By Not Detecting Gravitational Waves, Scientists Learn More about Black Holes

A team of scientists trying to detect gravitational waves report that by not being able to detect the waves, they have stumbled upon new information about the elusive phenomenon predicted by Albert Einstein's theory of relativity.

Thanks to Einstein, scientists know gravitational waves -- theoretical ripples in the structure of space itself generated by merging black holes -- exist. But they have never been able to directly detect one. However, they are trying. And their attempts, specifically with one tactic known as "pulsar timing arrays," have reached a new understanding about the frequency and strength of the black hole mergers that cause gravitational waves.

If a gravitational wave were to be detected, it would reveal more information about black holes and about the fundamental nature of gravity, the scientists said.

But their unsuccessful quest to detect a gravitational wave has not been a loss, instead revealing new information about the mass, frequency and distance from Earth of supermassive black hole mergers, according to the researchers, who published their work in the journal Science. The latest studies have also led to the ruling-out of a theory that the only way black holes could gain mass was through a merger with another black hole.

The team attempted to measure the gravitational wave by studying a network of pulsars, which are burnt-out cores of exploded stars. The pulsars emit beams of radio waves in a pulsating fashion, similar to a lighthouse beacon. The pulsars rotate so precisely they have been likened to atomic clocks.

"When gravitational waves pass through an array of multiple pulsars, 20 in the case of the new study, they set the pulsars bobbing like buoys. Researchers recording the radio waves from the pulsars can then piece together the background hum of waves," NASA's Jet Propulsion Laboratory explained in a statement.

Gravitational waves cause the space between Earth and the pulsars to stretch and squeeze, said Sarah Burke-Spolaor, who co-authored a new paper in Science.

It is expected that the pulsar timing arrays will be able to detect a gravitational wave within the next 10 years.

Click here to see a video explaining the pulsar timing arrays in more depth.

Meanwhile, a NASA program is using what's called the Laser Interferometer Gravitational-Wave Observatory (LIGO) in a complementary study.

"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, the principal investigator of the Deep Space Network pulsar-timing program at JPL. "All the strategies for detecting gravitational waves, including LIGO, are complementary, since each technique is sensitive to detection of gravitational 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."