U.S. astronomers reported on Wednesday that they have spotted a pair of super massive black holes orbiting each other within the same galaxy.

This is the best evidence so far for the long-theorized existence of "binary black hole system". Astronomers from the National Optical Astronomy Observatory in Arizona detailed their results in the March 5 issue of the journal Nature.

Using observation data from Apache Point Observatory in New Mexico, the astronomers calculated that the duo is orbiting each other about five billion years away from Earth. The bigger black hole's mass is a little bit less than one billion solar masses, while its smaller partner is about 20 million times the mass of our Sun.

It has long been accepted that most large galaxies harbor black holes at their centers. When galaxies collide and merge, scientists think, their black holes may attract each other because of their gravity. However, the evidence for black holes nearing and orbiting has so far been scant.

Previous studies have shown potential evidence of black holes heading for each other, "but the case presented by this team is special because the pairing is tighter and the evidence much stronger," wrote astronomer Jon Miller of the University of Michigan in an accompanying Nature analysis.

The astronomers believe the two orbiting black holes eventually may merge into an even larger single black hole. "They should merge, and we expect them to," said study team member Tod Lauer.

Source:Xinhua