Gravitational waves, explained

    Unless you live in a black hole, you’ve probably heard that scientists just discovered the existence of gravitational waves, a discovery that confirms Albert Einstein’s famous Theory of General Relativity.

    This is no light matter. But what does this all mean? If you’re relatively confused, NBN’s got you covered. After all, it’s not rocket science – it’s astrophysics.

    What even are gravitational waves?

    Gravitational waves are ripples in the fabric of spacetime. Black holes radiate gravitational waves, which are produced by accelerating masses. A gravitational wave is about 1,000 times smaller than a proton’s width. But don’t underestimate these tiny waves. At the speed of light, these waves can stretch and compress space on small scales. They can also project the force of massive bodies like black holes and neutron stars across long distances.

    Where do they come from?

    These detected waves come from a catastrophic event 1.3 billion years ago in a distant galaxy. Two black holes that were orbiting each other collided, merging into one massive, spinning black hole. In this collison's final fraction of a second, these waves were produced. While Albert Einstein predicted this collision in his original theory of relativity in 1916, no one had ever observed it. Until now.

    Why did I get an email about it from Northwestern?

    Two astrophysicists from Northwestern University, Vicky Kalogera and Shane L. Larson, were part of this research, which has been going on for decades and involves the work of scientists from all over the world. Kalogera leads the Laser Interferometer Gravitational-Wave Observatory (LIGO) research team at Northwestern. They made predictions for expected detections, interpreted the astrophysics results, analyzed data and characterized the detectors.

    Selim Shahriar, an electrical engineering and computer science professor, is also a LIGO member. He is working to improve the sensitivity of LIGO detectors and broaden the spectrum the detectors are sensitive to.

    “I think all of us are elated,” Larson said. “It's the simplest word. It doesn't describe how truly excited and overwhelmed we really are.”

    What's so great about these gravitational waves?

    They carry information about the black holes and the nature of gravity that scientists would not be able to obtain otherwise.

    This is the first time black holes have been directly detected. You can’t see black holes with telescopes. Up until now, scientists inferred that black holes existed by observing stars and the gas swirling around them, measuring the gravitational effect black holes have on other matter in the universe. But with this discovery, scientists detected gravitational signals directly from black holes. In addition, scientists can now learn more about binary black holes: how many there are in the universe, how often they merge, how often they are born and where they come from.

    It also opens a new window for astronomy and astrophysics. Currently, scientists study space via electromagnetic waves. Now, scientists study space with gravitational waves.

    “We’re going to start exploring the universe through this new window of gravitational waves, learning more about black holes but also about neutron stars,” Kalogera said. “The astronomy potential of this discovery is enormous. We worked all these years and we made the first measurement, and now we know we can do it. It’s a new beginning for physics and astronomy.”

    Plus, the waves confirmed one of Einstein’s predictions.

    So what was Einstein's prediction?

    A hundred years ago, Einstein stated that the gravitational pull between objects is a warping of space and time, and when very heavy objects like black holes are involved, gravity would manifest as ripples across the universe.

    When were these waves detected?

    These waves were detected at 5:51 a.m. on Sept. 14 by the twin LIGO detectors in Louisiana and Washington. After months of verifying the data, scientists from LIGO, Massachusetts Institute of Technology and California Institute of Technology announced this discovery Thursday at a press conference in Washington, D.C.

    “We're all amazed we detected gravitational waves and black holes,” Larson said, “but the most important thing is that LIGO was made possible by the work of thousands of people.”

    So what's next?

    This discovery is a starting point. Scientists will continue studying gravitational waves, and they hope to detect more. Shahriar’s team is working on improving the sensitivity of the detectors, allowing them to see a volume of space 8000 times greater. This way, scientists can detect waves from objects further away in the universe, thus seeing further into the past.

    “If you want to look at the past, you look at things that are very far away,” Shahriar said. “When you look at a star, if the star is a billion light years away, that means this signal started traveling to us a billion years ago, so you are actually looking back in time a billion years.”


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