Every large galaxy is thought to have a supermassive black hole at its center but the phenomena have proved difficult to study by direct observation, they said.
"This is the first time we've been able to use information about gravitational waves to study another aspect of the universe -- the growth of massive black holes," study co-author Ramesh Bhat of the International Center for Radio Astronomy Research reported.
Einstein had predicted gravitational waves, ripples in space-time generated by massive bodies changing speed or direction, like pairs of black holes orbiting each other.
Such events occur when galaxies merge and their central black holes are attracted to each other, astronomers said.
"When the black holes get close to meeting they emit gravitational waves at just the frequency that we should be able to detect," Bhat said.
Astronomers have been searching for gravitational waves with a giant radio telescope in Australia, learning more about the behavior of supermassive black holes.
"The strength of the gravitational wave background depends on how often supermassive black holes spiral together and merge, how massive they are, and how far away they are," Bhat said.
"Black holes are almost impossible to observe directly but armed with this powerful new tool we're in for some exciting times in astronomy," he said.
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