LIGO

LIGO, short for Laser Interferometer Gravitational-Wave Observatory, is a pair of large-scale physics experiments designed to detect gravitational waves. Two interferometers are located in the United States, at Hanford, Washington, and Livingston, Louisiana. The project is funded by the National Science Foundation and operated by Caltech and MIT.

Each observatory uses a laser and two perpendicular 4-kilometer-long arms in a vacuum to form a Michelson interferometer. Gravitational waves distort space-time, causing minute changes in arm lengths that shift the interference pattern. The detectors employ seismic isolation, precision optics, and advanced data analysis to extract signals from noise.

Initial LIGO operated from 2002 to 2010 but did not detect gravitational waves. After upgrading to Advanced LIGO in 2015, the first detection GW150914, a binary black hole merger, was observed. Subsequent detections included GW151226 and GW170104.

In 2017, Advanced LIGO and Virgo jointly detected GW170817, a binary neutron star merger, with electromagnetic emission observed across gamma-ray, optical, and radio wavelengths, inaugurating multi-messenger astronomy.

LIGO is part of a global network that includes Virgo in Europe and KAGRA in Japan, with LIGO-India planned. Data are analyzed by the LIGO Scientific Collaboration and the Virgo Collaboration, enabling tests of general relativity, improved astrophysical understanding, and cosmological measurements.

Funding comes from the U.S. National Science Foundation, with operations by the LIGO Laboratory at Caltech and MIT. Results are published in peer-reviewed journals, and public data releases support further research.