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Measuring gravitational waves using terrestrial sub-audio frequency detectors

Posted August 12, 2013
Interaction of TOBA's dual torsion beam con

Interaction of torsion-bar antenna’s (TOBA’s) dual torsion beam con guration with gravitational wave tidal-forces

The idea to detect gravitational waves in low frequency range is not entirely new. There are several scientific projects already running and aimed to solve the problem of detecting gravity fields emanating from massive celestial bodies: a network of kilometer-scale interferometers (LIGO, Virgo, KAGRA) and several space missions (LISA, DECIGOBBO) are being implemented for this purpose, although gravitational waves are yet to be discovered. And, scientists are already offering improvements how to increase the sensitivity of such measurements.

Detecting these waves would greatly expand our knowledge about the laws of the Universe. Detection of low-frequency gravitational waves could give us insights into evolution of galaxies and black holes.

Currently, kilometer-scale interferometers, such as LIGO, Virgo, GEO600 and KAGRA are aimed to perform direct detection of gravitational waves in the 10-10000 Hz frequency band. Several space-based interferometer missions, such as eLISA, DECIGO and BBO are also proposed with aim to avoid the interference from the gravitational field of Earth or from various ‘seismic’ sources of disturbances (natural or produced by humans).

An international team of scientists from Japan, USA, Italy and Australia proposed a combined atom and laser interferometry technique, which could be useful in order to extend the gravitational wave detection frequency band to the lower-frequency region, namely 0.1-10Hz. Compared to currently existing purely laser-based or so-called atom interferometry, combined method would feature an improved sensitivity of measurements.

Authors of the proposed new design argue, that such measurements still can be accomplished using terrestrial detector of gravitational waves. In paper published at, a torsion-bar antenna (TOBA) configuration was selected by team members as a basis for future gravitational wave detectors (shown in illustration above).

In TOBA, force induced by gravity fluctuations can be observed by measuring differential rotations between to orthogonal bars, ndependently suspended as torsion pendulums. They share the same suspension point, have their axis of rotation co-linear and centerof-mass co-incident. An incoming gravitational wave, incident into the page, will rotate the beams di erentially. The linear distance between the ends of the beams, Lx and Ly, will change. These changes can be measured using any standard interferometry methods, or, as the team suggests; using combined laser-atom interferometry.

The idea could definitely work, especially if the same principle would be applied in space-based detector setups, where the number of noise sources is minimal. However, scientists admit, that in order for this idea to work, some improvements to existing measurement technology have to be made.

Story by Alius Noreika,


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