The Laser Interferometer Gravitational-Wave Observatory (LIGO)

The Laser Interferometer Gravitational-Wave Observatory (LIGO), headquartered at Caltech, consists of two aligned, four-kilometer-long laser interferometers, one located in Hanford, Washington and the other in Livingston, Louisiana, 10 light-milliseconds apart. LIGO is dedicated to the detection of gravitational waves and the harnessing of this new window to the universe for research in astrophysics and relativity. Gravitational waves are ripples in the fabric of space and time produced by violent events in the distant universe. These waves will make tiny motions (smaller than an atomic nucleus) in the mirrors at opposite ends of these interferometers, and coincident detection of the resulting fringe shifts will encode the passing gravitational wave signals in the 30Hz – 2kHz band. Astrophysical sources of gravitational waves include the final minutes of merging binary neutron stars (proposed as models for short gamma-ray bursts), disruption of neutron stars by stellar-mass black holes, merging binary black holes of stellar mass, and more speculatively, asymmetric supernovae, low-mass X-ray binaries, highly magnetized neutron stars (pulsars), and cosmic superstrings.

Co-founded in 1992 by Kip Thorne and Ronald Drever of Caltech and Rainer Weiss of MIT, LIGO lab is run jointly by Caltech and MIT, while the LIGO Scientific Collaboration is a multinational effort involving more than 650 scientists from 11 countries, and includes joint data analysis with the smaller European interferometers GEO600 and VIRGO.

Initial LIGO, which operated until 2008, represented an advance over all previous searches of two or three orders of magnitude in sensitivity and in bandwidth. Its reach was such that, for the first time, signals due to neutron-star binary inspiral and merger from the Virgo Cluster (15 Mpc distance) could have been detectable.

Now operating (through 2010) is an enhanced LIGO with new detector hardware and a more powerful laser, extending the reach of initial LIGO by a factor of 1.5-2 in distance. Under construction is Advanced LIGO, funded by the NSF. This replaces all the optical and mechanical parts of initial LIGO and is designed to improve its sensitivity and bandwidth. This upgrade will increase LIGO’s reach by another order of magnitude, covering 1000 times the volume, and thus 1000 times the event rate of initial LIGO. When Advanced LIGO begins operation around 2014, it will have the reach to detect known sources such as merging binary neutron stars (even assuming conservative estimates of their event rate), and test models of the engines of gamma-ray bursts and supernovae, and black hole formation. It will also, for the first time, enable us to test general relativity in the strong-field regime.

Approximately 80 LIGO scientists and staff work at Caltech, carrying out research, development and operations on the interferometer systems, data analysis methods and operation, and astrophysical modeling. The numerical relativity group has close connections to LIGO data analysis. There is also an increasing effort to cross-trigger searches for electromagnetic counterparts to gravitational wave sources (and vice versa), involving Caltech’s other observatories.