Gravitational-wave astronomy

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The LIGO Hanford Control Room

Gravitational-wave astronomy is an emerging branch of observational astronomy which aims to use gravitational waves (minute distortions of spacetime predicted by Einstein's theory of general relativity) to collect observational data about objects such as neutron stars and black holes, about events such as supernovae and about the early universe shortly after the big bang. The Laser Interferometer Gravitational-Wave Observatory or LIGO, a joint project between MIT and Caltech is spearheading this new field of research along with equally ambitious projects such as LISA, VIRGO, TAMA 300 and GEO 600.


Noise curves for a selection of gravitational-wave detectors as a function of frequency. At very low frequencies are pulsar timing arrays, the European Pulsar Timing Array (EPTA) and the future International Pulsar Timing Array (IPTA); at low frequencies are space-borne detectors, the formerly proposed Laser Interferometer Space Antenna (LISA) and the currently proposed evolved Laser Interferometer Space Antenna (eLISA), and at high frequencies are ground-based detectors, the initial Laser Interferometer Gravitational-Wave Observatory (LIGO) and its advanced configuration (aLIGO). The characteristic strain of potential astrophysical sources are also shown. To be detectable the characteristic strain of a signal must be above the noise curve.[1]

So far, gravitational waves have only been detected indirectly, and gravitational-wave astronomy remains more of a possibility than an actuality. However, a number of gravitational-wave detectors are in operation with the aim of making gravitational-wave astronomy a reality. This young area of research is still in the developmental stages, however there is consensus within the astrophysics community that this field will evolve to become an established component of 21st century multi-messenger astronomy, and that gravitational-wave astronomers, working with ground and spaced-based detectors, will stand shoulder-to-shoulder with gamma-ray, x-ray, optical, infrared and radio astronomers in exploring the cosmos in the years to come.

Detecting gravitational waves promises to complement observations in the electromagnetic spectrum:[2] These waves also promise to yield information in ways not possible via detection and analysis of electromagnetic waves. Electromagnetic waves can be absorbed and re-radiated in ways that make extracting information about the source difficult. Gravitational waves behave, in some analogous to sound waves, in that they behave like composites of harmonic waves.[3] These harmonic composite waveforms carry the signature of their origin only and radiate in a way that doesn't allow them to become distorted due to interactions with matter between the source and the detectors.[4] This should allow astronomers to view the center of a supernova, stellar nebula's, and even colliding galactic cores in new ways.

Terrestrial detectors are expected to yield new information about the inspiral phase and mergers of binary stellar mass black holes, and binaries consisting of one such black hole and a neutron star (a candidate mechanism for some gamma ray bursts). They could also detect signals from core-collapse supernovae, and from periodic sources such as pulsars with small deformations. If there is truth to speculation about certain kinds of phase transitions or kink bursts from long cosmic strings in the very early universe (at cosmic times around 10^{-25} seconds), these could also be detectable.[5] Space-based detectors like LISA should detect objects such as binaries consisting of two white dwarfs, and AM CVn stars (a white dwarf accreting matter from its binary partner, a low-mass helium star), and also observe the mergers of supermassive black holes and the inspiral of smaller objects (between one and a thousand solar masses) into such black holes. LISA should also be able to listen to the same kind of sources from the early universe as ground-based detectors, but at even lower frequencies and with greatly increased sensitivity.[6]

Detecting emitted gravitational waves are rather difficult endeavor. It involves ultra stable high quality lasers and detectors calibrated with a sensitivity of at least 2·10^(-22)/√Hz as shown at the ground-based detector, GEO-600.[7] It has also been proposed that even from large astronomical events, such as supernova explosions, these waves are likely to degrade to vibrations as small as an atomic diameter.[8] In theory, the high sensitivity of terrestrial and space-based detection systems should be able to observe these elusive waves.


  1. ^ Moore, Christopher; Cole, Robert; Berry, Christopher (19 July 2013). "Gravitational Wave Detectors and Sources". Retrieved 17 April 2014. 
  2. ^ Cf. Thorne 1995.
  3. ^ See Golm & Postdam 2013, sec. 4
  4. ^ See Golm & Postdam 2013, sec. 4
  5. ^ See Cutler & Thorne 2002, sec. 2.
  6. ^ See Cutler & Thorne 2002, sec. 3.
  7. ^ See Seifert F., et al 2006, sec. 5.
  8. ^ See Golm & Postdam 2013, sec. 4.


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