Glasgow University plays a key role in the historic detection of gravitational waves

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Gravitational waves detected 100 years after Einstein’s prediction
Scientists have observed the warping of space-time, generated by the collision of two black holes more than a billion light-years from Earth

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Nathan Stilwell, Andrew McIntyre and Katy Scott
News Editor and News Reporters

For the first time, scientists have observed ripples in the fabric of spacetime, called gravitational waves, arriving at the Earth following the collision of two black holes 1.3 billion years ago.

This confirms a prediction made by Albert Einstein in 1915, and is thought to be a major breakthrough in helping scientists fully understand gravity and the Big Bang.

61 of the researchers involved in the discovery are based at the University of Glasgow, half of which are graduate students, which makes it the largest group working on the project in the UK.

University of Glasgow researchers have been working for decades to support the worldwide effort to detect gravitational waves, and co-led a group which detected the gravitational wave signal.

Scientists from the University’s Institute for Gravitational Research (IGR) led on the development, construction and installation of sensitive mirror suspensions at the heart of the Laser Interferometer Gravitational-wave Observatory (LIGO) detectors in Livingston, (Louisiana) and Hanford (Washington), which were crucial to the first detection.

Professor Sheila Rowan, Director of the Institute for Gravitational Research, said: “This is a monumental leap forward for physics and astrophysics – taking Einstein’s predictions and turning them into an entirely new way to sense some of the most fascinating objects in our Universe.

“In the past, we’ve relied on the information we collected from the electromagnetic spectrum to help learn more about the cosmos, from the other planets in our solar system to star systems millions of light years away.

“Now gravitational wave astronomy will give us the ability to make many exciting new discoveries. This first detection, in addition to confirming Einstein’s prediction, also gives us the first direct evidence of the existence of black holes, and the first observation of black holes merging, which is a fantastic result. We’re very much looking forward to new data from LIGO in the coming months and years, and to making our detectors even more sensitive.”

The longest-serving member of the University’s gravitational research community is Professor James Hough, who has worked in the field at the University since 1971.

Professor Hough said: “Alongside Professor Ronald Drever, I was involved in building early gravitational wave detectors here in Glasgow, which monitored outputs from piezoelectric transducers attached to aluminium bars.

“We thought it would take us about a year to make an initial detection, and in 1972, we found what looked very much like evidence of gravitational waves. However, since no other detectors were operating at the same time, we weren’t able to verify our observation. Nonetheless, that finding convinced me that we would one day find the evidence we were looking for.

“This discovery, 43 years later, is the culmination of my career in science. I’m immensely proud to have been involved in the project and I’m very excited to see the fascinating new discoveries gravitational wave astronomy will bring us in the future.”

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Gravitational waves carry information about their origins in the distant universe as well as the nature of gravity that cannot otherwise be obtained.

The Laser Interferometer Gravitational-wave Observatory (LIGO) collaboration operates a number of labs around the world that fire lasers through long tunnels, with the purpose of trying to detect  ripples in the fabric of space-time.

The signals are extremely faint, and disturb the machines, known as interferometers, by just a fraction of the width of an atom.

Scientists have concluded, however, that the detected gravitational waves were produced during the final fraction of a second, following the collision of two black holes to produce a single, massive, spinning black hole.

This merging of two black holes had been predicted, but never observed by scientists, until now.

Based on the signals observed, LIGO researchers estimate that the black holes 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.

The gravitational waves were detected on 14 September 2015 at 5:51 a.m. (Eastern Daylight Time) by both of the twin LIGO detectors, located in Livingston and Hanford.

Einstein  predicted that if the gravity in an area was changed suddenly,  waves of gravitational energy would ripple across the Universe at light-speed, manipulating space as they travelled.

The breakthrough is thought to be one the most significant scientific developments  since the discovery of the Higgs particle.

The LIGO scientific collaboration is an international group of more than 1000 scientists leading the efforts to detect ripples in spacetime that were predicted by Einstein.

There are 141 scientists across the UK involved in the LIGO collaboration, out of 1000 scientists globally involved in the project.

The LIGO detectors had been turned off for five years while upgrades were made, and in September 2015 the Advanced LIGO collaboration began. The ripples were detected almost as soon as the detectors were switched back on.

Improvements are still being made to the LIGO detectors which are not expected to reach the planned sensitivity for another two to three years. Scientists anticipate that it will exceed the sensitivity of Advanced LIGO tenfold. Following these improvements, the LIGO scientific collaboration is expecting to detect further gravitational waves from colliding neutron stars, black holes carrying neutron stars, and cosmic strings in the coming years.

Glasgow University’s contribution to the LIGO project

Staff & students gathered in the Senate Room to hear the historic announcement. Photo: Nathan Stilwell

Staff & students gathered in the Senate Room to hear the historic announcement. Photo: Nathan Stilwell

University of Glasgow staff and students gathered in the University’s Senate Room, to hear what Principal Anton Muscatelli described as “part of a historic moment” that would “move back the boundaries of knowledge”.

The first minister of Scotland, Nicola Sturgeon, said: “This is a world leading discovery that again puts Scotland at the forefront of science.”

The main focus of Glasgow University’s input was introducing and improving the sensitivity of the instruments used, specifically the suspension system used to hold the mirror system at precisely correct orientation – known as the quasi-monolithic fused silica suspensions.

Professor Kenneth Strain, of the University’s School of Physics and Astronomy, described the LIGO detectors as the “most sensitive instruments on planet”. He added that the suspensions used to hold the mirrors in place are the “stillest things on earth”.

Professor Martin Hendry, the Head of the School of Physics and Astronomy at the University, and a member of the IGR for 10 years, said: “Glasgow is at the forefront of UK contribution” and that the suspension system researched and developed at the University of Glasgow was “essential” to work done by LIGO.

Professor Strain is involved with involved with this unconventional form of astronomy, whereas Professor Hendry specialised in conventional astronomy, using light, telescopes and other specialised equipment, before moving into new astronomy.

Scientists from the University were also responsible for the improvements made to Advanced LIGO, from 2010 to 2015, when tests were first conducted.

The discovery of the ripples in spacetime were made soon after the new Advanced LIGO system was in operation. According to Professor Hendry, the discovery was made “during the last steps of tuning up”.