For months, the science world has been buzzing about the rumor that gravitational waves, the ripples in spacetime that Einstein predicted a hundred years ago, have finally been detected. Today, at press conferences all over the world, researchers at the Laser Interferometer Gravitational-Wave Observatory (LIGO, a pair of observatories located in Washington and Louisiana) confirmed that the hype is true.
“Ladies and gentlemen, we have detected gravitational waves,” announced LIGO director David Reitze this morning. “We did it.” On September 14 of last year, the LIGO location in Livingston, Louisiana picked up a gravitational-wave signal, and seven milliseconds later, its fellow observatory in Hanford, Washington detected an identical signal. This signal exactly matched the calculated behavior of gravitational waves produced when two black holes collide.
When two black holes merge, they begin by orbiting one another. As they rotate, they move closer together and their speed increases, until they are whipping around one another hundreds of times per second. Ultimately, they combine to form a larger, oddly shaped black hole. Finally, the new black hole “relaxes” back into a spherical shape. According to predictions, this incredibly violent event should produce a type of gravitational-wave signal called a chirp. And that’s exactly the signal that both LIGO locations detected last September. It came from a black hole merger occurring 1.3 billion light years away. The results were published in Physical Review Letters this morning.
You can listen to the chirp for yourself here:
“This is the first time this kind of system has ever been seen,” Reitze said. “It’s proof binary black hole systems exist.”
And that’s not the gravitational wave finding’s only major implication. It also confirms the predictions of Einstein’s theory of general relativity, and will help researchers test and further refine that theory. It proves the abilities of Advanced-LIGO, an experiment a hundred years in the making, which involves hundreds of scientists from more than 70 international research institutions and 16 countries.
Most important, this proves that LIGO can give us a brand-new way to study the cosmos.
“Up until today, we had been watching the sky,” Szabi Marka, a professor of physics at Columbia University, and lead of Columbia’s LIGO team, told Popular Science. “From tomorrow, we can also hear it.” A researcher using LIGO to observe the universe, he suggested, is like a deaf person hearing music for the first time. “Can you imagine the joy?” he asked. “The world would change. This is what LIGO is to astrophysics.”
Take black holes, for example. Until now, researchers proved they existed by detecting the radiation they emit—an indirect method. Looking at the gravitational waves a black hole produces is much more direct. “LIGO will let us see objects that had never been seen before, study objects that had never been studied,” Marka explained.
In addition to chirps, LIGO picks up other types of gravitational-wave signals from other cosmic events. For example, a “burst” of gravitational waves appears when a star explodes unevenly. A “continuous wave” is produced when quickly spinning neutron stars (incredibly dense bodies that pack more than the weight of our Sun into an object as small as Manhattan) contain small imperfections on their surfaces. As the star rotates, its surface scars produce a siren-like signal.
Marka is already looking forward to finding signs like these. “The machine is finished,” he told Popular Science. “Now we have to use it.” Or in Reitze’s words, “What’s really exciting is what comes next.”