A multitude of gravitational wave detectors
A roundup of the interferometer projects around the world
The US Laser Interferometer Gravitational-wave Observatory (LIGO) consists of two identical detection facilities with 4kmlong arms: one in Hanford, Washington, and the other in Livingston, Louisiana. The slightly smaller European Virgo detector, with 3km–arms, is located near Pisa, Italy. In early 2020, the underground Japanese Kamioka Gravitational-wave detector (KAGRA) came online, also with 3km arms.
Apart from LIGO, Virgo and KAGRA, a smaller experiment known as GEO600 is located near Hanover, Germany, but this facility is mainly used to test and qualify novel detection technologies – it is too small to detect all but the most powerful gravitational waves. Meanwhile, US and Indian physicists are teaming up to build LIGO India, working with spare parts from LIGO. It is expected to be completed later this decade.
In 2016, using their LISA Pathfinder space probe, the European Space Agency (ESA) successfully demonstrated the necessary technologies for its future Laser Interferometer Space Antenna (LISA), due to be launched in the 2030s. LISA will consist of three free-flying spacecraft, millions of kilometres apart; they are the vertices of a huge triangular gravitational-wave detector that has a similar design to the planned Einstein Telescope, but operating at much lower frequencies. Japan and China are also preparing space-based detectors, known as DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) and TianQin, respectively.