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Gravitational Waves Detected for the First Time


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In 1915 Einstein published the General Theory of Relativity, from which many predictions were made, and one of them has only recently been confirmed. Researchers have for the first time detected gravitational waves with the Laser Interferometer Gravitational-wave Observatory (LIGO). The waves were detected on September 14, 2015 by the twin LIGO detectors and likely the result of a pair of black holes merging some 1.3 billion years ago.

Gravitational waves are actual ripples made in spacetime as two massive objects revolve about each other, and eventually collide. Their existence was first demonstrated in the 1970s and '80s when a pulsar's orbit about a neutron star was discovered to be shrinking because of the creation of gravitational waves. In this case though, it was likely a pair of black holes weighing in at 29 and 36 solar masses. As the pair revolved about each other, gravitational waves would be produced, causing the orbit to shrink until they collide and merge into a single, more massive black hole. This merger also created a burst of gravitational waves as three solar masses were converted to energy following the famous E=mc2 formula. The peak power output was about 50 times that of the visible Universe.

As powerful as these waves are, they are hard to catch, which is why the LIGO detectors were built. These detectors are four kilometers long and work by splitting a laser into two beams and bouncing them between mirrors to precisely measure their positions. According to General Relativity, gravitational waves alter the distance between two points, and the two LIGO detectors are able to notice a change of 10-19 meters (a nanometer is 10-9 m). One detector is located in Louisiana and the other in Washington, and because the Louisiana detector picked it up 7 milliseconds before the other, we know the source was in the Southern Hemisphere.

Source: National Science Foundation



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