New map of the universe uses gravitational waves to reveal hidden black holes and cosmic structure

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

The study has 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.

The three studies offer new insights into the universe's largest 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.”

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.

Lead author for one of the studies and a researcher at OzGrav and Monash University, Rowina Nathan, says the map provides an unprecedented glimpse into the structure of our Universe.

“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," she said. "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."

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Using the MeerKAT radio telescope in South Africa, one of the world’s most sensitive and cutting-edge instruments, the researchers constructed the MeerKAT Pulsar Timing Array, using it to observe pulsars and time 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 variations that challenge previous assumptions.

Nathan says it’s often assumed that the gravitational wave background will be evenly distributed across the sky.

“However, the galactic-sized gravitational wave detector 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.”

These measurements open up exciting new questions about the formation of massive black holes and the early history of the universe. Continued observations with the MeerKAT array will refine these gravitational wave maps and may uncover new, previously hidden cosmic phenomena. The research also holds broad implications, offering data that could help scientists better understand the origins and evolution of supermassive black holes, the formation of galaxy structures, and potentially even the earliest events in the universe’s history.

Kathrin Grunthal, a researcher at the Max Planck Institute for Radio Astronomy and co-author of one of the studies, says in the future, they aim to understand the origin of the gravitational wave signal emerging from the data sets.

“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.”