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Fermi, Integral and LIGO signals
Fermi, Integral and LIGO signals
Constellation Water snake
equinox : J2000.0
Right ascension 13h 09m 48.09s
declination −23 ° 23 ′ 53.59 ″
Further data

26 to 48 Mpc

Dimensions 2.73 to 2.78

Fermi Gamma-ray Space Telescope, LIGO

Date of discovery

17th August 2017

Catalog names
GW170817, GRB 170817A, AT 2017gfo
Aladin previewer

GW170817 (English: G ravitational W ave) is the name for a gravitational wave signal , the various detectors on 17 August 2017 of the galaxy NGC 4993 in the constellation Hydra has been registered. Almost at the same time, a gamma-ray flash (catalog designation GRB 170817A, English: G amma R ay B urst) was recorded by the Fermi satellite .

In the following days, numerous telescopes , including the Hubble Space Telescope , observed an afterglow of the event at optical , infrared , X-ray and radio wavelengths . The catalog designation for the optical signal is: AT 2017gfo.

It was the first time that astronomers could measure both gravitational waves and electromagnetic radiation from the same astronomical event.

Discovery of gravitational waves

The signal of the gravitational waves could be detected at 12:41:04 universal time and lasted about 100 seconds. It spanned 3000 cycles, during which the frequency of the gravitational waves rose to several hundred Hertz . It first reached the Virgo detector in Italy, 22 milliseconds later the LIGO observatory in Louisiana, USA, and another 3 milliseconds later the LIGO Hanford detector in Washington, USA. With these three measurements, the source could be determined to an area of ​​28 square degrees in the southern sky with a 90% probability.

Discovery of the gamma-ray burst

The Fermi satellite recorded the gamma-ray burst at 12:41:06 UTC. The gamma radiation reached the earth about 2 seconds after the gravitational waves. It also lasted only 2 seconds.

Further observations

Hubble images of NGC 4993 with progression after 6 days

After the detection of the two signals, the corresponding area of ​​the sky was examined by numerous ground-based and space-based instruments. The object was discovered in the optical area within a few hours and the brightness and spectroscopic progression could be documented over the next few days and weeks. After two weeks, X-rays and radio waves were also measured from the area . A neutrino signal could not be measured.


The collision of two neutron stars was observed . This special case of a merger outbreak is also known as a kilonova . The two neutron stars were probably formed from a double system of two massive giant stars that exploded as a supernova at different times in the course of their stellar development, each leaving behind a neutron star. The two neutron stars remained gravitationally bound in a double system. Similar to the Hulse-Taylor double pulsar , the two compact celestial bodies orbited the common center of gravity; Through the emission of (non-measurable) gravitational waves, the system lost energy over the course of many millions of years, as a result of which the two neutron stars slowly came closer. Only in the last few minutes before the merger, in which the orbital speed increased rapidly, did the intensity and frequency of the gravitational waves increase to measurable values.

Determined data:

Mass of the first neutron star 1.36 to 1.60
Mass of the second neutron star 1.17 to 1.36
Mass of the new object 2.73 to 2.78
Energy converted into gravitational waves 0.025
Removal of the source 26 to 48 Mpc
Redshift 0.005 to 0.010

The lower mass neutron star was destroyed by the tidal forces of the heavier companion. While most of the matter of the disrupted star was accreted from an accretion disk onto the more massive companion , part of the mass of the destroyed neutron star is ejected isotropically at a speed of 0.1 to 0.2 times the speed of light . The neutron-rich matter is transformed within a few seconds by fission and beta decay into elements that are created by the r-process . The newly synthesized radioactive elements decay, and the radiation emitted is observed as an eruption lasting for a day. Such an event is considered to be an important source for the formation of heavier atomic nuclei , for which it is necessary to supply energy from outside. When two neutron stars merge, as the researchers observed, large amounts of heavy elements can be formed.

Long-term observations with the Chandra X-ray telescope suggest that the neutron stars have merged into a black hole .

Scientific importance

The event was the long-awaited first observation of gravitational waves from two colliding neutron stars instead of from the merging of black holes as before. Simultaneous observation via electromagnetic radiation was also the beginning of multimessenger astronomy with gravitational waves (just as SN 1987A was the beginning of multimessenger astronomy with neutrinos). The observation of the collision of the neutron stars also brought a new understanding of the origin of heavy elements in the universe.

The evaluation of the event also provided an independent estimate of the Hubble constant (H = 70) and upper limits for violations of the Lorentz invariance. It was also found with high accuracy that gravitational waves travel at the speed of light, which rules out certain alternative theories of gravitation, and a new test of the principle of equivalence resulted . According to a prediction from 2015, this refutes in particular theories that attempt to explain the accelerated expansion of the universe by modifying the general theory of relativity .


Web links

Individual evidence

  1. a b
  2. NASA Missions Catch First Light from a Gravitational-Wave Event , at: NASA JPL
  3. a b Robert Gast: Neutron star crash causes space-time to tremble , on: from October 16, 2017
  4. BP Abbott, R. Abbott, TD Abbott, et al .: Multi-messenger Observations of a Binary Neutron Star Merger. In: The Astrophysical Journal Letters. October 6, 2017. Retrieved October 17, 2017 .
  5. a b B. P. et al Abbott: GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral . In: Physical Review Letters . 119, No. 16, October 16, 2017. doi : 10.1103 / PhysRevLett.119.161101 .
  6. ^ NASA Missions Catch First Light from a Gravitational-Wave Event . In: NASA , October 16, 2017. 
  7. a b c Adrian Cho: Merging neutron stars generate gravitational waves and a celestial light show . In: Science , October 16, 2017. 
  8. ^ Andreas von Kienlin: GCN Circular; Number: 21520; GRB 170817A: Fermi GBM detection; 2017/08/17 20:00:07 GMT . In: Max Planck Institute for Extraterrestrial Physics . August 17, 2017. Retrieved August 28, 2017.
  10. First gravitational waves from neutron star collision ( Memento of the original from October 18, 2017 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , to: scinexx @1@ 2Template: Webachiv / IABot /
  11. ^ Brian D. Metzger, Edo Berger: What is the Most Promising Electromagnetic Counterpart of a Neutron Star Binary Merger? In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1108.6056v1 .
  12. David Pooley, Pawan Kumar, J. Craig Wheeler, Bruce Grossan: GW170817 Most Likely Made a Black Hole. 2018, arxiv : 1712.03240v2
  13. Markus Pössel: First evidence: Merging neutron stars. A Milestone for Astronomy, Stars and Space, December 2017, pp. 24–33, abstract
  14. Darach Watson, Camilla J. Hansen, Jonatan Selsing, Andreas Koch, Daniele B. Malesani: Identification of strontium in the merger of two neutron stars . In: Nature . tape 574 , no. 7779 , October 2019, ISSN  0028-0836 , p. 497-500 , doi : 10.1038 / s41586-019-1676-3 ( [accessed November 18, 2019]).
  15. ^ BP Abbott (LIGO) u. a., A gravitational-wave standard siren measurement of the Hubble constant, Nature, October 16, 2017, abstract
  16. LIGO, VIRGO, Fermi Gamma Ray Burst Monitor, INTEGRAL: Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A
  17. L. Lombriser, A. Taylor: Breaking a Dark Degeneracy with Gravitational Waves , in: JCAP03 (2016) 031, DOI: 10.1088 / 1475-7516 / 2016/03/031
  18. L. Lombriser, N. Lima: Challenges to Self-Acceleration in Modified Gravity from Gravitational Waves and Large-Scale Structure , in: Phys. Lett. B 765, 382 (2017), DOI: 10.1016 / j.physletb.2016.12.048
  19. Quest to settle riddle over Einstein's theory may soon be over . February 10, 2017. Retrieved October 29, 2017.