The search for gravitational waves

There has been a significant advance in the sensitivity of broadband searches for gravitational waves, using an international network of kilometer-scale laser interferometers. This network has recently concluded a 22-month search for gravitational waves, covering a frequency range from 50 Hz to several kHz. Sensitivity to strains in space of the order of 10^-21 brings a variety of potential signals into range, from distortions of spinning neutron stars in our galaxy to the mergers of neutron stars and black holes in the Virgo cluster of galaxies. Technology development for a second generation of interferometers has matured and construction of advanced LIGO interferometers began in 2008. This second generation of detectors, operating at the quantum limit, should provide a thousand-fold increase in the volume of space accessible to earthbound gravitational-wave detectors. Although the first detection of gravitational waves may be achieved by first-generation detectors before installation of advanced LIGO begins in 2011, second-generation detectors will enable the routine detection of sources needed for gravitational-wave astronomy. This article describes the first and second generation detectors, gives some insight into what we have learned from observations and outlines future directions in this field.