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 September 14, 2015 at 5:51 a.m. Eastern Daylight Time (10:50:45 UK local time)by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA. 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 Alberto Vecchio, from the University of Birmingham’s School of Physics and Astronomy, whose team has developed the techniques to extract the properties of the sources from the gravitational wave signatures, and has provided a significant contribution to the analysis of the LIGO data, 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.’
Professor Andreas Freise, from the University of Birmingham’s School of Physics and Astronomy, said: ‘It is amazing to think that we have been able to measure the echoes from the birth of a new black hole that happened more than a billion years ago. The Advanced LIGO detectors are a masterpiece of experimental physics. They are the most sensitive gravitational wave detectors ever built, and they have now for the first time done what they were built to do: there was a ‘disturbance in the gravitational force’, and the LIGO detectors have felt it!'
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.
Professor Freise continued: ‘We started with a well-known concept, a light interferometer, but it required new technologies that we have developed over several decades to create these extremely sensitive listening devices for gravity signals from the universe.’
Each LIGO site comprises two tubes, each four kilometres 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 metres (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.
Professor Vecchio continued: ‘The observation of gravitational wave GW150914 is the proof that binary black holes exist: they form, evolve and die. It is also the most convincing evidence to date that the strange mathematical objects predicted by Einstein's theory correspond to those produced by Nature. This completes our quest for the last elusive experimental validation of Einstein's theory. More significantly, it is the dawn of a new era for astronomy and astrophysics.’
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 just the beginning. UK scientists continue to contribute to the design and development of future generations of gravitational wave detectors.
Professor Vecchio continued: ‘I feel quite humble to think that we have just watched the last few orbits of two stellar-mass black holes moving at a third of the speed of light smashing into each other at a billion of light years from us. And we have captured the last whisper from the black hole produced by this collision.’
Notes to Editors
- 1. University of Birmingham’s Gravitational Wave Group
The University of Birmingham has been involved in the Advanced LIGO project since its inception and the Gravitational-Wave Group has developed and built components for the most sensitive instruments in the world – the high-performance sensors and control electronics for the LIGO suspension systems. Birmingham physicists have developed one of the main optical simulation tools, FINESSE, and contributed significantly to the design and commissioning of modern gravitational wave detectors. Experts in Birmingham are now investigating the behaviour of macroscopic quantum systems to explore new frontiers in precision measurement at the quantum limit.
The Birmingham group has also developed the techniques essential to tease out the signatures of gravitational waves from the data. The group has pioneered the theoretical framework and analysis algorithms that are at the heart of the study of the physics of compact binary systems, their astrophysical evolution and tests of Einstein's theory with gravitational-wave observatories. The group is involved with the ground-based detectors LIGO, GEO600 and Virgo, the space-based mission eLISA and the European and International Pulsar Timing Array.
- 2. LIGO
LIGO research is carried out by the LIGO Scientific Collaboration (LSC), a group of more than 1000 scientists from universities around the United States and in 14 other countries. More than 90 universities and research institutes in the LSC develop detector technology and analyze data; approximately 250 students are strong contributing members of the collaboration. The LSC detector network includes the LIGO interferometers and the GEO600 detector. The GEO team includes scientists at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, AEI), Leibniz Universität Hannover, along with partners at the University of Glasgow, Cardiff University, the University of Birmingham, other universities in the United Kingdom, and the University of the Balearic Islands in Spain.
LIGO was originally proposed as a means of detecting these gravitational waves in the 1980s by Rainer Weiss, professor of physics, emeritus, from MIT; Kip Thorne, Caltech’s Richard P. Feynman Professor of Theoretical Physics, emeritus; and Ronald Drever, professor of physics, emeritus, also from Caltech. The LIGO Observatories are funded by the National Science Foundation (NSF), and were conceived, built, and are operated by Caltech and MIT.
Virgo research is carried out by the Virgo Collaboration, consisting of more than 250 physicists and engineers belonging to 19 different European research groups: 6 from Centre National de la Recherche Scientifique (CNRS) in France; 8 from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; 2 in The Netherlands with Nikhef; the Wigner RCP in Hungary; the POLGRAW group in Poland and the European Gravitational Observatory (EGO), the laboratory hosting the Virgo detector near Pisa in Italy.
The discovery was made possible by the enhanced capabilities of Advanced LIGO, a major upgrade that increases the sensitivity of the instruments compared to the first generation LIGO detectors, enabling a large increase in the volume of the universe probed—and the discovery of gravitational waves during its first observation run. The US National Science Foundation leads in financial support for Advanced LIGO. Funding organizations in Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council, STFC) and Australia (Australian Research Council) also have made significant commitments to the project. Several of the key technologies that made
Advanced LIGO so much more sensitive have been developed and tested by the German UK GEO collaboration. Significant computer resources have been contributed by the AEI Hannover Atlas Cluster, the LIGO Laboratory, Syracuse University, and the University of Wisconsin-Milwaukee. Several universities designed, built, and tested key components for Advanced LIGO: The Australian National University, the University of Adelaide, the University of Florida, Stanford University, Columbia University in the City of New York, and Louisiana State University.
Images of Professor Alberto Vecchio and Andreas Freise can be found here:
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