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http://www.iop.org/EJ/article/1367-2630/7/1/204/nj...
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Gravitons in a gravitational-wave burst are (b)phase-coherent(/b); photons in electromagnetic signals are usually phase-incoherent. This arises from the fact that each graviton is generated from the same bulk motion of matter or of spacetime curvature, while each photon is normally generated by different, independent events involving atoms, ions or electrons. Thus GWs are similar to laser light. We can take advantage of the phase coherence of GWs to enhance their detectability. Matched filtering techniques for detecting GW bursts with well-modelled functional form (like those generated by coalescing compact binaries) extend the distance to which sources can be seen by a factor of roughly the square root of the number of cycles in the waveform, a significant gain.
[b]An extremely important consequence of this coherency is that the direct observable of gravitational radiation is the strain h, a quantity that falls off with distance as 1/r.[/b] Most electromagnetic observables are some kind of energy flux, and so fall off with a 1/r2 law; measuring coherent GWs is analogous to measuring a coherent, 1/r electromagnetic radiation field. This comparatively slow fall off with radius means that relatively small improvements in the sensitivity of GW detectors can have a large impact on their science: doubling the sensitivity of a detector doubles the distance to which sources can be detected, increasing the volume of the Universe to which sources are measurable by a factor of 8. Every factor of 2 improvement in the sensitivity of a GW observatory should increase the number of observable sources by about an order of magnitude.
отредактировано 30.09.2005 11:52 |
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