New upper limit on gravity-wave events

The International Gravitational Event Collaboration (IGEC) involves a network of five cryogenic resonant-cylinder gravity-wave detectors: two in Italy and one each in Switzerland, the US, and Australia. The search for passing gravity waves is a delicate art; in the resonant-cylinder approach, it means measuring strain displacements far smaller than the size of an atomic nucleus on the end faces of 3-meter-long, 2000-kg metal cylinders. The IGEC team has now reported that in its first operational period, covering 1997 and 1998, no gravity waves were detected. From this they calculated an annual upper limit of four events with a mean Fourier component exceeding 10⁻²⁰ Hz⁻¹ arriving at Earth. The IGEC typically used thresholds that correspond to the conversion of 0.04–0.11 solar masses to gravity waves in an astrophysical source…such as a coalescing binary system of neutron stars or black holes…at the Galactic center. The collaboration also demonstrated that a network of many detectors operating simultaneously can achieve a negligible false alarm rate. (Z. A. Allen et al., Phys. Rev. Lett. 85, 5046, 2000 http://dx.doi.org/10.1103/PhysRevLett.85.5046 .)