WASHINGTON D.C./MORGANTOWN, W.Va. 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 Sept. 14, 2015 at 5:51 a.m. Eastern Daylight Time (09:51 UTC) by both of the twin Laser Interferometer Gravitational-wave Observatory detectors, located in Livingston, Louisiana, and Hanford, Washington, USA. The LIGO Observatories are funded by the National Science Foundation, 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.
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WVU scientists make key contributions
West Virginia University astrophysicist Sean McWilliams is a member of the research team that detected the gravitational waves. His work focused on simulating and modeling the gravitational-wave emission in order to detect the incoming signals and infer details about their source.
Chair, Department of Physics and Astronomy
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“This is the culmination of literally hundreds of scientists’ work to build such an incredibly sensitive detector and to predict the details of potential signals with what has turned out to be remarkable accuracy,” McWilliams said.
“When I first joined the collaboration, we did not know what the strongest part of the signal should look like, and today, the observation agrees beautifully with the models that myself and other scientists have developed, so this detection represents both an incredible experimental achievement as well as a tremendous validation of ongoing efforts in theoretical gravitational-wave astronomy.”
McWilliams was part of a team of collaborators who performed some of the earliest supercomputer simulations of merging black holes. Since then he has worked extensively on simulating and developing models for these signals, which LIGO scientists expect to detect from across the universe.
These efforts made it possible to know that the source of the signal LIGO detected was a pair of merging black holes, making this not only the first discovery of gravitational waves, but also the first discovery of a binary black hole system.
“It is remarkable to see how well this event agrees with simulations and models that we developed starting back in 2006 and 2007, and to think that before that time, we had no way to reliably predict what such a signal would look like, let alone model the fine details of how the source parameters alter the signal,” McWilliams said.
McWilliams has most recently collaborated with Zachariah Etienne, assistant professor of mathematics at WVU, and WVU mathematics graduate student Caleb Devine to improve and optimize the most state-of-the-art models for the signal from a pair of spinning black holes, so that the model could be used to better characterize the parameters of the event.
McWilliams, an assistant professor of physics and astronomy in the Eberly College of Arts and Sciences, has been an LSC member since 2005. He is WVU’s institutional principal investigator for the LSC and is a member of the LSC Council.
In addition to making contributions to the writing and editing of the main detection paper and several of the companion papers, McWilliams was also one of a small group of experts who monitored incoming LIGO data in round-the-clock shifts during the first observing run, deciding when “triggers,” or relatively loud phenomena in the instrument, were actually cosmic events and should therefore be investigated further with regular telescopes.
In addition to McWilliams, WVU has three active members of the LSC: Etienne, Devine and physics graduate student Belinda Cheeseboro.
“It is very exciting to see that WVU faculty and students played a key role in the analysis and confirmation of this gravitational wave signal,” said Earl Scime, chair of physics and astronomy. “This result opens an entirely new window of observation of the universe, and WVU scientists will be at the forefront.”
Based on the observed signals, LIGO scientists estimate that the black holes for this event were about 29 and 36 times the mass of the sun, and the event took place 1.3 billion years ago. About three times the mass of the sun was converted into gravitational waves in a fraction of a second with a peak power output about 50 times that of the whole visible universe.
LIGO research is carried out by the LIGO Scientific Collaboration, a group of more than 1,000 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), Leibniz Universitat 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.
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 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, 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 probedand 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 of New York, and Louisiana State University.
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