First joint detection of gravitational waves with both the LIGO and Virgo detectors.
27 September 2017
Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky.
(Credit: Giuseppe Greco (Virgo Urbino group))
British-designed and built technology being used in the hunt for gravitational waves has enabled another scientific first – and is now also helping fix broken bones.
Scientists from 11 UK universities, and 20 other nations, have used a network of three observatories across the United States and Europe to detect the collision of two gigantic black holes, about 1.8 billion light years away. The use of three detectors allowed very precise measurement of the collision, which generated a huge burst of gravitational energy equivalent to about three times the total energy in our Sun. Gravitational waves are ripples in space, and cannot be detected through ordinary telescopes which use electromagnetic radiation such as visible light or gamma rays. Previous gravitational wave detections only used two detectors.
The historic three-detector observation was made mid-morning on 14 August, by both detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in Louisiana and Washington state in the US, and the Virgo detector near Pisa in Italy. The detectors recorded the burst of energy as the two black holes – about 31 and 25 times the size of our Sun – spun together.
Dr John Veitch, research fellow at the University of Glasgow’s School of Physics and Astronomy, co-led a team within the collaboration on working on the data analysis of the signal to determine the origins and properties of the source. He said: “This was a very strong first. The addition to the network of a signal from Virgo provided us with a lot of useful data. Having a third detector means that we can now triangulate the position of the source, and much more accurately determine the exact spot in the cosmos where the signal came from.”
UK Science Minister, Jo Johnson, said “The latest detection of gravitational waves is an excellent example of international collaboration, which was only made possible due to the breakthrough work undertaken by UK scientists and engineers.
“By developing our understanding of the Universe and identifying new fields of scientific research, we are continuing to build upon our reputation as being a world leader in science and innovation which is at the core of our Industrial Strategy.”
Chief Executive Designate at UK Research and Innovation, Sir Mark Walport said: “Research and innovation are global endeavours. Breakthroughs in science involving many partners, such as this one, reinforce the importance the UK places on continuing to be a leading partner in the global scientific landscape.”
Professor Brian Bowsher, Chief Executive of the UK’s Science and Technology Facilities Council said: “Today’s announcement helps us delve deeper into understanding how the Universe works. I am particularly pleased that the UK-built technology at the heart of this discovery is also now being used to improve medical treatments.”
The LIGO detectors rely on British-designed technology to remove vibrations caused by natural and human activity, so that the incredibly tiny distortions caused by the gravitational waves can be accurately detected. That technology is being used in reverse to test a process to grow human bone in a laboratory. The new technique - known as “nanokicking” – vibrates stem cells thousands of times a second, to stimulate the production of bone cells. The new ‘bone putty’ has the potential to be used to heal bone fractures and fill bone where there is a gap.
Professor Sheila Rowan, director of the Institute for Gravitational Research, said: “We’re proud to have played a role in this first new joint detection alongside our partners in the US and in Europe, which is an important advance for the field of gravitational wave astronomy.”
Professor Mark Hannam, from Cardiff University’s School of Physics and Astronomy, said: “Adding Virgo to the network has allowed us to pinpoint where the signal came from ten times better than before. This is an amazing improvement in the precision of gravitational-wave astronomy.”
Professor Andreas Freise, from the University of Birmingham’s Institute of Gravitational Wave Astronomy, said: “Once again, we have detected echoes from colliding black holes but this time we can pinpoint the position of the black holes much more accurately thanks to the addition of the Virgo detector to the advanced detector network. Around ten years ago I was in charge of designing the core interferometer of the Advanced Virgo project. To see that instrument become a reality, and now helping to deliver significant results, is really special.”
Professor Alberto Vecchio, also from the University of Birmingham’s Institute of Gravitational Wave Astronomy, added, “We’re really proud of how our team have helped contribute to the success of this international network, from designing the equipment to analysing and interpreting the data. It is a truly exciting time for astronomy and astrophysics as we try to unravel the mysteries of the universe.”
A paper about the event, known as GW170814, has been accepted for publication in the journal Physical Review Letters.
The announcement is being live-streamed at the home page of the Italian Ministry of Research.
A video showing aerial footage of the Virgo facility.
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It consists of more than 280 physicists and engineers belonging to 20 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in The Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with the University of Valencia; and EGO, the laboratory hosting the Virgo detector near Pisa in Italy.
It is funded by the NSF, and operated by Caltech and MIT, which conceived and built the project. Financial support for the Advanced LIGO project was led by NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council) making significant commitments and contributions to the project. More than 1,200 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. Additional partners are listed here.
Overall, the Universe volume which is likely to contain the source shrinks by more than a factor 20 when moving from a two-detector network to a three-detector network. The sky region for GW170814 has a size of only 60 square degrees, more than 10 times better than for the two LIGO interferometers alone; in addition, the accuracy with which the source distance is measured benefits from the addition of Virgo. Being able to point to a smaller volume is important as many compact object mergers – for example when neutron stars are involved – are expected to produce broadband electromagnetic emission in addition to gravitational waves. The precision pointing information enabled 25 facilities to perform follow-up observations based on the LIGO-Virgo detection but no counterpart was identified – as expected for black holes.
Virgo doesn’t respond in the exactly same way to passing gravitational waves as the LIGO detectors because of its orientation on Earth, meaning that one can test another prediction of general relativity, which is concerned with polarizations of gravitational waves. Polarization describes how space-time is distorted in the three different spatial directions as a gravitational wave propagates. Initial tests based on the transient GW170814 event compare extreme cases: on the one hand, pure general relativity-allowed polarizations; on the other hand, pure polarizations forbidden by Einstein’s theory. The analysis of the data shows that Einstein’s prediction is strongly favored. “The Virgo collaboration and the LIGO Scientific Collaboration have been working together for many years to analyze the data and extract precious information from the observed signals. A three-detector network opens up a new potential, allowing further fundamental tests of theoretical predictions,” says Frédérique Marion, senior scientist at LAPP, Annecy. In addition to this new result, other tests of general relativity already performed for the previous detections show an overall agreement between observations and general relativity.
It is the second generation instrument built and operated by the Virgo collaboration to search for gravitational waves. Giovanni Losurdo of the INFN, who led the Advanced Virgo project to completion: “This detection is a milestone for all the people who have dedicated their time to conceive, realize and operate Virgo and Advanced Virgo, first among them Alain Brillet, and Adalberto Giazotto. The whole enterprise was based, since its start, on a visionary goal: the creation of a network capable of localizing the sources in the sky and start the era of the multi-messenger investigation of the universe. And finally, after decades, we are there.” Advanced Virgo’s initial design was completed 10 years ago while the initial Virgo detector was taking its first data. The founder funding agencies of the Virgo project, CNRS and INFN, approved the project in December 2009, and significant contributions were made by Nikhef. With the end of observations with the initial Virgo detector in October 2011, the realization of the Advanced Virgo detector began.
The new facility was dedicated in February 2017 while its commissioning was ongoing. In April, the control of the detector at its nominal working point was achieved for the first time. During the following months, the instrument’s sensitivity underwent dramatic improvements, thanks to an extensive noise hunting campaign. Once the sensitivity reached by Advanced Virgo allowed to probe a volume of the Universe more than 10 times larger than for the initial Virgo detector, on August 1st, Advanced Virgo joined the two LIGO detectors for the final four weeks of the O2 data taking period. “The Virgo upgrade to Advanced Virgo had an ambitious objective: to significantly improve the sensitivity of our detector, in order to maximize the probability to detect gravitational wave signals,” says Federico Ferrini, director of the European Gravitational Observatory. “Reaching a level of performance to realize a three-detector network for a common data taking period took many years of intense and innovative work. As Virgo has observed its first event, I wish to recognize the dedication of the members of the Virgo collaboration, of the EGO staff and of the participating laboratories.”
It is a second generation gravitational-wave detector consisting of two identical interferometers located in Hanford, WA and Livingston, LA. It uses precision laser interferometry similar to Advanced Virgo to detect gravitational waves. Beginning operating in September 2015, Advanced LIGO has conducted two observing runs. The second ‘O2’ observing run began on Nov. 30, 2016 and ended on Aug. 25, 2017. David Reitze of Caltech, the executive director of the LIGO Laboratory that built and operates the LIGO observatories, adds “With this first joint detection by the Advanced LIGO and Virgo detectors, we have taken one step further into the gravitational-wave cosmos. Virgo brings a powerful new capability to detect and better locate gravitational-wave sources, one that will undoubtedly lead to exciting and unanticipated results in the future.”
LIGO consists of two L-shaped interferometers, one in Hanford, Washington, and one in Livingston, Louisiana. Each arm of each L is 2½ miles (4 km) long. Lasers look for changes in each arm's length as small as a millionth the diameter of a proton. Passing gravitational waves might distort space-time by that much.
A short film where UK collaborators discuss the search for gravitational waves.
Short film in 3 minutes on the key ideas in the theory.