Gravitational waves form 10 million light years after black holes merge

Gravitational waves are formed around 10 million years after two galaxies collide and their central black holes merge — about 100 times faster than previously thought, a new study has found.

Gravitational waves were detected for the first time earlier this year, over a century after Albert Einstein predicted the phenomenon in his General Theory of Relativity.

Until now, it was not possible to conclusively predict the point at which gravitational waves are triggered and spread throughout space when galaxies merge.

An international team of astrophysicists from the University of Zurich, the Institute of Space Technology in Pakistan, the University of Heidelberg in Germany and the Chinese Academy of Sciences has now calculated this for the first time using an extensive simulation.

Every galaxy has a supermassive black hole at its core, which can exhibit millions or even billions of solar masses.

In a realistic simulation of the universe, the merging of two roughly 3-billion-year-old galaxies lying relatively close to one another was simulated.

With the aid of supercomputers, researchers calculated the time the two central black holes with around 100 million solar masses needed to emit strong gravitational waves after the galaxies collided.

"The merging of the two black holes already triggered the first gravitational waves after 10 million years — around 100 times faster than previously assumed," said Lucio Mayer from the University of Zurich.

The computer simulation, which took more than a year, was conducted in China, Zurich and Heidelberg. The project required an innovative computational approach with various numerical codes on different supercomputers.

In the process, each supercomputer was responsible for calculating a certain phase of the orbital convergence of the two massive black holes and their parent galaxies.

Compared to previous models, the relation between the orbits of the central black holes and the realistic structure of the parent galaxies was factored into the present simulation.

"Our calculations therefore allow a robust forecast for the merging rate of supermassive black holes in the early stage of the universe," said Mayer.