San Francisco: In what is being hailed as a "groundbreaking discovery", astronomers have for the first time observed two supermassive black holes orbiting around each other in a distant galaxy.
In an article published in the Astrophysical Journal, researchers have detailed how they used radio telescopes to detect what appeared to be two black holes moving in relation to each other in a radio galaxy.
Potentially, it is the smallest-ever recorded movement of an object across the sky, also known as angular motion, Xinhua news agency reported.
"If you imagine a snail on the recently-discovered Earth-like planet orbiting Proxima Centauri, a bit over four light years away, moving at one centimetre a second, that's the angular motion we're resolving here," Roger W. Romani, Professor of physics at Stanford University and co-author of the paper, said.
Researchers led by Greg Taylor, Professor of physics and astronomy at the University of New Mexico, have taken snapshots of radio galaxy 0402+379, the one containing the two black holes over the past 12 years.
Officially discovered in 1995, the galaxy was confirmed in 2006 to have a supermassive black-hole binary system with an unusual configuration.
"For a long time, we have been looking into space to try and find a pair of these supermassive black holes orbiting as a result of two galaxies merging," Taylor said.
"Even though we have theorized that this should be happening, nobody had ever seen it, until now."
With a combined mass 15 billion times that of the sun, these black holes are among the largest ever found.
"The black holes are at a separation of about seven parsecs, which is the closest together that two supermassive black holes have ever been seen before," Karishma Bansal, a graduate student in Taylor's lab and lead author of the paper, was quoted as explaining in a news release.
In the paper, the team reported that one of the black holes moved at a rate of just over one micro-arc second per year, an angle about one billion times smaller than the smallest thing visible with the naked eye.
Based on this movement, the researchers hypothesize that one black hole may be orbiting around the other over a period of 30,000 years.
Although it is not the only supermassive black-hole binary ever found, the researchers believe that 0402+379 likely has a special history.
Given how slowly the pair is orbiting, the researchers think the black holes are too far apart to come together within the estimated remaining age of the universe, unless there is an added source of friction.