16 October 2017
In a galaxy far away, two dead stars begin a final spiral into a massive collision. The resulting explosion unleashes a huge burst of energy, sending ripples across the very fabric of space. In the nuclear cauldron of the collision, atoms are ripped apart to form entirely new elements and scattered outward across the Universe.
It could be a scenario from science fiction, but it really happened 130 million years ago -- in the NGC 4993 galaxy in the Hydra constellation, at a time here on Earth when dinosaurs still ruled and flowering plants were only just evolving.
Today, dozens of UK scientists and their international collaborators representing 70 observatories worldwide announced the detection of this event and the significant “scientific firsts” it has revealed about our Universe.
Those ripples in space finally reached Earth at 1.41pm UK time, on Thursday 17 August 2017, and were recorded by the twin detectors of the US-based Laser Interferometer Gravitational-wave Observatory (LIGO) and its European counterpart Virgo.
A few seconds later, the gamma-ray burst from the collision was recorded by two specialist space telescopes, and over following weeks, other space- and ground-based telescopes recorded the aftermath of the massive explosion. UK developed engineering and technology is at the heart of many of the instruments used for the detection and analysis.
Dr John Veitch, who is co-chair of LIGO’s Compact Binary Coalescence Search Group and Research Fellow at the University of Glasgow’s School of Physics and Astronomy and played a leading role in the GW170817 data analysis said: “One key difference between the gravitational wave signals from binary black holes and binary neutron stars is that neutron stars are many times lighter than black holes. This means that the gravitational wave signal from neutron stars linger for a much greater period in the detector – for around 100 seconds as opposed to just a fraction of a second for binary black holes. A longer signal means we can glean much more information about the source.”
Studying the data confirmed scientists’ initial conclusion that the event was the collision of a pair of neutron stars – the remnants of once gigantic stars, but collapsed down into approximately the size of a city.
UK Science Minister, Jo Johnson, said “Today’s announcement of the latest detection of gravitational waves is another important development in our understanding of the universe which has been made possible by UK research and technology.
“The recent awarding of the Nobel Prize for Physics to gravitational waves research is clear recognition of the importance of this area. The UK plays a significant role in these detections, enabling us to continue building our reputation as a world leader in science and innovation which is a core part of our Industrial Strategy.”
There are a number of “firsts” associated with this event, including the first detection of both gravitational waves and electromagnetic radiation (EM) - while existing astronomical observatories “see” EM across different frequencies (eg, optical, infra-red, gamma ray etc), gravitational waves are not EM but instead ripples in the fabric of space requiring completely different detection techniques. An analogy is that LIGO and Virgo “hear” the Universe.
The announcement also confirmed the first direct evidence that short gamma ray bursts are linked to colliding neutron stars. The shape of the gravitational waveform also provided a direct measure of the distance to the source, and it was the first confirmation and observation of the previously theoretical cataclysmic aftermaths of this kind of merger - a kilonova.
Additional research papers on the aftermath of the event have also produced new understanding of how heavy elements such as gold and platinum are created by supernova and stellar collisions and then spread through the Universe. More such original science results are still under current analysis.
By combining gravitational-wave and electromagnetic signals together, researchers also used a new technique to measure the expansion rate of the Universe. This technique was first proposed in 1986 by University of Cardiff’s Professor Bernard Schutz.
UK astronomers using the VISTA telescope in Chile were among the first to locate the new source. "We were really excited when we first got notification that a neutron star merger had been detected by LIGO,” said Professor Nial Tanvir from the University of Leicester, who leads a paper in Astrophysical Journal Letters today. “We immediately triggered observations on several telescopes in Chile to search for the explosion that we expected it to produce. In the end we stayed up all night analysing the images as they came in, and it was remarkable how well the observations matched the theoretical predictions that had been made."
Dr Kate Maguire, from Queen’s University Belfast was part of the team studying the burst of light from the smashing together of the two neutron stars “Using rapid-response triggering at some of the world’s best telescopes, we have discovered that this neutron-star merger scattered heavy chemical elements, such as gold and platinum, out into space at high speeds. These new results have significantly contributed to solving the long-debated mystery of the origin of elements heavier than iron in the periodic table."
Once the location of the collision was pin-pointed, scientists quickly maneuvered the Swift satellite to examine the aftermath with its X-ray and UV/optical telescopes.
“We didn’t detect any X-rays from the object, which was surprising given the gamma ray detection,” said Dr Phil Evans from the University of Leicester, lead-author of a paper published today in Science. “But we did find bright ultra-violet emission, which most people were not expecting. This discovery helped us to pin down what happened after the neutron star collision was detected by LIGO and Virgo.”
Professor Alberto Vecchio from the University of Birmingham’s Institute of Gravitational Wave Astronomy said: “Detecting for the first time gravitational waves from the coalescence of a binary neutron star is fantastic, and even more so that we could do it almost in real time and precisely locate this source in the sky. If fact, telescopes around the world could then point at that little patch in the sky and show us over hours, days and weeks extra-ordinary events set in motion by this cataclysmic collision as the emerging radiation swept the whole electromagnetic spectrum.”
Chief Executive Designate of UK Research and Innovation, Sir Mark Walport said: “Over a hundred years ago Einstein introduced his revolutionary General Theory of Relativity. In this, space and time were no longer absolute, no longer a fixed background to events, he proposed the existence of gravitational waves as a way to understanding the origins of the Universe.
“The latest gravitational waves announcement, today, includes the first direct evidence that short gamma ray bursts are linked to colliding neutron stars and is the result of outstanding international collaboration. This spectacular discovery is built on ambition and tenacity of international partnerships. I am proud that UK Science is at the heart of many of the instruments and detectors used for today’s historic announcement”
Dr Brian Bowsher, Chief Executive of the UK’s Science and Technology Facilities Council, said: "This new gravitational wave discovery will inspire many young people into the world of science as it reinforces the fact that there is still so much we can learn about how the Universe works. It offers new insights into the field of astronomy as well as showcasing how technological breakthroughs made by UK engineers and scientists made this latest understanding possible."
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The first detection of gravitational waves, made on September 14, 2015 and announced on February 11, 2016, was a milestone in physics and astronomy; it confirmed a major prediction of Albert Einstein’s 1915 general theory of relativity, and marked the beginning of the new field of gravitational-wave astronomy. The UK played a leading role in that detection and key technological and computing advances were made in the UK which enabled the historic first detection.
Since then, there have been three more confirmed detections, one of which (and the most recently announced) was the first confirmed detection seen jointly by both the LIGO and Virgo detectors. In addition the 2017 Nobel Prize for Physics was last week awarded to the team behind the gravitational waves breakthrough.
The published articles announcing LIGO’s first, second, and third confirmed detections have been cited more than 1,700 times (total), according to the Web of Science citation counts. A fourth paper on the three-detector observation was published on October 6; a manuscript was made publicly available on September 27.
Gravitational waves are ripples in space caused by massive cosmic events such as the collision of black holes or the explosion of supernovae. They are not electromagnetic radiation, and as a result have been undetectable until the technological breakthroughs at LIGO enabled by UK technology. The waves carry unique information about the origins of our Universe and studying them is expected to provide important insights into the evolution of stars, supernovae, gamma-ray bursts, neutron stars and black holes. However, they interact very weakly with particles and require incredibly sensitive equipment to detect.
More information on Gravitational Waves:
STFC - Gravitational waves: everything you need to know
More about the UK’s involvement in gravitational wave research:
STFC - Working together to ride the gravitational waves
The University of Glasgow’s Institute for Gravitational Research (IGR)
Supported by STFC funding, is focused on the development of detector hardware and software for sensing gravitational waves from astrophysical sources. The work of the IGR includes materials characterisation, advanced interferometry, precision manufacture and novel data processing. They also carry out research related to Advanced LIGO, GEO600, LISA Pathfinder and other gravitational wave detectors.
The Institute of Gravitational Wave Astronomy at Birmingham
The Institute of Gravitational Wave Astronomy at Birmingham brings together expertise from a wide spectrum of disciplines to open a new window on the Universe. As part of the UK Advanced LIGO project they have built sensors and control electronics for the suspension systems. They currently are working on a wide range of aspects - quantum measurements, interferometry and optics, sensors and metrology - for upgrades of Advanced LIGO and future generation instruments. They also have a very large involvement in data analysis and observations, for example, they have co-led on the inception, development and implementation of the methods and software used to compute many of the numbers around the masses, spins, distances, location in the sky, rates of binary black hole (and now neutron star) mergers as well as the actual analysis and science interpretation.
Gravitational Physics Group at Cardiff University
For the past decade, the Gravitational Physics Group at Cardiff University have laid the foundations for how we go about detecting gravitational waves and have developed novel algorithms and software that have now become standard search tools for detecting the elusive signals.
The Group also includes world-leading experts in the collision of black holes, who have produced large-scale computer simulations to imitate these violent cosmic events and predict how gravitational waves are emitted as a consequence. These calculations were instrumental in decoding all four of the observed gravitational-wave signals to date and to measure the properties of the black holes that were detected.