An international team of scientists have today announced the first-ever detection of gravitational waves. The discovery confirms a major prediction of Albert Einstein’s 1915 general theory of relativity, and was made possible by British and German advances in technology.
“This is a monumental leap forward for physics and astrophysics — taking Einstein’s predictions and turning them into an entirely new way to sense some of the most fascinating objects in our universe,” said Professor Sheila Rowan, Director of the University of Glasgow’s Institute for Gravitational Research, and a member of the discovery team.
The gravitational waves were detected on 14 September 2015 at 09:51 UK time by both LIGO (Laser Interferometer Gravitational-wave Observatory) detectors in Louisiana and Washington state in the US. They originated from two black holes, each around 30 times the mass of the Sun and located more than 1.3 billion light-years from Earth, coalescing to form a single, even more massive black hole.
Professor Alberto Vecchio, from the University of Birmingham, whose team has developed the techniques to extract the properties of the sources from the gravitational wave signatures, said: “This observation is truly incredible science and marks three milestones for physics: the direct detection of gravitational waves, the first observation of a binary black hole, and the most convincing evidence to-date that Nature’s black holes are the objects predicted by Einstein’s theory.”
The UK Minister for Universities and Science, Jo Johnson MP, said: “Einstein’s theories from over a century ago are still helping us to understand our universe. Now that we have the technological capability to test his theories with the LIGO detectors his scientific brilliance becomes all the more apparent. The Government is increasing support for international research collaborations, and these scientists from across the UK have played a vital part in this discovery.”
The discovery, accepted for publication in the journal Physical Review Letters, was made by the LIGO Scientific Collaboration (which includes the GEO Collaboration and the Australian Consortium for Interferometric Gravitational Astronomy) and the Virgo Collaboration using data from the two LIGO detectors.
Professor John Womersley, physicist and Chief Executive of the UK’s Science and Technology Facilities Council said: “It has taken 100 years and the combined work of many hundreds of the cleverest scientists, engineers and mathematicians on Earth to prove that this key prediction of Albert Einstein is correct, and show that gravitational waves exist. Of course Einstein was always the smartest guy in the room. Today’s results also remind us just how important the UK’s contribution to world leading science is — I’d certainly like to think that some of the smartest people on Earth today are living and working in the UK.”
Gravitational waves carry unique information about the origins of our universe and studying them is expected to provide important insights into the evolution of stars, supernovae, gamma-ray bursts, neutron stars and black holes. However, they interact very weakly with particles and require incredibly sensitive equipment to detect. The British and German teams, working with US, Australian, Italian and French colleagues as part of the LIGO Scientific Collaboration and the VIRGO Collaboration, are using a technique called laser interferometry.
Each LIGO site comprises two tubes, each four kilometers long, arranged in an L-shape. A laser is beamed down each tube to very precisely monitor the distance between mirrors at each end. According to Einstein’s theory, the distance between the mirrors will change by a tiny amount when a gravitational wave passes by the detector. A change in the lengths of the arms of close to 10-19 meters (just one-ten-thousandth the diameter of a proton) can be detected.
Independent and widely separated observatories are necessary to verify the direction of the event causing the gravitational waves, and also to determine that the signals come from space and are not from some other local phenomenon.
“Scientists have been looking for gravitational waves for decades, but we’ve only now been able to achieve the incredibly precise technologies needed to pick up these very, very faint echoes from across the universe,” said Professor Karsten Danzmann, the Director of the Albert-Einstein-Institut in Hannover, and a member of the LIGO collaboration. “We tested these technologies at the joint German-UK GEO600 detector near Hannover before fitting them to LIGO.”
“This is significant because this is an entirely new astronomy, it will give us ears to the universe where before we’ve only had eyes”
To ensure absolute accuracy, the consortium of nearly 1,000 scientists from 16 countries spent several months carefully checking and re-checking the data before submitting their findings for publication in Physical Review Letters.
Professor B S Sathyaprakash, from Cardiff University’s School of Physics and Astronomy, said: “We’ve calculated the waves originated from the collision of two black holes about 1.3 billion light-years away. The shock would have released more energy than the light from all the stars in the universe for that brief instant. The fusion of two black holes which created this event had been predicted but never observed.”
Professor Rowan said the detection was made possible by the advanced technologies developed by the UK team: “The mirrors at the end of the LIGO beams weight 40 kilograms each, and we need to be able to hold these large weights absolutely still. After a lot of development, we created precision fused-silica suspensions to do this.”
LIGO operations are funded by the US National Science Foundation (NSF), and the facility is operated by Caltech and MIT. The LIGO upgrade was funded by the NSF with financial and technical contributions from the UK’s Science and Technology Facilities Council (STFC), the Max Planck Society of Germany, and the Australian Research Council (ARC). STFC currently supports the operation of the Advanced LIGO detectors through computational support from UK institutions.
“Our observation of gravitational waves accomplishes an ambitious goal set out over 50 years ago to directly detect this elusive phenomenon and better understand the universe, and fulfills Einstein’s legacy on the 100th anniversary of his general theory of relativity,” said Caltech’s David H. Reitze, executive director of the LIGO Laboratory.
Over coming years, the Advanced LIGO detectors will be ramped up to full power, increasing their sensitivity to gravitational waves, and in particular allowing more distant events to be measured. With the addition of further detectors, initially in Italy and later in other locations around the world, this first detection is surely just the beginning. UK scientists continue to contribute to the design and development of future generations of gravitational wave detectors.
“This detection ushers in a new era of astronomy. The field of gravitational wave astronomy is now a reality,” said Gabriela González, LIGO Scientific Collaboration spokesperson and professor of physics and astronomy at Louisiana State University.
LIGO was originally proposed as a means of detecting these gravitational waves in the 1980s by Kip Thorne, Caltech’s Richard P. Feynman Professor of Theoretical Physics, Emeritus; Ronald Drever, professor of physics, emeritus also from Caltech; and Rainer Weiss, professor of physics, emeritus, from MIT.
A team from STFC’s Rutherford Appleton Laboratory were responsible for the design, technological development and production of the suspensions that provide the stability required to separate out the effects of tiny strains in space time from the much larger effects of seismic vibration. This work represents a major technological advance in the field and has made a substantial contribution on increasing the sensitivity of the instrument, and its ability to detect gravitational waves.
