Crashing neutron stars unlock secrets of the Universe

Cataclysmic collision. Image by NSF/LIGO/Sonoma State University/A Simonnet

A collision between two dead stars 130 million years ago has been detected by an international team of scientists, including academics at the University of Strathclyde.

The explosion resulting from the collision unleashed a huge burst of energy, sending ripples across the fabric of space. In the nuclear cauldron of the collision, atoms were ripped apart to form entirely new elements and scattered outward across the Universe.

The event occurred in in the NGC 4993 galaxy in the Hydra constellation, at a time when, on Earth, dinosaurs were still dominant and flowering plants were only just evolving.

Scientists representing 70 observatories worldwide today (Monday 16 October) announced the detection of this event and the significant scientific firsts it has revealed about the Universe.

Those ripples in space finally reached Earth at 1.41pm BST 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.

Less than two 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.

Professor Nicholas Lockerbie, formerly of Strathclyde’s Department of Physics, and now a Research Professor in the Department, has been involved for many years in the advanced LIGO project, as an Associate of the Institute for Gravitational Research at the University of Glasgow.

He said: “The field of gravitational wave astronomy has truly arrived, and multi-messenger detection using this new window on the Universe is now a reality.”

Professor Stuart Reid, of Strathclyde’s Department of Biomedical Engineering, has also played a role in the project. His laboratory is developing next-generation laser mirrors for the LIGO detectors, and works closely with colleagues at the University of Glasgow and in the US.

Key insights

He said: "For the first time, we have observed gravitational waves - along with light in the form of gamma rays - from colliding neutron stars. This not only provides key insights into fundamental physics, but will shed light on how the heaviest elements in the universe are produced.

"The window of gravitational wave astronomy continues to open wider, and observing both gravitational waves and light - gamma rays - from astrophysical events like this will provide key insights into various big questions in science."

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.

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), 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.

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.

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.”

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."