Neutron star merger

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17 August 2017: Gravitational wave (GW170817) detected from merger of two neutron stars[1][2][3] (00:23 video; artist concept).

A neutron star merger is a type of stellar collision. It occurs in a fashion similar to the rare brand of type Ia supernovae resulting from merging white dwarfs. When two neutron stars orbit each other closely, they spiral inward as time passes due to gravitational radiation. When the two neutron stars meet, their merger leads to the formation of either a more massive neutron star, or a black hole (depending on whether the mass of the remnant exceeds the currently poorly known Tolman–Oppenheimer–Volkoff limit). The merger can also create a magnetic field that is trillions of times stronger than that of Earth in a matter of one or two milliseconds. These events are believed to create short gamma-ray bursts.[4] The mergers are also believed to produce kilonovae, which are transient sources of fairly isotropic longer wave electromagnetic radiation due to the radioactive decay of heavy r-process nuclei that are produced and ejected during the merger process.[5]

Observed merger[edit]

On 17 August 2017, LIGO/Virgo collaboration detected a pulse of gravitational waves,[6][7] named GW170817, associated with the merger of two neutron stars in NGC 4993, an elliptical galaxy in the constellation Hydra. GW170817 also seemed related to a short (~ 2 second long) gamma-ray burst, GRB 170817A, first detected 1.7 seconds after the GW merger signal, and a visible light observational event first observed 11 hours afterwards, SSS17a.[8][1][2][3][9]

The association of GW170817 with GRB 170817A in both space and time is strong evidence that neutron star mergers do create short gamma-ray bursts. The subsequent detection of an SSS17a in the area in which GW170817 and GRB 170817A were known to have occurred and its having the expected characteristics for a kilonova is strong evidence that neutron star mergers do produce kilonovae.

References[edit]

  1. ^ a b Cho, Adrian (16 October 2017). "Merging neutron stars generate gravitational waves and a celestial light show". Science. Retrieved 16 October 2017. 
  2. ^ a b Landau, Elizabeth; Chou, Felicia; Washington, Dewayne; Porter, Molly (16 October 2017). "NASA Missions Catch First Light from a Gravitational-Wave Event". NASA. Retrieved 16 October 2017. 
  3. ^ a b Overbye, Dennis (16 October 2017). "LIGO Detects Fierce Collision of Neutron Stars for the First Time". The New York Times. Retrieved 16 October 2017. 
  4. ^ Rosswog, Stephan (2013). "Astrophysics: Radioactive glow as a smoking gun". Nature. 500 (7464): 535–6. Bibcode:2013Natur.500..535R. doi:10.1038/500535a. PMID 23985867. 
  5. ^ Tanvir, N. R.; Levan, A. J.; Fruchter, A. S.; Hjorth, J.; Hounsell, R. A.; Wiersema, K.; Tunnicliffe, R. L. (2013). "A 'kilonova' associated with the short-duration γ-ray burst GRB 130603B". Nature. 500 (7464): 547–9. arXiv:1306.4971Freely accessible. Bibcode:2013Natur.500..547T. doi:10.1038/nature12505. PMID 23912055. 
  6. ^ Abbott, B. P.; et al. (LIGO Scientific Collaboration & Virgo Collaboration) (16 October 2017). "GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral". Physical Review Letters. 119 (16). arXiv:1710.05832Freely accessible. Bibcode:2017PhRvL.119p1101A. doi:10.1103/PhysRevLett.119.161101. 
  7. ^ Scharping, Nathaniel (18 October 2017). "Gravitational Waves Show How Fast The Universe is Expanding". Astronomy. Retrieved 18 October 2017. 
  8. ^ Abbott, B. P.; 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:1710.05833Freely accessible [astro-ph.HE]. Bibcode:2017ApJ...848L..12A. doi:10.3847/2041-8213/aa91c9Freely accessible. 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. 
  9. ^ Krieger, Lisa M. (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. 

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