The first detection of gravitational waves was announced today by the LIGO/Virgo collaboration. Astronomers at the University of Leicester were among the first to respond to the detection, searching for the counterpart with X-ray and infra-red telescopes.

Gravitational waves were predicted by Einstein nearly a century ago. His theory of General Relativity says that the acceleration of massive bodies should produce gravitational waves, wobbles in the fabric of space and time which travel through the universe at the speed of light. These waves are so small that only the violent acceleration of massive bodies gives signals we can hope to detect.

“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,” explained Dr Phil Evans, of the University of Leicester Department of Physics and Astronomy. “However, searches for even these waves require extraordinarily sensitive instrumentation, and has only just become possible due to the construction of the advanced LIGO/VIRGO gravitational wave observatory.”

Last September, the latest generation of these detectors was undergoing tests when the first clear gravitational wave signal was picked up, as has been reported by the LIGO/Virgo collaboration today (Thursday 11 February). This information was rapidly passed to astronomers, including a team at the University of Leicester, allowing them to join a world-wide hunt to identify the source of the mysterious waves.

“This is a huge challenge: the direction the waves came from is not well constrained, and very large areas of the sky have to be scanned with sensitive telescopes, searching for the faint light that would be given off if the merging objects included at least one neutron star,” commented Prof Paul O’Brien, head of the Physics and Astronomy Department at the University. “Identifying the source of the gravitational waves is vital for understanding their origins and determining exactly where they occur.”

The University of Leicester team first used the Swift satellite to scan the region looking for X-rays from the explosion caused by the collision. “The X-ray camera on board Swift was built in Leicester, and it is the most capable satellite in space when it comes to rapidly responding to new, unexpected phenomena,” added Professor Julian Osborne, the local Swift lead in the X-Ray and Observational Astrophysics group at the University.

They reported the detection of 3 X-ray sources just 15 hours after the receiving news of the gravitational wave event, although it turned out that these objects were not related to the Gravitational Waves. A few days later they used the world’s most powerful infrared telescope, the VISTA telescope situated in Chile, to hunt for the collision remnant since infrared light is also expected to be produced in such events. After weeks of analysis no counterpart was found in these images. This result is consistent with the latest analysis of the gravitational wave data, which confirmed that the source was actually likely to be a merger of two black holes, and therefore not expected to emit light in any form, either X-ray or in infrared.

“So, although on this occasion our hunt for light was unsuccessful, nonetheless, the first detection of gravitational waves heralds a new era of physics and astronomy, in which we will be able to study these most violent of cosmic collisions using both gravitational and electromagnetic radiation,” said Professor Nial Tanvir, also from the Department of Physics and Astronomy at the University of Leicester.

About the LIGO Scientific Collaboration:

The LIGO Scientific Collaboration is a group of more than 1000 scientists worldwide who have joined together in the search for gravitational waves.

About Swift:

The Swift satellite is designed to discover new Gamma-Ray Bursts, which may result from the same event that causes a Gravitational Wave event. It is managed by NASA Goddard Space Flight Center, the mission operations center is run by Penn State University in the US. In addition to the University of Leicester, which provides the UK Swift Science Data Centre, Swift partners include the UCL Mullard Space Science Laboratory, and the Italian Space Agency and Brera Observatory in Italy. Funding for Swift in the UK is provided by the UK Space Agency.