Gravitational waves detected 100 years after Einstein’s prediction

LIGO opens new window on the Universe with observation of gravitational waves from colliding black holes, with Strathclyde researchers contributing to international discovery proving Einstein was right.

For the first time, scientists have observed ripples in the fabric of spacetime called gravitational waves, arriving at the earth from a cataclysmic event in the distant universe. This confirms a major prediction of Albert Einstein’s 1915 general theory of relativity and opens an unprecedented new window onto the cosmos.

Gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot otherwise be obtained. Physicists have concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole. This collision of two black holes had been predicted but never observed.

The gravitational waves were detected on 14 September 2015 at 09:51 UK time by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA. The LIGO Observatories are funded by the National Science Foundation (NSF), and were conceived, built, and are operated by Caltech and MIT. 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.

The University of Glasgow, along with the University of Strathclyde, the University of Birmingham and the STFC Rutherford Appleton Laboratory, played a key role in conceiving, designing and delivering the ultra-low-noise mirror suspension at the heart of the gravitational wave detectors.

Dr Nicholas Lockerbie, Reader in Physics at the University of Strathclyde, said: “The direct detection of gravitational waves marks the dawn of a new era in astronomy. I never expected to see an event of this kind in my lifetime. Gravity has now spoken to us, across vast tracts of the Universe. For the first time in mankind’s history, we have been able to hear it – and understand what it said.”

The gravitational waves originated from two black holes, each around 30 times the mass of the Sun and located approximately 1.3 billion light years from the Earth, coalescing to form a single, massive, black hole.

Dr Lockerbie added: “This event – known as GW150914 – is evidence of a stunning black-hole-black-hole merger, lasting less than one second. However, its detection is the result of decades of international, scientific and technical collaboration, culminating in the matchless gravitational wave sensitivity of the Advanced LIGO detectors in the USA. I’m personally delighted and honoured that Strathclyde research and technology has also helped create the system behind this incredible discovery.”

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.

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.

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 Sir Jim McDonald, Principal of the University of Strathclyde, said: “The remarkable discovery made by this truly international collaboration will open entirely new areas of scientific study, greatly improving our understanding of the Universe."

“Today’s announcement marks the beginning of a new era – and a new world of possibilities for the scientists and engineers of tomorrow.”

In the 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. 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.

February 2016