Updated gravitational wave detector will work this year

    Location of the LIGO

    detector The LIGO (Laser Interferometer Gravitational-Wave Observatory) laser gravitational wave detector equipment is nearing completion . Tests should begin this year, and they plan to launch the project 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 “practically 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 must exist. The rapid movement of massive objects, for example, a system of rotating neutron stars, should propagate such waves. These waves should bend space a little - and, by 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 laser radiation propagates. The laser beam is split by a divider into two perpendicular beams, each of which then falls into its own tunnel and is repeatedly reflected from the mirrors installed there. Part of the radiation goes back to the divider. If the length of both shoulders remains constant, then the returning waves go back to the laser. But if their length suddenly becomes different due to the influence of the gravitational wave, then the waves interfere in such a way that they get into the photodetector. And then - champagne and Nobel.

    LIGO Workflow

    First time use an optical interferometer ( Michelson interferometer) as a detector of gravitational waves was proposed by Soviet scientists M.E. Herzenstein and V.I. Pustovoit in 1962 . Then, American professor Rainer Weiss proposed increasing the effective length of the arms of the interferometer 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 will make a run of 300 km. As a result, the Weiss-proposed detector is able to measure the change in length of one of the shoulders by 10 -18 m.

    Professor Weiss

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

    Many difficulties had to be overcome to ensure the operation of the highly sensitive device. To exclude the vibrations that even the laser beam itself induces, the mirrors had to be made massive (more than 20 kg). To eliminate 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 no gravitational waves were recorded, despite the fact that during the period of operation the sensitivity of the complex was doubled by some improvements. Then the complex was closed for a large-scale update, which they plan to complete this year.

    The main candidate for the emission of gravitational waves remains binary systems of neutron stars. The first LIGO could detect the emission of stars about 50 million light-years from Earth. The new design will increase sensitivity by 10 times compared to the previous one, and therefore the amount of space that is available to him has increased by 1000 times. According to scientists, the number of systems existing in such a volume should provide about 10 wave detections per year.

    Comparison of the first and second versions

    There is also a more ambitious project to detect gravitational waves - LISA (Laser Interferometer Space Antenna). According to the plan, this interferometer will be composed of three spacecraft launched at different points in the solar system. They form a triangle with sides of millions of kilometers, which will become the most sensitive detector of humanity. But while this project is in the design stage, and it will be able to be implemented no earlier than 2034. An intermediate project that will demonstrate the system’s operability is called LISA Pathfinder - its launch is scheduled for September 2015.

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