Vacuum science has been integral to major scientific advancements. One of the most prominent of these is gravitational wave detectors. Gravitational waves are ripples in space-time that are caused by violent processes such as exploding stars, collisions between neutron stars or the merging of black holes – a concept predicted by Einstein’s theory of General Relativity in 1915.
The use of vacuum science in gravitational wave detection
In order for gravitational waves to be detected in an interferometer (consisting of light storage arms), vacuum conditions are needed. Without this, the gas molecules present in the interferometer arms can destroy the light or produce noise that conceals any changes in laser beams resulting from gravitational waves.
Vacuum pumps are therefore an essential part of gravitational wave detection systems. As pressure ranges of up to <10-09 mbar must be obtained, the most common vacuum pumps used are Magnetic Turbomolecular pumps, Ion pumps, Cyro Pumps and Dry fore-vacuum pumps. Other key factors to consider are low vibrations and acoustic noise, cleanliness (preferably oil-free) and electromagnetic emissions to avoid the disturbance of measurements.
Gravitational wave detectors projects and discoveries
Founded in 1997 and made up of over 100 institutions across 18 countries, LIGO is the world's largest gravitational wave observatory. This aims to explore the physics of gravity and mark the field of gravitational wave science as an instrument of astronomical discovery through the detection of gravitational waves.
Virgo is a giant laser interferometer aimed to detect gravitational waves. It operates in Cascina, Italy by an international collaboration of scientists in France, Italy, the Netherlands, Poland and Hungary.
In April 2019, LIGO and Virgo detectors registered gravitational waves, suspected to arise from a crash between two neutron stars. An additional and unlikely source was soon spotted; the collision of a neutron star and black hole. The impact of this discovery has redefined the nature of space research, enabling scientists to develop research on what was once thought to be impossible.
Ultra-high vacuum conditions in gravitational wave detection
In order to operate effectively, gravitational wave detectors must maintain ultra-high vacuum conditions. This is because sound waves are unable to cause vibrations in the vacuum system. Without this vacuum chamber, air currents within beam tubes would cause the laser to change direction, preventing the ability to detect gravitational waves.
Central to this is the installation of beam vacuum tubes. Due to the high sensitivity of the LIGO detector, these beams must be leak-free and made from materials with low outgassing effects. Additionally, the arms of the tube had to be assembled in a straight line and the Earth’s curvature had to be accounted for, highlighting the precision of the project.
One of the biggest barriers facing LIGO is the high level of quantum noise. In order to improve this, the vacuum variations that entered an interferometer can be replaced with squeezed light. This was carried out in 2011 at the LIGO Hanford Observatory and led to a reduction in noise frequencies as well as higher sensitivity levels.
Overall, the presence of ultra-high vacuum conditions has enabled scientists across the globe to work collaboratively towards detecting and measuring gravitational waves. With new and surprising detections continuing to challenge existing theories.
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