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GW170817 Multi-Messenger Case Study

Gravitational waves are waves of spacetime curvature produced by the relative motion of gravitating masses and which propagate away at the speed of light. They were first predicted by Albert Einstein as a consequence of his general theory of relativity, appearing as "ripples in spacetime curvature" : 326 : 117 Hundreds of these gravitational waves have since then been observed, first indirectly using binary-pulsar observations and, since 2015, directly through dedicated observatories. Gravitational waves transport energy as gravitational radiation, a form of radiant energy similar to electromagnetic radiation. Newton's law of universal gravitation, part of classical mechanics, does not provide for their existence, instead asserting that gravity has instantaneous effect everywhere.

Figures (10)

Primordial gravitational waves are hypothesized to arise from cosmic inflation, a phase of accelerated expansion just after the Big Bang (2014).[30][31][32]
A schematic diagram of a laser interferometer
Simplified operation of a gravitational wave observatory Figure 1: A beamsplitter (green line) splits coherent light (from the white box) into two beams which reflect off the mirrors (cyan oblongs); only one outgoing and reflected beam in each arm is shown, and separated for clarity. The reflected beams recombine and an interference pattern is detected (purple circle). Figure 2: A gravitational wave passing over the left arm (yellow) changes its length and thus the interference pattern.
Plot of correlation between pulsars observed by NANOGrav vs angular separation between pulsars, compared with a theoretical Hellings-Downs model (dashed purple) and if there were no gravitational wave background (solid green)[123][124]
LIGO measurement of the gravitational waves at the Hanford (left) and Livingston (right) detectors, compared to the theoretical predicted values.
Detached binary star system
Semidetached binary star system
Contact binary star system
Schematic of a binary star system with one planet on an S-type orbit and one on a P-type orbit
Linearly polarized gravitational wave

Key Points

  • Gravitational waves are constantly passing Earth; however, even the strongest have a minuscule effect since their sources are generally at a great distance.
  • In their work, they suggested that the radioactive ejecta from a neutron star merger is a source for powering thermal transient emission, later dubbed kilonova.
  • A kilonova (also called a macronova) is a transient astronomical event that occurs in a compact binary system when two neutron stars (BNS) or a neutron star and a black hole collide.
  • A neutron star is composed mostly of neutrons (neutral particles) and contains a small fraction of protons (positively charged particles) and electrons (negatively charged particles), as well as nuclei.
  • Using these relations, one can constrain the neutron star equation of state when gravitational waves from binary neutron star mergers are observed.
  • Gravitational-wave astronomy has the advantage that, unlike electromagnetic radiation, gravitational waves are not affected by intervening matter.

Terms

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