For the first time ever, not one, but three of the world’s biggest detectors have captured and tracked gravitational waves that have hit the Earth caused by the merging of two black holes. Gravitational waves are ripples in the curvature of spacetime that are produced when two very large, compact objects, such as black holes, merge.

The first two observations were made by LIGO’s two gravitational wave detectors in the United States, on August 14, 2017. The third detection was made in Italy by the Virgo Gravitational Wave Observatory on the same day. It’s exciting as this is the first time we’ve seen gravitational waves detected simultaneously by the detectors, and the first ever significant recording made by the Virgo detector.

“The Virgo Gravitational Wave Observatory joining forces with LIGO is a huge moment in astronomy,” said Chad Hanna, assistant professor of physics and astronomy & astrophysics and Freed Early Career Professor at Penn State. “It is our hope to one day detect gravitational waves and simultaneously observe the source of the gravitational wave with conventional telescopes so that we might learn even more about what causes the gravitational waves. In order to do that, we need to know where to look.

LIGO and Virgo together allow us to pinpoint the gravitational wave source in the sky far better than before, which will dramatically improve our chances of capturing the gravitational wave source with other telescopes.”

With Virgo now being added to the LIGO network, researchers can now test the polarization property of the wave, which was a key prediction of Einstein’s general theory of relativity.  “The two LIGO detectors alone are not able to infer the polarization property of gravitational waves because they alone could not fix the position of the source in the sky,” said B.S. Sathyaprakash, the Elsbach Professor of Physics and Professor of Astronomy and Astrophysics at Penn State. “The addition of Virgo as a third detector helps in localizing the source and hence allows us to infer the wave’s polarization.  As far as we can tell, Einstein is still right.”

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