1.3 billion-year-old ripple shows Einstein was right

Scientists have made one of the most exciting discoveries of the modern era after being able to observe for the first time ripples in the fabric of space time known as gravitational waves, arriving from a cataclysmic event in the distant universe 1.3 billion years ago.

A statement from LIGO Scientific Collaboration said: “This confirms a major prediction of Albert Einstein’s 1915 general theory of relativity and opens an unprecedented new window onto the cosmos.”

The discovery was made by scientists from the LIGO Scientific Collaboration and the Virgo Collaboration in work that involved more than 1,000 scientists and 90 universities and research institutes, as well as 250 students.

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.

Professor Stephen Hawking, interviewed by the BBC, said the finding “has the potential to revolutionise astronomy”.

“I would like to congratulate the LIGO team on their groundbreaking discovery. These results confirm several very important predictions of Albert Einstein’s theory of general relativity. It confirms the existence of gravitational waves directly.

“This discovery is the first detection of a black hole binary system and the first observation of black holes merging.”

He said the observed properties of the system were consistent with predications he made about black holes in Cambridge in 1970.

According to Nature magazine, the historic discovery — which physicists say will probably lead shortly to a Nobel Prize — opens up the new field of gravitational-wave astronomy, in which scientists will listen to the waves to learn more about the objects that can produce them, including black holes, neutron stars and supernovae.

The gravitational waves were detected on 14 September 2015 by both of the twin Laser Interferometer Gravitational-Wave Observatory, or LIGO, detectors, located in Livingston, Louisiana, and Hanford, Washington, United States.

The LIGO Observatories are funded by the National Science Foundation, and were conceived, built and are operated by the California Institute of Technology, or Caltech, and the Massachusetts Institute of Technology, or 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.

When black holes collide

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. By looking at the time of arrival of the signals – the detector in Livingston recorded the event seven milliseconds before the detector in Hanford – scientists can say that the source was located in the Southern Hemisphere.

According to general relativity, a pair of black holes orbiting around each other lose energy through the emission of gravitational waves, causing them to gradually approach each other over billions of years, and then much more quickly in the final minutes.

During the final fraction of a second, the two black holes collide into each other at nearly one-half the speed of light and form a single more massive black hole, converting a portion of the combined black holes’ mass to energy; according to Einstein’s formula E=mc2 [squared] energy is emitted as a final strong burst of gravitational waves. It is these gravitational waves that LIGO has observed.

The existence of gravitational waves was first demonstrated in the 1970s and '80s by Joseph Taylor Jr and colleagues. Taylor and Russell Hulse discovered in 1974 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 Nobel Prize in Physics in 1993.

The new LIGO discovery is the first observation of gravitational waves themselves, made by measuring the tiny disturbances the waves make to space and time as they pass through the earth.

“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, fulfils Einstein’s legacy on the 100th anniversary of his general theory of relativity,” said Caltech’s David H Reitze, executive director of the LIGO Laboratory.

Big Bang insight

Stephen Hawking said: “Until now our observations of the universe have exploited light, radio waves and other electro magnetic radiation. Gravitational waves provide a completely new way of looking at the universe.

“This will revolutionise what kind of things we could discover. Apart from testing general relatively we could hope to see black holes throughout the history of the universe. A cosmic distance ladder using these black holes would be extremely accurate, and complement existing distance ladders based, for example, on supernovae.

“We may even see relics of the very early universe during the Big Bang at the most extreme energies possible.”

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 organisations in Germany (Max Planck Society), the UK (Science and Technology Facilities Council) 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.

International collaboration

LIGO research is carried out by the LIGO Scientific Collaboration, or 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 analyse 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 or 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.

“With this discovery, we humans are embarking on a marvellous new quest: the quest to explore the warped side of the universe – objects and phenomena that are made from warped space time. Colliding black holes and gravitational waves are our first beautiful examples,” said Thorne.

“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 Weiss.