Gravitational wave detectors

Abstract

As outlined in the preceding talk by Dr Thome, there are many possible sources of gravitational radiation, ranging from the interactions of supermassive black holes to supernova explosions of stars. Detection of such radiation could give information which cannot be obtained otherwise, for example on events occurring in the cores of stellar systems, and could also provide important clues on the existence, nature and behaviour of black holes. Detection techniques essentially rely on sensing the change in the relative separation, Δ l , of masses separated by a distance l; and the possible sources are all characterized by the small value of the gravitational wave amplitude, A at the detector (e.g. 10 -19 -10 -21 for black hole events in globular clusters). In order to detect such small amplitudes and to cover as wide a frequency range as possible it seems promising to consider setting up experiments in Space. Long baselines between free masses are achievable leading to larger values of A for a given wave amplitude; and seismic disturbances and local gravity fields of moving objects will be smaller than on earth. Some possibilities of doing experiments in space - to search for the very low frequency (10 -1 to 10 -5 Hz) gravitational waves from supermassive black holes - are currently in the planning stage (Wahlquist et al. 1979). These would use the Earth and one or two interplanetary spacecraft as free masses. Gravitational radiation might be sensed by its interaction on the Doppler tracking signals used for navigational purposes. In the longer term, laser tracking between separate spacecraft (perhaps without using the Earth at all) may give considerably higher sensitivity, and greater flexibility for detecting different types of sources.