February 11, 2016
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
The LIGO facility in Hanford, Washington. More than 1,000 scientists from 15 countries make up the LIGO Scientific Collaboration.LIGO Laboratory
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 (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington. The LIGO Observatories are funded by the National Science Foundation, and were conceived, built, and are operated by California Institute of Technology and Massachusetts Institute of Technology. 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.
Two scientists from the University of Washington were part of the LIGO collaboration, physics professor Jens Gundlach and physics postdoctoral researcher Krishna Venkateswara.
“This is a huge achievement for our colleagues at LIGO,” said Gundlach. “They detected a phenomenally small signature of this black hole collision — and it marks the first time gravitational waves, predicted by Einstein in his theory of general relativity, have been directly measured.”
LIGO scientists estimate that the black holes for this event were about 29 and 36 times the mass of the sun. According to general relativity, a pair of black holes orbiting each other would lose energy through the emission of gravitational waves, and gradually approach each other over billions of years. During the final fraction of a second, the two black holes collide, releasing energy as a burst of gravitational waves about three times the mass of the sun. It is these gravitational waves that LIGO observed, though the collision occurred 1.3 billion years ago.
Gundlach and Venkateswara’s involvement with LIGO began when LIGO scientists and engineers were designing and upgrading the twin detectors in Louisiana and Washington.
“Our group at the University of Washington mostly specialized in testing fundamental aspects of gravity, not detecting gravitational waves,” said Gundlach. “But in the process, we learned about very subtle phenomena that can generate unwanted noise in gravitational wave detectors. For example, we studied the effects of residual gas molecules or minute amounts of electric charges on surfaces.”
More recently, the UW scientists also designed and constructed ultrasensitive tilt meters for the Washington-based LIGO detector, which help understand and reduce the effects of ground motion on the detector’s measurements.
“The LIGO detectors are a totally new type of instrument pushing many components to new extremes,” said Gundlach. “So, designing and constructing them required input from many researchers with a wide array of expertise. The detectors must sense incredibly minute length changes caused by the passing gravitational wave while they have to be insensitive to plethora of disturbances, including ground motion.”
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 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 and Louisiana State University.
LIGO research is carried out by the LIGO Scientific Collaboration (LSC), 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, 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.
Virgo research is carried out by the Virgo Collaboration, consisting of more than 250 physicists and engineers belonging to 19 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 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.
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For more information, contact Gundlach at 206-616-3012 or jens@phys.washington.edu.
Adapted from a release by LIGO.
Tag(s): astronomy & astrophysics • College of Arts & Sciences • Department of Physics • Jens Gundlach
