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The universe has a cosmic ‘hum’ caused by merging black holes

In the last decade, astronomers made a major discovery, confirming the existence of gravitational waves. These long-theorized ripples in spacetime are created when extremely massive bodies such as two black holes collide, creating shocks that spread out across the universe and can be detected from millions of light-years away.

Now, a 15-year study has provided more evidence of these gravitational waves, including those at very low frequencies. A large international team in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration used three ground-based telescopes, the Arecibo Observatory in Puerto Rico, the Green Bank Telescope in West Virginia, and the Very Large Array in New Mexico, to observe pulsars. These rotating neutron stars give off regular pulses of energy, and these pulses can be affected by gravitational waves. By looking for small deviations in the pulses, the researchers were able to see how spacetime was being rippled.

This artist’s concept shows stars, black holes, and nebula laid over a grid representing the fabric of space-time.
This artist’s concept shows stars, black holes, and nebula laid over a grid representing the fabric of space-time. Ripples in this fabric are called gravitational waves. The NANOGrav collaboration detected evidence of gravitational waves created by black holes billions of times the mass of the Sun. NANOGrav collaboration; Aurore Simonet

When massive objects like black holes merge, the gravitational waves they give off can overlap and create a background “hum” that affects the pulsar timing.

“With the confirmation of gravitational waves, our next objective is to employ these observations to scrutinize the sources generating this celestial hum,” explained researcher Sarah Vigeland of the University of Wisconsin-Milwaukee in a statement. One possibility is that the signal emanates from pairs of supermassive black holes, each with masses surpassing millions or billions of times that of our Sun. As these colossal black holes orbit each other, they produce low-frequency gravitational waves.”

The gravitational waves form a kind of background hum that can be studied to learn more about both black holes and the evolution of the universe. The strength of the hum suggests that there are many, many pairs of merging black holes out there — hundreds of thousands or even millions.

“It’s incredibly exciting to have helped open a new window to the universe,” said one of the researchers, Michael Lam of the SETI Institute.

The research is published in a series of papers including one in the journal The Astrophysical Journal Letters.

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Georgina Torbet
Georgina is the Digital Trends space writer, covering human space exploration, planetary science, and cosmology. She…
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