The updated gravitational wave detector will work this year.

Location of the detector LIGO

Approaching the completion of work on upgrading the equipment on a laser gravity wave detector LIGO (Laser Interferometer Gravitational-Wave Observatory). This year, the tests should begin, and the project is planned to be launched at full capacity no later than next year. The updated detector will receive 10 times greater sensitivity than the first version, and according to scientists, the detection of gravitational waves with its help "is almost guaranteed."

Gravitational waves were predicted by Einstein a century ago, but at first many scientists rejected their existence, and then for a long time it was believed that they could not be detected in principle. But by the 1950s, science, studying the behavior of neutron stars and black holes, came to the conclusion that such waves should exist. The rapid movement of massive objects, for example, a system of rotating neutron stars, should propagate such waves. These waves should slightly distort the space - and, measuring this curvature, they can theoretically be detected.

The LIGO detector is located in the US state of Louisiana. It is a construction of two perpendicular tunnels through which the laser radiation propagates. The laser beam is split by a divider into two perpendicular beams, each of which then enters its own tunnel and repeatedly reflects from the mirrors installed there. Part of the radiation goes back to the divider. If the length of both arms remains constant, then the returning waves come back to the laser. But if their length due to the influence of the gravitational wave suddenly becomes different, then the waves interfere in such a way that they fall into the photodetector. And then - champagne and nobel.
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LIGO work pattern

For the first time, the use of an optical interferometer ( Michelson's interferometer ) as a detector of gravitational waves was proposed by Soviet scientists M.Ye. Then, American professor Rainer Weiss proposed to increase the effective length of the interferometer arms due to multiple reflections of the optical beam from the mirrors located in each arm. That is, having run a shoulder 3 km back and forth a hundred times, the beam, as it were, will make a run of 300 km. As a result, the detector proposed by Weiss is able to measure a change in the length of one of the arms by 10 ^-18 m.


Professor Weiss

Armed with this idea, in 1990, Kip Thorn and Ronald Drever of Caltech and Rainer Weiss of MIT convinced the National Science Foundation of the need to finance the project. The construction of LIGO began in 1994, and the first measurements started in 2002.

To ensure the operation of a highly sensitive device, many difficulties had to be overcome. To eliminate the vibrations that even the laser beam itself induces, the mirrors had to be made massive (more than 20 kg). To exclude low-frequency vibrations, from seismic and tidal activity to the influence of trains on nearby railways, the entire system is suspended on a complex structure that dampens vibrations.

The measurements lasted 8 years, but gravitational waves were not recorded, despite the fact that during the period of operation the sensitivity of the complex was increased by some improvements twice. Then the complex was closed for large-scale renovation, which is planned to be completed this year.

The main candidate for the emission of gravitational waves remain binary systems of neutron stars. The first LIGO could detect the radiation of stars about 50 million light-years from Earth. The new design will increase the sensitivity by 10 times compared with the previous one, and therefore the volume of space that is available to it has increased 1,000 times. Scientists estimate that the number of systems that exist in this volume should provide about 10 wave detections per year.


Comparing the first and second versions

There is a more ambitious project to detect gravitational waves - LISA (Laser Interferometer Space Antenna). According to the plan, this interferometer will be made up of three spacecraft, derived in different points of the solar system. They form a triangle with sides of millions of kilometers, which will be the most sensitive detector available to mankind. But while this project is in the design stage, and it can be realized no earlier than 2034. An intermediate project that will demonstrate the performance of the system is called LISA Pathfinder - its launch is scheduled for September 2015.