A team of international scientists have found the first evidence of a cosmic gravitational wave background across the universe. They think it could be produced by hundreds of thousands of pairs of supermassive black holes orbiting each other for a couple of million years before they merge.
The stunning new discovery of these rumbles or ripples in spacetime in the background of the universe were made by detecting their distorting effect on light coming from pulsars, rapidly spinning dead stars that pulse every millisecond.
Galaxy-Sized Detector
By using 25 pulsars across the Milky Way, the astronomers were able to construct a galaxy-sized gravitational-wave detector. The 15 year study found gravitational waves that are very low frequency, with wavelengths of a few light years.
“This is key evidence for gravitational waves at very low frequencies,” said Stephen Taylor at Vanderbilt University, who co-led the search and is the current chair of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration, one of the groups involved in a paper on the detection published yesterday in The Astrophysical Journal Letters. “After years of work, NANOGrav is opening an entirely new window on the gravitational-wave universe,” he added.
Ripples in Spacetime
What the scientists found was evidence that the precise rhythms of the light coming from the pulsars are affected by the periodic stretching and squeezing of spacetime by these long-wavelength gravitational waves in the background.
This is not the first time that gravitational waves have been detected. That honor went to the Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015, which found short-wavelength fluctuations in spacetime caused by the merger of smaller black holes and some neutron stars.
This detection is of long-wavelength gravitational waves propagating in space is on a vastly different scale and was made using six of the largest radio telescopes in Europe and India:
- 100-m radio telescope in Effelsberg (Germany)
- Westerbork Synthesis Radio Telescope (Netherlands)
- Lovell Telescope at Jodrell Bank Observatory (United Kingdom)
- Sardinia Radio Telescope (Italy)
- Nançay Radio Telescope (France)
- Giant Metrewave Radio Telescope (India)
Other explanations for what causes this gravitational wave background include cosmic inflation or cosmic strings. “We think binaries are much more likely,” said Luke Zoltan Kelley, assistant adjunct professor of astronomy at the University of California, Berkeley. “To really be able to definitively say that this is coming from binaries, however, what we have to do is measure how much the gravitational wave signal varies across the sky.”
Wishing you clear skies and wide eyes.