A Nation-Wide Research Facility
Although it is considered one observatory, LIGO is comprised of four distinct facilities across the United States: two gravitational wave detectors (the interferometers) and two university research centers. The interferometers are located in fairly isolated areas of Washington (LIGO Hanford) and Louisiana (LIGO Livingston), and separated by 3,002 km (1,865 miles). The two primary research centers are located at The California Institute of Technology (Caltech) in Pasadena, California, and The Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts.
The detector sites in Hanford and Livingston are home to the interferometers that make LIGO an "observatory". About 40 people work at each observatory site, including engineers, technicians, and scientists who keep the instruments operating, and who monitor vacuum and computer systems around the clock. Administrative and business staff are also present, as are education and public outreach professionals who conduct public tours, facilitate field trips for local students, and arrange periodic public events.
As major academic and research institutions with world-class laboratories and facilities, Caltech and MIT are the home bases for LIGO engineers who spend their days finding ways to improve LIGO's sensitivity and stability, and the physicists and astrophysicists who strive to understand the properties of the physical phenomena that generate gravitational waves. These critical tasks are ongoing.
When in "Observing" mode, the Hanford and Livingston detectors collect data simultaneously, operating as one single observatory. This coordination is essential to LIGO's ability to verify a gravitational-wave detection, and was critical to LIGO confirming the world's first detection of gravitational waves emitted by two colliding black holes 1.3 billiion light years away (learn all about this history-making discovery in the Detection Portal). To find out why this is so fundamental to LIGO's success, visit LIGO's Dual Detectors.