WSU physicists contribute to major cosmic discovery
The recent detection of gravitational waves may represent the most globally significant physics discovery this century, and WSU researchers had an important role in the long-anticipated breakthrough.
More than a billion years ago in a faraway galaxy, two black holes spiraled together, and, in a split second, the massive celestial bodies merged. The terrifically energetic collision created gravitational waves—ripples in the fabric of space-time—that careened outward through the universe.
These waves passed through Earth on Sept. 14, 2015, and on Feb. 11, 2016, WSU physicists who were instrumental in helping detect them officially shared the discovery with the University community.
Sukanta Bose, professor of physics, Nairwita Mazumder, physics postdoctoral researcher, and Bernard Hall, physics graduate student, are members of the National Science Foundation-led team that detected the gravitational waves. Matt Duez, assistant professor of physics, and a number of former WSU graduate students also made important contributions to the discovery team’s research.
The first detection of gravitational waves at the Laser Interferometer Gravitational Wave Observatory (LIGO) in Hanford, Wash., and its twin facility in Livingston, La., marked the end of a forty-year quest, confirmed a major prediction of Albert Einstein’s 1915 general theory of relativity, and opened an unprecedented new window onto the cosmos.
“This is the most exciting thing in physics since Higgs-Boson—in my opinion, even more exciting. It has opened a whole new era in gravitational physics, and WSU was an important player on the ground floor of it.”
—Matt McCluskey, professor and chair, Department of Physics and Astronomy
Detecting gravitational waves
For almost two decades, Bose has played an integral role in the hunt for gravitational waves. His early work helped lay the foundation for using multiple detectors, located thousands of miles apart, to detect and corroborate fleeting gravitational wave signals amid a barrage of noisy data.
“This is loosely analogous to the challenge of picking out a single, very feeble beep of your cell phone in an extremely loud saw mill,” Bose said. “If multiple phones emit the same beep tone almost simultaneously, it becomes somewhat easier to discern their beeps against the mill noise. The same is true for gravitational wave signals arriving coincidentally in the two LIGO detectors.”
Bose and WSU collaborators contributed in several other key areas, as well.
Duez and his research team helped LIGO scientists determine how a gravitational wave would sound. They developed computer simulations of gravitational waves and the cataclysmic events that produce them.
Although they don’t make any actual noise, gravitational waves vibrate the mirrors in the two LIGO facilities’ 4-km-long interferometers at precise frequencies that can be heard by the human ear. Computer models created by theoretical physicists like Duez predicted the gravitational waves thrown outward from the collision of two black holes would, upon reaching Earth, vibrate LIGO’s interferometers at a frequency equivalent to the note of middle C.
Computer simulations also predicted that the merging of black holes would unleash more energy in a fraction of a second than the combined power of all the stars in the universe.
Listening for deep space noise
Scientists at WSU also contributed to the work of canceling out the other myriad noises picked up by the LIGO detectors that weren’t gravitational waves. LIGO’s detectors are designed to register the slightest of vibrations—1/10,000th the diameter of a proton—caused by signals from space. But the devices also detect other disturbances triggered by such earthly events as trucks on a highway, earthquakes, explosions, lightning strikes, and even waves crashing on the shore hundreds of miles away.
Bose, Mazumder, and Hall worked with other LIGO scientists to identify the frequencies of these disturbances. Akin to a giant set of noise-canceling headphones, their work helped researchers home in on deep space signals while blocking out everything else.
“The gravitational wave signal we recorded lasted for one-fifth of a second,” Bose said. “LIGO detects thousands of other signals every day and we had to know what each of these noise transients sounded like and what emitted them.”
Boosting location capabilities
Finding the exact location of the source of gravitational waves deep in space is challenging work. LIGO scientists were able to identify the wide patch of sky where the black hole merger took place but were unable to pinpoint its exact location.
Bose is helping to develop a third LIGO detector in India that will provide the triangulation necessary to more precisely locate gravitational wave-producing objects in space. The new facility is expected to be operational by the end of 2023.
While the existence of gravitational waves has huge implications for the world of physics, many non-scientists may wonder about the everyday benefits of their discovery.
Similar to computers, microwave ovens, and other technological spinoffs from the space race, LIGO technologies could find their way into the mainstream in the not-too-distant future. For example, the technology behind the ultra-stable laser used in LIGO’s interferometer could one day have applications in non-invasive surgery, Bose said.
“A hundred years ago, Einstein’s general theory of relativity didn’t seem to have any day-to-day applications,” he said. “But now, general relativity is an indispensable component of GPS. Humans have a way of capitalizing on new physics discoveries.”