Massive blackholes are emitting gravitational waves across the universe

29 Jun 2023

A view from the five-hundred-meter Aperture Spherical Telescope in Guizhou, China, which monitored pulsars to detect gravitational waves. Image: NAOC of CAS

The latest discovery making waves in the world of astronomy is the result of research conducted by astrophysicists over two decades, including at Trinity.

Scientists believe they now have strong evidence to suggest that the universe is permeated by a low hum of gravitational waves caused by the slow merger of supermassive blackholes.

After two decades of data collection, an international consortium of scientists led by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has published its findings in The Astrophysical Journal Letters today (29 June).

Trinity College Dublin is one of more than 10 institutions that are part of the European Pulsar Timing Array, which collaborated with Indian and Japanese astronomers from the Indian Pulsar Timing Array to make crucial contributions to the latest findings.

Together, they have been searching for ultra-low gravitational wave signals using six of the world’s most powerful radio telescopes. The telescopes monitor radio signals from rotating neutron stars, called pulsars, which can help scientists unravel mysteries of the early universe.

Prof Evan Keane, an associate professor of radio astronomy at Trinity’s School of Physics and head of the Irish LOFAR Telescope, described the results as “the start of something big.”

“Pulsars are basically super clocks in space. By monitoring the ‘ticks’ from these clocks, which are spread throughout our galaxy, we can see the impact of passing gravitational waves in making the pulsar signals arrive earlier or later,” he explained.

An infographic with an illustration of the gravitational waves around the Earth.

Infographic about the gravitational waves. Image: Danielle Futselaar/MPIfR

By harnessing the combined power of 25 of these pulsars, the team have been able to form a galactic sized gravitational-wave detector which measures the exact arrival time of the radio signals from pulsars.

As the signals travel through space and time, the presence of gravitational waves affects their path, creating characteristic irregularities.

Earth is ‘jiggling’ due to gravitational waves

So far, however, the results from the long study have been consistent with Albert Einstein’s theory of general relativity published more than a 100 years ago, which describes how massive objects warp space-time to create what we call gravity.

Prof Alberto Vecchio from the University of Birmingham’s Institute for Gravitational Wave Astronomy said the results presented today “mark the beginning of a radically new journey into the universe to unveil some of its mysteries”.

“Our analysis reveals a common signal which has been persistent throughout the many years of monitoring these pulsars, as if these cosmic clocks are pitching and rolling in the waves of space-time,” he explained.

“Although we are not able yet to confirm definitively the presence of ultra-low frequency gravitational waves, the presence of this common signal across all the pulsars in the array is consistent with what astrophysicists expect.”

Scott Ransom, an astrophysicist at the US National Radio Astronomy Observatory and a senior member of NANOGrav, said that the study shows the Earth is “jiggling” due to gravitational waves that are “sweeping” our galaxy.

“We’re not using the ‘d’ word – for detection – yet. But we do think this is strong evidence,” he said.

Keane added that as astronomers collect more data and more telescopes join in to refine analysis techniques, we can expect “an ever more precise view” of what the universe looks like in gravitational waves. “I can’t wait to add more layers to the painting.”

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Vish Gain is a journalist with Silicon Republic