Scientists say the recent discovery of three supermassive black holes orbiting each other in the core of a distant galaxy suggests such groupings of the cosmic behemoths may be unexpectedly common.

Most galaxies, including our Milky Way home, have been known to have giant holes, with masses equal to millions or possibly billion of stars, at their center cores.

New observations reported in Nature by an international team of scientists now suggest, however, that numerous galaxies possess not just one but two or even more supermassive black holes at their centers, spinning around each other and locked in tight gravitational dances that will likely end with them merging together into even more enormous objects.

The team of astronomers investigated a galaxy located almost 4.2 billion light years from Earth using the European VLBI Network, a collaboration of the major radio astronomy institutes in Europe, Asia and South Africa

Using the VLBI array of antennas spread around the globe as well as the 305-meter Arecibo Observatory in Puerto Rico, allowed the astronomers to study the galaxy in detail 50 times better than is possible with the Hubble Space Telescope.

One of the likely benefits of the discovery is that it may help astronomers understand how gravity behaves when stretched to extreme limits, the researchers said.

"General relativity predicts that merging black holes are sources of gravitational waves and in this work we have managed to spot three black holes packed about as tightly together as they could be before spiraling into each other and merging," study co-author Matt Jarvis of Britain's Oxford University said. "The idea that we might be able to find more of these potential sources of gravitational waves is very encouraging as knowing where such signals should originate will help us try to detect these 'ripples' in spacetime as they warp the universe."

Finding galaxies with just a pair of black holes has been difficult, astronomers say, possibly because such pairings merge fairly quickly and even before they merge are orbiting each other at such close distances they are hard to distinguish.

Studying the galaxy with the hefty name tag of SDSS J150243.09+1115573, they observed what they thought were two black holes, several thousand light years apart.

Further study, however, proved one of the objects was in fact two giant black holes, orbiting each other so closely they initially appeared to be a single object.

"Although they were predicted theoretically, these exotic black hole systems have remained elusive for decades," says Roger Deane of the University of Cape Town in South Africa, the study's lead author. "We were quite surprised to find it," he said, referring to the triple example just discovered.

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