GW170817
J2000.0 | |
Distance | 40 megaparsecs (130 Mly) |
---|---|
Redshift | 0.0099 |
Other designations | GW170817 |
Related media on Commons | |
] |
GW 170817 was a
The gravitational wave signal, designated GW 170817, had a duration of approximately 100 seconds, and showed the characteristic intensity and frequency expected of the
An intense observing campaign then took place to search for the expected emission at optical wavelengths. An
In October 2018, astronomers reported that
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
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
The gravitational wave signal lasted for approximately 100 seconds starting from a frequency of 24
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
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
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),
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
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
−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, inside a 12 km radius.[44]
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 total energy output of gravitational wave is ≃63 Foe.[45]
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.[46]
The neutron star merger event is thought to result in a spherically expanding kilonova,[47][48] 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.[49]
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.[50]
One search claimed to find evidence of a gravitational wave signal from the remnant neutron star or black hole,[51] the energy of which was below the estimated sensitivity of the LIGO search algorithms at the time [52] and has recently been confirmed by a statistically independent method of analysis revealing the central engine of GRB170817A.[53]
Scientific importance
Scientific interest in the event was enormous, with dozens of preliminary papers (and almost 100
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.[57] 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.
Gravitational wave signals such as GW 170817 may be used as a
−5.0 (km/s)/Mpc.[74][75][76] 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.[77][78]
Electromagnetic observations help support the theory that neutron star mergers contribute to rapid neutron capture (r-process) nucleosynthesis[30]—previously assumed to be associated with supernova explosions—and are therefore the primary source of r-process elements heavier than iron,[1] including gold and platinum.[49] The first identification of r-process elements in a neutron star merger was obtained during a re-analysis of GW170817 spectra.[79] The spectra provided direct proof of strontium production during a neutron star merger. This also provided the most direct proof that neutron stars are made of neutron-rich matter. Since then, several r-process elements have been identified in the ejecta including yttrium,[80] lanthanum and cerium.[81]
In October 2017, Stephen Hawking, in his last broadcast interview, discussed the overall scientific importance of GW170817.[82] 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.[83]
See also
Notes
References
- ^ .
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.
- ^ PMID 29099225.
- 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.
- ^ PMID 29269456.
- ^ a b c Schilling G (16 October 2017). "Astronomers catch gravitational waves from colliding neutron stars". Sky & Telescope.
because colliding black holes don't give off any light, you wouldn't expect any optical counterpart.
- ^ .
- ^ .
- ^ "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.
- EurekAlert!.
- 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.
- S2CID 145047934.
- 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.
- ^ National Geographic. Archived from the originalon 27 August 2017. Retrieved 27 August 2017.
- Gamma-ray Burst Coordinates Network. NASA Goddard Space Flight Center. 17 August 2017. Retrieved 19 October 2017.
- ^ Gamma-ray Burst Coordinates Network. NASA Goddard Space Flight Center. 17 August 2017. Retrieved 19 October 2017.
- ^ 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 & 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)
- ^ PMID 29038375.
- 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.
- S2CID 3974441.
- ^ "Neutron-star merger creates new mysteries".
- ^ Kaplan D, Murphy T (30 April 2018). "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.
- ISSN 2041-8213.
- ^ Troja E, Piro L, Ryan G, van Eerten H, Zhang B (18 March 2020). "ATel#13565 - GW170817: Continued X-ray emission detected with Chandra at 940 days post-merger". The Astronomer's Telegram. Retrieved 19 March 2020.
- S2CID 217180814.
- ^ Bravo S (16 October 2016). "No neutrino emission from a binary neutron star merger". IceCube South Pole Neutrino Observatory. Retrieved 20 October 2017.
- ^ Sokol J (25 August 2017). "What happens when two neutron stars collide? Scientific revolution". Wired. Retrieved 27 August 2017.
- ^ .
- PMID 30387654.
constrain R1=11.9+1.4−1.4 km and R2=11.9+1.4−1.4 km at the 90% credible level
- ^ "The Central Engine of GRB170817A and the Energy Budget Issue: Kerr Black Hole versus Neutron Star in a Multi-Messenger Analysis".
- S2CID 119471204.
- S2CID 256846834.
- ISSN 0190-8286. Retrieved 18 February 2023.
- ^ a b Berger E (16 October 2017). LIGO/Virgo Press Conference. Event occurs at 1h48m. Retrieved 29 October 2017.
- .
- .
we report on a possible detection of extended emission (EE) in gravitational radiation during GRB170817A: a descending chirp with characteristic time-scale τs = 3.01±0.2 s in a (H1,L1)-spectrogram up to 700 Hz with Gaussian equivalent level of confidence greater than 3.3 σ based on causality alone following edge detection applied to (H1,L1)-spectrograms merged by frequency coincidences.
- .
- .
- ^ "First identification of a heavy element born from neutron star collision - Newly created strontium, an element used in fireworks, detected in space for the first time following observations with ESO telescope". www.eso.org. Retrieved 27 October 2019.
- ^ "ArXiv.org search for GW 170817". Retrieved 18 October 2017.
- The Astrophysical Journal Letters(Editorial). 848 (2).
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).
- ^ DNews (7 August 2013). "Kilonova Alert! Hubble Solves Gamma Ray Burst Mystery". Seeker.
- ^ .
- ^ Kitching T (13 December 2017). "How crashing neutron stars killed off some of our best ideas about what 'dark energy' is". The Conversation – via phys.org.
- S2CID 73517974.
- S2CID 118486016.
- S2CID 119186001.
- ^ S2CID 206304918.
- ^ S2CID 38618360.
- ^ "Quest to settle riddle over Einstein's theory may soon be over". phys.org. 10 February 2017. Retrieved 29 October 2017.
- ^ "Theoretical battle: Dark energy vs. modified gravity". Ars Technica. 25 February 2017. Retrieved 27 October 2017.
- ^ "Gravitational waves". Science News. Retrieved 1 November 2017.
- S2CID 39068360.
- S2CID 119468128.
- S2CID 36160359.
- S2CID 119197181.
- ^ S2CID 205261622.
- ^ Scharping N (18 October 2017). "Gravitational waves show how fast the Universe is expanding". Astronomy. Retrieved 18 October 2017.
- S2CID 119547153. Retrieved 8 July 2019.
- 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.
- S2CID 52987203.
- S2CID 204837882.
- ISSN 0004-6361.
- ISSN 0004-637X.
- ^ Ghosh P (26 March 2018). "Stephen Hawking's final interview: A beautiful Universe". BBC News. Retrieved 26 March 2018.
- S2CID 119369873.
External links
- "Detections". LIGO.
- "Follow-up observations of GW 170817". Archived from the original on 17 September 2018. Retrieved 20 October 2017.
- 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
- NSF LIGO-Virgo press conference: 2 panels and Q&As (03:21) on