For the first time, physicists have observed ‘ripples’ in the fabric of space-time called gravitational waves.
The collision of two black holes is seen in this still from a computer simulation. Image credit: SXS.
Gravitational waves — ‘ripples’ in space-time produced by some of the most violent events in the cosmos — were predicted by Albert Einstein in 1916, when he showed that accelerating massive objects would shake space-time so much that waves of distorted space would radiate from the source.
These ripples travel at the speed of light through the Universe, carrying with them information about their cataclysmic origins, as well as invaluable clues to the nature of gravity itself.
“These waves are so small that only the violent acceleration of massive bodies gives signals we can hope to detect,” said team member Dr Phil Evans, of the University of Leicester, UK.
“The most likely source of such detectable waves would be the collision of either two incredibly dense stars called neutron stars, or two black holes, or possibly a neutron star and a black hole.”
The existence of gravitational waves was first demonstrated in the 1970s and 1980s by Joseph Taylor, Jr., and colleagues.
In 1974, Taylor and Russell Hulse discovered a binary system composed of a pulsar in orbit around a neutron star. Taylor and Joel M. Weisberg in 1982 found that the orbit of the pulsar was slowly shrinking over time because of the release of energy in the form of gravitational waves.
For discovering the pulsar and showing that it would make possible this particular gravitational wave measurement, Hulse and Taylor were awarded the 1993 Nobel Prize in Physics.
The new discovery — made by the LIGO Scientific Collaboration and the Virgo Collaboration using data from the Laser Interferometer Gravitational-wave Observatory (LIGO), the world’s largest gravitational wave observatory and one of the world’s most sophisticated physics experiments – is the first observation of gravitational waves themselves.
LIGO scientists 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.
The event, named GW150914, was detected on Sept. 14, 2015 at 5:51 a.m. EDT (09:51 UTC) by both of the twin LIGO detectors, located in Livingston, La., and Hanford, Wa.
Based on the observed signals, the researchers estimate that the black holes for this event were about 29 and 36 times the mass of the Sun.
GW150914 took place 1.3 billion years ago, according to the team.
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.
“On September 14, 2015 at 09:50:45 Greenwich Mean Time the LIGO Hanford and Livingston Observatories both detected a signal from GW150914,” the scientists said. “The signal was identified first by what we call low-latency search methods that are designed to analyze the detector data very promptly, looking for evidence of a gravitational-wavelike pattern but without modeling the precise details of the waveform.”
“Our results indicate that GW150914 was produced by the merger of two black holes with masses of about 36 times and 29 times the mass of the Sun respectively, and that the post-merger black hole had a mass of about 62 times the Sun’s mass.”
“Moreover, we infer that the final black hole is spinning – such rotating black holes were first predicted theoretically in 1963 by mathematician Roy Kerr.”
“Finally, our results indicate that the GW150914 occurred at a distance of more than one billion light years. So the LIGO detectors have observed a truly remarkable event that happened a long time ago in a galaxy far, far away!”
“Our observation of gravitational waves accomplishes an ambitious goal set out over five decades ago to directly detect this elusive phenomenon and better understand the Universe, and, fittingly, fulfills Einstein’s legacy on the 100th anniversary of his general theory of relativity,” said Prof. David H. Reitze, Executive Director of the LIGO project and a scientist at the California Institute of Technology.
“This detection is the beginning of a new era: The field of gravitational wave astronomy is now a reality,” said team member Prof. Gabriela Gonzalez, of Louisiana State University.
“The description of this observation is beautifully described in the Einstein theory of general relativity formulated 100 years ago and comprises the first test of the theory in strong gravitation. It would have been wonderful to watch Einstein’s face had we been able to tell him,” said Prof. Rainer Weiss from the Massachusetts Institute of Technology.
“With this discovery, we humans are embarking on a marvelous new quest: the quest to explore the warped side of the Universe — objects and phenomena that are made from warped space-time,” said Prof. Kip Thorne from the California Institute of Technology.
“Colliding black holes and gravitational waves are our first beautiful examples.”
“Einstein thought gravitational waves were too weak to detect, and didn’t believe in black holes. But I don’t think he’d have minded being wrong,” said Dr. Bruce Allen, managing director of the Max Planck Institute for Gravitational Physics.
“The Advanced LIGO detectors are a tour de force of science and technology, made possible by a truly exceptional international team of technicians, engineers, and scientists,” said Dr. David Shoemaker, the project leader for Advanced LIGO and a scientist at the Massachusetts Institute of Technology.
The results were published online today in the journal Physical Review Letters.
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B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration). 2016. Observation of Gravitational Waves from a Binary Black Hole Merger. Physical Review Letters 116, 061102; doi: 10.1103/PhysRevLett.116.061102
