A new model is bringing scientists a step closer to understanding the kinds of light signals produced when two supermassive black holes, which are millions to billions of times the mass of the sun, spiral toward a collision.

For the first time, a new computer simulation that fully incorporates the physical effects of Einstein’s general theory of relativity shows that gas in such systems will glow predominantly in ultraviolet and X-ray light.

Just about every galaxy the size of our own Milky Way or larger contains a monster black hole at its centre. Observations show galaxy mergers occur frequently in the universe, but so far no one has seen a merger of these giant black holes.

The new simulation shows three orbits of a pair of supermassive black holes only 40 orbits from merging.

The models reveal the light emitted at this stage of the process may be dominated by UV light with some high-energy X-rays, similar to what is seen in any galaxy with a well-fed supermassive black hole.

The simulation was run on the National Center for Supercomputing Applications’ Blue Waters supercomputer at the University of Illinois at Urbana-Champaign. Modelling three orbits of the system took 46 days on 9,600 computing cores.