image: ©Pitris | iStock
Yale and NANOGrav researchers have developed a system to locate individual pairs of merging supermassive black holes. By using pulsars as sensors and targeting bright quasars, the team identified two major candidates—nicknamed Rohan and Gondor—marking the start of a new era in cosmic mapping via gravitational waves
An international team of astrophysicists, including researchers from Yale, has successfully tested a new detection system designed to map the locations of supermassive black hole binaries across the universe.
Published in The Astrophysical Journal Letters, the study by the NANOGrav collaboration introduces a protocol that uses gravitational waves to locate these merging titans, creating a landmark “road map” for modern astronomy.
From background noise to individual beacons
In 2023, NANOGrav confirmed the existence of a “gravitational wave background”—a low-frequency hum caused by countless black hole mergers throughout space. The new research shifts the focus from this general background noise to identifying individual, continuous gravitational wave sources.
The team utilised pulsars—the rapidly rotating, collapsed cores of exploded stars—as a galactic-scale GPS. By monitoring the precisely timed radio signals from these pulsars, scientists can detect the subtle stretching and squeezing of spacetime caused by a specific pair of merging black holes.
The “quasar connection”
A critical breakthrough in the search came from the realisation that black hole mergers are five times more likely to occur in galaxies containing a quasar. Quasars are incredibly bright beacons fueled by gas falling into a black hole, making them the perfect targets for a “targeted search framework.”
A selection of galaxies shown to the same scale.
By focusing on 114 active galactic nuclei—areas where black holes are actively consuming matter—the researchers were able to narrow their search. This led to the identification of two prime candidates for merging binaries:
SDSS J1536+0411 (aka “Rohan”):
Named after the Yale student who first analysed the data.
SDSS J0729+4008 (aka “Gondor”):
Named in reference to The Lord of the Rings, signalling that the “beacons are lit” for future follow-up studies.
A new era of physics
Just as X-rays and radio waves transformed our view of the universe in the 20th century, gravitational wave mapping provides a vital new lens for physics. The study establishes the first concrete benchmarks for detecting individual sources, allowing scientists to anchor their maps of the cosmos to specific, high-mass events.
Yale professor Chiara Mingarelli notes that this framework will enable breakthroughs in everything from galaxy merger theory to black hole astrophysics. With these benchmarks in place, NANOGrav plans to continue populating this cosmic map, identifying more binaries that will help us understand how galaxies and their central black holes grow over billions of years.