the mergers of neutron stars contribute to rapid neutron capture r-process nucleosynthesisJOURNAL, Drout, M. R., etal, 10.1126/science.aaq0049, 29038375, free, Light curves of the neutron star merger GW 170817 / SSS 17a: Implications for r-process nucleosynthesis, Science (journal), Science, 358, 6370, 1570–1574, October 2017, 1710.05443, 2017Sci...358.1570D, and are significant sources of r-process elements heavier than iron,{{r|ApJ}} including gold and platinum.{{r|EdoBerger}}In October 2017, Stephen Hawking, in his last broadcast interview, presented the overall scientific importance of GW 170817.NEWS, Ghosh, Pallab, Stephen Hawking's final interview: A beautiful Universe,weblink 26 March 2018, BBC news, 26 March 2018, 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.JOURNAL, Rueda, J.A., etal, 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, 28 September 2018, 1802.10027, 10.1088/1475-7516/2018/10/006, 2018JCAP...10..006R,

See also

Notes

{{notelist}}

References

{{reflist}}

External links

{{Commons category}}
  • WEB,weblink Detections, LIGO,
  • WEB,weblink Follow-up observations of GW 170817,
  • Related videos (16 October 2017):
    • {{youtube|mtLPKYl4AHs|NSF LIGO-Virgo press conference: 2 panels and Q&As (03:21)}}
    • {{youtube|_SQbaILipjY|MPI: Sound of the merger (0:32)}}
    • {{youtube|e_uIOKfv710|AAAS (02{{sup|m}}42{{sup|s}})}}
    • {{youtube|lvejpeC6z5I|CalTech (03{{sup|m}}56{{sup|s}})}}
    • {{youtube|sgkDoSbHHVU|MIT (00{{sup|m}}42{{sup|s}})}}
    • {{youtube|JNfZ5qk_Pk8|SciNews (01{{sup|m}}46{{sup|s}})}}
{{Gravitational-wave observatories}}{{Breakthrough of the Year}}{{2017 in space}}

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