Ateam of astrophysicists, including a UCF researcher, have discovered the first compelling evidence for low-frequency gravitational waves permeating the universe.

The breakthrough was made by a collaboration of researchers, known as the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), who used large radio telescopes, like the Arecibo Observatory in Puerto Rico, to observe the timing of millisecond-period pulsars (MSPs).

The MSPs, which are rapidly spinning dead stars that sweep beams of radio waves, appear to pulse when seen from Earth and allowed the researchers to detect gravitational wave background based on subtle changes in the arrival time of their signals.

The results were published today in a series of five papers in the Astrophysical Journal Letters.

First predicted in Albert Einstein’s theory of general relativity, gravitational waves are “ripples” through spacetime, and carry energy and information about their sources.

The researchers refer to the gravitational wave background as a “hum” that fills the universe with gravity signals spanning periods of years to decades. Studying these signals can provide a better understanding of the early universe and of the sources of the gravitational waves, such as the movement of massive black holes merging in the center of distant galaxies.

Study co-author Bentege Perera, a NANOGrav researcher and UCF scientist with Arecibo Observatory who is involved in timing these MSPs and characterizing their noise properties, says the overlap of all the gravitational wave signals produced by supermassive black hole binaries is one of the possible sources of forming this “hum” that’s in the low, nanohertz frequency.

While earlier results from NANOGrav uncovered a puzzling timing signal common to all the pulsars they observed, it was too faint to reveal its origin. This 15-year data release, which includes high-precision timing of 68 MSPs monitored by the world’s largest telescopes, demonstrated that the signal is consistent with slowly undulating gravitational waves passing through our galaxy.

Aerial view of the Arecibo Telescope before its collapse in December 2020.
Aerial view of the Arecibo Telescope before its collapse in December 2020. Credit: Arecibo Observatory, a facility of the NSF

Before it collapsed in 2020, the Arecibo Observatory in Puerto Rico found nineteen of the MSPs that NANOGrav currently monitors.

While Arecibo was limited to seeing only about 30% of the total sky, its unparalleled sensitivity meant that for those pulsars in its vision, nothing could measure them better, the researchers say.

They say the telescope’s legacy lives on in NANOGrav’s data, as approximately one-half of gravitational wave sensitivity comes from Arecibo observations. The observatory is transitioning to a hub for STEM education, outreach and research.

Support from the U.S. National Science Foundation (NSF) has been critical to NANOGrav’s success by providing support for scientific work through the Physics Frontiers Center program and through access to multiple world-class radio telescopes. Future NANOGrav results will incorporate data from Canada’s CHIME telescope, added to the project in 2019.

“The NSF NANOGrav team created, in essence, a galaxy-wide detector revealing the gravitational waves that permeate our universe,” NSF Director Sethuraman Panchanathan says. “The collaboration involving research institutions across the U.S. shows that world-class scientific innovation can, should and does reach every part of our nation.”

Astrophysicists around the globe have been busy chasing this gravitational wave signal. Several papers released today by the Parkes Pulsar Timing Array in Australia, the Chinese Pulsar Timing Array, and the European Pulsar Timing Array/Indian Pulsar Timing Array report hints of the same signal in their data. Through the International Pulsar Timing Array consortium, regional collaborations are working together to combine their data in order to better characterize the signal and search for new types of sources.

“Our combined data will be much more powerful,” says Stephen Taylor, with Vanderbilt University who co-led the search and is the current chair of the collaboration. “We’re excited to discover what secrets they will reveal about our universe.”

The NANOGrav collaboration receives support from NSF Physics Frontiers Center award numbers 1430284 and 2020265, the Gordon and Betty Moore Foundation, NSF AccelNet award number 2114721, a Natural Sciences and Engineering Research Council of Canada Discovery Grant, and the Canadian Institute for Advanced Research . The Arecibo Observatory is a facility of NSF operated under cooperative agreement (#AST-1744119) by UCF in alliance with Universidad Ana G. Méndez and Yang Enterprises Inc. The Green Bank Observatory and The National Radio Astronomy Observatory are facilities of the NSF operated under cooperative agreements by Associated Universities Inc.