Scientists have detected for the first time the faint ripples in space and time caused by the motion of supermassive black holes in distant galaxies. The discovery, announced by a global collaboration of radio astronomers, opens a new window to study the universe and its history.
Gravitational waves are distortions in the fabric of the universe that are created by huge objects moving around and colliding in space. They were predicted by Albert Einstein’s theory of general relativity， but were not directly observed until 2015, when scientists used an experiment called LIGO to detect the high-frequency “chirps” of merging black holes and neutron stars.
But the gravitational waves detected by LIGO are very different from the ones reported by the new research. These are ultra-low-frequency waves that take years or even decades to oscillate, and are expected to come from pairs of gigantic black holes, billions of times the mass of our sun, that orbit each other at the centers of most galaxies.
To find these elusive waves, the scientists used pulsars, which are dead stars that emit flashes of radio waves as they spin around in space like lighthouses. By measuring the precise timing of these flashes, the scientists can detect tiny changes in space-time caused by the passing gravitational waves.
“We had to build a detector that was roughly the size of the galaxy,” said NANOGrav researcher Michael Lam of the SETI Institute.
The results released this week included 15 years of data from NANOGrav, which has been using telescopes across North America to search for the waves. Other teams of gravitational wave hunters around the world also published similar findings, including in Europe, India, China and Australia. The consistency among the groups lends weight to their conclusions.
The detection is consistent with predictions from theoretical models of supermassive black hole binaries, but other exotic sources of gravitational waves cannot be ruled out yet. The scientists hope to confirm the origin of the waves with more data and analysis in the future.
“This is a huge step forward in observational cosmology. It’s like turning on a new sense. We had no idea what we were going to find out there,” said Chiara Mingarelli, an astrophysicist at Yale University and a member of NANOGrav.
The detection of low-frequency gravitational waves also opens up new possibilities to study the universe and its history, as well as to test Einstein’s theory of general relativity in extreme conditions.
“Supermassive black hole binaries, slowly and calmly orbiting each other, are the tenors and bass of the cosmic opera,” said Szabolcs Marka, an astrophysicist at Columbia University who was not involved with the research.
Relevant articles:
– Scientists have finally ‘heard’ the chorus of gravitational waves that ripple through the universe, CP24, June 29, 2023
– At Last, There’s Evidence of Low-Frequency Gravitational Waves, WIRED, June 28, 2023
– Astrophysicists report solid evidence for a background hum of gravitational waves, MSN, June 29, 2023
– Ultra-low frequency gravitational waves that could reveal universe’s secrets seen for first time, Sky News, June 29, 2023