When black holes collide, gravitational waves form 10 million years later

Albert Einstein predicted the existence of gravitational waves in his general theory of relativity more than a century ago. This year, a historic announcement was made by the Laser Interferometer Gravitational-Wave Observatory (LIGO) stating they had detected them for the first time.

LIGO recorded the gravitational waves – or ripples in the curvature of space-time – that were caused by the merging of two massive black holes.

Until now, however, it has not been possible to conclusively predict at which point gravitational waves are triggered and spread throughout space when two galaxies collide and merge.

Now, an international team of researchers from the University of Zurich, the University of Heidelberg, the Chinese Academy of Sciences and the Institute of Space Technology Islamabad has calculated this for the first time.

In the core of every galaxy it is thought there lies a supermassive black hole, which could contain billions of solar masses. Using a sophisticated computer simulation of the universe, the researchers merged two roughly three-billion-year-old galaxies lying relatively close to each other. They calculated the time taken for the two central black holes, with around 100 million solar masses each, to emit strong gravitational waves after the collision.

"The result is surprising," said Lucio Mayer from the Institute for Computational Science of the University of Zurich. "The merging of the two black holes already triggered the first gravitational waves after 10 million years – around 100 times faster than previously assumed."

The supercomputer simulation took more than a year to complete due to the huge processing power required and the innovative computational approach taken by the team.

"Our calculations therefore allow a robust forecast for the merging rate of supermassive black holes in the early stage of the universe," said Mayer. "They may help assess the gravitational waves [that] eLISA [Evolved Laser Interferometer Space Antenna] is bound to find in the near future more effectively."