11 Years of Searching for Gravitational Waves Yields Nothing. What It Means

merging black holes
Simulation of black holes merging. Credit: Michael Koppitz / Albert Einstein Institute

In 1915, renowned theoretical physicist Albert Einstein published his theory of general relativity. More than 100 years later and his theory holds up to nearly every test thrown at it. There is one puzzle that remains to be solved. Gravitational waves. There is strong evidence these waves exist, but they have never been directly detected.

One team of scientists set out to change that. Dr. Ryan Shannon led the team that published their results in the journal Science.

Using CSIRO’s Parkes telescope, Shannon and his team spent 11 years searching for gravitational waves. And they left empty handed.

“This is probably the most comprehensive, high precision science that’s ever been undertaken in this field of astronomy,” Dr. Shannon said.

To try and detect gravitational waves, Shannon and his team observed a set of ‘millisecond pulsars.’ These small stars produce constant radio pulses. The team of scientists can record the time the pulsar signals arrive on Earth down to ten billionths of a second. As a gravitational wave passes between Earth and the pulsar, it should squeeze and stretch space. This would create a tiny change in the distance between the pulsar and Earth according to CSIRO.

But after studying these pulsars for 11 years, the scientists did not detect gravitational waves.

Let’s take a step back and talk gravitational waves. Every large galaxy is believed to have a supermassive black hole at its center. When two of these galaxies merge, so do their black holes. And when these black holes merge, Einstein’s theory predicts the collision sends ripples of gravitational waves through space-time.

Ok, now what?

Just because Shannon and his team didn’t detect gravitational waves doesn’t mean they don’t exist. There could be several reasons why gravitational waves were not detected. Scientists suspect that black holes may merge faster than they first thought and don’t spend much time generating gravitational waves.

Team member Dr. Paul Lasky offers a different possible explanation. “There could be gas surrounding the black holes that creates friction and carries away their energy, letting them come to the clinch quite quickly,” said Lasky.

It could also be that 11 years isn’t long enough. Scientists may need to record these pulsars for a lot longer.

Today’s results don’t throw this part of Einstein’s theory out the window. While not detecting gravitational waves is a surprise, there are several potential reasons for the non-detection.

Plus, other teams of scientists are using different telescopes and methods to detect gravitational waves. Co-author Dr. Vikram Ravi touches on this in a statement. “Ground-based detectors are looking for higher-frequency gravitational waves generated by other sources, such as coalescing neutron stars.”

The Parkes Observatory

Parkes telescope

I always like to take a look at the telescope behind the science.

The Parkes Observatory is located just north of Parkes, New South Wales, Australia. Its main telescope is a 64-meter (210 ft) movable dish telescope. It was one of the first large moveable dishes in the world and is the second largest in the Southern Hemisphere.

Did you know the Parkes Observatory was instrumental in one of humanity’s greatest accomplishments?

On July 20, 1969, Apollo 11 made history by landing on the moon. When televised images were beamed back to Earth, three radio antennas picked it up – the 64 meter Goldstone antenna in California, the 26 meter antenna at Honeysuckle Creek near Canberra and the 64 meter antenna at Parkes.

The Parkes signal was so good that NASA would end up using it for nearly all of the TV broadcast.

The Parkes telescope was also used as a model for the large antennas that make up NASA’s Deep Space Tracking Network (DSN). The DSN is vital for communication with orbiters throughout the solar system – from the Mars Reconnaissance Orbiter to New Horizons.

The Gist