Gravitational Wave Detectors
Gravitational Wave Detection is a global effort
On February 11, 2016, the LIGO Scientific Collaboration and Virgo Collaboration teams announced that they had made the first observation of gravitational waves using the Advanced LIGO detectors. The first Gravitational Wave Signal originated from a pair of merging black holes more than a billion light years. Since the initial announcement LIGO has confirmed two more (and one potential) detections of gravitational wave events. The two Advanced LIGO detectors, the British-German GEO600 detector which developed some key technologies to the Advanced LIGO detectors and the Italian-French Virgo detector are part of a world-wide network to observe Gravitational Waves. More than 1000 scientists and engineers work in this global community.
LIGO is the world's largest gravitational wave observatory and a cutting edge physics experiment. Comprised of two enormous laser interferometers located thousands of kilometers apart, LIGO exploits the physical properties of light and of space itself to detect and understand the origins of gravitational waves.
Though it's called an observatory, LIGO is unlike any other observatory on Earth. Ask someone to draw a picture of an observatory and odds are it will look something like the photo below: a typical telescope dome on a mountain-top. As a gravitational wave observatory, LIGO bears no resemblance to this whatsoever.
GEO600 is a ground-based interferometric gravitational wave detector located near Hannover, Germany. It is designed and operated by scientists from the Max Planck Institute for Gravitational Physics, along with partners in the United Kingdom and is funded by the Max Planck Society and the Science and Technology Facilities Council (STFC). GEO600 scientists together with the Laser Zentrum Hannover (LZH) built the lasers for Advanced LIGO.
Scientists at GEO600 have pushed the available technologies to the limits: laser stabilization, absorption-free optics, control engineering, vibration damping and data acquisition and processing got new impulses. A specialty of GEO600 is the amplification of laser light and signal called "dual recycling": By means of highly reflecting mirrors the laser light is constructively superposed with itself and thus enhanced ("power recycling"); and with an additional mirror the signal is superposed with itself ("signal recycling"). This technique allows a tuning of the detector to a certain frequency. The suspension of the mirror on glass fibers is anther one of the many groundbreaking developments of GEO600. GEO600 is also the first gravitational wave detector that uses squeezed laser light in order to improve sensitivity!
The Virgo interferometer is a large interferometer designed to detect gravitational waves predicted by the general theory of relativity. Virgo is a Michelson interferometer that is isolated from external disturbances: its mirrors and instrumentation are suspended and its laser beam operates in a vacuum. The instrument's two arms are three kilometres long and located near Pisa, Italy.
Virgo is part of a scientific collaboration of laboratories from five countries: France and Italy (the two countries behind the project), the Netherlands, Poland and Hungary. Other interferometers similar to Virgo have the same goal of detecting gravitational waves, including the two LIGO interferometers in the United States (at the Hanford Site and in Livingston, Louisiana). Since 2007, Virgo and LIGO have agreed to share and jointly analyze the data recorded by their detectors and to jointly publish their results. Because the interferometric detectors are not directional (they survey the whole sky) and they are looking for signals which are weak and infrequent, simultaneous detection of a gravitational wave in multiple instruments is necessary to confirm the signal and determine its origin.