Some early relativists were sceptical about the existence of gravitational waves; however, the 1993 Nobel Prize in Physics was awarded to Hulse and Taylor for their experimental observations and subsequent interpretations of the evolution of the orbit of the binary pulsar PSR 1913+16 [185, 295], the decay of the binary orbit being consistent with angular momentum and energy being carried away from this system by gravitational waves [316].
Gravitational waves are produced when matter is accelerated in an asymmetrical way; but due to
the nature of the gravitational interaction, detectable levels of radiation are produced only
when very large masses are accelerated in very strong gravitational fields. Such a situation
cannot be found on Earth but is found in a variety of astrophysical systems. Gravitational
wave signals are expected over a wide range of frequencies; from 10–17 Hz in the case of
ripples in the cosmological background to
103 Hz from the formation of neutron stars in
supernova explosions. The most predictable sources are binary star systems. However, there are
many sources of much-greater astrophysical interest associated with black-hole interactions
and coalescences, neutron-star coalescences, neutron stars in low-mass X-ray binaries such as
Sco-X1, stellar collapses to neutron stars and black holes (supernova explosions), pulsars, and the
physics of the early Universe. For a full discussion of sources refer to the material contained
in [273
, 272
, 115, 232].
Why is there currently such interest worldwide in the detection of gravitational waves? Partly because observation of the velocity and polarisation states of the signals will allow a direct experimental check of the wave predictions of general relativity; but, more importantly, because the detection of the signals should provide observers with new and unique information about astrophysical processes. It is interesting to note that the gravitational wave signal from a coalescing compact binary star system has a relatively simple form and the distance to the source can be obtained from a combination of its signal strength and its evolution in time. If the redshift at that distance is found, Hubble’s Constant – the value for which has been a source of lively debate for many years – may then be determined with, potentially, a high degree of accuracy [282, 180].
Only now are detectors being built with the technology required to achieve the sensitivity to observe such interesting sources.
http://www.livingreviews.org/lrr-2011-5 |
Living Rev. Relativity 14, (2011), 5
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