On the ground at LIGO, and around the world: There are ground-based gravitational wave observatories at sites around the world.
© Caltech/MIT/LIGO Laboratory
Scientists had been looking for gravitational waves at sites on the ground for 40 years before they found them. Since the search started, every generation of detectors that followed has been more sensitive than the last, each aiming to be the first to measure the telltale ‘wobble’ that indicates a gravitational wave passing through.
These complex machines are highly calibrated and balanced to do a very precise job. UK scientists and engineers have played important roles in designing and supplying the components that allow gravitational wave detectors to function all around the world...
The detector at the heart of the groundbreaking gravitational wave detection consists of two identical four-kilometre-long, L-shaped systems at sites in the US (Livingston, Louisiana and Hanford, Washington): Advanced LIGO (Advanced Laser Interferometry Gravitational-wave Observatory).
Gravitational wave detectors like LIGO rely on being able to measure the smallest changes in the lengths of their detector arms. The sensors and electronics (the optical components) are critical to the detectors functioning because they make it possible to guide, measure and analyse the laser signals. Many of these parts were designed and supplied by the UK.
A team of UK universities (including the Universities of Cardiff, Birmingham and Strathclyde), led by Glasgow and STFC, were responsible for designing and building the suspensions for LIGO’s mirrors. These mirrors guide the lasers back and forth along the arms and into the detectors that are essential for measuring small changes in detector arm length.
As well as helping to lay the foundations for the original LIGO detectors, the UK, along with Germany and Australia, has played a key role in making the upgrades that allowed Advanced LIGO to become the gravitational-wave-detecting machine it is. This will continue as the advanced LIGO detectors are updated, and when third detector is completed in India in 2024.
Before LIGO, there was GEO600 – one of the first gravitational wave detectors, built between 1996 and 2000.
This 600-metre-long gravitational wave interferometer is situated near Hannover and funded by the Max Planck Society, the state of Niedersachsen, the Leibniz University Hannover, STFC, the University of Glasgow and the Volkswagen Foundation. Although GEO600 didn’t actually detect gravitational waves, it has been an important proving ground for the technology. Many of the techniques and technologies developed for GEO600, in part by UK scientists, were adopted by LIGO.
Like GEO600, TAMA 300 was one of the ‘first generation’ of gravitational wave detectors.
With arms are 300-metres long, TAMA 300 is sensitive enough to detect the colliding neutron star binaries in our Galaxy – but these events only come along a few times every 100,000 years. To detect gravitational waves, the advanced detector KAGRA, a large-scale gravitational-wave telescope, is now being constructed in the Kamioka mine in Hida with input from UK experts.
The Virgo detector – a three-kilometre-long giant interferometer based in Cascina, Italy – is currently being upgraded in a programme that will see a ten-fold increase in detector sensitivity. When the new Advanced Virgo goes online later this year it will complete the so-called ‘second generation’ of gravitational wave observatories.
Today, there is a global network of detectors working together to detect and analyse gravitational waves, including those described above, but scientists have already started to look to the future.
While LIGO and Virgo only have one detector in each facility, a proposed design for the aptly-named Einstein Telescope will have three gravitational wave detectors housed in three ten-kilometre-long detector arms. The design was proposed by eight European research institutes (including the Universities of Birmingham, Cardiff and Glasgow).
When built, the Einstein Telescope will take gravitational wave detectors to the next level.
The future is looking bright for space-based gravitational wave detectors too, with the LISA, and the LISA pathfinder missions, extending our capabilities to ‘listen’ to the universe.