Giant Black Hole Mergers Don't Make a Big Splash

Giant black holes pepper our universe, tucked inside galaxies as they pair up and merge with other black holes. These massive bodies dance around each other in close embraces, sending out gravitational waves that ripple space and time themselves. Predicted by Einstein's theory of relativity, these waves have yet to be directly detected. Now, scientists have reached a milestone by discovering new information about the frequency and strength of black hole mergers.

If gravitational waves were detected, they would reveal more information about black holes as well as gravity. That's why scientists decided to hunt for these waves using pulsar-timing arrays. These arrays are designed to catch subtle gravitational waves using telescopes on the ground in addition to spinning stars called pulsars.

"We expect that many gravitational waves are passing through us all the time, and now we have a better idea of the extent of this background activity," said Sarah Burke Spolaor, one of the researchers, in a news release.

When gravitational waves pass through an array of multiple pulsars, they set the pulsars bobbing like buoys. Researchers recording the radio waves from the pulsars can then piece together the background hum of the waves. In this case, though, the scientists weren't able to detect any gravitational waves. Yet this has its own benefits.

The fact that researchers weren't able to detect the waves reveals new information about supermassive black hole mergers. More specifically, it shows their frequency, distance from Earth and masses. It also disproved on theory of black hole growth which stated that mergers alone are responsible for black holes gaining mass.

"Right now, the focus in the pulsar-timing array communities is to develop more sensitive technologies and to establish long-term monitoring programs of a large ensemble of the pulsars," said Walid Majid, one of the researchers, in a news release. "All the strategies for detecting gravitational waves, including LIGO [Laser Interferometer Gravitational-Wave Observatory], are complementary, since each technique is sensitive to detection of gravitation waves at very different frequencies. While some might characterize this as a race, in the end, the goal is to detect gravitational waves, which will usher in the beginning of gravitational wave astronomy. That is the real exciting part of this whole endeavor."

The findings reveal a little bit more about black holes. More specifically, they show future potential for this technology, which may show a bit more about our universe.

The findings are published in the journal Science.