Giant black holes most likely did not start out that way, so researchers are working to discover how the mysterious objects gain weight.
"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," co-author Doctor Ramesh Bhat from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) said in a statement.
"Black holes are almost impossible to observe directly, but armed with this powerful new tool we're in for some exciting times in astronomy. One model for how black holes grow has already been discounted, and now we're going to start looking at the others," he said.
Einstein was the first person to predict gravitational waves, which are "ripples in time" caused by giant objects dramatically changing their speed or direction; one example would be two supermassive black holes orbiting each other.
Sometimes two galaxies morph together, and their central black holes are forced to meet. Instead of shaking hands the two objects begin a cosmic "dance" that ends in the two black holes becoming one.
"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.
These gravitational waves repeat throughout the galaxy, causing a background of waves like "the noise from a restless crowd."
Researchers have been studying these waves using the Parkes radio telescope and types of stars called "pulsars."
The arrival of the spinning stars' time "pulse" on Earth can be measured within a tenth of a microsecond.
When the waves pass through an area of space-time they tend to "temporarily swell or shrink the distances between objects in that region, altering the arrival time of the pulses on Earth."
Parkes Pulsar Timing Array (PPTA) has looked at 20 years of time-pulse data, which is not enough to solidly detect gravitational waves, but is on the right track.
"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. So if the background is low, that puts a limit on one or more of those factors," Bhat said.
The team's studies ruled out that galactic mergers were the only factor in black hole growth, but they gained a deeper understanding of the mysterious phenomenon.
