WVU researchers probe spacetime ripples with nearly $6M NSF grant

Backed by $5.9 million in National Science Foundation funding, West Virginia University researchers are using stars that function like celestial clocks to search for spacetime ripples known as gravitational waves.

The sources of those ripples could be supermassive black holes. They could be "cosmic strings" - cracks in the universe that have only been theorized. They could even be reverberations from the Big Bang.

"Or there could be a huge surprise," said Maura McLaughlin, Eberly Family Distinguished Professor of Physics and Astronomy and recipient of the Shaw Prize in Astronomy. "We might see gravitational waves from something that hasn't even been predicted yet."

McLaughlin is chair of the Department of Physics in the WVU Eberly College of Arts and Sciences, which houses the WVU Center for Gravitational Waves and Cosmology. She is also a founding member of the North American Nanohertz Observatory for Gravitational Waves, or NANOGrav.

In 2023, McLaughlin and other WVU researchers associated with NANOGrav, including Sarah Burke-Spolaor, associate professor, and Emmanuel Fonseca, assistant professor, along with colleagues at other institutions, discovered the first evidence of low-frequency gravitational waves in perturbations in signals from "millisecond pulsars," or rotating neutron stars, using data from radio telescopes like the Green Bank Telescope in Pocahontas County.

The next phase of the NANOGrav research builds on that discovery and is supported by $5.9 million in funding from the NSF for the NANOGrav Physics Frontiers Center.

The research makes use of the fact that pulsars act like clocks, McLaughlin explained.

The stars rotate rapidly and precisely, meaning the times of arrival of their "ticks" on Earth can be measured with precision in the hundredths of nanoseconds. That allows astronomers to detect minuscule changes in timing. One reason those times can change is gravitational waves, which stretch and squeeze spaces between objects. As gravitational waves pass beneath Earth and a pulsar, they change the distance between the two.

"We can detect that by measuring the tick of this clock, which will arrive a little bit earlier or later than it would have otherwise," McLaughlin said.

However, she added, having detected gravitational waves, at first "all we could really say is that they exist."

Now the NANOGrav collaboration is taking the next step, looking at the spectrum of gravitational waves, or how much gravitational wave power exists at different frequencies, to find the waves' origins.

Researchers use a pulsar timing array to search for correlated deviations across a network of 70 pulsars, testing Einstein's theory of general relativity.

McLaughlin called the new phase "a really exciting time in the research, where there are multiple sources that could explain what we're seeing. But I think the most likely sources of these gravitational waves are pairs of supermassive black holes.

"We believe all galaxies have black holes at their centers," she said. "Sometimes galaxies merge with other galaxies and the black holes form supermassive binary pairs that orbit each other. If those are indeed the source of these low-frequency gravitational waves, we're going to be able to learn a lot about the process through which galaxies merge with other galaxies and how these black holes merge to form a single black hole. We don't understand these processes well because we can't observe black holes with light. They're invisible. With the pulsar timing experiment, we can observe black holes we can't see in any other way."

Black holes may not be the only source of gravitational waves, she acknowledged. There are possible sources from the realm of "exotic physics" as well.

For instance, some gravitational waves may be echoes from the first milliseconds following the Big Bang, when the cosmos cooled and fundamental fields settled into new states.

"If we can detect gravitational waves left over from the early universe, we could study physical conditions that existed fractions of a second after the Big Bang, including the energy density of the universe and the fundamental processes that shaped the particles and forces we observe today. This experiment is a unique tool, a new frontier and unexplored space for physics and astronomy," McLaughlin said.

The pulsars are monitored by several radio telescopes, including the CHIME telescope in Canada and the Very Large Array in New Mexico. The NSF award also supports development of pulsar timing infrastructure for a telescope that will be constructed in Nevada, the Deep Synoptic Array.

By far the greatest contributor to current signal sensitivity, however, is the Green Bank Telescope, which observes almost all the pulsars the group is timing.

In July, the Green Bank Observatory will host high school students and teachers and undergraduate students, providing hands-on with the research through participation in the NANOGrav STARS and Pulsar Science Collaboratory programs.

Additionally, thanks to a separate grant from the NSF PAARE program, led by WVU, McLaughlin and her NANOGrav colleagues are involving community and technical college students in their work by providing those students with funded research assistantships.

One success McLaughlin will share with students is the early detection of a "background" of gravitational waves.

"The background is from many sources combined - likely many supermassive black hole binaries. The next step, which could happen within the lifetime of this new NSF award, is the detection of an individual supermassive black hole binary," McLaughlin said.

"If we detect an actual single source, that would be really exciting. We might be able to tell what galaxy this thing is in and look at it with optical telescopes and other kinds of telescopes. When that happens, it will be a new era."

-WVU-

mm/6/11/26

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