However, the most promising design of gravitational-wave detectors, offering the possibility of very high sensitivities over a wide range of frequency, uses widely-separated test masses freely suspended as pendulums on Earth or in a drag-free craft in space laser interferometry provides a means of sensing the motion of the masses produced as they interact with a gravitational wave.
Effort also continues to be pursued into cryogenic spherical bar detectors, which are designed to have a wider bandwidth than the cylindrical bars, with the two prototype detectors the Dutch MiniGRAIL and Brazilian Mário Schenberg. Following the lack of confirmed detection of signals, aluminium bar systems operated at and below the temperature of liquid helium were developed, although work in this area is now subsiding, with only two detectors, Auriga and Nautilus, continuing to operate. Initial instruments were constructed by Joseph Weber and subsequently developed by others. The first gravitational-wave detectors were based on the effect of these forces on the fundamental resonant mode of aluminium bars at room temperature.
Gravitational waves are ripples in the curvature of space-time and manifest themselves as fluctuating tidal forces on masses in the path of the wave. New unexpected sources will almost certainly be found and time will tell what new information such discoveries will bring. Sources such as interacting black holes, coalescing compact binary systems, stellar collapses and pulsars are all possible candidates for detection observing signals from them will significantly boost our understanding of the Universe. Gravitational waves, one of the more exotic predictions of Einstein’s General Theory of Relativity may, after decades of controversy over their existence, be detected within the next five years. Beyond this, the concept and design of possible future “third generation” gravitational-wave detectors, such as the Einstein Telescope (ET), will be discussed. Looking to the future, the major upgrades to LIGO (Advanced LIGO), Virgo (Advanced Virgo), LCGT and GEO600 (GEO-HF) will be completed over the coming years, which will create a network of detectors with the significantly improved sensitivity required to detect gravitational waves. A review of recent science runs from the current generation of ground-based detectors will be discussed, in addition to highlighting the astrophysical results gained thus far. The main theme of this review is a discussion of the mechanical and optical principles used in the various long baseline systems in operation around the world - LIGO (USA), Virgo (Italy/France), TAMA300 and LCGT (Japan), and GEO600 (Germany/U.K.) - and in LISA, a proposed space-borne interferometer. The most promising design of gravitational-wave detector uses test masses a long distance apart and freely suspended as pendulums on Earth or in drag-free spacecraft. Sources such as coalescing compact binary systems, neutron stars in low-mass X-ray binaries, stellar collapses and pulsars are all possible candidates for detection. Significant progress has been made in recent years on the development of gravitational-wave detectors.
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