Groundbreaking discovery in astrophysics is making waves with ASU professors

Aug 30, 2023

After one of astrophysics' biggest developments in recent years, the universe can possibly be viewed through an entirely new paradigm, paving the way for massive future discoveries.

On June 29, a series of papers were published in The Astrophysical Journal Letters by the North American Nanohertz Observatory for Gravitational Waves that claimed evidence for the existence of a gravitational wave background.

The NANOGrav team, composed of scientists from the United States to India, came to this conclusion by analyzing 15 years of data compiled from stars known as pulsars, which are unique for their rhythmic electromagnetic emissions. Disruptions in the light from these celestial bodies led to the discovery of gravitational waves.

"A pulsar is a neutron star … a very dense star, but with a strong magnetic field … as a result, it's spinning. These spinning, magnetized stars emit beams of light. And every time that beam comes towards us, we see a pulse," Maulik Parikh, a professor at the Department of Physics, said.

"We've observed many of these. And so we have a bunch of essentially lighthouses in space. And now imagine then, that along comes a gravitational wave … if it stretches the space, then that pulsar that would normally have been a certain distance away would now be slightly further away … the amount of time it would take for that light to get to us would be delayed."

Scientists came to this conclusion after combing through data collected by radio telescopes such as the Very Large Array, the Green Bank Telescope and the Arecibo Telescope, with collections ranging from July 2004 to August 2020 on 67 different pulsars.

With 15 years worth of data, scientists came to the conclusion that there was evidence of background gravitational waves.

"Gravitational waves are a completely different way of looking at the universe. Everything we’ve ever seen from objects has always been something in the realm of either light or a particle," said Daniel Jacobs, an assistant professor at the School of Earth and Space Exploration. "Lots of objects can cause self-propagating gravitational distortions, and there’s things that we’ve never been able to look at directly before. We can see the evidence of it, but gravitational waves are a totally new phenomena."

While the existence of gravitational waves was conclusively proven in 2015 when LIGO Lab announced its detection of the effect, the NANOGrav's report is under more scrutiny.

"(NANOGrav's findings) show more potential than actual results. They don't have a clean detection of a nonzero background yet ... I think they quote four sigma, four standard deviations. A discovery usually requires by convention a five sigma data detection," said Nobel Laureate and distinguished professor of the Department of Physics, Frank Wilczek.

"So their signal-to-noise is not large enough to really claim detection of anything. But that's just the statistical error, and other scientists will ... pore over this dataset to see if they've done a good, credible job of estimating the systematic errors."

Despite this, there are great opportunities for researchers at ASU to utilize this data.

"There's a possibility there's something called ... multi-messenger astronomy now, where when a gravitational wave source is discovered, astronomers using all parts of the spectrum can point in that direction and try to see if the same object is visible in other kinds of radiation," Wilczek said.

Beyond ASU, another upcoming paper written by the International Pulsar Timing Array will build on these new findings by combining results taken from the Chinese Pulsar Timing Array, the Indian Pulsar Timing Array, the European Pulsar Timing Array, and the Parkes Pulsar Timing Array to create a more comprehensive survey spanning 24 years and covering 80 pulsars. This new paper is expected to add onto the conclusions drawn from NANOGrav’s survey data.

"It could be the beginning of a new chapter of astronomy, but … it's not even a paragraph. It's not even a word. It's kind of a fragment of a letter indicating that this chapter might begin someday soon," Wilczek said.

Edited by River Graziano, Sadie Buggle and Grace Copperthite.

Reach the reporter at [email protected].

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