An international study led by astronomers from Swinburne University of Technology and Monash University has created the most detailed maps of gravitational waves across the universe to date.

The study also produced the largest ever galactic-scale gravitational wave detector and found further evidence of a “background” of gravitational waves: invisible yet incredibly fast ripples in space that can help unlock some major mysteries of the universe.

This international effort, conducted with the MeerKAT radio telescope in South Africa, includes three studies published today in Monthly Notices of the Royal Astronomical Society. Together, these works offer new insights into the universe’s most massive black holes, how they shaped the Universe, and the cosmic architecture they left behind.

Lead author for two of the papers and a researcher at OzGrav and Swinburne, Dr Matt Miles, says the research opens new pathways for understanding the universe that we live in.

“Studying the background lets us tune into the echoes of cosmic events across billions of years,” Dr Miles explained. “It reveals how galaxies, and the universe itself, have evolved over time.”

The MeerKAT Pulsar Timing Array, an international experiment which uses the MeerKAT Radio Telescope in South Africa, one of world’s most sensitive and cutting-edge radio telescopes, observes pulsars and times them to nanosecond precision. Pulsars—rapidly spinning neutron stars—serve as natural clocks, and their steady pulses allow scientists to detect minuscule changes caused by passing gravitational waves. This galactic-scale detector has provided an opportunity to map gravitational waves across the sky, revealing patterns and strengths that challenge previous assumptions. Lead author for one of the studies and a researcher at OzGrav and Monash University, Rowina Nathan comments “it is often assumed that the gravitational wave background will be uniformly distributed across the sky.” Miss Nathan explains “the galactic-sized telescope formed by the MeerKAT pulsar timing array has allowed us to map the structure of this signal with unprecedented precision, which may reveal insights about its source.”

Key findings:

Unprecedented gravitational wave signal
The study uncovered further evidence of gravitational wave signals originating from merging supermassive black holes, capturing a signal stronger than similar global experiments, and in just one-third of the time.

“What we’re seeing hints at a much more dynamic and active universe than we anticipated,” Dr Miles said. “We know supermassive black holes are out there merging, but now we’re starting to ask: where are they, and how many are out there?”

Detailed gravitational wave maps with unexpected hotspots
Using the pulsar timing array, the researchers constructed a highly detailed gravitational wave map, improving upon existing methods. This map revealed an intriguing anomaly – an unexpected hotspot in the signal that suggests a possible directional bias.

“The presence of a hotspot could suggest a distinct gravitational wave source, such as a pair of black holes billions of times the mass of our Sun,” said Miss Nathan. “Looking at the layout and patterns of gravitational waves shows us how our Universe exists today and contains signals from as far back as the Big Bang. There’s more work to do to determine the significance of the hotspot we found, but this an exciting step forward for our field.”

These findings open up exciting questions about the formation of massive black holes and the Universe’s early history. Further monitoring with the MeerKAT array will refine these gravitational wave maps, potentially uncovering new cosmic phenomena. The research also has broad implications, offering data that may aid international scientists in exploring the origins and evolution of supermassive black holes, the formation of galaxy structures, and even hints of early universe events.

With continued work using the MeerKAT array and plans to better understand the pulsar network and gravitational wave signal, researchers aim to refine the map of the gravitational wave background and verify the underlying cosmic structure. “In the future, we aim to understand the origin of the gravitational wave signal emerging from our data sets. By looking for variations in the gravitational waves across the sky, we’re hunting for the fingerprints of the underlying astrophysical processes”, adds Kathrin Grunthal, a researcher from the Max Planck Institute for Radio Astronomy and a co-author of one of the studies.

“By looking for variations in the gravitational wave signal across the sky, we’re hunting for the fingerprints of the astrophysical processes shaping our universe.”

Dr Matthew Miles and researcher Rowina Nathan are available for interviews. For enquiries, please contact ozgrav.comms@swin.edu.au