Hundreds of physicists and students sat still in a University of Chicago auditorium Thursday, their eyes wide and necks craned forward, anxious to hear the recorded sound of two black holes colliding 1.3 billion light-years away.
For several seconds, they heard only a muffled rumble. And then, it happened — a fleeting thump. The barely audible noise sparked a ripple of gasps across the room.
“You might not be that excited if you’re not in the field,” said Daniel Holz, an associate professor of physics at U. of C. “But if you’re in the field and you’ve spent years thinking about this, dreaming about this? When that happens, it’s mind-blowing.”
He pointed at a couple of graphs that charted the noise’s frequency with parabolic waves.
“For those of us that do this, that’s the most beautiful thing you’ve ever seen,” he said.
Several local scientists at Chicago institutions, including U. of C., Northwestern University and the Adler Planetarium, are among the team of nearly 1,000 scientists across the world to discover the first, direct evidence of gravitational waves, ripples in space-time that Albert Einstein predicted a century ago. The noise affirms a paramount aspect of Einstein’s theory of relativity: the existence of black holes, bottomless pits where gravitational pull is so strong that even light can’t escape.
The detection was made by the Laser Interferometer Gravitational-Wave Observatory, known as LIGO, whose two detectors in Hanford, Wash., and Livingston, La., picked up the frequency together on Sept. 14. In the months since, members of the LIGO group, comprised of a global team of scientists, have worked tirelessly on a study detailing the discovery, which culminates their decadeslong search for signs of the phenomenon.
Gravitational waves occur as objects move through space, similar to a boat moving across a lake and sending ripples through the water’s surface. But they’re so tiny that until now it has been nearly impossible to detect them. To pick up on the signal, scientists have to look for violent events in the universe. In this case, two black holes combined and turned roughly three suns’ worth of mass into gravitational waves in a fraction of a second.
“We’re used to looking at the sky with our eyes, and now we can hear it,” said Shane Larson, one of three Northwestern University professors on the LIGO team. “It’s taken us 25 years from the day we funded LIGO to today. I’ve worked on it my whole career. And finally, to get to that thing — it’s a little bit overwhelming.”
While it’s “up to historians to decide,” Larson, also an astronomer at Adler Planetarium, said he believes the detection is among the most important astronomical discoveries in a century. Local scientists agree, saying the signal marked the first time mankind has been able to “hear” the universe.
At the U. of C.’s William Eckhardt Research Center on Thursday morning, students sat shoulder to shoulder on the floor of the auditorium, crouching to get a peek of the live-streamed announcement by the LIGO group and the National Science Foundation in Washington, D.C. Afterward, U. of C.’s four LIGO members explained their roles in the project.
In the months since the detection, they were primarily involved in two aspects of the study: interpreting the meaning of data collected during the detection and figuring out how those findings played into Einstein’s theory, Holz said. The process led to late nights of nonstop work through the winter break and a whir of conference calls with other LIGO members across the nation, all excitedly sharing findings and conclusions. Scientists joked that the discovery seemed “too perfect.”
But the most stressful part of the process, Holz said, was keeping the discovery a secret for almost half a year.
“In some ways it was awful. You’re so absorbed by this, but you can’t share it with anyone,” he said. “The energy within the LIGO members here was very extreme. People inferred something was up because we were constantly meeting, but we couldn’t tell anyone about it.”
But the work isn’t quite over, Holz said. Scientists now understand that pairs of black holes exist in the universe and will try to understand their properties, such as how they’ve grown to become so large. They’ll do this by using the detectors to identify more gravitational waves and studying their patterns.
“We have this probe,” Holz said. “Now, let’s use it to learn about the universe.”
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